O. Ternyak

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 ...

Correlation between diamond grain size and hydrogen retention in diamond films studied by scanning electron microscopy and secondary ion mass spectroscopy

The present work studies the incorporation of hydrogen in chemical vapor deposited polycrystalline diamond films with different grain sizes. Scanning electron microscopy and secondary ion mass spectroscopy were applied to investigate the film microstructure and hydrogen retention in the films, respectively. The present study provides the direct evidence of hydrogen concentration dependence on diamond grain size. The hydrogen retention in the diamond films increases with decreasing grain size, indicating that hydrogen is bonded and trapped in the grain boundary region. The two different sources—methane and hydrogen molecules—contribute to the hydrogen retention according to their abundance in the gas mixture.

Hydrogen bonding at grain surfaces and boundaries of nanodiamond films detected by high resolution electron energy loss spectroscopy

Hydrogenated nanodiamond films consisting of 300 and 10–30nm grain sizes were examined by high resolution electron energy loss spectroscopy. C–H stretching modes were identified at 350, 360, and 375meV. The mode at 375meV was enhanced in the case of 10–30nm grain size and it is stable up to in situ annealing to >800°C. Complete hydrogen desorption occurs upon annealing to 1000°C. Exposure of the nanodiamond film to atomic hydrogen results in a strong quenching of the 375meV C–H mode, most likely due to preferential etching of (sp2)-carbon-hydrogen at the surface and grain boundaries of the films.

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...

Hydrogen incorporation processes in nanodiamond films studied by isotopic induced modifications of Raman spectra

The effect of replacing H by D and C-12 by C-13 in the gas species used to grow different types of nanodiamond films on the Raman spectra of these films was studied. The modifications of the Raman spectra were investigated in submicron sized diamond films grown by hot filament chemical vapor deposition and in nanodiamond films prepared by energetic glow discharge plasma. The latter are nanocomposites of nanodiamond crystallites embedded in an a-C:H matrix. The different spectra of the two film types add insight to the hydrogen incorporation processes in nanodiamond films responsible for the C–H related (assigned to trans-polyacetylene) Raman peaks.

Vibrational study of hydrogen bonding to ion irradiated diamond surfaces

High resolution electron energy loss spectroscopy has been used to probe hydrogenated diamond film surfaces exposed to 1keV Ar+ ions at a dose of ∼1015cm−2 and thermal annealing. The defects induced on the upper atomic layers were identified with regard to the different hydrogenated species hybridization states as well as their thermal stability. Ion irradiation resulted in the coexistence of a partially hydrogenated disordered near surface region including CH species bonded in sp, sp2, and sp3 bonding configurations and CC dimers. Thermal annealing of the ion beam irradiated hydrogenated surface leads to complete hydrogen desorption at ∼650°C. This temperature is significantly lower compared to a well defined diamond surface for which an annealing temperature above 900°C is needed.

Selective Stiffening for Producing a Mass-Fabrication Compatible Motion Conversion Mechanism

We present a mechanism that converts in-plane to out-of-plane motions, which is fully compatible with mass-fabrication processes. By using selective stiffening, we induce coupling between in-plane and out-of-plane responses of the mechanism. The conversion ratio is constant (i.e., linear response), and it can be easily tailored by the number of stiffeners used in an otherwise unchanged design planform. The linearity of the motion conversion and the possibility to tailor it, are demonstrated experimentally using dedicated test devices. As a specific example of application, we use the motion conversion mechanism to achieve a parallel out-of-plane motion of a flat stage, which is driven by in-plane comb-drives.

Mass-fabrication compatible mechanism for converting in-plane to out-of-plane motion

We present a mechanism that converts in-plane to out-of-plane motion, which is fully compatible with standard mass-fabrication methods. The mechanism harnesses the well-established in-plane actuation achieved by comb-drives, and converts it to out-of-plane motion. The motion conversion ratio is constant (i.e. linear conversion), and it can be easily tuned by adding or subtracting modular elements, in an otherwise unchanged design planform. We experimentally demonstrate the linearity of the mechanism, and use dedicated test devices to show the tunability of the conversion ratio. With a different test device, we demonstrate parallel out-of-plane motion of a flat stage. The measurements of this device show good agreement with model predictions.

Fabrication of microchannels in polycrystalline diamond using pre-fabricated Si substrates

In this paper, we report on a simple, feasible method to fabricate microchannels in diamond. Polycrystalline diamond microchannels were produced by fabricating trenches in a Si wafer and subsequently depositing a thin layer of diamond onto this substrate using the hot filament vapor deposition technique. Fabrication of trenches in the Si substrate at different depths was carried out by standard photolithography, and the subsequent deposition of the diamond layer was performed by the hot filament chemical vapor deposition technique. The growth mechanism of diamond that leads to the formation of closed diamond microchannels is discussed in detail based on the Knudsen number and growth chemistry of diamond. Variations in the crystallite size, crystalline quality, and thickness of the diamond layer along the trench depths were systematically analyzed using cross-sectional scanning electron microscopy and Raman spectroscopy. Defect density and formation of non-diamond forms of carbon in the diamond layer were ...