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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]

Abstract: Photocurrent measurements on phosphorous-doped n-type diamond have been performed at liquid helium temperature and varying electric field. For increasing fields the onset of the experimental photocurrent versus photon energy shifts towards smaller photon energy. At relative small hν its slope is nearly constant, although smooth structures can be observed in the spectrum. These and other observations at low photon energy are interpreted using an impurity-assisted tunnelling model. The idea behind this model is that, at finite electric fields, the impurity electron tunnels a few times towards neighbouring neutral impurity atoms, until it arrives in a non-localized conduction band state and contributes to the photocurrent. The experimental results could be explained in a semi-quantitative way. The consequences for various experimental circumstances (varying field, temperature, photon energy, impurity concentration) are discussed. [Copyright &y& Elsevier]

A high sensitive approach is presented to detect in particular the low level absorption features in pure and blended organic semiconductor films, revealing a.o. defect induced sub gap absorption and new interactions between the materials. Because sub bandgap absorption features are typically characterized by very low absorption coefficients, it is not possible to resolve them using common transmission and reflection measurements. Therefore the very sensitive and ground state spectroscopic technique of Photothermal Deflection Spectroscopy (PDS) has been developed, and introduced to characterize thin films of MDMO-PPV and PCBM, as well as films of MDMO-PPV containing an increasing amount of PCBM ranging from 5 to 90% weight fraction. The measured spectra of MDMO-PPV are interpreted in terms of defect induced absorption phenomena. The spectral position of the observed transitions in PCBM have been determined and verified. The PDS-study on MDMO-PPV/PCBM blended films revealed for the first time interaction between the two materials in the ground state. To get more insight in the interaction mechanism between the constituting materials a systematic Transmission Electron Microscopy (TEM) study has been carried out to reveal the morphology of the films. The obtained TEM-results on nanomorphology of the blended films show clear correlations with the PDS-results. [ABSTRACT FROM AUTHOR]

The application of very sensitive photocurrent-based spectroscopic techniques have led to the detection of new levels for the electronic structure of the phosphorous donor in n-type CVD diamond. By combining quasi-steady-state photocurrent measurements (PC), photothermal ionisation spectroscopy (PTIS) and the highly sensitive Fourier transform photocurrent spectroscopy (FTPS) technique at different temperatures, ranging from liquid nitrogen temperature to 170 K, the resulting spectra point to a richer structure than assumed up to now. This is the consequence of the improved sample quality over the last years, opening up to a much larger attainable doping window. By using doping levels, ranging from 1019 cm−3 down to 1016 cm−3 on {111}-oriented Ib HPHT substrates, still giving rise to measurable n-type conductivity, spectra showed less line broadening and more fine structure. Finally, the results will be compared with spectra measured on active P-doped polycrystalline n-type films. [Copyright &y& Elsevier]

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]

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]

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]

Abstract: We report experimental results on photocurrent spectra and the transient decay of photocurrent in intrinsic CVD diamond films grown homoepitaxially on natural, (100) oriented, single crystal type IIa diamond substrates. The detectors fabricated from these layers were developed in the frame of the LYRA project (the LYman-alpha RAdiometer onboard the European satellite PROBA-2) and will be used in space for UV solar monitoring. The typical photosensitivity is about 10−2 A/W at 200 nm and 10−6 A/W at 300 nm; the typical response time well below 0.1 ms. The enhance in photosensitivity, related to defects in CVD diamond layer and accompanied by long, non-exponential tails in photocurrent transients (persistent photocurrent), is observed in some detectors. The enhancement in photosensitivity also correlates with a long effective lifetime of photo-excited carriers. New defects at about 3.8 eV and another at about 4.3 eV are observed in the photocurrent spectrum of the sample with enhanced photosensitivity. [Copyright &y& Elsevier]

In combination with CVD diamond, an aluminium nitride (AlN) thin film is one of the most promising piezoelectric materials for surface acoustic wave (SAW) applications. One of the critical issues of SAW devices is the electromechanical coupling coefficient, which depends on the AlN film thickness and its mechanical and piezoelectric properties. In this work, properties of well (002) oriented AlN films deposited on silicon and fused quartz substrates by reactive DC pulsed magnetron sputtering were measured. The mechanical, electromechanical and optical properties of AlN film deposited under optimal conditions were determined. Novel methods, using an atomic force microscope (AFM), were used to measure the d33 and d31 piezoelectric coefficients. The d33 piezoelectric coefficient measurement method allows a direct piezoelectric mapping. The experimental measurement results are in good agreement with the bulk values. [Copyright &y& Elsevier]

Scanning tunneling spectroscopy (STS) under high vacuum conditions (2×10−8 mbar), combined with high-resolution topographical imaging with the scanning tunneling microscope (STM), enabled us to investigate local variations in the electronic structure of the surface of chemical vapor deposited diamond films. We studied the variations in the current–voltage I(V) characteristics of hydrogen terminated films when varying the distance between tip and surface. Our STS measurements confirm the surface p-type conductance. We also studied the influence of changes in the hydrogen termination by annealing under high vacuum conditions. Annealing at relatively low temperatures is shown to dramatically influence the local I(V) characteristics measured with STM, confirming that hydrogen termination alone is not sufficient for explaining the enhanced surface conductance. [Copyright &y& Elsevier]

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 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]

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]

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

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 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]

A detailed conductive atomic force microscopic investigation is carried out to directly image the electron emission behavior for nitrogen-doped diamond nanorods (N-DNRs). Localized emission measurements illustrate uniform distribution of high-density electron emission sites from N-DNRs. Emission sites coupled to nanographitic phases at the grain boundaries facilitate electron transport and thereby enhance field electron emission from N-DNRs, resulting in a device operation at low turn-on fields of 6.23 V/μm, a high current density of 1.94 mA/cm 2 (at an applied field of 11.8 V/μm) and a large field enhancement factor of 3320 with a long life-time stability of 980 min. Moreover, using N-DNRs as cathodes, a microplasma device that can ignite a plasma at a low threshold field of 390 V/mm achieving a high plasma illumination current density of 3.95 mA/cm 2 at an applied voltage of 550 V and a plasma life-time stability for a duration of 433 min was demonstrated. [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]

[Display omitted] • Boron-doped diamond coating on carbon fibres. • Decrease of electrical resistance on coated fibres. • Increase of the local surface electrical response on coated fibres. • Electrical conductivity of the boron-doped diamond layer, 103 Ω-1∙mm-1. Carbon fibre reinforced polymers (CRFP) are extensively used in many industrial applications thanks to its mechanical properties and its low weight. Nevertheless, the orthotropic character of CRFP highly reduces its applications. The transversal electrical conductivity in CRFP is two orders poorer than in the longitudinal direction. To improve their electrical properties, this work proposes the use of polycrystalline boron doped diamond (BDD) as coating of the carbon fibres (CF). BDD coating is deposited on CF surface using microwave plasma enhanced chemical vapor deposition (MPCVD) system. The BDD coating forms a rigid conductive coating around the CF as a core–shell structure. Here, an electrical characterization of both, 12,000 filaments (a tow) and a single coated filament, are carried out in the longitudinal and cross-section directions. Macro, micro and local analysis using the Kelvin method, Conductive Atomic Force Microscopy (C-AFM), and Scanning Microwave Impedance Microscopy (sMIM), were carried out to evidence the improvement of the electrical properties. Macro measurement reveals that the BDD coating decreases to half the resistivity of the CF. The BDD coating raises the local electrical conductivity of the CF by an order of magnitude with respect to the uncoated ones. sMIM maps identified BDD locations in ring-like configurations. [ABSTRACT FROM AUTHOR]

Diamond n-type layers are crucial for the development of a new bipolar diamond-based electronic technology. However, the difficulties to incorporate impurity atoms into the diamond lattice make its growth a stage of technological research still in progress. Phosphorus doping has been carried out successfully on (111)-oriented diamond substrates, reaching high concentrations and good reproducibility. Nevertheless, such reproducible results have not been obtained for the (100) growth orientations yet, even though the (100) substrate orientation is still the most used diamond substrate for electronic applications. In this study, three samples are grown by microwave plasma-enhanced chemical vapor deposition on diamond (100)-oriented high pressure high temperature substrates. All samples are deposited with the same growth conditions except methane, which was varied between 1.5 % and 3.5 %. A different growth mechanism is observed for each of the methane content used. The step flow growth mechanism shows increased phosphorus incorporation, determined by cathodoluminescence (CL) in cross sectional view in focused ion beam preparations. This sample also shows a less rough surface and no crystal defects observable by transmission electron microscopy (TEM). That is why these growth conditions are used for the fabrication of the n-type layer of a p+/p−/n stack. Ellipsometry and TEM measurements on this sample yield a high growth rate of 3.5 μm/h with a phosphorus concentration of 4 × 1017 cm−3, estimated by CL spectroscopy. The sample shows a low density of surface defects, observed by optical microscopy. However, TEM observations show dislocations with 1/2 a〈110〉 burger vector and stacking faults with 1/3 〈111〉 displacement vector. [Display omitted] • High methane content in P-doped CVD diamond growth increases surface roughness. • High methane content in P-doped CVD diamond growth reduces P incorporation. • A high density of defects increases the growth rate and phosphorous incorporation. • A poor surface increases the density of defects, which increases the growth rate. • A poor surface increases the density of defects and promotes phosphorus incorporation. [ABSTRACT FROM AUTHOR]

Utilization of Au and nanocrystalline diamond (NCD) as interlayers noticeably modifies the microstructure and field electron emission (FEE) properties of hexagonal boron nitride nanowalls (hBNNWs) grown on Si substrates. The FEE properties of hBNNWs on Au could be turned on at a low turn-on field of 14.3 V μm−1, attaining FEE current density of 2.58 mA cm−2 and life-time stability of 105 min. Transmission electron microscopy reveals that the Au-interlayer nucleates the hBN directly, preventing the formation of amorphous boron nitride (aBN) in the interface, resulting in enhanced FEE properties. But Au forms as droplets on the Si substrate forming again aBN at the interface. Conversely, hBNNWs on NCD shows superior in life-time stability of 287 min although it possesses inferior FEE properties in terms of larger turn-on field and lower FEE current density as compared to that of hBNNWs-Au. The uniform and continuous NCD film on Si also circumvents the formation of aBN phases and allows hBN to grow directly on NCD. Incorporation of carbon in hBNNWs from the NCD-interlayer improves the conductivity of hBNNWs, which assists in transporting the electrons efficiently from NCD to hBNNWs that results in better field emission of electrons with high life-time stability. [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]

In this study, we show that synthetic sapphire (Al 2 O 3 ), an established implant material, can also serve as a platform material for biosensors comparable to nanocrystalline diamond. Sapphire chips, beads, and powder were first modified with (3-aminopropyl) triethoxysilane (APTES), followed by succinic anhydride (SA), and finally single-stranded probe DNA was EDC coupled to the functionalized layer. The presence of the APTES-SA layer on sapphire powders was confirmed by thermogravimetric analyis and Fourier-transform infrared spectroscopy. Using planar sapphire chips as substrates and X-ray photoelectron spectroscopy (XPS) as surface-sensitive tool, the sequence of individual layers was analyzed with respect to their chemical state, enabling the quantification of areal densities of the involved molecular units. Fluorescence microscopy was used to demonstrate the hybridization of fluorescently tagged target DNA to the probe DNA, including denaturation- and re-hybridization experiments. Due to its high thermal conductivity, synthetic sapphire is especially suitable as a chip material for the heat-transfer method, which was employed to distinguish complementary- and non-complementary DNA duplexes containing single-nucleotide polymorphisms. These results indicate that it is possible to detect mutations electronically with a chemically resilient and electrically insulating chip material. [ABSTRACT FROM AUTHOR]

This work presents a morphological and structural analysis of CVD diamond growth on silicon from nanodiamond seeds covered by a 50 nm thick chromium layer. The role of carbon diffusion as well as chromium and carbon silicide formation is analyzed. The local diamond environment is investigated by scanning transmission electron microscopy in combination with electron energy-loss spectroscopy. The evolution of the diamond phase composition (sp 3 /sp 2 ) is evaluated by micro-Raman spectroscopy. Raman and X-ray diffraction analysis are used to identify the interfacial phases formed during CVD growth. Based upon the observed morphological and structural evolution, a diamond growth model from nanodiamond seeds buried beneath a thin Cr layer is proposed. [ABSTRACT FROM AUTHOR]

Surface pretreatment by gas discharge plasmas of N 2 , O 2 and CF 4 is studied for enhanced diamond nucleation on Cr surfaces. The seeding density following the interaction of water-dispersed nanodiamonds (NDs) and the Cr surface is enhanced due to chemical modification of a surface. The surface that is untreated or pretreated with N 2 plasma possesses a suppressed electrostatic attraction of NDs, while the pretreatment with O 2 or CF 4 plasmas render a strong electrostatic attraction and high seeding density. Finally, by this method thin nanocrystalline diamond films are achieved on Cr surfaces after O 2 and CF 4 plasma pretreatments. [ABSTRACT FROM AUTHOR]

Results are presented on the thermal and elastic properties of a thin, 1.5 μm, nanocrystalline diamond coating (NCD), deposited on a silicon substrate by microwave plasma enhanced chemical vapor deposition. A combination of two all-optical measurement techniques, impulsive stimulated thermal scattering and grating induced laser beam deflection, was employed to launch and detect surface acoustic waves (SAWs). The relation between the dispersive propagation velocity of SAWs to the coating-substrate geometry is exploited to determine the elastic properties of the NCD coating. The elastic properties are found to be consistent with literature values. The thermal properties of the coating were determined by monitoring the thermal diffusion induced washing away of the laser induced transient surface temperature grating. The transient thermal grating signals were fitted by the low-frequency limit of a thermoelastic model for a multilayer configuration. Similar to the dispersion of the surface acoustic wave velocity, the characteristic time of the thermal diffusion driven grating decay evolves from a coating-dominated value at short grating spacings towards a substrate-dominated value at grating spacings well exceeding the coating thickness. The grating spacing dependence of the corresponding effective thermal diffusivity was experimentally determined and fitted, leading to a value for the thermal diffusivity of the NCD coating α NCD = 8.4 − 0.1 + 2.7 mm 2 ·s − 1 , which is an order of magnitude lower than that of the silicon substrate. The low value of the thermal diffusivity is interpreted with a simple touching model. [ABSTRACT FROM AUTHOR]

In this study we show an optical biosensor concept, based on elastic light scattering from sapphire microspheres. Transmitted and elastic scattering intensity of the microspheres (radius 500 μm, refractive index 1.77) on an optical fiber half coupler is analyzed at 1510 nm. The 0.43 nm angular mode spacing of the resonances is comparable to the angular mode spacing value estimated using the optical size of the microsphere. The spectral linewidths of the resonances are in the order of 0.01 nm, which corresponds to quality factors of approximately 10 5 . A polydopamine layer is used as a functionalizing agent on sapphire microspherical resonators in view of biosensor implementation. The varying layer thickness on the microsphere is determined as a function of the resonance wavelength shift. It is shown that polymer functionalization has a minor effect on the quality factor. This is a promising step toward the development of an optical biosensor. [ABSTRACT FROM AUTHOR]

In this article, we report on a label-free real-time method based on heat transfer resistivity for thermal monitoring of DNA denaturation and its potential to quantify DNA fragments with a specific sequence of interest. Probe DNA, consisting of a 36-mer fragment was covalently immobilized on a nanocrystalline diamond surface, created by chemical vapor deposition on a silicon substrate. Various concentrations of full matched 29-mer target DNA fragments were hybridized with this probe DNA. We observed that the change in heat transfer resistance upon denaturation depends on the concentration of target DNA used during the hybridization, which allowed us to determine the dose--response curve. Therefore, these results illustrate the potential of this technique to quantify the concentration of a specific DNA fragment and to quantify the hybridization efficiency to its probe. [ABSTRACT FROM AUTHOR]

We report on the use of the heat transfer method, a novel surface-sensitive technique based on heat transfer through solid-liquid interfaces, to detect phase transitions of model lipid membranes. We selected the lipid DPPC because of its rich phase behavior in an experimentally accessible temperature range. The vesicles were adsorbed on nanocrystalline diamond films, known as a versatile platform material for biosensing with outstanding heat-conduction properties. Complementary Peltier-element-based adiabatic scanning calorimetry (pASC) and quartz crystal microbalance with dissipation monitoring (QCM-D) measurements were carried out to monitor the phase transitions in multilamellar and small unilamellar vesicles, respectively. The heat-transfer measurements revealed reversible jumps upon heating and cooling in the thermal resistance in the vicinity of the expected transition temperature and they agree qualitatively with molecular simulations of the thermal conductivity across a lipid bilayer. The results show the capability of the heat transfer method to detect the main phase transition in DPPC, opening new perspectives for the study of more complex lipid systems and different solid platforms. This work confirms QCM-D as a useful tool for the assessment of the structural changes upon the phase conversion and shows the capability of pASC to provide high-resolution thermodynamic information on biophysical systems. Temperature profile of the heat transfer resistance Rth during the main phase transition of a DPPC supported vesicle layer adsorbed on a hydrogen-terminated nanocrystalline diamond substrate. The arrows indicate the sense of the run: heating (red solid line) and cooling (blue solid line). [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]

Carrier dynamics under interband carrier injection conditions (213 nm) was studied in undoped and boron-doped microcrystalline diamond layers with different grain size. The grain size, determined by scanning electron microscopy and electron backscattered diffraction, varied from 130 μm on the growth side to ∼1-2 μm on the nucleation side of a 1.0 mm-thick undoped layer. Carrier lifetimes measured by differential transmittivity (DT) technique varied from 1 to 4 ns on the growth side to ∼220 ps on the nucleation side. Also the carrier diffusivity was found higher on the growth side. The B-doped layer with 40 μm grain size at the growth side exhibited 380 ps carrier lifetime, which decreased to 130 ps on the nucleation side. Even shorter lifetimes (∼100-200 ps and ∼10 ps, correspondingly) were revealed in this layer by differential reflectivity decay due to impact of subsurface defects. Therefore we conclude that the recombination rate in presence of large grains is dominated by bulk non-radiative traps, as diffusion time of carriers to reach grain boundaries is much longer (few μs). An impact of grain boundaries to recombination is expected in case of smaller grains. Thermal grating decay provided values of thermal diffusivity Dth in the range of 12-6 cm2 s−1, respectively, on the growth and nucleation side of the layers, and its decrease with reduction of grain size was attributed to phonon scattering on grain boundaries. [ABSTRACT FROM AUTHOR]

Abstract: In this study the efficiency of electrochemical oxidation of aromatic pollutants, such as reactive dyes, at boron-doped diamond on silicon (Si/BDD) electrodes was investigated. The level of [B]/[C] ratio which is effective for the degradation and mineralization of selected aromatic pollutants, and the impact of [B]/[C] ratio on the crystalline structure, layer conductivity and relative sp3/sp2 coefficient of a BDD electrode were also studied. The thin film microcrystalline electrodes have been deposited on highly doped silicon substrates via MW PE CVD. Si/BDD electrodes were synthesized for different [B]/[C] ratios of the gas phase. Mechanical and chemical stability of the electrodes was achieved for the microcrystalline layer with relatively high sp3/sp2 band ratio. Layer morphology and crystallite size distribution were analyzed by SEM. The resistivity of BDD electrodes was studied using four-point probe measurements. The relative sp3/sp2 band ratios were determined by deconvolution of Raman and X-ray photoelectron spectra. The efficiency of degradation and mineralization of the reactive azo dye rubin F-2B was estimated based on the absorbance measurements at 545nm. The influence of commonly used electrolytes NaCl and Na2SO4 on the dye removal efficiency was also investigated. The results suggest that, in general, the oxidation occurs indirectly at the anode through generation of hydroxyl radicals •OH, which react with the dye in a very fast and non-selective manner. In NaCl electrolyte the dye was also decomposed by more selective, active chlorine species (Cl2, HOCl). However the efficiency of this process in BDD depended on the electrode's doping level. Higher amounts of dopant on the surface of BDD resulted in the higher efficiency of dye removal in both electrolytes. [Copyright &y& Elsevier]

Abstract: In this article, we report on the label-free real-time thermal monitoring of the denaturation of specific DNA fragments and its potential to detect and quantify single nucleotide polymorphisms (SNPs). Probe DNA, consisting of a 36-mer fragment was covalently immobilized on nanocrystalline chemical vapour deposition (CVD) diamond platforms and hybridized with a 29-mer target DNA fragment (full matching and/or with a point mutation). It was observed that the change in heat transfer resistance upon denaturation is dependent on the amount of DNA hybridized to the nanocrystalline diamond (NCD) surface. Furthermore the possibility to distinguish between a full matching sequence and its singularly mutated counterpart, when bound to the same NCD surface, was investigated. NCD surfaces were selectively hybridized with both full matching and mutated DNA fragments at different ratios (3:1, 2:2 and 1:3). A clear bipartite response in heat transfer resistivity was observed upon simultaneous denaturation of these DNA fragments. Denaturation temperature could be used to identify the DNA fragment to which each partial response could be attributed. Moreover, the partial increases in heat transfer resistivity related to the hybridized amount of non-mutated or mutated DNA, respectively. These results imply that heat transfer resistivity is a technique which can be used to (i) quantify DNA fragments of interest, (ii) detect and (iii) quantify SNPs in a mixture of mutated and non-mutated DNA fragments. Moreover, it illustrates the potential of this technique to detect SNPs without the necessity to design complex microarrays. [Copyright &y& Elsevier]

Probe DNA, consisting of a 36-mer fragment was covalently immobilized on nanocrystalline chemical vapour deposition (CVD) diamond electrodes and hybridized with a 29-mer target DNA. In this paper, we report on the label-free real-time electronic monitoring of DNA denaturation upon exposure to NaOH at different flow rates and molarities, using electrochemical impedance spectroscopy as readout technology. The impedance response was separated into a denaturation time constant and a medium exchange time constant by means of a double exponential fit. It was observed that the denaturation time is dependent on the flow rate as well as on the molarity of the NaOH. Surprisingly, it was observed that at low molarities (0.05 M) the DNA does not fully denature at low flow rates. Only after flushing the flow cell a second time with 0.05 M NaOH, complete denaturation was achieved. Confocal images were obtained and plotted in 3D graphs to confirm the results. This paper provides a systematic overview of measured denaturation times for different flow rates and at different molarities of NaOH. Optimization of these parameters can be a valuable asset in the field of mutation analysis. [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 report investigation of carrier recombination and diffusivity in bulk diamonds of different crystalline structure - microcrystalline (MC) CVD-grown and single crystalline HPHT diamonds. Presence of neutral and positively charged nitrogen and hydrogen defects was determined from NIR and UV-IR absorption spectra. Carrier injection into 1-mm thick bulk layers was realized by two-photon absorption at 351 nm wavelength. Carrier lifetimes of 150-330 ns in IIa type HPHT crystals correlated with N density, while the lifetimes in CVD crystal exhibited very fast (80 ps), slower one (3-8 ns), and µs-duration thermally-activated (∼1.5 eV) decay components. The initial two components correlated with the grain size at the front and backsides of the MC diamond. Linearly increasing with injection carrier recombination rates were observed in both CVD and HPHT samples at 800 K, and fitted with effective recombination coefficient B = 3-4 × 10−9 cm3/s. Ambipolar mobility and thermal diffusivity parameters in CVD and HPHT bulk crystals were measured by light-induced free carrier and thermal grating techniques. [ABSTRACT FROM AUTHOR]

The purpose of this work is to study the performance of resonantly driven microcantilevers excited with a piezoelectric aluminium nitride thin film as a mass sensor for the detection of interactions in the field of immunosensing. Two cantilevers with different width (i.e. 300 and 200 μm), but constant length and thickness of 300 and 20 μm were considered. The figures of merit of these structures, such as the mass sensitivity and the limit of mass detection, were determined. According to the results obtained, a cantilever being 300 × 200 μm in size and a high frequency mode was the best combination to detect antibody/antigen interactions. The previous combination was applied to detect the affinity between rabbit immunoglobulin G (IgG) and the complementary anti-rabbit IgG produced in goat. The binding was registered as a shift of the resonance frequency of the mode under investigation and the correlation between the added mass and the measured shift is analysed. [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]

The grain size dependence of the superconducting transition, the normal state resistivity, and the insulating behavior at high magnetic fields are studied on a series of boron-doped nanocrystalline diamond (B:NCD) thin films with different grain sizes. The systematic change of the grain size is achieved by varying the methane-to-hydrogen ratio (C/H ratio) for the growth of different B:NCD films. Even though a fixed trimethylboron-(TMB) to-methane gas ratio is supposed to induce the identical boron-doping level in all the B:NCD films, the boron concentration and the carrier density are found to be a decreasing function of the grain size. Another consequence of the increase in grain size is the decreasing grain boundary density. These two concurrent consequences of the chemical vapor deposition mode of B:NCD are responsible for the grain size dependence of the critical temperature Tc, the localization radius aH at the boron site, the normal state resistivity ρnorm the Hall mobility µH, the Ioffe-Regel product kFl, the HC2-T phase boundary, and the coherence lengthεGL. [ABSTRACT FROM AUTHOR]

Abstract: The application of oxidized chromium as a reusable platform for the development of immunosensors is presented. Chromium films were deposited on quartz crystal microbalances to study the affinity interaction between rabbit immunoglobulin G (IgG) and goat anti-rabbit IgG. A covalent approach, based on the silane chemistry, was followed for the grafting of either the rabbit IgG or the anti-rabbit IgG on the silane-modified chromium surface. Next the differences between the deposition of rabbit IgG on immobilized anti-rabbit IgG and the deposition of anti-rabbit IgG on immobilized rabbit IgG were investigated. The chromium layer could be reused between experiments, after the proper removal of the organic layers with piranha etch, obtaining a high repeatability in the steps of the functionalization protocol. [Copyright &y& Elsevier]

Abstract: The high prevalence of cardiovascular diseases (CVD) demands a reliable and sensitive risk assessment technique. In order to develop a fast and label-free immunosensor for C-reactive protein (CRP), a risk factor for this condition, anti-CRP antibodies were physically adsorbed to the hydrogen (H)-terminated surface of nanocrystalline diamond (NCD). An Enzyme-Linked ImmunoSorbent Assay (ELISA) reference technique showed that this was a suitable substrate for antibody–antigen recognition reactions. Electrochemical Impedance Spectroscopy (EIS) was used to electronically detect CRP recognition. The specificity of the immunosensor was demonstrated by incubation with CRP and plasminogen as reference molecule. A different impedance behavior was observed in real-time after CRP addition as compared to plasminogen addition: the impedance increased only during CRP incubation. Fitting the data showed that this corresponded with a decrease in capacitance of the molecular layer due to its increased thickness by specific CRP recognition. Sensitivity experiments in real-time showed a clear discrimination between 1μM, 100nM, and 10nM of CRP after 10min at 100Hz. Since, 10nM of CRP was still clearly distinguishable from buffer solution, our CRP-directed immunosensor prototype reaches a sensitivity that is within the physiologically relevant concentration range of this biomarker in healthy controls and CVD patients. Moreover, this prototype displayed real-time discriminating power between spiked and unspiked serum, and thus also shows its applicability in this biological matrix. [Copyright &y& Elsevier]

A systematic study on the morphology and electronic properties of thin heavily boron-doped nanocrystalline diamond (NCD) films is presented. The films have nominally the same thickness (≈150 nm) and are grown with a fixed B/C ratio (5000 ppm) but with different C/H ratios (0.5-5%) in the gas phase. The morphology of the films is investigated by x-ray diffraction and atomic force microscopy measurements, which confirm that lower C/H ratios lead to a larger average grain size. Magnetotransport measurements reveal a decrease in resistivity and a large increase in mobility, approaching the values obtained for single-crystal diamond as the average grain size of the films increases. In all films, the temperature dependence of resistivity decreases with larger grains and the charge carrier density and mobility are thermally activated. It is possible to separate the intra- and intergrain contributions for resistivity and mobility, which indicates that in these complex systems Matthiessen's rule is followed. The concentration of active charge carriers is reduced when the boron-doped NCD is grown with a lower C/H ratio. This is due to lower boron incorporation, which is confirmed by neutron depth profiling. [ABSTRACT FROM AUTHOR]

Abstract: When charge carriers are introduced in diamond, e.g. by chemical doping with Boron (B), the diamond:B can exhibit an insulator-to-metal transition . Under even heavier boron doping , diamond becomes superconducting. Using microwave plasma-assisted chemical vapor deposition (MPCVD) we have prepared diamond:B thin films with critical offset temperatures below 3K. We have investigated the transport properties of these diamond:B thin films, which show pronounced granular effects. It turns out, that this granularity is both intrinsic as well as extrinsic. The extrinsic granularity is the effect of the growth method which needs to start from a seeding of the substrate with detonation nanodiamond, which acts as nucleation centers for further MPCVD growth of the film. In using SPM/STM techniques, we also observed intrinsic granularity, meaning that within physical grains, we observe also a strong intragrain modulation of the order parameter. As a consequence of these granularities, the transport properties show evidence of (i) strong superconducting fluctuations and (ii) Cooper pair tunneling and/or quasiparticle tunneling. The latter effects explain the observed negative magnetoresistance. [ABSTRACT FROM AUTHOR]

Abstract: A capacitive field-effect EDIS (electrolyte–diamond–insulator–semiconductor) sensor with improved pH and penicillin sensitivity has been realised using a nanocrystalline-diamond (NCD) film as sensitive gate material. The NCD growth process on SiO2 as well as an additional surface treatment in oxidising medium have been optimised to provide high pH-sensitive, non-porous O-terminated films without damage of the underlying SiO2 layer. The surface morphology of O-terminated NCD thin films and the layer structure of EDIS sensors have been studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) methods. To establish the relative coverage of the surface functional groups generated by the oxidation of NCD surfaces, X-ray photoelectron spectroscopy analysis was carried out. The hydrophilicity of NCD thin films has been studied by water contact-angle measurements. A nearly Nernstian pH sensitivity of 54–57mV/pH has been observed for O-terminated NCD films treated in an oxidising boiling mixture for 80min and in oxygen plasma. The high pH-sensitive properties of O-terminated NCD have been used to develop an EDIS-based penicillin biosensor. A freshly prepared penicillin biosensor possesses a high sensitivity of 85mV/decade in the concentration range of 0.1–2.5mM penicillin G. The lower detection limit is 5μM. [Copyright &y& Elsevier]

Abstract: We report the use of a magnetic instability of the spin reorientation transition type to enhance the magnetoelectric sensitivity in magnetostrictive–piezoelectric structures. We present the theoretical study of a clamped beam resonant actuator composed of a piezoelectric element on a passive substrate actuated by a magnetostrictive nanostructured layer. The experiments were made on a polished 150μm thick 18×3mm2 lead zirconate titanate (PZT) plate glued to a 50μm thick silicon plate and coated with a giant magnetostrictive nanostructured Nx(TbCo2 5nm/FeCo5nm) layer. A second set of experiments was done with magnetostrictive layer deposited on PZT plate. Finally, a film/film structure using magnetostrictive and aluminium nitride films on silicon substrate was realized, and showed ME amplitudes reaching 30VOe−1 cm−1. Results agree with analytical theory. [Copyright &y& Elsevier]

Abstract: Future missions for space astronomy and solar research require innovative vacuum ultraviolet (VUV) photodetectors. Present UV and VUV detectors exhibit serious limitations in performance, technology complexity and lifetime stability. New developments of metal-semiconductor-metal (MSM) solar-blind photodetectors based on diamond, cubic boron nitride (c-BN), and wurtzite aluminium nitride (AlN) are reported. In the wavelength range of interest, the characteristics of the MSM photodetectors present extremely low dark current, high breakdown voltage, and good responsivity. Diamond, c-BN, and AlN MSM photodetectors are sensitive and stable under UV irradiation. They show a 200 nm to 400 nm rejection ratio of more than four orders of magnitude and demonstrate the advantages of wide band gap materials for VUV radiation detection in space. [Copyright &y& Elsevier]