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Abstract: Carbon nanotubes (CNTs) deposited by chemical vapor deposition (CVD) were treated by ball milling. The morphologies and field emission properties of the treated CNTs depending on milling time were studied. The emission turn-on field is increased, and the field emission current density is reduced, when the milling time increased from 0.5 to 3h. The as-deposited long CNTs were cut to short CNTs (∼1h) and micro-particles (>1h) with increasing of the milling time. It is found that the optimized milling time is 0.5–1h, the treated CNTs showed excellent field emission properties, such as low turn-on field, high emission current density and uniform luminescence spots distribution. [Copyright &y& Elsevier]

Cobalt-containing amorphous carbon (a-C:Co) composite films have been prepared by filtered cathodic vacuum arc at high negative pulsed bias voltage. After heat treatment at 580 °C in a mixture of acetylene and hydrogen gases, field emission properties of the a-C:Co films were significantly improved and the films deposited at higher negative bias voltage possessed better field emission properties. A relatively low threshold field of 2.1 V/μm (for emission current 1 μA/cm2) and a high emission current density of 2 mA/cm2 at the electric field of 6 V/μm has been achieved for the films deposited at the negative bias voltage of 7 kV. The morphologies and structures of the a-C:Co films were also studied in detail. It is suggested that the employed negative bias voltage increases the grain size and the sp2 content in the films, and further improves the field emission properties. [Copyright &y& Elsevier]

[Display omitted] • The dominance of Cu 2 S (chalcocite) crystal phase was confirmed via XPS, XRD and a dark I-V measurement. • The carrier selectivity originates from an induced junction at the Cu 2 S/n-Si interface instead of the conduction band offset. • No carrier-selectivity was observed for the Cu 2 S/p-Si device due to an insufficient band bending at the interface. Carrier selective contacts based on dopant free materials are receiving increased attention. Copper(I) sulfide (Cu 2 S), earth-abundant and non-toxic, shows potential for use in silicon (Si) solar cells, though its carrier selectivity mechanism remains unclear. We present a detailed investigation of the selectivity mechanisms behind thermally evaporated Cu 2 S on Si. Deposited Cu 2 S layers are studied by X-ray photoelectron spectroscopy, Auger electron spectroscopy, X-ray diffraction and UV/VIS (ultraviolet–visible) methods. From X-ray photoelectron spectroscopy and Auger electron spectroscopy, only sulfur related Cu(I) bonds are observed in the deposited film. X-ray diffraction measurements indicate that Cu 1.95 S (djurleite) may also exist in the film. The indirect and direct bandgaps are determined to be 1.2 eV and 2.2 eV, respectively. Band bending of ~0.6 eV is calculated for Cu 2 S/n-Si (~5 Ω·cm), while it is significantly lower (~0.07 eV) for Cu 2 S/p-Si (~2.25 Ω·cm). Current-voltage measurements indicate that the carrier selectivity originates from an induced junction at the Cu 2 S/n-Si interface, and not from a large band-offset of the conduction band. The Cu 2 S/p-Si structure displays no carrier selectivity, a finding attributed to the insufficient band bending at the interface. [ABSTRACT FROM AUTHOR]

Femtosecond laser beam cutting is becoming widely used to meet demands for increasing accuracy in micro-machining. In this paper, the effects of processing parameters in femtosecond laser beam cutting on the kerf size and microstructure in Inconel 738 have been investigated. The defocus, pulse width and scanning speed were selected to study the controllability of the cutting process. Adjusting and matching the processing parameters was a basic enhancement method to acquire well defined kerf size and the high-quality ablation of microstructures, which has contributed to the intensity clamping effect. The morphology and chemical compositions of these microstructures on the cut surface have been characterized by a scanning electron microscopy equipped with an energy dispersive X-ray spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Additionally, the material removal mechanism and oxidation mechanism on the Inconel 738 cut surface have also been discussed on the basis of the femtosecond laser induced normal vaporization or phase explosion, and trapping effect of the dangling bonds. [ABSTRACT FROM AUTHOR]

In this study, plasma nitrocarburizing at various temperatures in the range of 460–540 °C were carried out on M50NiL steel in order to improve wear properties. The nitrocarburizing temperature was optimized to obtain the best wear properties. The phase composition, microstucture and microhardness profiles of nitrocarburized layers of M50NiL steel were characterized by XRD, optical microscope and Vickers microhardness measurements, respectively. Pin-on-disc tribometer and SEM equipped with EDS were applied to measure friction and wear properties and analyze wear mechanisms involved. XRD results show that the amount of ɛ-Fe 2-3 (N,C) phase increased as the nitrocarburizing temperature rose form 460 °C to 500 °C and then decreased at 540 °C, while the amount of γ′-Fe 4 (N,C) phase increased as the treatment temperature rose. The hardness of the nitrocarburized layers showed an obvious improvement accompanied with the increasing nitrocarburizing temperature, and obtained the maximum surface hardness of 1287 HV at 540 °C. The results of wear tests carried out at various sliding speeds indicated that the wear mechanism depends on sliding speed rather than the nitrocarburizing temperature. With the increase of the sliding speed, the wear mechanism transfers from oxidation mode to abrasive mode. The gradually deceased wear rate of the specimen nitrocarburized at 500 °C with the increase of the sliding speed indicated the excellent wear resistance under high sliding speed condition. Therefore, 500 °C can be selected as an optimized nitrocarburizing temperature for M50NiL steel. [ABSTRACT FROM AUTHOR]

Highlights: [•] Depth-related microstructure of the modified layer of M50NiL steel is analyzed. [•] Depth-related wear mechanisms of RE treated layer of M50NiL steel is investigated. [•] The relationship between phase structure, hardness and wear mechanism is studied. [Copyright &y& Elsevier]

Highlights: [•] We study the interaction between lanthanum and nitrogen during plasma nitriding. [•] The addition of pure lanthanum could reduce the nitrogen content in the surface layer. [•] There is an attractive function between lanthanum and nitrogen. [Copyright &y& Elsevier]

Fluorinated amorphous diamond-like carbon films (a-DLC:F) were prepared on room-temperature Si(1 0 0) substrates using radio frequency plasma enhance chemical vapor deposition (rf PECVD) by varying the ratio of carbon tetrafluoride and methane (CF4:CH4).The films formed were investigated in terms of the surface morphology, chemical composition, microstructure, mechanical properties, and surface free energy by means of atomic force microscopy (AFM), X-ray photoelectron spectrum (XPS), micro-scratch test, nano-indenter test and contact angle measurement. Emphasis was placed on investigation of the factors affecting the film surface energy, which was calculated from three methods (the harmonic mean equation, the geometric mean equation and acid–base equation). It was observed that with increasing CF4:CH4, the roughness and F content of the a-DLC:F films increased while the hardness, Young’s modulus and surface energy decreased. The films also became more graphitized. The reduction of the film surface energy with varying F content is believed to be mainly due to the change of bonds in the film, i.e. the decrease of &z.sbnd;C&z.sbnd;CF bond and corresponding increase of &z.sbnd;CF, &z.sbnd;CF2. The roles of the roughness and the microstructure in affecting the film surface energy were negligible. [Copyright &y& Elsevier]

The wetting behavior and the interfacial reactions of molten Ti-40Ni-20Nb (at.%) filler alloy on the BN-SiO 2 ceramic were investigated by the a sessile drop method at 1453 K under a vacuum atmosphere. Results demonstrated that a good wettability with final contact angles of approximately 44°–15° was obtained. Interfacial microstructure examinations revealed that the Ti-40Ni-20Nb filler alloy reacted with the BN-SiO 2 ceramic, which resulted in the formation of TiN, TiB, Ti 5 Si 3 and Ti 3 O 5 at the interface. The wetting process of the Ti-40Ni-20Nb filler alloy on the BN-SiO 2 ceramic was identified into 3 stages: (i) rapid decreasing stage, (ii) sluggish spreading stage and (iii) final equilibrium stage. In order to reveal the essence of the reactive wetting, the wettability of the Ti-40Ni-20Nb (at.%) filler alloy on the BN-SiO 2 ceramic with three different BN contents were investigated. For the Ti-40Ni-20Nb/BN-SiO 2 system, the wettability mainly depended on the final interfacial chemistry of the system but the intensity of the interfacial reactions. The final contact angle of the Ti-40Ni-20Nb filler alloy on the BN-SiO 2 ceramic decreased as the BN content in the ceramic was increased from 20% to 80%. Unlabelled Image • Reaction layer mainly composed by TiN, TiB, Ti 5 Si 3 and Ti 3 O 5 is formed adjacent to the BN-SiO 2 ceramic. • The wetting of the TiNiNb filler alloy/BN-SiO 2 ceramic system can be explained by "Reaction Product Control" model. • With the improving of the BN content in the BN-SiO 2 ceramic, the ratio of (TiN+TiB):(Ti 5 Si 3 +Ti 3 O 5) in the reaction products increases, which can improve the wetting of the BN-SiO 2 ceramic. With BN content increases from 20% to 80%, the final contact angle decreases from 44° to 15°. [ABSTRACT FROM AUTHOR]

Abstract: We report enhanced up-conversion (UC) photoluminescence (PL) in Ag nanoparticles/SiO2/NaYF4: Yb, Er, Gd film sandwiched structures. The effect of SiO2 layer thickness on the up-converting optical properties in the sandwiched system was investigated. The UC emission enhancement shows a pronounced distance dependence for the silica spacer layer thickness below 20nm. The UC emission spectrum of the hybrid structured sample shows a continuous increase in intensity as the thickness of the SiO2 layer increases from 0nm to 15nm, but displays a quick decrease when the thickness of the SiO2 layer increases further from 15nm. Time-resolved photoluminescence spectroscopy reveals that the fluorescence lifetimes are reduced both for green and red emissions. PL spectroscopy and excitation power studies also show that Ag nanoparticles modified the UC process in this sandwiched structure. We demonstrate switching between PL quenching and enhancement by varying the silica interface thickness. This approach allows us to perform a quantitative analysis of the effect of a metal on the UC nanorods PL intensity. [Copyright &y& Elsevier]

Abstract: ZnS thin films have been prepared by chemical bath deposition (CBD) technique onto glass substrates deposited at about 80°C using aqueous solution of zinc sulfate hepta-hydrate, ammonium sulfate, thiourea, ammonia and hydrazine hydrate. Ammonia and hydrazine hydrate were used as complexing agents. The influence of the ratio of [Zn]/[S] on formation and properties of ZnS thin films has been investigated. The ratio of [Zn]/[S] was changed from 3:1 to 1:9 by varying volumes and/or concentrations of zinc sulfate hepta-hydrate and thiourea in the deposition solution. The structural and morphological characteristics of films have been investigated by X-ray diffraction (XRD), scanning electron microscope and UV–vis spectroscopic analysis. ZnS films were obtained with the [Zn]/[S] ratio ranged from1:1 to 1:6. In the cases of [Zn]/[S] ratio≥3:1 or ≤1:9, no deposition was found. Transparent and polycrystalline ZnS film was obtained with pure-wurtzite structure at the [S]/[Zn] ratio of 1:6. The related formation mechanisms of CBD ZnS are discussed. The deposited ZnS films show good optical transmission (80–90%) in the visible region and the band gap is found to be in the range of 3.65–3.74eV. The result is useful to further develop the CBD ZnS technology. [ABSTRACT FROM AUTHOR]

Abstract: Carbon nanotubes (CNTs) are prepared on NiCr alloy films by low pressure thermal chemical vapor deposition at 600°C. NiCr alloy films are deposited by magnetic co-sputtering method, and the various thickness and Ni/NiCr ratios are controlled by sputtering power. The diameter and length of CNTs, as well as the roughness of the CNTs films, mainly depend on the Ni/NiCr ratio. The field emission current density of the CNTs film increases with the increasing Ni/NiCr ratio from 65wt% to 83wt%, and decreases when the Ni/NiCr ratio is more than 87wt% in the alloy film. [Copyright &y& Elsevier]