Ideal two-dimensional (2D) Heisenberg magnets lack long range magnetic order. However, the XY model with spins confined to a plane shows a topological phase transition at a finite temperature corresponding to binding and unbinding of vortices. Experimental evidence for such Berezinskii-Kosterlitz-Thouless (BKT) transitions has been difficult to obtain in condensed matter systems, where, even a weak interlayer coupling that is invariably present leads to long-range order, pre-empting the BKT transition. The BKT signatures are still discernible above the long-range ordering temperature, however, in the characteristic exponential temperature dependence of the coherence length of the fluctuations. In this work we report that an applied magnetic field can induce such BKT correlations not only in quasi 2-dimensional systems but also in nominally 3-dimensional manganites undergoing antiferromagnetic transitions. We arrive at this unexpected conclusion based on our studies of temperature dependence of electron paramagnetic resonance (EPR) linewidth ΔH(T) of Cr3+ doped bismuth strontium manganite Bi0.5Sr0.5Mn1-xCrxO3 (x= 0.04, 0.1) (BSMCO04 and BSMCO10).

This paper focuses on describing the integration of ultrananocrystalline diamond (UNCD) coating on pure titanium-based dental implants (DIs) integrated with the surface pre-treatment by chemical-mechanical nano-structuring (CMNS) process. The combination of the UNCD coating with the CMNS metal surface treatment provides a transformational process to produce a new generation of metallic implants. CMNS promotes a uniform and dense titanium oxide interface and UNCD enables higher resistance to chemical-induced corrosion by oral fluids and enhanced bone attachment due to superior bone cell growth on C atoms (element of life in human DNA and cell). The main focus of the presented research is to establish the preliminary studies on the integration of the UNCD coating process on CMNS treated dental implants to promote corrosion resistance and biocompatibility. It is demonstrated that the CMNS process in the presence of an oxidizer (1M to be optimal) induces a tailored interface to promote UNCD coating capability through effective interface passivation leading to uniform surface coverage. The final implant product is observed to have improved corrosion potential and enhanced hydrophobicity indicating better biocompatibility providing the basis for a new generation of superior DIs. The findings can further be extended to the hip, knee, and other orthopedic metallic implants, which require major performance improvements, particularly in reducing or eliminating in-vivo body fluid-induced chemical corrosion.

Photodetectors based on a hybrid structure of graphene sensitized with lead selenide (PbSe) colloidal quantum dots (QDs) effective in the near-infrared (NIR) region with high responsivity were investigated. Colloidal PbSe nanocrystals were synthesized via a hot injection method. The bandgap of the synthesized nanocrystals was determined to be 0.68 eV by measuring their optical absorbance spectrum. Photodetectors based on PbSe QDs were investigated to examine their functionality. These devices were characterized by measuring the current-voltage curves in the dark and light and the spectral response spectrum. A photodetector was fabricated using a multilayer mechanically exfoliated graphene on a Si/SiO2 substrate with a PbSe QDs layer on top. A responsivity and detectivity of 1265A/W and 3.4 *1010cm.Hz0.5/W respectively were calculated based on current-voltage measurements.

Transition metal dichalcogenide materials MX2 (M = Mo;W;X = S; Se) are being thoroughly studied due to their novel two-dimensional structure, that is associated with exceptional optical and transport properties. From a computational point of view, Density Functional Theory simulations perform very well in these systems and are an indispensable tool to predict and complement experimental results. However, due to the time and length scales where even the most efficient DFT implementations can reach today, this methodology suffers of stringent limitations to deal with finite temperature simulations or electron-lattice coupling when studying excitation states: the unit cells required to study, for instance, systems with thermal fluctuations or large polarons would require a large computational power. Multi-scale techniques, like the recently proposed Second Principles Density Functional Theory, can go beyond these limitations but require the construction of tight-binding models for the systems under investigation. In this work, we compare two such methods to construct the bands of WSe2. In particular, we compare the result of (i) Wannier-based model construction with (ii) the band fitting method of Liu et al.,[1] where the top of the valence band and the bottom of the conduction band are modeled by three bands symmetrized to have mainly Tungsten dz2, dxy and dx2-y2character. Our results emphasize the differences between these two approaches and how band fitting model construction leads to an overestimation of the localization of the real-space basis in a tight-binding representation.

The contact angle is a material property determined by the surface tensions between substrate, liquid and the air. In this study, the surface wettability of vertical graphene nanosheets (VGNs) which are carbon nanostructures consisting of a few layers of graphene sheets vertically standing on the substrates, were developed by applying different voltages on the substrate. The contact angle of the water droplet on VGNs/Cu decreased from 123° to 16° with increasing the applied voltage which indicated the hydrophobic and hydrophilic transition of VGNs surfaces. It is anticipated that this member of the carbon material family (VGNs) could serve as a tunable wettability coting for future improvements in electronic devices and open a new perspective to the construction of smart material surfaces.