Showing papers on "Potential well published in 2022"

Quantum confinement effect on defect level of hydrogen doped rutile VO2 nanowires

Abstract: Accurate description of solubility and defect ionization energies in low dimensional nanostructures is critical for electronic applications of semiconductors with improved functionalities. Here, we present quantum confinement effect driven strategies for tuning defect level of hydrogen doping in the core region of rutile [Formula: see text](R) nanowires. The inverse dependence of a bandgap with a diameter ([Formula: see text]) confirms the presence of quantum confinement effect in nanowires. The hydrogen doping in both interstitial and substitution at the O site behaves as a deep donor in low diameter nanowires, where the effect of quantum confinement is significant. The position of a donor charge transition level becomes increasingly shallower with increased nanowire diameters. The ionization energies of hydrogen defects decrease for larger-diameter nanowires due to the dielectric screening effect increment. This indicates the possibility of achieving n-type dopability with large diameter [Formula: see text](R) nanowires. This study prescribes the strategies for optimizing doping and the defect level for extensive applications of highly correlated 1D nanostructured materials.

First Study on the Electronic and Donor Atom Properties of the Ultra-Thin Nanoflakes Quantum Dots

Abstract: Nanoflakes ultra-thin quantum dots are theoretically studied as innovative nanomaterials delivering outstanding results in various high fields. In this work, we investigated the surface properties of an electron confined in spherical ultra-thin quantum dots in the presence of an on-center or off-center donor impurity. Thus, we have developed a novel model that leads us to investigate the different nanoflake geometries by changing the spherical nanoflake coordinates (R, α, ϕ). Under the infinite confinement potential model, the study of these nanostructures is performed within the effective mass and parabolic band approximations. The resolution of the Schrödinger equation is accomplished by the finite difference method, which allows obtaining the eigenvalues and wave functions for an electron confined in the nanoflakes surface. Through the donor and electron energies, the transport, optoelectronic, and surface properties of the nanostructures were fully discussed according to their practical significance. Our findings demonstrated that these energies are more significant in the small nanoflakes area by altering the radius and the polar and azimuthal angles. The important finding shows that the ground state binding energy depends strongly on the geometry of the nanoflakes, despite having the same surface. Another interesting result is that the presence of the off-center shallow donor impurity permits controlling the binding energy, which leads to adjusting the immense behavior of the curved surface nanostructures.

Silicon-Carbide Nanocrystals from Nonthermal Plasma: Surface Chemistry and Quantum Confinement

Abstract: Silicon-carbide (SiC) nanocrystals (NCs) of controlled 2–4 nm size are produced in low-pressure nonthermal plasma from the simple alkylsilane precursor tetramethylsilane (TMS). Generating material on the slightly carbon-rich side of 50/50 Si/C, we establish a process for thermally removing residual carbon, which in turn promotes a degree of intrinsic solubility in polar solvents such as isopropanol (IPA). Using the size-dependent Tauc gap of luminescent silicon NCs (Si NCs) as a point of reference, we demonstrate quantum confinement in nanocrystalline β-SiC but without measurable luminescence. Surface-sensitive spectroscopic techniques reveal an oxide shell surrounding a nanocrystalline SiC core, where negative surface charge groups promote solubility while likely acting as efficient trap states for nonradiative recombination. An analytical model is presented that combines electrostatic repulsion with van der Waals attraction to explain experimental observations of concentration-dependent cluster formation and reversible NC aggregation. We anticipate that these materials will be of interest for use as nanofillers in polymer composites and in specialty coatings, while providing a foundation for exploring routes to band gap emission from nanocrystalline SiC.

Quantum confinement in chalcogenides 2D nanostructures from first principles

Abstract: We investigated the impact of quantum confinement on the band gap of chalcogenides 2D nanostructures by means of density functional theory. We studied six different systems: MoS2, WS2, SnS2, GaS, InSe, and HfS2and we simulated nanosheets of increasing thickness, ranging from ultrathin films to ∼10-13 nm thick slabs, a size where the properties converge to the bulk. In some cases, the convergence of the band gap with slab thickness is rather slow, and sizeable deviations from the bulk value are still present with few nm-thick sheets. The results of the simulations were compared with the available experimental data, finding a quantitative agreement. The impact of quantum confinement can be rationalized in terms of effective masses of electrons and holes and system's size. These results show the possibility of reliably describing quantum confinement effects on systems for which experimental data are not available.

Comparative energy bandgap analysis of zinc and tin based chalcogenide quantum dots

Abstract: Semiconductors with wide bandgap are crucial for optoelectronic devices and energy applications owing to their electron confinement, high optical transparency and tunable electrical conductivity. Therefore, in this study, the quantum confinement effect of the energy bandgap of chalcogenide semiconductor nanocrystals such as ZnS, ZnSe, ZnTe, SnS, SnSe and SnTe are studied based on the Brus model using the effective mass approximation, the hyperbolic band model and the cohesive energy model. The obtained results indicate that the value of energy bandgap differs from the bulk crystals related to the quantum confinement effect. These verdicts confirm the quantum confinement effects of materials and their potential applications in optoelectronic devices. Theoretical findings are compared with its valid experimental data.

Fading of rhodamine B using CdS quantum dots under solar light

Abstract: Abstract Plate like cadmium sulfide (CdS) quantum dots were prepared by using β-cyclodextrin as reductant. Photoluminescence and uv-visible diffused reflectance spectroscopic techniques are used to investigate the optical property of CdS. The blue shifted emission of CdS at 469nm than the bulk particle is observed. The calculated band gap of CdS quantum dot is 2.62 eV showed a difference of 0.2 eV energy greater than that of bulk, indicating quantum size effect. The synthesized quantum dot has size in the range of 3.5nm with zinc blende crystallite structure. The plate like nanoclusters of CdS are inferred from SEM images. The photocatalytic efficiency of prepared CdS was tested for the degradation of rhodamine B dye using natural solar light. Effect of weight of catalyst, concentration of dye, pH of solution and reusability of catalyst were investigated. Existence of isosbestic point observation of high intense absorbance peak at 550nm at 300min in different matrix circumstances confirms the formation of leuco Rh B .

Highly emissive zero-dimensional perovskite prepared in aqueous solution and its recombination dynamics

Abstract: Quantum confinement effect can be realized by decreasing the structural dimension of perovskites . Although zero-dimensional perovskites (Cs 4PbBr6) demonstrate high fluorescence efficiency, it is still controversy about the nature of green emission and carrier recombination dynamics. In this work, phase-pure Cs4PbBr6 powder has been prepared in aqueous solution which supplies enough CsBr during the reaction. The high photoluminescence quantum yield (56.4%) of Cs 4PbBr6 is ascribed to high exciton binding energy 172 meV, which likely confines the excitons in the separated octahedral unit and facilitates exciton radiative recombination. The carrier recombination process is mainly trap states mediated recombination rather than bimolecular recombination which dominates in CsPbBr 3 thin films/nanocrystals. Spatially and temporally resolved fluorescence measurement clearly shows the whole regions of Cs4PbBr6 are fluorescent. These observations confirm that the green emission of Cs4PbBr6 originates from the trap states rather than the CsPbBr3 impurities, which is beneficial to its application in the field of optoelectronic devices .