Measurements of Strain and Bandgap of Coherently Epitaxially Grown Wurtzite InAsP-InP Core-Shell Nanowires

Atomic Layer Deposition and Strain Analysis of Epitaxial GaN-ZnO Core-Shell Nanowires

We demonstrate the epitaxial coating of GaN NWs with an epitaxial ZnO shell by atomic layer deposition at 300 °C. Scanning transmission electron microscopy proves a sharp and defect-free coherent interface. The strain in the core-shell structure due to the lattice mismatch and different thermal expansion coefficients of GaN and ZnO was analyzed using 4D-STEM strain mapping and Raman spectroscopy and compared to theoretical calculations. The results highlight the outstanding advantages of epitaxial shell growth using atomic layer deposition, e.g., conformal coating and precise thickness control.

A novel CuBi2O4/polyaniline composite as an efficient photocatalyst for ammonia degradation

A novel polyaniline (PANI) coupled CuBi₂O₄ photocatalyst was successfully synthesized via in situ polymerization of aniline with pre-synthesized CuBi₂O₄ composites. The structure and morphology of the synthesized CuBi₂O₄/PANI composite photocatalyst were characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) and the photocatalytic performance were evaluated through degradation process of ammonia in water under visible light irradiation. The resultant CuBi₂O₄/PANI composite showed exceptional stability as its structure and morphology persisted even after being immersed in water for 2 days. The composite photocatalyst exhibited improved charge transport properties due to the electrical conductivity of the PANI protective layer, leading to enhanced photoelectrochemical activity in water and removal of ammonia. PANI with CuBi₂O₄ (10% wt) heterostructure was applied for photodegradation of ammonia and exhibited a 96% ammonia removal efficiency (30 mg/l with 0.1 g photocatalyst and 180 min), as compared to PANI (78%) and CuBi₂O₄ (70%). The degradation was attributed to the efficient charge transfer (e^- and h⁺) and formation of reactive oxygen species upon simulated sunlight exposure. The present work suggests that the CuBi₂O₄/PANI photocatalyst can be synthesized in a simple process and provides an excellent adsorption capacity, high photocatalytic activity, long term stability, and reusability making it a promising alternative for ammonia removal from wastewater.

Controllable vapor growth of CsPbBr3/CdS 1D heterostructures with type-II band alignment for high-performance self-powered photodetector

The controllable growth of CsPbBr3/CdS heterostructures with a unique 1D morphology and type-II band alignment for a high-performance self-powered photodetector.

Experimental and Numerical Investigation of Flow and Alignment Behavior of Waste Tire-Derived Graphene Nanoplatelets in PA66 Matrix during Melt-Mixing and Injection

Homogeneous dispersion of graphene into thermoplastic polymer matrices during melt-mixing is still challenging due to its agglomeration and weak interfacial interactions with the selected polymer matrix. In this study, an ideal dispersion of graphene within the PA66 matrix was achieved under high shear rates by thermokinetic mixing. The flow direction of graphene was monitored by the developed numerical methodology with a combination of its rheological behaviors. Graphene nanoplatelets (GNP) produced from waste-tire by upcycling and recycling techniques having high oxygen surface functional groups were used to increase the compatibility with PA66 chains. This study revealed that GNP addition increased the crystallization temperature of nanocomposites since it acted as both a nucleating and reinforcing agent. Tensile strength and modulus of PA66 nanocomposites were improved at 30% and 42%, respectively, by the addition of 0.3 wt% GNP. Flexural strength and modulus were reached at 20% and 43%, respectively. In addition, the flow model, which simulates the injection molding process of PA66 resin with different GNP loadings considering the rheological behavior and alignment characteristics of GNP, served as a tool to describe the mechanical performance of these developed GNP based nanocomposites.

Resonant Raman scattering of core-shell GaN/AlN nanowires

We have analyzed the electron-phonon coupling in GaN/AlN core-shell nanowires by means of Raman scattering excited at various wavelengths in the ultraviolet spectral range (335, 325 and 300 nm) and as a function of the AlN shell thickness. The detailed analysis of the multi-phonon spectra evidences important differences with excitation energy. Under 325 and 300 nm excitation the Raman process is mediated by the allowedA₁(LO) phonon mode, where the atoms vibrate along the NW axis. Considering its selection rules, this mode is easily accessible in backscattering along the wurtzitecaxis. Interestingly, for 335 nm excitation the scattering process is instead mediated by theE₁(LO) phonon mode, where atoms vibrate in thec-plane and that is forbidden in this configuration. This change is ascribed to the band anticrossing caused by the uniaxial strain imposed by the AlN shell and the proximity, at this particular excitation energy, of real electronic transitions separated by the energy of the longitudinal optical phonon modes. The energy and character of the electronic bands can be tuned by varying the AlN shell thickness, a degree of freedom unique to core-shell nanowires. The interpretation of the experimental results is supported by calculations of the electronic transitions of GaN under uniaxial strain performed within the framework of ak · pmodel.

On the piezotronic behaviours of wurtzite core-shell nanowires

The piezotronic behaviours of wurtzite core-shell nanowires (NWs) are studied in this paper by using a multiscale modelling technique. A difference between piezopotentials obtained from molecular dynamics simulations and finite element calculations indicates that due to the influence of small-scale effects the widely used conventional electromechanical theory is not accurate in describing the piezopotential properties of the present core-shell NWs. Although the residual strains intrinsically existing in core-shell NWs and the structural reconstruction at their surface and interface both account for these small-scale effects, the latter is found to play the dominate role, which makes the material properties of core-shell NWs significantly depend on their geometric size. A novel core-interface-shell-surface model is proposed here to analytically describe the size dependence of the material properties and thus the small-scale effects on the piezopotential of core-shell NWs. Besides possessing a good piezoelectric performance, our density functional theory calculations also show that the core-shell NWs under external loading can retain the semiconducting properties, which confirms the existence of piezotronic effects in them. However, owing to the intrinsic asymmetric Schottky barriers at the source and drain contacts induced by residual piezopotentials in core-shell NWs, the piezotronic effects of core-shell NWs are different to those of their conventional single-component counterparts. The superb piezopotential properties and unique piezotronic behaviours observed in wurtzite core-shell NWs make them good candidates for high performance components in novel piezotronic nanodevices.