Local symmetry breaking in SnO2 nanocrystals with cobalt doping and its effect on optical properties

Structural, optical and antibacterial activity of pure and co-doped (Fe & Ni) tin oxide nanoparticles

In this investigation, ferric (Fe) and nickel (Ni) co-doped tin oxide (SnO₂) nanoparticles structural, optical, morphological, and antibacterial characteristics were synthesised, characterised, and examined. By employing SnCl₂·2H₂O and the transition metal precursors FeCl₃ and NiCl₂·6H₂O with various Fe/Ni molar ratios, thermal annealing was carried out at a high temperature (700 °C). X-ray diffraction (XRD), UV-Visible spectroscopy, Photoluminescence (PL), FT-IR, and scanning electron microscopy (SEM) with energy dispersive X-ray techniques (EDX) were used to examine the materials' structural, chemical, optical, morphological, and anti-microbial capabilities. The average particle size of pure and co-doped SnO₂ nanoparticles was determined to be around 52 nm and 15 nm, and SnO₂ crystallites were observed to present tetragonal rutile structure with space group P_42/mmm (No.136). Metal ions were replaced in the Sn lattice, as shown by Fe and Ni co-doped SnO₂ nanoparticles. Pure and co-doped samples have capsule and sphere-like features in their SEM morphology. Using UV-visible diffuse reflectance spectroscopy, the optical property was examined, and it was observed that the band gaps for pure and co-doped SnO₂ were 3.73 eV and 3.53 eV, respectively. The functional groups and incorporation of Fe and Ni in the prepared powder were also validated by FT-IR and EDX studies. By utilising the agar well diffusion technique and Nutrient agar, the antibacterial properties of pure, Ni-Fe co-doped SnO₂ nanoparticles annealed at 700 °C were assessed. They were evaluated against various Gram-positive bacteria (Staphylococcus pheumoniae) and Gram-negative bacteria (Shigella dysenteria). The zone of incubation was found against the Gram +Ve and Gram -Ve bacterial strains.

Determination of intrinsic defects of functional KDP crystals with flawed surfaces and their effect on the optical properties

A practically nonlinear optical material, the functional KH₂PO₄ (KDP) crystal, has an extremely low laser-induced damage threshold (LIDT) due to manufacturing-induced surface defects. The low LIDT induced by these surface defects of KDP crystals hinders their application in laser fusion facilities. Herein, the effect of intrinsic point defects introduced by manufacturing-induced lateral cracks on laser damage was particularly investigated by a combination of spectral detection (i.e., photoluminescence, Raman and Fourier transformed infrared spectra) and first-principles calculation. It was determined that the manufacturing-induced lateral cracks would introduce more hydrogen vacancy and oxygen vacancy intrinsic defects than the ideal surface. These intrinsic defects would form cluster-type defects, lowering the LIDT to 6.600 J cm^-2 by introducing two defect levels of 2.83 eV and 4.89 eV within the band gap of the KDP crystal. To further investigate the effect of intrinsic defects introduced by lateral cracks on laser-induced damage growth, the transformation of charge states of intrinsic defects under laser irradiation was calculated. Combined with the spectral information of the lateral crack-induced laser damage site and the laser damage growth experiments, it was found that the intrinsic defects of lateral cracks have a large amount of evolution, making the crystal prone to severe damage growth. Overall, the avoidance of such lateral cracks with a large number of intrinsic defects is very beneficial for improving the laser damage resistance of KDP crystals.

Dual Enhancement of Sodium Storage Induced through Both S-Compositing and Co-Doping Strategies

As a promising alternative to lithium-ion batteries (LIBs), rechargeable sodium-ion batteries (SIBs) are attracting enormous attention due to the abundance of sodium. However, the lack of high-performance sodium anode materials limits the commercialization of SIBs. In this work, the dual enhancement of SnS₂/graphene anodes in sodium storage is achieved through S-compositing and Co doping via an innovative one-step hydrothermal reaction at a relatively low temperature of 120 °C. The as-prepared 7% Co-SnS₂/S@r-G composite consisting of 15.4 wt % S and 1.49 atom % Co shows both superior cycling stability (over 1000 cycles) and rate capability, giving high reversible specific capacities of 878, 608, and 470 mAh g^-1 at 0.2, 5, and 10 A g^-1, respectively. More encouragingly, the full-cell also exhibits an outstanding long-term cycling performance under 0.5 A g^-1, which delivers a reversible capacity of 500 mAh g^-1 over 200 cycles and still retains a high reversible capacity of 432 mAh g^-1 over 400 cycles. The enhancement mechanism is attributed to the favorable three-dimensional structure of the composite, Co doping, and S-composition, which can induce a synergistic effect.

Polycrystalline SnSe with a thermoelectric figure of merit greater than the single crystal

Thermoelectric materials generate electric energy from waste heat, with conversion efficiency governed by the dimensionless figure of merit, ZT. Single-crystal tin selenide (SnSe) was discovered to exhibit a high ZT of roughly 2.2-2.6 at 913 K, but more practical and deployable polycrystal versions of the same compound suffer from much poorer overall ZT, thereby thwarting prospects for cost-effective lead-free thermoelectrics. The poor polycrystal bulk performance is attributed to traces of tin oxides covering the surface of SnSe powders, which increases thermal conductivity, reduces electrical conductivity and thereby reduces ZT. Here, we report that hole-doped SnSe polycrystalline samples with reagents carefully purified and tin oxides removed exhibit an ZT of roughly 3.1 at 783 K. Its lattice thermal conductivity is ultralow at roughly 0.07 W m^-1 K^-1 at 783 K, lower than the single crystals. The path to ultrahigh thermoelectric performance in polycrystalline samples is the proper removal of the deleterious thermally conductive oxides from the surface of SnSe grains. These results could open an era of high-performance practical thermoelectrics from this high-performance material.

Two-dimensional electronic devices modulated by the activation of donor-like states in boron nitride

A two-dimensional (2D) layered material-based p-n diode is an essential element in the modern semiconductor industry for facilitating the miniaturization and structural flexibility of devices with high efficiency for future optoelectronic and electronic applications. Planar devices constructed previously required a complicated device structure using a photoresist, as they needed to consider non-abrupt interfaces. Here, we demonstrated a WSe₂ based lateral homojunction diode obtained by applying a photo-induced effect in BN/WSe₂ heterostructures upon illumination via visible and deep UV light, which represents a stable and flexible charge doping technique. We have discovered that with this technique, a field-effect transistor (FET) based on p-type WSe₂ is inverted to n-WSe₂ so that a high electron mobility is maintained in the h-BN/n-WSe₂ heterostructures. To confirm this hypothesis, we deduced the work function values of p-WSe₂ and n-WSe₂ FETs by conducting Kelvin probe force microscopy (KPFM) measurements, which revealed the decline of the Fermi level from 5.07 (p-WSe₂) to 4.21 eV (n-WSe₂). The contact potential difference (CPD) between doped and undoped junctions was found to be 165 meV. We employed ohmic metal contacts for the planar homojunction diode by utilizing an ionic liquid gate to achieve a diode rectification ratio up to ∼10⁵ with n = 1. An exceptional photovoltaic performance is also observed. The presence of a built-in potential in our devices leads to an open-circuit voltage (V_oc) and short-circuit current (I_sc) without an external electric field. This effective doping technique is promising to advance the concept of preparing future functional devices.

Role of size, alio-/multi-valency and non-stoichiometry in the synthesis of phase-pure high entropy oxide (Co,Cu,Mg,Na,Ni,Zn)O

Presence of multivalency/non-stoichiometry to accommodate a different-sized cation and maintaining electroneutrality were identified as the critical criteria for single-phase formation in multicomponent/high entropy systems.

Mesoporous Co x Sn(1-x)O2 as an efficient oxygen evolution catalyst support for SPE water electrolyzer

SPE water electrolysis is a promising method of hydrogen production owing to its multiple strengths, including its high efficiency, high product purity and excellent adaptability. However, the overpotential of the oxygen evolution reaction process and consumption of Ir during charging in SPE water electrolysis will inevitably result in large energy loss and then high cost. Under these circumstances, we propose a novel 40IrO₂/Co _x Sn_(1-x)O₂ (x = 0.1, 0.2, 0.3) anode catalyst, where the Co _x Sn_(1-x)O₂ support is synthesized by a hydrothermal method and IrO₂ is synthesized by a modified Adams fusion method. After modifying the component of Co _x Sn_(1-x)O₂, the 40IrO₂/Co _x Sn_(1-x)O₂ exhibits an increased specific surface area, electrical conductivity and surface active sites. Moreover, a single cell is fabricated by Pt/C as cathode catalyst, 40IrO₂/Co _x Sn_(1-x)O₂ as anode catalyst and Nafion 117 membrane as electrolyte. The 40IrO₂/Co_0.2Sn_0.8O₂ exhibits the lowest overpotential (1.748 V at 1000 mA cm^-2), and only 0.18 mV h^-1 of voltage increased for 100 h durability test at 1000 mA cm^-2. Consequently, Co _x Sn_(1-x)O₂ is a promising anode electrocatalyst support for an SPE water electrolyzer.

Investigation of Microstructure Effect on NO2 Sensors Based on SnO2 Nanoparticles/Reduced Graphene Oxide Hybrids

The microstructures of metal oxide-modified reduced graphene oxide (RGO) are expected to significantly affect room-temperature (RT) gas sensing properties, where the microstructures are dependent on the synthesis methods. Herein, we demonstrate the effect of microstructures on RT NO₂ sensing properties by taking typical SnO₂ nanoparticles (NPs) embellished RGO (SnO₂ NPs-RGO) hybrids as examples. The samples were synthesized by growing SnO₂ NPs on RGO through hydrothermal reduction (SnO₂ NPs-RGO-PR), which display the advantages such as high reactivity of the SnO₂ surface with NO₂, more oxygen vacancies (O_V) and chemisorbed oxygen (O_C), close contact between SnO₂ NPs and RGO, and large surface area, compared to the samples prepared by one-pot hydrothermal synthesis from Sn⁴⁺ and GO (SnO₂ NPs-RGO-IS), and the assembly of SnO₂ NPs on RGO (SnO₂ NPs-RGO-SA). As expected, the SnO₂ NPs-RGO-PR-based sensor presents high sensitivity towards 5 ppm NO₂ (65.5%), but 35.0% for the SnO₂ NPs-RGO-IS-based sensor and 32.8% for the SnO₂ NPs-RGO-SA-based sensor at RT. Meanwhile, the corresponding response time and recovery time calculated by achieving 90% of the current change of the SnO₂ NPs-RGO-PR-based sensor for exposure to NO₂ is 12 s and to air is 17 s, respectively, whereas 74/42 s for the SnO₂ NPs-RGO-IS-based sensor and 77/90 s for the SnO₂ NPs-RGO-SA-based sensor. The results can prove the tailoring sensing behavior of the gas sensor according to different structures of materials.