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Antibiotic resistance in bacteria is a current threat causing an increasing number of infections of difficult clinical management. While the overuse and misuse of antibiotics are investigated to reduce them, the need for alternatives to approaches is rising. Carbon-based materials shown recent moderate to high antibacterial properties and diamond, thanks to its superior mechanical, tribological, electrical, chemical and biological quality is a choice material to investigate for safe antibacterial films, coatings and particles. Here, the antibacterial properties of diamond films, nanodiamonds, DLC films and a comprehensive list of the composites developed from them are discussed along with a summary of the bacterial strains used and the most efficient composition and/or concentration discovered. In a later stage, the mechanisms of action and the parameters that are believed to influence them are discussed and finally, an overview of the biomedical and food industry applications is given.

The burgeoning multi-field applications of diamond concurrently bring up a foremost consideration associated with nitrogen. Ubiquitous nitrogen in both natural and artificial diamond in most cases ...

This article reports findings when using a molybdenum–tungsten (MoW) interlayer for diamond thin film deposition on steel substrates. The main focus was on the postdeposition stress within the diamond films and its impact on the coating’s tribological properties. The effect of MoW interlayer thickness and the effect of chemical vapor deposition (CVD) process temperature have been investigated. Nanocrystalline diamond films were deposited on steel substrates with MoW interlayers (thickness of 1.1, 4.5, and 8.3 µm) at two different deposition temperatures (650 and 875 °C). It was found that when depositing good quality diamond films on steel substrates, increasing interlayer thickness and decreasing CVD process temperature have to be jointly considered to obtain the optimal result. The diamond-coated steel substrates with the 8.3 µm interlayer deposited at the lower CVD processing temperature exhibited the least residual stress combined with excellent mechanical properties.

As we know that more effective synthesis of diamond combined with physical and chemical properties of hy- drogen termination in aqueous environment as well as device structure design can greatly facilitate the chemical and electrochemical applications of higher cost-performance diamond. For this purpose, the direct-current (DC) characteristics, surface reaction and reparation of a hydrogen-terminated DC arc jet plasma CVD polycrystalline diamond, which has a high cost-performance, were characterized byI-Vexperiments based on a FET-like structure device in multiple aqueous solutions. The variation trends of theI-Vproperties of device based on pH were similar in different aqueous solutions but could be affected by disparate ions (such as K+ions) or organic molecules (such as citric acid radicals or a benzene ring). Especially, owing to the founded replacement of hydrogen termination with hydroxyl (eOH), carboxyl radical (eCOOH) or carbon-oxygen bond (eCeOeCe) in mixed solution, i.e., KHP + H2SO4(and +NaOH) solutions, the resistance of the device was remarkably in- creased from 13.57 kΩto 95.78 kΩ. However, the raised resistance of surface reacted diamond (SRD) can be reduced prominently by repairing hydrogen termination through negative potential sweeps (NPS) at a low ne- gative potential (−1 to−3 V) if the SRD was introduced as an electrode in a strong inorganic acid. What's more, the NPS repaired device, which subsequently stored for four weeks, was more sensitive than the original hy- drogen plasma-treated diamond in aqueous solution environments. This repaired result was coming out of NPS re-formed CeH bonds with higher intensity. Thesefindings will be the references of failure and reparation of diamond hydrogen termination in aqueous environment.

The hydrogen plasma treatment of single crystal diamond was carried out by microwave plasma chemical vapor deposition equipment, and the normally-off hydrogen-terminated diamond field-effect transistors (FETs) with different gate lengths were prepared by atomic layer deposition (ALD) which deposited HfO2 as gate oxide. We systematically investigated the influence of hydrogen treatment duration, gate length, channel length and gate oxide material HfO2 on the hydrogen-terminated diamond FETs. Results show that the HfO2 gate oxide allows the fabricated FETs to exhibit a normally-off characteristic, which is advantageous for the practical application of power devices. The drain-source current, threshold voltage, subthreshold swing, and Ion/Ioff of the fabricated diamond FETs with gate length of 5 μm are 11 mA/mm, −2.9 V, 3 mS/mm, and 106, respectively. With the increase of the gate length (Lg = 5 μm, 20 μm, 50 μm), the drain current density, threshold voltage, and transconductance of the devices decrease, which is due to the higher channel resistance and inhomogeneity of the hydrogen surface termination. Keywords: H-diamond, MOSFET, high-k, Normally-off

To unfold the promise of diamond as an advanced technical material, single-crystal diamonds (SCDs) and polycrystalline diamonds (PCDs) were smoothed by high-precision three-dimensional movement dynamic friction polishing (3DM-DFP) to achieve the ultra-smooth surface with roughness

The synergetic effects of surface smoothing exhibited during the inductively coupled plasma reactive ion etching (ICP-RIE) of free-standing polycrystalline diamonds (PCDs) were investigated. Changing the assistive gas types generated variable surface oxidation states and chemical environments that resulted in different etching rates and surface morphologies. The main reaction bond mechanism (C–O) during ICP-RIE and the ratio of C–O–C/O–C=O associated with the existence of a uniform smooth surface with root mean square (RMS) roughness of 2.36 nm were observed. An optimal process for PCD smoothing at high etching rate (4.6 μm/min) was achieved as follows: 10% gas additions of CHF3in O2plasma at radio frequency power of 400 W. The further etched ultra-smooth surface with RMS roughness

The surface conductivity on the H-terminated diamond is still an interesting topic in the field of diamond electronics. Until now, the carrier mobility in the conductive channel has been limited to below 200cm2/Vs due to the various surface scattering mechanisms. In this paper, a high mobility conductive channel on the H-terminated diamond surface was reported. Firstly, the high quality diamond films were deposited on the commercial CVD diamond substrates. After polishing, the H-termination was obtained by hydrogen plasma treatment. The surface morphology of the H-terminated diamond was observed by atomic force microscope (AFM) and scanning electron microscope (SEM). The crystal quality on the diamond surface was characterized by Raman spectroscopy. The impurities in the crystals were tested by photoluminescence spectroscopy. The surface conductivity of H-terminated diamond was monitored comprehensively by Hall test. It can be found that the sheet resistance decreases much and the carrier mobility increases dramatically after the hydrogen plasma treatment and mechanical cleaning. The maximum mobility value is up to 365cm2/Vs with carrier density of 2.9 × 1012 cm−2, which is the highest value reported. Raman spectra of diamond surface show that a peak appears at 1121.4 cm−2 after the hydrogen plasma treatment, which corresponds to the nanocrystal diamond or carbon clusters of sp3 bonded material. The corresponding mobility enhancement mechanism on the H-terminated diamond surface was proposed.

The high-speed three-dimensional movement dynamic friction polishing (3DM-DFP) has been recognized as an efficient approach for ultra-smoothing single crystal diamond (SCD) surface. Continuing from the previous works focusing on the subsurface cleavage of diamond after 3DM-DFP, process optimization and surface reaction evolution mechanism as a fundamental building block is investigated, for the first time, for comprehensively understanding this fast-smoothing manner. By systematically adjusting the controlling factor, stronger load (0.3 MPa) and appropriate duration (0.5 h) as well as moderate sliding speed (in the range of 30 to 45 m s−1) is found to be able to obtain the smooth surface of SCD without uncontacted traces or break-surface cleavage. Subtle residual clues on SCD surface as a function of progressive DFP procedure indicate that Fe catalytic oxidation mainly produce Fe2O3 and partial intermediate oxides Fe1-yO. Meanwhile, the activated oxygen inserts sp3 C C bonds could form C O or C O and C-O-V (vacancy) at existing reactive surface sites. The (100) favorable C O bonds can be rebuilt if (100) surface is reformed, although the C O bonds associated with non-(100) rough surface would replace them during DFP procedure. The formed C O C and concomitant C-O-V as well as the oxidized graphite give rise to the increase of C O proportion, and finally the covered defective graphitic phase has an approximate C O/C O ratio of 1.25. All these are endowed potential value for future upgrading of DFP technique for diamond surface smoothing.

In this work, we study for the first time the influence of microwave power higher than 2.0 kW on bonded hydrogen impurity incorporation (form and content) in nanocrystalline diamond (NCD) films grown in a 5 kW MPCVD reactor. The NCD samples of different thickness ranging from 25 to 205 μm were obtained through a small amount of simultaneous nitrogen and oxygen addition into conventional about 4% methane in hydrogen reactants by keeping the other operating parameters in the same range as that typically used for the growth of large-grained polycrystalline diamond films. Specific hydrogen point defect in the NCD films is analyzed by using Fourier-transform infrared (FTIR) spectroscopy. When the other operating parameters are kept constant (mainly the input gases), with increasing of microwave power from 2.0 to 3.2 kW (the pressure was increased slightly in order to stabilize the plasma ball of the same size), which simultaneously resulting in the rise of substrate temperature more than 100 °C, the growth rate of the NCD films increases one order of magnitude from 0.3 to 3.0 μm/h, while the content of hydrogen impurity trapped in the NCD films during the growth process decreases with power. It has also been found that a new H related infrared absorption peak appears at 2834 cm-1 in the NCD films grown with a small amount of nitrogen and oxygen addition at power higher than 2.0 kW and increases with power higher than 3.0 kW. According to these new experimental results, the role of high microwave power on diamond growth and hydrogen impurity incorporation is discussed based on the standard growth mechanism of CVD diamonds using CH4/H2 gas mixtures. Our current experimental findings shed light into the incorporation mechanism of hydrogen impurity in NCD films grown with a small amount of nitrogen and oxygen addition into methane/hydrogen plasma.

In this work, we synthesized the hierarchical ZnO@C@NiO core-shell nanorods arrays (CSNAs) grown on a carbon cloth (CC) conductive substrate by a three-step method involving hydrothermal and chemical bath methods. The morphology and chemical structure of the hybrid nanoarrays were characterized in detail. The combination and formation mechanism was proposed. The conducting carbon layer between ZnO and NiO layers can efficiently enhance the electric conductivity of the integrated electrodes, and also protect the corrosion of ZnO in an alkaline solution. Compared with ZnO@NiO nanorods arrays (NAs), the NiO in CC/ZnO@C@NiO electrodes, which possess a unique multilevel core-shell nanostructure exhibits a higher specific capacity (677 C/g at 1.43 A/g) and an enhanced cycling stability (capacity remain 71% after 5000 cycles), on account of the protection of carbon layer derived from glucose. Additionally, a flexible all-solid-state supercapacitor is readily constructed by coating the PVA/KOH gel electrolyte between the ZnO@C@NiO CSNAs and commercial graphene. The energy density of this all-solid-state device decreases from 35.7 to 16.0 Wh/kg as the power density increases from 380.9 to 2704.2 W/kg with an excellent cycling stability (87.5% of the initial capacitance after 10000 cycles). Thereby, the CC/ ZnO@C@NiO CSNAs of three-dimensional hierarchical structure is promising electrode materials for flexible all-solid-state supercapacitors.

We investigate the impact of methane concentration in hydrogen plasma on the growth of large-grained polycrystalline diamond (PCD) films and its hydrogen impurity incorporation. The diamond samples were produced using high CH4 concentration in H2 plasma and high power up to 4350 W and high pressure (either 105 or 110 Torr) in a microwave plasma chemical vapor deposition (MPCVD) system. The thickness of the free-standing diamond films varies from 165 µm to 430 µm. Scanning electron microscopy (SEM), micro-Raman spectroscopy and Fourier-transform infrared (FTIR) spectroscopy were used to characterize the morphology, crystalline and optical quality of the diamond samples, and bonded hydrogen impurity in the diamond films, respectively. Under the conditions employed here, when methane concentration in the gas phase increases from 3.75% to 7.5%, the growth rate of the PCD films rises from around 3.0 µm/h up to 8.5 µm/h, and the optical active bonded hydrogen impurity content also increases more than one times, especially the two CVD diamond specific H related infrared absorption peaks at 2818 and 2828 cm−1 rise strongly; while the crystalline and optical quality of the MCD films decreases significantly, namely structural defects and non-diamond carbon phase content also increases a lot with increasing of methane concentration. Based on the results, the relationship between methane concentration and diamond growth rate and hydrogen impurity incorporation including the form of bonded infrared active hydrogen impurity in CVD diamonds was analyzed and discussed. The effect of substrate temperature on diamond growth was also briefly discussed. The experimental findings indicate that bonded hydrogen impurity in CVD diamond films mainly comes from methane rather than hydrogen in the gas source, and thus can provide experimental evidence for the theoretical study of the standard methyl species dominated growth mechanism of CVD diamonds grown with methane/hydrogen mixtures.

Carbon fiber reinforced plastics (CFRP) has demonstrated significant promise to improve the performance-to-weight ratio in automotive and aerospace sectors. Nevertheless, traditional thin-walled CFRP tubes still have several defects such as a high initial peak force with a relatively low mean crushing force and unstable collapse mode, which significantly reduce their performance when used as energy absorption devices. In this study, the full-diamond origami pattern was introduced to thin-walled CFRP tubes. The effect of the origami patterns on the energy absorption properties and collapse modes of these tubes subjected to quasi-static axial loads was investigated both experimentally and numerically. A comprehensive parametric study on the geometrical parameters and ply stacking sequence of pre-folded CFRP tubes was conducted. Moreover, a comparison between the pre-folded CFRP tube and the metal counterpart was performed, which shows that CFRP pre-folded tube can effectively reduce the initial peak forces while increasing the overall energy absorption capacity .

CuAlO2 has been examined as a potential luminescent material by substituting Eu for Al cations in the delafossite structure. CuAlO2:Eu3+ nanofibers have been prepared via electrospinning for the ease of mitigating synthesis requirements and for future optoelectronics and emerging applications. Single-phase CuAlO2 fibers could be obtained at a temperature of 1100 °C in air. The Eu was successfully doped in the delafossite structure and two strong emission bands at ~405 and 610 nm were observed in the photoluminescence spectra. These bands are due to the intrinsic near-band-edge transition of CuAlO2 and the f-f transition of the Eu3+ activator, respectively. Further electrical characterization indicated that these fibers exhibit semiconducting behavior and the introduction of Eu could act as band-edge modifiers, thus changing the thermal activation energies. In light of this study, CuAlO2:Eu3+ fibers with both strong photoluminescence and p-type conductivity could be produced by tailoring the rare earth doping concentrations.

Preliminary work is reported on 2-D and 3-D microstructures written directly with a Yb:YAG 1026 nm femtosecond (fs) laser on bulk chemical vapour deposition (CVD) single-crystalline diamond. Smooth graphitic lines and other structures were written on the surface of a CVD diamond sample with a thickness of 0.7mm under low laser fluences. This capability opens up the opportunity for making electronic devices and micro-electromechanical structures on diamond substrates. The fabrication process was optimised through testing a range of laser energies at a 100 kHz repetition rate with sub-500fs pulses. These graphitic lines and structures have been characterised using optical microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and atomic force microscopy. Using these analysis techniques, the formation of sp2 and sp3 bonds is explored and the ratio between sp2 and sp3 bonds after fs laser patterning is quantified. We present the early findings from this study and characterise the relationship between the graphitic line formation and the different fs laser exposure conditions.

Self-standing diamond films were grown by DC Arcjet plasma enhanced chemical vapor deposition (CVD). The feed gasses were Ar/H 2/CH 4, in which the flow ratio of CH 4 to H 2 (FCH4/FH2) was varied from 5% to 20%. Two distinct morphologies were observed by scanning electron microscope (SEM), i.e. the pineapple-like morphology and the cauliflower-like morphology. It was found that the morphologies of the as-grown films are strongly dependent on the flow ratio of CH 4 to H 2 in the feed gasses. High resolution transmission electron microscope (HRTEM) survey results revealed that there were nanocrystalline grains within the pineapple-like films whilst there were ultrananocrystalline grains within cauliflower-like films. X-ray diffraction (XRD) results suggested that (110) crystalline plane was the dominant surface in the cauliflower-like films whilst (100) crystalline plane was the dominant surface in the pineapple-like films. Raman spectroscopy revealed that nanostructured carbon features could be observed in both types of films. Plasma diagnosis was carried out in order to understand the morphology dependent growth mechanism. It could be concluded that the film morphology was strongly influenced by the density of gas phases. The gradient of C2 radical was found to be different along the growth direction under the different growth conditions.

Detonation nanodiamond (DND) is an attractive class of diamond material, which has a great potential to be used for a wide range of applications. In this paper, untreated DND was employed to perform hydrogen passivation process using microwave plasma enhanced chemical vapor deposition in order to investigate the influence of hydrogen-terminated surface on the DND's electrical properties. Impedance spectroscopy (IS) has been used to characterize the electrical properties of DND samples using a newly-developed measurement set-up. It is found that hydrogen-passivation process has increased the electrical conductivity of the DND by up to four orders of magnitude when compared with the untreated sample. An RC parallel equivalent circuit with a Warburg element has been proposed to model the DND's impedance characteristics.

Tailoring the electronic states of the dielectric oxide/diamond interface is critical to the development of next generation semiconductor devices like high-power high-frequency field-effect transistors. In this work, we investigate the electronic states of the TiO2/diamond 2 × 1-(100) interface by using first principles total energy calculations. Based on the calculation of the chemical potentials for the TiO2/diamond interface, it is observed that the hetero-interfaces with the C-OTi configuration or with two O vacancies are the most energetically favorable structures under the O-rich condition and under Ti-rich condition, respectively. The band structure and density of states of both TiO2/diamond and TiO2/H-diamond hetero-structures are calculated. It is revealed that there are considerable interface states at the interface of the anatase TiO2/diamond hetero-structure. By introducing H on the diamond surface, the interface states are significantly suppressed. A type-II alignment band structure is disclosed at the interface of the TiO2/diamond hetero-structure. The valence band offset increases from 0.6 to 1.7 eV when H is introduced at the TiO2/diamond interface.

In this work, we investigate the impact of minute amounts of pure nitrogen addition into conventional methane/hydrogen mixtures on the growth characteristics of nanocrystalline diamond (NCD) films by microwave plasma assisted chemical vapour deposition (MPCVD), under high power conditions. The NCD films were produced from a gas mixture of 4% CH4/H-2 with two different concentrations of N-2 additive and microwave power ranging from 3.0 kW to 4.0 kW, while keeping all the other operating parameters constant. The morphology, grain size, microstructure and texture of the resulting NCD films were characterized by using scanning electron microscope (SEM), micro-Raman spectroscopy and X-ray diffraction (XRD) techniques. N-2 addition was found to be the main parameter responsible for the formation and for the key change in the growth characteristics of NCD films under the employed conditions. Growth rates ranging from 5.4 mu m/h up to 9.6 mu m/h were achieved for the NCD films, much higher than those usually reported in the literature. The enhancing factor of nitrogen addition on NCD growth rate was obtained by comparing with the growth rate of large-grained microcrystalline diamond films grown without nitrogen and discussed by comparing with that of single crystal diamond through theoretical work in the literature. This achievement on NCD growth rate makes the technology interesting for industrial applications where fast coating of large substrates is highly desirable. (C) 2015 Elsevier Ltd. All rights reserved.

Temperature dependent DC and RF characteristics of p-type diamond metal?semiconductor field-effect transistors (MESFETs) on hydrogen-terminated surfaces are investigated. The device is thermally stable up to 100 ?C, because it does not deteriorate at all at higher temperatures. Temperature coefficients of transconductance (gm), drain conductance (gds), gate?source capacitance (Cgs), gate?drain capacitance (Cgd), cut-off frequency ( fT), and maximum drain current (Ids) were obtained from small-signal equivalent circuit analysis. The cut-off frequency ( fT) is almost totally independent of temperature. Intrinsic gm, gds, and Cgs decrease with increasing temperature. Cgd is almost totally independent of temperature. The threshold voltage shifts to the negative side with increasing temperature. We propose a band model of an Al-gate contact/H-terminated diamond to explain the temperature dependence of these components.

This paper reports the first studies on temperature dependent DC and RF characteristics of diamond metal-semiconductor field-effect transistors along with circular-transmission-line-method measurements on hydrogen-terminated diamond surface. In general, the device under study is thermally stable up to 100 °C as it does not deteriorate at higher temperatures with the cut-off frequency for current gain maintained at 8∼9 GHz. It is found that the sheet resistance is almost totally independent of temperature, contact resistance is negligible, and channel conductance underneath the gate decreases with increasing temperature. The threshold voltage for the device is found to shift to the negative side with increasing temperature. A small-signal equivalent circuit analysis reveals that both transconductance and gate-source capacitance decrease with increasing temperature, which results in the almost constant cut-off frequency for current gain. The experimental results can be explained by the fact that with increasing temperature, the band near the Al/H-terminated diamond surface bends upward more weakly, which leads to a decrease of buffer capacitance. At the same time the mobility decreases and the transconductance therefore decreases.

We report great improvement of RF output power for H-terminated diamond field-effect transistors (FETs). For the FET device with a gate width of 1 mm and a gate length of 0.4 μm, the maximum output power (Pout) is 1.26 W, the maximum power gain is 23.2 dB, and the power added efficiency (PAE) is 56.3%. The increase in the device temperature when output power is 0.84 W is only ∼0.6 °C. This is due to diamond having the highest thermal conductivity.

Dc current-voltage (I-V) measurement, Hall measurement, Deep-level transient-spectroscopy (DLTS), and flatband capacitance measurement have been used to investigate electrical activation energies in diamond. However, the deviations still exist in the published activation energies obtained by these methods. In this paper, we report the first measurement of impedance on free-standing diamond films from 0.1Hz to 10MHz up to 300°C. A wide range of CVD materials have been investigated, but here we concentrate on 'black' diamond grown by MWPECVD. The Cole-Cole (Z′ via Z″) plots are well fitted to a RC parallel circuit model and the equivalent Resistance and Capacitance for the diamond films have been estimated using the Zview curve fitting. The results show only one single semicircle response at each temperature measured. It was found that the resistance decreases from 62 MΩ at room temperature to 4 KΩ at 300°C, with an activation energy around 0.15eV. The equivalent capacitance is maintained at the level of 102 pF up to 300°C suggesting that the diamond grain boundaries are dominating the conduction. At 400°C, the impedance at low frequencies shows a linear tail, which can be explained that the AC polarization of diamond/Au interface occurs.

Diamond has shown great promise for the fabrication of high sensitivity, low dark current, fast and visible-blind deep UV photodetectors. In addition to careful choice of substrate material, defect passivation treatments applied to the diamond after growth have been found to considerably enhance the detector characteristics achieved. In this paper we report on the first purposefully designed 1-D CVD diamond imaging array for the detection of nanosecond 193 nm excimer laser pulses using this approach. It is shown to perform extremely well, giving less than 2% pixel-to-pixel variation in signal response, and is fast enough to avoid any sign of charge build up during prolonged operation.

In this paper, we report the first measurement of impedance on freestanding diamond films from 0.1 Hz to 10 MHz up to 300 °C. A wide range of CVD materials have been investigated, but here we concentrate on ‘black’ diamond grown by MWPECVD. The Cole–Cole (Z′ via Z″) plots are well fitted to a RC parallel circuit model and the equivalent resistance and capacitance for the diamond films have been estimated using the Zview curve fitting. The results show only one single semicircle response at each temperature measured. It was found that the resistance decreases from 62 MΩ at room temperature to 4 kΩ at 300 °C, with an activation energy around 0.51 eV. The equivalent capacitance is maintained at the level of 102 pF up to 300 °C, suggesting that the diamond grain boundaries are dominating the conduction. At 400 °C, the impedance at low frequencies shows a linear tail, which can be explained that the ac polarization of diamond/Au interface occurs.

Diamond grown by chemical vapour deposition (CVD) techniques has shown great promise for the fabrication of high sensitivity, low dark current, fast and visible-blind deep UV photodetectors. In addition to the careful choice of substrate material, defect passivation treatments applied to the diamond after growth have been found to considerably enhance the detector characteristics achieved. In this paper, we report on the first purposefully designed one-dimensional CVD diamond imaging array for the detection of nanosecond 193-nm excimer laser pulses using this approach. It is shown to perform extremely well, giving less than 2% pixel-to-pixel variation in signal response, and is fast enough to avoid any sign of charge build-up during prolonged operation.

Some color centers in diamond can serve as quantum bits which can be manipulated with microwave pulses and read out with laser, even at room temperature. However, the photon collection efficiency of bulk diamond is greatly reduced by refraction at the diamond/air interface. To address this issue, we fabricated arrays of diamond nanostructures, differing in both diameter and top end shape, with HSQ and Cr as the etching mask materials, aiming toward large scale fabrication of single-photon sources with enhanced collection efficiency made of nitrogen vacancy (NV) embedded diamond. With a mixture of O2 and CHF3 gas plasma, diamond pillars with diameters down to 45 nm were obtained. The top end shape evolution has been represented with a simple model. The tests of size dependent single-photon properties confirmed an improved single-photon collection efficiency enhancement, larger than tenfold, and a mild decrease of decoherence time with decreasing pillar diameter was observed as expected. These results provide useful information for future applications of nanostructured diamond as a single-photon source.

Diamond films were synthesized by a microwave plasma-enhanced chemical vapor deposition method using H 2 /CH 4 gas mixtures. A Fluke PM6306 RCL Meter was used to study the dielectric properties of the diamond films deposited. The dielectric dispersion measurement yielded the real and imaginary parts of impedance of diamond films in the form of a depressed semicircle in a complex plane. A Cole–Cole plot was observed at frequencies from 50 Hz to 1 MHz. The result was found to fit the theoretical resistor–capacitor parallel circuit model. The structure and quality of diamond films were analyzed by scanning electron microscopy, X-ray diffraction and Raman spectroscopy.

This work reports that the optimum diamond grain size can be controlled by adjusting the flow rate of Ar/H2 in the reaction chamber through orthogonal optimization. The dielectric properties of the diamond films were investigated using an RCL (resistance-capacitance-inductance) meter. It was found that (i) the dominating factors in controlling the grain size are in the following order: Ar/H2 gas ratio, gas total pressure, plasma power and substrate temperature; (ii) increasing the Ar gas fraction reduces the grain size of synthetic diamond films; and (iii) reducing the grain size lowers the dielectric constant. The grain size effect on the dielectric behaviour can be explained by the change of the crystal field caused by surface bond contraction of the nanosized particles.

Dielectric properties of diamond films grown by microwave plasma enhanced chemical vapor deposition (MPECVD) on tungsten carbide (WC) substrates from Ar–H2–CH4 gas mixture were studied using an impedance analyzer. The dielectric dispersion is observed in the frequency range from 100 Hz to 15 MHz. The real and imaginary parts of impedance of diamond films deposited at the different Ar ratios of the reactive gases consist of a semicircle in the complex plane and can be fitted to the theoretical circuit model. The frequency dependence of the imaginary part of the impedance implies different time constants τ, which are closely related to the diamond film’s AC resistivity ρ and dielectric constant e. The values of the resistivity of diamond films increase with increasing Ar gas ratio, which is an indication of lower graphite content of the samples with higher Ar gas ratio. Raman spectroscopy also confirmed the results. It is found that Ar ions in a microwave plasma possess the ability to remove the unexpected non-diamond phases and improve the diamond quality.

Measurements using TGA, SEM, Raman spectroscopy and XRD reveal that diamond oxidizes at around 750 K through oxygen impinging into the densely packed {111} planes throughout the course of the reaction. It is also found that diamond graphitizes under vacuum at about 1100 K without orientation preference, which also occurs under an Ar inert gas environment. The intriguing oxidation behaviour of diamond indicates that oxidation occurs with selectivity of the bonding environment. It is explained that the diamond {111} plane is more favourable than the {220} surface for the oxide tetrahedron formation, and that the oxide bond formation produces loosely bonded dipoles on the surface that are eroded away during the process of oxidation.

LCR measurements have been performed on type IIa and type Ib single crystal diamonds, in an attempt to identify any differences in their dielectric characteristics. It is found that the type IIa diamond, which contains little nitrogen, behaves as an ideal insulator, with the dielectric loss appearing to be frequency independent at low temperatures, whilst assuming a frequency dependence at high temperatures. In contrast, the type Ib diamond samples exhibited a dielectric loss peak in the temperature-dependent data, from which a thermal activated process with an Ea of 1.67 eV can be determined using a simple Debye law relationship. However, the data suggests that a dielectric relaxation constant (nitrogen-induced dipole) of 1017 Hz is evident in the Ib system, which is much higher than that predicted by the Debye model, as such it is unlikely due to the dipole moment itself. A possible physical mechanism responsible for this phenomena is simply the ionization of a nitrogen centre with a defect level lying at 1.7 eV below the conduction band.

A high-dielectric constant (high-k) TiOx thin layer was fabricated on hydrogen-terminated diamond (H-diamond) surface by low temperature oxidation of a thin titanium layer in ambient air. The metallic titanium layer was deposited by sputter deposition. The dielectric constant of the resultant TiOx was calculated to be around 12. The capacitance density of the metal-oxide-semiconductor (MOS) based on the TiOx/H-diamond was as high as 0.75 µF/cm2 contributed from the high-k value and the very thin thickness of the TiOx layer. The leakage current was lower than 10-13 A at reverse biases and 10-7A at the forward bias of -2 V. The MOS field-effect transistor based on the high-k TiOx/H-diamond was demonstrated. The utilization of the high-k TiOx with a very thin thickness brought forward the features of an ideally low subthreshold swing slope of 65 mV per decade and improved drain current at low gate voltages. The advantages of the utilization high-k dielectric for diamond MOSFETs are anticipated.

The dielectric behavior of nanostructured diamond films has been investigated by using an impedance analyzer up to 500 °C. Impedance data are presented in the form of the Cole–Cole plot. It is found that: (i) the resistivity contributed both from bulk grain interior and grain boundary decreases with increasing temperature; (ii) above 250 °C, the impurities at grain boundaries are thermally activated, and thus contribute to the dielectric relaxation; and (iii) the electrical conductivity of diamond films follows an Arrhenius law with an activation energy transition from 0.13 to 0.67 eV at 250 °C. Similar activation energy is found for the Arrhenius plot of relaxation frequencies from 0.14 to 0.73 eV. The dielectric transition is explained as the change of crystal field caused by the thermal expansion or by surface bond contraction of nanosized particles.

Nanometer-scale diamonds formed using a detonation process are an interesting class of diamond materials. Commercially supplied material is highly aggregated with ~ 5 nm diamond crystals forming particles with micron sizes. Previous models have suggested that nondiamond carbon is incorporated between the crystals, which would reduce the electrical and chemical usefulness of this form of diamond. However, using impedance spectroscopy we have shown that at temperatures below 350?°C the form of detonation nanodiamond being studied is a near to ideal dielectric, implying a full sp3 form. At temperatures above this the surfaces of the diamond crystals may support some nondiamond carbon

Nanocrystalline diamond (NCD) has been grown on oxide coated silicon wafers by microwave plasma assisted chemical vapour deposition using a novel seeding technique followed by optimised growth conditions, and leads to a highly-dense form of this material with grain sizes around 100nm for films approximately 1.5 microns thick. The electrical properties of these films have been investigated using Impedance Spectroscopy, which enables the contributions from sources characterised by differing capacitances, such as grain boundaries and grain interiors, to be isolated. After an initial acid clean the electrical properties of the film are not stable, and both grain boundaries and grains themselves contribute to the frequency dependant impedance values recorded. However, following mild oxidation grain boundary conduction is completely removed and the films become highly resistive (>1013 ohm/sq). This is most unusual, as conduction through NCD material is more normally dominated by grain boundary effects. Interestingly, the AC properties of these films are also excellent with a dielectric loss value (tan δ) as low as 0.002 for frequencies up to 10MHz. The dielectric properties of these NCD films are therefore as good as high quality free-standing (large grain) polycrystalline diamond films, and not too dissimilar to single crystal diamond, and are therefore ideally suited to future ‘silicon-on-diamond’ applications.

Impedance spectroscopy (IS) analysis is carried out to investigate the electrical properties of the metal-oxide-semiconductor (MOS) structure fabricated on hydrogen-terminated single crystal diamond. The low-temperature atomic layer deposition Al2O3 is employed as the insulator in the MOS structure. By numerically analysing the impedance of the MOS structure at various biases, the equivalent circuit of the diamond MOS structure is derived, which is composed of two parallel capacitive and resistance pairs, in series connection with both resistance and inductance. The two capacitive components are resulted from the insulator, the hydrogenated-diamond surface, and their interface. The physical parameters such as the insulator capacitance are obtained, circumventing the series resistance and inductance effect. By comparing the IS and capacitance-voltage measurements, the frequency dispersion of the capacitance-voltage characteristic is discussed.

This paper reported a three-dimensional microfluidic channel structure, which was fabricated by Yb:YAG 1026?nm femtosecond laser irradiation on a single-crystalline diamond substrate. The femtosecond laser irradiation energy level was optimized at 100?kHz repetition rate with a sub-500 femtosecond pulse duration. The morphology and topography of the microfluidic channel were characterized by a scanning electron microscope and an atomic force microscope. Raman spectroscopy indicated that the irradiated area was covered by graphitic materials. By comparing the cross-sectional profiles before/after removing the graphitic materials, it could be deduced that the microfluidic channel has an average depth of ~410?nm with periodical ripples perpendicular to the irradiation direction. This work proves the feasibility of using ultra-fast laser inscription technology to fabricate microfluidic channels on biocompatible diamond substrates, which offers a great potential for biomedical sensing applications.

Nanocrystalline diamond (NCD) has been grown using a nanodiamond seeding technique, leading to a dense form of this material, with grain sizes around 100 nm. The electrical properties of both intrinsic and lightly boron-doped NCD have been investigated using impedance spectroscopy and Hall effect measurements. For intrinsic material, both grain boundaries and grains themselves initially contribute to the frequency dependant impedance values recorded. However, boundary conduction can be removed and the films become highly resistive. Interestingly, the ac properties of these films are also excellent with a dielectric loss value ∼0.004 for frequencies up to 10 MHz. The dielectric properties of these NCD films are therefore as good as high quality large grain polycrystalline diamond films. In the case of boron-doped material, p-type material with good carrier mobility values (10–50 cm2/V s) can be produced at carrier concentrations around 1017 cm−3.

Impedance spectroscopy has been used to investigate conductivity within boron-doped diamond in an intrinsic/delta-doped/intrinsic (i-d-i) multilayer structure. For a 5 nm thick delta layer, three conduction pathways are observed, which can be assigned to transport within the delta layer and to two differing conduction paths in the i-layers adjoining the delta layer. For transport in the i-layers, thermal trapping/detrapping processes can be observed, and only at the highest temperature investigated (673 K) can transport due to a single conduction process be seen. Impedance spectroscopy is an ideal nondestructive tool for investigating the electrical characteristics of complex diamond structures.

The use of diamond as a semiconductor for the realization of transistor structures, which can operate at high temperatures (>700 K), is of increasing interest. In terms of bipolar devices, the growth of n-type phosphorus doped diamond is more efficient on the (111) growth plane; p-type boron-doped diamond growth has been most usually grown in the (100) direction and, hence, this study into the electronic properties, at high temperatures, of boron-doped diamond (111) homoepitaxial layers. It is shown that highly doped layers (hole carrier concentrations as high as 2×1020 cm-3) can be produced without promoting the onset of (unwanted) hopping conduction. The persistence of valance-band conduction in these films enables relatively high mobility values to be measured ( ~ 20 cm2/V?s) and, intriguingly, these values are not significantly reduced at high temperatures. The layers also display very low compensation levels, a fact that may explain the high mobility values since compensation is required for hopping conduction. The results are discussed in terms of the potential of these types of layers for use with high temperature compatible diamond transistors.

An important development in the field of diamond electronics has been the production of n-type electrical characteristics following homoepitaxial diamond growth on (111) diamond in the presence of phosphorus-containing gases. Several studies have reported that a phosphorus donor level forms with an activation energy in the range of 0.43–0.6eV; the ground state for the donor level is considered to be at 0.6eV. Little is currently known about other electrically active defects that may be produced alongside the donor state when phosphorus is introduced. In this paper we report upon the use of impedance spectroscopy, which can isolate the differing components that contribute to the overall conductivity of the film. In Cole-Cole plots, two semicircular responses are observed for all temperatures above 75°C; a single semicircle being seen at temperatures below this. The results suggest the presence of two conduction paths with activation energies of 0.53 and 0.197eV. The former can be attributed to the phosphor...

Great improvement in the output power density of diamond FETs on a diamond homoepitaxial layer grown using a high-purity source gas is reported. For a device with a gate length of 0.1 µm and gate width of 100 µm, at 1 GHz, maximum output power density of 2.1 W/mm, maximum power gain of 10.9 dB, and power added efficiency of 31.8% were obtained.

Nanocrystalline diamond films were synthesized by microwave plasma-enhanced chemical vapor deposition using Ar/H2/CH4 gas mixtures. A Fluke PM6306 RCL meter was used to study the electrical impedance of these diamond films in the frequency range 50 Hz to 1 MHz. The impedance dispersion measurement yields the real and imaginary parts in the form of a Cole-Cole plot in the complex plane. A single semicircular response of the impedance of nanocrystalline diamond films was observed at temperatures below 250 °C, with a second semicircular response appearing at low frequencies at temperatures above this. The semicircular responses were found to fit a double resistor-capacitor parallel circuit model. Physical mechanisms likely to be responsible for these observations are discussed in this paper.

The needle-like surface morphology evolution in oxygen plasma in combination with a secondary gas (Cl2, CHF3 or CF4) by inductively coupled plasma reactive ion etching (ICP-RIE) on a free-standing polycrystalline diamond was investigated. The addition of CF4 can produce trans-polyacetylene (t-PA), which is similar to the result when the pure O2 etching takes place, and generate compact needle-tip particles. However, the t-PA disappears with the introduction of Cl or H ions. The optimised etching parameters for the needle-like structure formation are as following: Cl2/O2 ratio 20% and RF-power (RFP) 100 W, where more compact and even nano-needles are realised with an average etching rate of 2 μm/min. The Cl2/O2 plasma etching results indicate that the time-dependent etching mechanism of diamond nano-needles results from (1 1 1) crystal plane selective etching and preferential graphitisation at the twin-plane boundary and dislocation area.

The ultra-smooth surface and hydrophobic nitrogen-incorporated ultra-nano-crystalline diamond (N-UNCD) was directly synthesized by equilibrating the etching effect of OH radical and growth promotion of CN and CH in the 5% CH4 added H2 plasma environment with additional feeding of constant 0.16% O2 and from 0.3% to 3.3% N2 contents. The initially decreasing and then increasing trend of surface roughness, i.e., from as-grown appearance with pits to smooth and then to worm-like surface, was resulted from the offset and even suppressive effect on OH etched holes by the faster growth rate that under the help of more N2 promoted chemical groups of CH and CN. In addition, chemical composition, i.e., the large amount of sp2 phases (sp2/sp3 ratio up to 1.399) and H termination of N-UNCD surface (proportion was 75.54 ± 3.8%), played an another enhancing function for repelling water (contact angle from 81.3° to 93.8°) although the surface roughness decreased to smoothest of 1.36 nm in Root-Mean-Square (RMS) in the presence of N2 addition from 0.3% to 1%. However, continuing adding N2 to 3.3%, the formed surface (RMS 8.98 nm) with worm-like ultra-nano diamond crystallites together with higher H reconstructed sp2 contents (sp2/sp3 ratio rose to 1.478) further boosted the hydrophobicity, at which the contact angle was finally increased to 110.2°. Therefore, in C-H-O-N gas system, ultra-smooth and uniform N-UNCD surface with excellent hydrophobicity can be obtained by a one-step method without any post-treatment.

Diamond thin films of about 10 μm thickness have been successfully deposited on silicon (001) substrates by means of microwave plasma-enhanced CVD (MPECVD) system. Preliminary results indicate that a two-stage growth method is necessary for high nuclei density and crystal quality. Optimum processing conditions were obtained by orthogonal experiments, which predict that the total pressure is the most significant parameter. Diamond films were characterized morphologically and structurally by scanning electron microscopy, Raman spectroscopy and X-ray diffraction, etc.

A diamond based insulated gate bipolar transistor is incorporated into a two-dimensional device simulator (MEDICI) to examine the current gain (β) and potential distribution across the device. Initially, work has focused on an important component of IGBT structure, the PNP bipolar transistor, which has been simulated and is reported upon in this paper. Empirical parameters for emitter and collector regions were used. Various carrier concentrations for base region were used to optimize the simulation. It was found that decreasing the thickness of base region leads to an increase in current gain. A buffer layer is needed to prevent the punch-through at low carrier concentration in the base region. Various approaches of increasing the current gain are also discussed in this paper.