Defects are detrimental for optoelectronics devices, such as stacking faults can form carrier-transportation barriers, and foreign impurities (Au) with deep-energy levels can form carrier traps and nonradiative recombination centers. Here, self-catalyzed p-type GaAs nanowires (NWs) with a pure zinc blende (ZB) structure are first developed, and then a photodetector made from these NWs is fabricated. Due to the absence of stacking faults and suppression of large amount of defects with deep energy levels, the photodetector exhibits room-temperature high photoresponsivity of 1.45 × 10 A W and excellent specific detectivity (D*) up to 1.48 × 10 Jones for a low-intensity light signal of wavelength 632.8 nm, which outperforms previously reported NW-based photodetectors. These results demonstrate these self-catalyzed pure-ZB GaAs NWs to be promising candidates for optoelectronics applications.

Accurate design of high‐performance 3D surface‐enhanced Raman scattering (SERS) probes is the desired target, which is possibly implemented with a prerequisite of quantifying formidable multiple coupling effects involved. Herein, by combining theory and experiments on 3D periodic Au/SiO 2 nanogrid models, a generalized methodology of accurately designing high performance 3D SERS probes is developed. Structural symmetry, dimensions, Au roughness, and polarization are successfully correlated quantitatively to intrinsic localized electromagnetic field (EMF) enhancements by calculating surface plasmon polariton (SPP), localized surface plasmon resonance (LSPR), optical standing wave effects, and their couplings theoretically, which is experimentally verified. The hexagonal SERS probes optimized by this methodology realize over two orders of magnitudes (405 times) improvement of detection limit for Rhodamine 6G model molecules (2.17 × 10 −11 m ) compared to the unoptimized probes with the same number density of hot spots, an enhancement factor of 3.4 × 10 8 , a uniformity of 5.52%, and are successfully applied to the detection of 5 × 10 −11 m Hg ions in water. This unambiguously results from the Au roughness‐independent extra 144% contribution of LSPR effects excited by SPP interference waves as secondary sources, which is very unusual to be beyond the conventional recognition.

High sensitivity, low limit of detection (LOD), and short response and recovery times at room temperature (RT) are critical for gas sensors. For NO2, different binary metal oxide-based sensors were developed to achieve superior performance at elevated temperatures instead of RT. Herein, we report on CuO@CuO and Cu3Mo2O9@CuO sensors with CuO and Cu3Mo2O9 micro/nanorods vertically aligned on the CuO layers, which were directly fabricated using a facile, low-cost, and catalyst-free chemical vapor deposition (CVD) technique. Their sensing performance tests revealed that the Cu3Mo2O9@CuO p–p heterojunction sensors exhibited a high response of 160% to 5 ppm NO2, an excellent sensitivity of 50% ppm–1, a low LOD of 2.30 ppb, a short response time of 49 s, and a rapid recovery of 241 s at RT, obviously better than those for CuO@CuO sensors. The superior performance of Cu3Mo2O9@CuO sensors could be attributed to the Schottky heterojunction formed between p-Cu3Mo2O9 micro/nanorods and p-CuO films, the catalytic effect, and the anisotropic nature of Cu3Mo2O9 micro/nanorods. This study not only provides a simple, low-cost, and batchable fabrication method of homo/heterojunction sensors with micro/nanorods vertically aligned on films but also opens an avenue for sensor design by tuning the Schottky barrier height to enhance RT performance.

Simultaneous achievement of high response, high sensitivity, low detection limit, and full recovery at room temperature (RT) is quite challenging for gas sensors. Herein, ultrathin titanium oxide/graphene Schottky heterojunction sensors (SHS) are fabricated with varying junction areas. Increasing junction area favors the sensing performance. A change of 11.822 meV in Schottky barrier height (SBH) is induced by 3 ppm NO2 exposure, accompanied by a change of −36.54% in current, ≈18 and 36 times that for bare titanium oxide and graphene sensors at RT, respectively. A high sensitivity of 10.430% ppm−1, low detection limit of 28 ppb, and complete recovery for 100 ppb NO2 are simultaneously achieved at RT. 100 ppm NH3 can be detected with full recovery as well. The superior performance of SHS is predominantly attributed to the effective modulation of SBH (exponential change in current) by gas adsorption and the charge transfer to interfaces enhanced by the presence of ultrathin continuous oxide layers. The sensing mechanism can be understood via energy band diagrams. This study proposes an idea of designing SHS with ultrathin n‐metal oxides and p‐graphene to simultaneously achieve high sensitivity, low detection limit, and full recovery for NO2 and other gases at RT.

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Ultrathin TiO2/graphene field effect transistor sensors with 100% titanium coverage (D100) favor the room temperature NH3 sensing performance at lower Schottky barrier height via switch in the sensing mode from p to n.

approaches compatible with the conventional semiconductor processes include patterning, etching, and evaporation, which would give rise to the contamination, the structural and chemical changes, and the damages of the sensing chip surface of sensors due to the unavoidable resist residues and/or thermal and radiative effects during fabrication processes. In sharp contrast, shadow mask approach may be adopted as an alternative of sensor fabrication like gas sensors etc. that could protect the sensing chip surface against the contamination, the unwanted structural and chemical changes, and the damages, which would guarantee a clean sensing chip surface with good enough reactivity with the gas molecules, particularly the one with a weak charge transfer nature like NH 3 . NH 3 , a kind of weak electron donor air pollutant, released as an industrial and combustion waste, is a serious threat to the human health and environment. [1] Many diversified gas sensors based on metal oxides, graphene/reduced graphene oxide (RGO), transition metal dichalcogenides and their reasonable hybrids etc., fabricated in chemiresistor or/and field effect transistor (FET) configurations have been reported for NH 3 detection. For instance, a gas sensor based on atomic layers of MoS 2 shows Both simultaneous achievement of high response, low limit of detection, and full recovery at room temperature (RT) for weak reducing gases like NH 3 and facile and batchable fabrication approach are quite challenging for sensors. Herein, ultrathin MoO x layers are hybridized with mono layer graphene with different coverage percentages, into MoO x /GFET (graphene field effect transistor) devices for selective NH 3 sensing fabricated by a facile, cost effective, and contamination-free shadow mask approach instead of conventional lithography processes. A response of −18.10% for 12 ppm NH 3 with full recovery of 356 s, superior repeatability, low detection limit of 310 ppb, and strong selectivity is simultaneously achieved for MoO x /GFET sensors at RT. The superior sensing and recovery performance of MoO x /GFET sensors is predominantly attributed to the effective tuning of Schottky barrier height and the Coulomb interaction between charged polar donor molecules and positively polarized surface enhanced by the positive bias voltage. The energy band diagrams well explain the sensing mechanism for reducing/oxidizing gases. The idea proposed in this study offers a feasible solution for highly selective sensing of different gases by oxides/graphene hybrid FET based gas sensors with superior RT performances fabricated by a facile, contamination-free, batchable, and generalized approach.A. Falak

We report the synthesis and electrical transport mechanism in ZnS semiconductor nanoparticles. Temperature dependent direct current transport measurements on the compacts of ZnS have been performed to investigate the transport mechanism for temperature ranging from 300 K to 400 K. High frequency dielectric constant has been used to obtain the theoretical values of Richardson-Schottky and Poole-Frenkel barrier lowering coefficients. Experimental value of the barrier lowering coefficient has been calculated from conductance-voltage characteristics. The experimental value of barrier lowering coefficient βexp lies close to the theoretical value of Richardson-Schottky barrier lowering coefficient βth,RS showing Richardson-Schottky emission has been responsible for conduction in ZnS nanoparticles for the temperature range studied.