Year 2014, Volume 34

Abstract

Thermionic electron emitters based on doped diamond films have shown significant emission at less than 500°C. Results have established that it is necessary to control the electron affinity, doping levels and concentration, and band bending, and these properties have been achieved with engineered multilayered structures with controlled morphology, doping and substrate. Recently, visible light photo-electron emission has been demonstrated using the same diamond film emitters. This report presents a spectroscopic and surface electron microscopy study of photo- and thermionic emission from nitrogen doped diamond films with controlled morphology on metal substrates. Electron emission spectra were recorded to 500°C, while illuminated with sub diamond band gap light. Significant photo-induced emission was observed with an efficiency greater than metal photo cathodes.

Abstract

In the research of Diamond-like carbon (DLC) Film deposited by pulsed laser, method of double pulsed laser deposition was presented. Ti:Sapphire (800nm, 120fs) laser and KrF (248nm, 20ns) laser were used orderly to ablate graphite target. Through controlling parameters of two laser beams, double-layer DLC film was deposited on silicon substrate. The hardness and inner-stress of the DLC film changed gradually from substrate to atmosphere-interface. Nanoindentation measurement system and fourier transfer infrared spectrograph were used to hardness and transmittance of the film. Meanwhile, adhesive tape, 9.8N rubber, NaOH liquor and boiling water were used to compare the adhesion and environment adaptability of double layer or monolayer DLC film samples qualitatively. Results showed that DLC film deposited by double beam pulsed laser not only had high transmittance and hardness, but also kept well and had no phenomenon of peeling off after the tests including dipped in boiled water, etc. Compared to DLC films deposited by single pulsed laser, the chemical and thermal inertness of the double-layer DLC film deposited by double pulsed lasers was much better.

Abstract

Chemical Vapor Deposition (CVD) is generally utilized for producing large area, good quality graphene films on suitable substrates. Copper (Cu) substrate is used mainly as a substrate and catalyst during graphene synthesis process by CVD technique. The purpose of the present work is to investigate the evolution of Cu surface morphology after graphene growth and its influence on grown graphene quality. In this study, graphene was grown using methane as the carbon source at temperature of 1040 oC for 5 minutes. Scanning electron microscopy (SEM), Optical Microscopy (OM) and atomic force microscopy (AFM) were utilized to analyze the change of Cu surface morphology after graphene synthesis. Raman spectroscopy was used to characterize the characteristics of grown graphene. SEM and AFM results showed that copper substrate surface morphology was modified after annealing and graphene growth associated with formation of large size Cu particles located basically on the surface terraces, resulting in deposition of multilayer, very small graphene domains aligned linearly along rolling marks direction.

Abstract

We introduce a new self-separation of graphene oxide flakes exploiting liquid crystalline phase formation. Moderately concentrated discotic GO aqueous solution spontaneously phase separates into isotropic phase and nematic phase. According to Onsager theory, larger flakes with higher aspect ratio tends to form nematic phase, while smaller flakes remain in isotropic phase. Simple isolation of bottom nematic phase (large graphene oxide; LGO) resulted in the LGO dominant dispersion preparation. We employed this size selection principle to investigate the influence of GO flake size upon the material properties of reduced graphene oxide. The electrical properties of spin cast rGO films are thoroughly investigated in terms of the GO flake sizes in the precursor aqueous dispersions. Interestingly, nitrogen doping in order to inject more electron charge carrier exhibit different behavior following flake size. Therefore, it was experimentally confirmed that quaternary nitrogen doping site acts as the dominant catalytic site in oxygen reduction reaction.

Abstract

Graphene, because of its exceptional properties such as very good electrical conductance, flexibility and high optical transparency in visible light spectrum, has proved to be an excellent nanomaterial for modern electronic applications. The natural point of view is to use this new nanomaterial for the development of unique textronic devices such as sensory systems for monitoring human body’s vital functions and atmospheric composition. The present review shows the state of art of materials science and possibilities of the smart textiles design with graphene. The most promising applications of graphene for the design of textronic devices are the development of conductive polymer composites (CPC) and the development of inks and pastes for printing conductive tracks on textile materials. The preliminary results of implementation of 2D carbon structure into textronic devices are presented.

Abstract

We propose development of an advanced type of "paper transistor" by using carbon- nanotube (CNT) composite papers (CNTCPs) and aim to apply our paper transistors to the construction of logic circuits. It is known that CNTs have many functions such as high electrical and thermal conductivities and metallic and semiconducting properties. Our CNTCP, which has various functions held by CNTs despite being paper, can be fabricated easily by scooping up and drying materials from a mixture of CNT and pulp (paper materials) dispersions. The CNTs have metallic or semiconducting properties, so metallic and semiconducting CNTCPs can be fabricated. By preparing such CNTCPs and normal paper as an insulator, we can produce the paper transistor. In previous work, we confirmed our prototype paper transistor could operate as a p-type transistor. However, the sample had problems, e.g., the internal resistance was rather high. In this study, we aim to overcome the problems by using a novel method for making the CNTCP. As the result of experiments, we succeeded in obtaining new paper transistors with better performance in comparison with the previous one. Moreover, we succeeded in finding a potential use as an n-type paper transistor by using an n-type doping material for semiconducting CNTCPs.

Abstract

We propose development of a novel functional thread that contains carbon nanotubes (CNTs), i.e., a CNT-composite thread (CNTCT), and of a "thread transistor." The CNT is expected to be a next-generation material because it has a lot of useful characters, e.g., it can have both metallic and semiconducting characteristics. Thread is flexible and an everyday material. In our study, we succeeded in developing the CNTCT easily by dipping thread in CNT dispersion like dyeing. Here, we also developed and demonstrated a novel type of field-effect transistor (FET), i.e., the thread transistor. To do this, we prepared a metallic (M) and a semiconducting (S) CNTCT. The S-CNTCT was coated with a non-conductive paint as an insulating layer for simplicity. To construct the thread transistor, we tensed the S-CNTCT that plays the role of a channel for the FET and tied the M-CNTCT around the S-CNTCT as a gate electrode. The source and drain electrodes can also be materialized by tying the M-CNTCTs. As a result of measurement, a drain-to-source current could be measured on the order of micro-amperes. Moreover, the current could be controlled by the gate voltage.

Abstract

Carbon nanotubes (CNT) have been investigated for a wide range of applications. The combination of the CNT structure with semiconductors oxides opens up various application possibilities: water separation for hydrogen generation, degradation of pollutants in aqueous contamination and sewage treatment, photoreduction of CO₂ activity in self-cleaning air purification and dyes for solar cells. The junction multi-walled carbon nanotubes with dioxide titanium and zinc oxide(MWCNT-TiO₂-ZnO), when used as support, can facilitate a change in electron transfer, increasing the photocatalytic activity. MWCNTs/TiO₂/ZnO nanocomposites were prepared by the modified sol-gel method using MWCNTs, titanium (IV) propoxide, commercial TiO2 (P25) as titanium sources, zinc oxide produced in the laboratory by thermal evaporation and commercial ZnO. The composites obtained from the titanium (IV) propoxide were prepared by solution processing followed by thermal treatment at 500° C. The results were associated with the characteristics of the nanocomposites using Raman spectroscopy. The photocatalytic activity on organic dye was associated to energy gap evaluated by diffuse reflectance spectroscopy.

Abstract

The carbon coils (d-CCs) having the diverse geometries were deposited on Al₂O₃ substrate by continuous injection of SF₆ in C₂H₂ source gas under the thermal chemical vapor deposition system. d-CCs with polyurethane (PU) composites (d-CCs@PU) were fabricated by dispersing d-CCs in PU solvent with dimethylformamide (DMF) additive. The electromagnetic wave shielding properties of d-CCs@PU composites were investigated in the frequency range of 0.25-1.5 GHz. The shielding effectiveness (SE) of d-CCs@PU composites were measured and discussed according to the weight percent of d-CCs in CCs@PU composites and the thickness of d-CCs@PU composites layers. Based on these results, we discussed the shielding properties of d-CCs@PU composites and the main mechanism of the SE in this work.

Abstract

Polycrystalline materials typically contain a very large number of grains whose surrounding grain boundaries evolve over time to reduce the overall energy of the microstructure. The evolution of the microstructure is influenced by the motion of the exterior surface since the grain boundaries couple to the exterior surface of the specimen; these effects can be appreciable especially in thin specimens. We model these effects using the classical framework of Mullins, in which grain boundaries move by mean curvature motion, V_n = Aκ, and the exterior surface evolves by surface diffusion, V_n = −BΔ_sκ. Here V_n and κ denote the normal velocity and the mean curvature of the respective evolving surfaces, and Δ_s is the surface Laplacian. A classical way to determine A, the "reduced mobility," is to make measurements based on the half-loop bicrystalline geometry. In this geometry one of the two grains, which embedded within the other, recedes at a roughly constant rate which can provide an estimate for A. In this note, we report on findings concerning the effects of the exterior surface on grain boundary motion and mobility measurements in the context of the half-loop bicrystalline geometry. We assume that the ratio of grain boundary energy to the exterior surface energy is small, and suitable assumptions are made of the specimen aspect ratio.

Abstract

High temperature solid oxide fuel cells (SOFCs) have high efficiency and low emissions and contribute to the saving of the fossil fuel and the decreasing of the CO₂ emission bringing about the global warning. As concerned about the development of electrolytes, oxide-ion conductors alternative to yttria-stabilized zirconia (YSZ) such as doped CeO₂, Sc-SZ and perovskite-type oxides (LaGaO₃) etc. have been reported to apply to the intermediate temperature SOFCs (IT-SOFCs). Some of perovskite-type oxides shows high proton conductivity at high temperature and are expected to the electrolyte materials for IT-SOFCs. In this paper we have investigated review the mixed electrical conductivity and the optical absorption spectrum of OH(D)-vibration of LaScO₃.We also evaluated its applicability to the electrolyte material for IT-SOFCs by testing the SOFC performance of Pt/LaScO₃/Pt single cell configuration.

Abstract

Elastic fields, generating by defects of the structure, influence the diffusion processes. It leads to the alteration of the phase transformation kinetic. One of the chief aims of our work is to obtain general equations for the diffusion fluxes under strain that give the possibility for using these equations at low temperatures, as in this case the strain influence on the diffusion fluxes is manifested in maximal degree. Our approach takes into consideration, that the strains can alter the surrounding atom configuration near the jumping one and consequently the local magnitude of the activation barrier and a rate of atom jump. The rates of atom jumps in different directions define the flux density of the vacancies. Now we take into account, that strain values are different in the saddle point and in the rest atom position, in differ from our consideration that was done by us earlier. As a result in the development of our approach the general equations for the vacancy fluxes are obtained for fcc and bcc metals. In our paper we discuss the main features of the theory of diffusion under stress and its applications. In particular we examine how elastic stress, arising from nanovoids, influence the diffusion vacancy fluxes and the growth rate of voids in metals.