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The high demand for pressure devices with miniaturization and a wide bearing range has encouraged researchers to explore new high-performance sensors from different approaches. In this study, a sensitive element based on graphene in-plane compression properties for realizing pressure sensing is experimentally prepared using microelectromechanical systems (MEMS) fabrication technology; it consists of a 50 µm thick, 1400 µm wide square multilayer component membrane and a graphene monolayer with a meander pattern. The prepared sample is extensively characterized and analyzed by using various techniques, including atomic force microscopy, Raman spectroscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, COMSOL finite element method, and density functional theory. The sensing performance of the new pressure sensor based on the sensitive element are obtained by theoretical analysis for electromechanical measurements of the sensitive element before and after low-temperature annealing in atmosphere. Results demonstrate that atmospheric annealing at 300 °C enhances the pressure sensing sensitivity by 4 times compared to pristine graphene without annealing, which benefits from the desorption of hydroxyl groups on the graphene surface during annealing. The sensitivity is comparable and even better than that of previous sensors based on graphene in-plane properties. Our results provide new insights into realizing high-performance MEMS devices based on 2D sensitive materials. [ABSTRACT FROM AUTHOR]

Ni-doped CdS nanowires were synthesized by a simple one-step method. X-ray diffraction, X-ray photoelectron spectroscopy, and photoluminescence spectroscopy confirmed that light Ni doping can form shallow surface states due to the presence of substitutional Ni ions, and heavy Ni doping can form deep surface states due to the presence of interstitial Ni ions. Surface photovoltage spectroscopy and transient photovoltage measurements revealed that the shallow surface states can prolong the lifetime of the photogenerated charge carriers, whereas the deep surface states lead to recombination of the photogenerated charge carriers. The relationship between different surface states and the photocatalytic performance of CdS nanocrystals are discussed. The enhanced density of shallow surface states due to light Ni doping significantly promotes photocatalytic H2 production. [ABSTRACT FROM AUTHOR]

CuS/Zn0.8Cd0.2S composites have been successfully prepared by simple hydrothermal and cation exchange method. The Cu species loaded on Zn0.8Cd0.2S, together with the intimate contact formed between CuS and Zn0.8Cd0.2S, was clearly demonstrated with X-ray photoelectron spectroscopy and transmission electron microscopy. The optimized CuS/Zn0.8Cd0.2S photocatalyst has a high H2 evolution rate of 2792 μmol g−1 h−1 at CuS content of 3 wt% and the apparent quantum efficiency of 36.7% at 420 nm. The photophysical mechanism of the photocatalytic activity was investigated with the help of surface photovoltage spectroscopy (SPS) and transient photovoltage (TPV) techniques. The results revealed that photogenerated charge separation efficiency in Zn0.8Cd0.2S was enhanced and the photogenerated electrons were trapped by the loaded CuS, which benefits photo-reduction. Those were the reasons for significant enhancement in the photocatalytic H2 evolution from water splitting. [ABSTRACT FROM AUTHOR]

Abstract: Carbon-doped anatase TiO2 was prepared by a facile hydrothermal process without adding additional carbon source. The as-prepared sample shows highly efficient photocatalytic activity, which only requires 4min and is about 11 times higher than that of Degussa P25 TiO2 in degradation of methyl orange (MO) dye under UV light irradiation. Moreover, a highly visible-light activity is also observed. UV–vis diffuse reflectance spectra and X-ray photoelectron spectroscopy confirm that the carbon atoms are incorporated into the interstitial positions of TiO2 lattice and form a strong interaction with titanium atoms and extend photoresponding range to 700nm. Surface photovoltage spectra (SPS) and transient photovoltage (TPV) suggest that the presence of interstitial carbons induce several localized occupied states in the gap, enhance the separation extent and restrain the recombination of the photo-induced electron and hole carriers in TiO2. [Copyright &y& Elsevier]

We propose an ECR ozone plasma re-oxidation annealing (ROA) method that can introduce high-concentration and high-reactivity O atoms to eliminate defects near the SiC/SiO 2 interface with low temperature (400 °C). This method can more effectively improve the electrical performance of SiC MOS capacitors compared with other ROA methods, including O 2 , O 3 and O 2 plasma ROA methods. Secondary ion mass spectroscopy (SIMS), atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS) are performed. Results indicate that the O3P-ROA can evidently re-oxidize near-interface defects, which optimize near-interface properties, including the elemental distribution of the near-interface region and the morphology of the SiC/SiO 2 interface. In addition, the effects of temperature and oxygen element on near-interface properties of SiC MOS capacitors are discussed in this paper. [ABSTRACT FROM AUTHOR]

In this paper, a series of BiOI/ZnO photocatalysts containing various BiOI contents were prepared by a facile two-step synthetic method. The structure and crystal phase, morphology, surface element analysis, optical property of as-prepared samples are measured by X-ray diffraction (XRD), Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and UV–Vis diffuse reflectance spectrometry (DRS). BiOI/ZnO photocatalytic activities of the prepared photocatalysts were evaluated by photocatalytic degradation of phenol under simulated light irradiation. The phenol degradation rate reached 99.9% within 2 h under simulated solar light irradiation. The probable photocatalytic mechanism of composites photocatalysts is discussed by active species trapping experiments, the surface photovoltage (SPV), the transient photovoltage (TPV) and photoluminescence (PL) measurements. The results manifest that the superior photocatalytic activity of BiOI/ZnO composites is derived from the strong internal electric field between BiOI and ZnO, which is beneficial for the effective separation and transfer of photogenerated charges in ZnO. Moreover, the loading of BiOI on the surface of ZnO inhibited the recombination of photogenerated charge carriers in ZnO, resulting in excellent photocatalytic activity. On the contrary, the effect of an extension of the light absorption range induced by the introduction of BiOI on the phenol degradation activity is not significant. [ABSTRACT FROM AUTHOR]

Abstract: An electron cyclotron resonance microwave nitrogen plasma post-oxidation annealing process was proposed to passivate the 4H-SiC MOS interface. The effects of this process on the electrical and physical properties of SiC MOS interface were investigated by current–voltage, capacitance–voltage, secondary ion mass spectrometry, and X-ray photoelectron spectroscopy measurements. By controlling the annealing period, this process could significantly reduce the density of interface traps (D it ) in the entire upper half of SiC band gap without degrading the oxide insulating properties. A 10-min annealing at 600°C produces the best result. The incorporated nitrogen, which is distributed throughout bulk SiO2 and SiO2/SiC interface, could reduce the content of SiO x C y and carbon clusters by forming some deep-level Si–N and C–N bonds. These results illustrate the physical modifications of SiC MOS interface induced by this process and explain the possible mechanism responsible for the observed reduction in D it in different energy ranges. [Copyright &y& Elsevier]

Abstract: N-type 4H–SiC (0001) surfaces were cleaned by low temperature hydrogen plasma in electronic cyclotron resonance (ECR) microware plasma system. The effects of the hydrogen plasma treatment (HPT) on the structure, chemical and electronic properties of surfaces were characterized by in situ reflection high energy electron diffraction (RHEED) and X-ray photoelectron spectroscopy (XPS). The RHEED results indicate that the structures of the films are strongly dependent on the treatment temperature and time. Significant improvements in quality of 4H–SiC films can be obtained with the temperature ranging from 200°C to 700°C for an appropriate treatment period. The XPS results show that the surface oxygen is greatly reduced and the carbon contamination is completely removed from the 4H–SiC surfaces. The hydrogenated SiC surfaces exhibit an unprecedented stability against oxidation in the air. The surface Fermi level moves toward the conduction band in 4H–SiC after the treatment indicating an unpinning Fermi level with the density of surfaces states as low as 8.09×1010 cm−2 eV−1. [Copyright &y& Elsevier]

Abstract: The surface structure of the iron oxide nanoparticles obtained by the co-precipitation method has been investigated, and a thin layer of α-FeOOH absorbed on surface of the nanoparticle is confirmed by analyses of Fourier transform infrared (FTIR), X-ray photoelectron spectra (XPS) and surface photovoltage spectroscopy (SPS). After annealed at 400°C, the α-FeOOH can be converted to γ-Fe2O3. The simple-annealed procedure resulted in the formation of Fe3O4@γ-Fe2O3 core/shell structure with improved stability and a higher magnetic saturation value, and also the simple method can be used to obtain core/shell structure in other similar system. [Copyright &y& Elsevier]

• Oxygen element improved the quality of SiC/SiO 2 interface and the voltage stability of SiC MOS devices. • Oxygen plasma ROA eliminated defects near SiC/SiO 2 interface. • Oxygen plasma ROA reduced the thicknesses of interface-transition region and Si-rich region. We proposed a solution to improve the interface property and voltage instability of silicon carbide metal–oxide–semiconductor (SiC MOS) capacitors by eliminating near-interface defects with a single oxygen element. Results indicated that the quality of the silicon dioxide (SiO 2) film and SiC/SiO 2 interface and the voltage stability of SiC MOS capacitors were simultaneously improved by the proposed process. The mechanism underlying the improvement in the electrical performance of SiC MOS capacitors by oxygen plasma re-oxidation annealing (OP-ROA) could be elaborated by analysing the results of secondary ion mass spectroscopy and X-ray photoelectron spectroscopy. We believe that the OP-ROA process can eliminate C- and Si-related defects and silicon oxycarbide (SiO x C y) and reduce the thicknesses of the interface–transition region, thereby decreasing relative Si and C contents near the SiC/SiO 2 interface. The evolution of C-related defect structures was simulated through density functional theory calculation, which was performed as a supplemental analysis. [ABSTRACT FROM AUTHOR]

• N O mixed plasma POA can greatly improve the interface property and BTI characteristics. • Synergistic mechanisms of N and O on improving the performance and stability were elaborated. • Implications for simultaneously suppressing the electron and hole trapping were discussed. Interface properties and bias temperature instability (BTI) determine the performance and stability of SiC metal-oxide semiconductor (MOS) devices. In this work, we propose an electron cyclotron resonance microwave nitrogen–oxygen (N O) mixed plasma post-oxidation annealing (POA) process to improve the interface properties and BTI of 4H-SiC MOS capacitors. Results showed that the N O mixed plasma POA reduces the density of interface traps, maintains the stability of the flat band voltage (V fb) hysteresis under four successive cycles of positive bias temperature stress (PBTS) and negative bias temperature stress (NBTS) at 423 K, and significantly reduces the V fb hysteresis under alternating PBTS and NBTS at 100 K. The oxide traps remarkably decreased to 2.27 × 1012 cm−2 after N O mixed plasma POA. The related passivation and improvement mechanisms were further studied by secondary ion mass spectroscopy, X-ray photoelectron spectroscopy, and density functional theory calculations. The synergistic effects of highly reactive N and O plasma promoted the considerable absorption of N at the interface and prevented further oxidation of the SiC substrate. We also elaborate on the effects of N, O, and N O plasma on the elimination and passivation of O vacancy defects, C-related defects (SiO x C y and C dimer), and Si interstitial defects and discuss implications of the simultaneous suppression of electron and hole trapping. [ABSTRACT FROM AUTHOR]