WO2007018959A2

WO2007018959A2 - Hexachloroplatinic acid assisted silicon nanoparticle formation method

Info

Publication number: WO2007018959A2
Application number: PCT/US2006/027243
Authority: WO
Inventors: Munir H. Nayfeh; Laila Abuhassan; David Nielsen; Addulrahman Almuhanna
Original assignee: The University Of Jordan; King Abdulaziz City For Science And Technology; The Board Of Trustees Of The University Of Illinois
Priority date: 2005-07-26
Filing date: 2006-07-14
Publication date: 2007-02-15
Also published as: WO2007018959A3; EP1908112A2

Abstract

The invention provides a silicon nanoparticle formation method that can rapidly produce substantial quantities of silicon nanoparticles, which are readily recoverable for subsequent uses. A preferred method includes treating a silicon substrate with hexachloroplatinic acid and etching the silicon substrate with HF/H2O2 to form silicon nanoparticles on the surface of the silicon. Preferred methods of the invention use a cathodization of silicon source material in hexachloroplatinic acid/HF/H2O2 to form Si nanoparticles. Other embodiments use a currentless immersion of silicon material in hexachloroplatinic acid followed by etching. In preferred embodiments of the invention, the silicon source material is a silicon substrate, e.g., a silicon wafer.

Description

HEXACHLOROPLATINIC ACID ASSISTED SILICON NANOPARTICLE FORMATION METHOD

FIELD

The invention concerns silicon nanoparticles. Applications of the invention include a wide range of electronic and opto-electronic applications.

BACKGROUND

Various methods exist in the art for the production of silicon nanoparticles. Most methods are directed to production of silicon nanoparticles having a wide size distribution. In addition, many prior methods, e.g., laser ablation of silicon material, make recovery of silicon nanoparticle for ex-situ uses difficult. There also exist in the art methods for producing size distributions of silicon nanoparticles, sometimes with small quantities of lnm particles, but typically having particles tending toward a IOnm size and greater. Laser ablation, pyrolosis of gas, and electron beam deposition are exemplary processes that have been used in the art to produce silicon nanoparticles, but the processes generally produce small quantities of particles, and in forms that are not readily accessed for subsequent processes.

The state of the art was advanced by methods for the controlled production of silicon nanoparticles that also permitted their recovery and ex- situ use. Silicon nanoparticles of ~ 1 nm diameter have been produce in quantity with high uniformity of the specific lnm size. See, Nayfeh et al. U.S. Patent Number 6,585,947, entitled METHOD FOR PRODUCING SILICON NANOPARTICLES; Nayfeh et al. U.S. Published Patent Application, as publication number 20020070121, published on July 13, 2002 and entitled FAMILY OF DISCRETELY SIZED NANOPARTICLES AND METHOD FOR PRODUCING THE SAME. See, also e.g., Akcakir et al, "Detection of luminescent single ultrasmall silicon nanoparticles using fluctuation correlation spectroscopy", Appl. Phys. Lett. 76 (14), p. 1857 (April 3, 2000). The family includes 1 (blue emitting), 1.67 (green emitting), 2.15 (yellow emitting), 2.9 (red emitting) and 3.7 nm (infrared emitting). See, also, e.g., G. Belomoin et al. "Observation of a magic discrete family of ultrabright Si nanoparticles," Appl. Phys. Lett. 80(5), p 841 (February 4, 2002).

SUMMARY OF INVENTION The invention provides a silicon nanoparticle formation method that can rapidly produce substantial quantities of silicon nanoparticles, which are readily recoverable for subsequent uses. A preferred method includes treating a silicon substrate with hexachloroplatinic acid and etching the silicon substrate with HFZH₂O₂ to form silicon nanoparticles on the surface of the silicon. Preferred methods of the invention use a cathodization of silicon source material in hexachloroplatinic acid/HF/H₂O₂ to form Si nanoparticles. Other embodiments use a currentless immersion of silicon material in hexachloroplatinic acid followed by etching. In preferred embodiments of the invention, the silicon source material is a silicon substrate, e.g., a silicon wafer.

DESCRIPTION OF EXEMPLARY PREFERRED EMBODIMENTS The invention provides silicon nanoparticle formation processes that proceed to completion quickly, permitting formation of large quantities of nanoparticles. The rapidity of preferred embodiments makes the formation methods especially well-suited to commercial manufacturing processes. Preferred embodiments will now be discussed. Artisans will appreciate broader aspects of the invention from the description of the preferred embodiments.

The invention provides a silicon nanoparticle formation method that can rapidly produce substantial quantities of silicon nanoparticles, which are readily recoverable for subsequent uses. A preferred method includes treating a silicon substrate with hexachloroplatinic acid and etching the silicon substrate with HFZH₂O₂ to form silicon nanoparticles on the surface of the silicon. Preferred methods of the invention use a cathodization of silicon source material in hexachloroplatinic acid/HF/H₂O₂ to form Si nanoparticles. Other embodiments use a currentless immersion of silicon material in hexachloroplatinic acid followed by etching. In preferred embodiments of the invention, the silicon source material is a silicon substrate, e.g., a silicon wafer.

A preferred embodiment of the invention is an electrochemical cathodization process in hexachloroplatinic acid/HF/H₂O₂ of silicon wafers to form fluorescent silicon nanoparticles. This process runs to completion in a shorter time (can be less than one third of the time), consumes less electrical power, uses less raw silicon wafer material, and is more efficient than anodization in HFfH₂O₂ used in U.S. Patent No. 6,585,947. However, the '947 patent produces highly uniform quantities of lnm particles, and the present process produces a distribution of nanoparticles. In a modification of this embodiment, the wafer may be swept into the solution.

Experiments concerning the above embodiment will now be discussed. The laboratory scale demonstrations of preferred embodiments will reveal additional features of the invention to artisans. Experiments used a silicon wafer as a silicon source material. A solvent solution was prepared. To prepare the solution, 0.1518 g of hexachloroplatinic acid (H₂PtCl₅ • H₂O) (HCPA) was dissolved in 30 ml of de- ionized water. This results in ~ 0.0089 M solution. To this solution was added 5 ml of 5% HF solution and some H₂O₂ to create an etchant solution. A silicon wafer piece is immersed in the etchant solution as a cathode (cathodization) by connecting it to the negative terminal of the biasing source with its mirrored side facing an anode (anodization) (which is another similar silicon piece connected to the positive terminal of the biasing source) and the etchant solution is stirred gently. A typical current was set at about (1.5) m A. Magnetic stirring was used. A typical duration for maintaining current was about 5 min. The current source and magnetic stirrer were switched off at the same time. Silicon nanoparticles form on the surface of the wafer.

After the nanoparticles were formed, the cathodized wafer sample was washed with de-ionized water, and flushed with inert gas. The etched film is seen by the naked eye as a stain on the immersed portion of the substrate. Under irradiation from commercial incoherent UV mercury lamp at 365 nm, red photoluminescence is observed with the naked eye. Sonicaton can be used to recover the nanoparticles from the surface of the wafer. The particles can be recovered in isopropyl, THF, DMSO, chloroform, or any other solvent. Although the procedure produces a size distribution, the range of size of the nanoparticles according to scanning electron microscopy is 6 to 1 nm with an average of ~ 3 nm, which exhibits red/yellow photoluminescence. The counter anodized wafer sample may also show some luminescence and the corresponding particles can also be harvested in a similar way In a modified embodiment, silicon wafer is cathodized in

HF/hexachloroplatinic acid followed by cathodization in chloroplatinic acid, and then dipped in HF/H₂O₂for 15 seconds. The total period of treatment is 15 minutes or less.

In a modified embodiment, silicon wafer is immersed in HF/hexachloroplatinic acid for 15 minutes. The wafer is then transferred and dipped in an HF/H₂O₂ mixture for 15 seconds. The process as such works in zero current.

While specific embodiments of the present invention have been shown and described, it should be understood that other modifications, substitutions and alternatives are apparent to one of ordinary skill in the art. Such modifications, substitutions and alternatives can be made without departing from the spirit and scope of the invention, which should be determined from the appended claims.

Various features of the invention are set forth in the appended claims.

Claims

1. A method for forming silicon nanoparticles, the method comprising steps of: treating a silicon substrate with hexachloroplatinic acid; and etching the silicon substrate with HFM₂O₂ to form silicon nanoparticles on the surface of the silicon substrate.

2. The method of claim 1 , wherein said steps of treating and and etching comprise: preparing an etchant solution of hexachloroplatinic acid, HF, water, and H₂O₂ ; exposing a silicon substrate to the etchant solution; creating current to etch the silicon substrate to form silicon nanoparticles on the surface of the substrate.

3. The method of claim 2, wherein said etchant solution comprises ~ 0.0089 M hexachloroplatinic acid (H₂PtCl₆ • H₂O) with added 5% HF solution and H₂O₂ .

4. The method of claim 3, further comprising a step of stirring said etchant solution while maintaining said current.

5. The method of claim 1, further comprising steps of: separating the substrate from the etchant solution; and cleaning the silicon substrate.

6. The method of claim 5, wherein said step of cleaning the silicon substrate comprises washing the substrate with de-ionized water and flushing the substrate with inert gas.

7. The method of claim 5, further comprising a step of separating the silicon nanoparticles from the silicon substrate.

8. The method of claim 7, wherein said step of separating the silicon nanoparticles from the silicon substrate comprises sonicating in a solvent.

9. The method of claim 1 , wherein said steps of treating and etching comprise: cathodizing the silicon substrate in HF/hexachloroplatinic acid followed by cathodization in chloroplatinic acid, and dipping the silicon substrate in HFZH₂O₂.

10. The method of claim 1, wherein said steps of treating and etching comprise : immersing the silicon wafer in HF/hexachloroplatinic acid; and dipping in an HF/H₂O₂.