WO2022211916A2 - Matrix assisted direct transfer - Google Patents

Abstract

A method of transferring molecular material to a surface, includes mixing either the molecular material or a precursor of the molecular material with a matrix material to produce a mixture, heating the mixture to melt the matrix material in the mixture, solidifying the mixture, turning the mixture into a powder, transferring the powder to a substrate, and sublimating the matrix material out of the mixture so that only the molecular material remains.

Description

MATRIX ASSISTED DIRECT TRANSFER

RELATED APPLICATION

[0001] This application claims priority to and the benefit of US Provisional Application No.

63/150,432 filed February 17, 2021, which is incorporated herein by reference in its entirety.

GOVERNMENT RIGHTS

[0002] This invention was made with government support under 1807474 and 1839098, awarded by the National Science Foundation, and under N00014- 16- 1-2921, and N00014-19-1-2503 awarded by the Office of Naval Research. The government has certain rights in the invention.

TECHNICAL FIELD

[0003] This disclosure relates to synthesis of isolated molecular structures, more particularly to a transfer approach of these structures or their precursors to a substrate.

BACKGROUND

[0004] The bottom-up synthesis of graphene nanoribbons (GNRs), quasi- ID strips of graphene that can host precisely tunable band gaps and topological engineered states, has largely been restricted to two complementary but mutually incompatible approaches. The first is an on-surface catalyzed radical step- growth mechanism well-suited for the detailed characterization of GNRs using advanced scanning probe microscopy (SPM) imaging and spectroscopy. The second is a more conventional solution-based approach that takes advantage of the superior control over critical performance parameters provided by modern step-growth and living polymerization techniques.

[0005] While the first technique has been a workhorse for the exploration of electronic properties emerging from lateral quantum confinement in graphene, the control over critical structural parameters, including GNR length, monomer sequence, number and position of interface states, and functional end- groups, all required for the integration of GNR technology into advanced electronic devices, has been limited by the shortcomings of surface-catalyzed radical step-growth polymerization.

[0006] In contrast, solution-based approaches can overcome many of the structural limitations encountered in the on-surface growth. Modern synthetic protocols give access to sequence controlled (co)polymer precursors to functional GNRs. Both the length and functional end-groups can be precisely controlled using living polymerization techniques. For either technique, the scope of the synthetically accessible GNR structures is largely dictated by unique sets of requirements imposed by either the underlying surface-growth or solution-based polymerization mechanisms and are often exclusive to either technique. Leading efforts to integrate bulk solution-synthesized GNRs with advanced surface- based characterization tools have relied on a direct contact transfer (DCT) sample preparation technique. While this approach has successfully been used to characterize solution-synthesized GNRs using SPM, the sample preparation suffers from the common trend of GNRs to aggregate into amorphous bundles through p-p stacking interactions. Furthermore, DCT of fully cyclized solution-synthesized GNRs fails to take advantage of a wealth of chemical transformations and structures exclusively accessible through on-surface growth techniques.

[0007] The problems discussed above with regard to GNRs has highlighted an issue with characterization of molecular structures, including but not restricted to GNRs. However, other molecular structures suffer from the same issues, these include three dimensional (3D) and two- dimensional (2D) materials such as graphene, boron nitride, transition metal dichalcogenides (TMDs), metalorganic frameworks (MOFs), covalent organic frameworks (COFs), one dimensional (ID) systems such as carbon nanotubes (CNTs), boron nitride nanotubes, graphene nanoribbons (GNRs), etc., and quasi 0D molecular species such as fullerenes, complex natural products, organic/inorganic complexes, organic and inorganic nanoparticles, organic and inorganic nanocrystals etc.. Manufacture of these structures in a manner that allows them to maintain their isolated nature so that they can undergo characterization with scanning probe microscopy (SPM) would also ensure that they would have appropriate isolation to allow them to be used in electronic devices.

BRIEF DESCRIPTION OF THE DRAWINGS [0008] FIGs. 1 A-1C show a schematic representation of matrix assisted direct contact transfer.

[0009] FIG. 2 shows a flowchart of a method of transferring molecular structures to a substrate.

[0010] FIG. 3 shows a diagram of an embodiment of producing a first polymer.

[0011] FIG. 4 shows a diagram of synthesis of a chevron graphene nanoribbon from a first polymer. [0012] FIGs. 5A-5H show graphs of characterization of different polymers used in a method of manufacturing graphene nanoribbons and accompanying STM images.

[0013] FIG. 6 shows a diagram of an embodiment of a synthesis of second polymer.

[0014] FIG. 7 shows diagram of an embodiment of a synthesis of armchair graphene nanoribbons from a second polymer.

[0015] FIGs. 8A-8K show STM images of armchair graphene nanoribbons.

[0016] FIGs. 9A-9B show STM images of a first polymer deposited on a surface after annealing using a standard direct transfer method with no matrix.

[0017] FIGs. 10A-10F show STM images of a first polymer deposited using matrix assisted direct contact method.

[0018] FIG. 11 shows STM images of a second polymer deposited using matrix assisted direct contact.

DETAILED DESCRIPTION OF THE EMBODIMENTS [0019] The embodiments here employ a matrix assisted direct contact, referred to here as MAD, method of transferring molecular structures to a substrate. The substrate in the examples here consist of common surfaces used in scanning tunneling microscopy (STM). MAD transfer of molecular samples to this type of substrate for characterization results in structures have the necessary precision, isolation, and orientation to be suitable for electronic devices and other applications. The discussion here may refer to the molecular structures as molecular samples or molecular material to differentiate it from the transfer matrix material.

[0020] The below discussion focuses on examples of the MAD techniques being used to manufacture isolated graphene nanoribbon (GNRs) from polymers. However, one should note that the MAD transfer methodology applies to any type of molecular structure including GNRs, two-dimensional materials such as graphene, carbon nanotubes (CNTs), metal organic frameworks, covalent frameworks, transition metal complexes, boron nitride flakes, and natural products, among many others. GNRs may take the form of armchair-GNRs, referred to as aGNRs, and chevron-type GNRs, referring to their shape.

[0021] The term “natural product” as used here refers to a chemical compound or substance produced by a living organism, which may or may not be isolated from natural sources. These molecular structures have high degrees of complexity and present challenges in trying to characterize them. Application of the MAD method will allow isolation of these structures to allow their characterization. The term “isolated” as used here means a structure that remains separated from other like or unlike structures. As will be discussed below, an issue that arises in current techniques is aggregation and loss of the isolation.

[0022] The term “molecular structure” or “sample” as used here includes GNRs and other molecular and macromolecular structures that suffer from the same issues. These include three dimensional (3D) and two-dimensional (2D) materials, such as graphene, boron nitride, transition metal dichalcogenides (TMDs), metal organic frameworks (MOFs), covalent organic frameworks (COFs), etc., one dimensional (ID) systems such as carbon nanotubes (CNTs), boron nitride nanotubes, graphene nanoribbons (GNRs), etc., and quasi 0D molecular species, such as fullerenes, complex natural products, organic/inorganic complexes, organic and inorganic nanoparticles, organic and inorganic nanocrystals, etc. [0023] As mentioned above, demonstration of the MAD method occurred in the context of GNRs. The discussion of these examples demonstrates the advantages and results of this process. The method employed in this process has wide applicability as discussed above.

[0024] The embodiments here show a hybrid bottom-up approach that successfully combines three key elements of advanced GNR synthesis. First, the embodiments have the exquisite structural control provided by solution-based polymerization techniques gives access to sequence-controlled (co)polymer GNR precursors featuring narrow and well-defined length distributions. Second, matrix-assisted direct (MAD) transfer of these GNR precursors onto solid substrates, such as gold, Au(l 11), enables surface catalyzed chemical transformations widely used in the on-surface synthesis of GNRs. Third, preparation of spatially isolated GNRs on scanning tunneling microscopy (STM) compatible substrates gives access to advanced bond-resolved imaging and spectroscopic characterization techniques previously reserved for surface grown GNRs. The substrate may comprise one of a catalytic substrate, a substrate suitable for SPM or STM characterization, and a substrate suitable for electronic device characterization.

[0025] FIGs. 1 A and IB show a schematic representation of the MAD transfer process. On the left side, at FIG. 1 A, a fiberglass applicator is loaded with polymer samples dispersed in a chemically inert matrix under ambient conditions. In the middle, at FIG. IB, the MAD transfer of polymer dispersion on an STM substrate under ultra-high vacuum (UHV). Finally, on the right at FIG. 1C, in these embodiments, the deposited sample of polymers undergo traceless sublimation of the bulk matrix, followed by cyclodehydrogenation leaving spatially isolated GNRs behind. One should note that the process may not require annealing if a matrix featuring a low heat of sublimation is selected.

[0026] FIG. 2 shows a generalized method of an embodiment of a MAD transfer process. The process may use some or all of the various sub-processes shown. The process mixes the molecular material or sample with the matrix material at 20. In some instances, the molecular material may comprise the final material that will result on the substrate, or it may comprise a precursor to the final material. [0027] The mixture then undergoes heating at 22 to melt the matrix material. The resulting mixed and melted material may then undergo more mixing to ensure homogenous dispersion. In order to powder the material, depending upon the nature of the matrix and the molecular structural, the resulting mixed and melted material may need freezing to crystallize the mixture as shown at 24. In alternative embodiments, the mixture may just be allowed to cool and solidify. Once the material has a form that allows grinding or other methods to product a powder, the process powders the mixture at 26. The powder particles may consist of a combination of the molecular material and the matrix material.

[0028] In the embodiment of FIG. 2, an applicator then picks up the powder particles at 28. In one embodiment, the surface onto which the applicator may deposit the powder may reside in a chamber. After being inserted in the chamber, the applicator is pumped down to an ultra-high vacuum (UHV).

The transfer of the powder to the substrate may occur in many different ways, using an applicator merely provides one example. The applicator then approaches the substrate and presses against it to transfer the molecular material at 30. In one embodiment, such as in formation of GNRs, the substrate may undergo further heating to a temperature to cause the matrix material to sublimate from solid to gas at 32. In some instances, the heating may take the form of annealing that will both form the final material on the substrate and sublimate the matrix, leaving behind isolated GNR structures.

[0029] Selection of a suitable matrix requires consideration of both chemical and materials properties. The matrix itself must be chemically inert across a wide range of temperatures to avoid undesired reactions with the polymer sample or uncontrolled thermal decomposition during processing. A low melting point, T_m, ensures that the polymer can readily be dissolved in a melt of the matrix under ambient conditions. Dispersion and dilution of the polymer sample is most effective if the non-covalent interactions between the matrix and the polymer sample are stronger, such as if the molten matrix is a good solvent for the sample, than the attractive interactions between molecules of the sample themselves. A poor solvent will lead to amorphous aggregates on the surface. Traceless removal of the matrix following deposition can only be achieved if the matrix exhibits a low enthalpy of sublimation, AH_sub°, and undergoes a solid/gas phase transition under reduced pressure, such as UHV. While a wide variety of hydrocarbons meet the criteria listed above, the experiments here relied on pyrene (T_m =

151.1 ± 0.5 °C, AH_sub° = 23.9 ± 0.3 kcal mol^-1) as auniversally accessible traceless matrix.

[0030] An initial experiment studied the thermally-induced surface catalyzed cyclodehydrogenation of poly-1 (Scheme 1), a precursor to chevron-type GNRs (cGNRs), deposited on Au(l 11) surfaces using the MAD transfer technique.

[0031] FIG. 3 shows an embodiment of a first polymer, referred to below as poly-1. The experiment proceeded as follows. Bis(cyclooctadiene)nickel(0) (0.154 g, 0.56 mmol), 1,5-cyclooctadiene (0.10 mL, 0.56 mmol), 2,2’-bipyridyl (0.088 g, 0.56 mmol), and DMF (2.5 mL) were added to a 25 mL sealable tube in a glovebox. The reaction mixture was sealed under N2, removed from the glovebox, and stirred at 55 °C for 30 min. In an oven-dried 20 mL scintillation vial, 1 (0.100 g, 0.145 mmol) was dissolved in dry toluene (3 mL) under N2. The resulting solution of 1 in dry toluene was added to the reaction mixture under N2 and the reaction mixture was stirred at 80 °C for 48 h. The reaction mixture was cooled to 24 °C and diluted with MeOH (50 mL) to precipitate crude poly-1 as a fine yellow powder. The crude solid was filtered over a 0.2 micron PTFE filter and washed with MeOH (100 mL), 1M HC1 (100 mL), MeOH (100 mL), 1M NaOH (100 mL), H₂0 (100 mL), MeOH (100 mL), and hexanes (100 mL) to yield poly-1 (0.76 g, 0.143 mmol, 99%) as a fine yellow powder. Poly-1 was characterized by analytical SEC, MALDI mass spectrometry, and 'H NMR before being subjected to preparative SEC with CHCh as the eluent yielding low M_n poly -In and high M_n poly-lb. FIG. 3 shows the scheme for synthesis of poly-1, and FIG. 4 shows the resulting chevron GNRs after MAD transfer to the substrate and annealing.

[0032] Size exclusion chromatography (SEC) analysis of samples of poly-1 prepared through Ni(cod)2 catalyzed Yamamoto step-growth polymerization of 6,11-dibromo- 1,2,3, 4-tetraphenyltriphenylene exhibit broad molecular weight distributions (D = 1.3, and that ranges between 2-12 kg mol^-1. Preparative SEC of a crude sample of poly- 1 soluble in CHCF, yielded a low M_a fraction poly- la (M= 2-7 kg mol^-1) and a high M_a fraction poly-Vo (M= 7-12 kg mol^-1). Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) of poly- la, shown in FIG. 5A shows a family of peaks separated by integer repeat units of the monomer mass ( Am/z = 530 u) ranging from the 5mer to the 13mer, m/z = 2661 u to m/z = 6905 u, respectively.

[0033] MALDI of the high M_a fraction poly- lb, shown in FIG. 5B reveals an analogous series of mass signals ( Am/z = 530 u) ranging from the 15mer to the 22mer (m/z = 7968 u to m/z = 11681 u), albeit at significantly lower intensities. End-group analysis suggests that the polymers are terminated by hydrogen atoms on either end of the chain.

[0034] With two unique fractions of poly-1 at hand, samples were prepared for MAD transfer onto Au(l 11) substrates. 0.1 wt% dispersions of poly- la and poly-Vo in a melt of pyrene were prepared and rapidly solidified at -78 °C before being ground into a fine powder and deposited in UHV onto a Au(l 11) surface using a fiberglass stamp as shown in FIG. 1. Gradual annealing of the molecule decorated surface at 300 °C for 10 min in UHV induces sublimation of the bulk matrix. STM images on Au(l 11) reveal a sub-monolayer coverage of the surface with islands of parallel aligned chains of poly- 1 separated by a random network of residual pyrene molecules, as shown in FIG. 5C.

[0035] The characteristic adsorption geometry and structural features of poly- 1 synthesized in solution and deposited by MAD transfer on a Au(l 11) surface are indistinguishable (0.28 ± 0.03 nm, 1.5 ± 0.1 nm, 1.5 ± 0.1 nm, height, width, and length of the polymer repeat unit) from an original sample prepared via a surface catalyzed radical step growth polymerization of 6,11-dibromo-l, 2,3,4- tetraphenyltriphenylene on Au(l 11). Further annealing of the sample at 420 °C for 10 min induces a thermal cyclodehydrogenation that transforms the polymer precursor poly-1 into the fully conjugated backbone of cGNRs, shown in FIGs. 5D and 5G. STM topographic images reveal the characteristic structural features of cGNRs (0.18 ± 0.03 nm, 2.5 ± 0.2 nm, 1.5 ± 0.1 nm, height, width, and length of the GNR repeat unit) separated by isolated matrix molecules, as shown in FIG. 5D.

[0036] Extending the annealing step from 10 to 30 min leads to the complete desorption of the pyrene matrix leaving only cGNRs behind (FIG. 2H) isolated by empty space. Direct comparison with a sample of poly- 1 deposited on Au(l 11) using a matrix-free DCT technique serves to highlight the critical role of the pyrene matrix in the embodiments of the MAD transfer process. STM topographic images reveal that, in the absence of a matrix, thermal annealing of poly- 1 leads exclusively to irregular carbon networks rather than discrete cGNRs.

[0037] To demonstrate the potential of the MAD transfer process a large area of topographic STM images were recorded and statistically analysis was performed of cGNRs grown from samples of poly- la (M= 2-7 kg mol^-1, 5-13 monomers units) and poly- lb (M= 7-12 kg mol^-1, 15-22 monomers units), as shown in FIGs. 5G and 5H. FIGs. 5E and 5F show histograms for cGNR length (as a function of monomer units) resulting from samples of poly- la (N= 130) and poly-Vo (N = 70). The mode, the mean, the median, the skewness (g), and even the kurtosis (AT) of the statistical length distribution of cGNRs mirrors the m!z distributions previously determined by MALDI-TOF MS of the original samples of poly- la FIG. 5A, and poly- lb, FIG. 5B. This remarkable correlation suggests that critical structural and functional parameters designed into a solution-synthesized GNR (co)polymer precursor, e.g. length, monomer sequence, and potentially even functional end groups, can be seamlessly translated into the structure of the resulting fully cyclized surface-supported GNRs.

[0038] To further illustrate the technological advancement enabled by MAD transfer experiments applied the technique to the synthesis of N₄-7-AGNR, a nanoribbon that, thus far, has been inaccessible using conventional bottom -up approaches. The structure of N₄-7-AGNRs can be derived from an alternating copolymer, poly- 2, formed through a Suzuki-Micmra step-growth polymerization of anthracene-9, 10-diyldiboronic (A) with 5,10-dibromopyrazino[2,3- ]quinoxaline (P). [0039] Synthesis of poly-2 involved a 20 mL scintillation vial charged under N2 with A (50 mg, 0.14 mmol), P (65 mg, 0.15 mmol), tetrakis(triphenylphosphine) palladium(O) (8.5 mg, 0.007 mmol), cesium carbonate (288 mg, 0.88 mmol) and dry toluene (12 mL). The reaction mixture was stirred at 110 °C for 24 h. The reaction mixture was cooled to 24 °C and concentrated on a rotary evaporator. The crude residue was suspended in MeOH (100 mL), sonicated, filtered, and washed with MeOH (2 x 100 mL). To ensure removal of Pd(0) prior to STM studies, the crude orange solid was resuspended in hot CH2CI2 (200 mL), sonicated, filtered over a pad of Celite, and washed with several portions of hot CH2CI2 (10 x 200 mL) until the orange color no longer persisted on the filter cake. The CH2CI2 filtrate was concentrated on a rotary evaporator in several batches yielding an oligomeric mixture of poly-2 (0.045 g, 0.13 mmol, 90%) as an orange solid. The solubility of oligomeric samples of poly-2 in common deuterated solvents is insufficient to acquire ¾ or ¹³C{ ¹H} NMR spectra. 'H NMR analysis in C2D2CL shows exclusively Bpin-terminated oligomers of poly-2.

[0040] The alternating (A-P)_n pattern of monomer building blocks in N₄-7-AGNR is incompatible with the typical requirement for a symmetric repeat unit used in on-surface radical step-growth polymerizations of GNRs. At the same time the oxidative cyclodehydrogenation of all /^//-positions in poly-2 involves the formation of C-N bonds, a challenging transformation in solution, yet readily accessible even at moderate temperatures on Au(l 11) surfaces. The introduction of MAD transfer techniques enabled us to design a bottom-up synthesis of N₄-7-AGNR that takes advantage of the superior sequence control imparted by solution-based transition metal catalyzed cross-coupling reactions, while retaining access to the surface-catalyzed cyclodehydrogenation sequence facilitated by the Au(l 11) substrate. FIG. 6 shows schematic of the synthesis process for poly- 2, and FIG. 7 shows a diagram of the MAD transfer and the resulting AGNR segments.

[0041] STM topographic images of short segments of N₄-7-AGNR prepared by depositing a dispersion of 0.1 wt% poly-2 in a pyrene matrix onto a Au(l 11) substrate followed by annealing of the molecule decorated surface at 280 °C for 10 min are shown in FIG. 8A. The uniform width (0.95 ± 0.05 nm) and height (0.19 ± 0.02 nm) of the molecular adsorbates is consistent with the expected dimensions of fully cyclodehydrogenated N₄-7-AGNR segments. The longitudinal dimension is an integer multiple of 0.5 ± 0.05 nm commensurate with the average length added by either an anthracene or a pyrazino[2,3- g-Jquinoxaline unit. STM with CO functionalized tips reveals that most N₄-7-AGNR feature an odd number of monomer units (>95%) and are terminated preferentially by anthracene groups. FIG. 8B shows a topographic image of a N₄-7-AGNR oligomer featuring an alternating (A-P-A-P-A) pattern of three anthracene and two pyrazino[2,3-g-]quinoxaline units. All eight pyrazino[2,3-g-]quinoxaline nitrogen atoms have successfully undergone surface catalyzed cyclodehydrogenation. d//dF maps of the same N₄-7-AGNR oligomer recorded across a bias of-1.8 V to +1.6 V. FIGs. 8C-8K show distinct features reflecting the molecular orbitals of the N₄-7 AGNR, which in comparison to the undoped 7- AGNR are spatially inhomogeneous as a result of the substitutional nitrogen atoms. The non-vanishing local density of states around the Fermi level (E_F) (FIGS. 3F-3H) is furthermore suggestive of small-gap semiconducting or even metallic GNR band structure.

[0042] MAD transfer samples were prepared and applied to an Au (111) substrate for STM characterization generally following the method discussed above. FIGs. 9A and 9B show STM images of samples of poly- 1 deposited using a conventional, matrix-free, direct transfer process followed by annealing to 420 °C for 10 minutes. As one can see in the photographs, amorphous networks formed during the annealing process from irregular aggregates and entangle chains of poly-1.

[0043] FIG. 10 shows STM images of a first polymer deposited using matrix assisted direct contact method. Panels A and B show images of short chevron GNRs resulting from annealing a MAD transferred sample of poly- la. Panels C-F show images of long chevron GNRs from resulting from annealing a MAD transferred sample of poly-Vo. FIG. 11 shows STM images of N₄-7 AGNR segments resulting from annealing a MAD transferred sample of poly-2. As one can see from comparing FIGs. 10A-10F and FIG. 11 with FIGs. 9A and 9B, the use of the MAD process results in isolated structures that do not suffer from the aggregation and entanglement shown in FIGs. 9 A and 9B.

[0044] In summary, the embodiments here demonstrate a new means of transferring molecular samples to a substrate that employs a matrix material. The resulting structures remain isolated and do not form amorphous aggregate structures, allowing for cleaner and more accurate characterizations. As mentioned above, if these resultant structures are pristine enough to undergo STM characterization, etc., the same MAD transfer technique will be applicable to the preparation of electronic devices.

[0045] The specific embodiments for GNRs involves a hybrid bottom-up synthetic approach relying on a MAD transfer of solution-synthesized polymer precursors onto a Au(l 11) substrate. Traceless removal of the bulk pyrene matrix followed by surface-assisted cyclodehydrogenation yields spatially isolated GNRs suitable for STM imaging and spectroscopy. The experiments above demonstrate that control over key structural parameters uniquely accessible through solution-based polymerization techniques can seamlessly be translated into the structure of the resulting surface-supported GNRs. The synergy between solution and surface-based bottom-up approaches enabled by the traceless MAD transfer technique not only provides synthetic avenues to complex functional GNR architectures that have thus far been inaccessible by conventional synthetic tools, but also paves the way for the integration of functional GNRs with lithographically patterned integrated circuit architectures.

[0046] The use of the MAD transfer techniques and methods also pave the way for many other molecular samples of many different types. The demonstration using GNRs merely serves as an example of how this method can produce structures with the desired characteristics.

[0047] All features disclosed in the specification, including the claims, abstract, and drawings, and all the steps in any method or process disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. Each feature disclosed in the specification, including the claims, abstract, and drawings, can be replaced by alternative features serving the same, equivalent, or similar purpose, unless expressly stated otherwise. [0048] It will be appreciated that variants of the above-disclosed and other features and functions, or alternatives thereof, may be combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the embodiments.

Claims

WHAT IS CLAIMED IS:

1. A method of transferring molecular material to a surface, comprising: mixing either the molecular material or a precursor of the molecular material with a matrix material to produce a mixture; heating the mixture to melt the matrix material in the mixture; solidifying the mixture; turning the mixture into a powder mixture; transferring the powder mixture to a substrate; and sublimating the matrix material out of the powder mixture on the substrate so that only the molecular material remains.

2. The method as claimed in claim 1, further comprising annealing the powder on the substrate to form a final structure.

3. The method as claimed in claim 1, further comprising performing cyclodehydrogenation after sublimating the matrix material to form spatially isolated graphene nanoribbons.

4. The method as claimed in claim 1, wherein performing cyclodehydrogenation comprises one of either thermal or surface catalyzed cyclodehydrogenation.

5. The method as claimed in claim 1, wherein transferring the powder to a substrate comprises transferring the powder to one of a catalytic substrate, a substrate suitable for SPM characterization, a substrate suitable for electronic device fabrication, and a substrate suitable for electronic device characterization.

6. The method as claimed in claim 1, wherein transferring the powder to a substrate comprises performing the transfer under an ultra-high vacuum.

7. The method as claimed in claim 1, wherein sublimating the matrix occurs under ultra-high vacuum.

8. The method as claimed in claim 1, wherein mixing the molecular material or a precursor of the molecular material with a matrix material comprises mixing the molecular material or a precursor of the molecular material with pyrene.

9. The method as claimed in claim 1, wherein mixing the molecular material or a precursor of the molecular material comprises: mixing Bis(cyclooctadiene) nickel(O), 1,5-cyclooctadiene, 2,2’-bipyridyl , and DMF; sealing the reaction mixture under nitrogen; dissolving and stirring the reaction mixture in dry toluene; and diluting the reaction mixture to produce the precursor of the molecular material.

10. The method as claimed in claim 9, wherein sublimating the matrix material comprises annealing the powder mixture on the substrate until chevron-type graphene nanoribbons form.

11. The method as claimed in claim 10, wherein annealing the powder mixture continues until no matrix material remains.

12. The method as claimed in claim 1, wherein mixing the molecular material or a precursor of the molecular material comprises: mixing anthracene-9, 10-diyldiboronic with 5,10-dibromopyrazinol [2,3-g]quinoxaline, tetrakis(tiphenylphosphine)palladium, cesium carbonate, and dry toluene; and removing the palladium to produce the polymer precursor.

13. The method as claimed in claim 12, wherein sublimating the matrix material comprises annealing the polymer precursor on the substrate.

14. A graphene nanoribbon structure, comprising: a substrate; isolated graphene nanoribbons on the substrate.

15. The structure as claimed in claim 14, wherein the graphene nanoribbons comprise chevron-type graphene nanoribbons.

16. The structure as claimed in claim 14, wherein the graphene nanoribbons comprises N₄-7- AGNRs.

17. The structure as claimed in claim 14, wherein the isolated graphene nanoribbons are separated by molecules of a matrix material.

18. The structure as claimed in claim 14, wherein the isolated graphene nanoribbons are separated by a random network of matrix material molecules.

19. The structure as claimed in claim 14, wherein the isolated graphene nanoribbons are separated by empty space.