Abstract: 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 mu m thick homoepitaxial phosphorus-doped diamond on a (110)-oriented diamond substrate, grown at a very high deposition rate of 33 mu m h(-1). A pristine diamond lattice is observed by high resolution transmission electron microscopy, which indicates the growth of high quality diamond. About 2.9 x 10(16) 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. Published by AIP Publishing.

Abstract: The optical properties of semiconductor quantum dots are greatly influenced by their strain state. Dark field electron holography has been used to measure the strain in InAsquantum dotsgrown in InP with a spatial resolution of 1 nm. A strain value of 5.4% ± 0.1% has been determined which is consistent with both measurements made by geometrical phase analysis of high angle annular dark field scanning transmission electron microscopy images and with simulations.

Abstract: Strain engineering in the conduction channel is a cost effective method of boosting the performance in state-of-the-art semiconductor devices. However, given the small dimensions of these devices, it is difficult to quantitatively measure the strain with the required spatial resolution. Three different transmission electron microscopy techniques, high-angle annular dark field scanning transmission electron microscopy, dark field electron holography, and nanobeam electron diffraction have been applied to measure the strain in simple bulk and SOI calibration specimens. These techniques are then applied to different gate length SiGe SOI pFET devices in order to measure the strain in the conduction channel. For these devices, improved spatial resolution is required, and strain maps with spatial resolutions as good as 1 nm have been achieved. Finally, we discuss the relative advantages and disadvantages of using these three different techniques when used for strain measurement.

Abstract: Polycrystalline diamond (PCD) was grown onto high-k dielectric passivated AlGaN/GaN-on-Si high electron mobility transistor (HEMT) structures, with film thicknesses ranging from 155 to 1000 nm. Transient thermoreflectance results were combined with device thermal simulations to investigate the heat spreading benefit of the diamond layer. The observed thermal conductivity (k(Dia)) of PCD films is one-to-two orders of magnitude lower than that of bulk PCD and exhibits a strong layer thickness dependence, which is attributed to the grain size evolution. The films exhibit a weak temperature dependence of k(Dia) in the measured 25-225 degrees C range. Device simulation using the experimental jDia and thermal boundary resistance values predicts at best a 15% reduction in peak temperature when the source-drain opening of a passivated AlGaN/GaN-on-Si HEMT is overgrown with PCD. Published by AIP Publishing.

Abstract: Strain has a strong effect on the properties of materials and the performance of electronic devices. Their ever shrinking size translates into a constant demand for accurate and precise measurement methods with a very high spatial resolution. In this regard, transmission electron microscopes are key instruments thanks to their ability to map strain with a subnanometer resolution. Here, we present a method to measure strain at the nanometer scale based on the diffraction of electron Bessel beams. We demonstrate that our method offers a strain sensitivity better than 2.5 × 10−4 and an accuracy of 1.5 × 10−3, competing with, or outperforming, the best existing methods with a simple and easy to use experimental setup.

Abstract: Ptychography provides highly efficient imaging in scanning transmission electron microscopy (STEM), but questions have remained over its applicability to strongly scattering samples such as those most commonly seen in materials science. Although contrast reversals can appear in ptychographic phase images as the projected potentials of the sample increase, we show here how these can be easily overcome by a small amount of defocus. The amount of defocus is small enough that it not only can exist naturally when focusing using the annular dark field (ADF) signal but can also be adjusted post acquisition. The ptychographic images of strongly scattering materials are clearer at finite doses than other STEM techniques and can better reveal light atomic columns within heavy lattices. In addition, data for ptychography can now be collected simultaneously with the fastest of ADF scans. This combination of sensitivity and interpretability presents an ideal workflow for materials science.

Abstract: Combined TiO2/SiO2 mesoporous materials were prepared by deposition of TiO2 nanoparticles synthesised via the acid-catalysed solgel method. In the first synthesis step a titania solution is prepared, by dissolving titaniumtetraisopropoxide in nitric acid. The influences of the initial titaniumtetraisopropoxide concentration and the temperature of dissolving on the final structural properties were investigated. In the second step of the synthesis, the titania nanoparticles were deposited on a silica support. Here, the influence of the temperature during deposition was studied. The depositions were carried out on two different mesoporous silica supports, SBA-15 and MCF, leading to substantial differences in the catalytic and structural properties. The samples were analysed with N2-sorption, X-ray diffraction (XRD), electron probe microanalysis (EPMA) and transmission electron microscopy (TEM) to obtain structural information, determining the amount of titania, the crystal phase and the location of the titania particles on the mesoporous material (inside or outside the mesoporous channels). The structural differences of the support strongly determine the location of the nanoparticles and the subsequent photocatalytic activity towards the degradation of rhodamine 6G in aqueous solution under UV irradiation.

Abstract: A new, two-step nanocasting method was developed to prepare N-doped ordered mesoporous carbon (NOMC) electrocatalysts for the reduction of O2 to H2O2. Our strategy involves the sequential pyrolysis of two inexpensive and readily available N and C precursors, i.e. aniline and dihydroxynaphthalene (DHN), inside the pores of a SBA-15 hard silica template to obtain N-doped graphitic carbon materials with well-ordered pores and high surface areas (764 and 877 m2g−1). By tuning the ratio of carbon sources to silica template, it was possible to achieve an optimal filling of the pores of the SBA-15 silica and to minimise carbon species outside the pores. These NOMC materials displayed outstanding electrocatalytic activity in the oxygen reduction reaction, achieving a remarkably enhanced kinetic current density compared to state-of-the-art N-doped carbon materials (−16.7 mA cm−2 at −0.35 V vs. Ag/AgCl in a 0.1 M KOH solution as electrolyte). The NOMC electrocatalysts showed high selectivity toward the two-electron reduction of oxygen to hydrogen peroxide and excellent long-term stability.

Abstract: Adaptation of the photoresponse of anatase TiO2 to match the solar spectrum is an important scientific challenge. Modification of TiO2 with noble metal nanoparticles displaying surface plasmon resonance effects is one of the promising approaches. Surface plasmon resonance typically depends on chemical composition, size, shape and spatial organization of the metal nanoparticles in contact with TiO2. AuxAg(1 − x) alloy nanoparticles display strong composition-dependent surface plasmon resonance in the visible light region of the spectrum. In this work, a general strategy is presented to prepare plasmonic TiO2-based photocatalysts with a visible light response that can be accurately tuned over a broad range of the spectrum. The application as self-cleaning material toward the degradation of stearic acid is demonstrated for a plasmonic TiO2 photocatalyst displaying visible light photoactivity at the intensity maximum of solar light around 490 nm.

Abstract: tSilver nanoparticles (NPs) were deposited on nickel, titanium and gold substrates using a potentiostaticdouble-pulse method. The influence of the support material on both the morphology and the electro-catalytic activity of Ag NPs for the reduction reaction of benzyl bromide was investigated and comparedwith previous research regarding silver NPs on glassy carbon. Scanning electron microscopy (SEM) dataindicated that spherical monodispersed NPs were obtained on Ni, Au and GC substrate with an averageparticle size of respectively 216 nm, 413 nm and 116 nm. On a Ti substrate dendritic NPs were obtainedwith a larger average particle density of 480 nm. The influence of the support material on the electrocat-alytic activity was tested by means of cyclic voltammetry (CV) for the reduction reaction of benzylbromide(1 mM) in acetonitrile + 0.1 M tetrabutylammonium perchlorate (Bu4NClO4). When the nucleation poten-tial (En) was applied at high cathodic overpotential, a positive shift of the reduction potential was obtained.The nucleation (tn) and growth time (tg) mostly had an influence on the current density whereas longerdeposition times lead to larger current densities. For these three parameters an optimum was present.The best electrocatalytic activity was obtained with Ag NPs deposited on Ni were a shift of the reduc-tion peak potential of 145 mV for the reaction of benzyl bromide was measured in comparance to bulksilver. The deposition on Au substrate yielded a positive shift of 114 mV. There was no indication of analtered reaction mechanism as the reaction was characterized as diffusion controlled and the transfercoefficients were in accordance with bulk silver. There was a beneficial catalitic activity measured due tothe interplay between support and NPs. This resulted in a shift of the reduction peak potential of 34 mV(Ag NPs on Au) and 65 mV (Ag NPs on Ni) compared to Ag NPs on a GC substrate.

Abstract: A series of BiVO4/3DOM TiO2 nanocomposites have been synthesized and their photocatalytic activity was investigated under visible light irradiation using the RhB dye as model pollutant molecule in an aqueous solution. The effect of the amount of BiVO4 as visible light sensitizer on the photocatalytic activity of BiVO4/3DOM TiO2 nanocomposites was highlighted. The heterostructured composite system leads to much higher photocatalytic efficiencies than bare 3DOM TiO2 and BiVO4 nanoparticles. As the proportion of BiVO4 in BiVO4/3DOM TiO2 nanocomposites increases from 0.04 to 0.6, the photocatalytic performance of the BiVO4/3DOM TiO2 nanocomposites increases and then decreases after reaching a maximum at 0.2. This improvement in photocatalytic perfomance is related to 1) the interfacial electron transfer efficiency between the coupled materials, 2) the 3DOM TiO2 inverse opal structure with interconnected pores providing an easy mass transfer of the reactant molecules and high accessibility to the active sites and large surface area and 3) the effect of light sensitizer of BiVO4. Intensive studies on structural, textural, optical and surface properties reveal that the electronic interactions between BiVO4 and TiO2 lead to an improved charge separation of the coupled BiVO4/TiO2 system. The photogenerated charge carrier densities increase with increasing the BiVO4 content, which acts as visible light sensitizer to the TiO2 and is responsible for the enhancement in the rate of photocatalytic degradation. However, the photocatalytic activity is reduced when the BiVO4 amount is much higher than that of 3DOM TiO2. Two reasons could account for this behavior. First, with increasing BiVO4 content, the photogenerated electron/hole pairs are accumulated at the surface of the BiVO4 nanoparticles and the recombination rate increases as shown by the PL results. Second, decreasing the amount of 3DOM TiO2 in the nanocomposite decreases the surface area as shown by the BET results. Moreover, the poor adsorptive properties of the BiVO4 photocatalyst also affect the photocatalytic performance, in particular at higher BiVO4 content. The present work demonstrates that BiVO4/3DOM TiO2 is a very promising heterojunction system for visible light photocatalytic applications.

Abstract: Transparent photocatalytic TiO2 thin films hold great potential in the development of self-cleaning glass sur-
faces, but suffer from a poor visible light response that hinders the application under actual sunlight. To alleviate this problem, the photocatalytic film can be modified with plasmonic nanoparticles that interact very effectively with visible light. Since the plasmonic effect is strongly concentrated in the near surroundings of the nano- particle surface, an approach is presented to embed the plasmonic nanostructures in the TiO2 matrix itself, rather than deposit them loosely on the surface. This way the interaction interface is maximised and the plasmonic effect can be fully exploited. In this study, pre-fabricated gold nanoparticles are made compatible with the organic medium of a TiO2 sol-gel coating suspension, resulting in a one-pot coating suspension. After spin coating, homogeneous, smooth, highly transparent and photoactive gold-embedded anatase thin films are ob- tained.