High-performance electronics using dense, perfectly aligned arrays of single-walled carbon nanotubes

Single-walled carbon nanotubes (SWNTs) have many exceptional electronic properties. Realizing the full potential of SWNTs in realistic electronic systems requires a scalable approach to device and circuit integration. We report the use of dense, perfectly aligned arrays of long, perfectly linear SWNTs as an effective thin-film semiconductor suitable for integration into transistors and other classes of electronic devices. The large number of SWNTs enable excellent device-level performance characteristics and good device-to-device uniformity, even with SWNTs that are electronically heterogeneous. Measurements on p- and n-channel transistors that involve as many as approximately 2,100 SWNTs reveal device-level mobilities and scaled transconductances approaching approximately 1,000 cm(2) V(-1) s(-1) and approximately 3,000 S m(-1), respectively, and with current outputs of up to approximately 1 A in devices that use interdigitated electrodes. PMOS and CMOS logic gates and mechanically flexible transistors on plastic provide examples of devices that can be formed with this approach. Collectively, these results may represent a route to large-scale integrated nanotube electronics.     

Screening of Water Dipoles Inside Finite-Length Armchair Carbon Nanotubes

The electronic structure and dielectric screening of finite-length armchair carbon nanotubes are studied with both tight-binding and ab initio methods. Good agreement is found in the band gap oscillation patterns and dielectric constants, which validates the tight-binding method as a reliable and fast approach to describe the screening effect of carbon nanotubes. For an illustration, our method is applied to a system consisting of a short (6,6) nanotube filled with six water molecules. Substantial screening of the water dipoles through the nanotube is observed. This polarization effect should have an important influence on the permeation of water and other biomolecules inside carbon nanotubes.     

Multiple aspect-ratio structural integration in single crystal silicon (MASIS) for fabrication of transmissive MOEMS modulators

A novel fabrication process, named MASIS (multiple aspect ratio structural integration in single-crystal-silicon), is introduced for the implementation of single-crystal-silicon microstructures characterized by distinct aspect ratios to be fabricated in the same device layer. The MASIS process was especially designed for fabrication of transmissive MOEMS (Micro-Opto-Electro-Mechanical-Systems) modulators incorporating large field areas, and driven by long-stroke comb-drive actuators combined with folded suspensions. The comb-drive actuators were designed to achieve large amplitude of vibration and high natural frequencies, which allow large aperture areas at high operational frequency. The MASIS process consists of selective thinning of the device thickness in the shutter area, reducing payload mass, while preserving higher thickness of the suspension springs and comb-drive transducer fingers, thereby increasing the natural frequency of the device and reducing actuation voltages. A modulator was successfully fabricated, demonstrating maximum displacement of 50 μm at 1 kHz in resonance using an actuation voltage of 15 Vpp in air. The MOEMS modulator was adapted as integral part of a solid-state photodetection system to overcome the low-frequency noise.     

Effect of wave-number error on the computation of path-length delay in white-light interferometry

We analyze the error in computed optical path-length delay when using a phase-shifting interferometry (PSI) algorithm with an error in the operating wavelength. The delay error decomposes into two terms. The first is the error in the conversion from a phase measurement to the delay because of the incorrect wavelength, and the second is the error made in the phase measurement itself that is due to the wavelength error. The most important aspect of this investigation is to ascertain this latter error. A general characterization is obtained, and a particularly simple formula is developed for the special case of least-squares estimation involving only the ratio of the wave-number error to the wave number and a multiplicative factor that is an a priori computable nonlinear function of the ratio of the modulator stroke length to the operating wavelength. Because the ultimate path-length error is a function of the two terms, a new set of PSI algorithms that compensate the computed phase error to cancel the conversion error is developed. Numerical simulations are presented to validate the analysis and establish the insensitivity of the new algorithms to wave-number error.     

Correlation between structure characteristics and adsorption properties of regenerated cellulose fibers

We correlate fine structure with the adsorption behavior of new (lyocell) and conventional (viscose, modal) regenerated cellulose fibers. We have studied the molecular structure, the fine structure and, most important of all, the amorphous regions and voids in the system. Differences in adsorption properties of all three-fiber types were determined by using several methods for quantification of water, dye and iodine adsorption. The structural analysis shows that higher molecular weight, a higher degree of crystallinity and a higher molecular orientation are found in lyocell fibers [1]. Our results obtained by several independent methods demonstrate clearly that the adsorption properties of cellulose fibers depend, with the exception of the portion and orientation of amorphous regions, predominantly on the void system (diameter, volume and inner surface of voids) [2]. Electronic Publication     

Large-scale analysis of self-disclosure patterns among online social networks users: a Russian context

Online social network services (SNS) provide an unprecedented rich source of information about millions of users worldwide. However, most existing studies of this emerging phenomenon are limited to relatively small data samples, with an emphasis on mostly “western” online communities (such as Facebook and MySpace users in Western countries). To understand the cultural characteristics of users of online social networks, this paper explores the behavioral patterns of more than 16 million users of a popular social network in the Russian segment of the Internet, namely, My.Mail.Ru (also known as “My World” or “Moj Mir” in Russian). Our main goal is to study the self-disclosure patterns of the site users as a function of their age and gender. We compare the findings of our analysis to the previous studies on Western users of SNS and discuss the culturally distinctive aspects. Our study highlights some important cultural differences in usage patterns among Russian users, which call for further studies in SNS in various cultural contexts.     

Homogeneous Tubular‐Flow Process for Monoolein Preparation

Esterification of fatty acids with glycerol is characterized by negligible solubility of the two liquid phases. The reactions to mono‐, di‐ and triglycerides taking place in the fatty acid phase, are limited by chemical equilibrium. The scope of this study is to investigate in a tubular reactor the conversion of a homogeneous mixture of oleic acid and glycerol in tert‐butanol. The liquid composition in this study was 1 mol of oleic acid, 6 mol of glycerol and 14 mol of tert‐butanol. Experiments were conducted in a tubular reactor at 35 atm over a temperature range of 200–240 °C and residence times of 0.7–17.6 h to determine the kinetics and the chemical equilibrium. The selectivity to monoolein was >95 mol %. A reversible second order reaction fits the data well.