bluuebunny/crossref_metadata_2025 huggingface dataset:
Control of Optical and Electrical Properties of ZnO Films for Photovoltaic Applications
Authors: Hunger Ralf , Iwata Kakuya , Fons Paul , Yamada Akimasa , Matsubara Koji , Niki Shigeru , Nakahara Ken , Takasu Hidemi
Published: April 2011

ZnO films were grown by radical-source molecular beam epitaxy (RS-MBE) on sapphire and glass substrates, and they were characterized in terms of Hall mobility and optical transmission. Undoped ZnO films exhibit a low intrinsic defect density and optical properties close to bulk ZnO. By Ga doping, a resistance ρ as low as 2×10−4 Ωcm could be achieved. Balancing high conductivity and low transmission losses due to free carrier absorption in the infrared, the optimum was obtained for ρ=3.4×10−4Ωcm, electron mobility μe=37 cm2/Vs and an average transmission T of 96% in the wavelength range 400-1100 nm. Polycrystalline growth on glass yields slightly reduced but still good film quality (μe=30 cm2/Vs, T=90%). By the incorporation of Mg, conducting Mg0.3Zn0.7O films with an increased band gap up to ∼ 4eV were realized.
Structure Investigations of Several In-rich (Cu2Se)x(In2Se3)1−x Compositions: From Local Structure to Long Range Order
Authors: Chang C.-H. , Wei Su-Huai , Ahrenkiel S. P. , Johnson J. W. , Stanbery B.J. , Anderson T.J. , Zhang S.B , Al-Jassim M.M. , Bunker G. , Payzant E.A. , Duran R.
Published: April 2011

The observed junction between α-CuInSe2 and the In-rich compositions in the β-phase domain (e.g. CuIn3Se5) appears to play an important role in the photovoltaic process [1]. There remain, however, inconsistencies and uncertainties about the boundary and structure of this phase. In general the structure of this phase belongs to defect tetrahedral family of structures [2], which can be described as normal tetrahedral structures with a certain fixed number of unoccupied structure sites. In this work, the local structures of various (Cu2Se)x(In2Se3)1−x semiconductor alloys in the β-phase domain were studied by Extended X-ray Absorption Fine Structure (EXAFS) and the results were compared to those for the α-CuInSe2 phase. The long- range order of these compositions was studied by X-Ray powder Diffraction (XRD) and electron diffraction. It was found the local structures of these compounds are well defined. These compounds, however, could not be well described by any long-range order structure model, especially the selenium position. First-principles band structure calculations were performed to assist in assigning crystal structures to CuInSe2, CuIn3Se5 and CuIn5Se8. The calculations indicated that the local environments of these compounds are well defined. Their long-range order might depend sensitively on growth history and the configurational entropies as suggested by the similar formation energies of several possible crystal structures for CuIn3Se5 and CuIn5Se8.
Theoretical and Experimental Study of Shunt Effects in Thin-film Photovoltaics
Authors: Karpov V. G. , Rich G. , Rose D. H. , Subashiev A. V. , Dorer G.
Published: April 2011

We present an analytical model that quantitatively describes the physics behind shunting in thin-film photovoltaics and predicts size-dependent effects in the I/V characteristics of solar cells. The model consists of an array of micro-diodes and shunt in parallel between the two electrodes, one of which mimics the TCO and has a finite resistance. We introduce the concept of the screening length L, over which the shunt affects the electrical potential of the system. The nature of this screening is that the system generates currents in response to the point perturbation caused by the shunt. L is expressed explicitly in terms of the system parameters. We find the spatial distribution of the electrical potential in the system and its I/V characteristics. The measured I/V characteristics depend on the relationship between the cell size l and L, being markedly different for the cases of small (l<>L) cells. This model is verified experimentally; good agreement is obtained.
A TEM Study of the Microstructure Evolution of Cu(In,Ga)Se2 Films from Cu-Rich to In-Rich
Authors: Yan Y. , Jones K.M. , AbuShama J. , Al-Jassim M.M. , Noufi R.
Published: April 2011

The microstructure of Cu(In,Ga)Se2 (CIGS) films with compositions ranging from Cu-rich to In-rich was investigated by transmission electron microscopy (TEM) and energy-dispersive Xray spectroscopy (EDS). We found that the Cu-rich samples have larger grain sizes than the Inrich sample. In the Cu-rich samples, sub-interfaces were observed. The two sides of the subinterfaces were found to have different Cu concentration. In the In-rich sample, Ga inhomogeneity across grains was observed.
Interface Engineering of Chalcogenide Semiconductors in Thin Film Solar Cells: CdTe as an Example
Authors: Fritsche J. , Kraft D. , Thissen A. , Mayer Th. , Klein A. , Jaegermann W.
Published: April 2011

In this paper the electronic properties of the different interfaces of CdTe thin film solar cells will be analysed by using a surface science approach. Experimental basis for the experiments is an integrated UHV systems which allows to prepare and analyse real solar cells as well as appropriate model interfaces. Recently obtained data on the ITO surface, the ITO/SnO2/CdS front contact, the CdS/CdTe heterojunction and the CdTe/Te back contact will be presented. In addition, bulk properties as doping and lateral inhomogeneities will be addressed. For all these interfaces experimentally determined band energy diagrams will be given and discussed in relation to solar cell performance. Finally, the sum of the results will be used to propose a modified band energy diagram of the complete CdTe thin film solar cell and its implication for further cell improvement will be presented.
Diffusion Behavior and Microstructural Properties of the CBD-ZnS/CIGS Interface Boundary
Authors: Nakada Tokio
Published: April 2011

The diffusion behavior and microstructural properties of the CBD-ZnS/Cu(In,Ga)Se2 (CIGS) interface of high-efficiency Cd-free CIGS thin film solar cells with efficiencies exceeding 17 % have been investigated using energy dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). CBD-ZnS thin layers are found to grow with small polycrystalline grains that consist of sphalerite and wurtzite phases. This is in sharp contrast to CBD-CdS layers which grow epitaxially on CIGS grains. Micro-EDX analysis revealed Zn indiffusion into the CIGS thin layer a distance of approximately 40 nm from the CBD-ZnS/CIGS interface boundary after air-annealing at 200°C, whereas no diffusion of Zn was observed before annealing. These results suggest that the main role of the air-annealing process is not substitution of Se vacancies by oxygen atoms but the diffusion of Zn into CIGS which may result in the formation of a pn homojunction. On the other hand, negligible Zn-diffusion into a CuGaSe2 thin film was found at the CBD-ZnS/CuGaSe2 interface boundary even after air-annealing. The cell performance of CBD-ZnS/CIGS thin film solar cells is discussed in connection with the Ga/(In+Ga) atomic ratio, conduction band-offset and Zn-diffusion.
CuIn1−XGaXSe2-Based Photovoltaic Cells From Electrodeposited Precursor Films
Authors: Bhattacharya Raghu N. , Fernandez Arturo M.
Published: April 2011

We have developed an electrodeposition bath based on a buffer solution so that the stability of the electrodeposition process is enhanced and no metal oxides or hydroxides precipitate out of solution. The buffer-solution-based bath also deposits more gallium in the precursor films. Asdeposited precursors are stoichiometric or slightly Cu-rich CuIn1−XGaXSe2 (CIGS). Only a minimal amount of indium was added to the electrodeposited precursor films by physical vapor deposition to obtain a 9.4%-efficient device.
Chemical Bath Deposition of Zinc Sulfide from Acidic Solutions
Authors: O'Hare Iain P. , Govender Kuvasani , O'Brien Paul , Smyth-Boyle David
Published: April 2011

At present, the soft processing of materials attracts considerable interest. Chemical bath deposition (CBD) effects film formation by means of a controlled chemical reaction. Adherent, uniform and reproducible films of zinc sulfide (ZnS) have been deposited, upon low iron-content microscope slides, under acidic conditions, from a solution containing zinc chloride, urea and thioacetamide. Scanning electron micrographs of the deposited layers suggest that, as the reaction proceeds, uniform film growth is associated with increasing particle size, rather than continuous nucleation and deposition of new primary particles. Energy Dispersive Analysis by X-Rays (EDAX) spectra are typical of CBD-deposited films of ZnS; signals attributable to elements within the glass substrate are also detected, an observation consistent with the thin nature of the films. Grain size distributions have been investigated using computational image analysis, and an average increase in the diameter of the deposited particles of 33.7 nanometres per hour has been calculated.
Cadmium Telluride Solar Cells on Molybdenum Substrates
Authors: Matulionis Ilvydas , Han Sijin , Drayton Jennifer A. , Price Kent J. , Compaan Alvin D.
Published: April 2011

We report on the development of Mo/CdTe/CdS/indium-tin-oxide, thin-film solar cells grown by radio-frequency magnetron sputtering. This is an inverted configuration compared to the conventional glass/tin-oxide/CdS/CdTe/metal cells. Molybdenum was chosen as a substrate because its thermal expansion coefficient and the work function are close to those of CdTe. We have achieved AM1.5 conversion efficiencies of 7.8 percent on 0.05 cm2 area devices. Our best cells had a nitrogen-doped ZnTe layer between the molybdenum and the CdTe for a somewhat improved back contact. However, we observe a significant rollover in the IV curve in forward current that indicates a back-diode effect. This implies the need for improvement of the electronic properties of the molybdenum - CdTe and possibly CdS - ITO interfaces.
CBD-In(OH)xSy Thin Films: An Approach to the Growth Mechanism
Authors: Bayón Rocío , Herrero José
Published: April 2011

The surface morphology of chemical bath deposited In(OH)xSy thin films has been studied using SEM and TEM. Different surface morphologies have been obtained depending on the deposition conditions (reactant concentrations, pH and bath temperature) as a consequence of the variation of both the homogeneous nucleation and particle-growth rates with them. The In(OH)3 colloids present in the bulk solution and on the substrate surface play an important role in the growth mechanism since they promote the In(OH)xSy formation. It has been found that the growth mechanism of the films is the socalled particle-by-particle or colloidal growth.
Device Analysis of Cu(In,Ga)Se2Heterojunction Solar Cells - Some Open Questions
Authors: Rau U. , Weinert K. , Nguyen Q. , Mamor M. , Hanna G. , Jasenek A. , Schock H. W.
Published: April 2011

The paper discusses the electronic properties of Cu(In,Ga)Se2–based heterojunction solar cells with a special focus on questions which at present are not satisfactorily understood. First, we discuss an apparent quantitative contradiction between measured concentrations of recombination centers in the Cu(In,Ga)Se2absorber material and the actual recombination rate in the solar cells. We propose, as a possible explanation for that observation, that the defect concentration in Cu(In,Ga)Se2is spatially inhomogeneous with a systematic increase towards the heterojunction interface. Second, we address the issue of electronic metastabilities in ZnO/CdS/Cu(In,Ga)Se2heterojunctions and, especially, in devices that use alternative buffer materials instead of CdS. Starting from a brief review of the experimentally observed types of metastabilities, we demonstrate by thermally stimulated capacitance measurements that a specific type of metastability that severely limits the performance of solar cells with non-CdS buffers is present also in high-efficiency standard devices though it has virtually no influence on the output parameters in the latter case. A possible explanation of this type of metastability points to a metastable defect reaction localized in the close to surface region of Cu(In,Ga)Se2. At the moment we cannot propose conclusive models for both open questions. However, we can localize the answers to both problems in the close-to-surface region of the Cu(In,Ga)Se2absorber.
Electrical Characteristics of TaOxNy/ZrSixOy Stack Gate Dielectric for MOS Device Applications
Authors: Jung Hyungsuk , Yang Hyundoek , Im Kiju , Hwang Hyunsang
Published: April 2011

This letter describes a unique process for the preparation of high quality tantalum oxynitride (TaOxNy) with zirconium silicate (ZrSixOy) as an interfacial layer for use in gate dielectric applications. Compared with conventional native silicon oxide and oxynitride as an interfacial layer, tantalum oxynitride (TaOxNy) MOS capacitors using zirconium silicate (ZrSixOy) as an interfacial layer exhibit lower leakage current levels at the same equivalent oxide thickness. We were able to confirm TaOxNy/ZrSixOy stack structure by auger electron spectroscopy (AES) and transmission electron microscope (TEM) analysis. The estimated dielectric constant of TaOxNy and ZrSixOywere approximately 67 and 7, respectively. The zirconium silicate is a promising interfacial layer for future high-k gate dielectric applications.
Investigation on the Thermal and Electrical Properties of Ti-Si-O Film Formed by the Composite Sputtering Deposition
Authors: Nishiyama Akira , Kaneko Akio , Koyama Masato , Kamata Yoshiki , Fujiwara Ikuo , Koike Masahiro , Yoshiki Masahiko , Koike Mitsuo
Published: April 2011

Ti-Si-O films were sputter deposited from TiO2+SiO2 composite targets with various SiO2 content. The phase separation occurred for every SiO2 content used in this experiment (from 14% to 75%) and it has been revealed that nanocrystalline (TiO2)1-x(SiO2)x films in which anatase TiO2 forms tiny grains were obtained when x in the film is larger than 0.26. The tiny grain was effective for suppressing the thermal grooving phenomenon of the thin films by the post deposition annealing which leads to the leakage current increase. The dielectric constant of the nanocrystalline film was varied with the SiO2 content from the value of the bulk anatase to SiO2.
A Comparative Study of Nickel Silicide Formation Using a Titanium Cap Layer and a Titanium Interlayer
Authors: Tan W.L. , Pey K. L. , Chooi Simon Y.M. , Ye J.H.
Published: April 2011

NiSi formation is known to be hindered by interfacial native oxide. Such oxide is easily formed on the Si surface through inefficient cleaning or a long time lag prior to Ni deposition. In this study, two methodologies were investigated to remove this layer of native oxide when no DHF clean was performed prior to metal deposition. Firstly, the deposition of a 100°C Ti cap layer after Ni deposition and secondly, the deposition of a middle 50Å Ti prior to Ni deposition. The samples were then rapid thermal annealed from 500 to 800°C. It was found for the Ti / Ni / SiO2 / Si stack, a layer of NiSi was formed starting from 600°C. Transformation to the NiSi2 phase begins at 750°C. As for the Ni / Ti / SiO2 / Si stack, a layer of NiSi was formed after 500°C annealing and conversion to NiSi2 also took place at 750°C. However, it was found that at low temperatures such as 500-600°C, facets of NiSi2 were identified under the thick NiSi layers, embedded in the Si substrate. Ternary phases like TixNiySiz were also identified at the surface of the sample.
Lack of hardening effect in TiN/NbN multilayers
Authors: Molina-Aldareguia Jon M. , Lloyd Stephen J. , Barber Zoe H. , Clegg William J.
Published: April 2011

There is evidence indicating that multilayer films can be harder than monolithic ones. To investigate this, TiN/NbN multilayers with bilayer thicknesses ranging from 4 nm to 30 nm have been grown on MgO (001) single crystals using reactive magnetron sputtering. The sharpness of the interface and the composition modulation, which would be expected to strongly influence dislocation motion, have been studied by X-ray diffraction (XRD). These experiments show that the interfaces remain reasonably sharp (interface thickness ∼1 nm) and the composition modulation amplitude is maximum for multilayers with bilayer thicknesses greater than ∼10 nm. With thinner bilayers, the composition modulation decreases but the layered structure remains. Despite this, the nanoindentation hardness of the multilayers is between 20 and 25 GPa, which is similar to that of TiN and NbN alone, and therefore, no hardening due to the layering is observed. The deformation mechanisms observed under the indent in the TEM are consistent with these results.
Development of Cross-Hatch Morphology During Growth of Lattice Mismatched Layers
Authors: Andrews A. Maxwell , Speck J.S. , Romanov A.E. , Bobeth M. , Pompe W.
Published: April 2011

An approach is developed for understanding the cross-hatch morphology in lattice mismatched heteroepitaxial film growth. It is demonstrated that both strain relaxation associated with misfit dislocation formation and subsequent step elimination (e.g. by step-flow growth) are responsible for the appearance of nanoscopic surface height undulations (0.1-10 nm) on a mesoscopic (∼100 nm) lateral scale. The results of Monte Carlo simulations for dislocation- assisted strain relaxation and subsequent film growth predict the development of cross-hatch patterns with a characteristic surface undulation magnitude ∼50 Å in an approximately 70% strain relaxed In0.25Ga0.75As layers. The model is supported by atomic force microscopy (AFM) observations of cross-hatch morphology in the same composition samples grown well beyond the critical thickness for misfit dislocation generation.
Anodic Bonding at Room Temperature
Authors: Baier Volker , Gebhardt Andreas , Barth Stefan
Published: April 2011

Special phosphate glasses (niobium-phosphate glasses) are used for anodic bonding experiments. They are optimized particularly with regard to elevated alkali ion conductivity at room temperature due to high contents of Li or Na ions. The compounds anodically bonded at room temperature show the strength of the breakage of the glass. Only a few seconds up to a few minutes at voltages of maximum 500 V are necessary for bonding. The glasses have a thermal expansion coefficient, which is not fitted to that of silicon. Therefore, stability of the bonded compounds is achieved only at temperature jumps up to 100 K in the case of bulk samples. For higher temperature jumps the probability of breakage increases continuously. It is possible to get thin films of these glasses with ac and dc magnetron sputter techniques for example on silicon. These thin layers are anodically bondable and the compounds with silicon show a higher temperature stability (at least 233 to 473 K).
Structured monocrystalline Si thin-film modules from layer-transfer using the porous Si (PSI) process
Authors: Richard Auer , Rolf Brendel
Published: April 2011

We demonstrate a novel technique for fabricating monolithically series connected solar modules from surface structured thin monocrystalline Si films that we prepare by layer transfer using porous Si (PSI process). The novel series connection technique bases on reactive ion etching of the silicon film in a microwave plasma prior and after layer transfer. The module has an area of 25 cm2 and consists of 5 unit cells that have a film thickness of 16 µm. We measure an open-circuit voltage of 3028 mV and a confirmed efficiency of 9.9%. The Si film has a randomly textured surface for light trapping.
Ablation Lithography for TFT-LCD
Authors: Suzuki Kenkichi , Hayashi Nobuaki , Masuhara Hiroshi , Lippert Thomas K.
Published: April 2011

Ablation lithography is based on the photo-decomposition ablation of polymer materials by excimer laser. It is a self-development process, and accordingly possible to reduce the throughput time and manufacturing cost of TFT-LCD. The major alterations from the conventional photolithography are the resist material and the mask. Developing both the technologies and using an experimental exposure& aligner, we fabricated a TFT pattern on 300 × 400 mm2 glass substrate. The result proves the feasibility of EAL as an high throughput lithography suitable for a-Si TFT.
Low Temperature Process Technologies for the Next Generation High Performance Polycrystalline Silicon Thin-Film Transistors
Authors: Higashi Seiichiro , Abe Daisuke , Inoue Satoshi , Shimoda Tatsuya
Published: April 2011

Low temperature process technologies for high performance polycrystalline silicon (poly-Si) thin-film transistors (TFTs) are discussed based on the investigations of pulsed laser crystallization, plasma treatment of poly-Si films, and SiO2/Si interface formation. Although highdensity (∼1018 cm−3) trap states localized at grain boundaries are introduced to the poly-Si films by laser crystallization, they are efficiently decreased to the order of 1016 cm−3 by following hydrogen plasma treatment. It is also shown that high quality SiO2/Si interfaces with the density of interface trap states (Dit) in the order of 1010 cm−2eV−1 are achieved using electron cyclotron resonance (ECR) plasma enhanced chemical vapor deposition (PECVD). By applying these low temperature process technologies to the fabrication process, high performance poly-Si TFTs with high n-channel mobility μn) of 187 cm2V−1s−1, low threshold voltage (Vth) of 1.97 V and small subthreshold swing (S) of 210 mV/dec. were obtained. These results indicate that the development of low temperature process technologies that can control trap states is the key to the next generation high performance poly-Si TFTs.
High Quality Growth of SiO2 at 80° C by Electron Cyclotron Resonance (ECR) for Thin Film Transistors
Authors: Rashid Riyaz , Flewitt A. J. , Grambole D. , Kreiβig U. , Robertson J. , Milne W. I.
Published: April 2011

Silicon dioxide (SiO2) films have been deposited at 80°C in an Electron Cyclotron Resonance (ECR) plasma reactor from a gas phase combination of He, O2 and SiH4. The ECR configuration provides a highly ionised plasma (∼1016 m−3) with low ion energies (∼10eV) that gives efficient dehydrogenation of the growing material whilst minimizing defect creation. The physical characterisation of the material gives a refractive index of 1.46, an etch rate in buffered HF below 3 nm/s and a hydrogen content of less than 2 at.%. Electrical tests reveal a resistivity in excess of 1014Ωcm, an average breakdown strength of 5 MV/cm, and fixed charge and interface state densities of 1011 cm−2 and 1012 eV−1cm−2 respectively. This has been achieved using a O2:SiH4 flow ratio ≍ 2:1.
Preparation and Characterization of Low Temperature Silicon Dioxide Thin Films Using Tetramethylsilane (TMS) for Microfabrication Applications
Authors: Lin Xin , Fonash Stephen J.
Published: April 2011

Low temperature silicon dioxide depositions have been carried out by plasma enhanced chemical vapor deposition (PECVD) using TMS as the Si precursor at 100-200°C at the pressure of 2-8 Torr. An RF power of 40 W and a TMS:O2 gas flow rate ratio of 1:500 without inert gas dilution were used in the depositions. It was found that the current-voltage (I-V) characteristics of as-deposited oxide films improved as the substrate temperature increased or deposition pressure decreased. Oxide films deposited at 2-3 Torr exhibited typical Fowler-Nordheim (F-N) tunneling characteristics and breakdown voltages greater than 8 MV/cm. The best capacitance-voltage (C-V) characteristics, giving a small flat band voltage shift, a small amount of positive oxide charge, a small hysteresis in bi-directional C-V sweep, and a low interface trap density, were obtained at 3 Torr. Post-deposition annealing in forming gas at the deposition temperature was performed and proved to be an effective approach for improving the electrical properties of the deposited oxide films without compromising the low temperature aspect of the process. By annealing at 200°C, the F-N tunneling barrier height increased by as much as 0.6 eV, the flat-band voltage and the hysteresis in C-V sweep were reduced by 0.74 V and 0.08 V, respectively. In addition, hydrogen was found to play a key role in the annealing treatment and its mechanisms were discussed.
Nano Crystalline Silicon Film Serves as the Emission Material for the Field Emission Pressure Sensor
Authors: Bo Liao
Published: April 2011

The prototype of a field-emission pressure sensor with a novel structure based on the quantum tunnel effect is designed and manufactured. Moreover the nano crystalline silicon film technology is introduced into the fabrication of the device effectively, which performs the function mostly as the field-emission material, the device field-emission characteristic of the nano silicon film is investigated, the experimental results show that the measured current density emitted from the effective area of the sensor can reach 53.5A/m2, when the exterior electric field is 5.6×105V/m.
Flat Panel Imagers Based on Excimer Laser Annealed, poly-Si Thin Film Transistor Technology
Authors: Lu J.P. , Schuylenbergh K. Van , Fulks R. T. , Ho J. , Wang Y. , Lau R. , Nylen P. , Mei P. , Mulato M. , Boyce J.B. , Street R.A.
Published: April 2011

Pulsed Excimer-Laser Annealing (ELA) has become an important technology to produce high performance, poly-Si Thin Film Transistors (TFTs) for large area electronics. The much-improved performance of these poly-Si TFTs over the conventional hydrogenated amorphous Si TFTs enables the possibility of building next generation flat panel imagers with higher-level integration and better noise performance. Both the on-glass integration of peripheral driver electronics to reduce the cost of interconnection and the integration of a pixel level amplifier to improve the noise performance of large area imagers have been demonstrated and are discussed in this paper.
Investigation of MgO and Mg1-xTixO thin Films by Electrostatic Spray Deposition Method for a Protective Layer of AC-Plasma Display Panel
Authors: Kim Soo Gil , Kim Young-Kee , Park Chung-Hoo , Kim Hyeong Joon
Published: April 2011

MgO and Mg1-xTixO thin films were deposited by the electrostatic spray deposition method using Mg(tmhd)2 and Ti(OiPr)2(tmhd)2 as source materials and tetrahydrofuran and 1-octyl alcohol as solvents. The refractive index of the films shows a strong change from 1.73 for MgO to 2.39 for TiO2. The optical band gap energy values are 3.83 eV for TiO2 film and higher than 5.1 eV for films of Mg/(Mg+Ti) > 0.67. The discharge voltage and current increased with a content of Ti in Mg1-xTixO films. All these changes are closely associated with different Mg/(Mg+Ti) ratios of the films.
Three Dimensional Thermal Effects in MEMS Devices
Authors: Keuren Edward Van , Currie John , Nelson Matthew , Paranjape Makarand , Schneider Thomas , Smith Ryan , Treado Pat , Ward John , White Robert
Published: April 2011

A three dimensional thermal imaging system is being developed for measuring temperature profiles in MEMS-biomedical devices. These devices rely on a thermal microablation of the dead-skin layer in order to sample transdermal fluids. This is accomplished using microheaters embedded into a PDMS microchannel device. In order to determine the proper functioning as well as long-term safety of the devices, a temperature profile of the device and the skin in contact with the heaters is needed. The results of simple analytical models are used to optimize a proto- type device. Using a three-dimensional chemical imaging microscope and temperature-depend- ent fluorophores, the temperature profile in a sample can be determined quantitatively as well. We demonstrate the technique on a model sample, and discuss extension to other applications such as thermal imaging in biological systems.
Piezoelectric Shear Mode Inkjet Actuator
Authors: Brünahl Jürgen , Grishin Alex M. , Khartsev Sergey I. , Österberg Carl
Published: April 2011

We report on comprehensive characterization of piezoelectric shear mode inkjet actuators micromachined into bulk Pb(Zr0.53Ti0.47)O3 (PZT) ceramics. The paper starts with an overview of different inkjet technologies such as continuous jet and drop-on-demand systems, whereat main attention is turned on piezoelectric systems particularly Xaar-type shear mode inkjet color printheads. They are an example of complex microelectromechanical systems (MEMS) and comprise a ferroelectric array of 128 active ink channels (75νm wide and 360νm deep). Detailed information about manufacturing and principles of operation are given. Several techniques to control manufacturing processes and to characterize properties of the piezoelectric material are described: dielectric spectroscopy to measure dielectric permittivity ε and loss tanσ; ferroelectric hysteresis P-E loop tracing to get remnant polarization Pr and coercive field Ec, and a novel pulsed technique to quantify functional properties of the PZT actuator such as acoustic resonant frequencies and electromechanical coupling factor. Stroboscope technique has been employed to find correlation between the degradation of ink-jet performance and heat/high voltage treatment resulting in ferroelectric fatigue.
The Fabrication of Stainless Steel Parts for MEMs
Authors: Garino Terry J. , Morales Alfredo , Buchheit Thomas , Boyce Brad
Published: April 2011

A micro-molding process was used to fabricate parts in the 0.1 to 10 mm size range from a stainless steel nano-powder. The two types of molds used were both produced from parts fabricated using the LIGA process so that they had precise dimensional tolerance and straight sidewalls. Rigid PMMA molds were made by injection molding and flexible silicone rubber molds were made by casting. Mold filling was accomplished by mixing the powder with epoxy to form a putty-like material that was then pressed into the mold cavities and allowed to cure. After pyrolysis of the epoxy, the parts were sintered in forming gas. The densification kinetics were measured in situ using a video system. Full densification was achieved after 1 hour at 1350°. The microstructure of the sintered parts was examined using the SEM. The mechanical strength, hardness, dimensional tolerance and surface roughness of the sintered parts were also measured.
Thermal Losses and Temperature Measurement in SOI MEMS Heater
Authors: Moelders Nicholas , Puscasu Irina , McNeal Mark P. , Pralle Martin U. , Last Lisa , Ho William , Greenwald Anton C. , Daly James T. , Johnson Edward A. , George Thomas , Choi Daniel S.
Published: April 2011

A sensor chip has been designed and tested that uses a MEMS strip heater as both source and detector of infrared radiation. An optical cavity reflects infrared radiation back onto the source filament. Changes in reflected light intensity modify heater temperature, and the measured signal is a change in resistance. The effects of processing on electrical and thermal isolation were characterized and used to evaluate device performance. Thermally isolated, uniformly heated emitters are achieved using a backside release etch process. The fully released devices demonstrated superior electric to thermal-optical conversion, with the requisite narrow band emission for CO2 detection. Using these sensor-chips, CO2 detection was demonstrated, with projected sensitivities ≤0.1%.
Potential Electric Power Applications for Magnesium Diboride
Authors: Grant Paul M.
Published: April 2011

The newly discovered superconductor, MgB2, has significant potential for a number of electric power applications, even though its critical temperature, TC, is “only” 39 K. In recent months, there has been rapid improvement in its critical state parameters, JC and H*, properties crucial to deployment in power devices, which now rival NbTi at 4.2 K, and equal or surpass many of the high temperature superconducting copper oxide perovskites in the 20 – 25 K range. Moreover, substantial progress has been achieved in realizing wire embodiments that appear economically scalable to commercial production. In this paper, we will review several opportunities to exploit these developments for transformer and electric cable applications, and hint at the possibility of a novel and visionary power delivery system centered on an MgB2-based dc cable cooled by gaseous or liquid hydrogen supplying both electrical and chemical energy to the end user.
Crystal Growth and Superconducting Properties of Bi2Sr2Ca2Cu3Oy (Bi2223) Single Crystals
Authors: Shimizu K. , Okabe T. , Horii S. , Otzschi K. , Shimoyama J. , Kishio K.
Published: April 2011

Bi2223 single crystals were grown by the floating zone method with an extremely slow growth rate of 0.05 mm / h. The largest size of the plate-like single crystal was approximately 3 × 2 × 0.1 mm3. The X-ray diffraction analysis and DC susceptibility measurements revealed that the grown crystals were almost single phase of Bi2223 with a very small percentage of Bi2212 intergrowth. Then carrier doping was systematically controlled in a wide range from underdoping to overdoping by post annealing under various conditions. Tc of the crystals was found to vary from 98 K (underdoped) to 108 K (overdoped) with Tc = 110 K for optimally-doped. In the optimally-doped phase the electromagnetic anisotropy factor, γ2 of Bi2223 was smaller than that of Bi2212. Abrupt resistivity drop was observed under fields below the second peak field of the magnetization hysteresis loops, suggesting a first order phase transition of the flux line lattice. Magnetic phase diagram of Bi2223 single crystals for H // c was found to be similar to that of Bi2212.
Observation of Vortices and Columnar Defects by 1-MV Lorentz Microscopy I
Authors: Kasai H. , Kamimura O. , Matsuda T. , Harada K. , Tonomura A. , Okayasu S. , Sasase M. , Nakayama Y. , Shimoyama J. , Kishio K. , Hanaguri T. , Kitazawa K.
Published: April 2011

A single crystalline Bi2Sr2CaCu2O8+8 which has columnar defects in its inside are observed by Lorentz microscopy using the newly developed 1-MV field emission electron microscope at the first time. The superconducting vortices are observed with higher contrast than ever. Simultaneous observation of vortices and columnar defect is succeeded in real time.
Thermoelectric Properties of Bi1-xSbx Nanowire Arrays
Authors: Lin Yu-Ming , Cronin Stephen B. , Rabin Oded , Ying Jackie Y. , Dresselhaus Mildred S.
Published: April 2011

We present here a thermoelectric transport property study of Bi1−xSbx alloy nanowires embedded in a dielectric matrix. Temperature-dependent resistance measurements exhibit nonmonotonic trends as the antimony mole fraction (x) increases, and a theoretical model is presented to explain the features that are related to the unusual band structure of Bi1−xSbx systems. Seebeck coefficient measurements are performed on nanowires with different diameters and compositions, showing enhanced thermopower over bulk Bi. The magneto-Seebeck coefficient of these nanowires also exhibits an unusual field dependence that is absent in bulk samples.
Thin Film Dispenser Cathodes for Thermionic Micro-Devices
Authors: Zavadil Kevin R. , King Donald B.
Published: April 2011

Electron emissive thin films that possess the thermionic properties of macroscale dispenser cathodes have been fabricated using standard RF sputter deposition techniques. These films are based on a compositionally modulated structure using W and a Ba-containing ternary oxide. These films exhibit uniform work function values of 1.9 to 2.2 eV with high emission coefficients of 2 to 26 A·cm−2K−2. Electron microscopy shows that W layer coalescence and continued particle growth occurs with prolonged annealing, eventually disrupting the original surface layer. Chemical modification of the oxide during deposition may provide a route to limit the extent of W coalescence and preserve surface metallization layers on these films. These films are designed to be integrated into thermionic micro-devices.
Electronic Structure of K2Bi8Se13
Authors: Bilc Daniel I , Larson Paul , Mahanti S.D. , Kanatzidis M.G.
Published: April 2011

K2Bi8 Se13 belongs to a class of complex Bi-Te-Se systems which show great potential for thermoelectric performance. This compound forms in two distinct phases α-K2Bi8 Se13 (triclinic with space group P-1) and β-K2Bi8 Se13 (monoclinic with space group P 21/m). In the β-phase, there is substantial disorder at four sites in the unit cell, occupied by two K and two Bi atoms. To understand the electronic properties of these two different phases we have carried out band structure calculations within ab initio density functional theory (DFT) using full potential linearized augmented plane wave (LAPW) method. The generalized gradient approximation (GGA) was used to treat the exchange and correlation potential. Spin-orbit interaction (SOI) was incorporated using a second variational procedure. The α. phase is found to be a semiconductor with an indirect band gap of 0.47eV. For the β-phase we have chosen two different ordered structures. The system is a semi-metal for one of the structures whereas for the other, it is a narrow gap semiconductor with a gap of 0.38eV in the absence of SOI, but the gap collapses and the system becomes a semimetal with low density of states at the Fermi energy when SOI is included.
Conservation of Lateral Momentum in Heterostructure Integrated Thermionic Coolers
Authors: Vashaee Daryoosh , Shakouri Ali
Published: April 2011

Thin film thermionic coolers use selective emission of hot electrons over a heterostructure barrier layer from emitter to collector resulting in evaporative cooling. In this paper a detailed theory of electron transport perpendicular to the multilayer superlattice structures is presented. Using Fermi-Dirac statistics, density-of-states for a finite quantum well and the quantum mechanical reflection coefficient, the currentvoltage characteristics and the cooling power density are calculated. The resulting equations are valid in a wide range of temperatures and electric fields. It is shown that conservation of lateral momentum plays an important role in the device characteristics. If the lateral momentum of the hot electrons is conserved in the thermionic emission process, only carriers with sufficiently large kinetic energy perpendicular to the barrier can pass over it and cool the emitter junction. However, if there is no conservation of lateral momentum, the number of electrons participating in thermionic emission will dramatically increase. The theoretical calculations are compared with the experimental dark current characteristics of quantum well infrared photodetectors and good agreement over a wide temperature range is obtained. Calculations for InGaAs/InGaAsP superlattice structures show that the effective thermoelectric power factor (electrical conductivity times the square of the effective Seebeck coefficient) can be improved comparing to that of bulk material. We will also discuss methods by which the conservation of lateral momentum in thermionic emission process can be altered such as by creating a controlled roughness at the interface of the superlattice barriers. The improvement in the effective power factor through thermionic emission can be combined with the other methods to reduce the phonon thermal conductivity in superlattices and thus obtain higher thermoelectric figure-of-merit ZT.
High Temperature Electrical Transport Properties of Eu and Yb-doped Skutterudites
Authors: Tedstrom R. H. , Lamberton G. A. , Tritt Terry M. , Nolas G. S.
Published: April 2011

Skutterudites are a class of materials that show promise for thermoelectric applications due to their high power factor and the ability to “tune” the thermal conductivity due to the addition of “rattling” atoms into the novel structure of these materials. Thermopower and resistivity is measured and reported for a series of Eu and Yb-doped skutterudites over a temperature range of approximately 100 K – 700 K using the High Temperature Thermoelectric Probe. Sample measurement techniques are briefly discussed. Data from various dopings is presented and compared in hope of showing trends that point towards improvements in these skutterudites.
Spectroscopic Ellipsometry as a Potential In-Line Optical Metrology Tool For Relative Porosity Measurements of Low- K Dielectric Films
Authors: Edwards N.V. , Vella J. , Xie Q. , Zollner S. , Werho D. , Adhihetty I. , Liu R. , Tiwald T.E. , Russell C. , Vires J. , Junker K.H.
Published: April 2011

The optical properties of organosilicate glass (OSG) samples were investigated with spectroscopic ellipsometry. We found that samples with dramatically higher hardness had higher indices of refraction (RI) and thus higher electron densities and lower relative porosities than films with lower hardnesses. The reverse was true for films with low hardnesses. As well, these films did not have the same optical properties as porous SiO2 across the spectral range measured, which we show has significant implications for the in-line optical metrology of these materials.
In-situ monitoring of nucleation stage during aluminum-CVD for nano-structure control
Authors: Iino T. , Sugiyama M. , Shimogaki Y.
Published: April 2011

Initial nucleation of Al in chemical vapor deposition (CVD) using dimethyl-aluminum- hydride was observed in order to obtain a principle for enhancing the nucleation density. The analysis employed in situ surface reflectivity measurement combined with X-ray photoelectron spectroscopy and scanning electron microscopy at the typical stage of reflectivity behavior. During the incubation period between the injection of DMAH and the nucleation of Al, a constant amount of Al existed on the surface while no nuclei was observed. The precursor of the nuclei seemed not DMAH itself but the reaction product of the adsorbed DMAH. The activation energy for reciprocal of the incubation period, which may be an index of the reaction rate of the adsorbed layer, is slightly larger than for the continuous growth of Al.
Sputter-Deposited Bcc Tantalum on Steel with the Interfacial Tantalum Nitride Layer
Authors: Patel Anamika , Gladczuk Leszek , Paur Charanjeet Singh , Sosnowski Marek
Published: April 2011

Tantalum has mainly two phases: alpha phase (bcc structure) and beta phase (tetragonal structure). The meta-stable beta phase is usually obtained in sputtered films. Alpha phase is preferred over the beta for some applications as beta phase is very brittle. One of such application is to protect steel from the erosive and the corrosive wear. It was found that with the intermediate layer of tantalum nitride the preferred alpha phase was grown on steel by DC magnetron sputtering technique. Electrical and structural properties of these films were studied by four-point probe measurement and x-ray diffraction (XRD). Stoichiometry of the interfacial tantalum nitride layer was investigated by nuclear reaction analysis (NRA). Influence of the interfacial film thickness and the ratio of argon and nitrogen gas during reactive deposition of tantalum nitride on the tantalum phase were investigated. This work also reports on the dependence of tantalum phase on the substrate temperature (100-400°C) during sputtering in Ar and Kr gases.
Thermal-Mechanical Effects of Ceramic Thermal Barrier Coatings on Diesel Engine Piston
Authors: Muchai Jesse G. , Kelkar Ajit D. , Klett David E. , Sankar Jagannathan
Published: April 2011

The purpose of this paper is to investigate the piston temperature and stress distribution resulting from varying coating thicknesses of Partially Stabilized Zirconia (PSZ) thermal barrier coatings for the performance in diesel engine applications. This analysis is based on the premise that coating thickness affects the heat transfer and temperature distribution in the piston. A gas dynamic engine cycle simulation code was used to obtain thermal boundary conditions on the piston then, a 2-D axisymmetric Finite Element Analysis (FEA) using ANSYS was performed to evaluate the temperature and stress distributions in the piston as a function of coating thickness. Coating thicknesses studied include 0.1, 0.2, 0.3, 0.5, 1.0, 1.5, and 2.0mm. The results indicate increased piston surface temperature with increasing coating thickness. The maximum stress on the coated piston surface was high while the substrate stress was less than the coating yield stress for all coating thicknesses. Further, the analysis showed that the interface stress at all coated conditions is low enough such that no separation of the coating is expected. The FEA results suggest an optimum coating thickness of 0.1 to 1.5 mm for diesel engine application to avoid unduly high stress in the ceramic.
Thermoelectric Properties of B12+xC3-x Thin Films Prepared by Pulsed Ion-Beam Evaporation
Authors: Suematsu Hisayuki , Kitajima Kazuo , Ruiz Ichiro , Suzuki Tetsuo , Jiang Weihua , Yatsui Kiyoshi , Kobayashi Katsuaki , Takeda Masatoshi
Published: April 2011

Thin films of boron carbide (B12+xC3-x) were prepared on glass substrates by a pulsed ion-beam evaporation method. A pulsed proton beam with an energy of 1 MV (peak) and a current of 60 kA was focused on sintered B12+xC3-x targets. Ablation plasma was formed from the irradiated targets and thin films were prepared on Pyrex and SiO2 glass substrates at room temperature. From results of X-ray diffraction, the thin films consisted of a B12+xC3-x phase. Using a known relationship between the composition and the lattice parameters, the composition of B12+x1C3-x thin films was estimated to be x = 0.3 and 1.0, which were close to the nominal composition of the targets. These results indicate that B12+x1C3-x with different carbon contents has been successfully prepared by IBE without substrate heating or sample annealing. Thermoelectric properties of the thin films were measured. A B12+x1C3-x thin film with estimated composition of x =0.9 exhibited the highest power factor at room temperature among the B12+x1C3-x samples reported.
A Versatile Approach for Biomaterial Patterning: Masked Ion Beam Lithography
Authors: Gonsalves Kenneth E. , He Wei , Poker David B. , Batina Nikola , Merhari Lhadi
Published: April 2011

We describe a new approach for biomaterial patterning, viz, masked ion beam lithography. Poly (methyl methacrylate) (PMMA) film was used as a model system and subjected to Ca+ and P+ ion implantations through masks. Ca+ ion implantation was performed at an energy of 85 keV with a fluence of 1×1014 ions/cm2. P+ ion implantation was done at an energy of 85 keV with fluences of 1×1015 and 1×1016 ions/cm2. Arrays of holes were generated during these processes. AFM showed that the depth of the holes is in the nanoscale region. The surface hydrophobicity of the exposed PMMA films was investigated by contact angle measurement. The results indicated that ion implantation changed the surface hydrophobicity.
Stable Adsorption of Lipid Vesicles on Modified Gold Surfaces
Authors: Sofou Stavroula , Thomas James L.
Published: April 2011

The use of vesicles as amplifiers in biosensors is receiving increasing attention. Because vesicles may entrap thousands of reporter molecules, strong signal amplification can be obtained if a small number of analytes can simply release the entrapped reporters. Surface immobilization of vesicles with sensitivities for different analytes could then provide for simultaneous amplified detection of a number of analytes on a single chip. To achieve this goal, vesicles must first be stably adsorbed to a surface, without rupture. We have varied vesicle composition and charge (phosphatidylcholine, phosphatidylcholine-phosphatidic acid at 4.6 molar ratio) and solution ionic strength, to study the adsorption of fluorescent vesicles to glass, gold, and gold modified with chemisorbed acetylcysteine. Surfaces were characterized with angle-resolved X-ray photoelectron spectroscopy (ARXPS), and vesicle integrity and behavior was studied using entrapped and lipophilic fluorescent markers either together or in separate experiments. Diffusion coefficients (by photobleaching recovery) and vesicle fusion (by energy transfer) were monitored using confocal fluorescence microscopy. Finally, as a “proof of principle”, release of a self-quenching entrapped reporter dye (calcein) by the detergent Triton X-100 was followed in real time.