Preparation and electrical characterization of Cd0.8Zn0.2Te/Si thin films

Thin films of Cd_0.8Zn_0.2Te/Si structures were prepared by vacuum evaporation technique. The electrical properties such as activation energy, barrier height, and transport mechanism along with the capacitance-voltage characteristics are analyzed. The zero field activation energy calculated from the saturation current density with the inverse absolute temperature is found to be 0.37 eV and the barrier height is 0.54 eV. As the applied bias voltage increases the activation energy decreases from 0.3 to 0.22 eV for the bias range of 0-2 V. From the observed current voltage characteristics it is found that the surface state density is high for the films deposited at room temperature. From the high-frequency (1 MHz) C-V measurement the built in voltage is found to be 0.15 V. The plot of 1/C² vs the applied bias voltage behaviour is linear, indicating the presence of abrupt junction. The acceptor concentration as obtained from the 1/C² vs bias voltage is 1.4×10¹⁶ cm⁻³.     

Sized controlled synthesis, purification, and cell studies with silicon quantum dots

This article describes the size control synthesis of silicon quantum dots with simple microemulsion techniques. The silicon nanocrystals are small enough to be in the strong confinement regime and photoluminesce in the blue region of the visible spectrum and the emission can be tuned by changing the nanocrystal size. The silicon quantum dots were capped with allylamine either a platinum catalyst or UV-radiation. An extensive purification protocol is reported and assessed using (1)H NMR to produce ultra pure silicon quantum dots suitable for biological studies. The highly pure quantum dots were used in cellular uptake experiments and monitored using confocal microscopy. The results showed that the amine terminated silicon nanocrystals accumulated in lysosome but not in nuclei and could be used as bio-markers to monitor cancer cells over long timescales.     

Ultra-High Capacity and Cyclability of β-phase Ca0.14V2O5 as a Promising Cathode in Calcium-Ion Batteries

Crystalline water-free β-phase Ca_0.14V₂O₅ is reported for the first time as a viable cathode material for calcium-ion batteries (CIBs). In contrast to layered α-V₂O₅ and δ-Ca_xV₂O₅·nH₂O, which have limited capacity, the β-phase delivers a reversible capacity of ≈247 mAh g⁻¹, which corresponds to the insertion/extraction of Ca²⁺ between Ca_0.14V₂O₅ and Ca_1.0V₂O₅. The process of Ca²⁺ insertion process and the accompanying structural relaxation are theoretically and experimentally verified. The initial insertion of Ca²⁺ into Ca_0.14V₂O₅ causes a slight shift of oxygen atoms surrounding hepta-coordination sites, creating penta-coordinated sites that are then partially filled up to Ca_0.33V₂O₅. Further insertion occurs through the stepwise occupation of up to 50% of neighboring hexa- and tetra-coordination sites to form Ca_0.67V₂O₅ and Ca_1.0V₂O₅, respectively. The rearrangement of oxygen atoms in Ca_0.14V₂O₅ also minimizes dimensional changes, leading to high cyclic stability during repeated charge/discharge cycles. The remarkable electrochemical performance of full cells containing a Ca_0.14V₂O₅ cathode and a K metal anode in Ca²⁺/K⁺ hybrid electrolytes, is also demonstrated, thanks to the inertness of K⁺ insertion into Ca_0.14V₂O₅ and the absence of calcium plating/stripping. The cyclic stability and high capacity of Ca_0.14V₂O₅ is not compromised in hybrid electrolytes, making it a viable CIB cathode.