bluuebunny/crossref_metadata_2025_split huggingface dataset:
High Mobility ZnO thin film transistors using the novel deposition of high-k dielectrics
Authors: Ngwashi D. K. , Cross R. B. M. , Paul S. , Milanov Andrian P. , Devi Anjana 
Published: September 2011

ABSTRACTIn order to investigate the performance of ZnO-based thin film transistors (ZnO-TFTs), we fabricate devices using amorphous hafnium dioxide (HfO2) high-k dielectrics. Sputtered ZnO was used as the active channel layer, and aluminium source/drain electrodes were deposited by thermal evaporation, and the HfO2 high-k dielectrics are deposited by metal-organic chemical vapour deposition (MOCVD). The ZnO-TFTs with high-k HfO2 gate insulators exhibit good performance metrics and effective channel mobility which is appreciably higher in comparison to SiO2-based ZnO TFTs fabricated under similar conditions. The average channel mobility, turn-on voltage, on-off current ratio and subthreshold swing of the high-k TFTs are 31.2 cm2V-1s-1, -4.7 V, ~103, and 2.4 V/dec respectively. We compared the characteristics of a typical device consisting of HfO2 to those of a device consisting of thermally grown SiO2 to examine their potential for use as high-k dielectrics in future TFT devices.
Influence of the annealing atmosphere on solution based zinc oxide thin film transistors
Authors: Busch C. , Theissmann R. , Bubel S. , Schierning G. , Schmechel R. 
Published: September 2011

ABSTRACTZinc oxide layers with a thickness of less than 10 nanometers have been synthesized from an aqueous solution for the application as active layer in thin film transistors. They have been conditioned by applying different oxidizing and reducing atmospheres during an annealing process at a temperature of 125°C. It is shown that the charge carrier mobility and threshold voltage is strongly influenced by the annealing atmosphere. Samples annealed in 10% forming gas (H2 in N2 - reducing atmosphere) show the highest field-effect-mobility of 0.6 cm2V-1s-1, but no saturation of the drain current, due to a high free carrier concentration. Samples treated under oxygen (strongest oxidizing atmosphere) show significantly lower mobilities. Subsequently, the samples have been exposed to synthetic air, with varying exposure times. Samples which have been annealed under hydrogen atmospheres show a pronounced decay of the drain current if exposed to synthetic air, whereas all samples conditioned under hydrogen-free atmospheres are significantly more stable under synthetic air. This enhanced sensitivity against oxygen after hydrogen treatment is attributed to residual hydrogen content in the sample that supports the formation of OH-groups which act as electron acceptors.
Refractive Index Engineering of Polymer Nanocomposites Prepared by End-grafted Polymer Chains onto Inorganic Nanoparticles
Authors: Tao Peng , Viswanath Anand , Li Yu , Rungta Atri , Benicewicz Brian C. , Siegel Richard W. , Schadler Linda S. 
Published: September 2011

ABSTRACTTransparent polymer nanocomposites with high refractive index were prepared by grafting polymer chains onto TiO2 nanoparticles. Reversible addition-fragmentation chain transfer (RAFT) polymerization was used to prepare poly(methyl methacrylate) (PMMA) polymer brushes grafted from TiO2 nanoparticles. The refractive index of the hybrid material increased from 1.49 for neat PMMA to 1.6 by increasing the loading of TiO2 to 40 weight percent. UV-vis spectra showed that grafted particles had a transparency of more than 90% in the visible light range. The hybrid particles can be processed into transparent, high refractive index coatings and self-standing films. The grafted TiO2 nanoparticles can also be easily dispersed into a polymer matrix forming thick, robust transparent polymer nanocomposites.
Outstanding Radiation Performance of an All-carbon Nanotube Patch
Authors: Stollberg David W. , Urbani Fabio , Verma Amit 
Published: September 2011

ABSTRACTWe report the fabrication and characterization of a microstrip patch antenna composed entirely out of multi-walled carbon nanotubes on a silicon substrate. The antenna showed excellent response in the X-band, for which it was designed. In addition, an observed left-shift resonance effect points towards significant potential for miniaturization. The antenna also showed very promising reliability under different operating conditions. Such antennas may therefore have significant promise for system-on-chip, space application, and other specialized applications.
Photo-electrical Effect of Pristine and Functionalized Graphene Grown by Chemical Vapor Deposition
Authors: Lin Jian , Zhong Jiebin , Reiber Kyle Jennifer , Penchev Miroslav , Ozkan Mihrimah , Ozkan Cengiz S. 
Published: September 2011

ABSTRACTIn this poster we will present the photo-electrical effect of pristine and nitric acid treated graphene field effect transistors made by chemical vapor deposition (CVD). The results of the decreased electrical conductance and shift of Dirac point arise from the molecular photodesorption from graphene. When post treated with nitric acid the photodesorption efficiency was decrease from 52% to 21%, which was proposed to be caused by the passivation of oxygen-bearing functionalities to CVD graphene structural defects. This result provides a new strategy of stabilizing the electrical performance of CVD graphene which is promising candidate as highly conductively photoelectrical material.
Electronic Structure of O-vacancy in High-kDielectrics and Oxide Semiconductors
Authors: Chang Kee Joo , Ryu Byungki , Noh Hyeon-Kyun , Bang Junhyeok , Choi Eun-Ae 
Published: September 2011

ABSTRACTFirst-principles density functional calculations are performed to investigate the electronic properties of O-vacancy defects in high-kHfO2, Si/HfO2interface, and amorphous oxide semiconductors. The role of O-vacancy in device performance is discussed by comparing the results of the GGA, hybrid density functional, and quasiparticle energy calculations.
Effect of thickness of thin film SnO2 based LPG sensors
Authors: Haridas Divya , Sreenivas K. , Gupta Vinay 
Published: September 2011

ABSTRACTThis paper reports the response characteristics of rf-sputtered SnO2 thin films (of varying thickness) for LPG detection. To monitor and precisely measure leakages, the development of a reliable LPG sensor with improved sensitivity is crucial in preventing fatal accidents. In the present study, thin film of SnO2 is used as the sensing element for LPG sensor. The thickness of a thin film is a very important parameter and determines their main operating characteristics, such as sensor response, rate of response, and working temperature. In the present study, thickness of SnO2 film is varied between 30 nm to 180 nm. The structure, composition and optical properties of SnO2 thin films have been examined by XRD, SEM, AFM and UV-Vis. The crystallite size for 90 nm thin film (for (110) plane) is found to be the smallest ~4-5 nm. Sensor response $(S &#x003D; \left( {{{R_a - R_g } \over {R_a }}} \right) \times 100\% )$ increases with thickness of the sensing film, with a highest sensor response (~67%) observed for 90 nm thin film and thereafter it decreases. The structural and optical properties clearly support the observed enhanced sensor response for 90 nm thin film.
ZnBeMgO thin films based UV Detectors by Spin Coating
Authors: Panwar Neeraj , Liriano J. , Katiyar Ram S. 
Published: September 2011

ABSTRACTBe and Mg co-doped ZnO films Zn1-x-yBexMgyO (0 ≤ x ≤ 0.10, 0 ≤y ≤ 0.20) have been deposited for the first time by novel chemical deposition or spin coating method. From the x-ray diffraction patterns it is noticed that the pristine ZnO film exhibits wurtzite polycrystalline structure, however, co-doped films are (0002) preferentially oriented. The (0002) peak intensity also increases with the corresponding increase in dopants concentrations. The systematic decrease in the c-axis lattice parameter value in the co-doped films as compared to pure ZnO film suggests the incorporation of smaller ions Be+2/Mg+2 at Zn+2 site. From the optical transmittance measurement it is noticed that all the films exhibited almost 80% transmittance in the visible region with sharp and single absorption edges in the UV region. The cut-off wavelength shifts from 375nm for the ZnO film to 330nm with 10 Be and 20% Mg co-doped film. The bandgap calculations revealed an increase in bandgap from 3.26eV (ZnO) to 3.60eV (Zn0.7Be0.1Mg0.2O) film. Such an increase in the co-doped films fabricated by a much simpler and cheaper process is very useful in the realization of UV radiation detection without having little interference from the visible light.
A Study of Increased Resistivity of FTO Back Contact for CZTS Based Absorber Material Grown by Electrodeposition-Annealing Route
Authors: Sarswat Prashant K. , Free Michael L. , Tiwari Ashutosh 
Published: September 2011

ABSTRACTCZTS (Copper zinc tin sulfide) thin films have been synthesized on transparent conducting oxide (TCO) back contacts on a glass substrate, allowing sun light to pass through the entire solar cell. Aqueous solution based co-electrodeposition followed by elevated temperature sulfurization, was used to grow CZTS on transparent fluorinated tin oxide. Loss in conductivity of FTO is observed after sulfurization, causing reduced device efficiency. Increased resistivity of the FTO is likely due to outdiffusion process. A systematic study of resistivity of back contact at various sulfurization temperatures and times is discussed. Various remedial measures for improved conductivity of back contact were proposed and conducted.
Thermal Conductivity of Amorphous Indium Zinc Oxide Thin Films
Authors: Endoh Ryo , Hirano Takayuki , Takeda Masaaki , Oishi Manabu , Oka Nobuto , Shigesato Yuzo 
Published: September 2011

ABSTRACTThe thermal conductivity of amorphous indium zinc oxide (IZO) thin films was measured by the 3ω method. Three IZO films were prepared by dc magnetron sputtering method on Si substrate under different O2 flow ratios (O2 / [Ar+O2]) of 0%, 1%, and 5%. The thermal conductivity of IZO films decreases with an increase in O2 flow ratio, the values of the thermal conductivity were 3.4, 3.1 and 1.2 W m-1 K-1 for O2 flow ratios of 0%, 1%, and 5%, respectively. To investigate relationships among the thermal conductivity, the structure and other physical properties, we were carried out nanoindentation, Rutherford back scattering (RBS), electron spin resonance (ESR). The result of ESR measurements indicated that the amount of conduction electron in the IZO film decreases with increasing O2 flow ratio. Increase of O2 flow ratio reduces the amount of oxygen vacancies for providing free electrons. Therefore, decreasing thermal conductivity with an increase in O2 flow ratio is attributed to decreasing conduction electrons as thermal carrier. On the other hand, the chemical composition of IZO films is independent of O2 flow ratio. Furthermore, density, Young’s modulus and hardness also show little changes with increasing O2 flow ratio. Density, Young’s modulus and hardness are strongly associated with the internal structure. It is probable that influence of oxygen vacancies on the internal structure of IZO film is negligibly small.
Encapsulation of Luminescent Silicon Nanocrystals within Mesoporous Silica Nanospheres: Synthesis and Effect on Photoluminescence
Authors: Regli Sarah , Kelly Joel A. , Veinot Jonathan G.C. 
Published: September 2011

ABSTRACTSilicon nanocrystals (Si-NCs) are of significant research interest owing to their quantum confined photoluminescent (PL) properties and biological inertness. A promising application of these NCs is as the luminescent component in multifunctional biomedical technologies. In this report, we demonstrate the encapsulation of alkyl terminated Si-NCs within a mesoporous silica shell as a multifunctional imaging and drug delivery architecture. The Si-NC concentration was found to critically impact the nanoshell morphology. The impact of the encapsulation process on the Si-NC PL was studied, showing a blue-shift and decrease in intensity attributed to the oxidation of Si-NCs under basic conditions.
Low Field Magnetoresistance at Room Temperature in CrO2 Doped Polyvinyl Alcohol Films
Authors: Biswas S. , Ram S. 
Published: September 2011

ABSTRACTFerromagnetic CrO2 nanoparticles embedded in a diamagnetic matrix of polyvinyl alcohol (PVA) presents an example of granular giant magnetoresistance (GMR) in a diluted magnetic composite structure. Usefully significant MR occurs at room temperature, viz. -6.8% in 3.0 wt% CrO2-PVA, at field as small as 1.1 kOe. We suggest that the system is a natural analogue to dilute ferro-fluid structures composed of nanoscale magnetic particles in a viscous organic fluid (diamagnetic as well as an electrical insulator), i.e., this material displays a GMR effect without an introduction of chemical interfaces. It has great potential in various applications and can also facilitate studies of magnetotransport properties in GMR materials.
Second-Harmonic Generation Spectroscopy from Time-Dependent Density-Functional Theory
Authors: Luppi E. , Hübener H. , Bertocchi M. , Degoli E. , Ossicini S. , Véniard V. 
Published: September 2011

ABSTRACTWe developed an ab initio formalism based on Time-Dependent Density-Functional Theory for the calculation of the second-order susceptibility Χ(2) (Luppi et al. J. Chem. Phys. 132, 241104(2010)). We apply this formalism to the calculation of second-harmonic generation spectra of hexagonal SiC polytypes, ZnGeP2 (ZGP) and GaP. Starting from the independent-particle approximation, we include manybody effects, such as quasiparticle via the scissors operator, crystal local fields and excitons. We consider two different types of kernels: the ALDA and the “long-range” kernel. We analyze the effects of the different electron-electron descriptions in the spectra, finding good agreement with experiments.
Roll-to-roll manufacture of pentacene-based thin film transistors with a flash-evaporated polymer dielectric cured with an e-beam
Authors: Abbas Gamal A. W. , Cheng Donna , Mallik Kanad , Assender Hazel E. 
Published: September 2011

ABSTRACTWe report our fabrication of pentacene field effect transistors (FETs) based on a vacuum processed and e-beam cured polymer electrolyte (i.e., tripropylene glycol diacrylate (TRPGDA)) as a gate dielectric layer on flexible wide web substrates. The deposition of the semiconductor and gate insulator layers is carried out in Oxford's roll-to-roll vacuum web processing facility and could be combined in-line with roll-to-roll pattern metallization. The aim of the work is to demonstrate the ability to create all-evaporated transistors, exploiting the kind of technologies at present extensively used in the food packaging industry, for example, in which all layers can be deposited at high web speeds. Ours is a room temperature and a solvent-free method with an ultrahigh deposition rate (web speeds in excess of 100 m/min are possible).The performance of the pentacene and the polymer dielectric materials within devices was investigated, demonstrating (1) the ability to deposit good quality pentacene layers in the roll-to-roll environment and (2) the importance of the e-beam curing conditions of the dielectric layer on the performance of the organic FET devices. This deposition route creates a smooth, pin-hole-free dielectric layer as it is deposited onto the substrate as a monomeric liquid, before curing, and there is no mass-loss such as in solvent-based deposition processes. These devices have a 250 μm channel length and an aspect ratio of 16. No self-assembled monolayer (SAM) or other surface modification had been applied to the insulator layer to achieve these properties.The tuning of the transistors' operating voltage and output characteristics was feasible through the ease of control of the polymer dielectric thickness achieving a threshold voltage of less than 10 V. On/off ratio in excess of 103, and mobility = 0.1 cm2V-1s-1 have been achieved.The ability to integrate such a high deposition rate polymer process, into a single step, multilayer, vacuum deposition process with conventional vacuum deposition sources provides a possible route to low cost and large area electronic device processing.
Large Area Graphene on Polymer Films for Transparent and Flexible Field Emission Device
Authors: Verma Ved Prakash , Das Santanu , Lahiri Indranil , Choi WonBong 
Published: September 2011

ABSTRACTLarge scale fabrication of graphene over transparent flexible polymer, Polyethelyne tetrapthalate (PET), and its application in flexible field emission display is reported here. We used Cu foil (~160 mm x 60 mm) to grow graphene by thermal chemical vapor deposition process and transfer the graphene over a polymer using a straightforward hot press lamination technique. The fabrication method is facile as there is no rigorous chemical process involved and the process is also applicable towards the fabrication of large scale graphene over a wide range of transparent flexible substrates for foldable micro-electronics applications. Further, we demonstrate the application of graphene/PET polymer film as anode of transparent flexible field emission display device. The device shows low turn-on voltage ~ 1.75V/μm and high current density of ~ 65μA/cm2 with field enhancement factor (β) ~1000.
Annealing Effects of Microstructure in Thin-film Silicon Solar Cell Materials Measured by Effusion of Implanted Rare Gas Atoms
Authors: Beyer W. , Lennartz D. , Prunici P. , Stiebig H. 
Published: September 2011

ABSTRACTIn thin film silicon solar cell technology, annealing (heat treatment) effects are of interest since (i) annealing of underlying films often cannot be avoided during deposition and (ii) heat treatment (e.g. by laser) may be actively used for improvement of as-deposited material. Changes in the microstructure of several thin film silicon solar cell materials like hydrogenated amorphous silicon, microcrystalline silicon and zinc oxide by heat treatment were investigated by effusion measurements of hydrogen and implanted helium. Densification is observed for all materials studied, i.e. interconnected voids disappear or are transformed to isolated voids. We attribute the observed annealing effects primarily to an incomplete polymerization during growth. Important for solar cell processing is the result that the annealing effects involving structural changes set in at temperatures close to the temperature of deposition.
Atomistic Simulations of the Silicon Surface Structure at the Interface of Silver Thick Film Contacts on n-Type Silicon
Authors: Kontermann Stefan , Ruf Alexander , Preu Ralf 
Published: September 2011

ABSTRACTNanoscale silver crystals at the interface of silver thick film contacts on n-type silicon carry the current across the contact and therefore control the contact resistance, which is a main performance limiting parameter for semiconductor devices. The silver crystals are located in pits at the silicon surface. The shape of the pits is different on Si-(111) and Si-(100). During contact formation, these pits form before the silver crystals. Hence they determine the crystal size and shape. Consequently, the pits with the crystals influence the contact resistance. We investigate these pits experimentally by scanning electron microscopy. We are the first to simulate the mechanism of pit formation at a contact interface by considering a model that is based on the removal probability of silicon surface atoms. This model leads to good agreement between experimental and simulated data. It enables the prediction of pit formation for arbitrary process parameters like temperature and duration for silver thick film contact formation on silicon.
High deposition rate of low resistive and transparent ZnO:Al on glass with an industrial moving belt APCVD reactor
Authors: Illiberi A. , Kniknie B. , Steijvers H.L.A.H. , Habets D. , Simons P.J.P.M. , Beckers E.H.A. , Van Deelan J. 
Published: September 2011

ABSTRACTAluminum doped ZnOx (ZnOx:Al) films have been deposited on glass in an in-line industrialtype reactor by a metalorganic chemical vapor deposition process at atmospheric pressure. ZnOx:Al films can be grown at very high deposition rates of ~ 14 nm/s for a substrate speed from 150 mm/min to 500 mm/min. ZnOx:Al films are highly conductive (R < 9 Ohm/sq, for a film thickness above 1300 nm) and transparent in the visible range (> 80%). Amorphous silicon p-i-n solar cells have been grown on as deposited ZnOx:Al films, without optimizing the surface texturing of ZnOx:Al films to enhance light scattering. An initial efficiency of approximately 8% has been achieved.
High Efficiency Sputtered CdS/CdTe Cells without CdCl2 Activation
Authors: Paudel N.R. , Wieland K.A. , Compaan A.D. 
Published: September 2011

ABSTRACTPolycrystalline thin-film CdS/CdTe PV cells nearly always require “activation” with vapors containing chlorine and oxygen near 400 oC in order to realize the highest cell performance, even when growth occurs near 600 oC. In this study we have used film growth near 270 oC by magnetron sputtering in an oxygen-free ambient and have studied the effects of post-deposition heat treatments for 20 minutes at 400, 425 and 450 oC without CdCl2 in a dry air ambient. The heat treatments enhanced grain growth and produced re-crystallization of the CdTe film at all three temperatures, but 450 oC was required to reach the best electrical performance. Grain size increased from a couple of hundred nanometers to more than a micron as the preferred (111) growth orientation decreased. Efficiencies up to 11.6% were achieved with no CdCl2 compared to ~13% with activation at 387 oC in the presence of CdCl2 vapors. X-ray diffraction and quantum efficiency measurements show interdiffusion of CdS and CdTe at 450 oC comparable with a standard CdCl2 treatment at 387 oC. The results are discussed in terms of CdSTe alloy gradients and minority-carrier diffusion lengths.
Enhanced Light Emission at Self-assembled GaN Inversion Domain Boundary
Authors: Liu Mei-Chun , Cheng Yuh-Jen , Chang Jet-Rung , Chang Chun-Yen 
Published: September 2011

ABSTRACTWe report the fabrication of GaN lateral polarity inversion heterostructure with self assembled crystalline inversion domain boundaries (IDBs). The sample was fabricated by two step molecular-beam epitaxy (MBE) with microlithography patterning in between to define IDBs. Despite the use of circular pattern, hexagonal crystalline IDBs were self assembled from the circular pattern during the second MBE growth. Both cathodoluminescent (CL) and photoluminescent (PL) measurements show a significant enhanced emission at IDBs and in particular at hexagonal corners. The ability to fabricate self assembled crystalline IDBs and its enhanced emission property can be useful in optoelectronic applications.
Kesterites and Chalcopyrites: A Comparison of Close Cousins
Authors: Repins Ingrid , Vora Nirav , Beall Carolyn , Wei Su-Huai , Yan Yanfa , Romero Manuel , Teeter Glenn , Du Hui , To Bobby , Young Matt , Noufi Rommel 
Published: September 2011

ABSTRACTChalcopyrite solar cells based on CuInSe2 and associated alloys have demonstrated high efficiencies, with current annual shipments in the hundreds of megawatts (MW) range and increasing. Largely due to concern over possible indium (In) scarcity, a related set of materials, the kesterites, which comprise Cu2ZnSnS4 and associated alloys, has received increasing attention. Similarities and differences between kesterites and chalcopyrites are discussed as drawn from theory, depositions, and materials characterization. In particular, we discuss predictions from density functional theory, results from vacuum co-evaporation, and characterization via x-ray diffraction, scanning electron microscopy, electron beam-induced current, quantum efficiency, secondary ion mass spectroscopy, and luminescence.