Crystallite

About: Crystallite is a research topic. Over the lifetime, 43231 publications have been published within this topic receiving 981094 citations.

Average Grain Size in Polycrystalline Ceramics

Abstract: A model is proposed which realistically characterizes the grain structure of polycrystalline ceramics. The average grain size of a log-normal distribution of grain sizes with tetrakaidecahedral (truncated octahedral) shape is related to the average intercept size by a proportionality constant. This result can be used to determine the average grain size of a sintered powder compact composed of nontextured grains which shows no discontinuous grain growth.

Vapour phase growth and grain boundary structure of molybdenum disulphide atomic layers

Abstract: Single-layered molybdenum disulphide with a direct bandgap is a promising two-dimensional material that goes beyond graphene for the next generation of nanoelectronics. Here, we report the controlled vapour phase synthesis of molybdenum disulphide atomic layers and elucidate a fundamental mechanism for the nucleation, growth, and grain boundary formation in its crystalline monolayers. Furthermore, a nucleation-controlled strategy is established to systematically promote the formation of large-area, single- and few-layered films. Using high-resolution electron microscopy imaging, the atomic structure and morphology of the grains and their boundaries in the polycrystalline molybdenum disulphide atomic layers are examined, and the primary mechanisms for grain boundary formation are evaluated. Grain boundaries consisting of 5- and 7- member rings are directly observed with atomic resolution, and their energy landscape is investigated via first-principles calculations. The uniformity in thickness, large grain sizes, and excellent electrical performance signify the high quality and scalable synthesis of the molybdenum disulphide atomic layers.

A simple model for the ionization potential, electron affinity, and aqueous redox potentials of small semiconductor crystallites

Abstract: Large semiconductor crystals have intrinsic electronic properties dependent upon the bulk band structure. As the crystal becomes small, a new regime is entered in which the electronic properties (excited states, ionization potential, electron affinity) should be strongly dependent upon the electron and hole in a confined space. We address the possibility of a shift in the photochemical redox potential of one carrier, as a function of crystallite size. As a semiquantitative guide, one might expect a shift on the order of h2/8em*R2 due to the kinetic energy of localization in the small crystallite. We model the elementary quantum mechanics of a charged crystallite using (a) the effective mass approximation, (b) an electrostatic potential for dielectric polarization, and (c) penetration of the carrier outside the crystallite in a cases of small effective mass. Shifts of several tenths of an eV appear possible in crystallites of diameter 50 A. The carrier charge density reside near the crystallite surface if ...

Controllable self-induced passivation of hybrid lead iodide perovskites toward high performance solar cells.

Abstract: To improve the performance of the polycrystalline thin film devices, it requires a delicate control of its grain structures. As one of the most promising candidates among current thin film photovoltaic techniques, the organic/inorganic hybrid perovskites generally inherit polycrystalline nature and exhibit compositional/structural dependence in regard to their optoelectronic properties. Here, we demonstrate a controllable passivation technique for perovskite films, which enables their compositional change, and allows substantial enhancement in corresponding device performance. By releasing the organic species during annealing, PbI2 phase is presented in perovskite grain boundaries and at the relevant interfaces. The consequent passivation effects and underlying mechanisms are investigated with complementary characterizations, including scanning electron microscopy (SEM), X-ray diffraction (XRD), time-resolved photoluminescence decay (TRPL), scanning Kelvin probe microscopy (SKPM), and ultraviolet photoemi...