41,858 research outputs found
3D characterisation of tool wear whilst diamond turning silicon
No full textNanometrically smooth infrared silicon optics can be manufactured by the diamond
turning process. Due to its relatively low density, silicon is an ideal optical
material for weight sensitive infrared (IR) applications. However, rapid diamond
tool edge degradation and the effect on the achieved surface have prevented
significant exploitation. With the aim of developing a process model to optimise
the diamond turning of silicon optics, a series of experimental trials were
devised using two ultra-precision diamond turning machines. Single crystal
silicon specimens (1 1 1) were repeatedly machined using diamond tools of the
same specification until the onset of surface brittle fracture. Two cutting
fluids were tested. The cutting forces were monitored and the wear morphology of
the tool edge was studied by scanning electron microscopy (SEM). The most
significant result showed the performance of one particular tool was
consistently superior when compared with other diamond tools of the same
specification. This remarkable tool performance resulted in doubling the cutting
distance exhibited by the other diamond tools. Another significant result was
associated with coolant type. In all cases, tool life was prolonged by as much
as 300% by using a specific fluid type. Further testing led to the development
of a novel method for assessing the progression of diamond tool wear. In this
technique, the diamond tools gradual recession profile is measured by performing
a series of plunging cuts. Tool shape changes used in conjunction with flank
wear SEM measurements enable the calculation of the volumetric tool wear rate.Wea
High quality heteroepitaxial diamond films on silicon
No full textS.1640-1645This paper reports the progresses made recently on the nucleation and growth of high-quality, [001]-oriented diamond films and discusses the problems to be resolved. The interface structure of diamond on silicon has further been investigated by transmission electron microscopy (TEM). Heteroepitaxial diamond films with increased lateral grain size and reduced grain boundary density were prepared in both microwave plasma chemical vapour deposition (MW-CVD) and hot filament chemical vapour deposition (HF-CVD) processes. Using a growth process combining a bias-assisted H+ etching an a [001]-textured growth smooth diamond films with large lateral grain size up to 10 mu m can be obtained at a film thickness of approximately 10 mu m. By controlling the [001]-textured growth process thick diamond films with a lateral grain size up to 30 mu m has been achieved in HF-CVD.9Nr.9-1
Diamond based nanostructures for electronic applications
No full textResearch in the area of CVD diamond thin films has increased significantly during the last decades to the point where single crystal diamond is now commercially available. The remarkable properties of diamond including its extreme hardness, low coefficient of friction, chemical inertness, high thermal conductivity, transparency and semiconducting properties make it attractive
for a number of applications, among which electronic devices is one of the key areas. A detailed knowledge of electrical properties of diamond films is
therefore critical.
This thesis describes (1) a Hall effect study of highly boron-doped (111)
diamond films (2) a Hall effect and impedance spectroscopic study of boron δ-doped diamond structures and (3) the synthesis of carbon nanotubes on single crystal diamond.
Systematic investigations have been carried out on single crystal, boron-doped (111) diamond films. The influence of ultra pure gases, doping concentration and temperature on carrier transport are discussed in detail.
A comprehensive study on boron δ-doped diamond films is also performed;
Hall effect and impedance spectroscopy are used to evaluate these films, providing valuable insight into the complex carrier transport mechanisms
occurring in these structures. The influence of temperature on carrier
mobility and the free carrier density are discussed. This is allied with
valuable information gained from impedance spectroscopy, where the
presence of multiple semicircular responses (conduction pathways),
modelled using a RC parallel circuit, yields data which leads to a greater
understanding on the influence of the interface between the boron δ-doped
layer and the surrounding intrinsic diamond layers. These semicircular
responses are thus attributed to different crystalline regions in these
structures, namely the boron δ -doped layer and the interfacial regions surrounding δ-layer. The influence of this interface region on the structures
overall conductivity is discussed.
Finally the synthesis of carbon nanotubes (CNTs) on single crystal diamond
is reported for the first time. Scanning electron microscopy combined with
Raman spectroscopy is used to understand the influence of temperature and
differing growth gas mixtures on the yield and crystallinity of these as-grown CNTs
Stability of electronic states of the vacancy in diamond
No full textThe vacancy in diamond is a fundamental defect which has been studied theoretically and experimentally for forty years. However, although early theories (Coulson C A and Kearsley M J 1957 Proc. R. Soc. A 241 433) were extremely successful in explaining the nature of the ground state of the neutral defect and the Jahn-Teller distortion expected (Lannoo M and Stoneham A M 1968 J. Phys. Chem. Solids 29 1987), there are still several questions which have not been answered satisfactorily. in particular, the many-electron effects and configuration interaction are vital. They determine not only the order of electronic levels in the vacancy, but also the best-known optical transition. GR1, which cannot be expressed in terms of one-electron levels alone.We bring together much of the derailed recent experimental data on the different charge states and excited states of the vacancy to build up a simple empirical model of the defect. We show that the stability of the states and their photoconductivity, or lack of it, can be reproduced. We can predict that other states of the neutral vacancy, observable by EPR, lie very close above the ground state. and another high-energy optical transition might be detectable
Wastewater treatment with diamond electrodes
No full textBoron doped diamond films have been deposited by large area hot-filament CVD (HFCVD) on silicon, silicon carbide, and different industrial electrode materials, like niobium, tantalum, titanium, tungsten, zirconium, and graphite on areas up to 40 cm * 60 cm. These diamond electrodes have been characterized with regard to their material and electrochem. properties. The oxidn. of org. compds. has been studied using alcs., org. acids and halogenated arom. mols. These org. model mols. are oxidized to CO2 without major amts. of other detectable byproducts even at very low concns. (< 3 ppm). Concd. (1 M) and dild. (3.1 * 10-4 M) cyanide solns. have been oxidized on diamond electrodes both in the presence and in the absence of chloride ions. At low concns., the oxidn. process is strongly catalyzed by the presence of Cl-. These exptl. data demonstrate the applicability of diamond electrodes for industrial processes of wastewater treatment. [on SciFinder (R)]GGE
Wastewater treatment with diamond electrodes
No full textS.473-483Boron doped diamond films have been deposited by large area hotfilament CVD (HFCVD) on silicon, siliconcarbide and different industrial electrode materials, like niobium, tantalum, titanium, tungsten, zirconium and graphite on areas up to 40 cm x 60 cm (Fig. 1). These diamond electrodes habve been characterized with regard to their material and electrochemical properties. The oxidation of organic compounds has been studied using alcohols, organic acids and halogenated aromatic molecules. These organic model molecules are oxidized to CO2 without major amounts of other detectable byproducts even at very low concentrations (<3ppm). Concentrated (1 M) and diluted (3.1x10-4M) cyanide solutions have been oxidized on diamond electrodes both in the presence and in the absence of chloride ions. At low concentrations, the oxidation process is strongly catalysed by the presence of Cl-. These experimental data demonstrate the applicability of diamond electrodes for industrial processes of wastewater treatment and purification
Metastable Nanosized Diamond Formation from Fluid Systems
No full textThe model of nanosized diamond particles formation at metastable P-T parameters from fluid is presented. It explains the specific of CVD diamond synthesis gases mixtures and hydrothermal growth of diamond at low P-T parameters as well as it explains the geneses of metamorphic and magmatic nano- and microdiamond in the shallow depth Earth rocks and the genesis of interstellar nanodiamond formations in the space
Investigation of the shape transferability of nanoscale multi-tip diamond tools in the diamond turning of nanostructures
No full textIn this article, the shape transferability of using nanoscale multi-tip diamond tools in the diamond turning for scale-up manufacturing of nanostructures has been demonstrated. Atomistic multi-tip diamond tool models were built with different tool geometries in terms of the difference in the tip cross-sectional shape, tip angle, and the feature of tool tip configuration, to determine their effect on the applied forces and the machined nano-groove geometries. The quality of machined nanostructures was characterized by the thickness of the deformed layers and the dimensional accuracy achieved. Simulation results show that diamond turning using nanoscale multi-tip tools offers tremendous shape transferability in machining nanostructures. Both periodic and non-periodic nano-grooves with different cross-sectional shapes can be successfully fabricated using the multi-tip tools. A hypothesis of minimum designed ratio of tool tip distance to tip base width (L/Wf) of the nanoscale multi-tip diamond tool for the high precision machining of nanostructures was proposed based on the analytical study of the quality of the nanostructures fabricated using different types of the multi-tip tools. Nanometric cutting trials using nanoscale multi-tip diamond tools (different in L/Wf) fabricated by focused ion beam (FIB) were then conducted to verify the hypothesis. The investigations done in this work imply the potential of using the nanoscale multi-tip diamond tool for the deterministic fabrication of period and non-periodic nanostructures, which opens up the feasibility of using the process as a versatile manufacturing technique in nanotechnology
Brittle–ductile transition during diamond turning of single crystal silicon carbide
No full textIn this experimental study, diamond turning of single crystal 6H-SiC was performed at a cutting speed of 1 m/s on an ultra-precision diamond turning machine (Moore Nanotech 350 UPL) to elucidate the microscopic origin of ductile-regime machining. Distilled water (pH value 7) was used as a preferred coolant during the course of machining in order to improve the tribological performance. A high magnification scanning electron microscope (SEM FIB- FEI Quanta 3D FEG) was used to examine the cutting tool before and after the machining. A surface finish of Ra=9.2 nm, better than any previously reported value on SiC was obtained. Also, tremendously high cutting resistance was offered by SiC resulting in the observation of significant wear marks on the cutting tool just after 1 km of cutting length. It was found out through a DXR Raman microscope that similar to other classical brittle materials (silicon, germanium, etc.) an occurrence of brittle-ductile transition is responsible for the ductile-regime machining of 6H-SiC. It has also been demonstrated that the structural phase transformations associated with the diamond turning of brittle materials which are normally considered as a prerequisite to ductile-regime machining, may not be observed during ductile-regime machining of polycrystalline materials
Properties of nanostructured diamond-silicon carbide composites sintered by high pressure infiltration technique
No full textA high-pressure silicon infiltration technique was applied to sinter diamond–SiC composites with different diamond crystal sizes. Composite samples were sintered at pressure 8 GPa and temperature 2170 K. The structure of composites was studied by evaluating x-ray diffraction peak profiles using Fourier coefficients of ab initio theoretical size and strain profiles. The composite samples have pronounced nanocrystalline structure: the volume-weighted mean crystallite size is 41–106 nm for the diamond phase and 17–37 nm for the SiC phase. The decrease of diamond crystal size leads to increased dislocation density in the diamond phase, lowers average crystallite sizes in both phases, decreases composite hardness, and improves fracture toughness
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