WO2022229297A2 - Methods of ligand exchange on surfaces comprising silicon and/or germanium - Google Patents

Abstract

A method for ligand exchange, the method comprising: providing a surface comprising a first ligand, wherein the surface comprises germanium, silicon, or a combination thereof; subjecting the surface comprising the first ligand to a catalyst in the presence of a second ligand that is different from the first ligand; and exchanging the first ligand for the second ligand.

Description

METHODS OF LIGAND EXCHANGE ON SURFACES COMPRISING SILICON

AND/OR GERMANIUM

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This patent application claims the benefit of U.S. Provisional Patent Application No. 63/180,697, filed April 28, 2021 , which is hereby incorporated herein by reference in its entirety for all purposes.

BACKGROUND

[0002] Germanium or silicon nanoparticle applications are largely dependent on the presence of specific surface chemistries suited for the intended purpose. However, synthetic methods and ligand-exchange chemistry are underdeveloped and poorly understood, often requiring multiple steps or surface activation pre-treatments.

[0003] Germanium and silicon nanoparticles (Ge and Si NPs) are fostering interest as an alternative to other semiconducting NPs (CdSe, PbTe, among others) as a result of their infrared emission, charge and ion transport properties, and their large Bohr exciton radius, which allows tuning the size-dependent properties with a broad size range.^111-41 Additionally, Ge and Si can be produced with different crystalline morphologies, namely amorphous Ge or Si (a-Ge or a-Si) and crystalline Ge or Si (c-Ge or c-Si).^15-91 These different crystallinities further expand the tunability of Ge and Si NPs for a variety of fields. The absorption cross-section, bandgap, and ion intercalation capacity are among the properties that can be modulated with different crystalline morphology. For instance, in the field of energy storage, c-Ge can easily intercalate Li- ions but not Na. In contrast, a-Ge shows high intercalation ability with both ions, thereby enabling the application of a-Ge NPs for Na-based devices.^110-141 Together, these properties make Ge and Si NPs highly promising in applications spanning across bioimaging, optoelectronics, and batteries, among others. Improvements in the size- selective synthesis of nanostructured Ge have established that the properties of Ge NPs are highly dependent on their surface chemistry and the types of ligands occupying their coordination shell. Frequently, due to a combination of favorable synthetic properties, long alkylic chain amines are employed during the synthesis of many Ge NPs.^115-211 These native long-chain aliphatic amine ligands offer the advantage of protection from oxidation and aggregation, modulation of growth, and dispersibility in non-polar solvents. Nevertheless, many potential applications of Ge nanocrystals require the exchange of such native ligands with new ligands more suited for the intended application, for example, to allow for charge separation and transport, drug carrier or tissue targeting, and ion transport, among others.¹¹⁵’²²’²³¹

[0004] For more than a decade, researchers have been working on improving the ability to exchange these surfaces. The Buriak group extensively reported on the hydrometallation of germanium surfaces.¹²⁴¹ Later, the Kauzlarich group successfully demonstrated the exchange of OAm with thiols on Ge NPs, which showed superior charge separation in comparison with the native oleylamine ligands (OAm).¹¹⁵¹ The Wheeler group extended the exchange procedure to inorganic ligands producing all inorganic Ge NPs surrounded by Na⁺ ions. With this method they observed a photovoltaic response upon illumination, which was previously absent in the presence of the as-synthesized Ge NPs with OAm ligand.¹²⁵¹ Despite efforts to control the surface chemistry of Ge NPs, it is important to note that the literature on ligand exchange is restricted either to hydrogenated surfaces or to methods requiring a surface activation pre-treatment,¹²⁴’^{26 271} which has been most frequently accomplished via coordination with hydrazine as the intermediate step.¹¹⁵’¹⁸’²⁰’^28-301 An even scarcer number of publications report the use of Grignard-like reactions on chlorinated surfaces or catalyzed exchanges with R^RίOIq.^131-371

[0005] In contrast, the same restriction is not present in many other nanostructured systems, where ligand exchanges are routinely performed. Of particular relevance to understanding the basis of ligand exchange mechanisms on nanoparticle surfaces is the work from M.H.L. Green, who laid the foundations of the Covalent Bond Classification (CBC) for ligand exchanges.¹³⁸¹ Initially developed for metallorganic molecular systems, the CBC has been rapidly developed and extended to include nanostructured materials.¹³⁹¹ [0006] According to the CBC, different ligand-types can be classified according to the number of electrons with which they partake in the bond, and can fall into L, X, and Z types. L-type ligands are neutral donors with a lone electron pair that coordinates the metal surface in a dative-like interaction. X-type ligands generally have an odd number of valence electrons, creating a bond with one electron from the ligand and one from the surface site. Conversely, the Z-type ligands are entirely acceptors, participating in the bond by accepting two electrons back-donated by the metallic surface. Based on the types of the initial and targeted exchange ligands, different classes of reaction can occur. The CBC and its extensions attempt to rationalize the likelihood of these reactions by considering several thermodynamic aspects that contribute to the exchange process. The electroneutrality principle is of particular relevance for exchanges involving different types of ligands where there may be a mismatch in the number of electrons during the exchange that is likely to result in the development of charged species. This implies that neutral exchanges (e.g., L to L') will be favored in apolar solvents, while non-neutral exchanges (e.g., L to X) will be more favored in polar solvents, which are better suited to stabilize the ions formed during the exchange. Another relevant aspect to consider is the strength of interaction between the different ligands and the surface. A good qualitative description can be based on the Hard-Soft Acid-Base (HSAB) theory, which briefly states that hard acids will interact more readily with hard bases rather than soft bases.¹⁴⁰¹ Similarly, soft acids will have a stronger interaction with soft bases than hard bases. Two other main factors can also be considered, namely chelate and steric effects. The chelate effect involves ligands that can interact with the surface via more than one functional group in the molecular structure. When all other parameters are equal, chelating ligands will have a more robust interaction with the NP surface relative to mono-dentate ligands. While the steric effect states that under identical conditions, smaller, less sterically hindered molecules can more easily penetrate the coordination sphere of the NPs, which can enable a more efficient displacement of the native ligand and a higher packing density.¹³⁹¹

[0007] Thus, there is a need for methods of ligand exchange. SUMMARY

[0008] Disclosed is a method for ligand exchange, the method comprising: providing a surface comprising a first ligand, wherein the surface comprises germanium, silicon, or a combination thereof; subjecting the surface comprising the first ligand to a catalyst in the presence of a second ligand that is different from the first ligand; and exchanging the first ligand for the second ligand.

BRIEF DESCRIPTION OF THE DRAWINGS [0009] FIG. 1. A schematic overview examples of catalyzed reactions.

[0010] FIG. 2. A schematic view of aspects of the methods disclosed herein.

[0011] FIG. 3. An IR spectrum demonstrating catalyzed ligand exchange on a-Ge surfaces.

[0012] FIG. 4. A ¹H NMR spectrum demonstrating catalyzed ligand exchange on a- Ge surfaces.

[0013] FIG. 5. A COSY-NMR spectrum demonstrating catalyzed ligand exchange on a-Ge surfaces.

[0014] FIG. 6. An IR spectrum demonstrating catalyzed ligand exchange on c-Ge and c-Si surfaces.

STATEMENTS REGARDING CHEMICAL COMPOUNDS AND NOMENCLATURE

[0015] In general, the terms and phrases used herein have their art-recognized meaning, which can be found by reference to standard texts, journal references and contexts known to those skilled in the art. The following definitions are provided to clarify their specific use in the context of the invention.

[0016] As used herein, “alkylic” generally is interchangeable with the term “alkyl,” or “alkylic” can mean having an alkyl character, such as an alkyl chain structure, alkenyl chain structure, or alkynyl chain structure. [0017] As used herein, “a straight or branched chain alkyl amine” means carbon chain with a straight or branched structure, in which the chain has at least one amine functional group. In some aspects, the amine functional group can be a primary amine or a secondary amine. The amine functional group generally is at or near a terminal end of the molecule, though it need not be. The alkyl group does not contain any alkene or alkyne functional groups and generally is composed only of carbon and hydrogen (e.g., is alkyl in nature), but may be substituted with other groups if desired, such as OH, an amine, an alkyl group, an aromatic group, and the like.

[0018] As used herein, “a straight or branched chain alkenyl amine” means a carbon chain with a straight or branched structure, at least one double bond, and at least one amine functional group. In some aspects, the amine functional group can be a primary amine or a secondary amine. The amine functional group generally is at or near a terminal end of the molecule, but need not be. The chain may also contain at least one triple bond (i.e., “a straight or branched chain alkenyl amine” may also be categorized as “a straight or branched chain alkynyl amine” if the chain contains both a double bond and a triple bond). The remainder of the chain generally is composed of only carbon and hydrogen (e.g., is alkyl in nature), but may be substituted with other groups if desired, such as OH, an amine, an alkyl group, an aromatic group, and the like.

[0019] As used herein, “a straight or branched chain alkynyl amine” means a carbon chain with a straight or branched structure, at least one triple bond, and at least one amine functional group. In some aspects, the amine functional group can be a primary amine or a secondary amine. The amine functional group generally is at or near a terminal end of the molecule, but need not be. The chain may also contain at least one double bond (i.e., “a straight or branched chain alkynyl amine” may also be categorized as “a straight or branched chain alkenyl amine” if the chain contains both a double bond and a triple bond). The remainder of the chain generally is composed of only carbon and hydrogen (e.g., is alkyl in nature), but may be substituted with other groups if desired, such as OH, an amine, an alkyl group, an aromatic group, and the like. [0020] As used herein, “a straight or branched chain alkyl thiol” means an alkyl group with a straight or branched structure, in which the alkyl group has at least one thiol functional group. The thiol functional group generally is at or near a terminal end of the molecule. The alkyl group does not contain any alkene or alkyne functional groups and generally is composed only of carbon and hydrogen (e.g., is alkyl in nature), but may be substituted with other groups if desired, such as OH, an amine, an alkyl group, an aromatic group, and the like. A “disulfide thereof means that the “straight or branched chain alkyl thiol” can be in the form of a dimer joined via a disulfide bond.

[0021] As used herein, “a straight or branched chain alkenyl thiol” means a carbon chain with a straight or branched structure, at least one double bond, and at least one thiol functional group. The thiol functional group generally is at or near a terminal end of the molecule, but need not be. The chain may also contain at least one triple bond (i.e. , “a straight or branched chain alkenyl thiol” may also be categorized as “a straight or branched chain alkynyl thiol” if the chain contains both a double bond and a triple bond). The remainder of the chain generally is composed of only carbon and hydrogen (e.g., is alkyl in nature), but may be substituted with other groups if desired, such as OH, an amine, an alkyl group, an aromatic group, and the like. A “disulfide thereof” means that the “straight or branched chain alkenyl thiol” can be in the form of a dimer joined via a disulfide bond.

[0022] As used herein, “a straight or branched chain alkynyl thiol” means a carbon chain with a straight or branched structure, at least one triple bond, and at least one thiol functional group. The thiol functional group generally is at or near a terminal end of the molecule, but need not be. The chain may also contain at least one double bond (i.e., “a straight or branched chain alkynyl thiol” may also be categorized as “a straight or branched chain alkenyl thiol” if the chain contains both a double bond and a triple bond). The remainder of the chain generally is composed of only carbon and hydrogen (e.g., is alkyl in nature), but may be substituted with other groups if desired, such as OH, an amine, an alkyl group, an aromatic group, and the like. A “disulfide thereof means that the “straight or branched chain alkynyl thiol” can be in the form of a dimer joined via a disulfide bond. [0023] As used herein, “a straight or branched chain alkene” means a carbon chain with a straight or branched structure and at least one double bond. The chain may also contain at least one triple bond (i.e. , “a straight or branched chain alkene” may also be categorized as “a straight or branched chain alkyne” if the chain contains both a double bond and a triple bond). The remainder of the chain generally is composed of only carbon and hydrogen (e.g., is alkyl in nature), but may be substituted with other groups if desired, such as OH, an amine, an alkyl group, an aromatic group, and the like. In some aspects, the straight or branched chain alkene contains one terminal alkene and the remainder of the chain being alkyl.

[0024] As used herein, “a straight or branched chain alkyne” means a carbon chain with a straight or branched structure and at least one triple bond. The chain may also contain at least one double bond (i.e., “a straight or branched chain alkyne” may also be categorized as “a straight or branched chain alkene” if the chain contains both a double bond and a triple bond). The remainder of the chain generally is composed of only carbon and hydrogen (e.g., is alkyl in nature), but may be substituted with other groups if desired, such as OH, an amine, an alkyl group, an aromatic group, and the like. In some aspects, the straight or branched chain alkyne contains one terminal alkyne and the remainder of the chain being alkyl.

[0025] As used herein, “electron-deficient,” “electronic-scarce,” and “electron-poor” generally are used interchangeably and have the same art-recognized meaning.

[0026] As used herein, “electron-rich” has its art-recognized meaning.

[0027] As used herein, the term “electron-dense” is typically used when comparing the electron-deficient and electron-rich character of a given atom or other species. For example, the more electron-deficient species may be referred to as less electron-dense, and the more electron-rich species may be referred to as more electron-dense.

[0028] As used herein, “adduct” (such as a planar adduct) in reference to a catalyst refers to the intermediate transient structure, possibly the transition state structure, formed between the catalyst, the first ligand, and the second ligand during the ligand exchange.

[0029] As used herein, when a number of carbon atoms of an alkyl, alkenyl, or alkynyl group is specified herein, it is intended that the number refers to the exact number of carbon atoms, or range of carbon atoms, that is specified. In other words, when a number of carbon atoms (or range thereof) is specified for an alkyl group, it is not intended that the alkyl group comprises that specified number of carbon atoms, but rather that the alkyl group contains the exact specified number. For example, if an alkyl is specified to contain 4 to 8 carbon atoms, an alkyl group containing 12 carbon atoms would not qualify; rather, only an alkyl group that contains 4, 5, 6, 7, or 8 carbon atoms would qualify. This same concept applies equally to the number of unsaturations.

DETAILED DESCRIPTION OF THE INVENTION [0030] Without wishing to be bound by any particular theory, there may be discussion herein of beliefs or understandings of underlying principles relating to the devices, chemical compounds, and methods disclosed herein. It is recognized that regardless of the ultimate correctness of any mechanistic explanation or hypothesis, an aspect of the invention can nonetheless be operative and useful.

[0031] In the following description, numerous specific details of the devices, device components and methods of the present invention are set forth in order to provide a thorough explanation of the precise nature of the invention. It will be apparent, however, to those of skill in the art that the invention can be practiced without these specific details.

[0032] In some aspects, a general working principle of methods disclosed herein, such as the direct CE, relies on lowering the reaction barrier associated with the ligand exchange, which, in some aspects, may employ the change of reaction pathways offered by the catalyst. For example, the catalyst forms a planar adduct with an electron-rich fraction of the molecule, most often heteroatom or unsaturations, as for example the members of the Lewis acid X2AICI. Specifically, for example, the electron- deficient portion of the catalyst (e.g., the aluminum center) may superimpose to the atom with the higher electron density, while the chlorine will superimpose to the less electron-dense atom. This planar adduct may approach the surface of the nanoparticles, creating a short-lived hypervalent intermediate of absorption, which triggers an electronic rearrangement resulting in a new bond formation with the surface. The process is depicted schematically in FIG. 2, with box 1 indicating catalyst-ligand adduct formation, box 2 indicating hypervalent intermediate adsorption on a surface, and box 3 indicating electron rearrangements and catalyst release. Although the surface shown is Ge, it is noted that Si surfaces can be employed, e.g., alone or in combination with Ge.

[0033] Regarding the expected efficiency of the exchanges, some relative considerations can be made considering the extended covalent bond classifications and hard-soft acid-base theory. In some aspects, based on the electronic requirements for the adduct and hypervalent intermediate formation, better efficiency is expected when working with L-type ligands in respect to X- or Z-type ligands.

[0034] With respect to crystalline versus amorphous surfaces, in some aspects it is expected a higher efficiency of harder ligands towards crystalline surfaces; conversely, softer ligands may be expected to exhibit a better affinity towards amorphous surfaces.

[0035] Other relevant effects include steric hindrance and chelating effects. Smaller ligands with smaller footprints are expected to displace bigger ligands better.

Meanwhile, under equal conditions, ligands with chelation possibilities will displace monodentate ligands based on entropic considerations.

[0036] In some aspects, disclosed is a method for a direct ligand exchange via a catalyzed mechanism (CE) for a-Ge and c-Ge NPs and silicon nanoparticles prepared according to different synthetic pedigrees, as simplification in contrast to and as an alternative to known methods.

[0037] In some aspects, the disclosed methods remove OAm as a native ligand via direct CE, which takes advantage of a labile interaction between OAm and Ge NPs. The Ge NP cores, arising from different synthetic pedigrees, showed excellent resilience when exposed to highly reactive environments. Complete and partial exchanges with exchanges > 70 % have been observed in CE. All the CE proved successful within the reaction time of approximately 15 hours, with the lowest efficiencies of 95% and 70% for the crystalline and amorphous samples, respectively. These results show that a surface-activation pretreatment can be avoided with some capping agents, particularly the thiol class. CE also showed a good agreement with the CBC and HSAB theoretical frameworks. In total, the methods disclosed herein offer the possibility of a direct exchange of the Ge or Si NP surface-chemistry catalytically via the replacement of the native ligand with the intended one, particularly in the case of thiols. In FIG. 1 a schematic overview of the catalyzed reaction examples is given. Although the surface shown is Ge, it is noted that Si surfaces can also be employed, e.g., alone or in combination with Ge.

[0038] In some aspects, disclosed is a method for ligand exchange, the method comprising: providing a surface comprising a first ligand, wherein the surface comprises germanium, silicon, or a combination thereof; subjecting the surface comprising the first ligand to a catalyst in the presence of a second ligand that is different from the first ligand; and exchanging the first ligand for the second ligand.

[0039] In some aspects, the first ligand is covalently attached to the surface.

[0040] In some aspects, subjecting the surface comprising the first ligand to a catalyst in the presence of a second ligand that is different from the first ligand is achieved in any suitable way, such as by preparing a solution or suspension of the second ligand in a fluid or liquid (e.g., comprising or consisting of an aprotic, preferably non-polar solvent, such as hexanes, dicholoromethane, , and so forth) and exposing the surface to such solution or suspension. In some aspects, method is performed in an aprotic solvent. In some aspects, the method is performed in a polar or a non-polar solvent. In some aspects, the method is performed in an aprotic, polar solvent. [0041] In some aspects, the first ligand is different from the second ligand. A first ligand is “different” from a second ligand when the chemical structure of the ligand is not the same (e.g., oleylamine vs. 1-octanethiol).

[0042] In some aspects, the exchanging step results from the catalytic activity of the catalyst, whereby the catalyst facilitates removing the first ligand from the surface and adding the second ligand to the surface. Without wishing to be bound by theory, it is believed that the catalyst coordinates to the first ligand and/or the second ligand to form a planar adduct during or near the transition state of this ligand exchange process, thus lowering the energy barrier for removing the first ligand from the surface and/or adding the second ligand to the surface (e.g., the exchange step). In addition, without wishing to be bound by theory, it is believed that in some aspects an electron-rich portion of the catalyst, an electron-deficient portion of the catalyst, the second ligand, or any combination thereof form a planar adduct during the method (e.g., during the exchange step), in which the electron-rich portion of the catalyst can be an atom (e.g., a halogen, such as chloride) that coordinates to an electron acceptor (e.g., proton, empty p-orbital, etc.) on the first ligand and/or second ligand, and the electron-deficient portion of the catalyst can be an atom (e.g., e.g., a metal ion such as aluminum) that coordinates to an electron donor (e.g., a lone pair or occupied p-orbital) on the first ligand and/or second ligand. In some aspects, the planar adduct is formed between an electron-rich portion of the catalyst, an electron-deficient portion of the catalyst, an electron acceptor of the second ligand, and an electron donor of the second ligand. In some aspects, the planar adduct is formed between an electron-rich portion of the catalyst, an electron- deficient portion of the catalyst, an electron acceptor of the first ligand, and an electron donor of the first ligand. In some aspects, the planar adduct is formed between an electron-rich portion of the catalyst, an electron-deficient portion of the catalyst, an electron acceptor of the first ligand, and an electron donor of the second ligand. In some aspects, the planar adduct is formed between an electron-rich portion of the catalyst, an electron-deficient portion of the catalyst, an electron acceptor of the second ligand, and an electron donor of the first ligand. In some aspects, an electron-rich portion of the catalyst, an electron-deficient portion of the catalyst, and the second ligand, or any combination thereof form a planar adduct during the method. [0043] In some aspects, the catalyst comprises an electron-rich portion and an electron-deficient portion. In some aspects, the electron-deficient portion of the catalyst comprises an aluminum ion, a boron ion, a lithium ion, or any combination thereof. In some aspects, the electron-rich portion of the catalyst is or comprises a chloride ion, a fluoride ion, an iodide ion, an oxygen atom, a nitrogen atom, a sulfur atom, or any combination thereof. In some aspects, the catalyst is a trigonal catalyst with a metallic active center.

[0044] In some aspects, the catalyst is a Lewis acid. Suitable examples of a Lewis acid include, for example, compounds containing B³⁺, Li⁺, or any combination thereof, including, for example, the compounds EtsA Cb, AICI₃, EtAIC , BF₃, or any combination thereof.

[0045] In some aspects, the catalyst is AIX₃, in which each X independently is as defined below. In some aspects, the catalyst is X₂AICI. In some aspects, the catalyst is XAICI₂. In some aspects, each X in any catalyst formula can be the same or different. In some aspects, Al is an electron-deficient portion of the catalyst. In some aspects, each X independently is an electron-rich portion of the catalyst. In some aspects, Cl and/or X is an electron-rich portion of the catalyst. In some aspects, optionally each X is independently selected from a halide (e.g., fluoride, chloride, or iodide) or an alkyl chain (e.g., methyl, ethyl, propyl, or butyl, or any other straight or branched alkyl chain having 1-10 carbon atoms, such as 1-4, 1-3, 2-4, 2-5, 4-8, 3-7, 5-10, or 3-10 carbon atoms).

[0046] In some aspects, a combination of at least two catalysts is employed in the methods disclosed herein.

[0047] In some aspects, the surface comprises amorphous silicon (a-Si), crystalline silicon (c-Si), amorphous germanium (a-Ge), crystalline germanium (c-Ge), or any combination thereof.

[0048] In some aspects, the surface is in a form of a nanoparticle or a wafer. In some aspects, the surface is in the form of a nanoparticle or wafer comprising amorphous silicon (a-Si), crystalline silicon (c-Si) (e.g., Si(100)), amorphous germanium (a-Ge), crystalline germanium (c-Ge), or any combination thereof.

[0049] In some aspects, the nanoparticle has any suitable average size. For example, in some aspects, the average size (nm) of the nanoparticle, as measured by dynamic light scattering, is 1-200, 5-175, 10-150, 20-125, 50-100, 50-150, 1-100, 1-50, 10-75, 100-200, 150-200, 1-10, 10-20, 20-40, 40-60, 60-90, 90-120, 120-150, 150-175, or 175-200.

[0050] In some aspects, the first ligand is selected from a straight or branched chain alkyl amine having 4 to 30 carbon atoms, a straight or branched chain alkenyl amine having 4 to 30 carbon atoms, or a straight or branched chain alkynyl amine having 4 to 30 carbon atoms. In some aspects, the first ligand is present as a plurality of first ligands, and the plurality of first ligands is selected from a straight or branched chain alkyl amine having 4 to 30 carbon atoms, a straight or branched chain alkenyl amine having 4 to 30 carbon atoms, or a straight or branched chain alkynyl amine having 4 to 30 carbon atoms, or any combination thereof. In some aspects, the first ligand, or plurality thereof, is selected from a straight chain alkyl amine having 4 to 30 carbon atoms, a straight chain alkenyl amine having 4 to 30 carbon atoms, or a straight chain alkynyl amine having 4 to 30 carbon atoms, or any combination thereof. In some aspects, any of the amines in this paragraph or anywhere else herein can be primary amines or secondary amines, or any combination thereof. In some aspects, the number of carbon atoms of the first ligand for any of the groups in this paragraph, or anywhere else herein where such features are mentioned, can be 4, 5, 6, 7, 8, 9, 10, 11 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22, 23, 24, 25, 26, 27, 28, 29, 30, or any range made therefrom, such as 4-30, 8-28, 10-26, 12-24, 14-22, 16-20, 6-10, 10-14, 14-18, 18-22, 22-26, 26-30, 6-10, 6-15, 6-20, 8-15, 8-20, 10-20, and the like.

[0051] In some aspects, the first ligand is selected from a straight or branched chain alkyl primary amine having 4 to 30 carbon atoms, a straight or branched chain alkenyl primary amine having 4 to 30 carbon atoms, or a straight or branched chain alkynyl primary amine having 4 to 30 carbon atoms. In some aspects, the first ligand is present as a plurality of first ligands, and the plurality of first ligands is selected from a straight or branched chain alkyl primary amine having 4 to 30 carbon atoms, a straight or branched chain alkenyl primary amine having 4 to 30 carbon atoms, or a straight or branched chain alkynyl primary amine having 4 to 30 carbon atoms, or any combination thereof.

In some aspects, the first ligand, a plurality thereof, is selected from a straight chain alkyl primary amine having 4 to 30 carbon atoms, a straight chain alkenyl primary amine having 4 to 30 carbon atoms, a straight chain alkynyl primary amine having 4 to 30 carbon atoms, or any combination thereof. In some aspects, the number of carbon atoms of the first ligand for any of the groups in this paragraph, or anywhere else herein where such features are mentioned, can be 4, 5, 6, 7, 8, 9, 10, 11 , 12, 13, 14, 15, 16,

17, 18, 19, 20, 21 , 22, 23, 24, 25, 26, 27, 28, 29, 30, or any range made therefrom, such as 4-30, 8-28, 10-26, 12-24, 14-22, 16-20, 6-10, 10-14, 10-18, 14-18, 18-22, 22-26, 26- 30, 6-10, 6-15, 6-20, 8-15, 8-20, 10-20, and the like.

[0052] In some aspects, the first ligand has any number of unsaturations (e.g., double bonds, triple bonds, or a combination thereof), such as 1 , 2, 3, 4, 5, or 6, or any range made therefrom, such as 1-6, 1-4, 1-2, 2-3, 2-4, or 3-6. In some aspects, the first ligand has 1 double bond, 1 triple bond, 2 double bonds, 2 triple bonds, 1 double bond and 1 triple bond, 3 double bonds, 3 triple bonds, 2 double bonds and 1 triple bond, and so forth. Any combination of double and triple bonds is contemplated herein. The double or triple bonds independently can be internal or terminal. In addition, each internal double bond can independently have either the E or Z configuration. In some aspects, the first ligand has one double bond in the Z configuration.

[0053] In some aspects, the first ligand is oleylamine or -H, or if present as a plurality of first ligands, a combination thereof. In some aspects when a plurality of the first ligand is present, the plurality is or comprises oleylamine, -H, or a combination thereof.

[0054] In some aspects, the first ligand is a native ligand present on the surface as a result of a process employed to synthesize the surface, optionally wherein the surface is in a form of a nanoparticle. For example, during the synthesis of nanoparticles, there is a native ligand present the surface of the nanoparticles as a result of the synthetic process used to make the nanoparticles, and in some aspects this native ligand is the first ligand herein (e.g., oleylamine).

[0055] In some aspects, the second ligand is selected from a straight or branched chain alkyl thiol having 4 to 30 carbon atoms or a disulfide thereof, a straight or branched chain alkenyl thiol having 4 to 30 carbon atoms or a disulfide thereof, a straight or branched chain alkynyl thiol having 4 to 30 carbon atoms or a disulfide thereof, a straight or branched chain alkene having 4 to 30 carbon atoms, or a straight or branched chain alkyne having 4 to 30 carbon atoms. In some aspects, the second ligand is present as a plurality of second ligands, and the plurality of second ligands is selected from a straight or branched chain alkyl thiol having 4 to 30 carbon atoms or a disulfide thereof, a straight or branched chain alkenyl thiol having 4 to 30 carbon atoms or a disulfide thereof, a straight or branched chain alkynyl thiol having 4 to 30 carbon atoms or a disulfide thereof, a straight or branched chain alkene having 4 to 30 carbon atoms, a straight or branched chain alkyne having 4 to 30 carbon atoms, or any combination thereof. In some aspects, the second ligand, or plurality thereof, is selected from a straight chain alkyl thiol having 4 to 30 carbon atoms or a disulfide thereof, a straight chain alkenyl thiol having 4 to 30 carbon atoms or a disulfide thereof, a straight chain alkynyl thiol having 4 to 30 carbon atoms or a disulfide thereof, a straight chain alkene having 4 to 30 carbon atoms, a straight chain alkyne having 4 to 30 carbon atoms, or any combination thereof. In some aspects, the number of carbon atoms of the second ligand for any of the groups in this paragraph, or anywhere else herein where such features are mentioned, can be 4, 5, 6, 7, 8, 9, 10, 11 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22, 23, 24, 25, 26, 27, 28, 29, 30, or any range made therefrom, such as 4- 30, 8-28, 10-26, 12-24, 14-22, 16-20, 6-10, 10-14, 10-18, 14-18, 18-22, 22-26, 26-30, 6- 10, 6-15, 6-20, 8-15, 8-20, 10-20, and the like.

[0056] In some aspects, the second ligand has any number of unsaturations (e.g., double bonds, triple bonds, or a combination thereof), such as 1 , 2, 3, 4, 5, or 6, or any range made therefrom, such as 1-6, 1-4, 1-2, 2-3, 2-4, or 3-6. In some aspects, the second ligand has 1 double bond, 1 triple bond, 2 double bonds, 2 triple bonds, 1 double bond and 1 triple bond, 3 double bonds, 3 triple bonds, 2 double bonds and 1 triple bond, and so forth. Any combination of double and triple bonds is contemplated herein. The double or triple bonds independently can be internal or terminal. In addition, each internal double bond can independently have either the E or Z configuration. In some aspects, the second ligand is an alkene having one double bond at the terminal end of the molecule. In some aspects, the second ligand is an alkyne having one triple bond at the terminal end of the molecule. In some aspects, the second ligand is an alkene having two double bonds, one at each terminal end of the molecule. In some aspects, the second ligand is an alkyne having two triple bonds, one at each terminal end of the molecule. In some aspects, the second ligand is an alkyne or alkene having one double bond and one triple bond, one present at each terminal end of the molecule.

[0057] In some aspects, the second ligand is selected from 1-octanethiol, 1- octadecene, or 1-dodecyne, or if present as a plurality of second ligands, any combination thereof.

[0058] In some aspects, the second ligand contains a terminal alkene or alkyne, and the exchanging step optionally results in (1) converting the terminal alkene to an alkyl upon attachment to the surface, (2) converting the terminal alkyne to alkenyl upon attachment to the surface, (3) converting the terminal alkyne to alkyl upon attachment to the surface, or (4) any combination thereof. As described elsewhere herein, in some aspects, when the second ligand contains a terminal alkene, upon attachment to the surface the second ligand converts to an alkyl. Also, as described elsewhere herein, in some aspects, when the second ligand contains a terminal alkyne, upon attachment to the surface the second ligand converts to an alkene or an alkyl, or a combination thereof. Even if such conversions take place upon attachment of the second ligand to the surface, the “second ligand” is still considered the “second ligand” so as to simplify nomenclature herein. In other words, even though the chemical structure of the second ligand may change upon attachment to the surface, the now chemically changed second ligand is still considered the second ligand. [0059] In some aspects, the first ligand is a straight chain alkenyl primary amine having 4 to 30 carbon atoms, and the second ligand is selected from a straight chain alkyl thiol having 4 to 30 carbon atoms or a disulfide thereof, a straight chain alkene having 4 to 30 carbon atoms, or a straight chain alkyne having 4 to 30 carbon atoms, or when present as a plurality of second ligands, any combination thereof. In some aspects, the first ligand is a straight chain alkenyl primary amine having 14 to 22 carbon atoms and an internal double bond (e.g., in Z configuration), and the second ligand is selected from a straight chain alkyl thiol having 6 to 15 carbon atoms or a disulfide thereof, a straight chain alkene having 14 to 22 carbon atoms, or a straight chain alkyne having 6 to 20 carbon atoms, or when present as a plurality of second ligands, any combination thereof. For clarity, the number of carbon atoms in this paragraph is merely exemplary, and any number of carbon atoms disclosed elsewhere herein can be employed.

[0060] In some aspects, the catalyst is EtAIC ; the surface comprises a-Ge, c-Ge, or Si(100); the first ligand is oleylamine; the second ligand is 1-octanethiol, 1-octadecene, or 1-dodecyne, or if present as a plurality of second ligands, any combination thereof; when the second ligand is 1-octadecene alone or as part of a combination, at least a portion of 1-octadecene is converted to 1-octadecyl upon attachment to the surface; and when the second ligand is 1 -dodecyne alone or as part of a combination, at least a portion of 1-dodecyne is converted to 1-dodecyl upon attachment to the surface.

[0061] In some aspects, the method is performed at any suitable temperature. For example, in some aspects the method is performed at room temperature, a temperature of 5 °C to 50 °C, a temperature of 10 °C to 35 °C, or a temperature of 15 °C to 25 °C.

[0062] In some aspects, the surface is not hydrogenated or exposed to a surface activation step to facilitate adding the second ligand to the surface. In some aspects, after the providing step and prior to the exchanging step, the surface is not hydrogenated or exposed to a surface activation step, optionally wherein the surface activation step comprises treatment with hydrazine. As described elsewhere herein, the methods disclosed herein enable addition of the second ligand to a surface without the need for preparing the surface via hydrogenation and/or surface activation; rather, the methods herein provide the ability to add the second ligand to a surface through a catalytic exchange method whereby a native ligand (e.g., the first ligand) present on the surface as a result of the synthetic process to prepare the surface (e.g., nanoparticles) is catalytically exchanged for a second ligand.

[0063] In some aspects, the surface comprises a plurality of the first ligand, and at least 70% (e.g., at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, at least 97%, at least 98%, at least 99%, or 100%) of the plurality of the first ligand are exchanged with a plurality of the second ligand during the method, as determined by at least one of IR spectroscopy and ¹H NMR spectroscopy. In some aspects, 70-100%, 70-99%, 70-98%, 70-95%, 75-95%, 80-90%, 84-88%, 70-90%, 70-85%, 70-80%, 75- 99%, 80-99%, 85-99%, 90-99%, 75-100%, 80-100%, 85-100%, 90-100%, 95-99%, or 95-100% of the plurality of the first ligand are exchanged with a plurality of the second ligand during the method, as determined by at least one of IR spectroscopy and ¹H NMR spectroscopy. In some aspects, such as those involving biological applications, it may be desirable to have partial exchange of the plurality of the first ligand with a plurality of the second ligand during the method. For example, in some aspects, 5-70%, 10-50%, 10-65%, 15-60%, 15-50%, 15-45%, 20-55%, 25-50%, 30-45%, 35-40%, 5- 20%, 20-35%, 35-50%, 50-70%, 5-40%, 20-40%, about 20%, about 40%, 10-45%, or 15-50% of the plurality of the first ligand is exchanged with a plurality of the second ligand during the method, as determined by at least one of IR spectroscopy and ¹H NMR spectroscopy. In some aspects, this partial exchange can be achieved, for example, by adjusting (e.g., decreasing) the amount of second ligand present during the method, controlling (e.g., decreasing) the duration of the method, and/or selecting (e.g., decreasing) the temperature at which the method is performed.

[0064] In some aspects, disclosed is a method for a direct catalyzed ligand exchange on germanium or silicon surfaces using a catalyst which forms a planar adduct with an electron-rich fraction of the molecule of the catalyst and whereas the center of the molecule is electron-scarce. [0065] In some aspects, the center of the molecule of the catalyst is an aluminum atom and the electron rich adduct is Cl.

[0066] In some aspects, the catalyst is X2AICI2.

[0067] In some aspects, disclosed is a method for ligand exchange on a surface comprising germanium, silicon, or both germanium and silicon, the method comprising: a. contacting the surface with a catalyst, wherein the catalyst comprises an electron-rich portion and an electron-deficient portion, and wherein the catalyst comprises a planar structure.

[0068] In some aspects, the electron-deficient portion comprises an aluminum atom and the electron-rich portion comprises Cl.

[0069] In some aspects, the catalyst is a Lewis acid.

[0070] In some aspects, the catalyst is X2AICI, or the catalyst is a combination of at least two catalysts.

[0071] In some aspects, each ligand independently is or comprises a thiol, 1- octanethiol, an alkene, 1 -octadecene, an alkyne, or 1-dodecyne.

[0072] In some aspects, the surface comprises a-Ge, c-Ge, a-Si, c-Si, or any combination thereof.

[0073] In some aspects, the method is performed in a polar solvent or an apolar solvent.

[0074] In some aspects, the method is performed at room temperature, or a temperature of 5 C to 50 C, or a temperature of 10 C to 35 C, or a temperature of 15 C to 25 C.

[0075] In some aspects, the surface is present on a nanoparticle. [0076] In some aspects, the ligand exchanged from the surface comprises oleylamine.

[0077] Various aspects are contemplated herein, several of which are set forth in the paragraphs below. It is explicitly contemplated that any aspect or portion thereof can be combined to form an aspect.

[0078] Aspect 1 : A method for ligand exchange, the method comprising: providing a surface comprising a first ligand, wherein the surface comprises germanium, silicon, or a combination thereof; subjecting the surface comprising the first ligand to a catalyst in the presence of a second ligand that is different from the first ligand; and exchanging the first ligand for the second ligand.

[0079] Aspect 2: The method of any preceding aspect, wherein the catalyst is a Lewis acid.

[0080] Aspect 3: The method of any preceding aspect, wherein the catalyst comprises an electron-rich portion and an electron-deficient portion.

[0081] Aspect 4: The method of aspect 3, or any preceding aspect, wherein the electron-deficient portion of the catalyst comprises an aluminum atom.

[0082] Aspect 5: The method of aspect 3 or aspect 4, or any preceding aspect, wherein the electron-rich portion of the catalyst comprises a chloride atom.

[0083] Aspect 6: The method of any one of aspects 3-5, or any preceding aspect, wherein the catalyst is AIX₃, each X can be the same or different, Al is the electron- deficient portion of the catalyst, Cl and/or X is the electron-rich portion of the catalyst, and optionally each X is independently selected from halide or an alkyl chain.

[0084] Aspect 7: The method of any one of aspects 3-6, or any preceding aspect, wherein the electron-rich portion of the catalyst, the electron-deficient portion of the catalyst, the second ligand, or any combination thereof form a planar adduct during the method. [0085] Aspect 8: The method of any preceding aspect, wherein the surface comprises amorphous silicon (a-Si), crystalline silicon (c-Si), amorphous germanium (a- Ge), crystalline germanium (c-Ge), or any combination thereof.

[0086] Aspect 9: The method of any preceding aspect, wherein the surface is in a form of a nanoparticle or a wafer.

[0087] Aspect 10: The method of any preceding aspect, wherein the first ligand is selected from a straight or branched chain alkyl amine having 4 to 30 carbon atoms, a straight or branched chain alkenyl amine having 4 to 30 carbon atoms, or a straight or branched chain alkynyl amine having 4 to 30 carbon atoms.

[0088] Aspect 11 : The method of any preceding aspect, wherein the first ligand is selected from a straight or branched chain alkyl primary amine having 4 to 30 carbon atoms, a straight or branched chain alkenyl primary amine having 4 to 30 carbon atoms, or a straight or branched chain alkynyl primary amine having 4 to 30 carbon atoms.

[0089] Aspect 12: The method of any preceding aspect, wherein the first ligand is present as a plurality of first ligands selected from a straight or branched chain alkyl amine having 4 to 30 carbon atoms, a straight or branched chain alkenyl amine having 4 to 30 carbon atoms, a straight or branched chain alkynyl amine having 4 to 30 carbon atoms, or any combination thereof.

[0090] Aspect 13: The method of any preceding aspect, wherein the first ligand is oleylamine or -H, or if present as a plurality of first ligands, a combination thereof.

[0091] Aspect 14: The method of any preceding aspect, wherein the first ligand is a native ligand present on the surface as a result of a process employed to synthesize the surface, optionally wherein the surface is in a form of a nanoparticle.

[0092] Aspect 15: The method of any preceding aspect, wherein the second ligand is selected from a straight or branched chain alkyl thiol having 4 to 30 carbon atoms or a disulfide thereof, a straight or branched chain alkenyl thiol having 4 to 30 carbon atoms or a disulfide thereof, a straight or branched chain alkynyl thiol having 4 to 30 carbon atoms or a disulfide thereof, a straight or branched chain alkene having 4 to 30 carbon atoms, or a straight or branched chain alkyne having 4 to 30 carbon atoms.

[0093] Aspect 16: The method of any preceding aspect, wherein the second ligand is present as a plurality of second ligands selected from a straight or branched chain alkyl thiol having 4 to 30 carbon atoms or a disulfide thereof, a straight or branched chain alkenyl thiol having 4 to 30 carbon atoms or a disulfide thereof, a straight or branched chain alkynyl thiol having 4 to 30 carbon atoms or a disulfide thereof, a straight or branched chain alkene having 4 to 30 carbon atoms, a straight or branched chain alkyne having 4 to 30 carbon atoms, or any combination thereof.

[0094] Aspect 17: The method of any preceding aspect, wherein the second ligand is selected from 1-octanethiol, 1-octadecene, or 1-dodecyne, or if present as a plurality of second ligands, any combination thereof.

[0095] Aspect 18: The method of any preceding aspect, wherein, when the second ligand contains a terminal alkene or alkyne, the exchanging step optionally results in (1) converting the terminal alkene to an alkyl upon attachment to the surface, (2) converting the terminal alkyne to alkenyl upon attachment to the surface, (3) converting the terminal alkyne to alkyl upon attachment to the surface, or (4) any combination thereof.

[0096] Aspect 19: The method of any preceding aspect, wherein: the catalyst is EtAIC ; the surface comprises a-Ge, c-Ge, or Si(100); the first ligand is oleylamine or -H, or if present as a plurality of first ligands, a combination thereof; the second ligand is 1-octanethiol, 1-octadecene, or 1-dodecyne, or if present as a plurality of second ligands, any combination thereof; when the second ligand is 1-octadecene alone or as part of a combination, at least a portion of 1-octadecene is converted to 1-octadecyl upon attachment to the surface; and when the second ligand is 1 -dodecyne alone or as part of a combination, at least a portion of 1-dodecyne is converted to 1-dodecyl upon attachment to the surface. [0097] Aspect 20: The method of any preceding aspect, wherein the method is performed at a temperature of 5 °C to 50 °C.

[0098] Aspect 21 : The method of any preceding aspect, wherein method is performed in a polar solvent or an apolar solvent.

[0099] Aspect 22: The method of any preceding aspect, wherein, after the providing step and prior to the exchanging step, the surface is not hydrogenated or exposed to a surface activation step, optionally wherein the surface activation step comprises treatment with hydrazine.

[0100] Aspect 23: The method of any preceding aspect, wherein the surface comprises a plurality of the first ligand, and at least 70% of the plurality of the first ligand is exchanged with a plurality of the second ligand during the method, as determined by at least one of IR spectroscopy and ¹H NMR spectroscopy.

[0101] Aspect 24: The method of any one of aspects 1-22, or any preceding aspect, wherein the surface comprises a plurality of the first ligand, and 5-70% of the plurality of the first ligand is exchanged with a plurality of the second ligand during the method, as determined by at least one of IR spectroscopy and ¹H NMR spectroscopy.

EXAMPLES

[0102] Further aspects of the methods disclosed herein are illustrated by the following non-limiting examples.

EXAMPLE 1

[0103] In some aspects, the direct ligand exchange methods disclosed herein are demonstrated for three different ligands each, namely l-octanethiol(OT), 1- octadecene(ODE), and l-dodecyne(DODY). The resilience of Ge NPs were assessed under the exchange conditions via Raman spectroscopy and XRD, while a combination of FTIR and NMR was used to investigate the NP surfaces before and after exchange. The results are interpreted based on the expanded CBC model. It was observed that generally, in some aspects, the CE method results in a high success rate in displacing the native ligand, which in some aspects may be at least partially due to the electroneutrality contribution of an L to L' neutral replacement.

[0104] Both the accessible Ge crystallinities have been investigated to assess the exchange efficiency differences with the two types of resulting surfaces. Additionally, the two different syntheses reviewed, necessary to produce the different Ge NPs crystallinities, have been chosen to be similar. Both are conducted with the same ligand, OAm, at high temperatures. The main difference in the synthesis of a-Ge is the presence of S as a reagent, which can remain in solution due to the formation of a polymer bridging OAm monomers that stabilizes the metastable amorphous product. In turn, this polymer results in a significantly higher steric hindrance of the native ligands. With respect to other nanostructured systems, two general exchange protocols can be established. Considering the preference of anoxic conditions for Ge, a more straightforward direct catalyst-based exchange (CE) was employed as an alternative to hydrazine use to displace the native ligand. Generally speaking, the replacement of any ligand is associated with an energy barrier.¹⁴⁰^³¹ To overcome this obstacle, it is possible either to provide an energetic drive to the system or to lower the energy barrier itself, namely a catalyzed exchange (CE).

[0105] The direct catalyzed exchange (CE) reaction exploits a metal-based Lewis acid, commonly AICI₃ or an organometallic member of the same family with the general formula X₂AICI. In some aspects, it is believed that the catalyst lowers the required energy barrier by forming an adduct with an electron-rich ligand position, such as an unsaturation or an electron-rich heteroatom. With respect to the CE, a catalyst offers the chance, in some aspects, as an additional advantage of the inventive method to perform the exchange at room temperature. Such low temperatures enable, in some aspects, the use of the most common apolar organic solvents and the vast majority of alkenes and alkynes as ligands. As for downsides, the catalyst is more challenging to handle, thus requiring careful storage and handling in a glove box. The CE is conducted after workup in an apolar, aprotic solvent where electroneutrality, in some aspects, may have a substantial impact on the stability of charged species. [0106] Preliminary nanoparticle morphology assessment

[0107] The CE is carried out on the Ge NPs after workup, under inert atmosphere, a mixture of the clean NP dispersion, catalyst, and exchange ligands are mixed in a hexane solution. The exposure of Ge NPs to a highly reactive catalyst could potentially alter their morphology, so a preliminary characterization was carried out before and after the exchange processes with Raman spectroscopy and XRD to assess the effect of the CE on the NP morphology. It was found that no change in morphology occurred, as demonstrated by the similarities in the XRD and Raman spectra before and after the exchange. This finding highlights the resilience of the NPs to highly reactive environments, indicating that they are robust materials applicable for a wide array of applications.

[0108] a-Ge NP Catalytic exchange

[0109] Both a- and c-Ge NPs have undergone ligand exchange under catalytic conditions. In terms of HSAB, a slightly lower affinity is expected between the a-Ge and the harder OT in respect to the softer ODE and DODY. This hypothesis is based on the lower refractive indexes and dielectric constants reported in the a-Ge literature in respect to c-Ge.^[45-4?l By approximation, it is possible to directly relate the refractive index and the dielectric constant to the polarizability of the electron density of a material, making materials with lower refractive index and dielectric constant more polarizable, and therefore softer. The CE products have been similarly investigated through the combination of IR spectroscopy and NMR spectroscopy as before.

[0110] In this example, OT has been considered a benchmark to compare the efficiency of the ligand exchange against the reported literature. OT belongs to the thiol class, which are among the most reported molecules for ligand exchanges on Ge NPs.

It has been shown that thiol-passivated Ge NPs exhibit higher stability in polar solvents, when compared to native OAm capped Ge NPs. More importantly, these NPs have shown efficient charge-carrier separation, indicating that the thiol-capping could lead to enhanced photovoltaic response in Ge-based optoelectronic devices. The OT is a pure L-type ligand interacting with the Ge NP surface with or without a proton mediation. Although less hard than OAm, it is believed the OT will displace OAm with a substantial contribution of the steric effect. Given the difference in chain length and conformation, it is believed that the cone angle of OT will be much narrower than that of OAm, resulting in a favorable infiltration and displacement of the native OAm. For the exchange of the a-Ge NPs with thiol, the IR analysis does not indicate any peaks related to OAm, specifically the vinylic proton and the stretching of the C=C are missing, as depicted in FIG. 3. This observation is clarified by the higher sensitivity of the NMR analysis, where it is possible to observe a minor contribution of the vinylic and allylic features of the native OAm, as shown in FIG. 4. Nevertheless, the intensity of these residual features is so low that they almost disappear in the background. It is noticeable in the NMR spectrum that there is a loss of the S-H signal in addition to a substantial intensity and multiplicity loss of the a, b, and d features of the thiol. A closer analysis also shows small peaks just behind the alkylic chain signal at d 1.26 ppm. Due to the low stability of the product, correlated spectroscopy (COSY)-NMR experiment has been performed, as shown in FIG. 5. The COSY-NMR reveals a correlation between these small features, which have been assigned to alcoholic contamination (i.e., EtOH) used as antisolvent during workup. Meanwhile, the feature at d 2.6 and 2.5 correlate with each other and both correlate with the feature at d 1 .55 ppm. Both these features belong to the proton in the a position of the thiol. The difference in chemical shift is a good indication that part of the ligands responsible for the feature at higher chemical shift are interacting more strongly with the NP surface, while the ligands that show no shift in respect to the pure ligand at d 2.5 ppm are unbound. This data points toward an almost complete displacement of the native OAm, with only minor residues (<5%). The presence of a thiolic deshielded a-proton feature at higher ppm suggests that the OT has entered the surface chemistry of the Ge NPs, coordinating the Ge NPs via the S atom. An analysis of the relative integral intensities in the ¹H-NMR spectra shows an exchange efficiency > 95%.

[0111] ODE and DODY are both linear unsaturated alkylic compounds. As previously described for ODE, DODY is also an apolar L-type ligand, with DODY expected to be slightly harder than ODE. Both unsaturated ligands are investigated under CE conditions to investigate any difference in the reactivity on an sp² and sp type of unsaturation. Due to the higher electronegativity of the sp unsaturation, DODY is considered a mildly harder ligand than ODE. Additionally, in comparison with ODE, DODY has a shorter alkylic chain, making it less sterically hindered. From a theoretical standpoint, it is interesting to observe whether these combined differences will result in different exchange efficiencies or counterbalance each other.

[0112] The a-Ge CE with ODE NPs show the removal of the native OAm, with a mismatch of the features observed in the fingerprint region, in respect to the pure ODE spectrum. It is possible to observe the loss of the unsaturation-related features. This result is contrary to the NMR result; although this measurement also confirms the displacement of the OAm, the NMR reveals the presence of some unreacted ODE surrounding the Ge NPs. This discrepancy has been attributed to the higher sensitivity of the NMR technique in respect to the IR. This hypothesis is supported by the relative intensity of the -(CH2) signal compared with the unsaturation-related features. Pure ODE possesses a total of 36 protons, three of them bound to the unsaturation at distinct positions, resulting in the three signals mentioned above. An integration analysis of pure ODE, taking as reference the alkylic signal, suggests a reduction of approximately 66% of the ODE. It is believed that the remaining 33% unreacted ODE is a free-floating ligand from an incomplete workup. These results show the complete removal of OAm, and the exchange with the reduced product of ODE, i.e. octadecane.

[0113] For the CE on DODY, the IR analysis shows the removal of the native OAm ligand and the loss of any unsaturation-related features, signaling the displacement of OAm and a complete reduction of the DODY from a triple bond to a single bond. It was initially believed that DODY would convert to dodecene, with a reduction from triple to double bond, but the data indicates a complete reduction to dodecane. This is further supported by NMR analysis, which shows only two features related to the compound, one prominent alkylic feature at d ^« 1.26 ppm and the terminal -CH₃ feature at d 0.88 ppm. Given the lack of any OAm signal and the presence of only alkylic-chain-related signals, it is believed that the exchange with DODY successfully displaced the native OAm and exchanged on the surface of the Ge NPs with the reduced product of DODY, i.e. dodecane. [0114] The results indicate a higher exchange efficiency for ODE and DODY with respect to OT. Additionally, the successful results with both the unsaturated ligands do not show any relevant differences in the different hybridization reactivities.

[0115] c-Ge N Ps Catalytic exchange

[0116] The c-Ge NPs were also catalytically exchanged under the same conditions as their amorphous counterparts. In respect to the a-Ge, it is believed a more efficient exchange with OT would be observed relative to ODE and DODY with reference to HSAB theory. In the case of c-Ge, it was believed a stronger affinity with the harder OT would be observed due to its harder nature than a-Ge, as discussed above.

[0117] The catalytic exchange on the crystalline NPs with OT is consistent with HSAB theory and the suitability of the thiol class as capping agents for the passivation of c-Ge NPs. The IR analysis shows a lack of unsaturation-related features coming from residual OAm. At higher magnification, one can see the overlap of multiple IR features, with an important feature at 1275 cm ¹ being assigned to the d CH2-S mode. The NMR analysis matches with these expectations. Asides from the S-H signal that cannot be observed in the c-Ge CE with OT, all the pure OT features are maintained. A more detailed analysis shows a sequentially greater upfield shift as the distance between the proton and the S decreases. Together with the lack of any amine-related feature, these results confirm the complete exchange of OAm with OT, and the coherent shift of the NMR signals also strongly suggests that there is a robust covalent interaction between the S and the Ge of the NP surfaces.

[0118] The IR analysis for the crystalline NPs exchanged with ODE shows no traces of residual OAm. At the same time, the removal of the double-bond related features was observed, signaling the complete reduction of ODE. Additionally, a broad feature at around 800 cm ¹ signals the development of a small quantity of Ge0₂. These findings are cross-confirmed by ¹H NMR analysis, where the higher sensitivity of NMR allows observation of the minor features arising from residual OAm. Subsequent integration analysis further confirms the complete reduction of ODE. When the feature at d 0.88 ppm is normalized at a value of 6, the alkylic chain feature at d 1.26 results in a value of 30.12, which sums to 36.12 protons. Depending on the type of ligation expected, either X- or L-type ligands, the expected hydrogen count is either 37 or 36, respectively. The integration supports an X-type coordination, but more in-depth analysis is needed to confirm this observation. The results also show a partial displacement of OAm with the ODE reduction product (octadecane) as the principal capping agent. A deeper NMR integration analysis, based on the contribution of the allylic and vinylic features of the native OAm in respect to the features of the terminal -CH₃ indicates a capping rate of 81% ODE, with the remaining ligands being OAm.

[0119] The comparison of pure DODY and c-Ge CE with DODY shows the loss of the triple bond features and a good overlap with dodecane, the alkane analog of DODY. For the a-Ge CE with DODY, it was believed that the triple bond would be reduced to a double bond, but the lack of features around 3100 cm ¹ suggests a complete reduction to dodecane. The NMR analysis corroborates this finding. Besides a small fraction of residual OAm observed with the signals at d 5.35 ppm and d 2.00 ppm as discussed previously, the only signals coming from the exchange product are related to long alkylic chains at d 1.26 ppm and the chain termination at d 0.88 ppm. NMR integration demonstrates an 70% exchange rate of DODY as dodecane.

[0120] The lower exchange efficiencies of ODE and DODY relative to OT are in line with HSAB theory. Additionally, the calculated exchange rate of ODE and DODY do not show any relevant differences in their hybridization reactivity, as observed in the case of exchanges onto the a-Ge surface. In table 1 an overview over the ligand exchange efficiencies is given.

Table 1 Summary of ligand exchange efficiencies

DODY Successful 70 % exchanged

EXAMPLE 2

[0121] This example demonstrates catalytic exchange on bulk Si surfaces. In this example, hydrogenated Si surfaces were prepared that normally would require^{11 481} a thermally or photo-activated reaction to functionalize with the desired ligands; however, the methods disclosed herein successfully functionalized the Si surface without the use of such thermally or photo-activated reactions.

[0122] Si (100) wafers were cleaned with solvents of decreasing polarity, followed by 15 min of air plasma cleaning to remove any residues. The cleaned wafers were then etched with HF before transferring to a N2 glove box. Under N2 atmosphere, the wafers were placed in beakers and submerged under 2 mL of anhydrous hexane and 2 mL of Ethyl aluminum dichloride (EtAIC ) (1.0 M in hexane). Subsequently, 4 mL of pure ligands (Oleylamine (OAm), octanethiol (OT), and octadecene (ODE)) were added slowly under medium non-turbulent stirring. The reaction is strongly exothermic and might result in bubbling and the production of vapors. The solution was kept stirring at room temperature overnight. The reaction mixture was then quenched with 12 mL of 1 :1 mixture of THF (tetrahydrofuran) and DCM (dichloromethane). Subsequently, the wafers were thoroughly rinsed first with hexane and then with isopropyl alcohol.

[0123] An IR investigation was carried out to demonstrate whether the ligand exchange was successful on the Si surface. The measurements were done in specular reflectance mode, under vacuum, with polarized light, and with a 45° angle of incidence. All samples were measured with single-channel spectra, p-polarized light, and divided internally by the software by the reference recorded with clean Si reference wafer with single-channel and s-polarized light. The spectra were all measured for 256 scans, and 15 spectra were averaged to get the final spectra. This measurement protocol is also applicable when the surface is or comprises Ge. [0124] The results are shown in FIG. 6, where the c-Si and c-Ge samples are compared after catalytic ligand exchange. FIG. 6 shows a stack of full spectra of c-Si wafers and c-Ge nanoparticles coupled based on ligands attached to the surface. The rectangles highlight the matching features between the nanostructured Ge and the bulk Si samples, which have been identified as follows: around 3250 cm ¹ is the stretching mode of N-H, between 3000-2800 cm ¹ is the stretching of C-H, between 1600 and 1500 cm^-1 is the H-N-H dihedral mode, and the feature between 1500-1420 cm^-1 is the CH₃ dihedral mode. The spectra show multiple features matching the results observed for nanostructured Ge, as expected for a successful exchange. In general, it is possible to observe hydrocarbon features in all the samples. Between 3000-2800 cm ¹, the two observed features relate to symmetric and asymmetric stretching of the C-H bonds, while the feature between 1500-1420 cm ¹ is ascribed to the terminal methyl group dihedral mode. In all cases, these features are observed, thereby demonstrating the presence of hydrocarbon-based ligands on all the samples after the catalyzed ligand exchange. Additionally, other IR active modes that are expected to develop after ligand exchange can be found in the c-Si sample exchanged with OAm, where the stretching mode of N-H can be observed at 3250 cm^-1, and confirmed by the peak arising from the H-N-H dihedral mode between 1600 and 1500 cm^-1, as highlighted in the boxes marked Ί” and “2” in FIG. 6. These results confirm that the catalyzed ligand exchange is successful in the case of Si.

[0125] References

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STATEMENTS REGARDING INCORPORATION BY REFERENCE

AND VARIATIONS

[0175] All references throughout this application, for example patent documents including issued or granted patents or equivalents; patent application publications; and non-patent literature documents or other source material; are hereby incorporated by reference herein in their entireties, as though individually incorporated by reference, to the extent each reference is at least partially not inconsistent with the disclosure in this application (for example, a reference that is partially inconsistent is incorporated by reference except for the partially inconsistent portion of the reference). [0176] The terms and expressions which have been employed herein are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments or aspects, exemplary embodiments or aspects and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention as defined by the appended claims. The specific embodiments or aspects provided herein are examples of useful embodiments or aspects of the present invention and it will be apparent to one skilled in the art that the present invention may be carried out using a large number of variations of the devices, device components, methods steps set forth in the present description. As will be obvious to one of skill in the art, methods and devices useful for the present methods can include a large number of optional composition and processing elements and steps.

[0177] As used herein and in the appended claims, the singular forms "a", "an", and "the" include plural reference unless the context clearly dictates otherwise. Thus, for example, reference to "a cell" includes a plurality of such cells and equivalents thereof known to those skilled in the art. As well, the terms "a" (or "an"), "one or more" and "at least one" can be used interchangeably herein. It is also to be noted that the terms "comprising", "including", and "having" can be used interchangeably. The expression “of any one of claims XX-YY” (wherein XX and YY refer to claim numbers) is intended to provide a multiple dependent claim in the alternative form, and in some aspects is interchangeable with the expression “as in any one of claims XX-YY.”

[0178] When a group of substituents is disclosed herein, it is understood that all individual members of that group and all subgroups, including any isomers, enantiomers, and diastereomers of the group members, are disclosed separately.

When a Markush group or other grouping is used herein, all individual members of the group and all combinations and subcombinations possible of the group are intended to be individually included in the disclosure. When a compound is described herein such that a particular isomer, enantiomer or diastereomer of the compound is not specified, for example, in a formula or in a chemical name, that description is intended to include each isomer and enantiomer of the compound described individual or in any combination. Additionally, unless otherwise specified, all isotopic variants of compounds disclosed herein are intended to be encompassed by the disclosure. For example, it will be understood that any one or more hydrogens in a molecule disclosed can be replaced with deuterium or tritium. Isotopic variants of a molecule are generally useful as standards in assays for the molecule and in chemical and biological research related to the molecule or its use. Methods for making such isotopic variants are known in the art. Specific names of compounds are intended to be exemplary, as it is known that one of ordinary skill in the art can name the same compounds differently.

[0179] Certain molecules disclosed herein may contain one or more ionizable groups [groups from which a proton can be removed (e.g., -COOH) or added (e.g., amines) or which can be quaternized (e.g., amines)]. All possible ionic forms of such molecules and salts thereof are intended to be included individually in the disclosure herein. With regard to salts of the compounds herein, one of ordinary skill in the art can select from among a wide variety of available counterions those that are appropriate for preparation of salts of this invention for a given application. In specific applications, the selection of a given anion or cation for preparation of a salt may result in increased or decreased solubility of that salt.

[0180] Every device, system, formulation, combination of components, or method described or exemplified herein can be used to practice the invention, unless otherwise stated.

[0181] Whenever a range is given in the specification, for example, a temperature range, a time range, or a composition or concentration range, all intermediate ranges and subranges, as well as all individual values included in the ranges given are intended to be included in the disclosure. It will be understood that any subranges or individual values in a range or subrange that are included in the description herein can be excluded from the claims herein.

[0182] All patents and publications mentioned in the specification are indicative of the levels of skill of those skilled in the art to which the invention pertains. References cited herein are incorporated by reference herein in their entirety to indicate the state of the art as of their publication or filing date and it is intended that this information can be employed herein, if needed, to exclude specific embodiments or aspects that are in the prior art. For example, when composition of matter are claimed, it should be understood that compounds known and available in the art prior to Applicant's invention, including compounds for which an enabling disclosure is provided in the references cited herein, are not intended to be included in the composition of matter claims herein.

[0183] As used herein, “comprising” is synonymous with "including," "containing," or "characterized by," and is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. As used herein, "consisting of' excludes any element, step, or ingredient not specified in the claim element. As used herein, "consisting essentially of" does not exclude materials or steps that do not materially affect the basic and novel characteristics of the claim. In each instance herein any of the terms "comprising", "consisting essentially of" and "consisting of' may be replaced with either of the other two terms. The invention illustratively described herein suitably may be practiced in the absence of any element or elements, limitation or limitations which is not specifically disclosed herein.

[0184] One of ordinary skill in the art will appreciate that starting materials, biological materials, reagents, synthetic methods, purification methods, analytical methods, assay methods, and biological methods other than those specifically exemplified can be employed in the practice of the invention without resort to undue experimentation. All art-known functional equivalents, of any such materials and methods are intended to be included in this invention. The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention that in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments, aspects, and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention as defined by the appended claims

Claims

We claim:

1. A method for ligand exchange, the method comprising: providing a surface comprising a first ligand, wherein the surface comprises germanium, silicon, or a combination thereof; subjecting the surface comprising the first ligand to a catalyst in the presence of a second ligand that is different from the first ligand; and exchanging the first ligand for the second ligand.

2. The method of any preceding claim, wherein the catalyst is a Lewis acid.

3. The method of any preceding claim, wherein the catalyst comprises an electron- rich portion and an electron-deficient portion.

4. The method of claim 3, wherein the electron-deficient portion of the catalyst comprises an aluminum atom.

5. The method of claim 3 or claim 4, wherein the electron-rich portion of the catalyst comprises a chloride atom.

6. The method of any one of claims 3-5, wherein the catalyst is AIX3, each X can be the same or different, Al is the electron-deficient portion of the catalyst, Cl and/or X is the electron-rich portion of the catalyst, and optionally each X is independently selected from halide or an alkyl chain.

7. The method of any one of claims 3-6, wherein the electron-rich portion of the catalyst, the electron-deficient portion of the catalyst, the second ligand, or any combination thereof form a planar adduct during the method.

8. The method of any preceding claim, wherein the surface comprises amorphous silicon (a-Si), crystalline silicon (c-Si), amorphous germanium (a-Ge), crystalline germanium (c-Ge), or any combination thereof.

9. The method of any preceding claim, wherein the surface is in a form of a nanoparticle or a wafer.

10. The method of any preceding claim, wherein the first ligand is selected from a straight or branched chain alkyl amine having 4 to 30 carbon atoms, a straight or branched chain alkenyl amine having 4 to 30 carbon atoms, or a straight or branched chain alkynyl amine having 4 to 30 carbon atoms.

11 . The method of any preceding claim, wherein the first ligand is selected from a straight or branched chain alkyl primary amine having 4 to 30 carbon atoms, a straight or branched chain alkenyl primary amine having 4 to 30 carbon atoms, or a straight or branched chain alkynyl primary amine having 4 to 30 carbon atoms.

12. The method of any preceding claim, wherein the first ligand is present as a plurality of first ligands selected from a straight or branched chain alkyl amine having 4 to 30 carbon atoms, a straight or branched chain alkenyl amine having 4 to 30 carbon atoms, a straight or branched chain alkynyl amine having 4 to 30 carbon atoms, or any combination thereof.

13. The method of any preceding claim, wherein the first ligand is oleylamine or -H, or if present as a plurality of first ligands, a combination thereof.

14. The method of any preceding claim, wherein the first ligand is a native ligand present on the surface as a result of a process employed to synthesize the surface, optionally wherein the surface is in a form of a nanoparticle.

15. The method of any preceding claim, wherein the second ligand is selected from a straight or branched chain alkyl thiol having 4 to 30 carbon atoms or a disulfide thereof, a straight or branched chain alkenyl thiol having 4 to 30 carbon atoms or a disulfide thereof, a straight or branched chain alkynyl thiol having 4 to 30 carbon atoms or a disulfide thereof, a straight or branched chain alkene having 4 to 30 carbon atoms, or a straight or branched chain alkyne having 4 to 30 carbon atoms.

16. The method of any preceding claim, wherein the second ligand is present as a plurality of second ligands selected from a straight or branched chain alkyl thiol having 4 to 30 carbon atoms or a disulfide thereof, a straight or branched chain alkenyl thiol having 4 to 30 carbon atoms or a disulfide thereof, a straight or branched chain alkynyl thiol having 4 to 30 carbon atoms or a disulfide thereof, a straight or branched chain alkene having 4 to 30 carbon atoms, a straight or branched chain alkyne having 4 to 30 carbon atoms, or any combination thereof.

17. The method of any preceding claim, wherein the second ligand is selected from 1-octanethiol, 1-octadecene, or 1-dodecyne, or if present as a plurality of second ligands, any combination thereof.

18. The method of any preceding claim, wherein, when the second ligand contains a terminal alkene or alkyne, the exchanging step optionally results in (1) converting the terminal alkene to an alkyl upon attachment to the surface, (2) converting the terminal alkyne to alkenyl upon attachment to the surface, (3) converting the terminal alkyne to alkyl upon attachment to the surface, or (4) any combination thereof.

19. The method of any preceding claim, wherein: the catalyst is EtAIC ; the surface comprises a-Ge, c-Ge, or Si(100); the first ligand is oleylamine or -H, or if present as a plurality of first ligands, a combination thereof; the second ligand is 1-octanethiol, 1-octadecene, or 1-dodecyne, or if present as a plurality of second ligands, any combination thereof; when the second ligand is 1-octadecene alone or as part of a combination, at least a portion of 1-octadecene is converted to 1-octadecyl upon attachment to the surface; and when the second ligand is 1-dodecyne alone or as part of a combination, at least a portion of 1-dodecyne is converted to 1-dodecyl upon attachment to the surface.

20. The method of any preceding claim, wherein the method is performed at a temperature of 5 °C to 50 °C.

21 . The method of any preceding claim, wherein method is performed in a polar solvent or an apolar solvent.

22. The method of any preceding claim, wherein, after the providing step and prior to the exchanging step, the surface is not hydrogenated or exposed to a surface activation step, optionally wherein the surface activation step comprises treatment with hydrazine.

23. The method of any preceding claim, wherein the surface comprises a plurality of the first ligand, and at least 70% of the plurality of the first ligand is exchanged with a plurality of the second ligand during the method, as determined by at least one of IR spectroscopy and ¹H NMR spectroscopy.

24. The method of any one of claims 1 -22, wherein the surface comprises a plurality of the first ligand, and 5-70% of the plurality of the first ligand is exchanged with a plurality of the second ligand during the method, as determined by at least one of IR spectroscopy and ¹H NMR spectroscopy