No abstract

No abstract

No abstract

Graphene-based chemical gas sensors normally show ultra-high sensitivity to certain gas molecules but at the same time suffer from poor selectivity and slow response and recovery times. Several approaches based on functionalization or modification of the graphene surface have been demonstrated as means to improve these issues, but most such measures result in poor reproducibility. In this study we investigate reproducible graphene surface modifications by sputter deposition of thin nanostructured Au or Pt layers. It is demonstrated that under the right metallization conditions the electronic properties of the surface remain those of graphene, while the surface chemistry is modified to improve sensitivity, selectivity and speed of response to nitrogen dioxide.

Hence, the suggested strategy is suitable for on demand ventilation control in indoor air quality application systems.

Compared with the most commonly used silicon and germanium, which need to work at cryogenic or low temperatures to decrease their noise levels, wide-bandgap compound semiconductors such as silicon carbide allow the operation of radiation detectors at room temperature, with high performance, and without the use of any bulky and expensive cooling equipment. In this work, we investigated the electrical and spectroscopic performance of an innovative position-sensitive semiconductor radiation detector in epitaxial 4H-SiC. The full depletion of the epitaxial layer (124 µm, 5.2 × 10 13 cm −3 ) was reached by biasing the detector up to 600 V. For comparison, two different microstrip detectors were fully characterized from −20 • C to +107 • C. The obtained results show that our prototype detector is suitable for high resolution X-ray spectroscopy with imaging capability in a wide range of operating temperatures. very low noise levels, even at the high electric fields applied during their operation. Moreover, the high thermal conductivity of 4H-SiC (3.8 W/cm • C) enables SiC devices to dissipate large amounts of excess generated heat, which would cause a temperature increase, responsible for degradation of the device's performance. High thermal conductivity is useful for increasing the radiation hardness of the detector, as well as for controlling the operating temperature when the front-end electronics are close to, or in contact with, the detector [16]. Furthermore, SiC can withstand an internal electric field over eight to ten times greater than GaAs or Si (2 MV/cm for 4H-SiC vs. 0.4 MV/cm for GaAs or 0.3 MV/cm for Si) without undergoing avalanche breakdown. This property enables the fabrication of very high-voltage devices [17]. In the case of X-ray detection and spectroscopy, the high breakdown field of 4H-SiC allows, in principle, the detector to work always in the regime of saturated-electron and hole-drift velocities, independently of the detector's active region width. When this operation condition is coupled with epitaxial material of high crystalline quality, a full and fast charge collection can be expected [16], as well as a high sensitivity, as already demonstrated [18]. Such properties allow SiC-based devices to be operated without any costly, bulky, and power-consuming cooling systems, as in the case of Si-or Ge-based devices, while maintaining an excellent signal-to-noise ratio over a wide range of temperatures. This leads to notable advantages in terms of the lower cost, more compact size, lighter weight, lower power consumption, and higher performance of SiC detectors. Further explanation of the electrical properties of SiC in connection with the ionizing detector performance benefits can be found in [16].Microstrip detectors find application where the position of the radiation interaction is necessary information for the physical process to be studied. The advantage of using microstrips with respect to other position-sensitive detectors, such as pixel detectors, is a lower number of readout channels. Se...

Abstract. High-temperature iridium-gated field effect transistors based on silicon carbide have been used for sensitive detection of specific volatile organic compounds (VOCs) in concentrations of health concern, for indoor air quality monitoring and control. Formaldehyde, naphthalene, and benzene were studied as hazardous VOCs at parts per billion (ppb) down to sub-ppb levels. The sensor performance and characteristics were investigated at a constant temperature of 330 • C and at different levels of relative humidity up to 60 %, showing good stability and repeatability of the sensor response, and excellent detection limits in the sub-ppb range.

A single-crystal silicon carbide (SiC) detector was used for measurements of soft x rays, electrons, and ion emission from laser-generated plasma obtained with the use of the Prague Asterix Laser System (PALS) at intensities of the order of 1016 W/cm2 and pulse duration of 300 ps. Measurements were performed by varying the laser intensity and the nature of the irradiated target. The spectra obtained by using the SiC detector show not only the photopeak due to UV and soft x-ray detection, but also various peaks due to the detection of energetic charged particles. Time-of-flight technique was employed to determine the ion kinetic energy of particles emitted from the plasma and to perform a comparison between SiC and traditional ion collectors. The detector was also employed by inserting absorber films of different thickness in front of the SiC surface in order to determine, as a first approximation, the mean energy of the soft x-ray emission from the plasma.