Synthesis of Single-Crystal Graphene on Copper Foils Using a Low-Nucleation-Density Region in a Quartz Boat

The nucleation of graphene at different locations in the quartz boat was studied, and the lowest nucleation density of graphene in the quartz boat was found. The nucleation density of graphene is the lowest at the bottom of the quartz boat near the gas inlet side. Based on the above results, a simple and reproducible way is proposed to significantly suppress the nucleation density of graphene on the copper foil during the chemical vapor deposition process. Placing the copper foil with an area of 1.3 cm × 1 cm in the middle of the bottom of the quartz boat or further back, and placing two copper pockets in front of the copper foil, an ultra-low nucleation density of ~42 nucleus/cm2 was achieved on the back of the copper foil. Single-crystal monolayer graphene with a lateral size of 800 μm can be grown on the back of copper foils after 60 min of growth. Raman spectroscopy revealed the single-crystal graphene to be in uniform monolayers with a low D-band intensity.

Chemical Vapor Deposition Synthesis of Carbon Nanotube Using Pyrolysis Gas Products of Apricot Kernel Shell

The results of a study of carbon nanotubes (CNTs) growth using apricot stone (AS) as a carbon source are presented. The described method here is two-zone thermal chemical vapor deposition (CVD) that uses cobalt acetate directly as deposition medium at different geometries under argon flow of 100 mL min–1. Argon gas was fed into the oven until pyrolysis of apricot kernel started. Since pyrolysis started, argon was passed through toluene immersed in hot water in the gas washing flask and sent to the furnace for CNT formation. This method allows the bulk metal acetate surface over a quartz road and in a quartz boat to act as catalyst for CNT growth. Our recent results obtained from the toluene assisted growth. The effect of growth temperature and purification of CNTs was studied. As-grown and purified CNTs were characterized by scanning electron microscopy (SEM), X-ray diffraction, differential thermal analysis and surface analysis. High yield of CNTs were obtained over quartz road at 900 °C and at the same temperature with 48 hours deposition time in quartz boat. The obtained CNTs were purified by refluxing using nitric acid.

Numerical Simulation of the Modified Two-Temperature Horizontal Bridgman Growth of Gallium Arsenide Crystals inside a Quartz Boat

A three-dimensional simulation of the modified two-temperature horizontal Bridgman growth of gallium arsenide crystals has been developed. The computer model solves time-dependent, Navier-Stokes equations with a Boussineq approximation by the finite difference method. A new model of nodal latent heat is adopted for melting and freezing processes. The interface of solid-liquid phases as well as flow and temperature fields of both phases are obtained. The simulation finds that the furnace pulling rate and the heat-loss prevention arrangement has an impact on the shape of the interface. The computed solidification fronts agree with the experimental data successfully. The radiation heat loss in the process plays a major role in the heat-transfer mechanism, which has been taken into consideration to obtain the correct trend for the simulation.

Studies of copper selenide ultrafine particles by newly developed gas evaporation method

The direct evaporation of metallic oxides or sulfides does not always given the same compounds with starting material, i.e. decomposition took place. Since the controll of the sulfur or selenium vapors was difficult, a similar production method for oxide particles could not be used for preparation of such compounds in spite of increasing interest in the fields of material science, astrophysics and mineralogy. In the present paper, copper metal was evaporated from a molybdenum silicide heater which was proposed by us to produce the ultra-fine particles in reactive gas as shown schematically in Figure 1. Typical smoke by this method in Ar gas at a pressure of 13 kPa is shown in Figure 2. Since the temperature at a location of a few mm below the heater, maintained at 1400° C , were a few hundred degrees centigrade, the selenium powder in a quartz boat was evaporated at atmospheric temperature just below the heater. The copper vapor that evaporated from the heater was mixed with the stream of selenium vapor,and selenide was formed near the boat. If then condensed by rapid cooling due to the collision with inert gas, thus forming smoke similar to that from the metallic sulfide formation. Particles were collected and studied by a Hitachi H-800 electron microscope.Figure 3 shows typical EM images of the produced copper selenide particles. The morphology was different by the crystal structure, i.e. round shaped plate (CuSe;hexagona1 a=0.39,C=l.723 nm) ,definite shaped p1 ate(Cu5Se4;Orthorhombic;a=0.8227 , b=1.1982 , c=0.641 nm) and a tetrahedron(Cu1.8Se; cubic a=0.5739 nm). In the case of compound ultrafine particles there have been no observation for the particles of the tetrahedron shape. Since the crystal structure of Cu1.8Se is the anti-f1uorite structure, there has no polarity.