RU2685665C1 - Method for producing thin diamond films - Google Patents

Abstract

FIELD: manufacturing technology.SUBSTANCE: invention relates to a method for producing thin diamond films and can be used in various fields of industry and science to produce thin-film hardening coatings and active layers of thin-film nanostructures. Method for producing thin diamond films on a substrate is proposed by vacuum laser action on targets and condensation of carbon on substrates, where pre-compacted detonation nanodiamond tablets and tablets from high-purity graphite used as targets, and the laser exposure is carried out in two steps: first, by a focused laser radiation based on yttrium aluminum garnet at wavelength of 1,064 nm with series of 10–20 pulses with pulse energy of 3.8–5.8 J, dispersing a target from a detonation nanodiamond and forming nanodiamond nucleation centers on the substrate; then fill the gaps between nucleation centers with carbon with mainly sp3-bonds condensed from a vapor-gas phase obtained by evaporation of the target from high-purity graphite by means of a defocused laser radiation of the same laser with pulse energy intensity of not lower than 1.6⋅10 W/cm. During condensation of carbon onto the substrate pre-populated with nucleating centers, mainly with size of 5.73 nm, observe their growth to particles with the size of about 285.15 nm. Set of such particles (islands) forms a flat thin-film close-packed hexagonal structure, which is a polycrystalline aggregate of islands, crystallographic similarly oriented relative to the film surface.EFFECT: method for producing thin diamond films is proposed.1 cl, 10 dwg, 3 tbl, 5 ex

Description

The invention relates to a method for producing thin diamond films by laser irradiation of carbon and nano-diamond targets and subsequent condensation of carbon from the vapor-gas phase to substrates in a vacuum and can be used in various fields of industry and science to produce thin-film hardening coatings and active layers of thin-film nanostructures.

A method of obtaining homoepitaxial diamond thin film [1], comprising two stages of chemical deposition on the surface of the substrate using plasma of carbon from the gas phase using a mixture of methane and hydrogen. At the first stage, a mixed gas with a concentration of a carbon source is used, at the second - a mixed gas with a concentration of a carbon source higher than at the first. Obtaining a diamond thin film is carried out at a very low rate of formation of the film structure. Thus, the method is characterized by low productivity and high complexity of its implementation, which does not allow to effectively obtain thicker diamond films. In addition, the kinetic energy of carbon in this method is low, which reduces the concentration of sp3 bonds in the carbon condensed on the substrate.

A method of obtaining diamond-like coatings combined laser exposure [2]. The method is implemented by a combined laser treatment of target material made of high-purity graphite (more than 99.9%), first with short-wavelength (less than 300 nm) pulsed radiation, as used by a KrF laser radiation with a wavelength of 248 nm and a specific energy of 5⋅10 ⁷ W / cm ² , then long-wave laser radiation from a gas CO ₂ laser or a solid-state fiber laser [2].

Diamond-like coatings are obtained in vacuum by sputtering the target material due to ablation when exposed to a pulsed laser and then exposed to the gas-plasma cloud by long-wave (more than 1 μm) laser radiation from a gas CO ₂ laser or a solid-state fiber laser emitter.

According to this method, the subsequent impact on the gas-plasma cloud by long-wave (more than 1 μm) laser radiation naturally increases the kinetic energy of the cloud particles, which leads to an increase in the diamond phase in the resulting coating. However, ablation primarily involves dispersion of the target, that is, the gas-flame cloud is a two-phase mixture of graphite particles and carbon vapor, as a result the film will be a two-phase condensate, which reduces the quality of the film.

As follows from the description of the method, its execution requires complex laser equipment, which significantly complicates the preparation of coatings or films. In addition, during ablation of the target, the output of the diamond component is significantly lower than 100%, and the structure of the film consists of extensive graphite grains and diamond islands.

A method of obtaining diamond-like films by sputtering a graphite target with a pulsed laser and vapor deposition on a substrate, taken as a prototype [3]. A diamond-like film is obtained by sputtering a target in vacuum using a TEA CO ₂ laser with a radiation power density of 1 ^⋅ 10 ⁷ - 5 ^⋅ 10 ⁸ W / cm ² with a distance of at least 7 cm from the target to the substrate.

The disadvantage of this method is the high intensity of laser radiation, which does not allow to get rid of the dispersion of the target, which leads to a significant deterioration in the quality of the diamond film, which will include extensive areas of the graphite phase.

The objective of the invention is to obtain a thin diamond film by nucleation of nanodiamond conglomerates with a certain density on a silicate glass substrate during the dispersion of a nanodiamond target by focused laser radiation from a 1064 nm aluminum yttrium garnet laser and the subsequent filling of the space between the diamond centers formed by a diamond phase. condensation of carbon from the vapor – gas phase obtained by evaporating carbon targets in vacuum by defocused laser radiation same laser.

The essence of the invention.

It is proposed to obtain diamond films by nucleation of nanodiamond growth centers on a silicate glass substrate by exposing in a vacuum from 13 to 20 pulses of focused laser radiation from a yttrium-aluminum garnet-based laser with a wavelength of 1.064 μm on a target made of a tablet with a diameter of detonation nanodiamond powder 5 mm and a thickness of 2 mm on the press at a pressure of about 25 kg / mm ² , and the subsequent condensation of carbon on glass substrates from the vapor-gas phase obtained by laser evaporation in vacuum carbon targets, where compacted tablets of high-purity graphite with a diameter of 5 mm and a thickness of 2-3 mm are used as a target, and defocused radiation of the same laser with a spot diameter of 3 mm, pulse energy not lower than 9.0 J, is used as a target, pulse duration of at least 8 ms (milliseconds), that is, the intensity of the laser radiation of 1.6 10 ⁴ W / cm ² . As a result, carbon is condensed onto the substrate from the vapor – gas phase, in which the proportion of sp3 bonds is no less than 80%, and the formed nanodiamond nucleation islands are the growth centers of a diamond film with a thickness of at least 100 nm. The method is implemented as follows.

1. Prepare two types of targets - tablets with a diameter of 5 mm and a thickness of 2-3 mm from high-purity graphite and tablets of the same size from detonation nanodiamond powder using a mold and a press with a force of up to 500 kg (pressure about 25 kg / mm ² ).

2. Place in vacuum with a residual pressure of 10 ^-5 mm. Hg target pillar and fixed silicate glass substrate.

3. They affect the target of detonation nanodiamond with 13-20 laser pulses of a laser based on yttrium aluminum garnet with a pulse energy of 3.8 -5.8 J to create nucleation nanodiamond growth centers of the diamond phase.

4. Then, the defocused laser radiation of the same yttrium garnet-based laser with a radiation intensity of at least 1.6 × 10 ⁴ W / cm ^{2 is} applied to the target surface to condense carbon with predominantly sp3 bonds onto a substrate with already formed growth centers (nucleation islands ), acting as matrices of growth of the diamond phase, filling the interparticle space on the substrate.

Examples of specific performance

Example 1

From the initial detonation nanodiamond powder manufactured according to TU 84-112-87 (manufactured by Altai Federal Research and Production Center), samples were prepared by pressing on a hydraulic press of a cylindrical shape with a diameter of 5 mm and a height of 2-3 mm and performed an x-ray and X-ray diffraction analysis. The radiograph of nanodiamond (Fig. 1) shows the brightest reflections of diamond (111), (220) and (311).

The broadening of reflections is due to the small size of nanocrystals or the growth of microstrains, leading to a change in the interplanar distances of the reflecting planes. In covalent ultrafine crystals, the microdeformation value Ad / d cannot be large, since the elastic moduli of diamond are high. Therefore, the main contribution to the broadening of the reflections is made by the small size of the detonation nanodiamond crystals. In this regard, the dimensions of the coherent scattering regions D are determined by a simplified formula, according to which the broadening is associated only with the dispersity effect.

Where:

D is the size of coherent scatter regions

λ is the x-ray wavelength in A

θ is the x-ray diffraction angle for the (hkl) plane

β - physical broadening of the x-ray reflex

Table 1 presents the data of X-ray analysis of detonation nanodiamond reflexes, shown in FIG. 1. The size of nanocrystals of detonation nanodiamond, calculated by the formula (1), is 4.5 nm.

Example 2

Cylindrical specimens were prepared from the initial powder of detonation nanocrystal nanocrystals (as in Example 1), and gravimetric and mass spectroscopic analysis was performed.

During heating, detonation nanodiamond releases a large amount of volatile compounds, as evidenced by the loss of sample mass during the annealing process (Fig. 2). When the sample is heated to a temperature of 900 ° C, the latter loses about 20% of its mass. In addition, the heating process is accompanied by exo- and endothermic effects, indicating the occurrence of reactions on the surface of nanocrystals of detonation nanodiamond.

To determine the molecular composition of volatile impurities, mass spectrometric analysis of samples of nanocrystals of detonation nanodiamonds is carried out on a Luxx 409 thermal analysis instrument combined with an Aelos 403 mass spectrometer. Heating is carried out in an argon atmosphere at a rate of 10 ° C / min to a temperature of 900 ° C. In tab. 2 presents the data of mass spectrometric measurements. As follows from the data of FIG. 2 and tab. 2 desorption of impurities is observed over the entire temperature range, from + 30 ° C to + (900-950) ° C.

The volatile substances released are represented by a wide range of molecular compounds, such as water, hydrogen, nitrogen, hydrogen sulfide, hydrocarbons, carbon dioxide and sulfur. That is, when detonation nanodiamond is heated in vacuum, it is partially cleaned. Example 3

Compressed detonation nano-diamond pellets are placed in the vacuum volume of the apparatus according to the effect of laser radiation on the substance (Fig. 3). The residual pressure in the vacuum volume reached 10 ^-5 mm. Hg pillar. The pulse energy was 3.8–5.8 J, the pulse duration was 1 ms, the number of pulses was from 13 to 20. During exposure to laser pulses, the transfer of the target substance (tablet) to the substrate is observed due to ablation.

FIG. 4 shows the structure of a diamond film obtained by laser ablation of a target from detonation nanodiamond.

According to FIG. 4, the substrate surface is predominantly filled with small particles less than 100 nm in size, the density of detonation nanodiamond on the substrate is 6.5 particles / μm ² .

Due to the fact that the main contribution to the particle distribution is made by small particles, an analysis of the structure of a film on a scale of 500 × 500 nm was carried out (Fig. 5).

The average particle size is 16.2 nm, and the density due to the shift of the maximum of the distribution to smaller sizes has already reached 1072 particles / μm ² . It should be noted that, in aggregate, conglomerates of particles are present and particles of about 4.5 nm in size. This is evidenced by the Fourier analysis of the structure (Fig. 6).

The Fourier image contains two symmetric reflections relative to the central spot, which indicates the coexistence of both large conglomerates (from the analysis of the cross section profile, the periodicity parameter is 284.7 nm) and small particles, the periodicity parameter of which is 5.73 nm. Thus, laser ablation of a nano-diamond target allows the substrate to be populated with growth centers from units of nm to units of microns. It is significant that single detonation diamond nanocrystals virtually densely populate the surface of the substrate (the periodicity parameter of 5.73 nm practically coincides with the average nanocrystal size of 4.5 nm, as determined by X-ray in example 1). At the same time, during the ablation, an effective purification of the nanocrystals from volatile impurity components occurs.

Example 4

Compressed graphite pellets with a diameter of 5 mm and a thickness of 2-3 mm are placed in the vacuum volume of the apparatus for the effects of laser radiation on the substance (Fig. 7). The laser beam (1) was inserted through the focusing lens (2) into the vacuum volume (3), where it was defocused, and the defocused laser beam with a laser intensity not lower than 1.6 × 10 ⁴ W / cm ² hit the graphite target (6), forming evaporating area with a diameter of 3.0 mm. The effect of defocused laser radiation on the target evaporates carbon and distributes it in the vacuum volume (3) in the form of a vapor-gas cloud (4) with high kinetic energy of atoms and condensation of carbon atoms onto a fixed glass substrate (5). The residual pressure in the vacuum volume reached 10 ^-5 mm. Hg pillar. The resulting stream of vaporized carbon from a heated to high temperature target was condensed onto a glass substrate, forming a diamond-like carbon film. During laser heating with a defocused laser beam, target fragmentation was absent.

When forming diamond-like films, the main thing is the formation of sp3 bonds in carbon condensate. The mechanism of formation of these bonds depends on the energy of carbon atoms deposited on the substrate. The proportion of diamond bonds is greater, the higher the carbon energy in pairs and the higher the temperature of deposition on the substrate. It is laser evaporation that makes it possible to obtain such a kinetic energy of carbon atoms in a vapor-gas cloud of up to 100 eV, which makes it possible to obtain up to 80% sp3 bonds during carbon condensation onto a substrate, the so-called ta-C carbon.

FIG. 8 shows a fragment of the film obtained in a transmission electron microscope. An electron diffraction pattern is also shown here, from which it follows that two reflections (two rings) are observed, indicating crystallographic misorientation of the regions on which the diffraction of electrons takes place. The rings are strongly blurred (broadened), such a broadening indicates the small sizes of the fragments on which the diffraction of electrons takes place.

Interpretation of the electron diffraction patterns showed that the film material has a diamond lattice, the rings correspond to diffraction from the (111) and (220) planes of the diamond crystal lattice. The interplanar distances d ₁₁₁ = 0.207 nm, d ₂₂₀ = 0.119 nm have close, but somewhat different from the corresponding values of the interplanar distances for the coarse-grained diamond, d ₁₁₁ = 0.205 nm and d ₂₂₀ = 0.125 nm, which is typical of diamond-like thin films.

Thus, the condensation of carbon on a substrate from the vapor-gas state leads to the formation of a diamond-like structure of a thin film. A characteristic feature of such a structure is the absence of interfaces, and substructural objects are clusters with a diamond lattice.

Example 5

We combine both operations into one technological cycle. For this purpose we place in the vacuum volume of the target from detonation nanodiamond and the target from high-purity graphite. First, by acting on a nano-diamond target with focused laser radiation (as in Example 3), we form diamond growth centers on the substrate. Then, acting on the graphite target with defocused laser radiation (as in Example 4), we fill the gaps between the diamond islands with carbon condensate. Since the growth centers are already a ready diamond lattice, carbon atoms, condensing on the substrate, are embedded in the already existing diamond lattice, forming a diamond film.

FIG. 9 shows the island structure of the film after nucleation and subsequent carbon condensation (scale 500 × 500 nm).

Statistical analysis of the island structure showed (Table 3) that the average island size is 39.07 nm, and the island density is 184 μm ^-2 .

The Fourier analysis of the islet structure shown in FIG. 9 indicates a clear periodicity in the arrangement of diamond particles (Fig. 10) and the tight packing of diamond islands on the surface of the substrate.

The radial distribution function of the islands has a maximum of about 0.0035 1 / nm, which corresponds to the periodicity parameter of 285.15 ± 0.63 nm. That is, during the condensation of carbon on a substrate preliminarily populated with nucleation centers with predominantly 5.73 nm in size, the growth of nanoscale particles from 4.5 nm to particles of about 285, 15 nm is observed. The combination of such particles (islands) forms a close-packed hexagonal structure of the diamond film. This structure is a polycrystalline aggregate of islands with an average size of 285.15 nm, equally oriented relative to the film surface.

The original growth nano-diamond islands are crystallographically differently oriented relative to the substrate plane, therefore, growth is mainly observed only in those areas where close-packed {111} planes parallel to the substrate plane will be formed. The formed diamond film is a set of diamond grains (islands), mainly crystallographically equally oriented with respect to the substrate, closely packed into flat polycrystalline hexagonal thin-film structures.

Bibliography:

1. TAKEUTI Daisuke (JP), OKUSI Hideyo (JP), KOJIMURA Koji (JP), WATANABE Hideyuki (JP). The method of obtaining homoepitaxial diamond thin film and device for its implementation. The patent of the Russian Federation №2176683

2. Grigoryants AG, Misyurov A.I., Shupenev A.E. The method of obtaining diamond-like coatings by combined laser exposure. The patent of the Russian Federation №2516632.

3. Tarasenko S.N. The method of obtaining diamond-like films. RF patent №1610949 from 10/15/1994

4. D.L. Pappas, K.L. Saenger, J. Bruley, W. Krakow, J.J. Cuomo, T. Gu, R.W. Collins. Pulsed laser deposition of diamond-like carbon films // J. Appl. Phys., 1992, v. 71, No. 11, p. 5675-5684.

Claims (1)

A method of producing thin diamond films on a substrate by the method of vacuum laser exposure to targets and carbon condensation on substrates, characterized in that pre-pressed tablets of detonation nanodiamond and tablets of high-purity graphite are used as targets, and laser irradiation is carried out in two stages: first by focused laser radiation on the basis of yttrium aluminum garnet with a wavelength of 1064 nm in a series of 10-20 pulses with a pulse energy of 3.8-5.8 J disperse the target from detonation nanodiamond and form on the substrate nanodiamond nucleation centers; then the gaps between nucleation centers are filled with carbon with predominantly sp3 bonds condensed from the vapor-gas phase obtained by evaporating a target from high-purity graphite by exposure to defocused laser radiation of the same laser with a pulse energy intensity not lower than 1.610 ⁴ W / cm ² .

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