bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of the Deposition and Integration of Hard Coatings for Moving MEMS Applications
Authors: Adams P.M. , Robertson R.E. , Cole R.C. , Hinkley D. , Radhakrishnan G.
Published: April 2011

Microelectromechanical systems (MEMS) have been identified as a key technology for small-scale satellites, integrated sensors, and intelligent control systems. Using methods developed for highly integrated electronics, mechanical components are co-fabricated on planar wafers and subsequently etched free for mechanical movements in three dimensions. A major design limitation for these systems is their inability to withstand prolonged sliding surface contact. The fundamental problem is that the surface properties of silicon and poly-silicon, two of the most widely used materials for MEMS, are highly unsuitable for moving MEMS devices, resulting in high wear during operation. This work explores the feasibility and benefits of depositing thin, wear-resistant, low-friction coatings on silicon or poly-silicon. To achieve this goal, three-dimensional test silicon microstructures have been fabricated. Wear-resistant titanium carbide (TiC) coatings are deposited on these test structures using a novel non-line-of-sight pulsed laser deposition (PLD) process. In parallel, this paper addresses the integration of the TiC coating directly into the MEMS fabrication processes and its compatibility with standard silicon processing.
MEMS Material Microstructure and Elastic Property Modeling
Authors: Last Howard R. , Hemker Kevin J. , Witt Ronald
Published: April 2011

Results from initial efforts to develop a quantitative understanding of the material microstructure – elastic properties relationship for electroplated LIGA nickel will be presented. Microsample tensile testing and microstructural characterization results including grain size and grain orientation measurements obtained using orientation imaging microscopy (OIM) are discussed. The use of these data in the development of a finite element modeling approach to represent the mechanical response of “meso-scale” LIGA nickel MEMS material will be highlighted.
Two- and Three-Dimensional Ultrananocrystalline Diamond (UNCD) Structures for a High Resolution Diamond-Based MEMS Technology
Authors: Auciello O. , Krauss A.R. , Gruen D.M. , Meyer E.M. , Busmann H.G. , Tucek J. , Sumant A. , Jayatissa A. , Moldovan N. , Mancini D. C. , Gardos M. N.
Published: April 2011

Silicon is currently the most commonly used material for the fabrication of microelectromechanical systems (MEMS). However, silicon-based MEMS will not be suitable for long-endurance devices involving components rotating at high speed, where friction and wear need to be minimized, components such as 2-D cantilevers that may be subjected to very large flexural displacements, where stiction is a problem, or components that will be exposed to corrosive environments. The mechanical, thermal, chemical, and tribological properties of diamond make it an ideal material for the fabrication of long-endurance MEMS components. Cost-effective fabrication of these components could in principle be achieved by coating Si with diamond films and using conventional lithographic patterning methods in conjunction with e. g. sacrificial Ti or SiO2 layers. However, diamond coatings grown by conventional chemical vapor deposition (CVD) methods exhibit a coarse-grained structure that prevents high-resolution patterning, or a fine-grained microstructure with a significant amount of intergranular non-diamond carbon. We demonstrate here the fabrication of 2-D and 3-D phase-pure ultrananocrystalline diamond (UNCD) MEMS components by coating Si with UNCD films, coupled with lithographic patterning methods involving sacrificial release layers. UNCD films are grown by microwave plasma CVD using C60-Ar or CH4-Ar gas mixtures, which result in films that have 3-5 nm grain size, are 10-20 times smoother than conventionally grown diamond films, are extremely resistant to corrosive environments, and are predicted to have a brittle fracture strength similar to that of single crystal diamond.
Stereochemical Structure for Sodium in Native and Thermal Silica Layers
Authors: Flank A.-M. , Tenegal F. , Lagarde P. , Mazzara C. , Jupille J.
Published: April 2011

Sodium-covered silica films formed on silicon substrates have been examined by X-ray photoemission spectroscopy (XPS) and X-ray absorption spectroscopy (EXAFS) in ultra-high vacuumconditions at 300K. The results show that sodium diffuses into the silica layer on a reversible manner and that it modifies the silica network in order to create its own site. Sodium atoms are surrounded by oxygen atoms at an average distance of 2.3 Å and by a second shell which is assigned to silicon atoms located at 3.8 Å. At high Na concentrations, sodium atoms are also present in the close environment of one sodium atom.
DC to 65 GHz Wide Bandwidth InGaAs Photodiodes and Photoreceivers
Authors: Joshi Abhay M.
Published: April 2011

We have developed 65 GHz Wide Bandwidth InGaAs Photodiodes and Photoreceivers for optical fiber driven telecommunication applications. The Photodiode operates at a nominal reverse bias of -3V and has a minimum responsivity of 0.5 A/W at 1300 and 1550 nm wavelength. The Ripple Factor is less than ± dB for a wide band of frequencies, DC to 50 GHz. The salient feature of the PIN is an on-chip co-planar waveguide output for proper impedance matching. We have also designed Ultra Wide Bandwidth Amplifiers using InGaAs p-HEMT technology and monolithically integrated them with InGaAs Photodiodes. These Opto-electronic Integrated Circuits (OEICs) which combine optical, microwave, and digital functions on the same chip is a technology that has significant potential for commercial applications such as ethernet fiber local area networks and optical communications systems (Synchronized Optical Network SONET, ISDN, telephony and digital CATV). Important inter-service military applications are optically fed phased array systems and optically controlled microwave networks for airborne and spaceborne systems.
Bandgap Variation and Miscibility Gaps of Thallium-Based Pseudo-Binary Alloys
Authors: Chen A.-B. , Piao J.
Published: April 2011

To stimulate further research on the TI-based semiconductor alloys for long-wave infrared (LWIR) application, we carried out detailed calculations for the variation of band gaps versus lattice constants and the alloy miscibility gaps of cation-substituted pseudo-binary alloys. These results are used to identify promising TI-based LWIR alloys and the lattice-matched non-TI bearing alloys for possible substrates and passivation caps. Although all the six Tl-bearing pseudo-binary alloys studied can have a 0.1 eV band gap, none of these systems are lattice matched to a pure III-V compound. Five of these six alloys can have a non-TI-bearing lattice-matched ternary alloy as the substrate, but only two do not have a serious problem with the miscibility gap. When further considering the difficulty of incorporating TI with a large concentration, the only promising LWIR pseudo-binary alloy left is In1−xTlxAs with x≍0. 16.
Growth of InSb on GaAs Substrates Using InAlSb Buffers for Magnetic Field Sensor Applications
Authors: Biefeld R. M. , Phillips J. D.
Published: April 2011

We report the growth of InSb on GaAs using InAISb buffers of high interest for magnetic field sensors. We have grown samples by metal-organic chemical vapor deposition consisting of ∼0.55µm thick InSb layers with resistive InAlSb buffers on GaAs substrates with measured electron mobilities of ∼40,000 cm2/V.s. We have investigated the In1−xAlxSb buffers for compositions x≤0.22 and have found that the best results are obtained near x=0.12 due to the tradeoff of buffer layer bandgap and lattice mismatch.
Surface Microchemical Reactions during Hydrogenated Silicon Growth Studied by In-situ ESR Technique
Authors: Yamasaki Satoshi
Published: April 2011

The in-situ ESR technique is applied to a plasma-enhanced chemical vapor deposition (PECVD) system in order to investigate the surface microchemical reactions during the growth of hydrogenated amorphous silicon (a-Si:H) and plasma treatments of H2 and Ar gases on a- Si:H. The growth model of a-Si:H and the role of H atoms on a-Si:H films are discussed using the experimental results. The recent results on the dynamic surface reactions of crystalline silicon with oxygen molecules in an ultra-high-vacuum ESR system are introduced.
Effects of buried insulator-sensor interface on the lateral conduction of high fill factor aSi:H imagers
Authors: Mulato M. , Lemmi F. , Ready S. E. , Lu J. P. , Van Schuylenbergh K. , Street R. A. , Ho J. , Lau R. , Boyce J. B.
Published: April 2011

The pixel cross-talk is investigated in two-dimensional amorphous silicon (a-Si:H) imager arrays based on the new high fill factor design. In this configuration a continuous a-Si:H sensor extends over the whole surface of the imager, and a buried insulator material with low dielectric constant is used to separate the sensor from the underlying active matrix readout circuit. We find that the lateral conduction between neighboring pixels is mainly determined by the quality of the buried insulator-sensor interface, rather than the specific buried material itself. Minimum cross-talk values below 1% are obtained for different insulator materials including silicon oxynitride and thicker polymer based resins. The quality of this interface also affects trapping and recombination of the photogenerated carriers, influencing important imager properties such as sensitivity and image lag.
a-SiN:H Thin Film Diode for Digital Radiography
Authors: Popov I.A. , Doorselaer G. Van , Calster A. Van , Smet H. De , Baets J. De , Callens F. , Boesman E.
Published: April 2011

Recent developments in the area of cost effective 2D direct x-ray sensor arrays on the base of a-SiN:H back-to-back Schottky diodes and no switching devices per pixel are presented. Discussion focuses on two major aspects: (i) x-ray sensitivity of the sensor itself and possibility of its improvement; (ii) the overall performance of the sensor array.
Investigation of Crystalline Silicon Surface Treatments in Amorphous – Crystalline Heterojunction Via Capacitance Measurements
Authors: Tucci M. , Rosa R. De , Roca F. , Caputo D. , Palma F.
Published: April 2011

In this work we investigate the density of states at amorphous-crystalline silicon interface that play the key role in the heterostructure solar cell application. In particular we analyzed the defect density arising from plasma treatment of the crystalline surface. This process is useful to clean the crystalline surface, but greatly influenced the electrical properties of the device. We used low temperature (20K-300K) capacitance measurement performed in a wide range of frequency of signal probe (1Hz-10kHz). Differences in the capacitance profile between samples with various plasma dry treatments indicate different defect density profile at interface. With the aid of a finite difference model of the capacitance as a function of temperature and frequency we extract information from the measurements about the defect energy distribution at interface. As a result, the density and the nature of defects at interface will be correlated to the technological parameters as: wafer cleaning procedure, hydrogen plasma treatment, type and concentration of dopants at interface.
Microstructures of Microcrystalline Silicon Solar Cells Prepared by Very High Frequency Glow-Discharge
Authors: Dubail J. , Vallat-Sauvain E. , Meier J. , Dubail S. , Shah A.
Published: April 2011

The microstructure of two different νc-Si:H solar cells was studied by Transmission Electron Microcopy (TEM). At the micrometer scale, a difference in the grain structure is observed close to the ZnO substrate: cracks are found in the cell deposited with the higher silane concentration. Surprisingly, the cell with the cracks close to the transparent conductive oxide shows the largest VOC (530 mV) and FF (68%). These first studies reveal that microstructures of fully microcrystalline silicon devices may show a quite large variation with corresponding effects in solar cell performance.
Hydrogenated Amorphous Silicon Photodiode Technology for Advanced CMOS Active Pixel Sensor Imagers
Authors: Theil Jeremy A. , Cao Min , Kooi Gerrit , Ray Gary W. , Greene Wayne , Lin Jane , Budrys AJ , Yoon Uija
Published: April 2011

Amorphous silicon photodiode technology is a very attractive option for image array integrated circuits because it enables large die-size reduction and higher light collection efficiency than c-Si arrays. We have developed a photodiode array technology that is fully compatible with a 0.35νm CMOS process to produce image sensors arrays with 10-bit dynamic range that are 30% smaller than comparable c-Si photodiode arrays. The VGA (640x480), array demonstrated here uses common intrinsic and p-type contact layers, and makes reliable contact to those layers by use of a monolithic transparent conductor strap tied to vias in the interconnect. The work presented here will discuss performance issues and solutions that lend themselves to cost-effective high-volume manufacturing. The various methods of interconnection of the diode to the array and their advantages will be presented. The photodiode dark leakage current density is about 80 pA/cm2, and its absolute quantum efficiency peaks about 85% at 550 nm. The effect of doped layer thickness and concentration on quantum efficiency, and the effect of a-Si:H defect concentration on diode performance will be discussed.
Hydrogenated Microcrystalline Silicon: From Material to Solar Cells
Authors: Wyrsch N. , Droz C. , Feitknecht L. , Goerlitzer M. , Kroll U. , Meier J. , Torres P. , VallatSauvain E. , Shah A. , Vanecek M.
Published: April 2011

Undoped hydrogenated microcrystalline silicon (νc-Si:H) layers and solar cells have been deposited by plasma-enhanced chemical vapour at low temperature and at different values of VHF plasma power and silane to hydrogen dilution ratios. Transport and defect density measurements on layers suggest that structural properties (e.g. crystallite shape and size) only marginally influence the electronic transport properties. The latter are influenced strongly by the Fermi level, which depends on the oxygen impurity content. Furthermore, they are best described by the quality parameter ν0τ0 (deduced from photoconductivity and ambipolar diffusion length). Cell efficiency correlates better with νoτ0 than with the defect density as determined from subbandgap absorption. Anisotropy of the transport properties in some νc-Si:H is also demonstrated but does not seem to play a major role in νc-Si:H cells deposited at high rates under VHF glow discharge conditions.
Improved Crystallinity of Microcrystalline Silicon Films Using Deuterium Dilution
Authors: Suzuki Susumu , Kondo Michio , Matsuda Akihisa
Published: April 2011

Deuterium dilution instead of hydrogen has been studied in microcrystalline silicon growth using plasma enhanced chemical vapor deposition with monosilane. It was found that the crystallinity for D2 dilution is significantly improved as compared to that for H2 dilution at the same growth rate. Optical emission spectroscopy measurement shows that the electron temperature of SiH4 + D2 plasma is lower than that of SiH4 + H2, indicating that the bombarding ion energy is reduced for D2 dilution. It was also found that the H-D exchange reaction on the surface has a certain threshold number of events and that microcrystalline formation occurs only above the threshold. The role of atomic hydrogen originating from a diluent in crystal formation is discussed.
Ultrafast Dynamics of Photoexcitations in HWCVD Hydrogenated Amorphous Silicon Alloys
Authors: Young J.E. , Nelson B.P. , Dexheimer S.L.
Published: April 2011

We present femtosecond studies of carrier dynamics in hydrogenated amorphous silicon-germanium alloys grown by the recently developed hot-wire assisted chemical vapor deposition (HWCVD) technique, which is promising for producing high-quality device-grade materials. We have used wavelength-resolved femtosecond pump-probe techniques, in which an intense pump pulse excites carriers in the sample and a time-delayed probe pulse measures the resulting change in optical properties as a function of time delay following the pump pulse, to study the dynamics of photoexcitations in these materials. Femtosecond dynamics measurements have been carried out on thin film samples under experimental conditions with varying sensitivity to carriers in extended states or in band tail states. The relaxation dynamics of carriers associated with extended states show a strong dependence on excitation density and follow a bimolecular recombination law, consistent with a number of earlier studies on related amorphous materials. In contrast, measurements involving carriers excited directly into band tail states reveal significantly altered dynamics, characterized by a marked deviation from simple bimolecular recombination at short times.
Novel Micro-Photodiodes for Retina Stimulation
Authors: Rojahn M. , Schubert M.B.
Published: April 2011

We present a new design of micro-photodiodes for in-vitro tests to electrically stimulate the ganglion cells of chicken and rat retinae upon light exposure of the photodiodes. Based on amorphous silicon, our laterally series connected double-stacked micro-photodiodes provide an open circuit voltage of 2.3 volts. Photolithographic steps as well as etching procedures for patterning the back contact, the amorphous silicon layers and the front contact are described. We analyse current- voltage-measurements performed with direct contact of the metal needles of a micro-positioning system to the device's electrodes. In order to test the performance of an individual micro-photodiode in an electrolyte environment, the stimulation electrode of the device is also contacted with a micro-droplet of buffer solution. Further improvement is needed, mainly addressing the problem of long-term stability of the device in electrolyte environments.
Ftir Spectroscopy and Spectroscopic Ellipsometry Study of Nanocrystalline Layers Formed by High-Dose Hydrogen and Deuterium Implantation of Silicon
Authors: Safronov L.N. , Spesivtsev E.V. , Popov V.P. , Antonova I.V. , Gutakovskii A.K. , Obodnikov V.I.
Published: April 2011

Structural study of a-Si layers formed by high fluence hydrogen or deuterium implantation (up to 5×1017 cm−2) using high current beams with means of current up 40 mA/cm2 was carried out in the present work. The Si:H(D) silicon films were characterized using FTIR spectroscopy, spectroscopic ellipsometry, transmission electron microscopy and secondary ion mass spectrometry. Hydrogen solubility in crystalline silicon is low but ion implantation allows one to introduce hydrogen atoms in the concentration of 1022cm−3 or even more in thin silicon layer. High defect concentration in combination with high hydrogen activity causes the formation of mixed amorphous and crystalline phases with structure similar to silicon produced PECVD or laser ablation. The transformation of optical properties of this film during annealing in temperature range of 200-1050°C was investigated. The changes in optical characteristics and number of Si-H or Si-D bonds in the spectra of IR absorption is correlated with increase in crystalline volume of silicon with a temperature.
Floating Body Induced Transient Characteristics in Polycrystalline Silicon TFTs
Authors: Xu Y.Z. , Clough F.J. , Narayanan E.M.S. , Cross R.
Published: April 2011

The floating body induced transient characteristics in polycrystalline silicon TFTs is reported. An obvious current surge, arising from the floating body effect, is observed. Using a 2D numerical simulator and comparisons to SIMOX FETs, the insight into the mechanisms governing the experimentally observed switching behavior of poly-Si devices is obtained. It is found that the defect states in poly-Si cause the current surge and exert an effect equivalent to doping in SIMOX FETs.
Integration and Characterization of Low Carbon Content SiOxCyHzLow κ Materials for < 0.18μm[ Dual Damascene Application
Authors: Lee Ju-Hyung , Chopra Nasreen , Ma Jim , Lu Yung-Cheng , Huang Tzu-Fang , Willecke Ralf , Yau Wai-Fan , Cheung David , Yieh Ellie
Published: April 2011

A CVD-based low κ film was evaluated for inter-metal dielectric in < 0.18 [.proportional]m generation devices. The film was deposited by conventional rf PECVD method using organosilane compound and oxygen. The measured dielectric constant of the film was 2.7∼2.75. The κ value of the film was stable over several weeks and the moisture absorption was minimal. The chemical composition was in the form of SiOxCyHz, where the carbon content was less than 5 atomic %. Blanket film integration study was conducted to find out the manufacturing compatibility. The largest increase in κ value occurred during etching and ashing steps. However, SIMS compositional analysis revealed that the damage from these steps were limited to within top 300 Å, and the initial low κ value was recovered after the top damaged layer was removed by CMP. The final integrated dielectric constant was less than 3.0. The film density was measured as 1.4, compared to 2.3 g/cm3of conventional SiO2. The low density of the film resulted from the termination of SiO2network structures by Si-CH3and Si-H.
Deposition of Smooth Thin Cu Films in Deep Submicron Trench by Plasma CVD Reactor with H Atom Source
Authors: Shiratani Masaharu , Jin Hong Jie , Nakatake Yasuhiro , Koga Kazunori , Kinoshita Toshio , Watanabe Yukio
Published: April 2011

Effects of H irradiation on purifying Cu films and improving their surface roughness as well as size and orientation of Cu grains in the films have been examined using a newly developed plasma CVD reactor equipped with an H atom source, in which Cu(hfac)2 is supplied as the source material. The H irradiation is effective in purifying the Cu films, increasing the grain size, and reducing the surface roughness, while it has no effect on the grain orientation. The decrease in dissociation degree of material gas leads to reduction of the surface reaction probability of Cu- containing radicals, which is important to realize conformal deposition in fine trenches. Using the control of dissociation degree of material gas independent of H irradiation, we have demonstrated conformal deposition of smooth Cu films in the trench using the developed plasma CVD reactor.
Kinetics Model for the Self-Encapsulation of Ag/Al Bilayers
Authors: Wang Y. , Alford T. L. , Mayer J. W.
Published: April 2011

A model is proposed to describe the temperature dependence of the aluminum oxynitride (AlxOyNz) diffusion barrier formation during a silver self-encapsulation process. These barrier layers form in the temperature range of 500-725 °C during anneals of the Ag/Al bilayers on oxidized Si substrates in an ammonia ambient. Experimental results show that temperature has a significant effect on the kinetics of this process. In this investigation, the diffusion of Al atoms through the Ag layers during self-encapsulation process is modeled using an analytical solution to a modified diffusion equation. This model shows that higher anneal temperatures will minimize the retardation effect byi) reducing the chemical affinity between Al and Ag atoms, andii) allowing more Al atoms to surmount the interfacial energy barrier between the metal layer (Ag) and the newly formed AlxOyNzdiffusion barriers. The theoretical predictions on the amount of segregated Al atom correlate well with experimental results from Rutherford backscattering spectrometry. This model in addition confirms the self-passivation characteristics of AlxOyNzdiffusion barriers formed by Ag/Al bilayers annealed between 500∼725 °C.
Real Time Substrate Temperature Control by Emissivity Compensated Pyrometry During InxGa1−xAs1−y/InP Growth on Production Scale Rotating Disc MOVPE Reactors
Authors: Ramer J. , Patel B. , Patel A. , Boguslavskiy V. , Gurary A.
Published: April 2011

Long term control of the substrate temperature in production scale MOVPE reactors is the most significant issue effecting yields in highly temperature sensitive epitaxial growth processes. Recent advances in non-contact emissivity compensated pyrometry wafer temperature measurements have allowed the development of a novel multi-wafer (6×2”) rotating disc MOVPE reactor with real time substrate temperature control. With this system, the substrate temperature is a directly controlled process variable, in contrast to some conventional MOVPE systems which use thermocouples for process temperature control. In addition to controlling the absolute temperature of the substrates, the temperature uniformity across the substrates is also controlled by pyrometry. This provides for a uniform temperature (+/- 1.5 °C) across the substrates independent of the flow conditions within the reactor. Thermal uniformity is also automatically maintained during temperature ramping. The highly temperature sensitive quaternary InGaAsP is used as an epitaxial metric for this novel control system, to demonstrate the advantages of pyrometry controlled substrate temperature. These advantages include: excellent long term substrate temperature reproducibility; invariance of substrate temperature to substrate doping level; the ability to transfer processes from one type of wafer carrier or reactor to another with minimal adjustment.
Atomistic Modeling of Ultrathin Fe Films on Cu (111)
Authors: Rakotomahevitra A. , Wille L. T. , Rakotomalala M. S.
Published: April 2011

We have used the embedded-atom method (EAM) to perform molecular-dynamics (MD) simulations of iron films grown on Cu (111). The iron atoms were randomly deposited, one at a time, above the surface just within the force range of the nearest surface atom. The growth mode is discussed by following the iron film coverage for an incident-atom energy ranged from 0.5eV to 15eV. A transition from island to layer by layer growth is observed as a function of incident energy. The effect of deposition rate is also studied.
A Hollow-Cathode Transient Plasma Process for Thin Film Growth
Authors: Witanachchi S. , Mahawela P. , Mukherjee P.
Published: April 2011

We have developed a vapor deposition method that produces a highly ionized transient plasma plume of metallic species in the presence of a low-pressure inert or reactive gas glow discharge. In this process, a transient electrical discharge is formed in a hollow-cathode by a pulse-forming network (PFN) which is triggered by a pulsed CO2 laser. Current pulses with peak currents of 100 kA and pulse widths of about 20 ms have been produced by the PFN. The effect of the PFN power input and the ambient gas pressure on the evaporated material yield is presented. These experiments also showed a higher evaporation rate of carbon in a nitrogen ambient than in an Ar ambient. Carbon films, with rates of deposition exceeding 18A per pulse that are uniform over a large area, have been deposited. The ionic content of the plasma, spatial distribution of ions, and plume expansion dynamics have been investigated by time-of-flight ion probe measurements and optical emission spectroscopy and are presented.
Diamond Synthesis with Completely Closed Eacvd Method
Authors: Kato Takashi , Nishida Masahiro , Takagi Yoshiki
Published: April 2011

Many experimental results were reported of CVD diamond synthesis with so called flow systems, which need introduction of source gas and evacuation of reactant gas. For few years, we had been concentrated of development completely closed diamond synthesizing system aimed for microgravity experiments. Recently we started the new method with graphite as a carbon source. With this method, completely closed system is successfully performed. Graphite rods are used as solid carbon source and at the same time as thermal energy source. Silicon (100) wafer was used for substrates. Hydrogen gas was introduced into the reaction chamber with the suitable initial pressure. and controlled with Joule heating. The deposits were identified with SEM and Raman spectrometry. We tried to synthesize diamond on Si substrate under the conditions of forward bias where the substrate is held at a positive potential relative to the graphite rod. And also we tried the experiment under the reverse bias.
A Drastic Change in Structure and Property of TiO2 Thin Films Deposited by Metal-Organic Chemical Vapor Deposition With Deposition Temperature
Authors: Park Jeong-Hoon , Cho Woon-Jo , Hong Kug-Sun
Published: April 2011

TiO2 thin films were deposited by metal-organic chemical vapor deposition (MOCVD) method using titanium tetraisopropoxide(TTIP). A drastic change in structural aspect and its property occurred when the deposition temperature increased above 400°C. Deposition kinetics was proved to transit from reaction controlled regime into diffusion controlled regime above about 400°C in Arrehnius plot. In X-ray diffraction (XRD)and infrared reflectance spectra, it was observed that the crystallinity was decreased significantly around 400°C. The surface microstructure has changed explicitly from dense structure with larger grains to porous one with smaller grains observed by scanning electron microscopy and transmission electron microscopy. Electrical resistance of the films jumped by 2 orders of magnitude, which is measured by the 4-point probe method. The refractive index calculated by Swanepoel's method has decreased from 2.45 to 2.28 at 630nm. The porous microstructure of films deposited at above 400°C was thought to be responsible for the significant decrease in electrical conductivity and refractive index of the films.
When A Mild Mannered 1-5 eV Photon Meets A Big 10 eV Bandgap: Studies Of Laser Desorption From Modified Surfaces of Ionic Single Crystals
Authors: Dickinson J. Thomas , Bandis Christos , Langford Stephen C.
Published: April 2011

Exposing wide-bandgap ionic materials to UV and IR photons can produce ion emissions with kinetic energies of several eV, well in excess of the photon energy. Electron emissions are also observed. This implies that these materials possess occupied electronic defect states within the band gap. We have investigated the consequences of a variety of defect-generating stimuli (electron irradiation, laser irradiation, mechanical treatments, and heating) on electron and ion emission from inorganic ionic crystals. These stimuli generate defects that strongly interact with the probe laser on a wide variety of ionic crystals, and dramatically decrease the probe laser intensities required for ion and neutral emissions, laser damage, and plume formation.
Plasma and DLC Film Characteristics from Pulsed Laser Ablation Of Single Crystal Graphite and Amorphous Carbon: A Comparative Study Employing Electrostatic Probe Measurements
Authors: Mayo R. M. , Newman J. W. , Sharma A. , Yamagata Y. , Narayan J.
Published: April 2011

In an ongoing effort to investigate plasma plume features yielding high quality DLC films, we have applied plasma plume diagnosis and film characterization to examine plume character distinction from KrF laser ablation of both amorphous carbon (a-C) and single crystal graphite (SCG) targets- The advancing plasma plume produced by these structurally different targets are observed to possess quantitatively similar total heavy particle inventory, ionized fraction, and electron thermal content, yet quite different ion kinetic energy, plume profile, C2 formation mechanism, and concentration of complex molecules. All data support the conclusion that the SCG target plasma plume is populated with heavier, more complex molecules than those in a-C which have been shown to be predominantly comprised of C and C+ under vacuum conditions with the addition of C2 at high fill pressure. Significantly smaller plume profile peaking factor, less energetic and slightly lower temperature plume conditions, laser energy (E1) dependent plume peaking, harder films produced at lower El strongly heterogeneous films, and lesser plume energy attenuation in high pressure background fill in SCG target plumes all support the conclusion of more massive plume species in SCG target plumes. Energy balance estimates indicate that ion kinetic energy dominates and that SCG target ablation liberates about twice the number of 12C atoms per unit El.
Photo-induced Large Area Growth Of Dielectrics With Excimer Lamps
Authors: Boyd Ian W. , Zhang Jun-Ying
Published: April 2011

In this paper, UV-induced large area growth of high dielectric constant (Ta2O5, TiO2and PZT) and low dielectric constant (polyimide and porous silica) thin films by photo-CVD and sol-gel processing using excimer lamps, as well as the effect of low temperature LW annealing, are discussed. Ellipsometry, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), UV spectrophotometry, atomic force microscope (AFM), capacitance-voltage (C-V) and current-voltage (I-V) measurements have been employed to characterize oxide films grown and indicate them to be high quality layers. Leakage current densities as low as 9.0×10−8 Acm−2 and 1.95×10−7 Acm−2 at 0.5 MV/cm have been obtained for the as-grown Ta2O5 films formed by photo-induced sol-gel processing and photo-CVD. respectively - several orders of magnitude lower than for any other as-grown films prepared by any other technique. A subsequent low temperature (400°C) UV annealing step improves these to 2.0×10−9 Acm−2 and 6.4× 10−9 Acm−2, respectively. These values are essentially identical to those only previously formed for films annealed at temperatures between 600 and 1000°C. PZT thin films have also been deposited at low temperatures by photo-assisted decomposition of a PZT metal-organic sol-gel polymer using the 172 nm excimer lamp. Very low leakage current densities (10−7 A/cm2) can be achieved, which compared with layers grown by conventional thermal processing. Photo-induced deposition of low dielectric constant organic polymers for interlayer dielectrics has highlighted a significant role of photo effects on the curing of polyamic acid films. I-V measurements showed the leakage current density of the irradiated polymer films was over an order of magnitude smaller than has been obtained in the films prepared by thermal processing. Compared with conventional furnace processing, the photo-induced curing of the polyimide provided both reduced processing time and temperature, A new technique of low temperature photo-induced sol-gel process for the growth of low dielectric constant porous silicon dioxide thin films from TEOS sol-gel solutions with a 172 nm excimer lamp has also been successfully demonstrated. The dielectric constant values as low as 1.7 can be achieved at room temperature. The applications investigated so far clearly demonstrate that low cost high power excimer lamp systems can provide an interesting alternative to conventional UV lamps and excimer lasers for industrial large-scale low temperature materials processing.
Quantification of Melt Ejection Phenomena During Laser Drilling
Authors: Voisey K.T. , Cheng C.F. , Clyne T.W.
Published: April 2011

During laser drilling, material removal in general occurs both by vaporisation and by the expulsion of molten material. The latter commonly arises as a result of the rapid build-up of gas pressure within the growing cavity as evaporation takes place, but the precise mechanisms responsible for the phenomenon are still unclear. The current work is aimed at gaining an insight into these mechanisms via measurements of the amount of material ejected from cavities during laser drilling under different conditions. Attention is first devoted to the issues which need to be considered when making experimental measurements of the fraction of material removed by melt ejection. These include the collection efficiency and the possibility of chemical changes occurring during the process. Results are then presented from work with a range of metallic substrates (mild steel, tungsten, copper, titanium, aluminium and nickel), drilled with a JK701 Nd-YAG laser under different conditions. Observed variations in the melt ejection levels have been studied for mild steel and aluminium and these are briefly considered in terms of the expected effects of certain material property values and the mechanisms of melt ejection. Results from an existing finite difference heat flow model are used to investigate the significance of melt ejection.
Preparation Of Crystalline Chromium Carbide Thin Films Synthesized By Pulsed Nd:YAG Laser Deposition
Authors: Doi Kazuya , Hiraishi Satoshi , Kawasaki Hiroharu , Suda Yoshiaki
Published: April 2011

Chromium carbide thin films are synthesized on Si(100) substrates by a pulsed Nd:YAG laser deposition (PLD) method as parameters of methane gas pressure. Glancing-angle X-ray diffraction patterns show that the film prepared by PLD method is a polycrystalline thin film composed of Cr3C2and Cr7C3, even in the base pressure. Diffraction patterns, however, are depended on the methane gas pressure. Grain size of the prepared film increases with increasing methane gas pressure. One of the reasons of these phenomena may be considered to the phase reaction between the ablated species, such as Cr, CrCx and CH4gas in the plasma plume.
Glass-Crystal Boundaries in Liquid-Phase Sintered Ceramics
Authors: Ravishankar N. , Carter C. Barry
Published: April 2011

The interface between dewet glass droplets and the free surface of a crystal and the interface between the intergranular glass and adjoining crystalline grains have been examined with particular emphasis on the influence of the crystallography of the free surface and the grain boundary. The wetting of liquid on the free surface has been shown to depend on the surface structure. The migration of boundaries containing a liquid phase has been studied. The migration is initiated by the difference in surface energy of the bounding planes. Faceting of the grain boundary planes has been examined. It is proposed that the boundary migrates by the motion of the facets.
Preferential dissolution along misoriented boundaries in heterogenite
Authors: Penn R. Lee , Stone Alan T. , Veblen David R.
Published: April 2011

High-Resolution Transmission Electron Microscopy (HRTEM) results show a strong crystal-chemical and defect dependence on the mode of dissolution of synthetic heterogenite (CoOOH) particles. As-synthesized heterogenite particles are micron-size plates (aspect ratio ∼ 1/30) constructed of crystallographically oriented ∼ 3-nm primary particles or are single ∼ 21-nm unattached heterogenite platelets (aspect ratio ∼1/7). Reductive dissolution, using hydroquinone, was examined in order to evaluate morphology evolution as a function of reductant concentration. Two end-member modes of dissolution were observed: 1) non-specific dissolution of macroparticles and 2) preferential dissolution along misoriented boundaries. In the case of non-specific dissolution, average macrocrystal size and morphology are not altered as building block crystals are consumed. The result is web-like particles with similar breadth and shape as undissolved particles. Preferential dissolution involves the formation of channels or holes along boundaries of angular misorientation. Such boundaries involve only a few degrees of tilt, but dissolution occurs almost exclusively at such sites. Energy-Filtered TEM thickness maps show that the thickness of surrounding material is not significantly different from that of undissolved particles. Finally, natural heterogenite from Goodsprings, Nevada, shows morphology and microstructure similar to those of this synthetic heterogenite.
Thermionic FEEM, PEEM and I/V Measurements of N-Doped CVD Diamond Surfaces
Authors: Köck F.A.M. , Garguilo J.M. , Brown B. , Nemanich R.J.
Published: April 2011

Imaging of field emission and photoemission from diamond surfaces is accomplished with a high resolution photo-electron emission microscope (PEEM). Measurements obtained as a function of sample temperature up to 1000°C display thermionic field emission images (TFEEM). The system can also record the emission current versus applied voltage. N-doped diamond films have been produced by MPCVD with a N/C gas phase ratio of 48. The surfaces display uniform emission in PEEM at all temperatures. No FEEM images are detectable below 500°C. At ∼680°C the T-FEEM and PEEM images are nearly identical in intensity and uniformity. This is to be contrasted with other carbon based cold cathodes in which the emission is observed from only a low density of highly emitting sites. The I/V measurements obtained from the N-doped films in the T-FEEM configuration show a component that depends linearly on voltage at low fields. At higher fields, an approximately exponential dependence is observed. At low temperatures employed (<700°C), the results indicate a thermionic component to the emitted current.
In-situ Plasma Diagnosis of Chemical Species in Microwave Plasma-assisted Chemical Vapor Deposition for the Growth of Carbon Nanotubes Using CH4/H2/NH3 Gases
Authors: Woo Y.S. , Han I.T. , Lee N.S. , Jung J.E. , Jeon D.Y. , Kim J.M.
Published: April 2011

Synthesis of multi-wall carbon nanotubes (MWNTs) was attempted by microwave plasma enhanced chemical vapor deposition using CH4/H2/NH3 gases on Ni/Cr-coated glass at low temperature. The synthesis was investigated by optical emission spectroscopy and quadrupole mass spectroscopy. It was observed that MWNTs could be grown within a very restrictive range of gas compositions. An addition of a small amount of NH3 resulted in a decrease of C2H2, which can be used to estimate the amount of carbon sources in plasma for the growth of MWNTs, and an increase of CN and Hα radicals acting as etching species of carbon phases. These results show that carbon nanotubes can be grown only under an appropriate condition that the growing process surpasses the etching process. The optimum C2H2 /Hα ratio in a gas mixture was found to be between 1 and 3 for the MWNT growth at low temperature.
The role of catalysts and temperature on morphology and field emission properties of decorated C:N nano-tubular structures
Authors: Kurt Ralph , Bonard Jean-Marc , Karimi Ayatollah
Published: April 2011

A hot filament chemical vapour deposition (HF-CVD) process was used to synthesise nitrogenated carbon (C:N) nanotubes characterised by feather-like decoration of the tube surface. As a function of deposition temperature the diameter of the produced tubular structures could be adjusted in a controlled way ranging from 1 µm to 50 nm. The influence of catalysts was demonstrated comparing the morphology of catalytically grown tubes with tubes grown onto pure Si wafers. High resolution TEM reveals that the nanotubes are hollow with a wall structure consisting of inner ordered walls and an outer more disordered surface. A possible growth mechanism will be discussed. Furthermore, field emission in vacuum was studied and showed a spectacular correlation to the deposition temperature and therefore the diameter of the C:N tubes.
Energetics and Structural Investigation of Double-Walled Carbon and Silicon Nanotubes
Authors: Fagan Solange B. , Sartor Daniela S. , Mota R. , Baierle R. J. , da Silva Antônio J. R. , Fazzio A.
Published: April 2011

Using two different approaches: Monte Carlo simulations with Tersoff empirical potential and first principles calculations, the energetics and the structural properties of double-walled carbon and silicon nanotubes are investigated. Through Tersoff potential, the changes on cohesive energies for the Si and C systems are determined for several outer tubules for a fixed inner tube. Adopting first principles calculations, based on density functional theory, the trends, in terms of the cohesive energies, are compared with the corresponding obtained results using Tersoff empirical potential. The structures, specially of the most stable double-walled nanotubes, are discussed.
Comparison of the adsorption properties of krypton on multi-walled carbon nanotubes and on graphite.
Authors: Bougrine Abdelhafid , Varlot Karine , Dupont-Pavlovsky Nicole , Ghanbaja Jaafar , Billaud Denis , Béuin François
Published: April 2011

Krypton adsorption has been investigated on multi-walled carbon nanotubes prepared by catalytic decomposition of acetylene. Isotherms measured between 77.5 and 83.7K from the first stages of adsorption to the adsorbate saturation vapor pressure are compared to those obtained in the same conditions on graphite. The results are discussed in the light of the nanotube morphology, as determined by transmission electron microscopy.

Krypton adsorption proceeds, as on graphite, by successive monomolecular layer condensations on a same surface. From the morphology of the tubes, adsorption probably occurs only on their external surfaces. The first adsorbed layer is commensurate with the substrate. At its completion, it undergoes a transition into an incommensurate solid of higher density. The curvature of the graphene sheets, with respect to those of graphite, produces a stabilization of the commensurate film. The isosteric heat of adsorption Qst was measured to be 11.6 kJ/mol (ΔQst/Qst = 6%) and is lower than that of krypton on graphite.

Moreover, the monolayer condensation pressures are higher than those observed with graphite, which probably leads to an incomplete wetting of the surface by limiting the number of krypton monomolecular layers adsorbed before its bulk condensation.
Direct Fabrication of All-Inorganic Logic Elements and Microelectromechanical Systems from Nanoparticle Precursors
Authors: Bulthaup Colin , Wilhelm Eric , Hubert Brian , Ridley Brent , Jacobson Joe
Published: April 2011

Here we describe the fabrication of electrostatic motors by liquid embossing, a contact stamp-based method of patterning liquids with sub-micron resolution. We also demonstrate AFM nano-assembly which can produce sub-40 nm dots and lines by transferring either liquid or solid material from a reservoir to a deposition area. Both of these non-lithographic patterning techniques are applicable to nanocrystal, organic, and polymeric solutions and liquids.
DNA Electrophoresis on Two-dimensional Arrays of SiO2 Beads
Authors: Seo Young-Soo , Samuilov V.A. , Sokolov J. , Rafailovich M. , Gersappe D. , Chu B.
Published: April 2011

A novel approach of fabricating 2-D arrays of SiO2 beads on a Si surface using the Langmuir-Blodgett (LB) technique is reported. The corrugated surfaces were tested as a separation media for surface electrophoresis of DNA molecules. The measured electrophoretic mobility for λ-DNA is only 20% slower than previously measured on a flat Si wafer. This indicates that the separation mechanism is due to surface friction rather than biased reptation as reported by Tinland in the three dimensional Silica bead matrix where the mobility is two orders of magnitude smaller.
Materials Challenges and Alternatives for Advanced Photolithographic Patterning: From 193 to 157 nm and Beyond
Authors: Reichmanis Elsa , Nalamasu Omkaram , Houlihan Francis M.
Published: April 2011

In the last decade, major advances in fabricating electronic devices have placed increasing demands on microlithography, the technology used to generate today's integrated circuits. Within the next few years, a new form of lithography will be required that routinely produces features of less than 0.1 μ. As the exposing wavelength of light decreases to facilitate higher resolution imaging, the opacity of traditional materials precludes their use; and major research efforts to develop alternate materials are underway. Through understanding of materials structure and its relationship to device process requirements and performance, cycloolefin based polymers provide for sub-0.1 μm imaging capability using 193 nm exposure. Alicyclic monomers such as norbornene are readily copolymerized with other units to afford a wide range of alternative matrices that exhibit transparency at the exposing wavelength and aqueous base solubility. Further reduction in imaging wavelength necessitates renewed research to define alternative materials platforms. Materials transparency is the key issue to be addressed for 157 nm or EUV lithography. Novel polymer architectures including fluorinated polymers will be required to effect sufficient transparency coupled with requisite solubility, sensitivity, contrast etching resistance, shelf life and purity. Each of these issues will be discussed from the perspective of polymer materials chemistry.