Nanoengineering of Anisotropic Materials for Creating the Active Optical Cells with Increased Energy Efficiency

In this paper the state-of-the-art for exploiting the unique physical and chemical properties of crystalline materials and their possible applications for development of crystalline nanocomposites with the tailored anisotropy were discussed. Using a method of growing crystals from a solution the KDP and TGS nanocrystalites were grown in the mezopores of the Al2O3 matrix. To investigate the developed nanocrystalline samples the X-ray analysis was used. A form of the obtained diffractograms and our calculations show the predominant crystallization of the KDP and TGS in the direction [100], which coincides with the direction of the cylindrical pores. Thus, diffractograms contain only reflexes of crystallographic planes (200) and (400). The achieved result indicates the possibility of growing of nanocrystals in mesopores of such Al2O3 structures developed by us and provides the prospect of creating optical cells with increased energy efficiency

Investigation of Negative Differential Resistance Phenomena in Quantum Well Heterostructures

Increasing interest in entirely new possibilities for quantum mechanical description of carriers transport is becoming more evident with the developing advancements in epitaxial growth technique. Consequently, molecular beam epitaxy (MBE) technique is considered to be the most precise technique that allows the growth of ultra-thin layers of different compositions. Those structures can be designed to investigate the wave-nature of carriers, which broadens the possibilities in device design and fabrication for a specific area. In this thesis the fundamental study of the real space charge transfer (RST) mechanism that took place in quantum well heterostructures and led to the negative differential resistance observation is presented. Using the Hall effect measurement technique, the mobility and carrier concentration were measured and analyzed by considering different scattering mechanisms and carrier thermal activation phenomena, respectively. Deep level noise spectroscopy (DLNS) was used to investigate and probe the materials for the presence of defects and impurity states, which were needed to achieve the RST. The pulsed I-V measurements were performed to observe the negative differential resistance (NDR). Finally, the lock-in technique and pulsed I-V technique with light excitation and temperature cycling were used to prove the presence of RST mechanism in our system. The results of this study can be implemented to create devices for high frequency applications

Coherent Laser Induced Synthesis of Rare Earth Doped Nanocrystallites of 50PbO-25Bi2_2O3_3-20Ga2_2O3_3-5BaO

A principal possibility of formation the nanostructures on the surfaces of 50PbO-25Bi$_2$O$_3$-20Ga$_2$O$_3$-5BaO (doped by Eu3+, Er3+, Dy3+) is demonstrated by using multi-coherent beams. As a sources of the photoinducing coherent light we have used nanosecond Nd:YAG and Er:Yb lasers generating at 1064 nm and 1540 nm, respectively. The morphology of the photoinduced surfaces is sensitive to the type of rare earth ions. The thickness of the layer was about 20-30 nm. Possible mechanisms are explained by coherent photoinduction of the valence electrons

Paraelectric KH2_2PO4_4 Nanocrystals in Monolithic Mesoporous Silica: Structure and Lattice Dynamics

Combining dielectric crystals with mesoporous solids allows a versatile design of functional nanomaterials, where the porous host provides a mechanical rigid scaffold structure and the molecular filling adds the functionalization. Here, we report a study of the complex lattice dynamics of a SiO$_2$:KH$_2$PO$_4$ nanocomposite consisting of a monolithic, mesoporous silica glass host with KH$_2$PO$_4$ nanocrystals embedded in its tubular channels $\sim$12 nm across. A micro-Raman investigation performed in the spectral range of 70-1600 cm$^{-1}$ reveals the complex lattice dynamics of the confined crystals. Their Raman spectrum resembles the one taken from bulk KH$_2$PO$_4$ crystals and thus, along with X-ray diffraction experiments, corroborates the successful solution-based synthesis of KH$_2$PO$_4$ nanocrystals with a structure analogous to the bulk material. We succeeded in observing not only the high-frequency internal modes ($\sim$900-1200 cm$^{-1}$), typical of internal vibrations of the PO$_4$ tetrahedra, but, more importantly, also the lowest frequency modes typical of bulk KH$_2$PO$_4$ crystals. The experimental Raman spectrum was interpreted with a group theory analysis and first-principle lattice dynamics calculations. The analysis of calculated eigen-vectors indicates the involvement of hydrogen atoms in most phonon modes corroborating the substantial significance of the hydrogen subsystem in the lattice dynamics of paraelectric bulk and of KH$_2$PO$_4$ crystals in extreme spatial confinement. A marginal redistribution of relative Raman intensities of the confined compared to unconfined crystals presumably originates in slightly changed crystal fields and interatomic interactions, in particular for the parts of the nanocrystals in close proximity to the silica pore surfaces.Comment: 10 pages, 4 figures, in pres

CdS Nanocrystallines: Synthesis, Structure and Nonlinear Optical Properties

We report the synthesis, structure and nonlinear optical properties of cadmium sulphide (CdS) nanocrystallines (NCs) synthesized electrochemically both with and without detergent ATLAS G3300. Relevant structural and morphological features are explored by X-ray diffraction and scanning electron microscopy (SEM) techniques. The efficiency of the second harmonic generation (SHG) appears to be strongly dependent on the energy density of the incident fundamental laser radiation and NC sizes.Comment: 2020 IEEE 15th International Conference on Advanced Trends in Radioelectronics, Telecommunications and Computer Engineering (TCSET), Conference Location: Lviv-Slavske, Ukraine, 25-29 February 2020, 5 pages, 8 figures, 3 table