Papers by Keyword: Nanocrystal

Abstract: Semiconductor nanostructures are referred to semiconductor heterostructures confined in one, two, or all three dimensions, which are known as quantum wells, quantum wires, and quantum dots (QDs), respectively. QDs are semiconductor nanocrystals with significant potential for high-performance photonic and electronic devices based on III–V semiconductor alloys. To fabricate these structures, several methods have been developed, including chemical synthesis of colloidal QDs, Stranski–Krastanov (S–K) growth technology, and droplet epitaxy (DE). DE is an epitaxial technique primarily employed for fabrication of nanostructures based on III–V semiconductors for quantum information technology applications. This work presents a DE technology of growth of InGaP nanocrystals on GaP surface. The technology includes the electrochemical deposition of group III metals on the III–V semiconductor surface, followed by annealing in inert gas atmosphere. The photoelectric and photonic properties of the resulting nanomaterials are analyzed. Based on the experimental results and literature data, the growth mechanism of InGaP nanocrystals on the GaP surface is described, and a phenomenological model for the formation of InGaP/GaP nanostructures is proposed.

Abstract: Pyrolytic technology was developed to grow Zn-based nano- and microstructures. It was based on the application of a mixture of ammonium chloride, Zn and ZnO powders as source materials. Two temperature profiles were used for the synthesis. In the first and second growth processes, the maximum substrate temperatures of 250 and 410°C were reached, respectively. The granular layer of micrometer range ZnO crystals was produced in the first process. By depleting the source with NH₄Cl, the Zn polyhedra, and layered spheres were produced within 50–65 min in the second process. By increasing the NH₄Cl content in the source to 0.9 g, the Zn/ZnO core–shell spheres were synthesized. The further increase of process duration led to the out-diffusion of Zn from the core, its oxidation, and the formation of a thick, dense ZnO spherical shell. Even further annealing in residual gases caused the increase of the Zn vapor pressure inside the shell. As a result, at a certain Zn vapor pressure, the shell bursts, causing the formation of a hollow ZnO microsphere.

Abstract: In this study, the use of the Fourier synthesis and the so-called Maximum Entropy Method (MEM) are evaluated in order to reveal the crystalline defect of the T’-type structure of one of 214 cuprate system, namely Pr_2-xCe_xCuO₄ (PCCO) powders. In the low-level density, the MEM calculations give a clear picture of the scattering and can eliminate the secondary scattering which may bother the main electron distribution of the specific atomic site. The covalent-bond is even clearer to be seen rather than the one obtained by the Fourier synthesis. This brings a further suggestion to use the MEM calculations in case of describing the scattering density of electron. Moreover, by means the used of the MEM calculations, the defect induced magnetism including the role of the tetravalent ionic doping and the annealing reduction effect is briefly discussed in this report.

Abstract: In the research, we show that suboxidic Ti₇O₁₃ and rutile TiO₂ phases formed in addition to the general Ti₃O₅ phase when the sintering temperature was set at constant argon gas flow rate. Suboxidic Ti₇O₁₃ and rutile TiO₂ phases were removed by tuning the flow rate of argon gas at constant sintering temperature. At the 1300°C temperature, the smallest Ti₃O₅ nanocrystals with a size of ~9 nm were produced. Flat shaped particles of Ti₃O₅ crystals were observed in SEM measurements.

Abstract: CoO nanocrystal is well-known photocatalyst for overall water splitting. However it suffers from a very short lifetime of only 1 h. The poor stability is derived from carrier recombination-induced thermal oxidation. This research will provide information about synthesis of CoO/ZnO nanocrystalline that can potentially enhance photocatalysts. CoO has been synthesized first under hydrothermal method, followed by calcination process. Thereafter, CoO has been used to produce CoO/ZnO under precipitation method. The samples were characterized using XRD (X-Ray Diffraction), FTIR (Fourier Transform Infrared Spectroscopy), and UV-VIS (UV–Visible Spectroscopy) to analyze their composition, chemical functional group, optical absorption, and band gap. The XRD spectrum showed that CoO/ZnO had cubic spinel and hexagonal phase structure with crystallite size of 69.0, 46.4, 32.8, and 32,4 nm. The bands in obtained FTIR spectrum at 586.36, 671.23, and 410-429 cm⁻¹ were correlated with vibrations of the Co³⁺ in octahedral hole, the Co²⁺ in tetrahedral hole, and Zn-O, respectively. The band gap energy of CoO, CoO/ZnO with variation of 1:1 and 1:3 were 4.39, 4.14, and 3.65 eV, respectively. The photocatalytic activities of CoO/ZnO were confirmed by methylene blue dyes photodegradation of 663 nm under UV light irradiation in aqueous solution. The 22.4% methylene blue can be removed within 3 h. Overall, these findings reveal the potential of CoO/ZnO for practical application.

Abstract: There are various different types of nanocellulose such as nanofibrillated cellulose (NFC), nanocrystal cellulose (NCC), and nanocrystal sphere (NCS). Each nanocellulose contains ordered nanocrystallites and low-ordered nano domains (amorphous). Nanocellulose can be used in several different applications such as coating for a wearable sensor device, film for supercapacitors, flexible fire-resistant foams for architecture, manufactory, and aerospace. All of these were made, following some chemical and mechanical processes. Some nanocellulose has a highly crystalline structure that has the potential to improve mechanical properties for industrial applications. Therefore, the present review compiles the most recent information on nanocellulose crystallinity influence on the polymer composites. In this review, the crystallinity of nanocellulose from different sources is discussed. The preparation of several nanocrystals cellulose via chemical treatment, particularly cellulose hydrolysis are described. It can be concluded that , the cellulose crystalline structure as filler or reinforce was responsible for the improvement of polymer matrix properties.

Abstract: Gallium nitride (GaN)-based thin films consist of its nanocrystals are grown on some metal-foils and a multi-crystalline silicon (Si) substrates. Their morphologies are compared with each other and the differences are discussed. Pillar-shaped nanocrystals are observed in the film grown on the multi-crystalline Si substrate while such structures are not observed in the films grown on the metal-foils when they are grown at higher growth temperatures. On the other hand, the morphologies of the films grown on the metal-foils approach to pillar-like structures by reducing the growth temperature. Band-edge emission is clearly observed in a cathodoluminescence spectrum of the film grown on the metal-foil at the reduced growth temperature.

Abstract: Mesoporous magnetic hydroxyapatite nanocrystals (MPmHAp NCs) were successfully prepared through one-step co-precipitate process. From the results, the MPmHAp NCs kept HAp lattice structure and had short rod-like morphology with superparamagnetic property. The size of MPmHAp was 60-80 nm in length and 10-20 nm in width. It also had excellent cell viability when coculture with 3T3 cells in vitro. In addition, MPmHAp NCs not only possessed mesoporous architecture with high surface area for effective drug loading capacity and drug release. The above results indicate that the biocompatible MPmHAp NCs showed great potential as multifunctional therapeutic nanoagent for biomedical application.

Abstract: Pure MgO, ZrO₂ and mixture MgO/ZrO₂ nanocrystals were annealed in air from 100 to 1200°C. Variation of the microstructure and defects was investigated by positron lifetime spectroscopy and X-ray diffraction. The experiment results showed that the average positron lifetime of mixture MgO/ZrO₂ was more larger than that of single phase MgO and ZrO₂, and decreased with the increasing annealing temperature. Thermal annealing below 600°C, the movement of grain boundaries mainly led a reduce of the number of microvoids, and vacancy defects began to recover due to the growth of MgO nanoparticles after annealing between 600 to 900°C. Furthermore, ZrO₂ nanoparticles began to grow above 900°C, meanwhile the recovery of vacancy and vacancy clusters in MgO/ZrO₂ nanoparticles are restrained because of synergic effect between MgO and ZrO₂ nanoparticles.

Abstract: The assembly process of nanostructures from nanoparticles in solution is fundamental for bottom-up fabrication of functional materials and devices. In a similar way, bottom-down fabrication approach requires etching of materials. We take advantages of emerging in-situ liquid cell transmission electron microscopy (TEM) technique and explored several liquid processes such as: (1) nanoparticle-nanoparticle interaction in thin fluid layer, (2) wet etching of nanostructures and (3) pinning and de-pinning of nanodroplets at solid surface. Our approach is to directly visualize nanoscale liquid process, which is important for development of new nanofabrication processes for the design of next generation nanoscale devices. Our finding of nanodroplet pinning has important implications on surface cleaning at the nanoscale.