JP3200626B2 - Manufacturing method of spherical optical functional material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a spherical optical functional material and a method for producing the same. For more information,
In the present invention, a molten material such as a metal or
65Pa freely down in an inert gas, such as: helium, those concerning the manufacturing how spherical optical functional material, characterized by forming a solidified by spheres during the fall. The solidified product obtained by solidifying the droplet without contacting the tube wall etc. under the microgravity environment obtained by free fall is close to a perfect crystal with very few lattice defects, has high mechanical strength, It is a spherical optical functional material having characteristics that could not be achieved by conventional methods such as high light receiving efficiency due to its spherical surface or light emission at a wide angle.

[0002]

2. Description of the Related Art An existing optical functional material is TiO which is a photocatalyst.
No. ₂ , the state of powder or the state of a thick film obtained by aggregating powder [for example, “Application of Photocatalyst to Water Treatment”, Ceramics, Vol. 10, 825 (1996)], or Ge used as a photoelectric conversion element is used by cutting a thin film or a single crystal manufactured by vapor deposition or the like into a plate shape [for example, “Semiconductor Handbook (No. 2nd Edition) "(1994), p. 443 (Ohmsha). Ti
A photocatalyst used in the form of a powder or a thick film obtained by aggregating powders, such as O ₂ , requires that a reactant, water, and light simultaneously exist at the catalytically active site. In this case, the surface of the TiO ₂ catalyst layer has many active points, the reactants and water are present in the vicinity thereof, and the TiO ₂ catalyst layer must be easily exposed to light. Therefore, the catalyst layer must be porous. As a result, the catalyst has a low mechanical strength because it has a structure in which the powder or the powder agglomerates and the space necessary for the photoreaction exists between the particles, rather than a dense structure in which no space exists between the particles. Becomes Thin-film solar cells consisting of amorphous silicon deposited on a substrate or a silicon single crystal thin plate are generally used.
These have a flat surface, and require the attitude to receive sunlight perpendicular to the surface in order to receive sunlight most efficiently. It is usually used in a fixed position in the midday sun regardless of the movement of the sun.

[0003]

[SUMMARY OF THE INVENTION The present invention is that the surface which can not be prepared in a conventional manner to provide a manufacturing how the efficient optical functional material having a spherical morphology and Problems.

[0004]

Means for Solving the Problems The present inventors have made intensive studies to solve the above problems, and as a result, completed the present invention. That is, according to the present invention, a method of shape manufacturing an optical functional material is spherical, microgravity, a melt of the material forming the optical functional material or entity, in microgravity, Two Consisting of heavy pipes, inner and outer pipes
665 Pa in the drop tube in which the refrigerant is circulated in the gap between
A method for producing a spherical optical functional material is provided, which comprises a spheroidizing step of free-falling under a gas atmosphere and cooling and solidifying during the fall.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a photovoltaic material includes a solar cell such as silicon for converting sunlight into electricity,
Photovoltaic materials such as germanium photodiodes that increase current using the photovoltaic effect of light irradiation,
Examples include photoconductive materials such as cadmium sulfide and germanium that convert optical signals into electrical resistance, and photocatalysts that use light energy to induce a chemical reaction on the surface.

[0006] The method of making the optical functional material spherical in the present invention utilizes the fact that the surface tension of the liquid becomes remarkable under the microgravity environment, so that the optical functional material is formed into a sphere. The main material, for example, a melt obtained by heating and melting a metal or the like is allowed to freely fall under a gas atmosphere of 665 Pa or less without contacting other objects, and is cooled and solidified during the fall to form a spherical shape. This is a method for obtaining an optical functional material. As a means for obtaining a microgravity environment, a drop tube is preferably used. In this case, a heating device such as an induction heating device or an electric resistor heating device for melting and solidifying a metal or the like constituting the optical functional material is installed on a top portion of the drop tube, and a melt generated immediately below the heating device is provided thereunder. A drop tube body that falls inside is installed. At the bottom of the drop tube, a receiver for collecting the spherical optical functional material in which the melt has solidified is installed. The inside of the drop tube can be evacuated, filled with an inert gas such as helium to a predetermined pressure, or at a predetermined pressure, a constant flow rate from the upper part (heating unit) or the lower part (receiver) through the drop tube. Gas can also be supplied. As a method of supplying the metal constituting the optical functional material to the heating section above the drop tube, a rod-shaped metal may be supplied to the heating section at a constant speed, or graphite may be provided near the center of the heating section. Powder or strips may be supplied to a crucible made of steel or the like. Drops can be dropped freely by changing the diameter and melting temperature of the rod when using a rod-shaped sample, or by adjusting the diameter and melting temperature of the small hole provided at the bottom of the crucible when using a crucible. It is possible to change the amount of the droplet to be formed, and as a result, it is possible to adjust the diameter of the sphere. The drop tube may be made of any material, such as iron or glass, as long as it can maintain a vacuum. The diameter of the drop tube is larger than the diameter of the droplet or sphere, and it is installed so as not to contact the wall of the tube during the fall. The length of the drop tube is determined by the amount of the droplet, the melting point of the metal or the like constituting the optical functional material, and the like.
100 m, preferably 3 to 15 m. The pipe is a double pipe, and a refrigerant such as liquid nitrogen flows between the inner pipe and the outer pipe.
The space between the tubes can be filled. By cooling the tube wall with a refrigerant, the temperature difference between the droplets is increased, and the droplets are easily cooled by radiation when falling. In order to promote cooling, it is necessary to devise measures such as making the inner wall of the tube black or reducing the tube diameter as much as possible. The receiver at the bottom of the drop tube is cooled below the melting point, and the solid metal and other constituents of the optical functional material can be obtained.However, the receiver is filled with tin powder to cool it to a temperature that can be easily handled. ing. Further, when the temperature of the solidified sphere is low, the sphere may be filled with a highly volatile liquid having low volatility such as silicone oil having high viscosity.

A material having an optical function can be manufactured by doping or forming a surface layer of a sphere such as a metal constituting the obtained optical function. For example, in the case of a germanium sphere, an n-type semiconductor is formed on the sphere surface when doped with pentavalent atoms of phosphorus, and a p-type semiconductor is formed on the sphere surface when doped with trivalent atoms of boron. In addition, a titanium sphere formed by solidification of a droplet during free fall of a drop tube can form an active titanium oxide layer on its surface by anodic electrolytic etching in a nitric acid aqueous solution. This active titanium oxide layer has a photocatalytic effect. Furthermore, a p-type silicon semiconductor sphere can be formed by solidifying the boron-doped silicon melt with a drop tube. By subjecting the sphere to anodic electrolytic etching in a hydrogen fluoride solution, a porous silicon layer that emits visible light can be formed on the sphere surface.

[0008] The spherical optical functional material that can be produced by solidification of the melt with a drop tube has a crystal structure close to a perfect crystal with almost no defects. Its crystallinity is 9
5% or more, and is substantially perfect crystal. In the process of solidification of the melt, the melt does not come into contact with the tube wall during free fall in the drop tube, so it is conceivable that many nuclei generated in the process of solidification are uniformly generated in the melt. Generally, in the process of solidification from the melt, nucleation occurs from a point in contact with the tube wall. There is no contact with the tube wall in the melt during free fall, and it is expected that the nuclei are uniformly distributed in the melt.
As for the temperature at which solidification from uniform nucleation occurs, solidification does not occur at a normal solidification temperature, but a supercooling phenomenon in which solidification occurs at a temperature lower than this temperature appears. Therefore, when the liquid drops during free fall reach the solidification temperature, solidification occurs instantaneously, and crystallizes at a speed higher than the speed at which defects develop, so that a sphere having a lattice close to a perfect crystal is generated. By doping such a sphere with impurity atoms, an n-type or p-type semiconductor can be formed on the sphere surface. For example, by heating silicon or germanium spheres in an atmosphere containing diborane (B ₂ H ₃ ) or phosphine (PH ₃ ), trivalent boron or pentavalent phosphorus atoms can be added to the tetravalent silicon or germanium lattice. To form n-type and p-type semiconductor layers. In this case, the lattice structure of the sphere is close to a perfect crystal, and a semiconductor having performance equivalent to that of a single crystal which is not affected by lattice defects or the like can be produced. The spherical body obtained by the present invention is substantially a true sphere, and has a particle size of 0.1 to 20 mm, preferably 0.5 to 10 mm.

The spherical optical functional material obtained in the present invention has a high mechanical strength due to its spherical shape, and has a spherical surface, so that it can receive light when applied to a solar cell, a light receiving element or a photocatalyst. It is an easy form. In addition, when applied to a light-emitting element, light can be emitted at a wide angle, so that it can be expected to have characteristics such as less directivity than a flat surface.

[0010]

Next, the present invention will be described in more detail with reference to examples.

1. Production of spherical germanium A drop tube consisting of a double glass tube having a free fall distance of 13 m was used. The top of the drop tube is 1m quartz tube with an outer diameter of 30mm
The top is a water-cooled cap with a vacuum inside or 6
A vacuum pump and a gas inlet are provided so that the gas atmosphere such as helium of 65 Pa or less can be adjusted. At the center inside the quartz tube, a thin germanium wire with a diameter of 1 mm is vertically placed.
A high-frequency power source of V, 17A is applied to heat and melt the germanium thin wire. The drop tube body has a double-tube structure, and the inner tube is made of a hard glass tube having an outer diameter of 34 mm and an inner diameter of 30 mm. An outer tube made of a hard glass tube having an outer diameter of 80 mm and an inner diameter of 73 mm covers the inner tube. The drop tube main body is composed of seven 1.5-meter tubes with spherical surfaces, each of which is installed so as not to leak and to be vertical. Liquid nitrogen can be filled between the double tubes. 300m internal volume at the bottom of the drop tube
1 is connected to a three-necked round bottom flask, and 150 ml of tin powder having a particle size of 200 mesh or less is connected inside.
Is filled. A vacuum pump and a gas outlet are provided from the flask. 1m diameter for production of spherical germanium
m was used, but the thin wire was placed in a quartz tube with an inner diameter of 1 mm.
A fine-grained germanium powder having a particle size of 50 mesh or less was filled and solidified in a vacuum melting furnace to obtain a fine wire.
This thin wire was placed in a quartz tube placed at the top of the drop tube, and its tip was positioned so that it was located at the center of an induction coil placed outside. A high-frequency power source was applied to melt the thin wire and solidify it in a falling tube whose wall was cooled with liquid nitrogen while falling, thereby producing a spherical germanium having a diameter of about 1.5 mm. For recovery of the spherical germanium, the spherical germanium was dropped into tin powder in a flask provided at the bottom of the drop tube, and the solidified germanium was cooled. In addition, the inside of the heating unit, the drop tube, and the collection flask was set to a vacuum atmosphere of 0.01 Torr or less, and spherical germanium was produced. The spherical cross section of the obtained germanium is polished to a mirror surface, and the polished surface 2% HF + 60
% HNO ₃ solution for etching, and the etched surface was observed with an optical microscope. The result is shown in FIG. FIG. 2 shows the result of observing the lattice image with a transmission electron microscope. For comparison, about 60 coagulation experiments on the ground
mg of Ge particles (melting point: 958.5 ° C.) was sealed in a quartz ampoule in a vacuum atmosphere, and a platinum wire wound around the ampoule was heated to 1140 ° C. and heated and melted, and the ampoule was liquefied CO _2.
And cooled to 400 ° C. for 8 seconds, and a piece of solidified germanium was used. In the case of melting and solidifying on the ground, no solidified spherical product was obtained because solidification started from the part in contact with the ampoule while the germanium melt was in contact with the quartz ampule wall. FIG. 3 shows an optical micrograph of a cross section of germanium obtained by melting and solidification on the ground after etching, FIG. 4 shows a transmission electron micrograph of a defective portion, and FIG. 5 shows a lattice image near the defective portion.

The optical microscope photographs and lattice images shown in FIGS. 1 and 2 are compared with the germanium coagulates produced on the ground shown in FIGS. 3 to 5 to obtain a complete crystal having almost no defects due to free fall in a drop tube. It is clear that a close germanium sphere was formed.

2. Production of Spherical Titanium Oxide Layer-Coated Titanium A 1 mm diameter titanium fine wire was melted in the same procedure as germanium, and the resulting melt was solidified during free fall in a drop tube to obtain a spherical titanium having a diameter of about 1.5 mm. . A spherical tube is filled into a quartz tube having an inner diameter of 2 mm and one end of which is squeezed to a diameter of 1 mm to a height of 2 cm.
Soaked in t% nitric acid solution. A copper wire was brought into contact with a titanium ball on one of the unimmersed portions, and a current density of 50 A / m ² ,
Anode electrolytic oxidation was performed for one hour. As a result, the formation of a 10 μm titanium oxide layer on the spherical titanium surface was confirmed.

[0014]

According to the present invention, a spherical optical functional material having high mechanical strength and capable of efficiently receiving light can be manufactured using a drop tube. Further, according to the present invention, an optical functional material having a structure close to a perfect crystal can be manufactured.

[Brief description of the drawings]

FIG. 1 shows an optical micrograph of a product of the present invention in which the surface of a germanium sphere has been subjected to an etching treatment.

FIG. 2 shows a transmission electron micrograph (lattice image) of a product of the present invention in which the surface of a germanium sphere has been subjected to an etching treatment.

FIG. 3 shows an optical microscope photograph of a comparative product obtained by subjecting a surface of a germanium piece to an etching treatment.

FIG. 4 shows a transmission electron micrograph of a lattice defect portion of a comparative product in which the surface of a germanium piece has been subjected to an etching treatment.

FIG. 5 shows a transmission electron micrograph (lattice image) of a vicinity of a lattice defect portion of a comparative product in which the surface of a germanium piece is subjected to an etching treatment.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Yoshinori Nakata Inventor, Hokkaido Industrial Technology Research Institute, 2-17-1, Higashikan, Toyohira-ku, Sapporo, Hokkaido 2-17-1, Higashi 2-17-17 Hokkaido Institute of Industrial Technology, Institute of Industrial Science and Technology (72) Inventor Masaaki Suzuki 2-17-2, Tsukikan Higashi 2-1, 2-2-1, Higashikan, Sapporo, Hokkaido (56) References JP-A-2-55292 (JP, A) JP-A-2-185975 (JP, A) JP-A-3-254832 (JP, A) JP-A-10-33969 (JP, A) US Pat. (US, A) WO 98/15983 (WO, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) C30B 1/00-35/00 B01J 35/02 H01L 31/04 H01L 33/00 CA (STN) JICST Airu (JOIS)

Claims (1)

(57) [Claims] 1. A method for producing an optically functional material having a spherical shape, comprising: in a microgravity environment, a melt of the optically functional material or a material constituting the optically functional material;
It consists of a double pipe, and the refrigerant flows through the gap between the inner pipe and the outer pipe.
A method for producing a spherical optical functional material, comprising a step of free-falling in a gas atmosphere of 665 Pa or less through a falling pipe passed through the pipe and cooling and solidifying during the fall.