JP4674279B2 - Method for producing columnar nanocrystal - Google Patents

Description

The present invention relates to the production how the columnar crystals of silicon down or Ranaru nanosized.

  In recent years, carbon nanotubes have been attracting attention as nano-sized materials that can be applied to a wide range of fields such as electronic materials and catalyst materials. A method is disclosed. However, in the manufacturing method of carbon nanotubes using the conventional laser ablation method as described in the same publication, it is necessary to heat the atmosphere to a high temperature of several hundred degrees Celsius in the process, and development of a more efficient manufacturing method has been developed. It was desired.

On the other hand, silicon is considered as a nano-sized material that can be applied to an electronic material, a catalyst material, and the like in the same manner as carbon nanotubes. A method for producing such an optoelectronic material is disclosed. However, any silicon material that can be produced by a method using the conventional laser ablation method as described in the publication is a spherical microcrystal, and any other method conventionally obtains a silicon columnar crystal. I couldn't.
JP 2001-89117 A Japanese Patent Laid-Open No. 10-214995

The present invention, the has been made in view of the problems of the prior art, aims to provide a way capable of producing a columnar crystal of silicon down or Ranaru nanosized efficiently and reliably And

As a result of intensive studies to achieve the above object, the present inventors surprisingly ablated when using pulsed laser light having a much higher irradiation intensity than the laser light used in the conventional laser ablation method. crystals grown in a columnar when scattered particles are attached, found that columnar crystals of silicon down or Ranaru nanosized obtained, and have completed the present invention.

That is, in the method for producing a columnar nanocrystal of the present invention, the target made of a material containing a silicon element is irradiated with a pulse laser beam having an irradiation intensity of 10 ¹⁵ W / cm ² to 10 ²¹ W / cm ^2. It is a method characterized by generating scattered particles of elements and forming columnar nanocrystals of the elements formed by combining the scattered particles of the elements.

The pulse laser beam used in the method for producing the columnar nanocrystal of the present invention has a pulse width of 1 picosecond or less, a wavelength of 200 nm to 1 μm, and a fluence of 10 ² J / cm ² to 10 ^11. J / cm ² is preferred.

The reason why the columnar nanocrystals of silicon are formed by the present invention is not necessarily clear, but the present inventors infer as follows. That is, when a target made of a material containing silicon element is irradiated with pulsed laser light having an irradiation intensity of 10 ¹⁵ W / cm ² to 10 ²¹ W / cm ² , the material constituting the target is turned into plasma, and silicon element Become neutral atoms and ions. The plasma temperature at this time exceeds 1 million ° C., which is 10 to 1000 times higher than the temperature of the plasma generated during conventional laser ablation. In the process of expansion and cooling of the plasma, clusters formed by combining some of neutral atoms and ions are scattered at a high speed of several times the sound speed with high energy . In the present invention, since the irradiation intensity of the pulse laser beam is as high as 10 ¹⁵ W / cm ² to 10 ²¹ W / cm ² , a high electric field of about 10 ⁶ V / m to ^{10 10} V / m is formed. By applying this voltage to the ionized scattered particles, the direction of crystal growth is aligned. Therefore, the present inventors infer that the crystal grows so as to form columnar crystals when the scattered particles are combined, and nano-sized columnar crystals of the element are formed.

In the method for producing a columnar nanocrystal of the present invention, the target is irradiated with the pulsed laser light in a vacuum state of 10 ⁻³ Torr or less (particularly preferably, a vacuum state of 10 ⁻⁴ Torr or less) in a container. It is preferable to do. As described above, when a container having a vacuum state of 10 ⁻³ Torr or less (particularly preferably, a vacuum state of 10 ⁻⁴ Torr or less) is used, the absorption of energy due to discharge is sufficiently suppressed, and the columnar nanocrystal Tends to be obtained more efficiently.

According to the present invention, without particular heating or the like the atmosphere in the manufacturing apparatus, it is possible to produce a columnar crystal of nano-sized made of silicon efficiently and reliably.

Hereinafter, about the production how the columnar nano-crystals of this invention will be described in detail with reference to preferred embodiments thereof.

  FIG. 1 is a schematic diagram showing a basic configuration of a preferred embodiment of a columnar nanocrystal production apparatus suitable for the present invention. The columnar nanocrystal production apparatus shown in FIG. 1 is a so-called laser ablation apparatus 1. It is configured. That is, the laser ablation apparatus 1 shown in FIG. 1 includes a laser light source 2, and a laser light source 2 and a target 4 to which a laser beam L emitted from the laser light source 2 is irradiated are obtained. A substrate 6 for collecting the columnar nanocrystals 5 is disposed.

The laser light source 2 is condensed by an optical system such as a condenser lens 7 and the irradiation intensity with respect to the target 4 is 10 ¹⁵ W / cm ² to 10 ²¹ W / cm ² (more preferably, 10 ¹⁵ W / cm ² to Any laser beam generator that can irradiate the pulsed laser beam L of 10 ¹⁸ W / cm ² ) may be used, and the laser beam generator is not particularly limited, but is preferably configured by a femtosecond laser oscillator. Further, when the target 4 is irradiated with the pulse laser beam L, the pulse laser is used so that scattered particles (neutral atoms, ions, clusters, etc. of the material constituting the target) a are efficiently generated from the surface of the target 4. The irradiation angle of the pulse laser beam L is adjusted by appropriately arranging an optical system such as a mirror 8 in the middle of the optical path of the light L.

The processing container 3 is a container (for example, a stainless steel container) for housing the above-described components therein, and a vacuum pump (for example, a rotary pump or a turbomolecular pump) 9 is connected to the piping 10 in the processing container 3. And the inside of the processing vessel 3 can be maintained in a vacuum state at a predetermined pressure. Thus, when the processing container 3 in which the inside is in a vacuum state is used, energy absorption due to discharge is sufficiently suppressed, and the columnar nanocrystal body 5 can be obtained more efficiently. In addition, as a pressure at the time of maintaining the inside of the container 3 in a vacuum state, the pressure which becomes a vacuum state below 10 < ^-3 > Torr is preferable, and the pressure which becomes a vacuum state below 10 < ^-4 > Torr is especially preferable.

The target 4 is made of a material (target material) that generates silicon element scattering particles (neutral atoms, ions, clusters, etc.) a by irradiation with the pulse laser beam L described above, and is made of a material containing a silicon element. It will be . The material constituting the data Getto 4 can expect applications to optoelectronic materials and the like, those containing silicon (silicon) element from the viewpoint of not giving environmental impact. Et al is, it is preferable the material for the target 4 is made of only the silicon, may contain other ingredients which do not affect the formation of the columnar nanocrystals. Examples of such other components include phosphorus and antimony. When such other components are included, the content is preferably 5% by weight or less. The shape of the target 4 is not particularly limited, and a bulk material made of the target material formed into a plate shape, a rod shape, or the like, or a tape formed by applying, evaporating, or sticking the target material on a tape. A shaped target or the like can be used.

  The substrate 6 is not particularly limited as long as it can collect the columnar nanocrystals 5 obtained on the surface and / or inside thereof. For example, a carbon mesh, a carbon film, a silicon substrate, a resin substrate, Inorganic crystals, metal plates and the like are preferably used. Further, the shape, size, and thickness of the substrate 6 are not particularly limited, and a film shape, a plate shape, or the like is appropriately selected according to the columnar nanocrystal 5 to be collected.

  The positional relationship between the substrate 6 and the target 4 is not particularly limited, and the target 4 is efficiently collected on the surface of the substrate 6 so that the scattered particles a and the columnar nanocrystals 5 generated from the surface of the target 4 are collected. In FIG. 1, the substrate 6 is disposed at a position where the angle Θ in the normal direction of the substrate 6 with respect to the irradiation direction of the laser light L is 45 °. In addition, a target driving device (for example, a target turntable) 11 is connected to the target 4, and a fresh surface of the target (laser light non-irradiated surface) is sequentially fed out to the irradiation position of the laser light L.

  As mentioned above, although one Embodiment of the manufacturing apparatus of the columnar nanocrystal suitable for this invention was described, the apparatus suitable for this invention is not limited to the said embodiment. That is, for example, in the above-described embodiment, all the components of the manufacturing apparatus are arranged inside the processing container 3, but from the laser light source 2 arranged outside the processing container 3 through a window (for example, a quartz window). Then, the laser beam L may be introduced into the container 3.

  Further, in the above embodiment, the substrate 6 is disposed at a position where the angle Θ is 45 °, but the positional relationship is not particularly limited, and the angle Θ is in the range of about 10 ° to 60 °. The board | substrate 6 may be arrange | positioned in the position used as. Further, for example, a substrate 6 that can transmit the laser light L is used, the substrate 6 is disposed opposite to the target 4 between the condenser lens 7 and the target 4, and the laser light L transmitted through the substrate 6 is the target. 4 may be irradiated.

Then, with the one preferred form status of the manufacturing method of the columnar nano-crystals of this invention will be described with reference to FIG.

In the method for producing a columnar nanocrystal of the present invention, the irradiation intensity of the target 4 is 10 ¹⁵ W / cm ² to 10 ²¹ W / cm ² (particularly preferably 10 ¹⁵ W / cm ² to 10 ¹⁸ W / cm. ² ) is irradiated from the laser light source 2. Then, a very high temperature plasma P is formed on the surface of the target 4, and the silicon neutral atoms and ions in the plasma P and some of the neutral atoms and ions are combined during expansion and cooling. The formed clusters scatter very quickly with high energy. If the irradiation intensity of the pulsed laser light L applied to the target 4 is less than 10 ¹⁵ W / cm ² , the scattered particles a become spherical microcrystals or amorphous when combined, and a nano-sized columnar crystal body. Cannot be obtained. On the other hand, when the irradiation intensity exceeds 10 ²¹ W / cm ² , the plasma diverges due to the strong electromagnetic field, and the atoms and ions that constitute the crystal are also dispersed so that the crystal cannot be formed.

The pulse laser beam L according to the present invention has a pulse width of 1 picosecond or less (more preferably 10 femtoseconds to 500 femtoseconds) and a wavelength of 200 nm to 1 μm (more preferably 400 nm to 800 nm). The fluence is preferably 10 ² J / cm ² to 10 ¹¹ J / cm ² (more preferably 10 ² J / cm ² to 10 ⁵ J / cm ² ). When the pulse width exceeds 1 picosecond, the plasma formation and heating processes are delayed, and the strong electromagnetic field tends to be less affected. In addition, when the wavelength exceeds 1 μm, the efficiency of the target to absorb laser light decreases, and plasma formation and the heating process tend to be delayed. On the other hand, when the wavelength is less than 200 nm, absorption occurs only on the longest surface of the target. There is a tendency that an amount of plasma having a sufficient density to form the film cannot be obtained. Further, if the fluence is less than 10 ² J / cm ² , the plasma that becomes the source of atoms constituting the crystal tends to be insufficient, whereas if it exceeds 10 ¹¹ J / cm ² , the plasma size is imparted with a strong electromagnetic field. There is a tendency that crystals having anisotropy cannot be formed because the crystal becomes too larger than the region.

  The fine scattered particles (ablator) a generated from the surface of the target 4 by the irradiation of the pulse laser beam L in this way are repeatedly collided with other scattered particles a in the process of being scattered at high speed to form a columnar shape. Crystal growth causes columnar nanocrystals 5 to be formed and collected on the surface and / or inside of the substrate 6. Further, scattered particles a are also collected on the surface and / or inside of the substrate 6, and when they are deposited there, they are combined with other scattered particles a or columnar nanocrystals 5 to grow into columnar crystals. Crystal 5 is formed.

  In addition, in the manufacturing method of the columnar nanocrystal of the present invention described above, it is not necessary to heat the atmosphere in the processing container 3 to a particularly high temperature, and the temperature in the processing container 3 is generally about 0 to 30 ° C. I just need it.

The columnar nanocrystal obtained in this way is a nano-sized columnar crystal made of silicon according to the target material used. According to the production method of the present invention, the average diameter is 1 to 20 nm (more preferably It is also possible to obtain nano-sized needle-like crystals having an average aspect ratio of 10 or more. Since such a columnar nanocrystal has nano-size anisotropy, it has characteristics that are not found in conventional materials in terms of electromagnetic characteristics, optical characteristics, etc., and includes electronic materials, light-emitting elements, photoelectric elements, It is a very promising material for a wide range of applications such as fuel cell electrodes.

In particular, it is a nano-sized columnar crystal made of silicon obtained using silicon as a target material, having an average diameter of 1 to 20 nm (more preferably 5 to 15 nm), and an average aspect ratio of 10 or more. Is obtained by the method for producing a silicon columnar nanocrystal of the present invention. Such divorced columnar nanocrystals may or light emitting device to be described below, it is a very promising material for a wide range of applications photoelectric elements, fuel cells such as electrodes. In other words, it is generally known that when a strong electric field is applied to the metal surface, free electrons in the metal are emitted into the vacuum due to the quantum mechanical tunneling effect (field electron emission). ing. In order to generate such field electron emission, a high electric field of several tens of MV (megavolt) per 1 cm is necessary. To generate such a high electric field, a metal needle having a very thin tip is used. Is required. Upper carboxymethyl silicon columnar nanocrystals, because the tip is very small and 1 to 20 nm (more preferably 5 to 15 nm), are very suitable as a needle for generating an electric field electron emission of the For example, in a light emitting device using this as an electrode, the electron emission efficiency is improved, and strong light emission can be obtained with a small amount of current.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

Example 1
Femtosecond laser oscillator as laser light source 2 (peak output 550 TW, shortest pulse width 33 femtosecond, owned by Japan Atomic Energy Research Institute Kansai Research Center for Photon Science), vacuum container (made of stainless steel, capacity of about 100 liters) ), Using a silicon plate (diameter 3 mm, thickness 0.1 mm) as the target 4 and a carbon film (diameter 3 mm, thickness 0.001 mm) as the substrate 6, the columnar nanocrystal manufacturing apparatus shown in FIG. 1 was produced. . The substrate 6 is disposed at a position where the angle Θ is 30 °, and the distance between the substrate 6 and the target 4 (the distance between the laser light irradiation position of the target 4 and the center of the substrate 6) is 300 mm. .

Next, using the manufactured apparatus, the inside of the processing vessel 3 is brought into a vacuum state at a pressure of 5.5 × 10 ⁻⁵ Torr, and the target 4 is translated on an XY table, and then the laser light source 2 To a laser beam irradiation area on the target 4 of φ20 μm so that the pulse laser beam L {wavelength 800 nm, irradiation intensity 8.3 × 10 ¹⁶ W / cm ² , pulse width 40 femtoseconds, energy 10 mJ per pulse, The target 4 was irradiated 20 times with a single shot at a fluence of 10 ⁴ J / cm ² }. Since the inside of the container 3 is in a vacuum state, the pulsed laser light L reaches the target 4 without absorbing energy due to discharge, and a high-temperature plasma P is formed on the surface of the target 4, and from the surface of the target 4 into the silicon. Fine scattering particles (ablators) a such as sex atoms, ions and clusters were scattered at high speed. The scattered particles a repeatedly collide with other scattered particles a in the process of being scattered at a high speed to grow into a columnar crystal to form columnar nanocrystals 5, which are collected on the surface and inside of the substrate 6. It was. Further, the scattered particles a that reached the surface and inside of the substrate 6 were also bonded to other scattered particles a or the columnar nanocrystals 5 to grow into a columnar shape, thereby forming the columnar nanocrystals 5. The irradiation time was 10 seconds, and the temperature inside the container was about 25 ° C.

  When the columnar nanocrystals 5 collected on the substrate 6 were observed with a transmission electron microscope, the diameter was about 5 to 15 nm (average diameter about 10 nm) and the length was about 100 to 1000 nm (average) as shown in FIG. It was confirmed to be a nano-sized columnar shape (needle shape) having a length of about 500 nm and an average aspect ratio of about 50.

  Further, when the columnar nanocrystals 5 collected on the substrate 6 were photographed with an electron beam diffractometer, clear ring-shaped diffraction was observed as shown in FIG. 3, and this caused the columnar silicon structure to crystallize. It was confirmed that

  Furthermore, when the surface of the silicon target 4 after laser irradiation was observed with an optical microscope, an irradiation mark of φ20 μm was observed as shown in FIG. 4, and it was confirmed that the irradiation intensity was a target value. It was confirmed that columnar nanocrystals were also formed in the vicinity of the irradiation mark.

(Comparative Example 1)
Implemented except that the irradiation conditions of the pulsed laser beam L were set to a wavelength of 532 nm, an irradiation intensity of 1 × 10 ⁹ W / cm ² , a pulse width of 7 nanoseconds, an energy per pulse of 1 J, a fluence of 10 ² J / cm ² , and a frequency of 10 Hz. The test was conducted in the same manner as in Example 1.

  When the substance collected on the substrate 6 was observed with a transmission electron microscope, it was minute spherical amorphous silicon as shown in FIG.

As described above, according to the present invention, without particular heating or the like the atmosphere in the manufacturing apparatus, it is possible to produce a columnar crystal of nano-sized made of silicon efficiently and reliably.

Then, columnar nanocrystals obtained by the production method of the present invention is an electronic material, the light-emitting element, a photoelectric element, a very promising material for a wide range of applications of the electrode of the fuel cell, among others by the production method of the present invention According to the obtained silicon columnar nanocrystal, the electron emission efficiency of the light emitting device can be improved.

It is a schematic diagram which shows the basic composition of suitable one Embodiment of the manufacturing apparatus of the columnar nanocrystal suitable for this invention. 2 is a transmission electron micrograph of the columnar nanocrystal obtained in Example 1. FIG. It is a photograph which shows the crystal structure which image | photographed the columnar nanocrystal obtained in Example 1 with the electron beam diffraction apparatus. 2 is an optical micrograph of the surface of a silicon target after laser irradiation used in Example 1. 2 is a transmission electron micrograph of the substance obtained in Comparative Example 1.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Manufacturing apparatus of columnar nanocrystal body, 2 ... Laser light source, 3 ... Processing container, 4 ... Target, 5 ... Columnar nanocrystal body, 7 ... Substrate, 7 ... Condensing lens, 8 ... Mirror, 9 ... Vacuum pump, DESCRIPTION OF SYMBOLS 10 ... Pipe, 11 ... Target drive device, L ... Pulse laser beam, a ... Scattering particle | grains, P ... Plasma.

Claims (3)

A target made of a material containing silicon element is irradiated with pulsed laser light having an irradiation intensity of 10 ¹⁵ W / cm ² to 10 ²¹ W / cm ² to generate scattered particles of the element, and the scattered particles of the element A method for producing a columnar nanocrystal comprising forming the columnar nanocrystal of the element by bonding. The pulse width of the pulse laser beam is 1 picosecond or less, the wavelength is 200 nm to 1 μm, and the fluence is 10 ² J / cm ² to 10 ¹¹ J / cm ² . A method for producing a columnar nanocrystal. 3. The method for producing a columnar nanocrystal according to claim 1, wherein the target is irradiated with the pulsed laser light in a vacuum state of 10 ⁻³ Torr or less.