Impurity conduction in synthetic semiconducting diamond

Biofouling and performance of boron-doped diamond electrodes for detection of dopamine and serotonin in neuron cultivation media

Boron doped diamond has been considered as a fouling-resistive electrode material for in vitro and in vivo detection of neurotransmitters. In this study, its performance in electrochemical detection of dopamine and serotonin in neuron cultivation media Neurobasal™ before and after cultivation of rat neurons was investigated. For differential pulse voltammetry the limits of detection in neat Neurobasal™ medium of 2 µM and 0.2 µM for dopamine and serotonin, respectively, were achieved on the polished surface, which is comparable with physiological values. On oxidized surface twofold higher values, but increased repeatabilities of the signals were obtained. However, in Neurobasal™ media with peptides-containing supplements necessary for cell cultivation, the voltammograms were notably worse shaped due to biofouling, especially in the medium isolated after neuron growth. In these complex media, the amperometric detection mode at +0.75 V (vs. Ag/AgCl) allowed to detect portion-wise additions of dopamine and serotonin (as low as 1-2 µM), mimicking neurotransmitter release from vesicles despite the lower sensitivity in comparison with neat NeurobasalTM. The results indicate substantial differences in detection on boron doped diamond electrode in the presence and absence of proteins, and the necessity of studies in real media for successful implementation to neuron-electrode interfaces.

In Situ Raman Microdroplet Spectroelectrochemical Investigation of CuSCN Electrodeposited on Different Substrates

Systematic in situ Raman microdroplet spectroelectrochemical (Raman-μSEC) characterization of copper (I) thiocyanate (CuSCN) prepared using electrodeposition from aqueous solution on various substrates (carbon-based, F-doped SnO₂) is presented. CuSCN is a promising solid p-type inorganic semiconductor used in perovskite solar cells as a hole-transporting material. SEM characterization reveals that the CuSCN layers are homogenous with a thickness of ca. 550 nm. Raman spectra of dry CuSCN layers show that the SCN⁻ ion is predominantly bonded in the thiocyanate resonant form to copper through its S−end (Cu−S−C≡N). The double-layer capacitance of the CuSCN layers ranges from 0.3 mF/cm² on the boron-doped diamond to 0.8 mF/cm² on a glass-like carbon. In situ Raman-μSEC shows that, independently of the substrate type, all Raman vibrations from CuSCN and the substrate completely vanish in the potential range from 0 to −0.3 V vs. Ag/AgCl, caused by the formation of a passivation layer. At positive potentials (+0.5 V vs. Ag/AgCl), the bands corresponding to the CuSCN vibrations change their intensities compared to those in the as-prepared, dry layers. The changes concern mainly the Cu−SCN form, showing the dependence of the related vibrations on the substrate type and thus on the local environment modifying the delocalization on the Cu−S bond.

Boron Doped Diamond: A Designer Electrode Material for the Twenty-First Century

Boron doped diamond (BDD) is continuing to find numerous electrochemical applications across a diverse range of fields due to its unique properties, such as having a wide solvent window, low capacitance, and reduced resistance to fouling and mechanical robustness. In this review, we showcase the latest developments in the BDD electrochemical field. These are driven by a greater understanding of the relationship between material (surface) properties, required electrochemical performance, and improvements in synthetic growth/fabrication procedures, including material postprocessing. This has resulted in the production of BDD structures with the required function and geometry for the application of interest, making BDD a truly designer material. Current research areas range from in vivo bioelectrochemistry and neuronal/retinal stimulation to improved electroanalysis, advanced oxidation processes, supercapacitors, and the development of hybrid electrochemical-spectroscopic- and temperature-based technology aimed at enhancing electrochemical performance and understanding.

The Electronic and Optical Properties of Diamond; Do they Favour Device Applications?

The electronic and optical properties of diamond are reviewed, with particular emphasis on current research into the production of semiconducting devices. Although many of the properties of diamond seem, at first sight, to be ideally suited to the development of high power microwave and optoelectronic devices, there are also a number of obstacles to be overcome before diamond may be successfully exploited for device applications.

Epitaxial Growth of Diamond and Diamond Devices

For the practical application of diamond semiconductor devices, the manufacture of planar-type devices is important. Homoepitaxial growth of diamonds would be a useful technique for making semiconducting diamond films. Homo-epitaxial growth of diamonds is achieved by microwave plasma CVD. The properties of epitaxial diamond films depend on the deposition condition and the substrate orientation. Boron doping was easily carried out by this method and boron doped films were determined to be ptype semiconductors. Properties of boron doped epitaxial films were found to be similar to those of natural IIb diamond. The Schottky junction on boron doped epitaxial films was obtained by the deposition of tungsten and aluminum. The Schottky properties of this combination were affected by the surface roughness of the epitaxial films. A field effect transistor and a light emitting device were successfully fabricated using boron doped epitaxial films and Schottky junctions.

Cathodoluminescence Studies of Bound Excitons and Near Band Gap Emission Lines in Boron- and Phosphorus-Doped CVD-Diamonds

Cathodoluminescence measurements at cryogenic temperatures are reported on boron- and phosphorus-doped CVD-diamond films grown on silicon substrates. Boron and phosphorus concentrations were determined by SIMS measurements; for boron, they reached from unintentional background doping levels up to 3500 ppm. At increasing boron concentrations, the radiative recombination of boron bound excitons (BEto) at 5.22 eV photon energy systematically broadens and shifts down to 4.99 eV whereas the free exciton emission (FEto) disappears for 40 ppm and higher. In the phosphorus-doped films we observe new lines at 5.16 eV and 4.99 eV which we ascribe to TO- and (TO+Or)-phonon assisted transitions of an exciton bound to a shallow impurity other than boron, possibly phosphorus or a phosphorus-related shallow complex.

Dependence of the superconducting transition temperature on the doping level in single-crystalline diamond films

Homoepitaxial diamond layers doped with boron in the 10(20)-10(21) cm(-3) range are shown to be type II superconductors with sharp transitions (approximately 0.2 K) at temperatures increasing from 0 to 2.1 K with boron contents. The critical concentration for the onset of superconductivity in those 001-oriented single-crystalline films is about 5-7 10(20) cm(-3). The H-T phase diagram has been obtained from transport and ac-susceptibility measurements down to 300 mK.

Superconductivity in diamond

Diamond is an electrical insulator well known for its exceptional hardness. It also conducts heat even more effectively than copper, and can withstand very high electric fields. With these physical properties, diamond is attractive for electronic applications, particularly when charge carriers are introduced (by chemical doping) into the system. Boron has one less electron than carbon and, because of its small atomic radius, boron is relatively easily incorporated into diamond; as boron acts as a charge acceptor, the resulting diamond is effectively hole-doped. Here we report the discovery of superconductivity in boron-doped diamond synthesized at high pressure (nearly 100,000 atmospheres) and temperature (2,500-2,800 K). Electrical resistivity, magnetic susceptibility, specific heat and field-dependent resistance measurements show that boron-doped diamond is a bulk, type-II superconductor below the superconducting transition temperature T(c) approximately 4 K; superconductivity survives in a magnetic field up to Hc2(0) > or = 3.5 T. The discovery of superconductivity in diamond-structured carbon suggests that Si and Ge, which also form in the diamond structure, may similarly exhibit superconductivity under the appropriate conditions.

The optical and electronic properties of semiconducting diamond

In this paper I review the evidence that shows that the optical and electronic properties of semiconducting diamond can be understood in terms of boron acceptors partially compensated by deep donors. In natural semiconducting diamond, in which the total impurity concentration is less than 1 ppm, there is a lot of fine structure in the acceptor absorption spectrum that is not fully understood, and the electrical conductivity is primarily associated with the thermally activated excitation of holes from the acceptor ground state to the valence band. Some of the problems regarding the analysis of Hall effect data in this material are discussed, including the temperature dependences of the scattering mechanisms, of the contribution from the split-off valence band and of the population of excited states. There are no adequate theoretical descriptions of any of these processes, and this leads to some uncertainties in the values of the parameters derived from the temperature dependence of the Hall coefficient. For boron-doped synthetic diamond, and thin film diamond grown by chemical vapour deposition (CVD), the defect concentrations are generally much higher, and much more inhomogeneous, than in natural semiconducting diamond. This results in a substantial broadening of the acceptor absorption spectrum and the electronic properties are greatly modified by increasing contributions from impurity band conduction as the acceptor concentrations are increased, leading to very low mobility values. For both poly crystalline and single crystal homoepitaxial CVD diamond, measurements of the electrical properties can be completely invalidated by the presence of a surface layer of non-diamond carbon.