Anshu Gaur

Bio: Anshu Gaur is an academic researcher from Indian Institute of Technology Kanpur. The author has contributed to research in topics: Carbon nanotube & Materials science. The author has an hindex of 16, co-authored 29 publications receiving 3214 citations. Previous affiliations of Anshu Gaur include Applied Materials & University of Illinois at Urbana–Champaign.

Solution Casting and Transfer Printing Single-Walled Carbon Nanotube Films

Abstract: This paper presents methods for solution casting and transfer printing collections of individual single-walled carbon nanotubes (SWNTs) onto a wide range of substrates, including plastic sheets. The deposition involves introduction of a solvent that removes surfactant from a suspension of SWNTs as it is applied to a substrate. The subsequent controlled flocculation (cF) produces films of SWNTs with densities that can be varied between a few tubes per square micron to thick multilayers in a single deposition step and with orientation determined by the direction of solution flow. High-resolution rubber stamps inked in this manner can be used to print patterns of tubes with geometries defined by the relief structure on the surface of the stamp. Thin film transistors fabricated with these techniques demonstrate their potential use in flexible “macroelectronic” systems.

High‐Performance n‐ and p‐Type Single‐Crystal Organic Transistors with Free‐Space Gate Dielectrics

Abstract: [17] The diameters of a large number of spheres (typically ~ 200 spheres) were obtained from scanned TEM images processed using ImageJ and tabulated. The size distribution, defined as the standard deviation divided by the mean sphere diameter, was subsequently evaluated as such for all samples reported. The shell thickness cannot be obtained by simply taking the difference in mean diameters between the coated and bare spheres because shrinking of the cores can occur as a result of condensation of unreacted Si-OH groups when the spheres are re-dispersed in a basic solution for coating. [21] The quantum yield was determined as follows: the optical densities of the index matched coated spheres in a toluene/ethanol mixture and an appropriate reference dye in methanol were closely matched at the wavelength of excitation. To ensure that no reabsorption of the dye emission occurs, the optical densities were always maintained at a value below 0.1 at the excitation wavelength. The photo-luminescence spectra of both the sample of coated spheres and the reference dye were acquired using a SPEX Fluorolog 1680 spectrometer. Comparison of their corresponding integrated emission allowed the quantum yield of the sample to be determined. [22] Although the quantum yields of as-synthesized core±shell CdSe/ZnS NCs used were as high as 38 %, subsequent loss of the original surface ligands due to cap-exchange with AP and APS can lead to diminished quantum yields. Furthermore, the decline in the quantum yield due to processing is very dependent on the quality and thickness of the ZnS shell on the NCs, which can vary from sample to sample. [23] The standard deviation is more significant than the absolute value of the ratio due to the curvature of the microsphere, which may introduce inherent systematic error into the WDS measurement. [24] R. Study of intrinsic transport properties in single-crystal organic semiconductors has the potential to yield fundamental insights into the behavior of plastic transistors for flexible electronics. [1±4] The organic field-effect transistors (OFETs) that facilitate these studies are, however, complex structures whose properties depend on interactions between the semiconductor , gate dielectric, and electrodes. [5±7] Carrier trapping , charge doping, molecular reorientation, dipole formation , and a range of possible chemical interactions are among the many phenomena that can occur at the semiconductor/di-electric interface and degrade device performance. [8±11] We introduce an unusual device design that entirely avoids these effects by replacing the standard solid dielectric layer …

Polymer Imprint Lithography with Molecular-Scale Resolution

Abstract: We show that small diameter, single-walled carbon nanotubes can serve as templates for performing polymer imprint lithography with feature sizes as small as 2 nm − comparable to the size of an individual molecule. The angstrom level uniformity in the critical dimensions of the features provided by this unusual type of template provides a unique ability to investigate systematically the resolution of imprint lithography at this molecular scale. Collective results of experiments with several polymer formulations for the molds and the molded materials suggest that the density of cross-links is an important molecular parameter that influences the ultimate resolution in this process. Optimized materials enable reliable, repetitive patterning in this single nanometer range.

Guided growth of large-scale, horizontally aligned arrays of single-walled carbon nanotubes and their use in thin-film transistors.

Abstract: A convenient process for generating large-scale, horizontally aligned arrays of pristine, single-walled carbon nanotubes (SWNTs) is described. The approach uses guided growth, by chemical vapor deposition (CVD), of SWNTs on miscut single-crystal quartz substrates. Studies of the growth reveal important relationships between the density and alignment of the tubes, the CVD conditions, and the morphology of the quartz. Electrodes and dielectrics patterned on top of these arrays yield thin-film transistors that use the SWNTs as effective thin-film semiconductors. The ability to build high-performance devices of this type suggests significant promise for large-scale aligned arrays of SWNTs in electronics, sensors, and other applications.

p-Channel, n-Channel Thin Film Transistors and p−n Diodes Based on Single Wall Carbon Nanotube Networks

Abstract: This paper demonstrates the use of arrays of networks of single wall carbon nanotubes (SWNTs) and electrical breakdown procedures for building thin film transistors (TFTs) that have good, reproducible performance and high current output. Channel length scaling analysis of these TFTs indicates that the resistance at the source/drain contacts is a small fraction of the device resistance, in the linear regime. When measured with the channel exposed to air or coated by poly(methyl methacrylate) (PMMA), these transistors operate in the unipolar p mode. By spin-coating the polymer polyethylenimine (PEI) on the channel region, these transistors can be switched to operate in the unipolar n mode. Patterning the exposure of a single channel to PMMA and PEI yields p -n diodes. These results indicate that SWNT-TFTs can provide the building blocks of complex complementary circuits for a range of applications in macroelectronics, sensors, and other systems.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Prospects of Colloidal Nanocrystals for Electronic and Optoelectronic Applications

Abstract: Nanocrystals (NCs) discussed in this Review are tiny crystals of metals, semiconductors, and magnetic material consisting of hundreds to a few thousand atoms each. Their size ranges from 2-3 to about 20 nm. What is special about this size regime that placed NCs among the hottest research topics of the last decades? The quantum mechanical coupling * To whom correspondence should be addressed. E-mail: dvtalapin@uchicago.edu. † The University of Chicago. ‡ Argonne National Lab. Chem. Rev. 2010, 110, 389–458 389

Monitoring dopants by Raman scattering in an electrochemically top-gated graphene transistor

Abstract: The recent discovery of graphene has led to many advances in two-dimensional physics and devices. The graphene devices fabricated so far have relied on $SiO_2$ back gating. Electrochemical top gating is widely used for polymer transistors, and has also been successfully applied to carbon nanotubes. Here we demonstrate a top-gated graphene transistor that is able to reach doping levels of up to $5\times 10^{13} cm^{-2}$, which is much higher than those previously reported. Such high doping levels are possible because the nanometre-thick Debye layer in the solid polymer electrolyte gate provides a much higher gate capacitance than the commonly used $SiO_2$ back gate, which is usually about 300 nm thick. In situ Raman measurements monitor the doping. The G peak stiffens and sharpens for both electron and hole doping, but the 2D peak shows a different response to holes and electrons. The ratio of the intensities of the G and 2D peaks shows a strong dependence on doping, making it a sensitive parameter to monitor the doping.

Semiconducting π-conjugated systems in field-effect transistors: a material odyssey of organic electronics.

Abstract: Since the discovery of highly conducting polyacetylene by Shirakawa, MacDiarmid, and Heeger in 1977, π-conjugated systems have attracted much attention as futuristic materials for the development and production of the next generation of electronics, that is, organic electronics. Conceptually, organic electronics are quite different from conventional inorganic solid state electronics because the structural versatility of organic semiconductors allows for the incorporation of functionality by molecular design. This versatility leads to a new era in the design of electronic devices. To date, the great number of π-conjugated semiconducting materials that have either been discovered or synthesized generate an exciting library of π-conjugated systems for use in organic electronics. 11 However, some key challenges for further advancement remain: the low mobility and stability of organic semiconductors, the lack of knowledge regarding structure property relationships for understanding the fundamental chemical aspects behind the structural design, and realization of desired properties. Organic field-effect transistors (OFETs) are a kind of device consisting of an organic semiconducting layer, a gate insulator layer, and three terminals (drain, source, and gate electrodes). OFETs are not only essential building blocks for the next generation of cheap and flexible organic circuits, but they also provide an important insight into the charge transport of πconjugated systems. Therefore, they act as strong tools for the exploration of the structure property relationships of πconjugated systems, such as parameters of field-effect mobility (μ, the drift velocity of carriers under unit electric field), current on/off ratio (the ratio of the maximum on-state current to the minimum off-state current), and threshold voltage (the minimum gate voltage that is required to turn on the transistor). 17 Since the discovery of OFETs in the 1980s, they have attracted much attention. Research onOFETs includes the discovery, design, and synthesis of π-conjugated systems for OFETs, device optimization, development of applications in radio frequency identification (RFID) tags, flexible displays, electronic papers, sensors, and so forth. It is beyond the scope of this review to cover all aspects of π-conjugated systems; hence, our focus will be on the performance analysis of π-conjugated systems in OFETs. This should make it possible to extract information regarding the fundamental merit of semiconducting π-conjugated materials and capture what is needed for newmaterials and what is the synthesis orientation of newπ-conjugated systems. In fact, for a new science with many practical applications, the field of organic electronics is progressing extremely rapidly. For example, using “organic field effect transistor” or “organic field effect transistors” as the query keywords to search the Web of Science citation database, it is possible to show the distribution of papers over recent years as shown in Figure 1A. It is very clear

A high-mobility electron-transporting polymer for printed transistors

Abstract: Printed electronics is a revolutionary technology aimed at unconventional electronic device manufacture on plastic foils, and will probably rely on polymeric semiconductors for organic thin-film transistor (OTFT) fabrication. In addition to having excellent charge-transport characteristics in ambient conditions, such materials must meet other key requirements, such as chemical stability, large solubility in common solvents, and inexpensive solution and/or low-temperature processing. Furthermore, compatibility of both p-channel (hole-transporting) and n-channel (electron-transporting) semiconductors with a single combination of gate dielectric and contact materials is highly desirable to enable powerful complementary circuit technologies, where p- and n-channel OTFTs operate in concert. Polymeric complementary circuits operating in ambient conditions are currently difficult to realize: although excellent p-channel polymers are widely available, the achievement of high-performance n-channel polymers is more challenging. Here we report a highly soluble ( approximately 60 g l(-1)) and printable n-channel polymer exhibiting unprecedented OTFT characteristics (electron mobilities up to approximately 0.45-0.85 cm(2) V(-1) s(-1)) under ambient conditions in combination with Au contacts and various polymeric dielectrics. Several top-gate OTFTs on plastic substrates were fabricated with the semiconductor-dielectric layers deposited by spin-coating as well as by gravure, flexographic and inkjet printing, demonstrating great processing versatility. Finally, all-printed polymeric complementary inverters (with gain 25-65) have been demonstrated.