bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractSuperparamagnetic 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

AbstractIn 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

AbstractTransient 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

AbstractThe 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

AbstractThe 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

AbstractIntersubband 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

AbstractRecent 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

ABSTRACTThe 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

ABSTRACTIn 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

ABSTRACTFor 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

ABSTRACTPrevious 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

ABSTRACTWe 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

ABSTRACTAn 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

ABSTRACTMeasurements 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

ABSTRACTResults 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

ABSTRACTDevice 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

ABSTRACTThe 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

ABSTRACTWe 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

ABSTRACTWe 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

ABSTRACTAMorphous 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

ABSTRACTAlloying 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

ABSTRACTIn 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

ABSTRACTA 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

ABSTRACTThe 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.