Active properties of carbon nanotube field-effect transistors deduced from S parameters measurements

AC performances of carbon nanotube field-effect transistors (CNT-FETs) are analyzed by means of scattering parameters measurements. The active ac properties of CNT-FETs are clearly demonstrated up to 80 MHz and indications of active behavior are obtained up to 1 GHz. From these measurements, a small signal equivalent circuit is proposed and validated up to 10 MHz. The extraction procedure and the determination of the intrinsic ac elements of CNT-FETs are pointed out.     

Homogeneous precipitation of Dy2O3 nanoparticles-effects of synthesis parameters

The experimental parameters that control the size and size distribution of dysprosium oxide nanoparticles synthesized by homogeneous precipitation technique have been systematically investigated. The particles were characterized with respect to their size, shape, and thermal decomposition behavior. It was found that the precipitated particles were spherical, uniform in size, and amorphous, which upon heating in air, decomposed into the oxide form with no change in morphology. The size and size distribution of the particles showed strong dependence on the metal cation concentration ([Dy3+]) and weak dependence on urea concentration and aging time. In addition, the presence of chlorine ions (Cl-) was found to have significant effect on the growth and agglomeration of the particles. Aggregation mechanism as the growth mechanism is offered to explain the effects of these synthesis parameters on the morphology, size, and size distribution of dysprosium oxide particles.     

Synthesis of PEOlated Fe3O4@SiO2 Nanoparticles via Bioinspired Silification for Magnetic Resonance Imaging

Inspired by the biosilification process, a highly benign synthesis strategy is successfully developed to synthesize PEOlated Fe₃O₄@SiO₂ nanoparticles (PEOFSN) at room temperature and near‐neutral pH. The success of such a strategy lies in the simultaneous encapsulation of Fe₃O₄ nanocrystals and silica precursors into the core of PEO‐based polymeric micelles. The encapsulation results in the formation of a silica shell being confined to the interface between the core and corona of the Fe₃O₄‐nanocrystal‐loaded polymeric micelles. Consequently, the surface of the Fe₃O₄@SiO₂ nanoparticle is intrinsically covered by a layer of free PEO chains, which enable the PEOFSN to be colloidally stable not only at room temperature, but also upon incubation in the presence of proteins under physiological conditions. In addition, the silica shell formation does not cause any detrimental effects to the encapsulated Fe₃O₄ nanocrystals with respect to their size, morphology, crystallinity, and magnetic properties, as shown by their physicochemical behavior. The PEOFSN are shown to be good candidates for magnetic resonance imaging (MRI) contrast agents as demonstrated by the high r₂/r₁ ratio with long‐term stability under high magnetic field, as well as the lack of cytotoxicity.     

Flexible gigahertz transistors derived from solution-based single-layer graphene

Flexible electronics mostly relies on organic semiconductors but the limited carrier velocity in polymers and molecular films prevents their use at frequencies above a few megahertz. Conversely, the high potential of graphene for high-frequency electronics on rigid substrates was recently demonstrated. We conducted the first study of solution-based graphene transistors at gigahertz frequencies, and we show that solution-based single-layer graphene ideally combines the required properties to achieve high speed flexible electronics on plastic substrates. Our graphene flexible transistors have current gain cutoff frequencies of 2.2 GHz and power gain cutoff frequencies of 550 MHz. Radio frequency measurements directly performed on bent samples show remarkable mechanical stability of these devices and demonstrate the advantages of solution-based graphene field-effect transistors over other types of flexible transistors based on organic materials.     

第二届中国国际全印展大型展团全力助阵全球推广声势浩大

将于2006年6月14-17日在上海新国际博览中心盛大开幕的第二届中国国际全印展（All in Print China 2006），经过任德鲁巴（drupa 2004），南非第八届世界印刷大会、第七届世界印刷峰会论坛，第七届亚洲印刷技术论坛年会以及今年5月在北京举办的新闻发布会等海内外大规模巡回宣传和推广之后，在令球印刷界引起了很大的轰动和反响。     

Metamorphic In0.4Al0.6As/In0.4Ga0.6As HEMTs on GaAs substrate

New In_0.4Al_0.6As/In_0.4Ga_0.6 As metamorphic (MM) high electron mobility transistors (HEMTs) have been successfully fabricated on GaAs substrate with T-shaped gate lengths varying from 0.1 to 0.25 μm. The Schottky characteristics are a forward turn-on voltage of 0.7 V and a gate breakdown voltage of -10.5 V. These new MM-HEMTs exhibit typical drain currents of 600 mA/mm and extrinsic transconductance superior to 720 mS/mm. An extrinsic current cutoff frequency f_T of 195 GHz is achieved with the 0.1-μm gate length device. These results are the first reported for In_0.4 Al_0.6As/In_0.4Ga_0.6As MM-HEMTs on GaAs substrate     

Structural and quantitative evolution of organic matters in oil shale during two different retorting processes

In this study, traditional strongly endothermic anaerobic retorting (AR) and relatively novel self-heating retorting (SHR) processes for oil shale (OS) were investigated and compared in detail. These studies mainly involve the structural and quantitative evolution of organic matters in OS during retorting, including varieties of crystallite parameters, carbon framework structure, amounts of various structural carbons and toxic polycyclic aromatic hydrocarbons, and so on. The obtained results well elucidate some reaction pathways in AR and SHR as well as certain differences between the two retorting processes. Moreover, based on our former work that verifies SHR greatly simplifies retorting operation by in situ generating heat to replace external heat carrier/provision, this study further demonstrates that SHR also alleviates the environmental effect of organic toxic residues as compared to AR. The present study provides some critical results not only for penetrating the reaction mechanism but also for assessing or controlling the environmental impact of both retorting processes.     

Nonlinear Characterization and Modeling of Carbon Nanotube Field-Effect Transistors

We report for the first time to our knowledge large-signal measurements performed at 600 MHz and in time domain on carbon nanotube field-effect transistors (CNFETs) using a large-signal network analyzer. To overcome the very high mismatch between the high CNFET impedance and the basic 50-$Omega$ configuration of the setup, the output impedance was matched with the help of an experimental active load–pull configuration. Hence, we were able to observe under large-signal conditions the nonlinear behavior of CNFETs. Static measurements and continuous-wave ${ S}_{ ij}$-parameter measurements were made for many different biases. They were used in order to determine a nonlinear electrical model that has been validated thanks to the nonlinear measurements. The developed model opens the way for electrical CNFET circuit simulation and nonlinear applications of these devices.