bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis of Propylene Carbonate Catalyzed by Copper-containing Hydrotalcite-like Compounds
Authors: Xie Xianmei , Duan Lian , Wu Zhenghuang , Wang Lina , Yan Kai , Du Lei
Published: April 2011

CuFe-Hydrotalcite-Like Compounds (CuFe-HTLcs) were synthesized by coprecipitation with Cu(NO3)2·6H2O, Fe(NO3)3·9H2O, NaOH and Na2CO3 solution. The sample with Cu2+ / Fe3+ = 2 was of the highest crystalline characterized by XRD and particle size distribution. The synthesis of propylene carbonate from 1,2-propanediol (PG) and urea was performed to evaluate the catalytic activities of the CuFe-HTLcs. The effects of reaction time, temperature, dosage of catalyst on the synthesis of propylene carbonate were fully discussed. The optimal reaction conditions were determined by using orthogonal test design: reaction temperature 170 °C, dosage of catalyst 0.2 g, and molar ratio of PG to urea 2:1, reaction time 3 h. Under the optimal conditions, the conversion of urea nearly reached 100 %, and the selectivity of propylene carbonate was up to 90.4%.
Microwave Hydrothermal Synthesis of Bimetallic (Ti-V) Ions Modified MCM-41 for Epoxidation of Styrene
Authors: Guo Yajie , Wang Guangjian , Wang Yuran , Li Zhengwang , Liu Guangqing , Liu Yiwu
Published: April 2011

Mesoporous molecular sieves MCM-41 modified by single (Ti) and bimetal (Ti-V) ions with highly ordered hexagonal arrangement of their cylindrical channels were prepared by direct synthesis under microwave–hydrothermal (M–H) conditions at 403K. Characterizations with powder X-ray diffraction (XRD), 29Si magic-angle spinning (MAS) NMR, N2 adsorption–desorption, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray photoelcctron spectra(XPS) and transmission electron microscopy (TEM) showed that Ti and V ions were introduced into MCM-41 under M-H conditions and Ti/V-Si bond was formed. Results revealed that all the samples were of a typical hexagonal arrangement of mesoporous structure. The modified materials were high active and selective in the epoxidation of styrene at 343 K in comparison with single-functional MCM-41. Moreover, compared to conventional method, the presented microwave hydrothermal synthesis of molecular sieves greatly improved the selectivity to styrene oxide, e.g., it reached 58.6% at styrene conversion of 18.7% over Ti-V-MCM-41 (50).
Hydrogen Storage in Ti-Zr Based Systems
Authors: Salmones J. , Zeifert B. , Ortega-Avilés M. , Contreras-Larios J. L. , Garibay-Febles V.
Published: April 2011

This research contributes to the study of hydrogen storage of two Ti-Zr based systems using (I) titanium dioxide (TiO2) + zirconium acetylacetonate (C20H28O8Zr) and (II) titanium dioxide (TiO2) + zirconium tetrachloride (ZrCl4) as starting materials. Both systems were prepared by mechanical grinding under the same conditions, with composition of 50 wt.% Ti and Zr and milling time of 2, 5, 7, 15, 30 and 70 hrs. The samples were evaluated by hydrogen absorption tests and characterized by BET, XRD and TEM. The results of hydrogen storage at different pressures but same temperature showed that samples of the system I absorbed the largest quantities of hydrogen but difficult to release them, while the system II absorbed less amount of hydrogen but completely desorbed the absorbed hydrogen. The increase of the mechanical grinding time is directly associated with changes in hydrogen absorption capacity and formation of new components. The formation of oxide nanoparticles of Ti and Zr on the surface of TiO2in samples from series II was associated with the hydrogen absorption capacity. Keywords: hydrogen storage, Ti-Zr, mechanical milling, sorption.
Wet Air Oxidation of Phenol over Ru Based Catalysts – Effects of Support
Authors: des Los Monteros A. E. Espinosa , Lafaye G. , Torres G. , Barbier J.
Published: April 2011

Catalytic wet air oxidation (CWAO) of aqueous solutions of phenol was performed on ruthenium catalysts supported on different oxides: TiO2, ZrO2 and their doped ceria mixtures. Phenol was chosen as a model pollutant molecule because of its wide use in industrial processes. All the samples were found to be highly active for phenol oxidation and the various titania-ceria mixtures were the most efficient for total organic carbon (TOC) removal. ICP analysis of the remaining solution after reaction revealed that ruthenium has not leached. Moreover, elementary analysis of the used catalysts showed that the deposition of carbonaceous species on the surface of the catalysts was rather low and was dependent on the nature of the support.
Photodegradation of Reactive Black 5 by Titanium Oxide Film Obtained with Ultrasonic Pyrolysis Technique
Authors: L. R. T. Hernández , Hernández-Pérez I. , V. D. Y. Medina , Becerril N. , Soyuqui S.
Published: April 2011

The present work reports the photodegradation results of the Reactive Black 5 (RB5) izo dye by using titanium oxide films as photocatalysts. The films were obtained by ultrasonic spray pyrolysis deposit technique from a 0.0076 M of Ti(IV)-acetyl-acetonate and N, Ndimethylformamide solution over corning glasses as substrates. The film obtained by deposition at 450 °C for 6.0 min shows the best photocatalysis behavior, which may degrade 50% of 100 ppm RB5 in a period of 120 min, as monitored with a spectra-photometer UV-Vis between 190 to 900 nm. After 180 minutes of degradation, a 70% conversion could be obtained. These results are better than that obtained with TiO2 powders as photocatalyst.
Natural polymer coated magnetic nanoparticles for biosensing
Authors: Longinotti Gloria , Lloret Paulina , Peter-Gauna Regina , Roberti Mariano , Malatto Laura , Rey-Serantes Diego , Ciocchini Andrés , Hermida Laura , Ybarra Gabriel , Fraigi Liliana , Moina Carlos
Published: April 2011

Superparamagnetic iron oxide nanoparticles coated with natural polymers have found many applications in the field of biosensors as magnetic carriers due to the combination of two characteristics: the possibility of controlling the particles movement by applying external magnetic fields and attaching biomolecules to the particle through a chemical bond. The aim of this work was to prepare long-term stabilized particles with acid groups available to be used as magnetic carriers of biomolecules. In this study, we present the synthesis of maghemite nanoparticles coated with alginate, a natural polymer. Particles were characterized by electron microscopy. Magnetic properties were studied by vibrating sample magnetometry, which revealed the superparamagnetic behavior of maghemite nanoparticles. Horseradish peroxidase (HRP) was chemically bonded to the maghemite-alginate particles and the enzymatic activity of HRP was determined by a colorimetric technique. The maghemite-alginate particles were immobilized onto the surface of a gold electrode by means of a magnet and the HRP activity was followed electrochemically, showing that these particles can be successfully used in amperometric sensors. Furthermore, maghemite-alginate particles were also used for the diagnosis of the foot-and-mouth disease by means of an enzyme-linked immunoassay with electrochemical detection. 3ABC protein, a non-structural protein of the virus, was linked to the maghemite-alginate particles and used to selectively detect anti-3ABC antibodies in cattle sera.
Incorporation of NSAID Drug Gel Derived from Cellulose and Polyacrylamide
Authors: Morales C. A. , Castillo M. C. , Díaz Z. N. , González S. J. , Kharissova V. O.
Published: April 2011

In this paper, the incorporation and release of two types of drugs was carried out in microgels of hydroxypropylcellulose/polyacrylamide (HPC/PAAM) and hydroxyethylcellulose/polyacrylamide (HEC/PAAM). The two drugs were NSAIDs (nonsteroidal, anti-inflammatory drugs)—one antipyretic and one analgesic—acetylsalicylic acid (aspirin, ASP) and iuprofen (IBU), respectively. First, the microgels were synthesized and characterized by Fourier Transform Infrared Spectroscopy (FTIR) in order to identify the presence of functional groups for each polymer. The incorporation of the drug was made by swelling the microgels in a drug solution and finally carrying out the release of the substances listed at 37° C. The results were obtained by UV-visible spectroscopy.
Excess Carrier Lifetimes in (HgCd)Te Grown by Mocvd Interdiffused Multilayer Process
Authors: Mitra P. , Schimert T. R. , Tyan Y. L. , Brouns A. J. , Case F. C.
Published: April 2011

Transient lifetime measurements on p- and n-type Hg1−xCdxTe epitaxial films, grown by the MOCVD-interdiffused multilayer process (IMP) on CdTe and CdZnTe, are reported. Lifetimes have been measured on undoped n-type, vacancy and arsenic doped p-type (HgCd)Te for x-values of 0.20–0.28 over the 25K–300K temperature range. Lifetime characterization has been carried out primarily by non-contact transient millimeter wave reflectance as well as by standard photoconductive decay. It is shown that Auger limited lifetimes are achievable in undoped n-type material. N-type lifetime results are analyzed within the framework of a multilevel Shockley-Read model which provide insight into the nature and density of defect states in the material. In p-type (HgCd)Te, for the same carrier concentration, longer lifetimes are obtained by As-doping than in vacancy doped material.
Study of different Cadmium Telluride Materials doped with V, Zn and Cl grown by vertical Bridgman Furnace and by THM.
Authors: Steer Ch. , Chibani L. , Koebel J.M. , Hage-Ali M. , Siffert P.
Published: April 2011

The properties of Cadmium Telluride are very sensitive to impurities. The growth method has also a strong impact on the material characteristics. Crystals grown by THM have good X-ray detector properties, while normal undoped Bridgman grown crystals do not detect. We have grown pure and doped samples by Bridgman and THM methods. As doping materials we used V, Zn and Cl, also in different combinations. The samples were characterized by several methods, including resistivity, TSC and nuclear detection measurements.
Infrared-Photoconductivity Due to Sub-Band Transitions in PbTe/Pb1−xEuxTe and PbSe/Pb1−xMnxSe
Authors: Yuan Shu , Springholz G. , Frank N. , Krenn H. , Bauer G. , Kriechbaum M.
Published: April 2011

The photoconductive (PC) properties of MBE grown PbTe/Pb1−xEuxTe (x<6.7%) and of PbSe/Pb1−xMnxSe (x<3%) multi quantum (MQW) well samples were investigated in the midinfrared region from 100 meV to 500 meV in the temperature range from 5 K up to 210 K. Whereas in PbTe/Pb1−xEuxTe MQW's electrons and holes are confined in the PbTe layers, PbSe/Pb1−xMnxSe forms a staggered system with electrons confined in the PbSe/Pb1−xMnxSe layers and holes confined in the PbSe layers. Consequently, the transitions between electric subbands in the PbTe/Pb1−xEuxTe MQW's give rise to a step like increase of the PC signal whenever the photon energy hv coincides with the interband transition energies between hole and electron subbands (selection rule Δn = 0). For the range of well widths investigated (42 Å to 91 Å ) distinctive steps in the photoconductivity spectra were observed. In the PbSe/Pb1−xMnxSe MQW's the absorption signals show a typical type II superlattice (SL) behaviour and thus the photoconductivity response is also much weaker than for the PbTe/Pb1−xEuxTe MQW's.
Intersubband Transitions in In0.07Ga0.93As/Al0.4Ga0.6As Multiple Quantum Wells
Authors: Szmulowicz F. , Manasreh M. O. , Kutsche C. , Stutz C. E.
Published: April 2011

Intersubband transitions in a series of well-doped ([Si] = 2.0×1018cm−3) In0.07Ga0.93As/Al0.4Ga0.6As multiple quantum well samples were studied as a function of the well width by using the optical absorption technique. A single intersubband transition is observed in samples in which the Fermi energy level is between the ground and the first excited states in the quantum well. On the other hand, two intersubband transitions were recorded in samples where the Fermi energy level lies between the first and the second excited states. These two intersubband transitions were attributed to ground-to-first excited states and first-to-second excited states transitions. The energy separation between the latter two intersubband transitions was found to increase as the well width is increased. The fact that two intersubband transitions were observed in certain samples may suggest that specially designed quantum wells can be used for two color long wavelength infrared detectors.
Movpe Growth of MCT for LWIR Detectors
Authors: Irvine S.J.C. , Bajaj J. , Bubulac L.O.
Published: April 2011

Recent progress in the growth of Hg1−xCdxTe (MCT) by metal organic vapor phase epitaxy (MOVPE) is reviewed. The preferred diode structure for LWIR detectors is the p/n heterostructure, which requires extrinsic doping of both n and p-type layers and good compositional control of the base and cap layers. Uniform n-type doping has been demonstrated using a new precursor, TIPIn, with Auger-limited lifetime down to a doping concentration of 1 × 1015 cm−3. p-type doping has been more difficult to control because Group V dopants can occupy either Group II or Group VI sites, leading to autodoping. Some encouraging progress has been made by doping under metal rich conditions. An alternative approach to p-type doping during growth is the Rockwell-developed process of As implantation, diffusion and activation annealing, which has been used to demonstrate near diffusion-limited LWIR diodes at 77K. Major strides in the reproducibility of the MOVPE process have been achieved by in situ monitoring. Laser reflectometry has been used to monitor growth rates and morphology throughout the growth of multiple layer structures. This wafer monitoring has been complemented by system monitoring, using Epison concentration monitors and pyrometry to measure temperature.
Study of Amorphous Silicon Nitride films by Brillouin Spectroscopy
Authors: Carlotti G. , Socino G. , Xia Hua , Li Z.F. , Zhang Wei , Qu X.X. , Chen K.J. , Zhang X.K.
Published: April 2011

The elastic properties of hydrogenated silicon nitride (a-SiNx:H) films, with x=1, have been investigated by means of the Brillouin light scattering technique. The films were deposited on an opaque substrate (silicon) in order to improve the scattering efficiency from acoustic phonons in the film. Measurement of the frequency shift of Brillouin peaks relative to both the surface Rayleigh Mode and the longitudinal bulk waves enabled us to determine the two independent elastic constants c11 and c44.
Evidence of Energy Relaxation of Charged Defects in Amorphous Silicon Via Forward Bias Capacitance Measurements
Authors: Caputo D. , de Cesare G. , Masini G. , Palma F. , Pastore A. , Tucci M.
Published: April 2011

In this paper we show that the usual behaviour of forward bias C-V-f measurements performed on p-i-n structure, Modifies at the lowest test frequencies when the measurement is performed at high temperature (120°C), or if the cell under test is at a certain stage of the degradation process. We relate the effect to the relaxation of charged defects toward dangling bonds in the i-layer of a p-i-n structure. In capacitance measurements under forward bias, the applied sinusoidal test voltage periodically changes the density of injected charge and the defect occupancy in the intrinsic layer. We show that this effect may Modulate the tendency of defects to relax to lower energy configuration. Relaxation changes the time scale of the subsequent thermal emission of the trapped charge; this reflects on the measured capacitance which drops at low frequency. We also demonstrate the possibility to obtain the relaxation parameters from the frequency dependence of the measured capacitance.
Hydrogen Diffusion and Solubility in A-Si:H
Authors: Beyer Wolfhard , Wagner Heribert
Published: April 2011

For plasma-grown a-Si:H films deposited at substrate temperatures between 100 and 580°C the diffusion of hydrogen was studied by SIMS profiling of H/D interdiffusion and by hydrogen evolution. The solubility for deuterium penetration into a-Si:H is found to be limited by the hydrogen concentration. Diffusion prefactors and activation energies evaluated for a constant diffusion length follow a Meyer-Neldel rule. The diffusion free energies obtained by interdiffusion and evolution experiments agree closely up to about 400°C but disagree at higher substrate temperatures.
Effect of Light Soaking on the Local Motion of Hydrogen in Hydrogenated Amorphous Silicon
Authors: Hari P. , Taylor P. C. , Street R. A.
Published: April 2011

Previous measurements of local hydrogen motion in intrinsic, doped, and compensated hydrogenated Amorphous silicon (a-Si:H) using the 1H nuclear magnetic resonance (NMR) dipolar echo method have shown that the local hydrogen motion is much faster than the macroscopic diffusion would indicate but that the local motion follows the same trends with doping and defect density as the macroscopic diffusion. We report the effect of light soaking on the local motion of hydrogen in hydrogenated Amorphous silicon. Measurements are presented on 10−3 P-doped a-Si:H at 297 K. After light soaking with infrared-filtered, white light of intensity -400 MW/cm2 for 75 hours, the electron spin resonance (ESR) spin density increases to -101 spins/cm After light soaking 1H NMR dipolar echo measurements on this sample show that the dipolar spin-lattice relaxation time, T1D, is ∼4 Ms. After thermal annealing at 190 C for two hours the value of T1Dreturns to its pre-irradiation value of ∼ 11 Ms. The local rate of motion, which scales with TID-1 thus increases with the paramagnetic defect density. The general implications of this result for descriptions of both microscopic and macroscopic Motion of hydrogen in a-Si:H are discussed.
Polarized Electroabsorption and Carrier Mobilities in Amorphous Silicon Alloys
Authors: Tsutsumi Y. , Okamoto H. , Hattori K. , Hamakawa Y.
Published: April 2011

We report on the free carrier Mobilities Measured by polarized electroabsorption Method. The result shows that the electron mobility reaches about 11.2cm2/Vs for device quality undoped a-Si:H, while the hole mobility is about 20% of the electron Mobility. Alloying with carbon leads to a continuous reduction of Mobility, with the largest drop (15%) for a carbon concentration of about 10 at.%, this being in sharp contrast to a less-pronounced effect by germanium alloying.
Transport Studies by Steady-State and Transient Photocarrier Grating Methods
Authors: Schwarz R. , Wang F. , Schuster D.
Published: April 2011

An overview is given on the time and carrier density range covered by steady-state and transient photocarrier grating experiments which are commonly used to determine ambipolar transport parameters. In addition to the optically-detected transient grating method we discuss some details of a new version of the transient grating Method, the electrically-detected transient grating technique (EDTG) applied to hydrogenated Amorphous and microcrystalline silicon films. Numerical simulation shows that the diffusion coefficient is time and intensity dependent as expected for dispersive transport.
Non-Gaussian Noise Statistics in Undoped Hydrogenated Amorphous Silicon
Authors: Khera G. M. , Kakalios J.
Published: April 2011

Measurements of coplanar conductance fluctuations in undoped a-Si:H are described. Statistical tests show that the 1/f noise is non-Gaussian and has a power-law frequency dependent second spectrum, as observed in n-type a-Si:H. By careful consideration of the thermal history of the sample, the noise statistics are found to be different above and below the equilibration temperature, which has been associated with hydrogen diffusion. These results suggest that the non-Gaussian noise in a-Si:H is influenced by the motion of bonded hydrogen and is not significantly dependent upon doping.
Thermal Quenching and Photo-Enhancement of μτ Products in a-Si:H - The Role of Dangling Bonds and Band Tails
Authors: Morgado E.
Published: April 2011

Results from numerical calculations with a recombination model involving one class of correlated dangling-bond states and exponential band tails, in a-Si:H, are reported. Fermi level, light intensity and temperature dependences of the μτ products are studied. The results are consistent with experimental data. It is found that photo-enhancement of (μτ)e, or superlinear photoconductivity, as well as thermal quenching, are associated with a capture cross section of the band tails smaller than the capture cross sections of the dangling-bond states.
Factors Influencing the Quality of a-Si:H Films Deposited by the “HOT WIRE” Technique
Authors: Molenbroek Edith C. , Mahan A. H. , Johnson E. J. , Gallagher A. C.
Published: April 2011

Device quality a-Si:H has been deposited at 3 Å/s using the “hot wire” technique with 1% SiH4 in He as a source gas. To achieve this deposition rate despite the high dilution, the filament was positioned at 1–2 cm from the substrate. This short distance introduces a large non-uniformity across the substrate in the deposition rate as well as in the film properties. This experimental fact was used to analyze which factors in the deposition determine film quality. We find that radiation from the filament is not an important factor. Data taken from samples deposited at various distances, pressures and flows suggest that the film quality is influenced by radical reactions with SiH4. However, this assumption alone predicts too strong a pressure dependence. The influence of deposition rate as an additional factor can explain the results.
Space-Charge-Enhanced Post-Transit-Currents in A-Si:H
Authors: Schauer F. , Eliat A. , Nesládek M. , Adriaenssens G.J. , Stals L.M.
Published: April 2011

The space-charge-limited current mode in the post-transit time-of-flight method was used to determine the density of states (DOS) in the band gap of a-Si:H. SCLC conditions result in an enhancement of the occupancy of deep states, leading consequently to an improved sensitivity. In comparison with the small signal case, the emission time of deep traps changes as a function of the time dependent occupancy of traps. The change in the emission time of traps is explained by consideration of the deep defect relaxation concept.
Effect of Ion Doping Temperature on Electrical Properties of APCVD A-Si
Authors: Lee Kyung Ha , Moon Byeong Yeon , Chung Yoo Chan , Lee Seung Min , Kim Sung Chul , Kim Donggil , Jang Jin
Published: April 2011

We have studied the effect of ion doping on the electrical properties for atmospheric pressure chemical vapor deposition (APCVD) Amorphous silicon (a-Si) films. The room temperature conductivities after ion doping at optimum doping temperatures for n- and p-type a-Si films were found to be > 10−2 and > 10−4 S/cm, respectively. The unintentional hydrogen incorporation into a-Si during ion doping enhances the quality of ion doped APCVD a-Si as compared to that of plasma enhanced CVD (PECVD) a-S.i.H. We obtained the field effect mobility of > 1 cm2/Vs for APCVD a-Si TFT using ion doped n+-layer.
Very High-Gap Tetrahedrally Coordinated Amorphous Silicon-Carbon Alloys
Authors: Solomon Ionel , Tessler Leandro R.
Published: April 2011

We have prepared a series of hydrogenated Amorphous silicon-carbon alloys a-Si1-xCx:H in conditions where the power delivered to the plasma is below the threshold of primary decomposition of CH4 (“low-power regime”). Carbon is therefore incorporated into the growing film in the form of methyl groups -CH3, thus preserving the sp3 hybridization in the solid. Since the carbon is deposited only by chemical reaction with the radicals produced by the decomposition of SiH4, its concentration in the alloys cannot exceed the value x=0.5.

The variations of the optical gap and of the “average gap” with x, as measured by optical transmission, indicate as expected the predominantly tetrahedral coordination of the carbon, with a record value of EQ4=3.6 eV for x=0.42 (3.95 eV if corrected for the Urbach-tail absorption). Since the Si-C network does not relax to a more stable lower sp2 coordination, the material is highly strained, with an Urbach tail larger than that of the standard Material.
Defect Distribution and Bonding Structure in High Band Gap a-Si1−xCx:H Films Deposited in H2 Dilution
Authors: Galloni R. , Rizzoli R. , Summonte C. , Demichelis F. , Giorgis F. , Pirri C. F. , Tresso E. , Ambrosone G. , Catalanotti C. , Coscia U. , Rava P. , Della Mea G. , Rigato V. , Madan A. , Zignani F.
Published: April 2011

AMorphous silicon carbide films were deposited by the PECVD technique in SiH4+CH4 gas mixtures at various CH4 flow rates with and without H2 dilution of the reactive Mixture. A detailed analysis of defect distribution in the gap has been performed by PDS and the results have been correlated with the structural (IR) and the compositional properties (RBS, ERDA). The effect of hydrogen dilution on the electronic properties of the films was investigated by dark and photo electrical conductivity Measurements.
Electronic and Optical Properties of a-Si:H Films Alloyed with Sulfur
Authors: Wang S.L. , Lin Z.H. , Viner J.M. , Taylor P.C.
Published: April 2011

Alloying a-Si:H with small amounts of sulfur (≤ 4 × 1020 cm−3) results in a significant enhancement in the photoconductivity and a suppression of the optically-induced degradation of the photoconductivity (Staebler-Wronski effect). The Magnitudes of the activation energies for conductivity imply that these films remain essentially intrinsic in nature. When the sulfur concentration is increased to about 2 to 3 at. %, the Fermi level rises by about 0.25 eV, a fact that suggests that sulfur may act as a very inefficient dopant in a-Si:H.
Amorphous Si1−xBx ALLOYS: Atomic Fine Structure and Optical Properties
Authors: Carlsson J. R. A. , Bandmann C. , Csillag S. , Li X.-H. , Johansson M.
Published: April 2011

In order to study the dependence of the atomic fine structure and optical band gap of the amorphous alloy on concentration and annealing temperature, thin Si1−XBX alloy films were grown and then annealed at temperatures from 400 to 1050 °C. The films were characterized by Extended Energy Loss Fine Structure spectroscopy (EXELFS), High Resolution transmission Electron Microscopy (HREM), Auger Electron Spectroscopy (AES), and light absorption spectro-photometry. It is shown that all the amorphous Si1−XBX alloys are thermally stable (e.g., >1050 °C for x=0.6) as compared to a-Si, and that the optical band gap of the alloys increases gradually with annealing temperatures up to 700 – 900 °C. When annealed at higher temperatures the band gap increased rapidly, corresponding to a phase transformation between two amorphous phases.
Growth of Germanium Carbon Alloy by Pecvd Using Silane as a Growth Promoter
Authors: Moffitt Paul R. , Naseem H. A. , Ang S. S. , Brown W. D.
Published: April 2011

A possible alternative to a-SiGe for use in multijunction solar cells is a-GeC alloy. Only preliminary work has been done so far on this alloy, Mostly for use as an IR anti-reflection coating, with little study done on its optoelectronic properties. GeC films were grown by the PECVD Method from a novel gas mixture using GeF4 as the germanium source gas. Methane was used as the carbon source, with H2 being added for additional hydrogenation of the film. It was found that adding silane to the mixture would increase the growth rate from less than 1 Å/s up to 30 Å/s. The films contained no detectable silicon, even at mixture ratios of five SiH4 to one GeF4. Varying the amount of methane in the gas mixture allowed the film optical bandgap to be adjusted from 1.1 eV to 1.8 eV. The effect of other parameters such as RF power level and H2 flow rate on bandgap and growth rate were also explored. Optoelectronic properties in the 1.2 to 1.4 eV bandgap range will also be reported.
Diffusion Lengths in a-Si:H/a-Sic:H and a-Si:H/a-Sige:H Multilayers Determined by the Grating Method
Authors: Bernhard Norbert , Bauer Gottfried H.
Published: April 2011

The technique of the steady-state photocarrier grating (SSPG) has been applied to different series of a-Si:H/a-Si1-xCx:H and a-Si:H/a-Si1-xGex:H Multilayers. In dependence on the electronic well and barrier widths of the Multilayers, characteristic changes of the measured ambipolar diffusion lengths Lambi have been found. The general trend of Lambi can be understood in terms of interface recombination and scattering, when the mean composition of the multilayers is kept constant. In some cases, values of Lambi of multilayers were higher than the corresponding value of a homogeneous a-Si:H reference layer, a fact which might be explained by a dimensional effect. The effect in a-Si:H/a-Si1-xCx:H Multilayers was reduced with green HeNe-laser illumination with photon energies above the Taue gap of the barrier Material, instead of a red illumination generating photocarriers only in the potential wells.
Stability Studies of Hydrogenated Amorphous Silicon Alloy Solar Cells Prepared with Hydrogen Dilution
Authors: Yang J. , Xu X. , Guha S.
Published: April 2011

We have fabricated hydrogenated amorphous silicon alloy solar cells using hydrogen dilutions at 175 °C and 300 °C, and obtained improved photovoltaic characteristics in both the initial and degraded states for the highly diluted cells; both the fill factor and the open-circuit voltage exhibit higher values before and after light soaking. Infrared analyses reveal that for a given deposition temperature the amount of bonded hydrogen has similar concentrations between the high and low hydrogen diluted samples. Optical Modelling shows a 20 MeV difference in their optical bandgap. Defect densities obtained from constant photocurrent measurements give similar values for a given deposition temperature both before and after light soaking, inconsistent with solar cell performance.
Control of the Electron and Hole Drift mobilities in Plasma Deposited a-Si:H
Authors: Ganguly Gautam , Matsuda Akihisa
Published: April 2011

The ‘time-of-flight’ technique measured electron and hole drift mobilities are shown to be independent of deposition parameters in capacitively coupled, diode type RF-PECVD a-Si:H. However, the carrier mobilities can be varied by orders of magnitude by changing the bias applied to the mesh type controlling electrode in a triode type reactor. The room temperature hole drift mobility increases to 10−1cm2/Vs when an appropriate bias is applied to the mesh providing optimum energy ion stimulation of the film growth surface during deposition. Analysis of the field and temperature dependences of the drift mobilities shows that in the best specimens the conduction (valence) band tail density of states are approximately exponential with a reciprocal slope of lOMeV (25MeV).
Considerations for Large Area Fabrication of Integrated a-Si and Poly-Si TFTs
Authors: Mei P. , Anderson G. B. , Boyce J. B. , Fork D. K. , Hack M. , Johnson R. I. , Lujan R. A. , Ready S. E.
Published: April 2011

The combination of a-Si low leakage pixel TFTs with poly-Si TFTs in peripheral circuits provides an excellent method for reducing the number of external connections to large-area imaging arrays and displays. To integrate the fabrication of the peripheral poly-Si TFTs with the a-Si pixel TFTs, we have developed a three-step laser process which enables selective crystallization of PECVD a-Si:H. X-ray diffraction and transmission electron microscopy show that the polycrystalline grains formed with this three-step process are similar to those crystallized by a conventional one step laser crystallization of unhydrogenated amorphous silicon. The grain size increases with increasing laser energy density up to a peak value of a few Microns. The grain size decreases with further increases in laser energy density. The transistor field effect mobility is correlated with the grain size, increasing gradually with laser energy density until reaching its maximum value. Thereafter, the transistors suffer from leakage through the gate insulators. A dual dielectric gate insulator has been developed for these bottom-gate thin film transistors to provide the correct threshold voltages for both a-Si and poly-Si TFTs.
The Origin and Nature of Contact Resistance in a-Si:H TFTs
Authors: Gadelrab Serag M. , Chamberlain Savvas G.
Published: April 2011

The origin of contact resistance in a-Si:H TFTs is investigated by formulating a model for the contact limited current. The Model accounts for the independent contributions of the Metal–n+a-Si:H interface resistance and the space charge limited conduction through the intrinsic a-Si:H film. Using our contact current model we investigated the I–V behavior of an n–i–n structure with a thin a-Si:H layer (=700Å) and found that the resistance of the Metal–n+a-Si:H interface is nonlinear. We incorporated the contact limited current expression into a full TFT Model and simulated the TFT performance for a wide range of Metal–n+a-Si:H interface resistance values and intrinsic a-Si:H film thicknesses. We found that the Metal–n+a-Si:H interface resistance dominates over space charge limited conduction for the thicknesses of intrinsic a-Si:H films used in AM-LCD switches. This trend is sustained even when the effective resistance of the Metal–n+a-Si:H interface decreases due to the nonlinear current conduction across it.
A Novel α-Si(C):H Color Sensor Array
Authors: Zhu Q. , Stiebig H. , Rieve P. , Fischer H. , Böhm M.
Published: April 2011

A novel α-Si(C):H color sensor array has been developed. In this device a single pixel consists of a combination of an amorphous silicon nipin detector and a crystalline operational amplifier. Steady state and transient opto electronic behavior of the nipin structure have been studied in order to optimize the design of the image sensor. Nipin structures are found to exhibit excellent dynamic range (125 dB) and linearity. The crystalline electronics causes only very little signal distortion which makes this sensor device a potential candidate for color image capture and processing for a wide range of illumination levels.
In Situ Ellipsometric Study of the Dependence of a-Si:H Film Growth on Substrate Properties and Ignition Procedures
Authors: Schmidt U.I. , Herbst W. , Schröder B. , Oechsner H.
Published: April 2011

In situ ellipsometry reveals that particle formation influences the growth of glow discharge a-Si:H. This particle formation is observed even under discharge conditions leading to the deposition of device quality Material. It is found that less dense material is deposited during the particle-induced initial transient stage of the discharge which influences the properties of the subsequently growing “bulk” film. The effect of special power gradient ignition procedures is discussed. A significant increase of solar cell efficency is achieved by choosing “soft” start conditions for the i-layer deposition.
Characterization of Chemical-Mechanical Polishing Dielectrics for Multilevel Metallization
Authors: Sun S.C. , Yeh F.L. , Tien H.Z.
Published: April 2011

This paper presents the results obtained from a systematic study on dielectric planarization using a chemical mechanical polishing (CMP) technique. This technique is readily applicable to intermetal and pre-metal dielectric films for advanced CMOS device fabrication. Results indicate that polishing rates vary with different dielectrics; with BPSG having the highest removal rate, while PECVD nitride having the lowest removal rate. Key parameters in determining the polishing rate are down force pressure and platen rotation speed. It is demonstrated that planarization becomes a reality on patterned wafers.
Surface Effects in the Mocvd of Copper
Authors: Nuesca G. M. , Prasad J. , Kelber J. A.
Published: April 2011

Recent findings concerning the surface chemistry of Cu(I)) and Cu(II) betadiketonate precursors on metal and TiN surfaces are reviewed. Interactions of Cu(I) hexafluoroacetylacetonate (L) (Cu(I)(hfac)(L); L=Lewis base) with the surface result in an adsorbed Cu(I)hfac intermediate. Cu(II)(hfac)2 adsorbtion yields the Cu(I)hfac intermediate plus adsorbed hfac. Subsequent exposure to atomic hydrogen volatilizes the adsorbed hfac and results in the reduction of Cu(I) via disproportionation: 2Cu(I)(hfac) ⇒ Cu(0) + Cu(II)(hfac)2 (desorbed). These results demonstrate that disproportionation can occur on contaminant free surfaces under UHV conditions, and that the mechanisms for Cu(I) and Cu(II)/H2 film growth are similar. Implications for selectivity and low temperature deposition are explored. Potential shortcomings of TiN as an adhesion/diffusion barrier are also discussed.
Process Integration and Manufacturasility Issues for High Performance Multilevel Interconnect
Authors: Jeng Shin-Puu , Havemann Robert H. , Chang Mi-Chang
Published: April 2011

Interconnect delay is shown to be a performance-limiting factor for ULSI circuits when feature size is scaled into the deep submicron region, due to a rapid increase in interconnect resistivity and capacitance. Dielectric materials with lower values of permittivity are needed to reduce the line-to-line capacitance as metal spacing decreases. However, the challenge is to successfully integrate these materials into on-chip interconnects. A new multilevel interconnect scheme has been developed that gives improved performance through insertion of a low-dielectric-constant material between metal leads. A novel polymer/Si02 composite dielectric structure provides lower line-to-line capacitance while alleviating many of the integration and reliability problems associated with polymers in standard interconnect processing.
Fast Thermal Cycling and Electro-Migration Properties of Si/TaSi2/TiN/Al-Si Multilayer Thin Film Contacts
Authors: V.Baranov Valentin , M.Ivkin Victor , L.Sakovitch Elena
Published: April 2011

For the electromigration test of Si/TaSi2/(Al-1wt%Si) and Si/TaSi2/TiN/(Al-1wt%Si) multilayer contacts we employed the special test structures which allow to passage a pulsed electrical current through the semiconductor region lying under investigated contacts and insulated from them by n+/p-junction. The contacts were tested in the optimal conditions (temperature was cycled in the ranges from 50°C to 175°C with 300ms thermal cycle period at 25 mA constant electrical current passaged through the investigated contacts). It has been shown that the electromigration life time has been shortened by more than an order of the magnitude compared to 200°C constant temperature test. SEM investigations of the sputter deposited thin film of multilayer contact have also shown that the Al-Si thin film on the TaSi2 layer had a fine structure with the average grain size about 0,3 μm. However a presense of the TiN interlayer with the thickness of 0.05 - 0.1 pm results in an increase of the average grain size of the upper Al-Si film up to 0,8μm. The result is the increase in the electromigration process activation energy that improves the electromigration life time contacts containing the TiN interlayer.
Lateral Variation in the Schottky Barrier Height and Observation of Critical Lengths at Au/PtSi/(100)Si and Au/(100)GaAs Diodes
Authors: Talin A. Alec , Ngo Tue , Stanley Williams R. , Morgan Brent A. , Ring Ken M. , Kavanagh Karen L.
Published: April 2011

Lateral variations in the Schottky barrier height (SBH) formed at Au/PtSi/(100)Si and Au/(100)GaAs diodes were measured on length scales ranging from a few to several hundred nanometers using ballistic electron emission microscopy (BEEM). All of the contacts investigated showed SBH spatial inhomogeneity. The most severe SBH variations observed were 0.09eV/0.7nm in Au/(100)GaAs contacts and 0.08eV/14nm for Au/PtSi/(100)Si contacts. Based on the lateral maps of the SBH at each interface, the difference between the locally averaged SBH and the globally averaged BEEM SBH was computed. This analysis showed that there is a critical diode length scale below which the SBH deviates significantly from the SBH averaged over a macroscopic length scale. This result implies that the uniformity of electrical characteristics of arrays of small devices (e.g.. PtSi/Si photodetectors and GaAs FET gates) can be expected to deteriorate significantly when device dimensions decrease below the critical length.
Rapid Thermal Nitridation of Tungsten-Capped Shallow Ohmic Contacts to GaAs
Authors: Kaminska E. , Piotrowska A. , Mizera E. , Guziewicz M. , Barcz A. , Dynowska E. , Kwiatkowski S.
Published: April 2011

We report on the use of AuGeNi/W and AuZn/W metallizations and their further processing by rapid thermal nitridation. Nitrided tungsten serves as a cap suppressing the sublimation of As. To study the effect of annealing conditions on the properties of the W cap, comparative experiments involving conventional annealing in H2, and RTA in N2 or O2 flow, have been performed. TEM, XRD, RBS, and SIMS have been employed to investigate contact microstructures. The obtained results prove the superiority of the contacts with nitrided W cap over conventional insulating cap. No W-N phase is observed in nitrided W layers, which is consistent with the model of a "stuffed" barrier by Nicolet.
Au/Zn Contacts to p-InP: Electrical and Metallurgical Characteristics and the Relationship Between Them
Authors: Weizer Victor G. , Fatemi Navid S. , Korenyi-both Andras L.
Published: April 2011

The metallurgical and electrical behavior of Au/Zn contacting metallization onp-type InP was investigated as a function of the Zn content in the metallization. It was found that ohmic behavior can be achieved with Zn concentrations as small as 0.05 atomic percent Zn. For Zn concentrations between 0.1 and 36 at.%, the contact resistivity ρc was found to be independent of the Zn content For low Zn concentrations the realization of ohmic behavior was found to require the growth of the compound Au2P3 at the metal-InP interface. The magnitude of ρc is shown to be very sensitive to the growth rate of the interfacial Au2P3 layer. The possibility of exploiting this sensitivity to provide low resistance contacts while avoiding the semiconductor structural damage that is normally attendant to contact formation is discussed.
Vlsi Metallization by Coherent Magnetron Sputtering
Authors: Guo Xin S. , Van Gogh Jim , Raaijmakers Ivo
Published: April 2011

Magnetron sputtering has been used extensively to deposit interconnect layer, diffusion barrier layer, adhesion layer and anti-reflection layer in semiconductor production. As the dimension of VLSI devices get smaller, it is becoming increasingly difficult to deposit these metal layers into high aspect ratio contacts and vias using conventional sputtering method. Coherent sputtering, where a perforated plate (collimator) is placed between the sputtering target and wafer, improves bottom coverage and step coverage. In the recent years, coherent sputtering has been used to deposit titanium, titanium nitride and aluminum films. However, the existence of collimator changes the deposition processes and properties of the deposited films. In this article, we will discuss some of the properties of coherent deposition.
Manufacturability Versus Reliability Issues Relevant to Interconnect Metallizations.
Authors: Rodbell K.P. , Colgan E.G. , Hu C-K.
Published: April 2011

Interconnections on silicon-based integrated circuits are almost exclusively aluminum alloys (Al-Si, Cu and various other solutes, e.g., Pd, Sc). The effects of film microstructure (grain size, grain size distribution, crystallographic texture and precipitate distribution) on the reliability of single level Al metallization has been well established. The final film microstructure obtained is dependent on both the deposition conditions and the thermal history during the manufacturing process. This paper will consider the role of microstructure in multi-level interconnects consisting of (1) AI(Cu) lines (in SiO2) with W and/or AI(Cu) studs and (2) an all Cu/polyimide multi-level structure. Methods for microstructure optimization during manufacturing of both Al and Cu based multilevel structures are explored. The variables important in determining the reliability of submicrometer single level versus multi-level structures and reliability testing methods (e.g., samples with versus without reservoirs and wafer level techniques) will be reviewed. Two relevant questions raised are; (1) What can be done during manufacturing to "build-in" reliability?, and (2) What are the trade-offs between manufacturing complexity (i.e., cost) and inherent reliability?
Eutectic Bonding for Inducing In-Plane Strain in Gaas and Gaas/Algaas MQW Thin Films
Authors: Lu Y. , Kuo H. C. , Lin C. H. , Shen H. , Ren F. , Wraback M. , Pamulapati J. , Taysing-Lara M. , Dutta M. , Kuo J. M.
Published: April 2011

We present a process for creating in-plane anisotropic strain in (100) GaAs and GaAs/AlGaAs multiple quantum well (MQW) thin films. The host substrates used for bonding include (100) GaAs, (100) silicon, and lithium tantalate (LiTaO3) with a special crystalline orientation. A mutilayer metallization consisting of Au-Sn (Au: 80 wt% , Sn: 20 wt%, 0.95μm), Ti (500Å) adhesion layer and Pt (500Å) barrier layer is deposited on the thin films and the host substrates. By choosing a proper annealing temperature (380°C) and thickness of eutectic layer, the thin films and the substrates are bonded together. Photoluminescence measurements do not reveal any thermally induced strain in the thin films bonded to GaAs; however, they show the existence of in-plane biaxial strain in the films bonded on Si. Linearly polarized reflectance measurements reveal an optical anisotropy in the MQW bonded to LiTaO3, which possesses an orientation-dependent thermal expansion. This indicates that the in-plane strain in the thin films is induced by the different thermal expansions between the thin films and the substrates. This process can be used to develop a new class of devices with an artificially induced in-plane strain.
Enhanced Adhesion of Copper Films to SiO2, PSG and BPSG by Refractory Metal Additions
Authors: Rafalski S.A. , Spreitzer R.L. , Russell S.W. , Alford T.L. , Li J. , Moinpour M. , Moghadam F. , Mayer J.W.
Published: April 2011

Copper films generally exhibit poor adhesion on dielectrics. It has been shown that the addition of refractory metals promotes adhesion via an interfacial reaction or better wetting to the dielectric. We investigate the adhesion of Cu-refractory metal (Cr, Ti) alloy films and bilayers on various silicon oxide substrates (SiO2, PSG, BPSG) after annealing in the temperature range 400-600°C by conventional furnace using N2/H2 forming gas. Rutherford backscattering spectrometry (RBS) was used to determine the interfacial reaction characteristics. The efficacy of a variation of the standard Scotch™ tape testing was evaluated. We found that the combined Scotch™ tape/scribe adhesion test revealed excellent qualitative bonding information and could be correlated well to RBS characterization. We were able to optimize the sample configurations and chemical compositions to achieve the best adhering film.
Investigation of Chromium Nitridation Using Ion Beam Resonance Analysis
Authors: Russell S.W. , Bair A.E. , Rack M.J. , Adams D. , Spreitzer R.L. , Alford T.L. , Culbertson R.J.
Published: April 2011

We investigate the nitridation of chromium films in an NH3 ambient at 500°C. Rutherford backscattering spectrometry using 2.0 MeV He2+ was utilized to determine the compositions of thick reacted layers and to provide calibration for the other techniques. In addition, analysis was performed using the 14N(α,α)14N resonance at 3.72 MeV in order to enhance sensitivity to nitrogen. Sputter-deposited TiN was used as a calibration for the cross section a for this resonance over the energy range 3.05-3.85 MeV and compared to the literature value. We find that analysis just above the peak in the resonance provides excellent sensitivity to N concentration in the nitride layers. This approach may be readily used in conjunction with 2.0 MeV backscattering to determine the overall composition and sample configuration. Auger electron spectroscopy was used to provide more depth sensitivity in compositional profiling and to monitor the oxygen impurity distribution. X-ray diffraction was used to identify phases in both as-deposited and annealed films.