A trend of increased near-surface valence band maximum band bending with increasing O∕Ga relative fraction was observed, extrapolating to 2.7eV±0.1eV for pristine GaN surfaces (0% O 1s peak area). This trend of apparent oxide overlayer coverage affecting the band bending linearly could lead to better understanding and characterization of oxidized GaN surfaces to control band bending for sensors or other devices.
Chemical functionalization of hemin molecules onto InAs and InP is reported. X-ray photoelectron spectroscopy (XPS), atomic force microscopy, and spectroscopic ellipsometry (SE) analyses are used to characterize the III-V surfaces. One notable feature of the C 1s core level spectra is a peak at ∼284eV observed for the functionalization chemistries, which is attributed to CN bonding within the porphyrin molecule. This is corroborated by the observation of N 1s, Fe 2p, and other distinguishable chemical bonding peaks. For example, in the As 3d and P 2p core levels, –COOH bonding is observed to the As and P anion in the InAs and InP samples, respectively, which implies chemisorption of the functional groups to the material surfaces. Another result of the XPS analysis is the impact of the surface functional group on the electronic state of the surface causing upward band bending of the valence band maximum, indicating surface charge transfer as explored in previous work [Garcia et al., Appl. Phys. Lett. 88, 013506 (2006)]. SE analysis on the functionalization process provides data for the effect of hemin and benzoic acid solution concentrations. The authors discuss the dependence of the band bending, surface coverage, and hemin layer thickness as determined by XPS and SE.
Current production and emerging NOx sensors based on optical and nanomaterials technologies are reviewed. In view of their potential applications in mechatronics, we compared the performance of: i) Quantum cascade lasers (QCL) based photoacoustic (PA) systems; ii) gold nanoparticles as catalytically active materials in field-effect transistor (FET) sensors, and iii) functionalized III-V semiconductor based devices. QCL-based PA sensors for NOx show a detection limit in the sub part-per-million range and are characterized by high selectivity and compact set-up. Electrochemically synthesized gold-nanoparticle FET sensors are able to monitor NOx in a concentration range from 50 to 200 parts per million and are suitable for miniaturization. Porphyrin-functionalized III-V semiconductor materials can be used for the fabrication of a reliable NOx sensor platform characterized by high conductivity, corrosion resistance, and strong surface state coupling.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.