Investigating the Role of Surface Depletion in Governing Electron Transfer Events in Colloidal Plasmonic Nanocrystals

Doped metal oxide nanocrystals (NCs) attract immense attention because of their ability to exhibit a localized surface plasmon resonance (LSPR) that can be tuned extensively across the infrared region of the electromagnetic spectrum. LSPR tunability triggered through compositional and morphological changes during the synthesis (size, shape and doping percentage) is becoming well-established while the principles underlying dynamic, post-synthetic modulation of LSPR are not as well understood. Recent reports have suggested that the presence of a depletion layer on the NC surface may be instrumental in governing the LSPR modulation of doped metal oxide NCs. Here, we employ post-synthetic electron transfer to colloidal Sn-doped In2O3 NCs with varying size and Sn doping concentration to investigate the role of the depletion layer in LSPR modulation. By measuring the maximum change in LSPR frequency after NC reduction, we determine that a large initial volume fraction of the depletion layer in NCs results in a broad modulation of the LSPR energy and intensity. Utilizing a mathematical Drude fitting model, we track the changes in the electron density and the depletion layer volume fraction throughout the chemical doping process, offering fundamental insight into the intrinsic NC response resulting from such electron transfer events. We observe that the maximum change in electron density that can be induced through chemical doping is independent of Sn concentration, and subsequently, the maximum total electron density in the presence of excess reductant is independent of the NC diameter and is dependent only on the as-synthesized Sn doping concentration. This study establishes the central role that surface depletion plays in the electronic changes occurring in the NCs during post-synthetic doping and the results will be instrumental in advancing the understanding of optical and electrical properties of different colloidal plasmonic NCs.

SnO2 -SiO2 1D Core-Shell Nanowires Heterostructures for Selective Hydrogen Sensing

SnO2 is one of the most employed n-type semiconducting metal oxide (SMOX) in chemo-resistive gas-sensing although it presents serious limitations due to a low selectivity. Herein, we introduce one-dimensional (1D) SnO2-SiO2 core-shell nanowires (CSNWs). SnO2 nanowires (NWs) are synthesized by vapor–liquid–solid deposition and the amorphous SiO2-shell layer with varying thicknesses (1.8-10.5 nm) was grown by atomic layer deposition (ALD). SiO2-coated SnO2 CSNWs show lower baseline conductance as compared to the Pristine SnO2 NWs, due to an enhancement of the electron depletion layer. The SnO2-SiO2/N CSNWs (N representing the number of SiO 2 ALD cycles) sensors show a dramatic improvement of the selectivity towards hydrogen. Moreover, the sensing-response markedly depends on the thickness of the SiO2-shell layer and the working temperature. The SnO2-SiO2/60 CSNWs sensor (ca. 4.8 nm SiO2 shell thickness) was the best performing sensor in terms of selectivity and sensitivity exhibiting a response of 160 (ca. 7-folds higher than the pristine SnO2 NWs) towards 500 ppm of hydrogen at 500 °C with a lower detection limit at ppb-level (0.082 ppm). The selectivity and enhanced sensing-response are related to the masking effect of the SiO2 shell and an increased in the width of the electron depletion layer due to the strong electronic coupling between the SnO2 core and SiO2-shell layer, respectively. The remarkable sensing performances of the SnO2-SiO2/N CSNWs can be attributed to the homogeneous and conformal SiO2 shell layer by ALD,<br>electronic coupling between the core and the shell, the optimized shell thickness and high surface area provided by the 1D SnO2 NWs network.<br>

SnO2 -SiO2 1D Core-Shell Nanowires Heterostructures for Selective Hydrogen Sensing

SnO2 is one of the most employed n-type semiconducting metal oxide (SMOX) in chemo-resistive gas-sensing although it presents serious limitations due to a low selectivity. Herein, we introduce one-dimensional (1D) SnO2-SiO2 core-shell nanowires (CSNWs). SnO2 nanowires (NWs) are synthesized by vapor–liquid–solid deposition and the amorphous SiO2-shell layer with varying thicknesses (1.8-10.5 nm) was grown by atomic layer deposition (ALD). SiO2-coated SnO2 CSNWs show lower baseline conductance as compared to the Pristine SnO2 NWs, due to an enhancement of the electron depletion layer. The SnO2-SiO2/N CSNWs (N representing the number of SiO 2 ALD cycles) sensors show a dramatic improvement of the selectivity towards hydrogen. Moreover, the sensing-response markedly depends on the thickness of the SiO2-shell layer and the working temperature. The SnO2-SiO2/60 CSNWs sensor (ca. 4.8 nm SiO2 shell thickness) was the best performing sensor in terms of selectivity and sensitivity exhibiting a response of 160 (ca. 7-folds higher than the pristine SnO2 NWs) towards 500 ppm of hydrogen at 500 °C with a lower detection limit at ppb-level (0.082 ppm). The selectivity and enhanced sensing-response are related to the masking effect of the SiO2 shell and an increased in the width of the electron depletion layer due to the strong electronic coupling between the SnO2 core and SiO2-shell layer, respectively. The remarkable sensing performances of the SnO2-SiO2/N CSNWs can be attributed to the homogeneous and conformal SiO2 shell layer by ALD,<br>electronic coupling between the core and the shell, the optimized shell thickness and high surface area provided by the 1D SnO2 NWs network.<br>

Модификация электронных свойств поверхности n-InP(100) сульфидными растворами

Photoluminescence and Raman spectroscopy are used to study the electronic properties of n-InP(100) surfaces passivated with different sulfide solutions. Such a passivation results in the increase in photoluminescence intensity of the semiconductor evidencing for the reduction in the surface recombination velocity. The increase in the photoluminescence intensity is accompanied by the narrowing of the surface depletion layer, as well as by the increase of the electron density in the probed volume of InP. The efficiency of electronic passivation of the n-InP(100) surface depends on the composition of the sulfide solution.

Analysis of junction capacitance characteristics of trench gate IGBT

Trench gate field termination IGBT represents the latest structure of insulated gate bipolar transistor (IGBT). Because the internal current of IGBT includes the charging and discharging current of gate capacitance and internal junction capacitance during switching transient, the influence of junction capacitance should be considered. The conductive channel of trench gate structure is different from that of planar gate structure, and the analysis method of junction capacitance using planar gate structure will inevitably bring some deviation. Based on the characteristics of trench gate structure, this paper analyzes the different expressions of internal gate-drain junction capacitance in two cases according to whether the base depletion layer can be widened to cover the trench gate, and finally carries out simulation and experimental verification.

Direct observation of potential phase at joining interface between p-MgO and n-MgFe2O4

Visualization of the depletion layer is a significant a guideline for the material design of gas sensors. We attempted to measure the potential barrier at the interface of core–shell microspheres composed of p-MgO/n-MgFe2O4/Fe2O3 from the inside out by means of Kelvin probe force microscopy (KPFM) as a first step to visualizing enlargement of the depletion layer. As determined by high-angle annular dark-field scanning transmission electron microscopy, ca. 70% of the microspheres were hollow with a wall thickness of ca. 200 nm. Elemental mapping revealed that the hollow particles were composed of ca. 20 nm of MgO, ca. 80 nm of MgFe2O4, and ca. 100 nm of Fe2O3. A difference of 0.2 V at the p-MgO/n-MgFe2O4 interface was clarified by KPFM measurements of the hollow particles, suggesting that this difference depends on the formation of a p–n junction. The potential barrier enlarged by the formation of a p–n junction was considered to increase the resistance in air (Ra), since the Ra of the core–shell hollow microspheres was higher than that of MgO, Fe2O3, MgO–Fe2O3, and MgO/MgFe2O4/Fe2O3 particles with irregular shapes. Measurement of the potential barrier height by KPFM is a promising potential approach to tuning the gas sensitivity of oxide semiconductors.