R. Akhvlediani

Nanometer rough, sub-micrometer-thick and continuous diamond chemical vapor deposition film promoted by a synergetic ultrasonic effect

Abstract In this paper we report on a surface treatment to seed substrates for the promotion of diamond nucleation. This surface treatment consists of an ultrasonic abrasion process using poly-disperse slurry composed of a mixture of small diamond particles ( 3 μm) which may consist of diamond, alumina, titanium, etc. Whereas ultrasonic abrasion with a mono-disperse diamond slurry results in a diamond nucleation density of ∼2–3×108 particles/cm2, treatment with poly-disperse slurries results in diamond nucleation density of values up to ∼5×1010 particles/cm2. This effect was found to display a similar effectiveness on a variety of substrates such as silicon, sapphire, quartz, etc. The enhancement in diamond nucleation is interpreted by a ‘hammering’ effect whereby the larger particles insert very small diamond debris onto the treated surface, thus increasing the density of nuclei onto which diamond growth takes place during the chemical vapor deposition process. By increasing the nucleation density to values of ∼5×1010 particles/cm2, continuous diamond films of thickness of less than ∼100 nm were grown after only 5 min of deposition. The roughness of continuous diamond films grown on substrates treated at optimum conditions obtains values of 15–20 nm. The effect of ultrasonic treatment on silicon substrates and the deposited films was investigated by atomic force microscopy (AFM), high-resolution scanning electron microscopy (HR-SEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy.

Hydrogen concentration and bonding configuration in polycrystalline diamond films: From micro-to nanometric grain size

The present work studies the incorporation of hydrogen and its bonding configuration in diamond films composed of diamond grains of varying size which were deposited by three different methods: hot filament (HF), microwave (MW), and direct current glow discharge (dc GD) chemical vapor deposition (CVD). The size of diamond grains which constitute the films varies in the following way: hundreds of nanometers in the case of HF CVD (“submicron size,” ∼300nm), tens of nanometers in the case of MW CVD (3–30nm), and a few nanometers in the case of dc GD CVD (“ultrananocrystalline diamond,” ∼5nm). Raman spectroscopy, secondary ion mass spectroscopy, and high resolution electron energy loss spectroscopy (HR-EELS) were applied to investigate the hydrogen trapping in the films. The hydrogen retention of the diamond films increases with decreasing grain size, indicating that most likely, hydrogen is bonded and trapped in grain boundaries as well as on the internal grain surfaces. Raman and HR-EELS analyses show that ...

Hydrogen content and density in nanocrystalline carbon films of a predominant diamond character

Nanocrystalline carbon films possessing a prevailing diamond or graphite character, depending on substrate temperature, can be deposited from a methane hydrogen mixture by the direct current glow discharge plasma chemical vapor deposition method. While at a temperature of ∼880 °C, following the formation of a thin precursor graphitic film, diamond nucleation occurs and a nanodiamond film grows, at higher and lower deposition temperatures the films maintain their graphitic character. In this study the hydrogen content, density and nanocrystalline phase composition of films deposited at various temperatures are investigated. We aim to elucidate the role of hydrogen in nanocrystalline films with a predominant diamond character. Secondary ion mass spectroscopy revealed a considerable increase of the hydrogen concentration in the films that accompanies the growth of nanodiamond. It correlates with near edge x-ray adsorption spectroscopy measurements, that showed an appearance of spectroscopic features associat...

Field electron emission from undoped, continuous, submicron-thick diamond films

The present work shows that the field electron emission (FEE) properties of polycrystalline diamond films can be enhanced by control over the film thickness. The FEE properties of undoped, continuous, and smooth submicron-thick diamond films with initial nucleation densities of ∼5×1010particles∕cm2 were investigated as a function of diamond film thickness. A set of films with thickness ranging from 70–100to830nm yielded turn-on field values of 6–8V∕μm and threshold field values of 8.5–17.5V∕μm (for 0.3μA∕cm2), respectively, without any conditioning. It was found that the films of thickness up to ∼370nm can sustain stable current density as high as 0.1A∕cm2 without morphological modification. The thicker films, however, suffer from a strong degradation of the film and breakdown. The best FEE (lower turn-on and threshold fields and morphological stability) was obtained for a thin (100nm) continuous diamond film. This result is suggested to be attributed mainly to the efficient electron conduction from the b...

Oxide-free InSb (100) surfaces by molecular hydrogen cleaning

We report that annealing of an oxidized InSb (100) single-crystal sample at 250°C under molecular hydrogen flow [molecular hydrogen cleaning (MHC)] results in complete desorption of the surface oxides. Following this process, the surface morphology is found to be very smooth at the nanometric scale without any droplet structure and a nearly 1:1 In:Sb stoichiometry. MHC was applied to remove the native oxide of an epi-ready InSb(100) substrate used for molecular beam epitaxy growth of InSb films. These results suggest that MHC of InSb can be used as a very effective cleaning process for epitaxial film growth.

Oxidation of diamond films by atomic oxygen: High resolution electron energy loss spectroscopy studies

Diamond surface oxidation by atomic oxygen, annealing up to ∼700°C, and in situ exposure to thermally activated hydrogen were studied by high resolution electron energy loss spectroscopy (HREELS). After atomic oxygen (AO) exposure, HREELS revealed peaks associated with CHx groups, carbonyl, ether, and peroxide-type species and strong quenching of the diamond optical phonon and its overtones. Upon annealing of the oxidized surfaces, the diamond optical phonon overtones at 300 and 450meV emerge and carbonyl and peroxide species gradually desorb. The diamond surface was not completely regenerated after annealing to ∼700°C and in situ exposure to thermally activated hydrogen, probably due to the irreversible deterioration of the surface by AO.

Hydrogenation and thermal stability of nano- and microcrystalline diamond films studied by vibrational electron spectroscopy

The influence of high temperature annealing of hydrogenated diamond films with average grain size of ∼300 and ∼5 nm on surface degradation by graphitization is reported. Ex situ microwave plasma hydrogenation was applied to obtain fully hydrogenated diamond surfaces. Hydrogen bonding and near surface phase composition of both films were studied by high resolution electron energy loss spectroscopy (HR-EELS) and electronic EELS. C–H vibrational modes, phonon losses, and their overtones were measured by HR-EELS and bulk and surface plasmons by EELS. In situ vacuum annealing at 1000 °C results in hydrogen desorption and reconstruction of both kinds of surfaces, detected by vanishing of C–H peaks and appearance of sp2 hybridized carbon features. Our results suggest that graphitization induced by hydrogen desorption occurs to a larger extent on the surface of ∼5 nm grain size films. Subsequent in situ atomic hydrogen exposure of both films’ surfaces results in hydrogen adsorption and recovery of the diamond sur...

Ion-induced electron emission from undoped sub-micron thick diamond films

The number of electrons emitted per impinging ion is known to be very high for hydrogenated B-doped diamond films. However, following ion bombardment the yield of emitted electrons rapidly decreases due to structural and chemical changes induced by the irradiation process. These changes eventually result in negative electron affinity loss and graphitization of the diamond film. Here we report results on ion-induced electron emission (IIEE) from undoped, sub-micron thick and hydrogenated diamond films. We found that the IIEE properties of these films are more stable upon similar bombardment conditions as compared to those of micron and sub-micron thick B-doped films. The enhanced IIEE properties of the sub-micron films are most likely associated with a reduced charging.

Temperature enhancement of secondary electron emission from hydrogenated diamond films

The effect of temperature on the stability of the secondary electron emission (SEE) yield from ∼100-nm-thick continuous diamond films is reported. At room temperature, the SEE yield was found to decay as a function of electron irradiation dose. The SEE yield is observed to increase significantly upon heating of the diamond surface. Furthermore, by employing moderate temperatures, the decay of the SEE yield observed at room temperature is inhibited, showing a nearly constant yield with electron dose at 200 °C. The results are explained in terms of the temperature dependence of the electron beam-induced hydrogen desorption from the diamond surface and surface band bending. These findings demonstrate that the longevity of diamond films in practical applications of SEE can be increased by moderate heating.

Desorption of InSb(001) native oxide and surface smoothing induced by low temperature annealing under molecular hydrogen flow

The preparation of InSb (001) oxygen-free surfaces by thermal annealing at relatively low temperatures under molecular hydrogen flow is reported. This process is compared with thermal oxide desorption (TOD) at 400°C under ultrahigh vacuum conditions. Molecular hydrogen cleaning (MHC) at substrate temperature of 250°C and at hydrogen pressure of 5×10−6Torr resulted in complete desorption of the native oxide layer. Furthermore, no carbon contamination was observed on the surface following this treatment. The surface morphology of the samples following this process was found to be very smooth without any droplet structure. The In:Sb surface stoichiometry was nearly 1:1 along the MHC process. In addition, annealing the sample at 400°C in vacuum after oxide removal by MHC maintains the smoothness and the stoichiometry of the surface. In contrast, TOD at 400°C of an oxidized InSb surface in vacuum does not result in complete oxide removal from the surface. Furthermore, small droplets associated with In are prod...