Comparative study on dry etching of polycrystalline diamond thin films

The reactive ion etching (RIE) technique was used to etch polycrystalline diamond thin films. In this study we investigate the influence of process parameters (total pressure, rf power, gas composition) of standard capacitively coupled plasma RIE system on the etching rate of diamond films. The surface morphology of etched diamond films was characterized by Scanning Electron Microscopy and the chemical composition of the etched film part was investigated by Raman Spectroscopy.We found that the gas composition had a crucial effect on the diamond film morphology. The use of CF₄ gas resulted in flatter surfaces and lateral-like etching, while the use of pure O₂ gas resulted in needle-like structures. Addition of argon to the reactant precursors increased the ion bombardment, which in turn increased the formation of non-diamond phases. Next, increasing the rf power from 100 to 500 W increased the etching rate from 5.4 to 8.6 μm/h. In contrast to this observation, the rise of process pressure from 80 to 150 mTorr lowered the etching rate from 5.6 down to 3.6 μm/h.     

Junction like behavior in polycrystalline diamond films

We have successfully fabricated polycrystalline diamond rectifying junction devices on n-type (1 0 0) silicon substrates by Hot Filament Chemical Vapor Deposition (HFCVD) using methane/hydrogen process gas and trimethyl borate and trimethyl phosphite dissolved in acetone as p- and n-type dopants, respectively. Impedance spectroscopy and current-voltage analysis indicates that the conduction is vertical down the grains and facets and not due to surface effects. Electrical characteristics were analyzed with In and Ti/Au top metal contacts with Al as the substrate contact. Current-voltage characteristics as a function of temperature showed barrier potentials of 1.1 eV and 0.77 eV for the In and Ti/Au contacts, respectively. Barrier heights of 4.8 eV (In) and 4.4 eV (Ti/Au) were obtained from capacitance-voltage measurements.     

Structure of diamond polycrystalline films deposited on silicon substrates

The article presents results of structural studies of polycrystalline diamond thin films deposited by hot filament CVD on silicon substrates. The films were characterized using Scanning Electron Microscopy (SEM), Raman Spectroscopy (RS), Electron Backscattered Diffraction (EBSD), Energy Dispersive Spectroscopy (EDS) and Secondary Ion Mass Spectroscopy (SIMS). Both the EBSD patterns and Raman spectra confirm that the grains visible in the electron micrographs are diamond micro-crystallites. The residual stress in the films is found to be in the range between −4.29 GPa and −0.56 GPa depending on the sample thickness. No evidence of lonsdalite and graphite has been registered in the polycrystalline material of the investigated samples. Evidence of the existence of silicon carbide at the diamond/silicon interface is presented. It is also suggested that an amorphous carbonaceous film covers the silicon surface in the regions of holes in the thin diamond layers.     

Field emission characteristics of high-energy ion-irradiated polycrystalline diamond thin films

Diamond thin films have been synthesized by hot-filament chemical vapor deposition process using a mixture of methane and hydrogen gases. The samples were subjected to very high-energy ion irradiation (100 MeV Au⁷⁺ ions). The field emission characteristics of ion-irradiated samples have been studied. High emission currents and low turn-on and threshold fields were obtained for ion-irradiated samples. The as-deposited and the ion-irradiated samples have been characterized by X-ray Diffraction, Scanning Electron Microscopy and Micro-Raman Spectroscopy techniques and the resulting changes are correlated with field emission results.     

Reversible wettability on polycrystalline diamond films between superhydrophobicity and superhydrophilicity

Reversible wettability on the polycrystalline diamond film was investigated through the alternation of hydrogen and oxygen plasma treatment. This can be ascribed to the reversible switching of the surface terminal chemical properties between two different states. The water contact angle could be varied between 5.9 degrees and 88.9 degrees when the diamond film was prepared on a flat substrate. When diamond films with multi-scaled roughness were fabricated, the wettability conversion could be amplified, leading to switching between superhydrophobicity and superhydrophilicity.     

CVD金刚石膜的场发射机制

利用热灯丝化学气相沉积方法在光滑的钼上沉积了金刚石膜,用扫描电子显微镜和Raman谱对金刚石膜进行了分析。结果表明金刚石膜是由许多金刚石晶粒组成,晶粒间界主要是石墨相,并且在膜内有许多缺陷。金刚石膜的场发射结果表明高浓度CH4形成的金刚石膜场发射阈位电场较低浓度CH4形成的金刚石为低。这意味着杂质（如石墨）和缺陷（悬挂键）极大地影响了膜的场发射性能。根据以上结果,提出了一种CVD金刚石膜的场发射机制即膜内的缺陷增强膜内的电场,石墨增大电子的隧穿系数以增强CVD金刚石膜的场发射。     

Charge-based deep level transient spectroscopy of B-doped and undoped polycrystalline diamond films

The undoped and B-doped polycrystalline diamond thin film was synthesized by hot filament chemical vapor deposition and microwave plasma, respectively. The structural characterization was performed by scanning electron microscopy, X-ray diffraction and Raman spectroscopy. The electrical properties of synthesized diamond layer were characterized by dc-conductivity method and charge deep level transient spectroscopy. The B-doped diamond layers show higher sp²/sp³ ratios in comparison with that of undoped layers what can have an essential influence on the localized density of states associated with shallow hydrogen acceptor states what is reflected in the values of activation energies which reached the values of 38 meV for B-doped and 55 meV for undoped diamond layers, respectively. The existence of deep level traps, as, for example, associated with B-related acceptors, was not observed.     

Surface morphology of polycrystalline diamond films etched by Ar+ beam bombardment

Polycrystalline diamond films etched by Ar⁺ beam bombardment were investigated by scanning electron microscopy and Raman spectroscopy. In an ion sputtering apparatus, an etching rate of 14 m C^–1 was obtained when 10 kV-accelerated Ar⁺ ions penetrated with an angle of 15–30° from the normal. A number of cavities were created on the surface treated at low incidence angle. In contrast, micro-prominence was seen under the condition of high incidence angle. The degree of surface roughness on etched films was also changed with the incidence angle of the beam. A relatively smooth surface appeared after the treatment with an incidence angle of 15°. Raman spectroscopy revealed that the physical etching of diamond is effective in obtaining high quality surface of polycrystalline diamond films.     

红外光学材料硫化锌衬底上沉积金刚石膜的研究

采用微波等离子体化学气相沉积法,在预镀陶瓷过渡层的硫化锌衬底上沉积金刚石膜。在以前的实验中,我们发现在陶瓷过渡层上沉积金刚石膜极其困难,但采用金刚石诱导形核方法后,我们已经在过渡层／硫化锌试样表面获得了很小面积（约1mm宽的环状区域）的金刚石形核。本文对前期的诱导形核工作进行了一定改进,目前已经使形核生长范围大大增加,沉积面积超过原来10倍。此外,本文对金刚石／过渡层／硫化锌试样的红外透过特性以及金刚石膜质量等进行了评价。     

Conduction mechanism in sputtered polycrystalline zinc oxide thin films

Conductivity and Hall effect data are reported for columnar polycrystalline zinc oxide films between 1 and 4 μm thick deposited onto insulating substrates by r.f. reactive sputtering. Crystallites are (00.1) oriented, typically a few hundred nanometers in diameter and 98%–99% packed. Resistivities between 10⁷ and 10¹¹ Ω cm at 300 K typically decrease by between one and three orders of magnitude for a 100 K temperature increase. The shallow oxygen vacancy donor is the only impurity level present in significant densities; IR absorption indicates densities greater than 10¹⁷ cm^-3, but Hall measurements show apparent carrier concentrations of between 10⁴ and 10⁸ cm^-3.This anomaly is resolved by invoking the Petritz diode model of conduction in discontinuous materials, modified to include the case of highly doped crystallites and applied to zinc oxide with deplectively chemisorbed intercrystalline states. Quantitative agreement is found for conductivity against temperature. The measurable Hall carrier concentration, deduced from the empirical intracrystallite carrier densities of between 1 × 10¹⁵ and 1 × 10¹⁹ cm^-3 and barrier heights of between 0.6 and 1.2 eV, agrees well with Hall effect measurements. Crystallite surface state densities of about 10¹³ cm^-2 are indicated as responsible for these effects.     

HF CVD diamond nucleation and growth on polycrystalline copper: A kinetic study

This paper reports on the kinetics of diamond nucleation and growth on polycrystalline copper investigated by in situ Auger Electron Spectroscopy and Scanning Electron Microscopy. Copper is a reference substrate to study the diamond nucleation from graphite. The substrate is first treated with diamond paste. However the diamond seeds let on the surface by the pre-treatment are almost completely transformed into graphite. The nucleation of CVD diamond can be well described in the framework of carbon phase transformations. Diamond seeds deposited on the substrate are first transformed into graphitic layers. A process occurring on the edges site of graphite is subsequently postulated, in agreement with the Lambrecht model.     

A positron annihilation study on the defect properties of doped diamond films

Doppler broadening measurements were performed on undoped, boron doped, and sulfur doped diamond films. The defect properties in these different diamond films were analyzed and the effect of boron concentration in the B-doped diamond films on these properties was studied. The Doppler broadening measurements were characterized with the shape parameter S and the wing parameter W. From these fitted characteristic S and W values of the diamond films and plots of S vs. position implantation energy, it was deduced that undoped and S-doped diamond films are rich of vacancy-like defects, while B-doped diamond films are poor of vacancy-like defects. This difference may originate from possible different charge state of the vacancy-like defects and from the incorporation of impurities in the different growth ambient of the films. By comparing the parameters obtained in the Doppler broadening measurements of diamond films with different boron concentration, we found that S values of B-doped diamond did not decreased with the increasing of boron concentration, which suggests that more damaged regions form in the higher boron concentration samples.     

Effective improvement in the distribution of single crystalline diamond nanorods fabricated from the randomly-oriented polycrystalline films

By using the bias-assisted reactive ion etching technique and the etching masks of Au nanodots, the high-density single crystalline diamond nanorods have been obtained from the polycrystalline diamond films with randomly-oriented grains grown on silicon substrates. The inhomogenous distribution of the nanorods mainly results from the existence of grain boundaries in the films, and can be effectively improved by adding the graphite sheet under the substrate. Furthermore, the fabrication mechanism of the nanorod array is carefully investigated in this paper. The morphological evolution is observed by using a scanning electron microscopy technique. Raman measurements are carried out to monitor the phase change during the etching process. It is found that the non-diamond phases are present during the experimental process, and then are completely removed away in the end.     

A study of cutting force variations in turning silumins using round polycrystalline diamond inserts

Based on the correlation and spectral analyses of experimental results, we have established the influence of machining conditions on the cutting force in turning silumins using tools equipped with round polycrystalline diamond inserts. The paper gives some practical recommendations of how to choose appropriate machining conditions.     

A study of polyaniline deposited nanocrystalline diamond films for glucose detection

Nitrogen-doped nanocrystalline diamond (NCD) films have been deposited on Si substrates in CH4/Ar/N2 gas mixtures by the microwave plasma enhanced chemical vapor deposition (MPECVD) technique. Such films contain very small diamond grains (10 to 30 nm) with high electrical conductivity (126 ohms(-1) cm(-1)) compared to un-doped ones. The films were characterized by scanning electron microscopy (SEM) and Raman spectroscopy. Near edge X-ray fine structure studies showed that the nitrogen-doped NCD had slightly higher sp2/sp3 bonding ratio compared to the un-doped sample. A nitrogen-doped NCD electrode was functionalized by conducting polymer films (polyaniline) to work as an interface for biomedical applications. Glucose sensing has been demonstrated based on this functionalized electrode. Linear response of the sensor has been observed for glucose concentration up to 9 mM.     

A general mechanism of polycrystalline growth

Most research into microstructure formation during solidification has focused on single-crystal growth ranging from faceted crystals to symmetric dendrites. However, these growth forms can be perturbed by heterogeneities, yielding a rich variety of polycrystalline growth patterns. Phase-field simulations show that the presence of particulates (for example, dirt) or a small rotational-translational mobility ratio (characteristic of high supercooling) in crystallizing fluids give rise to similar growth patterns, implying a duality in the growth process in these structurally heterogeneous fluids. Similar crystallization patterns are also found in thin polymer films with particulate additives and pure films with high supercooling. This duality between the static and dynamic heterogeneity explains the ubiquity of polycrystalline growth patterns in polymeric and other complex fluids.     

新型MPCVD装置在高功率密度下高速沉积金刚石膜

使用自行研制的新型MPCVD装置,以H2-CH4为气源,在输入功率为5kW,沉积压力分别为13.33、26.66kPa和不同的甲烷浓度下制备了金刚石膜。利用等离子体发射光谱法对等离子体中的H原子和含碳的活性基团浓度进行了分析。用扫描电镜、激光拉曼谱对金刚石膜的表面和断口形貌、金刚石膜的品质等进行了表征。实验结果表明,使用新型MPCVD装置能够在较高的功率密度下进行金刚石膜的沉积;提高功率密度能使等离子体中H原子和含碳活性基团的浓度明显增加,这将提高金刚石膜的沉积速度,并保证金刚石膜具有较高的质量。     

A comparative study of p-type diamond films using Raman and transport measurements

The influence of deposition temperature in the properties of synthetic diamond films grown by two different chemical vapor deposition (CVD) techniques, hot-filament- and microwave-plasma-assisted, was investigated. These samples were obtained using the optimal growth conditions previously achieved in this work. Raman spectroscopy was employed in order to investigate the diamond film quality as a function of the deposition temperature. It was found that the nondiamond carbon bands decrease as the deposition temperature increases for both the deposition methods, leading to higher-quality diamond films. The micro- and macro-Raman spectra showed that the nondiamond band is already present in a single diamond grain. Both techniques provided well homogeneous diamond films and with equivalently good quality. Boron-doped diamond films with different carrier concentration levels were also studied. In order to get details about the electrical properties of the films, resistivity as a function of the boron concentration—in association with Raman spectra—and temperature-dependent transport measurements were employed. The results showed that the boron doping is the main responsible for the conductivity and that the variable range hopping (VRH) mechanism dominates the transport in these doped diamond films.     

Machining MMC engineering components with polycrystalline diamond and diamond grinding

Abstract

The high specific strength of metal matrix composite (MMC) materials is derived from the combined effects of light, ductile and hard, brittle materials being incorporated in a matrix composite. The hard, brittle phase in this composite can cause problems when machining such materials. The most commonly encountered problems are those involved in producing an acceptable surface finish, avoiding very rapid tool wear and achieving acceptable machining costs, through the use of higher machining speeds. However, in order for MMC materials to be widely accepted into the mainstream automotive, aerospace, and mechanical engineering industries, cost effective machining solutions will be required. Increasingly, machining with polycrystalline diamond (PCD) and grinding with diamond abrasives (two examples of ultra hard materials) are being utilised as the most effective machining methods in the manufacture of MMC components. The present paper explores the inherent problems involved in the machining of MMCs and the suitability of ultrahard tooling technology in overcoming many of these problems. The importance of PCD grade selection and optimised machining conditions are particularly important when machining MMCs, and these are reviewed in detail. The versatility of PCD for use in practically all metal cutting operations is also illustrated. The paper concludes with a number of case studies demonstrating how ultrahard tooling technology has been applied to produce economically a wide range of engineered MMC components in the automotive, aerospace, and mechanical engineering industries.