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We discuss graphene-on-SiC dies for blood-type sensing. For the sensor application, chemical species to be detected adsorb on the graphene surface and act as electron donors or acceptors resulting in resistance changes of the graphene channel. In this work, graphene films were formed on 4H-SiC substrates by thermal decomposition of the (0001) silicon surface in Ar ambient at a high temperature of 1800–2000oC. The graphene functionalization was performed by the covalent bonding of a nitrophenyl group (C6H5NO2) followed by its reduction to a phenylamine group (C6H5NH2) by using a cyclic voltammetry process. There was a clear and prompt response (current change) of the antibody-coated graphene/SiC dies when the blood antigen matched the antibody. No response occurred when the antibody on the graphene surface mismatched the blood antigen. The experiments demonstrated that a functionalized graphene-on-SiC die has capability in blood sensing, opening a way to manufacture biosensors for detecting blood types and for other applications.
Photoluminescence (PL) was used to estimate the concentration of point defects in GaN. The results are compared with data from positron annihilation spectroscopy (PAS), secondary ion mass spectrometry (SIMS), and deep level transient spectroscopy (DLTS). Defect-related PL intensity in undoped GaN grown by hydride vapor phase epitaxy increases linearly with the concentration of related defects only up to 1016 cm-3. At higher concentrations, the PL intensity associated with individual defects tends to saturate, and accordingly, does not directly correlate with the concentration of defects. For this reason, SIMS analysis, with relatively high detection limits, may not be helpful for classifying unidentified point defects in GaN. Additionally, we highlight challenges in correlating defects identified by PL with those by PAS and DLTS methods.
The structural, chemical, and electronic properties of epitaxial graphene films grown by thermal decomposition of the Si-face of a semi-insulating 6H-SiC substrate in an argon environment are studied by Raman spectroscopy, X-ray photoelectron spectroscopy and angle-resolved photoemission. It was demonstrated the possibility of fabrication of the gas and biosensors that is based on grown graphene films. The gas sensors are sufficiently sensitive to NO2 at low concentrations. The biosensor operation was checked using an immunochemical system comprising fluorescein dye and monoclonal anti fluorescein antibodies. The sensor detects fluorescein concentration on a level of 1-10 ng/mL and bovine serum albumin- fluorescein conjugate on a level of 1-5 ng/mL. The proposed device has good prospects for use for early diagnostics of various diseases.
The structural, chemical, and electronic characteristics of graphene grown by thermal decomposition of a singlecrystal SiC substrate in Ar atmosphere are presented. It is shown that this technology allows the creation of high-quality monolayer graphene films with a small fraction of bilayer graphene inclusions. The performance of graphene on SiC as a gas sensor or a biosensor was tested. The sensitivity of gas sensors to NO2 on the order of 1 ppb and that of biosensors to fluorescein with concentration on the order of 1 ng/mL and to bovine serum albumin-fluorescein conjugate with concentration on the order of 1 ng/mL were determined.
The investigation and identification of point defects in GaN is crucial for improving the reliability of light-emitting and high-power electronic devices. The RY3 defect with a characteristic emission band at about 1.8 eV is often observed in photoluminescence (PL) spectra of n-type GaN grown by hydride vapor phase epitaxy, and it exhibits unusual properties. Its emission band consists of two components: a fast (10-ns lifetime) RL3 with a maximum at 1.8 eV and a slow (100-300 mu s lifetime) YL3 with a maximum at 2.1 eV and zero-phonon line at 2.36 eV. In steady-state PL measurements, the YL3 component emerges with increasing temperature from 90 to 180 K, concurrently with a decrease in the RL3 intensity. The activation energy of both processes is about 0.06 eV. In time-resolved PL, the YL3 intensity abruptly rises when the RL3 intensity begins to saturate. These and other phenomena can be explained using a model of an acceptor with two excited states. A delocalized, effective-mass state at about 0.2 eV above the valence band captures photogenerated holes. These holes transition to the ground state, which produces the RL3 component with a lifetime of similar to 10 ns. Alternatively, they may nonradiatively transition over a 0.06 eV-high barrier to a localized excited state with a level at 1.13 eV above the valence band. Recombination of free electrons or electrons at shallow donors with the holes at this localized excited state is responsible for the YL3 component. The relative intensities of the RL3 and YL3 components are dictated by the probabilities of holes at the shallow excited state to transition to the ground or to the localized excited states. Transition metals and complex defects are considered as the main candidates for the RY3 center.