RU2796247C1 - Method for obtaining a functionalized nanostructure based on porous silicon - Google Patents

Abstract

FIELD: chemical industry.

SUBSTANCE: methods for the synthesis of composite nanostructures, and in particular methods for manufacturing porous functionalized layers made on the surface of single-crystal silicon. The invention can be used in the manufacture of optical communication systems, light guides, optical resonant sensors, filters in the optical and near ultraviolet band, substrates for analysis by surface Raman scattering. First, a porous silicon substrate is obtained, the surface layer is removed mechanically, either by chemical etching, or using focused ion beam method, after which the substrate is kept in a solution of monohydric alcohol, for example, isopropanol, methanol or ethanol. Then the substrate is functionalized by immersing it in a solution of fullerenols doped with the required functionalizing elements, obtained by dispersing the indicated fullerenols in distilled water. The desired functionalizing elements are selected from metals and/or non-metals. Then, the substrate is held in this solution either statically or dynamically, for example, by centrifugation. After holding the substrate, it is removed from the solution and dried.

EFFECT: obtaining a functionalized nanostructure based on porous silicon with an increased penetration depth of the functionalizing element into the porous silicon layer and to ensure uniform coverage of the functionalizing element both over the surface and in the depth of the porous layer.

5 cl, 7 dwg, 2 ex

Description

The invention relates to a technology for the synthesis of composite nanostructures, and in particular to methods for manufacturing porous functionalized layers made on the surface of single-crystal silicon.

Functionalization refers to the modification of the surface of a nanostructure for subsequent use in various fields: biological, medical, engineering, etc. Functionalization is carried out using a wide range of materials represented by metals, nonmetals, organic molecules, colloidal quantum dots, magnetic nanoparticles, etc., which act as as functional elements. In practice, this type of porous silicon-based nanostructures can be used in a wide range of devices, including as signal sources in the visible range of electromagnetic radiation of photo- and electroluminescent elements for infocommunication systems of optical communication (MAYERGOYZ ID. Plasmon Resonances in Nanoparticles. World Scientific 2013. 325 pp., ISBN 978-981-4350-65-5). Depending on the degree of porosity and the effective refractive index on the basis of these structures, it is possible to implement both semiconductor and dielectric layers in devices and integrated circuits, in particular, to create planar optical fibers, optical resonant sensors (SAARINEN J, WEISS S, FAUCHET P, SIPE J. Optical sensor based on resonant porous silicon structures, Opt Express, May 2005, v.16, no. Porous silicon as efficient surface enhanced Raman scattering (SERS) substrate Applied Surface Science Sep 254 No 22 15 pp 7494-7497), as well as optical and near ultraviolet filters (LIU J, CAI H, TANG K, KONG L. Plasmonic Filters Based on Lithographically Patterned Hexagonally Arranged Triangular Silver Nanoparticles Array, Advances in Materials Science and Engineering, July 2015, Vol. 195320, 9 pp.

There are various methods for obtaining functionalized nanostructures based on porous silicon. For example, there is a known method for obtaining a functionalized nanostructure based on porous silicon, presented in patent RU 2699310 "Method of manufacturing sensitive to giant Raman substrates based on porous silicon containing silver nanoparticles", H01L 21/265, B82Y 40/00, publ. 09/04/2019, where silver acts as a functionalizing element. The method includes the procedure of ion implantation of the initial surface of single-crystal silicon with silver ions with an energy of 4-120 keV, an irradiation dose that ensures the concentration of the introduced metal atoms in the irradiated substrate 1.0⋅10 ¹⁹ - 6.5 10 ²³ atoms/cm ³ and the current density of the ion beam 2⋅10 ¹² - 1 10 ¹⁴ ion/cm ² .

The disadvantage of the known method is the limited penetration depth (10 nm), as well as the uneven distribution of the functionalizing element in the form of silver in the pores of the porous silicon substrate. In addition, the cost of using the ion implantation mechanism is quite high, and efficient bombardment of the target by all types of particles is impossible (in this case, the use of heavy particles can lead to the formation of significant defects in the porous silicon substrate).

Also known is a method for obtaining a functionalized nanostructure based on porous silicon, presented in the article CHAN S, KWON S, KOO TW, LEE LP, BERLIN AA. Surface-Enhanced Raman Scattering of Small Molecules from Silver-Coated Silicon Nanopores. Adv. mater. October 2003, vol. 15, no. 19, p. 1595-1598, where silver acts as a functionalizing element. The method includes the procedure for etching a silicon substrate to obtain a porous silicon substrate, passivation of the porous silicon surface by plasma oxidation, drying the resulting substrate with an argon flow, functionalizing the porous silicon substrate by immersing in a metal-containing Ag salt solution, removing excess Ag salt solution with a nitrogen flow, heating silver-functionalized substrate to a temperature of 100 C for 20 minutes to evaporate the solvent and adsorb the Ag salt on the pore walls, heating the metal-functionalized substrate to a temperature of 500 C for 30 minutes to decompose the salt into Ag and NO ₂ and O ₂ gases.

A disadvantage of the known method is the limited depth of penetration of the functionalizing element in the form of silver into the pores of the porous silicon substrate, which is 10 μm. In addition, the practical implementation of the method presents a certain complexity due to the multi-stage and duration of the process, and the stage of microarc (plasma) oxidation requires expensive equipment.

Also known is a method for obtaining a functionalized nanostructure based on porous silicon, presented in the article NATIV-ROTH E, RECHAV K, PORAT Z. Deposition of gold and silver on porous silicon and inside the pores. Thin Solid Films. March 2016, vol. 603, p. 88-96, where the functionalizing element is selected from the range of silver, gold. The method includes the procedure for etching a p-type silicon substrate with a crystallographic orientation of 100 and a resistivity of 0.002-0.005 Ohm⋅cm to obtain a porous silicon substrate, ultrasonic treatment of the porous silicon substrate in ethanol, functionalization of the porous silicon substrate by immersion in a solution of metal salts selected from a series of Ag, Au.

The disadvantage of the known method is an insignificant depth (of the order of 100 nm) and uneven penetration of functionalizing elements selected from a series of silver, gold, into the layer of porous silicon due to the presence of gaseous hydrogen in the pores, the hydrophobic nature of the resulting surface of porous silicon, the high rate of reduction of ions metals, compared with their diffusion rate, as well as the uncontrolled formation of Ag and Au agglomerates up to 500 µm in size on the surface of porous silicon.

Also known is a method for obtaining a functionalized nanostructure based on porous silicon, presented in the article HARRAZ F, TSUBOI T, SASANO J, SAKKA T, OGATA Y. Metal Deposition onto a Porous Silicon Layer by Immersion Plating from Aqueous and Nonaqueous Solutions. Journal of The Electrochemical Society. August 2002, vol. 149, p. C456-C463, where the functionalizing element is selected from the range of silver, copper, nickel. The method includes the procedure of etching a p-type silicon substrate with a crystallographic orientation of 100 and a resistivity of 10 Ohm⋅cm to obtain a porous silicon substrate, removing the surface layer formed on the surface of the porous silicon substrate by chemical etching in a 5% aqueous solution of hydrofluoric acid, drying the resulting substrates with an argon flow, functionalization of a porous silicon substrate by immersion in a solution of metal salts selected from the range of Ag, Cu, Ni.

The disadvantage of this method is the impossibility of deposition of functionalizing elements evenly over the entire depth of the porous layer. In addition, there are technological difficulties in the functionalization of a porous silicon substrate with a functionalizing element in the form of nickel, since the oxidation of porous silicon is observed, which occurs simultaneously with the deposition of the metal, and there are also cardinal differences in the technology parameters associated with the potentials of the redox pairs of each metal in a salt solution. .

Also known is a method for obtaining a functionalized nanostructure based on porous silicon, presented in the article HARRAZ F. Synthesis and surface properties of magnetite (Fe ₃ O ₄ ) nanoparticles infiltrated into porous silicon template. Applied Surface Science. December 2016, vol. 287, pp. 203-210, where magnetite nanoparticles are used as a functionalizing element. The method includes the procedure of electrochemical etching of an n-type silicon substrate with a crystallographic orientation of 100, a resistivity of 0.010-0.018° Ohm⋅cm, and a thickness of 381 μm to obtain a substrate of porous silicon, hydrothermal synthesis of magnetite nanoparticles, dissolving the obtained nanoparticles in toluene to obtain a suspension of nanoparticles magnetite, functionalization of a porous silicon substrate by immersing it in a suspension of magnetite nanoparticles.

The disadvantage of the known method is the low thickness of the obtained functionalized nanostructure based on porous silicon, which is 1 μm, as well as the uneven penetration of the functionalizing element in the form of magnetite nanoparticles into the porous silicon layer due to the presence of air in the pores, the hydrophobic nature of the resulting porous silicon surface and uncontrolled agglomeration of nanoparticles. magnetite.

Closest to the claimed technical essence is a method for obtaining a silver-functionalized structure based on porous silicon, presented in the article SMERDOV RS, LOBODA VV, SPIVAK YUM, MOSHNIKOV VA Blocking filter for the visible and near ultraviolet range for a fluorescent microscope based on the phenomenon of plasmon resonance. Scientific and technical statements of St. Petersburg State Polytechnical University. Computer science. Telecommunications. Control. September 2016, No. 3 (247), pp. 13-22, which includes electrochemical etching of a silicon substrate to obtain a porous silicon substrate, and functionalization of the porous silicon substrate by cathodic electrochemical deposition of a functionalizing element in the form of metal (silver) from an aqueous solution of silver nitrate.

The disadvantages of the prototype are the low depth of penetration of the functionalizing element in the form of metal (silver) into the layer of porous silicon, uneven coverage of the functionalizing element both on the surface and in the depth of the porous layer, due in particular to the uncontrolled formation of silver agglomerates up to 1.5 μm on the surface. porous silicon.

The objective of the claimed invention is to create a method for obtaining a functionalized nanostructure based on porous silicon, which makes it possible to provide a technical result that consists in increasing the penetration depth of the functionalizing element into the porous silicon layer and achieving uniformity of the functionalizing element coverage both over the surface and in the depth of the porous layer.

The essence of the invention lies in the fact that in a method for obtaining a functionalized nanostructure based on porous silicon, including obtaining a substrate from porous silicon and its further functionalization, before functionalization, the surface layer formed on the surface of the porous silicon substrate is removed, then the porous silicon substrate is kept in solution monohydric alcohol, and its functionalization is carried out by immersing in a solution of doped fullerenols, which is obtained by dispersing fullerenols doped with the required functionalizing elements in distilled water, and holding the porous silicon substrate in a solution of doped fullerenols, and then the resulting functionalized nanostructure is removed and dried .

The removal of the surface layer formed on the surface of the porous silicon substrate can be carried out either by chemical etching, mechanical removal, or focused ion beams.

The monohydric alcohol solution can be made using either isopropanol, or methanol, or ethanol.

The required functionalizing elements with which fullerenols are doped can be either metals or non-metals, or metals and non-metals together.

Exposure of a porous silicon substrate immersed in a solution of doped fullerenols can be carried out either statically or dynamically, for example, by centrifugation.

The essential differences of the present invention are as follows:

removal of the surface layer formed on the surface of the porous silicon substrate opens access to the system of pore channels in porous silicon, facilitating the direct penetration of functionalizing elements and their more uniform distribution in the porous silicon layer;

keeping the porous silicon substrate in a solution of monohydric alcohol (isopropanol, methanol, ethanol) prevents the formation of an air pocket, improves the wettability of the porous silicon surface, reducing its surface tension, which contributes to a deep and uniform distribution of functionalizing elements in the porous silicon layer;

the use of fullerenols doped with the required functionalizing elements ensures their improved delivery into the porous nanostructure. Fullerenol is characterized by small size (on the order of 1 nm) and the presence of OH groups. The presence of OH groups leads to an increase in the penetration depth and uniform distribution of the functionalizing element with which fullerinol is doped, since the surface of porous silicon, aged in monohydric alcohol, has the property of hydrophilicity. The small size of doped fullerenol facilitates its penetration into the pores of porous silicon, even the smallest sizes (for example, into micropores with a diameter of less than 2 nm). In addition, doped fullerenol makes it possible to functionalize porous silicon with a wide range of metals, non-metals, or metals and non-metals together, which is extremely difficult or impossible in other ways;

the use of distilled water (polar liquid) for dispersing doped fullerenol ensures its high solubility, contributing to the uniform distribution of functionalizing elements in a porous silicon substrate with a hydrophilic surface;

During the dynamic or static soaking of porous silicon substrates in a polar solution of doped fullerenols, diffusion of functionalizing elements occurs and their uniform adsorption over the entire depth of the porous silicon layer. The use of dynamic exposure enhances the convection of a solution of fullerenols doped with functionalizing elements into a porous silicon substrate.

Exposure of a porous silicon substrate immersed in a solution of doped fullerenols is carried out either statically or dynamically, for example, by centrifugation, to improve the penetration of functionalizing elements

The combination of the described essential differences of the present invention makes it possible to achieve a technical result, which consists in increasing the depth of penetration of the functionalizing element into the porous silicon layer and achieving uniformity of the coating with the functionalizing element both over the surface and in the depth of the porous layer.

The invention is illustrated by the following images.

Fig. 1. Scanning electron microscope (SEM) image showing the surface of porous silicon coated with a surface layer.

Fig. 2. SEM image (top view) of the functionalized nanostructure obtained in Example 1.

Fig. 3. SEM image (cleavage) of the functionalized nanostructure obtained according to Example 1:

a) the size of the scale line is 20 µm;

b) the size of the scale line is 2 µm.

Fig. Fig. 4. Maps of the distribution of functionalizing elements on the cleavage of the functionalized nanostructure obtained according to Example 1:

a) a summary map of the distribution of elements (Ag, Si, Al, O, C);

b) Si distribution map;

c) Ag distribution map;

d) distribution map C;

e) O distribution map.

Fig. 5. SEM image (top view) of the functionalized nanostructure obtained in Example 2.

Fig. 6. SEM image (cleavage) of the functionalized nanostructure obtained according to Example 2.

In FIG. Fig. 7. Maps of the distribution of chemical elements on the cleavage of the functionalized nanostructure obtained according to Example 2.

a) a summary map of the distribution of elements (Cu, Cr, S, Si, O);

b) Si distribution map;

c) O distribution map;

d) Cr distribution map;

e) distribution map S;

e) Cu distribution map;

g) K distribution map.

The method is carried out as follows.

Porous silicon substrates are obtained from silicon, for example, by electrochemical, chemical, spark erosion, combined electrochemical and chemical etching methods, etc.

The surface layer formed on the surface of the porous silicon substrate is removed. The removal of the surface layer can be carried out either by chemical etching, mechanical removal, or using focused ion beam technology.

The resulting porous silicon substrate is kept in a solution of monohydric alcohol. As the monohydric alcohol, either isopropanol, or methanol, or ethanol can be used.

Choose fullerenols doped with the required functionalizing elements.

Get a solution of doped fullerenols in a polar liquid.

Then, porous silicon substrates are immersed in a solution of doped fullerenols, and dynamic (for example, by centrifugation) or static holding of the porous silicon substrate in a solution of doped fullerenols is carried out.

The resulting functionalized nanostructures are removed from the solution and dried in air or, for example, in an inert atmosphere.

Examples of the implementation of the proposed method.

Example 1. Electrochemical etching of a p-type silicon substrate with a crystallographic orientation of 100 and a resistivity of 12 Ohm⋅cm (KDB-12) was carried out to obtain a porous silicon substrate using an anodizing current density of 20 mA/cm ² for 10 min (Fig. 1, where 1 is the surface layer, 2 is porous silicon, and 3 is silicon). The surface layer formed on the surface of the porous silicon substrate was removed by chemical etching in a 20% aqueous solution of hydrofluoric acid for 2 minutes. The resulting porous silicon substrate was kept in an isopropanol solution.

We chose fullerenols doped with the required chemical elements: silver and copper.

A solution of doped fullerenols in distilled water was obtained.

The porous silicon substrates were then immersed in a solution of doped fullerenols, and the immersed substrates were dynamically held using centrifugation at a frequency of 13500 rpm for 30 min. The resulting functionalized nanostructures were removed from the solution and dried in air.

Fig. 2 illustrates a view of the resulting functionalized nanostructure based on porous silicon (top view). On FIG. 2, a uniform distribution of functionalizing elements over the surface of porous silicon is observed. Fig. 3a illustrates the uniformity of the distribution of functionalizing elements over the depth of the porous silicon layer; in FIG. 3b shows the uniformity of coverage of the individual elements of the porous silicon layer.

The uniform distribution of the required elements throughout the porous layer is confirmed by the characteristic x-ray spectra obtained by the EDX method (Fig. 4). From FIG. Figure 4 shows that the EDX maps contain signals from both the porous silicon substrate and the functionalizing elements throughout the entire depth of the porous layer.

Example 2

An n-type silicon substrate with a crystallographic orientation of 111 and a resistivity of 4.5 Ω cm (KEF-4.5) was electrochemically etched to obtain a porous silicon substrate using an anodization current density of 20 mA/ ^cm2 for 10 min. The surface layer formed on the surface of the porous silicon substrate was removed by chemical etching in a 20% aqueous solution of hydrofluoric acid for 2 minutes. The resulting porous silicon substrate was kept in an isopropanol solution.

We chose fullerenols doped with the required chemical elements: chromium, sulfur, copper, and potassium.

A solution of doped fullerenols in distilled water was obtained.

The porous silicon substrates were then immersed in a solution of doped fullerenols, and the immersed substrates were statically held. The resulting functionalized nanostructures were removed from the solution and dried in air.

Fig. 5 illustrates a view of the resulting functionalized nanostructure based on porous silicon (top view). On FIG. 5, a uniform distribution of functionalizing elements over the surface of porous silicon is observed. Fig. 6 illustrates the uniformity of the distribution of functionalizing elements over the depth of the porous silicon layer.

The uniform distribution of the required elements throughout the porous layer is confirmed by the characteristic x-ray spectra obtained by the EDX method (Fig. 7). From FIG. Figure 7 shows that the EDX maps contain signals from both the porous silicon substrate and the functionalizing elements over the entire depth of the porous layer.

Thus, compared with the prototype, the proposed method makes it possible to manufacture nanostructures based on porous silicon uniformly functionalized with the required functionalizing elements, using doped fullerenol, static or dynamic (for example, by centrifugation) exposure of immersed substrates in a solution of doped fullerenol, as well as the exposure process porous silicon substrates in a solution of monohydric alcohol (isopropanol, methanol, ethanol) to improve penetration into pores throughout the entire depth of the porous layer obtained on the silicon surface. At the same time, unlike the prototype in the proposed method, it is possible to functionalize with a wide range of materials, not limited only to metals, which leads to an increase in the number of possible applications for this class of nanostructures.

The proposed method makes it possible to increase the depth of penetration of the functionalizing element into the layer of porous silicon and to achieve uniformity of the coating by the functionalizing element both over the surface and in the depth of the porous layer.

Claims (5)

1. A method for obtaining a functionalized nanostructure based on porous silicon, including obtaining a substrate from porous silicon and its further functionalization, characterized in that, before functionalization, the surface layer formed on the surface of the porous silicon substrate is removed, then the porous silicon substrate is kept in a solution of monohydric alcohol , and its functionalization is carried out by immersing in a solution of doped fullerenols, which is obtained by dispersing fullerenols doped with the required functionalizing elements in distilled water, and holding the porous silicon substrate in a solution of doped fullerenols, and then the resulting functionalized nanostructure is removed and dried. 2. A method for obtaining a functionalized nanostructure based on porous silicon according to claim 1, characterized in that the surface layer formed on the surface of the porous silicon substrate is removed either by chemical etching, or mechanical removal, or using the technology of focused ion beams. 3. A method for obtaining a functionalized nanostructure based on porous silicon according to claim 1, characterized in that the monohydric alcohol solution is performed using either isopropanol, or methanol, or ethanol. 4. A method for obtaining a functionalized nanostructure based on porous silicon according to claim 1, characterized in that the required functionalizing elements with which fullerenols are doped are selected from the range: metals, non-metals, metals and non-metals together. 5. A method for obtaining a functionalized nanostructure based on porous silicon according to claim 1, characterized in that the holding of a porous silicon substrate immersed in a solution of doped fullerenols is carried out either statically or dynamically, for example, by centrifugation.

Images