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A high-temperature procedure to hydrogenate diamond films using molecular hydrogen at atmospheric pressure was explored. Undoped and doped chemical vapour deposited (CVD) polycrystalline diamond films were treated according to our annealing method using a H2 gas flow down to ∼50 ml/min (STP) at ∼850 °C. The films were extensively evaluated by surface wettability, electron affinity, elemental composition, photoconductivity, and redox studies. In addition, electrografting experiments were performed. The surface characteristics as well as the optoelectronic and redox properties of the annealed films were found to be very similar to hydrogen plasma-treated films. Moreover, the presented method is compatible with atmospheric pressure and provides a low-cost solution to hydrogenate CVD diamond, which makes it interesting for industrial applications. The plausible mechanism for the hydrogen termination of CVD diamond films is based on the formation of surface carbon dangling bonds and carbon-carbon unsaturated bonds at the applied tempera-ture, which react with molecular hydrogen to produce a hydrogen-terminated surface. [ABSTRACT FROM AUTHOR]

Time-of-Flight (ToF) experiments were carried out to study the electrical transport and charge trapping properties of oxidized freestanding single crystalline (100) CVD diamond crystals. It is shown that the diamond surface and properties of the electrical contacts are of extreme importance, influencing measured charge carrier mobility values. While sputtered Al contacts yield textbook ToF spectra and electron mobilities μe exceeding 1860 cm2/Vs, thermally deposited contacts suffer from enhanced trapping. We propose a model in which the observed polarization effects can be explained by charge transfer to oxygen-related surface states, which interact with surface adsorbates, according to the well-known transfer-doping model. [ABSTRACT FROM AUTHOR]

The systematics of the suppression of superconductivity with increasing magnetic field in boron-doped nanocrystalline chemical vapor deposition diamond is studied in a broad temperature range. At the temperature of TS0 which is above the critical temperature, a plateau is observed in the resistivity versus temperature curve ρ(T) taken at zero magnetic field. When a magnetic field of B=BSN(N=1,2,...,5) is applied, the plateau moves to low temperature with the thermoresistivity maximum located at TSN (N=1,2,...,5). The ρ(B) curves, measured at different temperatures around TSN, intersect in the ρ-B plane at the field of B=BSN. By tuning BSN from 0 to 5 T, a series of plateaus in the ρ-T plane and the corresponding intersections in the ρ-B plane are observed. The intersections quadratically chain up in the ρ-B plane, separating the superconducting from the insulating region. The thermoresistivity maxima exponentially group up in the ρ-T plane, thus defining a phase fluctuation zone. The phase boundary, composed of the intersections and separating the superconducting states from the insulating state, is shown to be a generic consequence of granularity. [ABSTRACT FROM AUTHOR]

In this work, we investigate the stress developed in phosphorus-doped layers grown on (110)-textured polycrystalline diamond templates. To that end, we follow the shifts of the diamond Raman diffusion and the exciton recombination energies by Raman and cathodoluminescence spectroscopies, respectively. With each approach, a high tensile strain of several gigapascal is evidenced. Moreover, Raman mapping performed in cross section shows (i) at the grain boundaries, a strain in tension that propagates along the growth direction from the template to the deposited layer and (ii) at the center of each grain, a tensile strain of the phosphorus-doped layer with respect to the underlying undoped grain. Concerning the second, we observe also an increase in strain effects at high phosphorus incorporation, together with a structural degradation. The possible origins of such high lattice deformation of phosphorus-doped layers are discussed. [ABSTRACT FROM AUTHOR]

We report on the observation of a negative magnetoresistance (NMR) regime in boron-doped nanocrystalline diamond films at low temperatures. A comparative analysis of our experimental results and those reported for systems composed of superconducting granules embedded in an insulating matrix (also referred as granular films) suggest the presence of superconducting regions inside the insulating films as causing the NMR. By considering the latter scenario, the experimental observations are explained by modeling the systems as consisting of a distribution of superconducting granules whose global properties are tuned by the intergrain distance. [ABSTRACT FROM AUTHOR]

We report the optical property measurements on boron-doped diamond (BDD) films which were synthesized by microwave plasma-assisted chemical vapor deposition technique on Si (100) using methane in high hydrogen dilution and trimethylboron as precursors with varying boron concentration such that [B]/[C]gas=100, 500, 1000, 2000, 4000, and 6467 ppm. These BDD films were investigated using a rotating analyzer variable angle spectroscopic ellipsometry (SE) from the near IR to UV range (830–193 nm). By applying the conventional Bruggeman effective medium approximation and linear regression analyses to the raw SE data that is, [ψ(λi),Δ(λi)] and pseudodielectric function (<[variant_greek_epsilon]r(λi)>,<[variant_greek_epsilon]i(λi)>), we determined the most appropriate model fit. The SE modeling was performed through the normal and point-by-point fit methods combined with the coupled and uncoupled bulk and surface layer approaches providing the details about the thin films’ microstructure in terms of the (a) multilayer (component and surface) structure and component layer thickness of the films, (b)volume fraction of constituents [fsp3 C, fsp2 C and void (fv) in the component layer], (c) inhomogeneity of the structure along the growth axis and its variation with boron concentration, and (iv) surface roughness layer thickness (ds) with dimensions less than the optical wavelength that is not otherwise available. A simplified three-layer structural model consisting of an interfacial layer, an intermediate (or bulk) layer, and a top surface roughness layer has been proposed, which simulates the ellipsometry data reasonably well with coupled point-by-point method. An estimator, i.e., mean squared error (χ2), is used to assess the accuracy of the model fit. The... [ABSTRACT FROM AUTHOR]

The influence of oxidation, hydrogenation, and annealing on the dielectric properties of microwave plasma enhanced chemical vapor deposited diamond films was measured in the 45 MHz-20 GHz range using an open-ended coaxial probe. A dielectric response was detected around 10[sup 8]-10[sup 9] Hz for the hydrogenated samples, in contrast to the oxidized films, which showed no response in that frequency range. The amplitude and position of the detected response were clearly dependent on the sample quality and the state of the surface. Fitting of the experimental data to the Cole-Cole expression for dielectric relaxation showed a near-Debye behavior of the dielectric permittivity. We propose that the dielectric response is a result of two-dimensional plasmons, corresponding with a hole concentration of ∼10[sup 13] cm[sup -2] at the diamond surface, induced by the hydrogen termination. Analogous to the well-known hydrogen-induced surface conductivity, the dielectric signal disappeared after annealing the diamond films at 200 °C. [ABSTRACT FROM AUTHOR]

The incorporation efficiency of phosphorus was studied as a function of the surface orientation of grains in (110)-textured polycrystalline chemical vapor deposited diamond. Cathodoluminescence mapping of such films exhibits large local differences in relative intensities stemming from P-bound and free excitons. Combined with electron backscattering diffraction mapping, these data allow assessing of the donor concentration as a function of the grain orientation. While [P] can vary between 1015 and >1018 cm-3 within one film, misorientation angles of more than 10° with respect to the exact [110] axis assure an enhanced incorporation of P with concentrations surpassing 5×1017 cm-3. The role of the surface morphology in the observation of these large incorporation differences is explained. [ABSTRACT FROM AUTHOR]

The field electron emission (FEE) properties of nitrogen-incorporated nanocrystalline diamond films were enhanced due to Li-ion implantation/annealing processes. Li-ion implantation mainly induced the formation of electron trap centers inside diamond grains, whereas post-annealing healed the defects and converted the a-C phase into nanographite, forming conduction channels for effective transport of electrons. This resulted in a high electrical conductivity of 11.0 S/cm and enhanced FEE performance with a low turn-on field of 10.6 V/µm, a high current density of 25.5 mA/cm² (at 23.2 V/µm), and a high lifetime stability of 1,090 min for nitrogen incorporated nanocrystalline diamond films. [ABSTRACT FROM AUTHOR]

A "patterned-seeding technique" in combination with a "nanodiamond masked reactive ion etching process" is demonstrated for fabricating vertically aligned diamondgraphite hybrid (DGH) nanorod arrays. The DGH nanorod arrays possess superior field electron emission (FEE) behavior with a low turn-on field, long lifetime stability, and large field enhancement factor. Such an enhanced FEE is attributed to the nanocomposite nature of theDGH nanorods, which contain sp2-graphitic phases in the boundaries of nano-sized diamond grains. The simplicity in the nanorod fabrication process renders the DGH nanorods of greater potential for the applications as cathodes in field emission displays and microplasma display devices. [ABSTRACT FROM AUTHOR]

The fabrication of n-type diamond is essential for the realization of electronic components for extreme environments. We report on the growth of a 66 lm thick homoepitaxial phosphorus-doped diamond on a (110)-oriented diamond substrate, grown at a very high deposition rate of 33 μmh-1. A pristine diamond lattice is observed by high resolution transmission electron microscopy, which indicates the growth of high quality diamond. About 2.9 × 1016 cm-3 phosphorus atoms are electrically active as substitutional donors, which is 60% of all incorporated dopant atoms. These results indicate that P-doped (110)-oriented diamond films deposited at high growth rates are promising candidates for future use in high-power electronic applications. [ABSTRACT FROM AUTHOR]

Surface conductivity in hydrogen-terminated single crystal diamond is an intriguing phenomenon for fundamental reasons as well as for application driven research. Surface conductivity is also observed in hydrogen-terminated nanocrystalline diamond although the electronic transport mecha-nisms remain unclear. In this work, the piezoresistive properties of intrinsic surface conductive nanocrystalline diamond are investigated. A gauge factor of 35 is calculated from bulging a dia-mond membrane of 350 nm thick, with a diameter of 656 µm and a sheet resistance of 1.45 MΩ/sq. The large piezoresistive effect is reasoned to originate directly from strain-induced changes in the resistivity of the grain boundaries. Additionally, we ascribe a small time-dependent fraction of the piezoresistive effect to charge trapping of charge carriers at grain boundaries. In conclusion, time-dependent piezoresistive effect measurements act as a tool for deeper understanding the com-plex electronic transport mechanisms induced by grain boundaries in a polycrystalline material or nanocomposite. [ABSTRACT FROM AUTHOR]

Polycrystalline aluminum nitride (AIN) thin films are exposed to hydrogen and hydrogen/methane plasmas at different conditions. The latter plays an indispensable role in the subsequent deposition of nanocrystalline diamond thin films on AIN. The changes of AIN properties are investigated by means of Fourier transform infrared (FTIR) and Raman spectroscopies as well as atomic force microscopy. The E1(TO) and ... phonon mode frequencies blue-shift after the exposure to plasmas. The damping constant of E1(TO) phonon, calculated from FTIR transmission spectra using the factorized model of a damped oscillator, and the width of ... peak in Raman spectra decrease with increasing substrate temperature till the decomposition of AIN thin film becomes notable. It is proven that these changes are driven by the plasmas as annealing in vacuum does not induce them. [ABSTRACT FROM AUTHOR]

Glass and diamond are suitable materials for harsh environments. Here, a procedure for fabricating ultra-thin nanocrystalline diamond membranes on glass, acting as an electrically insulating substrate, is presented. In order to investigate the pressure sensing properties of such membranes, a circular, highly conductive boron-doped nanocrystalline diamond membrane with a resistivity of 38mΩcm, a thickness of 150 nm, and a diameter of 555 μm is fabricated in the middle of a Hall bar structure. During the application of a positive differential pressure under the membrane (0-0.7 bar), four point piezoresistive effect measurements are performed. From these measurements, it can be concluded that the resistance response of the membrane, as a function of differential pressure, is highly linear and sensitive. [ABSTRACT FROM AUTHOR]

A high-current annealing technique is used to fabricate nanogaps and hybrid diamond/graphite structures in boron-doped nanocrystalline diamond films. Nanometer-sized gaps down to ∼1 nm are produced using a feedback-controlled current annealing procedure. The nanogaps are characterized using scanning electron microscopy and electronic transport measurements. The structural changes produced by the elevated temperature, achieved by Joule heating during current annealing, are characterized using Raman spectroscopy. The formation of hybridized diamond/graphite structure is observed at the point of maximum heat accumulation. [ABSTRACT FROM AUTHOR]

We study the vibrational properties of AlN thin films deposited on silicon (100) substrates by the reactive DC-pulsed magnetron sputtering. The frequencies and lifetimes of the E1(TO) and A1(LO) optical phonons are calculated from Fourier transform infrared spectra using the factorized model of a damped oscillator. We analyze the structural properties by the x-ray diffraction technique to correlate the elongation of phonon lifetimes with increasing film thickness. The lifetimes of the phonon modes in AlN thin films are compared to the values in a single crystal. [ABSTRACT FROM AUTHOR]

Hybrid giant magnetostrictive-piezoelectric film/film structures exhibiting magnetoelectric (ME) effect associated with a magnetic instability of the spin reorientation transition type are presented. We first present the theoretical study of a clamped beam actuator composed of a piezoelectric layer on a substrate actuated by a magnetostrictive layer. The actuator is a polished 50 μm thick 18×5 mm2 silicon substrate coated by an electrode, aluminum nitride, and magnetostrictive nanostructured layer. A ME coefficient of 30 V Oe-1 cm-1 at a 35 KHz longitudinal resonance was measured. Nonlinear excitation of this mode showed a “nonlinear” dynamic ME coefficient of 4 V Oe-1 cm-1. [ABSTRACT FROM AUTHOR]

The optical properties of heavily boron-doped nanocrystalline diamond films grown by microwave plasma enhanced chemical vapor deposition on silicon substrates are presented. The diamond films are characterized by spectroscopic ellipsometry within the midinfrared, visible, and near-ultraviolet regions. The ellipsometric spectra are also found to be best described by a four-phase model yielding access to the optical constants, which are found distinct from previous nanocrystalline diamond literature values. The presence of a subgap absorption yielding high extinction coefficient values defined clearly the boron incorporated films in comparison to both undoped and composite films, while refractive index values are relatively comparable. [ABSTRACT FROM AUTHOR]

A method for mapping the surface conductivity of hydrogen-terminated (H-terminated) diamond on a sub-100 nm scale is presented. The measuring technique relies on electrostatic force microscopy imaging of the voltage distribution of a current-carrying H-terminated diamond film. The uniform linear voltage drop in highly conductive H-terminated diamond surface layers indicates that the layers behave as homogeneous, diffusive conductors with a well-defined value of the sheet resistance. On the other hand, we observe conductive as well as insulating regions that coexist for not perfectly H-terminated diamond surfaces with poor electric conductivity. [ABSTRACT FROM AUTHOR]

Since the development of the atomic force microscope, interest in microfabricated cantilevers has grown. Cantilevers are excellent micromechanical sensors. In this work, we use a commercially available piezoelectric bimorph cantilever as pressure and temperature sensor. The piezoelectric layer acts as both sensor and actuator. The sensor detects the change in the resonance frequencies due to the drag force of the surrounding gas. The frequency shift of the resonant modes is measured as a function of the pressure and the temperature. The results show that both pressure and temperature can be measured simultaneously using the piezoelectric bimorph cantilever’s resonant frequencies. [ABSTRACT FROM AUTHOR]

This letter reports on highly sensitive optical absorption measurements on organic donor-acceptor solar cells, using Fourier-transform photocurrent spectroscopy (FTPS). The spectra cover an unprecedented dynamic range of eight to nine orders of magnitude making it possible to detect defect and disorder related sub-band gap transitions. Direct measurements on fully encapsulated solar cells with an active layer of poly[2-methoxy-5-(3′,7′-dimethyl-octyloxy)]-p-phenylene-vinylene:(6,6)-phenyl-C61-butyric-acid (1:4 weight ratio) enabled a study of the intrinsic defect generation due to UV illumination. Solar cell temperature annealing effects in poly(3-hexylthiophene):PCBM (1:2 weight ratio) cells and the induced morphological changes are related to the changes in the absorption spectrum, as determined with FTPS. [ABSTRACT FROM AUTHOR]

A correction to the article "Surface States and Photo-Induced Charge Transfer on Oxygen-Terminated Chemical Vapor Deposition Diamond" is presented.

The surface of polycrystalline aluminum nitride (AlN) thin films is exposed to different gas discharge plasmas (N2, O2, and CF4) followed by a water-based colloidal seeding of ultra-dispersed nanodiamond particles. Fluorination of the AlN surface enhances the seeding density, whereas the oxidized surface does not yield any nucleation sites. In the former case, the seeding density improves by almost three orders of magnitude as compared to the untreated and N2 pretreated samples, and allows to grow pinhole-free nanocrystalline diamond film on AlN. Finally, we demonstrate a route towards selective diamond growth on AlN thin films by employing CF4 plasma pretreatment together with photolithography. [ABSTRACT FROM AUTHOR]

Quantitative analysis of X-ray absorption and dichroism data requires knowledge of the beamline photon flux during the measurements. We show that thin conductive (B-doped) diamond thin films can be an alternative to the widely used gold meshes for monitoring the beam intensity of soft X-ray beamlines in situ. Limited by the carbon extended x-ray absorption fine structure oscillations, the diamond films become applicable beginning from about 600 eV photon energy, where the important transition metal edges and the rare-earth edges are found. The 100 nm and 250 nm thick free-standing diamond films were grown and tested against standard gold meshes in real-life dichroism experiments performed at beamline ID08 of the European Synchrotron Radiation Facility, Grenoble, France. Quantitative agreement was found between the two experimental data sets. The films feature an extremely high transmission of about 90% and, at the same time, yield a sufficiently strong and clean reference signal. Furthermore, the thin films do not affect the shape of the transmitted beam. X-rays passing mesh-type monitors are subject to diffraction effects, which widen the beam and become particularly disturbing for small beamsizes in the micrometer range. [ABSTRACT FROM AUTHOR]

Interactions between ethanol-water mixtures and a hydrophobic hydrogen terminated nanocrystalline diamond surface, are investigated by sessile drop contact angle measurements. The surface free energy of the hydrophobic surface, obtained with pure liquids, differs strongly from values obtained by ethanol-water mixtures. Here, a model which explains this difference is presented. The model suggests that, due to a higher affinity of ethanol for the hydrophobic surface, when compared to water, a phase separation occurs when a mixture of both liquids is in contact with the H-terminated diamond surface. These results are supported by a computational study giving insight in the affinity and related interaction at the liquid-solid interface.