氮离子注入对类球状微米金刚石聚晶膜的影响

利用微波等离子体化学气相沉积法,在覆盖金属钛层的陶瓷衬底上制备出类球状微米金刚石聚晶膜,后对膜的表面进行氮离子的注入.通过扫描电子显微镜、拉曼光谱、X射线衍射谱及二级结构场发射测试,对膜进行了注入前后的分析.氮离子注入后场致电子发射的效果变强,这可能是氮离子的注入增加了类球状微米金刚石聚晶膜表面的缺陷度,从而增加了价带和导带间的缺陷能级,使电子更容易跃迁到高能级上,提高了场致电子的发射效果.     

Carbon-Based Materials: Growth,Properties, MEMS/NEMS Technologies,and MEM/NEM Switches

Micro- or nanoelectromechanical system (MEMS/NEMS) is a multidisciplinary field, which has witnessed explosive growth during the past decades. The current materials for MEMS are dominated by Si thanks to the fully based technology for CMOS. However, Si has its own intrinsic limitations such as poor mechanical or tribological properties and poor thermal stability. Carbon-based materials such as diamond, carbon nanotube, and graphene possess excellent properties such as low mass, high Young's modulus, high thermal conductivity, hydrophobic surface, and tailorable electronic configuration, which make these materials promising for MEMS/NEMS applications with diverse and much better performance than Si. In this review, we describe the recent progress of carbon-based materials for MEMS/NEMS with focus on diamond, carbon nanotube, and graphene. The growth of these carbon materials is briefly described and only selected properties are discussed with respect to MEMS/NEMS applications. The fabrication process for suspended structures of these materials toward MEMS/NEMS is comprehensively reviewed from the recent literatures. Special attention is devoted to the state-of-the-art of MEM/NEM switches based on these carbon materials, one of the most important fields in MEMS/NEMS. Finally, the application of carbon-based MEM/NEM switches to microwave field is critically analyzed.     

Cluster Tilted Algebras with a Cyclically Oriented Quiver

In association with a finite dimensional algebra A of global dimension two, we consider the endomorphism algebra of A, viewed as an object in the triangulated hull of the orbit category of the bounded derived category, in the sense of Amiot. We characterize the algebras A of global dimension two such that its endomorphism algebra is isomorphic to a cluster-tilted algebra with a cyclically oriented quiver. Furthermore, in the case that the cluster tilted algebra with a cyclically oriented quiver is of Dynkin or extended Dynkin type then A is derived equivalent to a hereditary algebra of the same type.     

Evidence of reduction in spin disorder by Ho3+ doping in La0.7Ca0.3MnO

We have shown in a recent study that substitution of Ho³⁺ ions (4f¹⁰; magnetic momen _μB) in La_0.7Ca_0.3MnO₃ causes significant reduction in electrical resistivity compared with Y³⁺ (4d⁰; non-magnetic) ion substitution. This reduction in resistivity was attributed to the reduced spin disorder scattering in La_0.7Ca_0.3MnO₃ samples containing magnetic Ho³⁺. We have estimated the Mn-spin canting angles in Ho³⁺ - and Y³⁺-doped La_0.7Ca_0.3MnO₃ compounds from the resistivity data using the magnetic localization model. We find that the canting angles of the Mn spins in the Ho³⁺ doped compounds are smaller than those obtained for the Y³⁺-doped compounds for all compositions and at all applied magnetic fields, showing clearly a reduction in the spin disorder in the former. The difference between the T _C values for Ho³⁺ - and Y³⁺-doped compounds for all compositions may be attributed to the presence of an internal field due to Ho³⁺ doping. This internal field may be responsible for the decrease in spin disorder in the Ho³⁺-doped compounds. The increase in the canting angles with increase in Ho³⁺ and Y³⁺ content could be attributed to the decrease in the strength of the ferromagnetic exchange interactions. A strong ferromagnetic coupling (as discussed recently by the present authors and co-workers) of Ho³⁺ moments with the Mn moments is responsible for the observed behaviour.     

Molecular dynamics simulations of diffusion of carbon into iron

Molecular dynamics (MD) simulations of diffusion couple tests were conducted between carbon (diamond/graphite) and iron at three different temperatures (300, 800 and 1600 K) and contact times (0, 40 and 80 ps) to investigate the chemical interaction between carbon and iron. Two different carbon structures, namely, diamond (cubic) and graphite (hexagonal), were considered. Diffusion of carbon into iron was observed only when a graphite interlayer was added to the diamond surface. When diamond alone was used, no diffusion was observed. This result provides corroborating evidence that diamond tool wear in the machining of iron occurs via a mechanism that involves an initial graphitization of diamond followed by diffusion of the newly formed graphite into the iron workpiece.     

High quantum efficiency UV detection using a‐Se based photodetector

High‐sensitivity ultraviolet (UV) photodetection has been attempted by utilizing the carrier multiplication effect in amorphous selenium. The prototype photodetector presented in this Letter showed an extremely high sensitivity to UV light, so that up to 1000 carriers are generated per incident photon. This result should lead to the development of an ultrahigh‐sensitivity photodetector that can be used for spectrometric applications covering the visible to UV region. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The peculiarities of ion scattering by crystals due to surface halfchannels,formed by close packed atomic rows

The ion scattering by the surface of crystals has been studied when there are halfchannels on the crystal surface, which are formed by close packed atomic rows of the first and the second layers of crystals. The obtained results are compared with one of ion scattering by directions, which have no surface halfchannels.     

Exploring the possible interlinked structures in single‐wall carbon nanotubes under pressure by Raman spectroscopy

High‐pressure Raman measurements on single‐wall carbon nanotubes (SWNTs) have been carried out in a diamond anvil cell by using two wavelength lasers: 830 and 514.5 nm. Irrespective of using a pressure transmitting medium (PTM) or not, we found that nanotubes undergo similar transformations under pressure. The pressure‐induced changes in Raman signals at around 2 and 5 GPa are attributed to the nanotube cross‐section transitions from circle to ellipse and then to a flattened shape, respectively. Especially with pressure increasing up to 15–17 GPa, we observed that the third transition takes place in both the Raman wavenumber and the linewidth of G‐band. We propose explanations that the interlinked configuration with sp³ bonds forms in the bundles of SWNTs under pressure, which was the cause for the occurrence of those Raman anomalies, similar to the structural‐phase transition of graphite above 14 GPa. Our TEM observations and Raman measurements on the decompressed samples support this transition picture. Copyright © 2012 John Wiley & Sons, Ltd.     

Experimental determination of vibrational anharmonic contributions

This article deals with the experimental determination of separate vibrational anharmonic contributions to the self‐energy of phonons in any crystals based on temperature dependence of their Raman spectra. We propose a new approach to find each anharmonic contribution by using special temperature points. We apply the approach to diamond, silicon, and crystalline α‐S₈ and show that our results for summarized anharmonicity in diamond and silicon are in good agreement with the values obtained previously for these systems by other researchers. Copyright © 2013 John Wiley & Sons, Ltd.