In this study, we report originally the excellent electrochemical performance of a micro-supercapacitor based on diamond-coated silicon nanowire (SiNW) electrodes using an aqueous electrolyte (0.1M LiClO4). The deposition of a nanometric boron-doped diamond coating on SiNWs allowed the enlargement of the electrochemical window up to 3V maintaining an extraordinary capacitive electrochemical response due to its high overvoltage. Thereby, the device exhibited an areal capacitance of 0.4 mF cm-2, a high power density of 50 mW cm-2 as well as an outstanding cycling stability after 2·106 galvanostatic charge-discharge cycles at a high current density of 10mA cm-2. In addition, an ultra-fast charge-discharge rate was determined to be 1.5ms, demonstrating the supercapacitor's enormous ability to deliver high power values at very rapid pulse times (Pmax: 321 mW cm-2). These results also evidence the potential of diamond coating to overcome the main drawbacks of silicon (e.g. rapid silicon oxidation due to presence of water) to be employed in aqueous electrolyte supercapacitors. Consequently, the role of diamond paves the way to high performance SiNW-based micro-supercapacitor development at large electrochemical windows in aqueous electrolytes, which are at present limited to 1V.

The silicon vacancy center (SiV) in diamond is promising for future quantum applications due to its unique properties like narrowband emission in the near infrared regime at 738 nm and photostability at room temperature. In this paper we investigate the photoluminescence and electroluminescence properties of SiV centers incorporated into the intrinsic-layer of single crystalline diamond p–i–n junction diodes via in-situ doping during CVD-growth. The experiments reveal electrical excitation of the SiV emission by applying forward currents. The electroluminescence and photoluminescence properties are compared and discussed.

For a long time sp2 carbon has been the dominating material for supercapacitor applications. In this paper a new concept of using boron-doped diamond for supercapacitors is proposed. Diamond surface enlargement is realized via bottom-up template-growth. In this method, silicon nanowire electrodes are coated with a thin (~100nm) layer of nanocrystalline diamond (NCD) by microwave enhanced chemical vapor deposition (MWCVD). The quality of overgrowth is characterized by high resolution scanning electron microscopy which reveals a homogeneous coverage of diamond on Si nanowire surface. To enhance the potential window to 4V, a room temperature ionic liquid is used as electrolyte. The dilution of the ionic liquid is investigated in terms of conductivity and specific capacitance. The capacitance as measured via cyclic voltammetry reaches 105μF/cm2. An energy density of 84μJ/cm2 and a high power density of 0.94mW/cm2 are obtained in combination with good stability of over 10,000charging/dischargingcycles.

Silicon nanowires (SiNWs) were successfully coated by uniform, adherent and homogenous ultra-thin crystalline diamond films through microwave enhanced chemical vapor deposition (MWCVD). The as-grown functionalized nanowires were employed as electrodes in a symmetric micro-supercapacitor (MSC) using a protic ionic liquid electrolyte [triethylammonium bis(trifluoromethylsulfonyl)imide; Et3NH TFSI]. The electrochemical performance of the device delivered a specific capacitance of 1.5mFcm−2 and a power density of 25mWcm−2 using an enlarged cell voltage of 4V. Furthermore, a remarkable cycling stability was evaluated after 1·106galvanostatic cycles at a high current density of 10mAcm−2 with an excellent capacitive behavior. These results confirm that diamond-coated SiNW micro-supercapacitors exhibit very promising performances dealing with MSCs based on CVD-grown SiNWs.

Charge-states modulation of nitrogen-vacancy (NV) centers incorporated into single crystal diamond films attracts increasing attention for solid-state qubits applications. Here, we discuss the electro- and photoluminescence emission properties of NV centers incorporated by gas phase nitrogen delta-doping of the intrinsic diamond layer of a positive-intrinsic-negative (PIN) junction diode. The experiments show that the charge state of NV centers can be intentionally controlled by applying well-defined external bias voltages. It can be switched from the negatively charged state NV− to the neutral charged state NV0 when a strong forward bias potential is applied. This can be switched back by application of reverse potentials. These results will be discussed assuming basic electronic properties of diamond PIN diodes, including the variation of spectral properties as well as the dynamics of charge state transitions.

Highly sensitive infrared detectors have to be protected against the impact of intense infrared radiation, for example from lasers or sun light. Conventional laser safety filters work only in a limited wavelength range, electro-optical shutters reduce the transmission significantly and micro-opto mechanical systems (MOEMS) show problems with picture quality due to difficulties in aligning precisely all mirrors. As in many applications the IR illumination originates from a local spot in the image field, filters consisting of many segments that can be switched individually from "transparent" to "opaque" are therefore desirable. Individual switching requires a sophisticated combination of infrared materials and an optimized geometrical design, to achieve fast switching in combination with negligible crosstalk between neighbouring segments. We have realized fast switchable matrix-addressable infrared filters in the optical range between 2 and 12 μm based on complex composite devices. Vanadium dioxide (VO2) was used as a thermochromic layer, diamond as a heat-conducting layer, and chalcogenide glass as a heat insulating submount. Finite element calculations accompanied by an extensive series of experiments showed, that switching times less than lms can be achieved if all materials are properly designed, prepared and matched together. A first prototype with a 10×10 pixel array has been realized at Fraunhofer IAF and successfully tested. The measurements confirmed the numerical simulations and proved the great potential of these devices.

To counteract plasma instabilities like Neoclassical Tearing Modes (NTM-modes) in nuclear fusion reactors (JET, ITER, DEMO) high power microwaves are used for the Electron Cyclotron Resonance Heating (ECRH) and for the plasma current drive (CD). The foreseen power level for ITER (Cadarache, France) is P tot = 24 MW at f = 170 GHz. Each transmission line is designed for a maximum of 2 MW power. The vacuum and tritium barrier to the ITER vacuum vessel is realized by a CVD diamond disk window assembly. Diamond has an extremely high thermal conductivity of about k = 2100 W/Km and a very low loss tangent of tan δ < 10 -5 for this frequency and shows therefore a very small microwave absorption. The normalized absorbed power A=P abs /P 0 can be calculated as A = (f/c) • π • (1+ε r ‘) • tan δ • t (with the rule of thumb estimate: (f/c)=0.5 mm -1 ; π • (1+ε r ‘) = 20; tan δ =10 -5 ; A=10 -4 • t [mm]); i.e. each t = 1 mm thickness of diamond absorbs P abs = 100 W of P o = 1 MW microwave power transmitted through the CVD diamond window with an effective tanδ of 10 -5 .

All-diamond ultra-microelectrode arrays (UMEAs) were fabricated using standard photolithography processes. The array consists of typically 45 ultra-microelectrodes with a diameter of 10 mu m and with a center-to-center spacing of 60 mu m. The quasi-reference and counter electrodes are made from conductive diamond and integrated on a 5 x 5 mm(2) chip. The arrays with different surface terminations were characterized using cyclic voltammetry and the redox couple of Fe(CN)(6)(3-/4-) as probes. A peak-shaped voltammogram was detected on electrochemically hydrogen-terminated surface if scanned with a slow scan rate (e.g. 20 mV/s), resulting in a higher ratio of the Faradaic current (signal) to capacitive charging current (background current). A sensitive and reproducible detection of hydrogen peroxide was achieved by using the UMEA. The net-charge for the oxidation of hydrogen peroxide at 0.4 V (vs. C) is linear with the concentration of hydrogen peroxide in the range of 6.5-650 mu M. The detection limit is 2.0 mu M, which is 100 times better than that obtained on the macro-sized boron-doped diamond electrode. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This study presents diamond film growth, preparation, and characterization using microwave plasma-assisted chemical vapor deposition for gyrotron window materials intended for fusion plasma ignition in magnetic and inertial confinement fusion such as ITER. A surface polishing technique is utilized to polish the films to a mirror grade surface finish. A fine-grained film surface morphology is realized to avoid any deformation caused by shock wave fronts during compression.

Tribological components made from CVD diamond are commonly used for protection against abrasion in rough environments. Such components can be used e.g. in textile industry as thread guiding devices provided that surface roughness and resultant friction are low. In this work we report on the fabrication of CVD diamond components of non-planar shape. These devices were fabricated in a negative replication approach on mechanically structured substrates. Using this technique cylindrically shaped diamond devices with smooth surfaces were produced by using the nucleation side of the diamond layers as the exposed surface, thus making subsequent polishing steps unnecessary. Applying an improved two-step nucleation method further reduced surface roughness. Sensing elements in the form of resistors made from boron-doped CVD diamond were integrated into the device surface. Device performance was characterized with respect to the temperature dependence of the resistors and the suitability as abrasion sensor.

Conventional loudspeaker membranes made of metal or synthetic material such as fabric, ceramics or plastics suffer from nonlinearities and cone breakup modes at fairly low audio frequencies. Due to their mass, inertia and limited mechanical stability the speaker membranes made of conventional materials cannot follow the high frequency excitation of the actuating voice-coil. Low sound velocity causes phase shift and sound pressure losses due to interference of adjacent parts of the membrane at audible frequencies. Therefore, loudspeaker engineers are searching for lightweight but extremely rigid materials to develop speaker membranes whose cone resonances are well above the audible range. With its extreme hardness, paired with low density and high velocity of sound, diamond is a highly promising candidate for such applications. We report on the realization of dome shaped CVD diamond membranes by deposition on curved silicon substrates. Domes with diameters between 20 and 65 mm and with a thickness ranging from 50 to 120 μm were prepared. After deposition, the substrate is dissolved and the rim of the diamond dome is cut by laser scribing. Free standing diamond membranes are mounted onto dynamic voice coils and integrated into tweeter and/or midrange driver chassis. Extended tests and optimisations led to loudspeaker systems that show a second and third harmonic distortion behaviour in the important frequency range between 3 to 10 kHz that is reduced by 40% in comparison to already excellent established values obtained with sapphire membranes. Cone resonance frequencies of CVD diamond membranes are increased by a factor of two, as predicted by simulations.

The infrared absorption of CVD diamond at a wavelength of 10.6 mu m was measured as a function of temperature between 20 and 500 degrees C. CVD diamond of different structural quality was investigated. Optical spectroscopy and infrared Raman scattering were used for the structural characterization. Laser calorimetry was applied to measure the IR absorption at elevated temperatures. For these measurements, CVD diamond devices with integrated heater and temperature sensor were prepared. The optical absorption at a given temperature was determined by comparing the temperature rise induced by CO2 laser irradiation with the equivalent electrically induced temperature rise.Samples with a room temperature absorption coefficient of alpha=0.096 cm(-1) and alpha=0.85 cm(-1) were investigated. Despite this large difference, the absolute increase of the absorption coefficient with increasing temperature was found to be similar for the two samples. It increased by a value of about 0.5 cm(-1) between 0 and 500 degrees C. (c) 2005 Elsevier B.V. All rights reserved.

To investigate the in plane thermal diffusivity of chemical vapor deposited diamond layers, two new techniques were developed based on electrically induced converging and linear thermal waves. With these methods, free-standing, laser-cut diamond samples, 100 μm or larger in thickness can be analyzed. Laser cutting leaves a graphitic surface layer along the cutting edge. Therefore, a short high voltage pulse, applied at the graphitic rim resistor, is used to generate a thermal transient. The propagation of the wave is measured optically either in the center of the circular disk or at one side of a bar shaped sample. Both techniques require only very little sample preparation. They are shown to be simple, accurate, and independent of sample thickness and induced energy. In order to analyze the experimental data we present both an analytical model and a numerical simulation.

The low pressure deposition of polycrystalline diamond and the preparation of diamond windows at the Fraunhofer-IAF is reported. Using microwave plasma CVD, large area (2-6' diameter) diamond wafers with thicknesses of up to 2 mm have been grown. The deposition is carried out in a novel microwave plasma system which uses an ellipsoid cavity to generate very intense, spatially extended plasmas. Several of these plasma reactors with 6 to 60 kW microwave power are presnetly used at the IAF. The diamond wafers are ground and polished and laser- cut to the desired dimensions. To assess the optical and thermal properties, the residual absorption in the 10 micrometer range is determined by CO2 laser calorimetry, and temperature dependent and spatially resolved measurements of the thermal conductivity are performed. In addition, thermal expansion and refractive index measurements as a function of temperature are reported. Using high-purity process gases and optimized CVD conditions, diamond windows with a residual absorption at 10.6 micrometer below 0.1 cm-1 and a thermal conductivity over 20 W/cmK have been realized. In addition, low dielectric losses of tan(delta) equals 0.6 X 10-4 at 140 GHz have been measured.

Polycrystalline diamond films have been grown by microwave assisted chemical vapor deposition from methane/hydrogen gas mixtures. The addition of small amounts of nitrogen with concentrations below 50 ppm to the process gas was found to drastically increase the deposition rate depending on the microwave power. At 4.2 kW microwave power a five times higher growth rate compared to nitrogen-free depositions was achieved. The optical transmission and thermal conductivity have been measured. The incorporation of small amounts of nitrogen does not degrade the infrared transmission of the samples; the thermal conductivity measured at room temperature decreased only slightly from 20.5 to 18 W/(cm K).

The infrared Raman spectrum of chemical vapor deposited (CVD) diamond films has been correlated with the in-plane thermal conductivity of the films. The scattering strength of the 1332 cm−1 zone-center phonon line of diamond, measured relative to the intensity of the nondiamond carbon phase, was found to increase strongly with increasing thermal conductivity. A good correlation between these two properties was found even for the highest quality CVD diamond films with peak thermal conductivities up to 54 W/cm K. The dependence of the peak thermal conductivity on the intensity of the 1332 cm−1 phonon line normalized to the scattering strength of the nondiamond carbon phase can be described by a power law with an exponent of 0.5.

We describe a high-precision measuring system for the determination of the in-plane thermal conductivity of CVD diamond samples al temperatures between 77 and 900 K. The thermal conductivity is determined by establishing a well-defined steady-state heat flux through a diamond bar and by measuring the temperature gradient, using an array of eight thermocouples. The heat is supplied by a meander-shaped microheater located al one edge of the bar. By measuring the temperature distribution without heat production in the microheater, radiation losses are detected and corrected for. At room temperature the in-plane thermal conductivity of polished CVD diamond samples is determined with an accuracy better than 1%.A variety of CVD diamond samples deposited by microwave plasma CVD under different growth conditions was investigated. Some of the samples showed extraordinarily high thermal conductivities of up to 54 W cm(-1) K-1 at -150 degrees C. To our knowledge, this is the highest value reported so far for CVD diamond. The temperature dependence of the thermal conductivity is well described by Callaway's theory. By fitting theoretical curves to the experimental values, information about defect densities and grain boundaries is derived.

Considerable progress in the development of CVD techniques for the deposition of diamond films has been achieved recently. Despite the polycrystalline structure of this material, its physical properties are now approaching those of natural type IIa diamond crystals. This paper will give some insight into the current status of CVD diamond thechnology with emphasis on optical and thermal applications. The role of process gas impurities like nitrogen will be discussed.

The photothermal displacement technique at transient thermal gratings and photothermal microscopy, both providing a spatial resolution on a micrometer scale, were used to investigate the thermal properties of crystallites and regions located between crystallites of diamond grown by microwave plasma chemical vapour deposition. The thermal properties are related to the structural properties by micro-Raman/photoluminescence spectroscopy and infrared spectroscopy. In the vicinity of a highly defective region located between crystallites, which exhibits a preferential incorporation of non-diamond carbon, silicon-vacancy complexes and hydrogen, a reduction of the thermal diffusivity by about 35% was observed. Depending upon whether this region is a grain boundary or a defect-filled microcrack, the decrease in the thermal diffusivity is caused by enhanced phonon scattering from these defects accumulated at the boundary or by a vanishing transmission probability of phonons across the crack. High thermal conductivities between 1500 W m(-1)K(-1) and 1700 W m(-1)K(-1) were determined within the crystallites at room temperature.

Isotopically marked 13C diamond films were deposited by microwave-plasma-assisted chemical vapour deposition homoepitaxially on {100} and {111} natural diamond substrates. The deposition was performed at 0.5 and 1.5 vol.% 13CH4 diluted in H2. In order to study the influence of nitrogen on diamond growth, N2 was admixed with the process gas for some samples. The thickness of the homoepitaxial films was determined by Rutherford backscattering, the crystalline quality by ion channelling measurements and hydrogen concentrations by nuclear reaction analysis. The defect density and growth rate of {111} films were found to increase at the higher methane concentration. The growth rate of {100} films also increased, but the defect density decreased at the higher methane concentration. The admixture of nitrogen with the process gas yielded about 25% higher growth rates and better crystalline qualities.