DL-Polylactide (DL-PLA) Based Polyaniline Composite for Hydrogen Gas Sensors

Different inorganic acids like HCl, HNO3, H2SO4 and H3PO4-doped based DL-PLA/PANI-ES composites were synthesized by in-situ chemical oxidation polymerization technique using liquid aniline as precursors. The doped composite have observed fibril-like morphology with different average sized diameter (178 nm for HCl doped composite, 162 nm (H2SO4 doped composite), 153 nm (H3PO4 doped composite) and 163 nm (HNO3 doped composite), respectively. Analysis of presence of functional groups and other chemical groups of as prepared composites was done by FTIR experiment in ATR mode. The optical (direct) band gap was estimated from UV-Visible absorption spectra. The estimated band gap values are to be 160 eV, 1.37 eV, 1.46 eV, and 1.69 eV for HCl, HNO3, H2SO4 and H3PO4-doped DL-PLA/PANI-ES composite, respectively. The electrical conduction mechanism of HCl-, H2SO4- and H3PO4-doped DL-PLA/PANI-ES composites were taken to study the conduction mechanism in detail in the low temperature regime (77-300 K) with and without applied of the magnetic field. Different models such as variable range hopping (VRH) and Arrhenius model were taken to explain the conduction mechanism of as prepared composites. In the Mott type VRH model, the density of states at the Fermi level, which is constant in the temperature range of 77-300 K were estimated. In the absence of magnetic field, DC conductivity of HCl-, H2SO4- and HNO3-, H3PO4- doped DL-PLA/PANI-ES composite was measured. Also, magnetoresistance (MR) was measured at room temperature for as prepared doped DL-PLA/PANI-ES composites and showed negative MR. In addition, we were discussed the response of hydrogen (H2) gas with polyaniline-based sensor materials.

Response Enhancement of Pt–AlGaN/GaN HEMT Gas Sensors by Thin AlGaN Barrier with the Source-Connected Gate Configuration at High Temperature

AlGaN/GaN HEMT hydrogen gas sensors were optimized by AlGaN barrier thickness in the gate-source connected configuration demonstrated high response and robust stability up to 500 °C. First, we found that the hydrogen sensing performance of a conventional normally-on HEMT-based sensor was enhanced when zero voltage was applied on the gate in comparison with a floating-gate condition due to a reduced level of the base current. In the next step, to take advantage of the response increase by VGS = 0 V, a new type of sensor with a source-connected gate (SCG) was fabricated to utilize the normally-on operation of the GaN HEMT sensor as a two-terminal device. AlGaN barrier thickness was thinned by the dry-etching process to gain higher transconductance at a zero-gate bias with the reduction of the distance from the 2DEG channel to the AlGaN surface, thereby significantly improve the hydrogen response. The SCG GaN sensor with an ultra-thin AlGaN barrier (9 nm) exhibited responses of 85% and 20% at 200 and 500 °C, respectively, onto 4%-hydrogen gas, which demonstrates a promising ability for harsh environment applications.