CN1676678A - ZnO nano crystal column/nano crystal filament composite structure product and its preparing process - Google Patents

Abstract

The ZnO nanometer crystal bar / nano crystal filament composite structure product in this invention belongs to a kind of oxide microstructure material made with the technology of gas phase denotation. At the beginning, the hexagonal structure ZnO nano crystal bar array is growing on the surface of substrate, with the characteristics of growing strictly in the orientation of c-axis, high density and homogeneous distribution. After that, ZnO nano crystal filament will come out on the ZnO nano crystal bar array, nearly paralleling the surface of the substrate, with high density. The characteristics of the producing process of this product is that it adopts the technology of the electron bundle reaction evaporation, and though the craft of 'two-step deposition', we can get the product by once-and-for-all growing on the surface of the substrate.

Description

ZnO nanocrystalline column/nanocrystalline wire composite structure product and its preparation process

technical field

The invention belongs to the technical field of oxide microstructure materials and vapor phase epitaxy preparation thereof, and specifically relates to a hexagonal ZnO nanocrystal column/nanocrystal wire composite structure product and its use of electron beam reaction evaporation equipment through a "two-step deposition" process The preparation technology of the product is obtained by one-time growth on the surface of the substrate.

technical background

In recent years, the research on ZnO-based microstructure materials has attracted worldwide attention. Among numerous ZnO-based microstructure materials (such as nanocolumns, nanowires, nanorings, nanobelts, nanodisks, and nanopropellers), ZnO in the form of nanopillars or nanofilaments is characterized by its unique quasi-one-dimensional or tetraacicular ( Such as whiskers) spatial structure and its single crystal characteristics, so that it has extremely high elastic modulus, extremely low thermal expansion rate, good high temperature resistance and good semiconductor and piezoelectric properties, and is used in shock absorption, noise reduction, and wave absorption , wear resistance, high temperature resistance, antistatic and antibacterial and many other fields have a wide range of uses, such as shock absorption and noise reduction of high-speed railways, aircraft absorbing stealth, microwave heat conversion and other aspects have important applications, known as the 21st century important emerging materials. Zinc oxide nanowires are usually obtained by oxidation of zinc powder (Hong Jin Fan, Roland Scholz, Florian M.Kolb, and Margit Zacharias, Two-dimensional dendritic ZnO nanowires from oxidation of Zn microcrystals, Applied Physics Letters, 85(2004) 4142); or obtained by ZnO powder via carbon reducing agent, by thermochemical reaction and vapor transport deposition (MH Huang, S.Mao, H.Feick, et al, Scince, 292(2001)1897). In these two methods, controlling the reaction gas phase supersaturation in the reactor is the key to the preparation of high-quality ZnO nanowires. If the gas phase supersaturation in the reactor is well controlled, it can be synthesized with high purity, complete crystal structure, Scale-controllable ZnO nanowires. However, the control of high-precision gas phase supersaturation is more complicated, and these two methods usually require the introduction of metal catalysts (Seu Yi Li, Chia Ying Lee, Tseung Yuen Tseng, Copper-catalyzed ZnO nanowires on silicon(100) grown by vapor- liquid-solid process, Journal of Crystal Growth 247(2003) 357-362; Woong Lee, Min-Chang Jeong, Jae-Min Myoung, Catalyst-free growth of ZnO nanowires by metal-organic chemical vapor deposition (MOCVD) and thermal evaporation, Acta Materialia 52(2004)3949-3957; X.Wang, QWLi, ZBLiu, J.Zhang, ZFLiu, Low-temperature growth and properties of ZnO nanowires, Applied Physics Letters, 84(2004)4941-4943; XHKong, XMSun, XLLi, YDLi, Catalytic growth of ZnO nanotubes, MaterialsChemistry and Physics, 82 (2003) 997-1001), the prepared zinc oxide nanowires are in the shape of soft cotton wool, generally need to do secondary processing when doing specific applications, and secondary processing The obtained product inevitably has a series of problems such as poor bonding strength between the ZnO nanowire and the matrix material. The crystal structure analysis of the ZnO nanowire product obtained by the Zn powder oxidation method shows that the product is often polycrystalline and contains metal Zn (BJChen, XWSun, CXXu, BKTay, Growth and Characterization of zinc oxide nano/micro-fibers by thermal chemical reactions and vapor transport deposition in air, Physica E, 21(2004) 103-107). If a catalyst is introduced during the preparation, for example with Au (X.Wang, QWLi, ZBLiu, J.Zhang, ZFLiu, Low-temperature growth and properties of ZnO nanowires, Applied Physics Letters, 84(2004) 4941-4943 ^[3] ) or NiO (TYKim, JYKim, SHLee, et al, Characterization of ZnO needle-shaped nanostructures grown on NiO catalyst-coated Si substrates, Synthetic Metals, 144 (2004) 61-68) nanoparticles as a catalyst), then in ZnO nanowire The finished product will also contain catalyst components, which reduces the quality of ZnO nanowires, especially limiting its application in special fields (such as microelectronics, optoelectronics).

The research status of the preparation of ZnO-based microstructure materials (such as nanocolumns, nanowires, nanorings, nanobelts, nanodisks, and nanopropellers) is as follows: (1) The control process of the gas phase supersaturation in the reactor is complicated. Improper, then the product that obtains is often ZnO thin film, (2) ZnO nanowire finished product is single cotton-wool shape usually macroscopically, needs to do secondary processing during practical application, (3) ZnO nanowire preparation process is due to introducing Catalyst, the finished product contains metal Zn and catalyst components, and the crystal quality is not ideal.

Contents of the invention

The present invention adopts a relatively simple electron beam reaction evaporation method, using polycrystalline ZnO ceramic target material and NH ₃ /H ₂ mixed gas as raw materials, without adding a metal catalyst, through the "two-step deposition" process directly on the The ZnO nanocrystalline column/nanocrystalline filament composite structure product with high crystal quality can be obtained by one-time growth on the surface of the substrate. The inventive product can meet some special purposes, for example, it can be used as a high-performance microwave-absorbing invisible material or a microwave heat conversion material.

The ZnO nanocrystal column/nanocrystal wire composite structure product of the present invention is characterized in that there are high-density and uniformly distributed hexagonal structure ZnO nanocrystal column arrays on the surface of the ZnO ceramic substrate. There are high-density ZnO nanocrystalline filaments parallel to the substrate surface on the column array; using electron beam reactive evaporation method, using polycrystalline ZnO ceramic target and NH ₃ /H ₂ mixed gas as raw materials, through "two-step deposition "The process directly grows on the surface of the substrate at one time to obtain ZnO nanocrystalline column/nanocrystalline wire composite structure products.

The ZnO nanocrystalline column/nanocrystalline wire composite structure product of the present invention is obtained by electron beam reaction evaporation method, and its specific process steps are as follows:

(1) Clean the substrate and load it into the substrate rack, and put the substrate rack into the growth chamber. Place the pressed and sintered ZnO ceramic target in the crucible in the growth chamber, and use a baffle to isolate the target and the substrate;

(2) Use a vacuum pump to pump the growth chamber to a background vacuum of ≤3×10 ^-3 Pa;

(3) First fill the NH ₃ /H ₂ mixed gas at a small flow rate of 10sccm-20sccm, and at the same time properly adjust the high vacuum pumping valve of the growth chamber to make the vacuum degree in the growth chamber reach 3×10 ^-2 Pa and keep it constant;

(4) heating the substrate to a suitable growth temperature;

(5) Align the ZnO target with a high-energy focused electron beam first, adjust the beam current of the electron beam, and heat the target at a lower beam current to degas the target;

(6) After degassing, adjust the electron beam current to a certain current value of 30mA~40mA, so that the ZnO target material starts to evaporate; according to the different requirements of the growth rate, adjust the electron beam spot area and the position of the beam spot center and other parameters, control the vapor pressure (partial pressure) of the ZnO target at 2.0×10 ^-2 Pa～5.0×10 ^-2 Pa, so that the ZnO target can be evaporated stably and uniformly; open the baffle to start the ZnO nanocrystalline column/nanocrystalline wire First-stage growth of composite microstructures;

(7) After the first stage of growth has gone through 20 minutes to 30 minutes, increase the flow rate of the mixed gas to 50sccm to 60sccm, and enter the second stage of growth;

(8) When the second stage of growth lasts for 30 minutes to 40 minutes, turn off the high voltage of the electron gun to end the growth;

(9) After the growth is completed, while still maintaining the NH ₃ /H ₂ mixed gas flow rate of 50sccm-60sccm, gradually reduce the substrate temperature, and when the substrate temperature drops to ≤200°C, cut off the mixed gas source;

(10) After the substrate temperature drops to room temperature, open the growth chamber and take out the sample.

The substrate mentioned in the process step (1) of the present invention may be a single crystal Si polished sheet, a single crystal sapphire polished sheet or quartz glass.

Mention cleaning substrate in process step (1) of the present invention, the cleaning step of Si polished sheet substrate is:

To remove organic matter - put the silicon wafer into a solution mixed with concentrated sulfuric acid and hydrogen peroxide at a ratio of 1:1 and boil for 10 minutes to 15 minutes;

De-oxidation - immerse the silicon wafer in 10% hydrofluoric acid solution for 20 to 30 seconds, and then rinse it repeatedly with deionized water;

Inorganic matter removal - silicon wafers are bathed in a 1:1:6 solution of hydrogen peroxide, hydrochloric acid, and deionized water at 80°C for 15 to 20 minutes, and rinsed with deionized water after removal;

Immerse the silicon wafer cleaned by the above steps in 10% hydrofluoric acid solution for 5-10 seconds;

Finally, dry the silicon wafer with nitrogen gas in a vertical laminar flow clean bench, and quickly put it into the growth chamber.

The ZnO ceramic target material mentioned in the process step (1) of the present invention is formed by pressing ZnO powder with a purity of 99.99% and sintering at high temperature (1200° C.).

The _NH3 / _H2 mixed gas mentioned in the process step (3) of the present invention is formed by mixing NH3 _gas and _H2 gas with a purity of 99.999%, wherein the volume percentage of _NH3 gas is 1vol. %~50vol.%.

In the process step (3) of the present invention, it is mentioned that "first fill the NH ₃ /H ₂ mixed gas with a small flow rate of 10sccm to 20sccm", if the flow rate is too large, it will not be able to ensure that the mixed gas will reach the substrate surface in a diffusion manner, thereby affecting the ZnO The nucleation rate of crystal nuclei.

The suitable substrate temperature mentioned in the process step (4) of the present invention can be 400°C, 450°C or 500°C, too low or too high temperature is not conducive to growing single crystal ZnO nanocolumn/nanowire composite film.

The lower beam current mentioned in the process step (5) of the present invention is 5mA-10mA, and the target is heated for 5-10 minutes to degas the target.

The vapor pressure of the ZnO target evaporated by the high-energy electron beam mentioned in the present invention is 2×10 ^-2 Pa～5×10 ^-2 Pa, which can be controlled by adjusting the parameters of the electron gun.

The ZnO nano crystal column/nano crystal wire composite microstructure product of the present invention is realized in a commercial electron beam reactive evaporation deposition system. The focused electron beam with higher energy emitted by the electron gun directly bombards the ZnO target material, and the kinetic energy of the electron beam becomes thermal energy, so that the thermally evaporated ZnO molecules leave the target surface, scatter and deposit on the heated substrate surface, and are adsorbed Molecules or atoms form crystal nuclei through diffusion movement; at the same time, _{NH 3 , H 2} molecules, due to the thermal radiation of the substrate surface and the collision of ZnO particles evaporated by heat, are partially decomposed into atomic N and atomic H. These supersaturated atomic N and atomic H cover the entire substrate surface and also surround the formed ZnO crystal nucleus, making it difficult for them to quickly grow into ZnO crystal grains and further form a whole ZnO crystal film. These supersaturated atomic N and atomic H interact with the ZnO crystal nucleus through a series of molecular dynamics interactions (some of the N atoms enter into the ZnO crystal lattice by replacing O; and the atomic H due to its strong reduction, it will selectively inhibit the growth of ZnO crystal nuclei along the non-c-axis orientation), resulting in the ZnO crystal nuclei selectively growing along the c-axis orientation perpendicular to the substrate surface, forming a uniform density distribution single crystal ZnO nanopillars. The above process generally lasts for 20 minutes to 30 minutes, and is the first step in the "two-step deposition" process. At this time, the ZnO nanocrystal column has grown to a height of 100 nm to 200 nm.

After the growth process lasts for 20 minutes to 30 minutes, enter the second step of the "two-step deposition" process, and increase the flow rate of the NH ₃ /H ₂ mixed gas (such as increasing to 60 sccm, the flow rate is also corresponding increase), so that the gas mixture basically reaches the substrate surface in a conduction (ie, convection, not diffusion) manner. At this time, the conditions for the c-axis oriented ZnO nanocrystalline column to grow further along the direction perpendicular to the substrate are disturbed, and then it gradually grows into a disorderly oriented nanowire shape, although it still grows along the c-axis , but at this time the c-axis is no longer perpendicular to the substrate, but randomly oriented. After continuing in this way for 30 minutes to 40 minutes, a ZnO nanocrystalline column/nanocrystalline wire composite structure product is finally obtained. Since this is grown by a two-step method (that is, the NH ₃ /H ₂ mixed gas flow rate is small first and then large), so the duration of the first and last two processes and the gas flow of the two stages are well controlled. , the morphology and other characteristics of ZnO nanocrystalline column/nanocrystalline wire composite structure products can be effectively modulated.

Field emission scanning electron microscope (FESEM), X-ray diffraction (XRD) and energy dispersive X-ray diffraction (EDX) techniques were used to analyze the surface morphology, crystal structure and composition content of the grown ZnO microstructure material samples, respectively. The results showed that the grown sample had the morphology of ZnO nanocrystalline column/nanocrystalline filament composite structure, and the elemental composition of N and H was not detected in the sample.

The main technical advantages of the present invention are:

The composite microstructure of ZnO nanocrystalline column/nanocrystalline wire adopts a commercialized electron beam reaction evaporation system, using the easily available polycrystalline ZnO ceramic target and NH ₃ /H ₂ mixed gas as source materials, through the "two-step deposition" process It is obtained by one-time growth on the surface of the substrate, and the preparation process is easy to control, which is suitable for the preparation of large-area composite thin films, has low preparation cost, and is beneficial to industrial production.

The advantages of the finished product of the present invention are:

Compared with the cotton-like ZnO crystal filament product obtained by zinc powder oxidation and carbon reduction of ZnO powder, the present invention obtains a new type of ZnO with controllable surface morphology, firm bonding with the substrate, and high purity. Nanocrystalline column/nanocrystalline wire composite structure products. It is characterized by first growing an array of ZnO nanocrystal columns uniformly distributed, highly c-axis oriented and perpendicular to the substrate surface on the substrate surface, and then growing uniformly and densely on the array along a direction almost parallel to the substrate Interlaced ZnO nanocrystalline wires. It is because of its unique surface morphology that it is especially suitable for applications such as microwave absorbing stealth and microwave heat conversion.

Description of drawings

Fig. 1 is a field emission scanning electron microscope (FESEM) surface topography photograph of a ZnO nanocrystalline column/nanocrystalline filament composite structure sample grown according to a preferred embodiment of the present invention at a magnification of 50,000 times.

Fig. 2 is the field emission scanning electron microscope (FESEM) surface topography photo of the grown ZnO nanocrystal post/nanocrystal wire composite structure sample under 5000 times magnification according to a preferred embodiment of the present invention

Fig. 3 is an electron energy dispersive X-ray diffraction (EDX) spectrum of a ZnO nanocrystalline column/nanocrystalline wire composite structure sample grown according to a preferred embodiment of the present invention.

Fig. 4 is an X-ray diffraction (XRD) spectrum of a ZnO nanocrystalline column/nanocrystalline filament composite structure sample grown according to a preferred embodiment of the present invention.

Detailed ways

Example

1. Put the Si substrate into a solution mixed with concentrated sulfuric acid and hydrogen peroxide at a ratio of 1:1 and boil for 10 minutes to remove surface organic matter; then immerse the Si substrate in 10% hydrofluoric acid solution for 30 seconds, take it out and use it Rinse repeatedly with deionized water; then boil the Si substrate in a solution mixed with HCl:H ₂ O ₂ :deionized water at a ratio of 1:1:6 for 15 minutes to remove surface inorganic matter; after taking it out, rinse it repeatedly with deionized water and place it on the Soak in HF solution for a few seconds, dry the substrate with N ₂ and put it into the growth chamber quickly.

2. Place the ZnO ceramic target material with a purity of 99.99% that has been pressed and sintered at a high temperature of 1200°C in a crucible, and the target source is separated from the substrate by a baffle. Use a vacuum pump to evacuate the background pressure of the reaction chamber to about 3×10 ^-3 Pa.

3. Fill the NH ₃ /H ₂ mixed gas with a NH ₃ content of 2.7vol.% at a flow rate of 10 sccm (the purity of both NH ₃ and H ₂ is 99.999%), and at the same time properly adjust the high vacuum pumping valve of the growth chamber, Make the vacuum in the reaction chamber reach 3×10 ^-2 Pa and keep it constant; then heat the substrate;

4. After the substrate is heated to 450°C, heat the ZnO target with a high-energy electron beam with an accelerating voltage of 6KV, and degas the target for 5 minutes: adjust the beam current of the electron gun to about 5mA, adjust the beam spot area of the electron beam and Position the center of the beam spot so that the area of the beam spot just covers the surface of the entire target and keep it for 5 minutes.

5. Adjust the beam current of the electron gun to 35mA, and adjust the beam spot area and the position of the beam spot center of the electron beam. When the partial pressure of the ZnO target reaches 3×10 ^-2 Pa, open the baffle and start the first composite film Stages of growing growth. During the growth process, the substrate temperature was kept constant at 450°C, and the gas pressure was kept constant by fine-tuning the beam current, beam spot size and its position, so as to ensure a constant growth rate.

6. After the first stage of growth lasts for 20 minutes, without cutting off the electron beam source, increase the flow rate of the NH ₃ /H ₂ mixed gas to 50 sccm, and enter the second stage of the growth process of the composite thin film.

7. When the first stage of growth lasts for 30 minutes, turn off the electron gun beam current and high voltage to end the growth.

8. After the growth is finished, while still maintaining the NH ₃ /H ₂ mixed gas at a flow rate of 50 sccm, gradually lower the substrate temperature, and cut off the mixed gas source when the substrate temperature drops to 200°C.

After the temperature of the substrate drops to room temperature, the growth chamber is opened, and the sample is taken out to obtain a ZnO nanocrystal column/nanofilament composite structure product.

The field emission scanning electron microscope (FESEM) surface topography photos of the ZnO nanocrystalline column/nanocrystalline wire composite structure sample grown in this embodiment are shown in Fig. A high-density and uniformly distributed hexagonal structure ZnO nanocrystal column array on the bottom surface, and a high-density ZnO nanocrystal wire parallel to the substrate surface on the ZnO nanocolumn array; the diameter of the nanocolumn and nanowire is 140nm The length of the nanowire is about 4400nm.

The electron energy dispersive X-ray diffraction (EDX) spectrum of the ZnO nanocrystalline column/nanocrystalline wire composite structure sample grown in this embodiment is shown in FIG. 3 . The presence of N and H elements was not detected in the sample.

The X-ray diffraction (XRD) spectrum of the ZnO nanocrystalline column/nanocrystalline wire composite structure sample grown in this embodiment is shown in FIG. 4 . The ZnO nanocrystalline pillars and nanocrystalline filaments in the sample exhibited a high degree of c-axis orientation.

Claims (7)

1, a kind of ZnO nano crystal column/nano crystal filament composite structure product, its constitutional features is: have perpendicular to substrate surface, high-density and equally distributed hexagonal structure ZnO nano crystal column array at substrate surface, be parallel to substrate surface, highdensity ZnO nano crystal filament on the ZnO nano column array; Adopt the electric beam evaporation method, with ZnO ceramic target and NH ₃/ H ₂Gas mixture is a raw material, directly obtains the ZnO nano crystal column/nano crystal filament composite structure product in the disposable growth of substrate surface by " two step depositions " technology.

2, the described ZnO nano crystal column/nano crystal filament composite structure product of claim 1 preparation technology, processing step is as follows:

A) clean the substrate and the substrate holder of packing into, substrate holder is put into the growth room.In the crucible of polycrystalline ZnO ceramic target in the growth room of putting compacting and sintering, isolate target and substrate with baffle plate;

B) take out the growth room to≤3 * 10 with vacuum pump ^-3The base vacuum degree of Pa;

C) elder generation charges into NH with the low discharge of 10～20sccm ₃/ H ₂Gas mixture, the suitable simultaneously fine pumping valve of adjusting the growth room makes the vacuum tightness in the growth room reach 3 * 10 ^-2Pa also keeps constant;

D) heated substrate is to suitable growth temperature;

E) earlier with high-energy focusing electron beam alignment ZnO target, regulate the electron beam line, under lower line, the heating target is so that to the target degasification;

F) after degasification finishes line is adjusted to a certain current value of 30～40mA, makes ZnO target start vaporizer; According to the different requirements of growth velocity speed, by regulating the parameters such as position at electron beam spot area, bundle spot center, the vapour pressure (partial pressure) of ZnO target is controlled at 2.0 * 10 ^-2～5.0 * 10 ^-2Pa makes stable, the evaporation equably of ZnO target; Open baffle plate and begin the fs growth of ZnO nano crystal column/nano crystal filament composite structure;

G) after the fs, growth was experienced 20～30 minutes, mixed gas flow is transferred greatly to 50～60sccm, entered into the subordinate phase process of growth;

H) continue 30～40 minutes when the subordinate phase process of growth, close the electron beam gun high pressure, finish growth;

I) after the end growth, at the NH that still keeps 50～60sccm ₃/ H ₂Under the situation of mixed gas flow, reduce underlayer temperature gradually, treat underlayer temperature reduce to≤200 ℃ the time, cut off the gas mixture source of the gas;

J) treat that underlayer temperature reduces to room temperature, open the growth room, take out product.

3, according to claim 1,2 described ZnO nano crystal column/nano crystal filament composite structure product preparation technologies, it is characterized in that: described substrate material is single crystalline Si polished section, silica glass or sapphire polished section.

4, according to claim 1,2 described ZnO nano crystal column/nano crystal filament composite structure product preparation technologies, it is levied the spy and is: described ZnO ceramic target material is repressed and form through 1200 ℃ of high temperature sinterings by the ZnO powder of purity 99.99%.

5, according to claim 1,2 described ZnO nano crystal column/nano crystal filament composite structure product preparation technologies, it is levied the spy and is: described NH ₃/ H ₂NH in the gas mixture ₃Volumn concentration be 1vol.%～50vol.%.

6, according to the described ZnO nano crystal column/nano crystal filament composite structure product of claim 2 preparation technology, it is levied the spy and is: described suitable growth temperature is 400 ℃, 450 ℃ or 500 ℃.

7, according to the described ZnO nano crystal column/nano crystal filament composite structure product of claim 2 preparation technology, it is levied the spy and is: described lower line is 5～10mA, heating target 5～10 minutes.

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