71,414 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
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
Counterpropagating frequency mixing with terahertz waves in diamond
No full textFrequency conversion by means of Kerr nonlinearity is one of the most common and exploited nonlinear optical processes in the UV, visible, IR, and mid-IR spectral regions. Here we show that wave mixing of an optical field and a terahertz wave can be achieved in diamond, resulting in the frequency conversion of the terahertz radiation either by sum-or difference-frequency generation. In the latter case, we show that this process is phase matched and most efficient in a counterpropagating geometry. (C) 2013 Optical Society of America</p
Electrical characterization of a graphite-diamond-graphite junction fabricated by MeV carbon implantation
No full textThe Deep Ion Beam Lithography technique has been extensively adopted in
recent years for the fabrication of graphitic electrodes in bulk diamond
with a wide range of technological applications. Particularly, it has
been recently shown that a high current can be driven in devices
consisting of micrometer-spaced sub-superficial graphitic electrodes.
This effect has been exploited to stimulate electroluminescence from
color centers placed in the active region of the device.
A deep understanding of the conduction mechanisms governing charge
transport in micro-regions of defective diamond comprised between
graphitic electrodes is necessary in order to fully exploit the
functionality of these opto-electronic devices, as well as to assess the
ion-beam-micromachining of diamond as a convenient technique for the
fabrication of solid-state micro-devices.
In this work, a temperature-dependent characterization of the electrical
properties of a sub-superficial graphite diamond-graphite junction is
presented and discussed. The ohmic behavior observed at low bias
voltages is ascribed to a donor level with an activation energy of
(0.217 +/- 0.002) eV, a value compatible with previous reports on
nitrogen-related defects. A transition to a high-current regime above a
critical voltage V-c was also observed, and interpreted in terms of the
Space-Charge-Limited Current model. The temperature-dependent
measurements allowed to investigate the role of charge trapping in the
charge injection mechanism of the junction. By fitting the temperature
dependence in the high-current regime it was possible to determine the
relevant trap level of the associated Poole-Frenkel mechanism, leading
to a value of (0.278 +/- 0.001) eV from the conduction band. The
Poole-Frenkel conduction model in high-current regime enabled also a
preliminary investigation in the effects of ion implantation on the
modification of the dc dielectric constant of diamond. (C) 2017 Elsevier
B.V. All rights reserved
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
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
Electrochemical behavior of synthetic diamond thin film electrodes
No full textThe inertness and unique electrochem. properties of diamond present great potential for a variety of applications in aggressive environments. Preliminary results showed the widest known electrochem. window before water decompn., allowing new possibilities for both anodic and cathodic reactions. Studies of the oxidn. of org. compds. was performed with alcs. such as isopropanol, phenol and org. acids. Cyclic voltammetry demonstrates no activity in the potential range where water is stable. In the potential region of oxygen evolution, the org. compds. are mainly oxidized to CO2. No deactivation or redn. in the thickness of the electrode was obsd. No fouling of the diamond surface was detected. Also, no hydrodynamic effects were obsd. Concd. (1 M) and dild. (3 * 10-4 M) cyanide solns. were oxidized on diamond electrodes both in the presence and in the absence of chloride ions. The results show a direct oxidn. with a current efficiency of .apprx.40% for concd. solns. At low cyanide concns., the current efficiency is strongly increased by the presence of Cl-. Electrochem. redn. of cadmium and copper was carried out on diamond electrodes. Nonadherent deposits were obtained on diamond cathodes. [on SciFinder (R)]GGE
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
Analysis of traps in high quality CVD diamond films through the temperature dependence of carrier dynamics
No full textThe analysis of the time behavior of pulses generated by CVD diamond films irradiated with a-particles has been recently shown to be a general and powerful tool to investigate trap properties in diamond films (M. Marinelli et al., Phys. Rev. B 64 (2001) 195205). We use here this technique to measure the activation energy of traps in CVD diamond films, through the analysis of the temperature dependence of the dynamics of carriers generated by a-particle irradiation. The samples used in this study are high quality films deposited in a microwave tubular reactor and show very narrow diamond Raman peaks (FWHM approximately 2.4 cm(-1)) and extremely low photoluminescence background. The time evolution of the response of alpha-particle detectors built from these films exhibit both a fast and a slow component. Quantitative analysis leads to the conclusion that only deep traps limit the electron mean free path before trapping, while for holes both deep and shallow centers must be taken into account, the latter becoming the limiting factor in the pumped state. The changes in the pulse shapes are analyzed when the film temperature T is varied from -40 to 20 degreesC. A systematic speed-up of the response is found with increasing temperature, confirming that the slow component is due to thermally activated detrapping from the relative shallow defects. The detrapping time constant tau(D) is connected to the activation energy E-D of the defects through the formula 1/tau(D) = s exp(- E-D/kT), where s is the attempt frequency. Plotting 1n(tau(D)) vs. 1/T allows to determine the activation energy of the shallow defects, which is found to be 0.35 eV. (C) 2003 Elsevier Science B.V. All rights reserved
- …
