CN107190246A - A kind of graphene/diamond compound film with excellent field emission performance and preparation method thereof - Google Patents

Abstract

The invention discloses a graphene/diamond composite film with excellent field emission performance and a preparation method thereof, belonging to the technical field of optoelectronic materials. The main steps are 1) growing a non-doped diamond film on the substrate; 2) growing a layer of Ni film with a thickness of 100-600 nm on the diamond film substrate; 3) then making the film mixed in Ar + H ₂ Annealing in the atmosphere, the carbon atoms in the diamond film dissolve in the Ni layer; 4) Cool down to room temperature at a rate of 0.5~1°C/s, the carbon atoms are precipitated to the surface and recrystallized to form graphene, that is, the graphene/diamond Composite film. The invention directly uses the diamond film as the precursor of the graphene growth, and the method is simple and easy to operate; the graphene and the surface of the diamond film in the obtained composite film can realize atomic bonding, and the bonding property is strong and the stability is good.

Description

A graphene/diamond composite film with excellent field emission performance and its preparation method

technical field

The invention relates to a graphene/diamond composite film with excellent field emission performance and a preparation method thereof, belonging to the technical field of semiconductors.

Background technique

Diamond is a typical covalent bond structure, with excellent physical and chemical properties such as high hardness, good chemical stability, wide band gap, high electron and hole mobility, high breakdown field strength, and low dielectric constant. Ideal cathode material for permanent, long-life field emission devices. However, diamond is a wide-bandgap semiconductor material. The resistivity of diamond film is very high, and it is difficult for electrons to transport inside the material, so it is difficult to replenish electrons in the conduction band, which limits the field emission performance of diamond materials. In recent years, researchers at home and abroad have attempted to dope impurities such as P, N, O, Ag, and Au into diamond films during the growth process or by ion implantation in order to improve their electrical conductivity. However, doped diamond films have low electrical conductivity and low electron mobility, making them difficult to use as electronic devices.

Graphene is a two-dimensional honeycomb crystal structure composed of flat single-layer carbon atoms closely packed. In the graphene plane, carbon atoms are arranged periodically in the form of six-membered rings, and each carbon atom is connected to three adjacent carbon atoms through a σ bond, forming an sp2 hybrid structure. A carbon atom has 4 valence electrons, 3 of which form sp2 bonds, that is, each carbon atom contributes an unbonded electron in the pz orbital, and the pz orbitals of the neighboring atoms form a π orbital in the direction perpendicular to the plane. At this time, π The bonds are in a half-filled state, and π electrons can move freely in the plane of the graphene crystal. This electronic structure gives graphene its excellent electrical properties. Therefore, the preparation of graphene on diamond has important scientific significance and engineering value for the development of graphene/diamond composite film with high field emission performance and its application in semiconductor devices, field emission displays and other fields.

In recent years, researchers have developed a variety of methods for preparing graphene, mainly including micromechanical exfoliation, graphite oxide reduction, and chemical vapor deposition. Among them, the graphene obtained by the mechanical exfoliation method has excellent performance, but the efficiency is very low, the process is uncontrollable, and the repeatability is poor; although the graphite oxide reduction method has a high preparation efficiency, the introduction of the reducing agent destroys the conjugated structure of graphene. , which reduces the inherent electrical properties of graphene; chemical vapor deposition can prepare large-area graphene films, but this method is complex in operation and the controllability of the obtained graphene film thickness is poor.

Contents of the invention

The present invention aims to provide a graphene/diamond composite film with excellent field emission performance, and deposit a graphene film on the diamond film by ion implantation and thermal annealing, so as to produce high-quality graphene/diamond in a simple and controllable manner Composite film; the product combines the excellent comprehensive properties of graphene and diamond to meet the stringent performance requirements of field emission cathode materials. Another object of the present invention is to provide the preparation method of the above-mentioned graphene/diamond composite film, which is simple and easy to operate, and the excellent comprehensive performance of the graphene/diamond composite film is reflected.

The invention provides a kind of preparation method of the graphene/diamond composite film with excellent field emission property, comprises the following steps:

(1) Preparing a diamond film on a substrate;

(2) growing a layer of 100-600nm Ni film on the surface of the diamond film obtained in step (1);

(3) Heat the diamond film with Ni film grown on the surface obtained in step (2) to 800~1000°C in a mixed atmosphere of Ar and _H2 , and keep it warm for 20-80 min. The carbon atoms in the diamond film are in the Ni layer dissolve;

(4) The diamond film treated in step (3) is lowered to room temperature at a rate of 0.5-1°C/s, carbon atoms are precipitated to the surface and recrystallized to form graphene, and a graphene/diamond composite film is obtained.

In the above method, the diamond thin film in the step (1) can be prepared according to conventional methods in the field, such as microwave plasma chemical vapor deposition, hot wire chemical vapor deposition, and DC arc plasma jet chemical vapor deposition.

In the above method, the substrate is one of single crystal silicon, silicon carbide, molybdenum, and silicon carbide.

In the above method, the diamond film is a micro-diamond film or an ultra-nano-diamond film;

In the above method, the preparation method of the micron diamond film is as follows: using chemical vapor deposition equipment, using H2 with a purity of 99.999% and _CH with a purity of 99.9% as reaction gases, the deposition temperature is _750-950 ° C, and the deposition time is 10 ~100h, a micron diamond film with a thickness of 5~100μm was prepared.

In the above method, the preparation method of the ultra-nano-diamond film is as follows: using chemical deposition equipment, with a purity of 99.999% Ar and H ₂ and a purity of 99.9% CH ₄ as reaction gases, the deposition temperature is 750 ~ 950 ° C, the deposition time for 2-10 hours, and prepare ultra-nano-diamond films with a thickness of 200 nm-5000 nm.

In the above method, in the step (2), the growth method of the Ni thin film is one of magnetron sputtering, ion beam assisted deposition or electron evaporation.

In the above method, in the step (3), the time for raising the temperature of the diamond film with the Ni thin film grown on the surface to 800-1000° C. is 25-50 min.

In the above method, the volume ratio of Ar and H ₂ in the mixed atmosphere is H ₂ : Ar =5%:95%.

In the above method, the graphene formed in the step (4) is single-layer, double-layer or multi-layer.

The invention provides a graphene/diamond composite film obtained by the above preparation method.

The principle of the present invention is: prepare a layer of 100-600nm Ni film on the surface of the diamond film, and as the precursor of growing graphene, the diamond film provides carbon atoms; in the subsequent annealing process, the carbon atoms are deposited in the Ni substrate Dissolution, when the carbon atoms in the Ni film are saturated, the solubility of carbon decreases as the temperature decreases, and it precipitates from the Ni film to surface recrystallization to form graphene. In the obtained composite film, the graphene and the surface of the diamond film can realize atomic bonding.

Beneficial effects of the present invention:

(1) The present invention can be realized only by two processes of growth and annealing of the Ni film, and the method is simple and easy to operate;

(2) The growth process of graphene in the present invention is a self-evolving, controllable in-situ growth process, and the number of layers of graphene can be regulated by controlling heat treatment conditions;

(3) Graphene and diamond achieve atomic bonding, which has good stability;

(4) The field emission performance of the prepared composite film is good, which has important scientific significance and engineering value for realizing its application in semiconductor devices, field emission displays and other fields.

Description of drawings

Fig. 1 is the Raman picture of the graphene/micron diamond composite film prepared by embodiment 1;

Fig. 2 is the field emission test result figure of the graphene/micron diamond composite film prepared by embodiment 1;

Fig. 3 is the Raman picture of the graphene/super nano-diamond composite film that embodiment 2 prepares;

Fig. 4 is the field emission test result diagram of the graphene/super nano-diamond composite film prepared in Example 2.

detailed description

The present invention is further illustrated by the following examples, but not limited to the following examples.

Example 1:

1) Preparation of micro-diamond film: First, the grease on the surface of the Si substrate was cleaned with acetone and methanol solution in sequence, and then the surface of the single crystal silicon substrate was ground with diamond powder with a particle size of 5nm, and the The substrate was ultrasonically cleaned for 45 minutes, and finally dried with hot air to serve as the substrate for the growth of micron diamond films. Using self-developed microwave plasma chemical vapor deposition equipment with a frequency of 2.45 GHz, a micron diamond film was grown on a silicon wafer with a diameter of 6 cm and a thickness of 1.2 cm. The reaction gas ratio used in the experiment was H ₂ (98.6%)/CH ₄ (1.4%), the microwave power was kept at 7 kW, the gas flow rate was 406 sccm, the total pressure was 10 kPa, the temperature was 850°C, and the growth time was 20 h. A diamond film with a grain size of 10-30 μm is produced.

2) Growth of Ni film: grow a 200 nm Ni film on the surface of the micron diamond film by magnetron sputtering;

3) Growth of graphene: Place the graphene-coated diamond film prepared in step 2) in a tube furnace, vacuumize until the pressure in the reaction chamber drops below 0.1Pa, and pass Ar gas and H ₂ gas into the Mix the gas to standard atmospheric pressure, control the flow rate of the mixed gas to 200sccm, raise the temperature to 900°C in 25 minutes, and keep it warm for 30 minutes. Carbon atoms are precipitated from the Ni film to the surface, and the temperature is lowered to room temperature at 30°C/min. The solid solubility of carbon varies with temperature. During the cooling process, enough carbon is precipitated and recrystallized to form graphene.

4) Analyze the sample prepared in this embodiment: the Raman spectrum of the obtained graphene/micro-diamond composite film is shown in FIG. 1 , and the field emission curve of the obtained graphene/micro-diamond composite film is shown in FIG. 2 .

It can be seen from the Raman spectrum that the position of the D peak is 1345 cm ^-1 , the position of the G peak is 1584 cm ^-1 , the position of the 2D peak is 2701 cm ^-1 , and I _G / I _D ≈ 4 shows that the graphene obtained by the present invention has few defects and high quality. I _2D /I _G ≈ 1.1, and the 2D peak is a single peak with good symmetry, indicating that the graphene prepared in this example is a single layer or a double layer.

The field emission test was carried out in a high vacuum (10 ^-5 Pa) field emission test system. ITO glass was used as the anode, and the diamond film was used as the cathode. The distance between the cathode and the anode was 150 μm. The IV characteristic curve was measured by Keithley 237. It can be seen from FIG. 2 that the micro-diamond film prepared in this embodiment basically has no emission current within the test range. However, the opening electric field of the graphene/micro-diamond composite film prepared in this example is as low as 6.25V/μm (the opening electric field is defined as the FN inflection point), and a current density of 0.65 mA/ ^cm2 is obtained under an electric field of 11.35 V/μm . It can be seen that the preparation of graphene layer on the surface of micro-diamond can significantly improve the field emission performance of micro-diamond film.

Example 2

1) Preparation of ultra-nano-diamond film: A self-developed microwave plasma chemical deposition equipment was used to prepare an ultra-nano-diamond film on a silicon nitride substrate. Firstly, the ethanol suspension of diamond micropowder (with a particle size of 0.5 μm) was used to ultrasonically vibrate the silicon nitride wafer for 30 minutes, and then cleaned with ethanol after ultrasonication. Then dry the silicon nitride sheet with hot air as the substrate for the growth of ultra-nano-diamond film. Using self-developed microwave plasma chemical vapor deposition equipment with a frequency of 2.45 GHz, a super-nano-diamond film was grown on a 1×1 cm silicon nitride wafer. The experiment used a mixed gas of Ar, H ₂ , and CH ₄ , and the total gas flow rate was 166sccm, where the flow rates of each gas are: Ar is 122sccm-136sccm, _H2 is 24-38sccm, _CH4 is 6 sccm, the deposition power is 1.0 kW, the pressure is 13 kPa, the deposition temperature is 830 °C, and the deposition time is 6 h . The grain size of the ultra-nano-diamond film is 8 nm and the thickness is 5 μm.

2) Growth of Ni film: A Ni film with a thickness of 500 nm was grown on the surface of ultra-nanodiamond by magnetron sputtering.

3) Graphene growth: Place the graphene-coated diamond film prepared in step 2) in a tube furnace, vacuumize the reaction chamber until the pressure is below 0.1Pa, and pass Ar gas and H ₂ gas into the Mixed gas (H ₂ (5%): Ar (95%)) to standard atmospheric pressure, control the flow rate of the mixed gas to 200sccm, raise the temperature to 1000°C in 40 minutes, and keep it warm for 80 minutes. Carbon atoms are precipitated from the Ni film to the surface. When ℃/min drops to room temperature, the solid solubility of carbon decreases with the decrease of temperature. During the cooling process, enough carbon is precipitated and recrystallized to form graphene.

4) Analyze the samples prepared in this embodiment: the Raman spectrum of the obtained graphene/super nano-diamond composite film is shown in Figure 3, and the field emission curve of the obtained graphene/super nano-diamond composite film is shown in Figure 4.

It can be seen from the Raman spectrum that the D peak position is 1356 cm ^-1 , the G peak position is 1554 cm ^-1 , and the 2D peak position is 2660 cm ^-1 . I _2D /I _G ≈ 0.16, indicating that the graphene prepared in this example is multilayer.

The field emission test was carried out in a high vacuum (10 ^-5 Pa) field emission test system. ITO glass was used as the anode, and the diamond film was used as the cathode. The distance between the cathode and the anode was 150 μm. The IV characteristic curve was measured by Keithley 237. It can be seen from FIG. 4 that the ultra-nano-diamond film prepared in this embodiment basically has no emission current within the test range. However, the opening electric field of the graphene/super nano-diamond composite film prepared in this example is relatively low, which is 3.7 V/μm (defining the FN inflection point as the opening electric field), and the electric field of 71 μA/cm is obtained under the electric field of 7.3 V/ ^μm current density. It can be seen that the preparation of graphene layer on the surface of ultra-nano-diamond can significantly improve the field emission performance of ultra-nano-diamond film.

Through the above examples, the Raman results prove that graphene has been formed, and the field emission results prove that the field emission performance of the composite film is good.

Claims (10)

1. a kind of preparation method of graphene/diamond compound film with excellent field emission performance, it is characterised in that including with Lower step：

（1）Diamond thin is prepared on substrate；

（2）In step（1）One layer of 100-600nm of superficial growth Ni films in obtained diamond thin；

（3）By step（2）Obtained superficial growth has the diamond film of Ni films in Ar and H₂It is warming up to 800 in mixed atmosphere ~ 1000 DEG C, and the carbon atom being incubated in 20-80 min, diamond film dissolves in Ni layers；

（4）Will be through step（3）The diamond film of processing is down to room temperature with 0.5 ~ 1 DEG C/s speed, and carbon atom precipitate into surface weight Crystallize and form graphene, obtain graphene/diamond compound film.

2. the preparation method of graphene/diamond compound film according to claim 1 with excellent field emission performance, its It is characterised by：The step（1）Middle diamond thin uses microwave plasma CVD method, Hot Filament Chemical Vapor Any of deposition process, Dc arc plasma jet CVD chemical gaseous phase depositing process are prepared from.

3. the preparation method of graphene/diamond compound film according to claim 1 with excellent field emission performance, its It is characterised by：The substrate is one kind in monocrystalline silicon, carborundum, molybdenum, carborundum.

4. the preparation method of graphene/diamond compound film according to claim 1 with excellent field emission performance, its It is characterised by：The diamond thin is micron diamond film or super nano-diamond film.

5. the preparation method of graphene/diamond compound film according to claim 4 with excellent field emission performance, its It is characterised by：The preparation method of micron diamond film is as follows：Using chemical vapor depsotition equipment, using purity as 99.999% H₂With the CH that purity is 99.9%₄For reacting gas, depositing temperature is 750 ~ 950 DEG C, and sedimentation time is 10 ~ 100h, is prepared Thickness is 5 ~ 100 μm of micron diamond film.

6. the preparation method of graphene/diamond compound film according to claim 4 with excellent field emission performance, its It is characterised by：The preparation method of super nano-diamond film is as follows：Using chemical deposition equipment, the Ar using purity as 99.999% And H₂And the CH that purity is 99.9%₄For reacting gas, depositing temperature is 750 ~ 950 DEG C, and sedimentation time is 2 ~ 10 h, is prepared Thickness is 200 nm ~ 5000nm super nano-diamond film.

7. the preparation method of graphene/diamond compound film according to claim 1 with excellent field emission performance, its It is characterised by：The step（2）In, the growing method of the Ni films is that magnetron sputtering, ion beam assisted depositing or electronics steam One kind in hair.

8. the preparation method of graphene/diamond compound film according to claim 1 with excellent field emission performance, its It is characterised by：The step（3）In, the time that the diamond film that superficial growth has Ni films is warming up into 800 ~ 1000 DEG C is 25-50 min；The Ar and H₂The volume ratio of the two in mixed atmosphere is 95:5.

9. the preparation method of graphene/diamond compound film according to claim 1 with excellent field emission performance, its It is characterised by：The step（4）The graphene of middle formation is individual layer, double-deck or multilayer.

10. graphene/diamond compound film that one kind is obtained using the preparation method described in any one of claim 1 ~ 9.