WO2017112880A1

WO2017112880A1 - Formation of porous silicon materials with copper-containing pores

Info

Publication number: WO2017112880A1
Application number: PCT/US2016/068361
Authority: WO
Inventors: Sibani L. BISWAL; Abirami DHANABALAN; Steven L. Sinsabaugh; Eric TALBERT
Original assignee: William Marsh Rice University; Lockheed Martin Corporation
Priority date: 2015-12-22
Filing date: 2016-12-22
Publication date: 2017-06-29

Abstract

Disclosed are methods of forming a porous silicon material by applying a solution of hydrogen fluoride and copper (e.g., copper metals, and/or copper oxides) to a surface of a silicon substrate, where the applying coats the surface of the silicon substrate with copper. The copper-coated silicon substrate is then etched to form the porous silicon material. The etching can occur in the presence of the solution through copper-assisted electrochemical etching. The etching can remove at least a portion of the copper from the surface and uniformly deposit the copper on pore walls of the porous silicon material in the form of copper nanospheres. The methods can also include steps of separating the porous silicon material from the silicon substrate and incorporating the porous silicon material into energy storage devices. Also disclosed are the porous silicon materials comprising a plurality of pores and copper embedded within the plurality of pores.

Description

TITLE

FORMATION OF POROUS SILICON MATERIALS WITH COPPER-CONTAINING

PORES

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 62/271,131, filed on December 22, 2015. The entirety of the aforementioned application is incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0002] Not applicable.

BACKGROUND

[0003] Current methods of forming porous silicon materials with copper containing pores suffer from numerous limitations, including multiple steps and the formation of aggregated pores. Various embodiments of the present disclosure address the aforementioned limitations.

SUMMARY

[0004] In some embodiments, the present disclosure pertains to methods of forming a porous silicon material by applying a solution containing hydrogen fluoride and a copper to a surface of a silicon substrate. The applying coats the surface of the silicon substrate with the copper from the solution. Thereafter, the copper-coated silicon substrate is etched to form the porous silicon material.

[0005] In some embodiments, the copper in the solution includes, without limitation, copper metals, copper oxides, and combinations thereof. In some embodiments, the etching occurs in the presence of the solution. In some embodiments, the etching includes copper-assisted electrochemical etching.

[0006] In some embodiments, the etching removes at least a portion of the copper from the surface of the copper-coated silicon substrate and uniformly deposits the copper on pore walls of the porous silicon material. In some embodiments, the copper is in the form of copper nanospheres within the pore walls. [0007] In some embodiments, the methods of the present disclosure also include a step of separating the porous silicon material from the silicon substrate. In some embodiments, the separation occurs by gradually increasing the electric current in sequential increments.

[0008] In additional embodiments, the methods of the present disclosure also include a step of incorporating the porous silicon material as a component of an energy storage device. For instance, in some embodiments, the porous silicon material is utilized as an electrode (e.g., anode) in the energy storage device. In some embodiments, the energy storage device is a battery.

[0009] In additional embodiments, the present disclosure pertains to the formed porous silicon materials. In some embodiments, the porous silicon materials include a plurality of pores and copper embedded within the plurality of pores.

FIGURES

[0010] FIGURE 1 provides a scheme of a method of forming a porous silicon material.

[0011] FIGURES 2A-F provide images of copper-coated silicon substrates and porous silicon materials formed from the silicon substrates. FIG. 2A shows an image of a copper-coated porous silicon wafer. FIG. 2B shows a scanning electron microscopy (SEM) image of the copper-coated porous silicon wafer in FIG. 2A. FIG. 2C is another SEM image of the copper- coated silicon wafer in FIG. 2A, where copper is shown to be deposited on the surface of the copper-coated porous silicon wafer. FIG. 2D shows an SEM image of a porous silicon material fabricated by the copper assisted electrochemical etching (CAE) of copper-coated silicon wafers. FIG. 2E is a side view SEM image of the porous silicon material in FIG. 2D, where copper is shown inside the pores. FIG. 2F is a magnified SEM image of the porous silicon material in FIG. 2D, where copper is shown at a higher resolution inside the pores.

DETAILED DESCRIPTION

[0012] It is to be understood that both the foregoing general description and the following detailed description are illustrative and explanatory, and are not restrictive of the subject matter, as claimed. In this application, the use of the singular includes the plural, the word "a" or "an" means "at least one", and the use of "or" means "and/or", unless specifically stated otherwise. Furthermore, the use of the term "including", as well as other forms, such as "includes" and "included", is not limiting. Also, terms such as "element" or "component" encompass both elements or components comprising one unit and elements or components that comprise more than one unit unless specifically stated otherwise.

[0013] The section headings used herein are for organizational purposes and are not to be construed as limiting the subject matter described. All documents, or portions of documents, cited in this application, including, but not limited to, patents, patent applications, articles, books, and treatises, are hereby expressly incorporated herein by reference in their entirety for any purpose. In the event that one or more of the incorporated literature and similar materials defines a term in a manner that contradicts the definition of that term in this application, this application controls.

[0014] Deposition of copper and other noble metal impurities from hydrogen fluoride (HF) based solutions on silicon has been utilized in the semiconductor industry. For instance, such processes have utilized copper salts (e.g., CuS0₄, CuCl₂, and Cu(N0₃)₂) and HF to deposit copper films on silicon. However, such methods suffer from numerous limitations, including multiple steps and the formation of porous silicon materials with aggregated copper-containing pores. As such, more efficient methods are needed to form porous silicon materials with uniform copper-containing pores.

[0015] In some embodiments, the present disclosure pertains to methods of forming porous silicon materials. In some embodiments illustrated in FIG. 1, the methods of the present disclosure include a step of applying a solution that includes hydrogen fluoride and copper to a surface of a silicon substrate (step 10), such that the applying coats the surface of the silicon substrate with copper to form a copper-coated silicon substrate (step 12). In some embodiments, the methods of the present disclosure also include a step of etching the copper-coated silicon substrate (step 14) to form the porous silicon material (step 16). In additional embodiments, the methods of the present disclosure also include one or more steps of separating the porous silicon material from the silicon substrate (step 18), and incorporating the porous silicon material as a component of an energy storage device (step 20). Additional embodiments of the present disclosure pertain to porous silicon materials that are formed by the methods of the present disclosure.

[0016] As set forth in more detail herein, the methods of the present disclosure can have various embodiments. For instance, various methods may be utilized to apply various solutions of hydrogen fluoride and copper to surfaces of various silicon substrates to form various types of copper-coated silicon substrates. Various methods may also be utilized to etch the copper-coated silicon substrates to form various types of porous silicon materials. Various methods may also be utilized to separate the formed porous silicon material from a silicon substrate. Furthermore, the porous silicon materials may be utilized as various components of various energy storage devices.

[0017] Solutions

[0018] The methods of the present disclosure may apply various solutions onto a silicon substrate. The solutions of the present disclosure generally include hydrogen fluoride and copper. In some embodiments, the solutions of the present disclosure can also include various solvents and hydrogen scavengers.

[0019] The solutions of the present disclosure may include various amounts of hydrogen fluoride. For instance, in some embodiments, the hydrogen fluoride in the solution has a concentration of more than about 5% by volume. In some embodiments, the hydrogen fluoride in the solution has a concentration ranging from about 5% by volume to about 75% by volume. In some embodiments, the hydrogen fluoride in the solution has a concentration ranging from about 5% by volume to about 50% by volume. In some embodiments, the hydrogen fluoride in the solution has a concentration ranging from about 40% by volume to about 50% by volume. In some embodiments, the hydrogen fluoride in the solution has a concentration ranging from about 45% by volume to about 50% by volume.

[0020] The solutions of the present disclosure may also include various types of coppers. In some embodiments, the copper is dissolved in the solution. In some embodiments, the copper includes, without limitation, copper metals, copper oxides, and combinations thereof. [0021] In some embodiments, the copper in the solution includes copper metals. In some embodiments, the copper metals include, without limitation, pure copper metals, copper (I) metals, copper (II) metals, copper alloys, organocopper compounds, and combinations thereof. In some embodiments, the copper metal is derived from a metal impurity, such as a scrap metal component.

[0022] In some embodiments, the copper in the solution includes copper oxides. In some embodiments, the copper oxides include, without limitation, copper (II) oxides, copper (I) oxides, copper (II) hydroxides, and combinations thereof.

[0023] In some embodiments, the copper in the solution lacks copper salts. In additional embodiments, the copper in the solution includes copper salts. In some embodiments, the copper salts include, without limitation, CuS0₄, CuCl₂, Cu(N0₃)₂, and combinations thereof.

[0024] The solutions of the present disclosure may include various amounts of coppers. For instance, in some embodiments, the solutions of the present disclosure include a total copper content that ranges from about 0.1 wt% to about 75 wt%. In some embodiments, the solutions of the present disclosure include a total copper content that ranges from about 0.1 wt% to about 50 wt%. In some embodiments, the solutions of the present disclosure include a total copper content that ranges from about 0.1 wt% to about 25 wt%. In some embodiments, the solutions of the present disclosure include a total copper content that ranges from about 1 wt% to about 25 wt%. In some embodiments, the solutions of the present disclosure include a total copper content that ranges from about 0.1 wt% to about 15 wt%.

[0025] Additional copper amounts can also be envisioned. For instance, in some embodiments, the amount of copper in a solution may only be limited by the solubility of the copper (e.g., copper salts) in the solution.

[0026] In some embodiments, the solutions of the present disclosure also include a solvent. The solutions of the present disclosure may include various solvents. For instance, in some embodiments, the solvent includes, without limitation, organic solvents, aqueous solvents, inorganic solvents, methanol, dimethylformamide, and combinations thereof. In some embodiments, the solvent includes methanol. [0027] In some embodiments, the solutions of the present disclosure also include a hydrogen scavenger. In some embodiments, the hydrogen scavenger assists in the adhesion of copper to a surface of a silicon substrate.

[0028] The solutions of the present disclosure may include various hydrogen scavengers. For instance, in some embodiments, the hydrogen scavenger includes, without limitation, methane, hydrocarbons, sulfur dioxide, hydrogen sulfide, hydrazine, ascorbic acid, tocopherol, naringenin, antioxidants, glutathione, alkylating electrophiles, and combat ions thereof. In some embodiments, the hydrogen scavenger includes ascorbic acid.

[0029] Application of solutions to silicon substrate surfaces

[0030] Various methods may be utilized to apply the solutions of the present disclosure to silicon substrate surfaces. For instance, in some embodiments, the applying occurs by at least one of contacting, deposition, drop-casting, pouring, coating, immersion coating, spray coating, deposition, electroless deposition, reductive deposition, and combinations thereof.

[0031] In some embodiments, the application of the solutions of the present disclosure to silicon substrate surfaces occurs by electroless deposition. Additional application methods can also be envisioned.

[0032] Silicon Substrates

[0033] The solutions of the present disclosure may be applied to various types of silicon substrates. For instance, in some embodiments, the silicon substrates include, without limitation, silicon wafers, n-type silicon substrates, p-type silicon substrates, polished silicon substrates, metal-coated silicon substrates, porous silicon substrates, and combinations thereof.

[0034] In some embodiments, the silicon substrates include p-type silicon substrates. In some embodiments, the silicon substrates include polished silicon substrates. In some embodiments, the polished silicon substrates include a polished surface. In some embodiments, the methods of the present disclosure also include a step of polishing the surface of a silicon substrate.

[0035] The silicon substrates of the present disclosure may have various shapes. For instance, in some embodiments, the silicon substrates of the present disclosure are in the form of at least one of silicon films, silicon particles, silicon layers, and combinations thereof. Additional silicon substrate shapes can also be envisioned.

[0036] Copper-coated silicon substrates

[0037] The application of the solutions of the present disclosure to silicon substrate surfaces can result in the formation of various types of copper-coated silicon substrates. For instance, in some embodiments, the copper-coated silicon substrates include a copper coating. In some embodiments, the copper coating partially coats a surface of the silicon substrate. In some embodiments, the copper coating fully coats a surface of the silicon substrate.

[0038] The copper coatings of the copper-coated silicon substrates may also be in various forms. For instance, in some embodiments, the copper coating is in the form of a film. In some embodiments, the copper coating is in the form of particles. Additional forms can also be envisioned.

[0039] The copper coatings of the copper-coated silicon substrates may also have various thicknesses. For instance, in some embodiments, the copper coatings have a thickness ranging from about 10 nm to about 10 μιη. In some embodiments, the copper coatings have a thickness ranging from about 10 nm to about 100 nm. Additional thicknesses can also be envisioned.

[0040] In some embodiments, the thickness of the formed copper coating is controllable by controlling reaction conditions. For instance, in some embodiments, the copper coating thickness can be controlled by adjusting copper concentration in the solution and solution application time.

[0041] Etching of copper-coated silicon substrates

[0042] Various methods may also be utilized to etch copper-coated silicon substrates in order to form porous silicon materials. For instance, in some embodiments, the etching occurs by electrochemical etching. In some embodiments, the etching occurs by copper-assisted electrochemical etching. Additional etching methods can also be envisioned.

[0043] The etching of copper-coated silicon substrates may occur under various conditions. For instance, in some embodiments, the etching occurs in the presence of the solutions of the present disclosure. In some embodiments, the etching occurs in a container, such as a container that contains the solutions of the present disclosure.

[0044] In some embodiments, the etching occurs in the presence of a current. In some embodiments, the current includes a constant current. In some embodiments, the current includes a variant current, such as a gradually increasing current. In some embodiments, the current ranges from about 1 mA to about 500 mA. In some embodiments, the current ranges from about 1 mA to about 250 mA. In some embodiments, the current ranges from about 50 mA to about 500 mA. In some embodiments, the current ranges from about 50 mA to about 250 mA. In some embodiments, the current ranges from about 50 mA to about 100 mA. In some embodiments, the current ranges from about 1 mA to about 100 mA. In some embodiments, the current ranges from about 1 mA to about 10 mA.

[0045] Current can be supplied during etching in various manners. For instance, in some embodiments, the current is supplied by electrodes in a container. In some embodiments, the copper-coated silicon substrate in the container serves as a positive electrode while another composition (e.g., a platinum coil) serves as a negative electrode.

[0046] The etching of copper-coated silicon substrates can occur under various conditions. For instance, in some embodiments, the etching occurs under ambient conditions. In some embodiments, the ambient conditions include room temperature and atmospheric pressure.

[0047] Etching can occur for various periods of time. For instance, in some embodiments, the etching occurs for a time sufficient to form porous silicon materials. In some embodiments, the etching occurs from about 10 minutes to about 10 hours. In some embodiments, the etching occurs from about 10 minutes to about 3 hours. In some embodiments, the etching occurs from about 10 minutes to about 30 minutes.

[0048] Etching can have various effects on copper-coated silicon substrates. For instance, in some embodiments, etching removes at least a portion of the copper from the surface of the copper-coated silicon substrate. In some embodiments, the etching completely removes the copper from the surface of the copper-coated silicon substrate. [0049] Without being bound by theory, it is envisioned that the removal of copper from the surfaces of copper-coated silicon substrates can occur by various mechanisms. For instance, in some embodiments, the removal of copper occurs by galvanic displacement of copper through electrochemical reduction of copper and simultaneous dissolution of silicon.

[0050] In some embodiments, the etching can also incorporate the copper from the surface of the coppper-coated silicon substrate into the pores of the porous silicon material. In some embodiments, the copper becomes incorporated into the pores of the porous silicon materials during etching. In some embodiments, the copper becomes incorporated into pre-existing pores of the porous silicon materials during etching. In some embodiments, the copper becomes incorporated into pores that are formed during etching.

[0051] Without being bound by theory, it is also envisioned that the incorporation of copper from surfaces of coppper-coated silicon substrates into the pores of the porous silicon materials can occur by various mechanisms. For instance, in some embodiments, electrochemical etching of a coper-coated silicon substrate is initiated by holes at silicon substrate/solution interfaces and driven by current density and fluoride anions at a pore tip. The copper on the surface of the copper-coated silicon substrate can then be driven into the pores as the etching process continues.

[0052] Copper may be associated with the pores of the porous silicon materials in various manners. For instance, in some embodiments, the copper becomes uniformly deposited on pore walls of the formed porous silicon materials. In some embodiments, the copper is in the form of copper nanospheres within the pores of the porous silicon materials. In some embodiments, the copper nanospheres are laced inside the pore walls. In some embodiments, the copper nanospheres are dispersed on pore walls. In some embodiments, the formed porous silicon materials have most of the copper nanospheres inside the pores with only trace amounts of copper on the surface. In some embodiments, the copper can be deposited as a thin layer on the pore walls of the porous silicon materials.

[0053] Separation of porous silicon materials from silicon substrates [0054] The etching of copper-coated silicon substrates forms porous silicon materials from the silicon substrates. In additional embodiments, the methods of the present disclosure also include a step of separating the formed porous silicon materials from the silicon substrates. Various methods may be used to separate the formed porous silicon materials from the silicon substrates. For instance, in some embodiments, the separation occurs by physically separating the porous silicon materials from the silicon substrates.

[0055] In some embodiments, the separation of porous silicon materials from silicon substrates occurs by gradually increasing the electric current in sequential increments. In such embodiments, a "lift-off process is implemented, where the increased current results in the separation of the porous silicon materials from the silicon substrates. In some embodiments, a multi-step scheme in which the current is step-wise increased incrementally may be required to achieve the lift-off.

[0056] A current can be increased in an amount and for a time period to provide for the separation of porous silicon materials from the silicon substrates. For instance, in some embodiments, the gradual increase of the electric current during the separating step includes an increase of the electric current by about 1-100 mA per sequential increment. In some embodiments, the gradual increase of the electric current during the separating step includes an increase of the electric current by about 1-50 mA per sequential increment. In some embodiments, the gradual increase of the electric current during the separating step includes an increase of the electric current by about 25-50 mA per sequential increment.

[0057] In some embodiments, each sequential increment takes from about 1 minute to about 60 minutes. In some embodiments, each sequential increment takes from about 10 minutes to about 30 minutes. In some embodiments, each sequential increment takes from about 10 minutes to about 20 minutes.

[0058] Incorporation of porous silicon materials into energy storage devices

[0059] In some embodiments, the methods of the present disclosure also include a step of incorporating the formed porous silicon materials of the present disclosure into an energy storage device. The formed porous silicon materials of the present disclosure may be utilized as one or more components of energy storage devices. For instance, in some embodiments, the formed porous silicon materials are utilized as an electrode in the energy storage device. In some embodiments, the porous silicon material is utilized as an anode in the energy storage device.

[0060] The porous silicon materials of the present disclosure may be incorporated into various energy storage devices. For instance, in some embodiments, the energy storage device includes, without limitation, capacitors, batteries, photovoltaic devices, photovoltaic cells, transistors, current collectors, fuel cell devices, water- splitting devices, and combinations thereof. In some embodiments, the energy storage device includes batteries, such as lithium-ion batteries. In some embodiments, the copper associated with porous silicon materials (e.g., in the form of a copper coating) enables better contact with current collectors of energy storage devices.

[0061] Porous silicon materials

[0062] The methods of the present disclosure can form various types of porous silicon materials. Additional embodiments of the present disclosure pertain to the porous silicon materials. In some embodiments, the porous silicon materials of the present disclosure include a plurality of pores and copper embedded within the plurality of pores.

[0063] In some embodiments, the copper includes, without limitation copper metals, copper oxides, and combinations thereof. Suitable copper metals and copper oxides were discussed previously. In some embodiments, the copper lacks copper salts.

[0064] In some embodiments, the copper is uniformly deposited on pore walls of the porous silicon material. In some embodiments, the copper is in the form of copper nanospheres.

[0065] In general, the porous silicon materials of the present disclosure include a plurality of pores. In some embodiments, the pores include, without limitation, nanopores, mesopores, micropores, and combinations thereof. In some embodiments, the pores include diameters between about 1 nanometer to about 5 micrometers. In some embodiments, the pores include diameters between about 500 nanometers to about 3 micrometers. In some embodiments, the pores include diameters between about 1 micrometer to about 5 micrometers. [0066] The porous silicon materials of the present disclosure can also have various porosities. For instance, in some embodiments, the porous silicon materials of the present disclosure have porosities that range from about 10% to about 75%. In some embodiments, the porous silicon materials of the present disclosure have porosities that range from about 25% to about 60%. In some embodiments, the porous silicon materials of the present disclosure have porosities that range from about 40% to about 60%. In some embodiments, the porous silicon materials of the present disclosure have porosities that range from about 45% to about 55%.

[0067] The porous silicon materials of the present disclosure can also have various types of pore spans. For instance, in some embodiments, the porous silicon materials of the present disclosure include pores that span at least 50% of a thickness of the porous silicon material. In some embodiments, the porous silicon materials of the present disclosure include pores that span an entire thickness of the porous silicon material.

[0068] The porous silicon materials of the present disclosure can have various thicknesses. For instance, in some embodiments, the porous silicon materials of the present disclosure have a thickness ranging from about 10 micrometers to about 200 micrometers. In some embodiments, the porous silicon materials of the present disclosure have a thickness ranging from about 10 micrometers to about 50 micrometers. In some embodiments, the porous silicon materials of the present disclosure have a thickness ranging from about 20 micrometers to about 25 micrometers.

[0069] The porous silicon materials of the present disclosure can also be in various forms. For instance, in some embodiments, the porous silicon material is in the form of at least one of silicon films, silicon particles, silicon layers, and combinations thereof. In some embodiments, the porous silicon materials of the present disclosure are in the form of a porous silicon layer. In some embodiments, the porous silicon materials of the present disclosure are in the form of a porous silicon film. In some embodiments, the porous silicon materials of the present disclosure are in crystalline form.

[0070] Applications and Advantages

[0071] The methods and porous silicon materials of the present disclosure can provide numerous applications and advantages. For instance, in some embodiments, the presence of copper without an anion like sulfate in the silicon etching solution provides a major advantage of uniformly coating the pores of the porous silicon materials with copper nanospheres.

[0072] In some embodiments, the solutions of the present disclosure could aid in the recycling of copper from heavily oxidized or trace sources. In some embodiments, the solutions of the present disclosure provide a single environment to dissolve copper, deposit the copper on the silicon substrate surface, and insert the copper into the pores of the formed porous silicon material. In some embodiments, such a single environment can be used to eliminate the mass transfer limitation of deposition.

[0073] Furthermore, the formed porous silicon materials of the present disclosure can find numerous applications. For instance, in some embodiments, the porous silicon materials could be utilized as electrodes in various energy storage devices, such as lithium-ion batteries.

[0074] Additional Embodiments

[0075] Reference will now be made to more specific embodiments of the present disclosure and experimental results that provide support for such embodiments. However, Applicants note that the disclosure herein is for illustrative purposes only and is not intended to limit the scope of the claimed subject matter in any way.

[0076] Example 1. Facile copper deposition process for enhanced electrical contact and etching of porous silicon

[0077] In this Example, Applicants describe the deposition of copper from a copper metal or metal oxide source (instead of copper salts) onto a silicon surface. A solution of methanol and hydrogen fluoride (i.e., more than 5% HF by volume) was used for dissolution of copper metal or oxide, followed by redox deposition of copper film on silicon. Methanol and HF are important for the dissolution of copper from the metal and removal of silicon oxide from the silicon surface, respectively. In addition, the thickness of the formed copper film is controllable by the copper ion concentration in the solution and time of deposition. The process can take advantage of copper solubility in methanol and the redox reaction illustrated in Equation 1 (Eq. 1). 2Cu ⁺+ 6HF + Si 2Cu + SiF₆ ^~ + H₂ + 4H⁺ Eq. 1

[0078] The displacement of silicon by copper ions is thermodynamically favorable in HF based solutions and is limited by the diffusion of copper ions. The formed films are shown in FIGS. 2A-B. The aforementioned solutions were also used to coat the surface of porous silicon with copper through immersion coating and galvanic displacement techniques (FIG. 2C).

[0079] Copper was also coated inside the pore walls of the porous silicon materials through a process known as copper-assisted electrochemical etching (CAE). First, a copper film was deposited on the silicon wafer surface (as described previously). Next, the wafer was electrochemically etched, thereby depositing copper nanospheres uniformly on the pore walls inside the porous silicon (FIGS. 2D-F). The electrochemical etching of silicon was initiated by the holes at the silicon/electrolyte interface and was driven by the current density and F^" ion concentrations at the pore tip. The copper on the surface of the silicon wafer was then driven into the pores as the etching process continued.

[0080] Example 1.1. Preparation of the copper solution

[0081] The copper solution was prepared by mixing hydrogen fluoride (HF, 48% in water) and methanol to contain at least 5% (volume) HF. Copper foil was initially immersed into the HF/methanol solution for a time period ranging from minutes to hours. The dissolved copper ion concentration increased with time and a function of the solution solubility.

[0082] Example 1.2. Coating of copper on silicon surface

[0083] The solution from Example 1.1 was dropped or poured onto a silicon wafer surface (i.e., a p-type, 10-20 Ohm-cm, (lOO)-Si wafer with a thickness of 275 μιη). This resulted in the deposition of a silicon film or silicon nanospheres on the surface.

[0084] Example 1.3. Copper coating inside pores

[0085] Copper was deposited inside the pores of a porous silicon layer using metal-assisted electrochemical etching. In order to achieve this, a copper film was first deposited on the silicon wafer surface in accordance with the steps outlined in Example 1.2. [0086] Next, the wafer was etched by using an electrochemical etching method. The silicon wafer was used as the positive electrode. A platinum coil was used as the negative electrode with an electrolyte mixture of HF/N-N dimethylformamide (1:5) in a Teflon etch cell. A current density of about 4 mA/cm was applied for 5 hours followed by an incremental increase in the current density in order to remove the porous layer from the silicon substrate. The porous layer formed had most of the copper nanospheres inside the pores with only trace amounts of copper on the surface.

[0087] Without further elaboration, it is believed that one skilled in the art can, using the description herein, utilize the present disclosure to its fullest extent. The embodiments described herein are to be construed as illustrative and not as constraining the remainder of the disclosure in any way whatsoever. While the embodiments have been shown and described, many variations and modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the invention. Accordingly, the scope of protection is not limited by the description set out above, but is only limited by the claims, including all equivalents of the subject matter of the claims. The disclosures of all patents, patent applications and publications cited herein are hereby incorporated herein by reference, to the extent that they provide procedural or other details consistent with and supplementary to those set forth herein.

Claims

WHAT IS CLAIMED IS:

1. A method of forming a porous silicon material, said method comprising:

applying a solution comprising hydrogen fluoride and copper to a surface of a silicon substrate, wherein the applying coats the surface of the silicon substrate with the copper to form a copper-coated silicon substrate; and

etching the copper-coated silicon substrate, wherein the etching forms the porous silicon material.

2. The method of claim 1, wherein the applying occurs by a method selected from the group consisting of contacting, deposition, drop-casting, pouring, coating, immersion coating, spray coating, deposition, electroless deposition, reductive deposition, and combinations thereof.

3. The method of claim 1, wherein the applying comprises electroless deposition.

4. The method of claim 1, wherein the solution comprises a solvent.

5. The method of claim 4, wherein the solvent is selected from the group consisting of organic solvents, aqueous solvents, inorganic solvents, methanol, dimethylformamide, and combinations thereof.

6. The method of claim 1, wherein the solution further comprises a hydrogen scavenger.

7. The method of claim 6, wherein the hydrogen scavenger is selected from the group consisting of methane, hydrocarbons, sulfur dioxide, hydrogen sulfide, hydrazine, ascorbic acid, tocopherol, naringenin, antioxidants, glutathione, alkylating electrophiles, and combinations thereof.

8. The method of claim 1, wherein the hydrogen fluoride in the solution has a concentration of more than about 5% by volume.

9. The method of claim 1, wherein the hydrogen fluoride in the solution has a concentration ranging from about 5% by volume to about 50% by volume.

10. The method of claim 1, wherein the copper is selected from the group consisting of copper metals, copper oxides, and combinations thereof.

11. The method of claim 1, wherein the copper comprises copper metals.

12. The method of claim 11, wherein the copper metals are selected from the group consisting of pure copper metals, copper (I) metals, copper (II) metals, copper alloys, organocopper compounds, and combinations thereof.

The method of claim 1, wherein the copper comprises copper oxides.

14. The method of claim 13, wherein the copper oxides are selected from the group consisting of copper (II) oxides, copper (I) oxides, copper (II) hydroxides, and combinations thereof.

15. The method of claim 1, wherein the copper lacks copper salts.

16. The method of claim 1, wherein the silicon substrate is selected from the group consisting of silicon wafers, n-type silicon substrates, p-type silicon substrates, polished silicon substrates, metal-coated silicon substrates, porous silicon substrates, and combinations thereof.

17. The method of claim 1, wherein the silicon substrate comprises p-type silicon substrates.

18. The method of claim 1, wherein the silicon substrate is in the form of at least one of silicon films, silicon particles, silicon layers, and combinations thereof.

19. The method of claim 1, wherein the copper-coated silicon substrate comprises a copper coating.

20. The method of claim 19, wherein the copper coating partially coats the surface of the silicon substrate.

21. The method of claim 20, wherein the copper coating fully coats the surface of the silicon substrate.

22. The method of claim 20, wherein the copper coating is in the form of a film.

23. The method of claim 20, wherein the copper coating is in the form of particles.

24. The method of claim 1, wherein the etching occurs in the presence of the solution.

25. The method of claim 1, wherein the etching comprises electrochemical etching.

26. The method of claim 1, wherein the etching comprises copper-assisted electrochemical etching.

27. The method of claim 1, wherein the etching occurs in the presence of a current.

28. The method of claim 27, wherein the current ranges from about 1 mA to about 500 mA.

29. The method of claim 27, wherein the current ranges from about 1 mA to about 10 mA.

30. The method of claim 1, wherein the etching removes at least a portion of the copper from the surface of the copper-coated silicon substrate.

31. The method of claim 30, wherein the copper becomes uniformly deposited on pore walls of the porous silicon material.

32. The method of claim 31, wherein the copper is in the form of copper nanospheres.

33. The method of claim 1, wherein the porous silicon material comprises a plurality of pores selected from the group consisting of nanopores, mesopores, micropores, and combinations thereof.

34. The method of claim 1, wherein the porous silicon material comprises pores that span at least 50% of a thickness of the porous silicon material.

35. The method of claim 1, wherein the porous silicon material comprises pores that span an entire thickness of the porous silicon material.

36. The method of claim 1, further comprising a step of separating the porous silicon material from the silicon substrate.

37. The method of claim 36, wherein the separating comprises a gradual increase of electric current in sequential increments.

38. The method of claim 37, wherein the gradual increase of the electric current during the separating step comprises an increase of the electric current by about 1-100 mA per sequential increment.

39. The method of claim 1, further comprising a step of incorporating the porous silicon material as a component of an energy storage device.

40. The method of claim 39, wherein the porous silicon material is utilized as an electrode in the energy storage device.

41. The method of claim 40, wherein the porous silicon material is utilized as an anode in the energy storage device.

42. The method of claim 39, wherein the energy storage device is a battery.

43. A porous silicon material comprising: a plurality of pores; and copper embedded within the plurality of pores.

44. The porous silicon material of claim 43, wherein the copper is selected from the group consisting of copper metals, copper oxides, and combinations thereof.

45. The porous silicon material of claim 43, wherein the copper comprises copper metals.

46. The porous silicon material of claim 45, wherein the copper metals are selected from the group consisting of pure copper metals, copper (I) metals, copper (II) metals, copper alloys, organocopper compounds, and combinations thereof.

47. The porous silicon material of claim 43, wherein the copper comprises copper oxides.

48. The porous silicon material of claim 47, wherein the copper oxides are selected from the group consisting of copper (II) oxides, copper (I) oxides, copper (II) hydroxides, and combinations thereof.

49. The porous silicon material of claim 43, wherein the copper lacks copper salts.

50. The porous silicon material of claim 43, wherein the copper is uniformly deposited on pore walls of the pores of the porous silicon material.

51. The porous silicon material of claim 43, wherein the copper is in the form of copper nanospheres.

52. The porous silicon material of claim 43, wherein the plurality of pores are selected from the group consisting of nanopores, mesopores, micropores, and combinations thereof.

53. The porous silicon material of claim 43, wherein the plurality of pores comprise diameters between about 1 nanometer to about 5 micrometers.

54. The porous silicon material of claim 43, wherein the plurality of pores comprise diameters between about 500 nanometers to about 3 micrometers.

55. The porous silicon material of claim 43, wherein the plurality of pores comprise diameters between about 1 micrometer to about 5 micrometers.

56. The porous silicon material of claim 43, wherein the plurality of pores comprise pores that span at least 50% of a thickness of the porous silicon material.

57. The porous silicon material of claim 43, wherein the plurality of pores comprise pores that span an entire thickness of the porous silicon material.

58. The porous silicon material of claim 43, wherein the porous silicon material is in the form of at least one of silicon films, silicon particles, silicon layers, and combinations thereof.

59. The porous silicon material of claim 43, wherein the porous silicon material is a component of an energy storage device.

60. The porous silicon material of claim 59, wherein the porous silicon material is utilized as an electrode in the energy storage device.

61. The porous silicon material of claim 60, wherein the porous silicon material is utilized as an anode in the energy storage device.

62. The porous silicon material of claim 61, wherein the energy storage device is a battery.