CN105755448A - Nano diamond thin film and preparation method thereof - Google Patents

Abstract

The invention discloses a method for preparing a nano-diamond film by using a hot wire chemical vapor deposition method. This method only uses methane and hydrogen as reaction precursors without adding other inert gases. The content of methane must be greater than 6%, and the temperature of the hot wire should be controlled above 2000°C; the reaction pressure can be controlled under medium and low pressure conditions, and the maximum pressure can even reach 6kPa; the substrate surface temperature is the best choice in the range of 750-850°C. The nano-diamond thin film prepared by the method has a crystal grain size ranging from several nanometers to tens of nanometers, and the film growth rate is greater than 500nm/h. The preparation method of the present invention is simple, the reaction gas source is single, no other inert gas needs to be added, and the deposition rate is fast, which is much higher than that of microwave plasma chemical vapor deposition. The prepared nano-diamond film has high quality and uniform distribution, and the method is very suitable for Large-area diamond films.

Description

A kind of nano-diamond film and preparation method thereof

technical field

The invention relates to the preparation of nano-diamonds, in particular to a method for preparing nano-diamond films under hydrogen-rich conditions by adopting a hot wire chemical vapor deposition method.

Background technique

Diamond has many excellent properties, such as high hardness, high Young's modulus, good stability and chemical inertness. And when the grain size of diamond is reduced to the nanometer level (generally from several nanometers to hundreds of nanometers), its characteristics will also change accordingly. When the grain size decreases, the sp ² bond carbon content in the diamond will increase accordingly, and the surface roughness of the diamond film will also be significantly reduced, and its friction coefficient will also be greatly reduced. It is these unique properties of nanodiamonds that make them widely used in fields such as microelectromechanical systems, electron field emission devices, and electrochemical anode materials.

The preparation of nano-diamond films mainly includes microwave plasma chemical vapor deposition (MPCVD) and hot filament chemical vapor deposition (HFCVD). No matter which method is used, the most common preparation method of nano-diamond film is to add inert gas (Ar, He, etc.) to the reaction precursor to form methane, hydrogen, inert gas or a mixture of methane and inert gas to participate in the reaction. In addition, there are also reports on the preparation of nano-diamond films under the condition of only methane and hydrogen as precursors. This method is mostly seen in reports using MPCVD technology, and the ratio of methane is required to be maintained at about 10%. Recently, Zeng et al. (Carbon84(2014) 103–117) used HFCVD technology to prepare nano-diamond films under the conditions of methane ratio of 10%, reaction pressure of 5 Torr, and substrate temperature of 750 °C, but this method generally requires pressure maintenance. At lower levels, less than 15 Torr (about 3kPa) is required.

Contents of the invention

The purpose of the invention is to overcome the deficiencies of the prior art and provide a method for preparing a nano-diamond film.

A method for preparing a nano-diamond film, comprising: using a mixed gas of methane and hydrogen as a reaction precursor, and preparing a nano-diamond film on the surface of a substrate by a hot wire chemical vapor deposition method;

Wherein, the temperature of the hot wire is above 2000°C, the surface temperature of the substrate is between 750°C and 850°C, and the reaction pressure is a medium-low pressure condition.

The invention adopts the technology of hot wire chemical vapor deposition, uses methane and hydrogen as the reaction precursors, and controls the experimental parameters such as methane ratio, reaction pressure, substrate surface temperature, etc. High-quality nano-diamond film is grown on the surface, and the rapid and large-area growth of diamond film is realized.

There is an optimum temperature range for the substrate surface temperature, and the optimum temperature is in the range of 750-850°C. When the substrate temperature is 700°C or 900°C, the prepared diamond grains will increase slightly, but the size is still below 100nm.

The reaction precursor is a mixed gas of methane and hydrogen. The content of methane in the precursor gas is the main factor affecting the diamond grain size. When the proportion of methane is less than 6%, the prepared diamond grain size is mainly in the micron order, and the crystal form is regular. When the proportion of methane is greater than 6%, nano-diamonds are mainly generated, and the grain size varies from several nanometers to tens of nanometers. Preferably, the mixed gas only contains methane and hydrogen, and the volume percentage of methane is above 6%.

The temperature of the hot wire needs to ensure the complete dissociation of the hydrogen. As a preference, the temperature of the hot wire is 2000-2500°C, and the hydrogen can be dissociated well at this temperature.

In the present invention, the reaction pressure range can be very wide, need not be controlled under very low condition (<3kPa), even applicable when pressure increases to 6kPa, as preferably, reaction pressure is 3kPa～6kPa. Within this pressure range, the pressure change has no particularly great influence on the growth of nano-diamonds, and high-quality nano-diamond films can be grown.

The growth rate of the nano-diamond film is relatively fast, and the growth rate of the nano-diamond film can reach 660nm/h under the conditions of a methane concentration of 8%, a substrate temperature of 800°C, and a reaction pressure of 4kPa, which is much higher than that of microwave plasma The speed at which nanodiamonds are grown by chemical vapor deposition. Preferably, in the hot wire chemical vapor deposition method, the growth rate of the nano-diamond film is greater than 500nm/h.

The invention also provides a nano-diamond film prepared by the preparation method. The nano-diamond prepared by the method has high quality, uniform film distribution, grain size ranging from several nanometers to tens of nanometers, and the prepared nano-diamond film can have a diameter ranging from 1 cm to 10 cm.

The preparation method of the present invention can be applied to the growth method of large-area nano-diamond film, and only needs to increase the number of hot wires so that the tiled hot wires can completely cover the surface of the substrate to ensure uniform heat distribution on the substrate surface. By controlling the output power of the heating wire heating motor, the heating power of each heating wire is always maintained to ensure that the temperature of the heating wire is basically consistent. By this method, an enlargement of the substrate material for deposition can be achieved.

Compared with the prior art, the beneficial effects of the present invention are reflected in:

The preparation method of the present invention is simple, the reaction gas source is single, no other inert gas needs to be added, and the deposition rate is fast, which is much higher than that of microwave plasma chemical vapor deposition. The prepared nano-diamond film has high quality and uniform distribution, and the method is very suitable for Large-area diamond films.

Description of drawings

Fig. 1 is used to prepare the schematic diagram of the hot wire chemical vapor deposition system of nanodiamond film;

Fig. 2 is the surface scanning electron microscope picture of nano-diamond thin film;

Fig. 3 is the cross-sectional scanning electron microscope picture of nano-diamond film;

Fig. 4 is the Raman spectrogram of nano-diamond film;

Fig. 5 is the surface scanning electron microscope picture of micron diamond thin film;

Fig. 6 is a Raman spectrogram of the micron diamond film.

detailed description

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments, but the implementation method of the present invention is not limited thereto.

Example 1

Figure 1 is a schematic diagram of a hot wire chemical vapor deposition system used to prepare nanodiamond films. As shown in Figure 1, the hot wire chemical vapor deposition system includes a gas mass flowmeter 1, an intake pipe stop valve 2, a vacuum system 3, and a reaction chamber 4 , intake ring 5, hot wire 6, substrate material tantalum sheet 7, rotating substrate table 8, outlet ring 9, water cooling device 10, control panel 11, external heating motor 12, industrial chiller 13, maintenance pump 14.

The specific preparation method of the nano-diamond film of the present embodiment is as follows:

(1) Pre-treat the substrate: polish the tantalum sheet with metallographic sandpaper, then place the tantalum sheet in an acetone solution for 30 minutes of ultrasonic cleaning; then place the tantalum sheet in a diamond paste acetone solution with a particle size of 1 μm for 1 hour; Finally, the tantalum sheet was ultrasonically cleaned in ultrapure water for 30 minutes, dried with nitrogen gas, and quickly placed in the reaction chamber.

(2) Vacuuming: use the vacuum system of the HFCVD system to evacuate the chamber until the chamber pressure reaches the order of 10 ⁻³ Pa.

(3) Carbonization of tantalum wire: a mixed gas of methane and hydrogen (the ratio of methane is 3%) is introduced, and the pressure of the chamber is maintained at the pressure value required for the reaction process; the hot wire is heated by an external heating motor, Gradually and slowly increase the motor current until the output power of the motor reaches the required value (the HFCVD system purchased in this laboratory controls the heating power of a single heating wire to 600W). When the desired temperature is reached, continue to maintain the condition and carbonize the tantalum wire for 30 minutes.

(4) Deposit nano-diamonds: raise the substrate table to the required height, and adjust the ratio of methane and hydrogen at the same time, so that the ratio of methane is the ratio required for the reaction (> 6%). At this time, the deposition of nano-diamonds is considered to be started. During the deposition process, care should be taken to control the output power of the heating to maintain the reaction temperature in the chamber within a relatively stable range.

(5) Cool down: After the deposition reaction is over, turn off the methane, cool down under the condition of only hydrogen, gradually reduce the current of the heating motor, and finally wait until the temperature in the chamber cools down to room temperature before venting and opening the chamber to take out sample.

Example 2

In this embodiment, a nano-diamond film is deposited on the surface of a tantalum sheet (with a specification of 1 cm*1 cm*1 mm), and the film is characterized. The deposition conditions adopted in this embodiment are: the proportion of methane is 8%, the total gas flow rate is 400 sccm, the chamber reaction pressure is 4 kPa, the power of a single heating wire is 600 W, the deposition temperature on the surface of the tantalum sheet is 800° C., and the deposition time is 5 h. According to the method shown in Example 1, using the above reaction conditions, the prepared diamond film is a nano-diamond film.

Fig. 2 is the surface scanning electron microscope picture of the nano-diamond film that makes in embodiment 2. It can be seen from the figure that the diamond particles are evenly distributed, and the film-forming quality is high. The diamond particles are long strips, and the particle size is basically kept within 20nm.

3 is a cross-sectional scanning electron microscope image of the nanodiamond film prepared in Example 2. It can be seen from the figure that the thickness of the diamond film is about 3.3 μm, and the corresponding film growth rate is about 660 nm/h.

Fig. 4 is the Raman spectrogram of the nanodiamond thin film that makes in embodiment 2. The figure shows typical nanodiamond features, mainly including four different peaks. The peak at about 1340 cm ^-1 is the D peak of carbon, the peak at about 1580 cm ^-1 is the G peak of carbon, and there are also peaks at about 1150 and 1480 cm ^-1 which are ethynyl groups.

Example 3

In this embodiment, a micron diamond film is deposited on the surface of a tantalum sheet (1cm*1cm*1mm), and the film is characterized. Except for methane concentration, other deposition conditions adopted in this embodiment are all the same as in embodiment 2: methane ratio 2%, gas total flow 400sccm, chamber reaction pressure 4kPa, single heating wire power 600W, tantalum sheet surface deposition temperature 800°C, the deposition time is 5h. According to the method shown in Example 1, using the above reaction conditions, the prepared diamond film is a micron diamond film.

FIG. 5 is a surface scanning electron microscope image of the micron diamond film prepared in Example 3. It can be seen from the figure that the diamond particles have an obvious grain structure, and its crystal forms are mainly hexahedron, octahedron, etc., and the particle size is basically kept at about 1 μm.

Fig. 6 is the Raman spectrogram of the micron diamond film prepared in embodiment 3. This figure shows typical diamond features, the peak with wave number 1332cm ^-1 is the characteristic peak of sp ³ diamond, and this peak is very sharp, except for this, it basically does not contain other peaks.

Example 4

In this embodiment, a nano-diamond film is deposited on the surface of a large-size tantalum sheet (with a specification of Φ10cm*1mm), and the film is characterized. Except for the number of hot wires, other deposition conditions used in this embodiment are the same as those in Embodiment 2. The distance between the heating wires is 7 mm. In Example 2, 11 heating wires are used, the distance of which is much larger than 1 cm (the size of the tantalum sheet), so that the surface temperature of the tantalum sheet can be evenly distributed. In Example 4, since the size of the tantalum sheet is increased, 19 heating wires are used in order to obtain the same uniform temperature field on the substrate surface. The nano-diamond film prepared under this condition is also uniformly distributed, and the diamond quality is high.

Claims (6)

1. the preparation method of a nano-diamond film, it is characterised in that including: using the mixing gas of methane and hydrogen as precursors, adopts hot filament CVD to prepare nano-diamond film at substrate surface；

Wherein, hot-wire temperature is more than 2000 DEG C, and substrate surface temperature is between 750～850 DEG C, and reaction pressure is 3000～6000Pa.

2. the preparation method of nano-diamond film according to claim 1, it is characterised in that only contain only methane and hydrogen in described mixing gas, and the ratio of methane is more than 6%.

3. the preparation method of nano-diamond film according to claim 1, it is characterised in that hot-wire temperature is 2000～2500 DEG C.

4. the preparation method of nano-diamond film according to claim 1, it is characterised in that in described hot filament CVD, nano-diamond film growth rate is more than 500nm/h.

5. the nano-diamond film that the preparation method described in any one of Claims 1 to 4 prepares.

6. nano-diamond film according to claim 5, it is characterised in that the particle diameter of described nano-diamond film is between 1nm～99nm, the diameter of described nano-diamond film is 1cm～10cm.