bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemical Composition and Microchemistry of “Free Galloping Horse” Bronze Punic Coins
Authors: Ingo G.M. , Manfredi L-I. , Caroli S. , Bultrini G. , Chiozzini G. , Femmine P. Delle
Published: April 2011

A large group of the so called “free galloping horse” bronze Punic coins, that is the most common series largely diffused in the Mediterranean basin, has been found during the archaeological excavation at Tharros (western Sardinia, Italy). Forty-seven coins have been studied in order to determine the chemical composition and the microchemical structure of the copper alloys used by Punies for the coinage of this series and to gain further information about the metal ores used to produce the metals. The results have shown that copper, tin, iron, silver, antimony, lead, zinc and arsenic vary significantly thus indicating different trends in the alloys production. The content of the major and minor elements has also indicated that Punic metallurgists controlled only the content of some elements to within quite narrow limits and when deliberate adding was used just to increase the metal to fill the mould, as might sometimes be the case with the addition of lead instead of the more expensive tin.
Quantitative Analysis of Displacement at 90° Domain Boundaries In BaTiO3 and PbTiO3
Authors: Ross Frances M. , Kilaas Roar , Snoeck Etienne , Hÿtch Martin , Thorel Alain , Normand Laurent
Published: April 2011

In this paper we discuss the measurement of long range displacement fields associated with 90° domain boundaries in the ferroelectric ceramics BaTiO3 and PbTiO3. We have calculated displacement fields from high resolution lattice images by two techniques: firstly, measuring the positions of peaks in the images, and secondly, using a geometric phase analysis technique to magnify small lattice distortions. We describe the results and consider the complementary use of Fresnel contrast analysis to characterize local strain and electric fields near the boundaries.
Creation of Nanocrystals Via a Tip-Induced Solid-Solid Transformation
Authors: Zhang Jian , Liu Jie , Huang Jinlin , Kim Philip , Lieber Charles M.
Published: April 2011

Scanning tunneling microscopy (STM) is a powerful tool for nanoscale research since it can both create and probe the properties of nanostructures. We have used STM to create T-phase TaSe2 nanocrystals embedded in H-phase TaSe2 through a tip-induced solid-solid phase transition at liquid He temperature. Atomic-resolution images have been used to develop a structural model to understand this solid-solid phase transformation. Furthermore, STM studies of the charge density wave (CDW) state in the T-TaSe2 nanocrystals have been used to address CDW physics in finite dimensions.
The Conversion of Czochralski Silicon from P-Type to N-Type by Hydrogen Plasma Enhanced Thermal Donor Formation
Authors: Job R. , Borchert D. , Bumay Y. A. , Fahrner W. R. , Grabosch G. , Khorunzhii I. A. , Ulyashin A. G.
Published: April 2011

Our experiments show a hydrogen plasma assisted creation of p-n junctions in p-type Cz silicon due to a hydrogen enhanced thermal donor (TD) formation at temperatures ≤450 °C. Applying DC or HF plasma treatments a conversion of p-type into n-type Cz silicon by TD formation occurs. One can distinguish one step processes (p-n junction formation appears just after the plasma exposure) and two step processes (p-n junction formation requires subsequent post hydrogenation annealing). The samples are studied by depth resolved spreading resistance probe (SRP), capacitance-voltage (CV) and Hall measurements. For the one step processes a kinetic model for hydrogen enhanced TD formation is presented.
Diffusion of Silicon Interstitials in thin Silicon Films on Insulator in Neutral and Oxidising Annealing Ambients
Authors: Silvestre Guénolé C.M.
Published: April 2011

Silicon-On-Insulator (SOI) materials have emerged as a very promising technology for the fabrication of high performance integrated circuits since they offer significant improvement to device performance. Thin silicon layers of good crystalline quality are now widely available on buried oxide layers of various thicknesses with good insulating properties. However, the SOI structure is quite different from that of bulk silicon. This paper will discuss a study of point-defect diffusion and recombination in thin silicon layers during high temperature annealing treatment through the investigation of stacking-fault growth kinetics. The use of capping layers such as nitride, thin thermal oxide and thick deposited oxide outlines the diffusion mechanisms of interstitials in the SOI structure. It also shows that the buried oxide layer is a very good barrier to the diffusion of point defects and that excess silicon interstitials may be reincorporated at the top interface with the thermal oxide through the formation of SiO species. Finally, from the experimental values of the activation energies for the growth and the shrinkage of stacking-faults, the energy of interstitial creation is evaluated to be 2.6 eV, the energy for interstitial migration to be 1.8 eV and the energy of interstitial generation during oxidation to be 0.2 eV.
Vacancies and Interstitial Atoms in Irradiated Silicon
Authors: Ehrhart P. , Zillgen H.
Published: April 2011

Differently doped Si-wafers were irradiated with 2.5MeV electrons and subsequently investigated by X-ray diffraction methods. We show that a high concentration of defects (>1016 cm−3) can be frozen in at 4K and that a large fraction of the defects is stabilized in the form of close Frenkel pairs. These Frenkel pairs are characterized by the nearly perfect cancellation of the long-range displacement fields of the interstitial atom and the vacancy. We discuss the absolute size of these displacements as well as the introduction rate of the defects, which is of the order of Σ = 1cm−1. Similar results are obtained for weakly doped Cz-Si or FZ-Si and for degenerate p-type Si(B) and n-type Si(As), i.e., the results are independent of the oxygen content of the samples and of the position of the Fermi level. The high defect introduction rates are at variance with the results of electrical and EPR investigations and indicate that these methods detect only a few percent of the total defect concentration which is produced and frozen in at 4K. The consequences for the understanding of the defect production in Si and for the assumption of an athermal migration of interstitial atoms are discussed. In addition we compare the defect patterns observed after 4K irradiation to those observed after room-temperature irradiations and discuss the thermally activated defect reactions up to the final annealing at 1000K.
Extracting Information from a Supercell Calculation
Authors: Harrison W. A.
Published: April 2011

A number of corrections must be made to a first-principles defect supercell calculation if the results are to be of use in calculating properties of isolated defects. These are illustrated for a tetrahedral self-interstitial in silicon, which places two electrons in the conduction band. One correction arises from the familiar Coulomb enhancement of the gap relative to local-density-approximation (LDA) calculations. The second is for the capture of these electrons in a double donor state. The third arises from the extra kinetic energy of the electrons due to their partial filling of the conduction band for a finite-sized supercell. The fourth is the partial occupation of the defect resonance, lowering the kinetic energy but increasing the Coulomb energy. A model is introduced which allows estimates of each of these corrections, with parameters which can be tuned to LDA supercell calculations. It allows then prediction of a wide range of properties dependent upon the defect in question.
Diffusion of Gold into Heavily Boron-Doped Silicon
Authors: Bracht H. , Rodriguez Schachtrup A.
Published: April 2011

Diffusion of Au into dislocation-free and highly dislocated Si with high B-background doping levels has been investigated with the aid of neutron activation analysis in conjunction with mechanical sectioning. The high B-doping level causes extrinsic conditions, i.e., the hole concentration exceeds the intrinsic carrier concentration even at diffusion temperatures between 900°C and 1100°C. All profiles are accurately described on the basis of the kick-out diffusion model and a mechanism which takes into account segregation of Au at dislocations. Our analysis provides solubility data of Au in Si and effective diffusion coefficients related to interstitial Au and Si self-interstitials I. The dependence of these quantities on the B-background doping level is well described by the Fermi-level effect. This analysis supports singly positively charged states in p-type Si of Au on interstitial (Aui) and substitutional (Aus) sites and of Si self-interstitials. Successful fitting of additionally requires an acceptor level of Aus. The electrical properties deduced for Aui, Aus and I are summarized in Table 2. Au profiles in highly dislocated Si obtained especially after diffusion at 900° C give evidence of Au trapped at dislocations. From our preliminary experimental results we determine an enthalpy difference of 2.7 eV between Au on substitutional sites and Au captured at dislocations.
The Role of Vacancies and Interstitials in Transient Enhanced Diffusion of Arsenic Implanted into Silicon
Authors: Venables D. , Krishnamoorthy V. , Gossmann H.- J. , Lilak A. , Jones K. S. , Jacobson D. C.
Published: April 2011

Boron and antimony doped superlattices (DSLs) were implanted with arsenic at 40 keV to doses of 2×1014 cm−2, 5×1015 cm−2 and 2×1016 cm−2. Increasing the arsenic dose above 5×1015 cm−2 resulted in a reduction in the extent of arsenic transient enhanced diffusion (TED) following annealing at 700°C, 16 hr. Concurrent with this reduction in TED was a reduction in the number of free interstitials beyond the end-of-range, as measured by the boron diffusion enhancement in the doped superlattices. No enhancement in antimony diffusivity was observed in this region, indicating that vacancies play no direct role in the diffusion of arsenic in this region, although an indirect role for vacancies as recombination centers for mobile interstitials is not precluded by these experiments. We conclude that interstitials dominate arsenic diffusion in the end-of-range region and beyond. Interpretation of the DSL data in the projected range region is complicated by Fermi level and segregation effects and no definitive conclusion can be reached about the point defect populations in this region.
A PAIR-DIFFUSION MODEL FOR ARSENIC IN SILICON CONSIDERING ARSENIC DEACTTVATION-INDUCEDINTERSTITIAL-SDLICON EMISSION
Authors: Hiroi Masayuki , Ikezawa Takeo , Hane Masami , Matsumoto Hiroshi
Published: April 2011

An arsenic diffusion model was proposed with the emphasis on a new deactivation process which accounts for excess interstitial silicon generation. Appropriate parameter set for the binding energies of arsenic-point defect pairs were obtained for reproducing various arsenic activation levels and interaction with boron in the case of co-diffusion. Such parameters were extracted from the data of carefully performed secondary ion mass spectroscopy with lowering the primary beam energy.
Detection of Metastabile Defective Regions in Ion-Implanted Silicon by Means of Metal Gettering
Authors: Kögla R. , Posselt M. , Yankov R. A. , Kaschny J. R. , Werner P. , Danilin A. B. , Skorupa W.
Published: April 2011

High-energy, self-ion implantation has been used to form deep gettering layers in Si. Subsequently samples have been contaminated with Cu and subjected to heat treatment. The residual defects act as gettering centres for Cu. The decoration of defects byCu making them detectable by secondary ion mass spectromety analysis. Metastable defect complexes have been detected which, because of their small size, are not directly detectable by other analytical techniques such as transmission electron microscopy and MeV-particle channeling. These defects are probably of interstitial type and have been found mainly midway between the sample and the projected ion range, i.e. around Rp/2. The gettering ability of these small defect complexes may largely exceed that of the post-anneal damage at the projected i.e range, Rp. The results obtained demonstrate that by means of metal gettering the formation, growth and dissolution of very small defect complexes in ion-implanted Si can be studied.
Identification of Microdefects in Multicrystalline Silicon
Authors: Werner M. , Möller H. J. , Wolf E.
Published: April 2011

Microdefects in multicrystalline silicon grown by directional solidification have been investigated by transmission electron microscopy. Their density (=106 cm−2) correlates with the density of shallow etch pits observed after chemomechanical polishing and selective etching. Different types of microdefects (size 10 – 100 nm) could be identified: i) spherical precipitates most likely amorphous silicon dioxide, ii) small plates lying on {111} planes and iii) groups of closely spaced stacking faults having the character of dipoles. It is argued that these defects are the result of agglomeration process of intrinsic point defects and impurities, where oxygen and carbon are the main candidates. A qualitative comparison to the point defects agglomeration observed in Cz material will be given.
X-Ray Microanalysis of Al/Zr Multilayers in the Transmission Electron Microscope
Authors: Wall M. A. , Barbee T. W. , Bentley J.
Published: April 2011

A one-nanometer scale transmission electron microscope electron probe X-ray microanalysis characterization of as-deposited and annealed aluminum - 11.5 at.% zirconium multilayer samples in cross-section synthesized by magnetron sputtering is reported on here. Composition line profiles were acquired across Zr layers in as-deposited material and samples isochronnally annealed in a differential scanning calorimeter to temperatures of 290°C and 485°C. A spatial resolution of approximaty 1.5 to 2.0 nm was achieved in these experiments and will be improved by deconvoluti on of the instrumental electron probe function from the data. The as-deposited structure consisted of crystalline Al and Zr layers with thin amorphous layers at the Al/Zr interfaces. The amorphous interface layers increased in thickness upon annealing to 290°C. Additionally, at 290”C a metastable cubic alloy forms at the Zr deposited on Al interface. Upon heating to 485°C a multilayer of Al and metastable cubic AlxZr1-xphase is formed. The electron microscopic experimental technique, observations and data analysis will be discussed as applied to these multilayered materials.
Interfacial Reactions in Thin Film and Bulk Iron/Silicon Couples
Authors: Zhang Yuhong , Ivey Douglas G.
Published: April 2011

Initial phase formation in thin film and bulk Fe/Si couples has been investigated using transmission and scanning electron microscopy (TEM and SEM). For the thin film couples, ≈165 nm of Fe was deposited by electron beam evaporation onto <111> oriented Si substrates. SiO2 capping layers (≈100nm thick) were used to protect the Fe from oxidation during subsequent annealing. Bulk diffusion couples were fabricated by clamping together polycrystalline Fe pieces and <111> oriented single crystal Si pieces and sealed in evacuated (≈10-4 torr) quartz capsules. Annealing of thin film couples was done at temperatures ranging from 300°C to 500°C for up to several hours. Bulk couples were annealed at 700°C for up to ≈1000hrs.

Interfacial reactions were detected in as deposited thin film couples. A layer =5nm thick was identified, through electron diffraction, as poorly crystalline off-stoichiometric Fe3Si. Iron was the major diffuser during the formation of Fe3Si. During annnealing off-stoichiometric Fe3Si transformed to stoichiometric Fe3Si. FeSi was the next phase to form - initially detected after annealing at 300°C for 3 hrs. Similar results were obtained for bulk couples. The first phase to form was ordered stoichiometric Fe3Si (initially detected after 7 hrs), followed by FeSi (≈23 hrs) and then FeSi2 (>200 hrs). The formation behavior of these phase is discussed.
Nucleation-Based Control of Low-Temperature Diamond Film Deposition on Optical Substrates
Authors: Gilbert Donald R. , Carasso Melanie L. , Demkowicz Paul A. , Singh Rajiv K. , Adair James H.
Published: April 2011

Microstructural control is a critical issue in the use of diamond films in a variety of engineering applications. Using a novel, electrostatic-based particle seeding process, we have investigated the deposition of diamond films with varying areal nucleation densities. Depositions were performed at 1.000 Torr in a modified electron cyclotron resonance plasma system. Methyl alcohol was the primary diamond precursor species. SEM and Raman spectroscopy were used to evaluate microstructure and composition characteristics. Comparisons in deposition characteristics were made based on relative nucleation density.
Microstructure Evolution of Amorphous Si1-xGex Thin Films
Authors: Tong H. Y. , Jiang Q. , Hsu D. , King T. J. , Shi F. G.
Published: April 2011

The composition dependence of the nucleation free energy barrier W* in amorphous Si1-xGex thin films is investigated. Within the composition range of x = 0.25 ∼ 0.52, the nucleation free energy barrier exhibits a maximum, which is in a good agreement with our theoretical analysis. The results are significant for processing polycrystalline SiGe thin films with desirable microstructures for thin film transistor applications. In addition, the incubation time of crystallization of amorphous Si1-xGex (x=0.5) thin films is investigated as a function of temperature.
Megasonic Irradiation Induced Chemical Reaction in the Solution
for Silicon Wafer Cleaning
Authors: Ohmi T. , Toda M. , Katoh M. , Kawada K. , Morita H.
Published: April 2011

We have already proposed chemical vapor free and room temperature wet
cleaning (UCT cleaning) for Si substrate surface, instead of conventional
RCA cleaning, which consumes very little amount of chemicals and ultrapure
water compared to that of RCA cleaning. This new wet cleaning has been
developed by scientifically understanding contaminants removal mechanism as
follows;

(1) Particles can be removed by simultaneously satisfying following two
conditions,

(a) particles and substructure surface must have same polarity of zeta
potential in the cleaning solution to exhibit repulsive electric coulomb
force with each other.

(b) adhered particles must be lifted off from substrate surface by slight
etching to make electric repulsive force greater than van der Waals
force,

(2) Redox potential of the cleaning solution must be larger than a critical
value to enable removal of electrons from adhered metals in order to
dissolve them into the cleaning solution as positive ions and to decompose
adhered organic molecules to CO2, H2O etc.

Megasonic irradiation is very essential in UCT cleaning, particularly to
remove particles by lifting them off from substrate surface. In this study,
chemical reaction in the cleaning solution induced by megasonic irradiation
is mainly discussed. Irradiation of ultrasonic having frequencies higher
than a few hundred KHz (Megasonic) to ultrapure water has been confirmed to
be able to decompose H2O molecules to H radicals and OH radicals.
Decomposition efficiency of H20 molecules is strongly dependent on remaining
gas components and their volume in the ultrapure water. When the remaining
gas volume is decreased to less than 0.2 ∼0.3ppm, H2O molecules
decomposition to H radicals and OH radicals has not been observed. Generated
OH radicals have been confirmed to produce H2O2, and
NH4+, NO2−, NO3− ions by reacting. with remaining N2 gas. Thus the
cleaning capability of the cleaning solutions can be controlled by
irradiating megasonic.
The Impact of Temperature and Concentration on SC2 Cost and
Performance in a production Environment
Authors: Riley D. J. , Glick J. S. , Parks V. , Matamis G.
Published: April 2011

Recent studies have shown that extremely dilute HCl mixtures can offer
considerable cost savings and improved particle performance relative to
traditional SC2 formulations. This work indicates, however, that extreme
levels of dilution are not necessary to secure many of the benefits
suggested for dilute HCI. Significant benefit can be attained by pursuing
moderate concentration and temperature alterations. In this study, an
intermediate dilution and temperature reduction are evaluated to assess
potential production advantage. Comparison of a 1:1:20 formulation at 60 C
is made to a more traditional 1:1:6 mixture at 85 C. The impact of the
chemistry and temperature alteration on peroxide decomposition rate is shown
to be dramatic. While initial pour-up ratios suggest that the dilute recipe
could require 1/3 as much peroxide as the traditional chemistry, chemical
savings are significantly more dramatic due to the ability of the solution
to maintain concentration over time. An additional benefit associated with
the alternative pour-up is a marked reduction in particle levels on silicon
surfaces; particle levels on thermal oxide wafers have not shown the same
trend. VPD-ICPMS measurements are used in this study to illustrate that the
recipe change results in comparable metallic removal efficiency.
A New Class of Materials with Promising Thermoelectric Properties: MNiSn (M = Ti, Zr, Hf)
Authors: Hohl H. , Ramirez A. P. , Kaefer W. , Fess K. , Thurner Ch. , Kloc Ch. , Bucher E.
Published: April 2011

TiNiSn, ZrNiSn and HfNiSn are members of a large group of intermetallic compounds which crystallize in the cubic MgAgAs-type structure. Polycrystalline samples of these compounds have been prepared and investigated for their thermoelectric properties. With thermopowers of about –200 μV/K and resistivities of a few mΩcm, power factors S2/ρ as high as 38 μW/K2cm were obtained at 700 K. These remarkably high power factors are, however, accompanied by a thermal conductivity which is too high for applications. In order to reduce the parasitic lattice thermal conductivity, solid solutions Zrl−xHfxNiSn, Zrl−xTixNiSn, and Hfl−xTixNiSn were formed. The figure of merit of Zr0.5Hf0.5NiSn at 700 K (ZT= 0.41) exceeds the end members ZrNiSn (ZT= 0.26) and HfNiSn (ZT= 0.22).
Computational Studies of Novel Thermoelectric Materials
Authors: Singh D.J. , Mazin I.I. , KIM S.G. , Nordstrom L.
Published: April 2011

The thermoelectric properties of La-filled skutterudites and β-Zn4Sb3 are discussed from the point of view of their electronic structures. These are calculated from first principles within the local density approximation. The electronic structures are in turn used determine transport related quantities. β-Zn4Sb3 is found to be metallic with a complex Fermi surface topology, which yields a non-trivial dependence of the Hall concentration on the band filling. Calculations of the variation with band filling are used to extract the carrier concentration from the experimental Hall number. At this band filling, which corresponds to 0.1 electrons per 22 atom unit cell, we calculate a Seebeck coefficient and temperature dependence in good agreement with the experimental value. The high Seebeck coefficients in a metallic material are remarkable, and arise because of the strong energy dependence of the Fermiology near the experimental band filling. Virtual crystal calculations for La(Fe,Co)4Sb12 show that the system obeys almost perfect rigid band behavior with varying Co concentration, and has a substantial band gap at a position corresponding to the composition LaFe3CoSb12. The valence band maximum occurs at the Γ point and is due to a singly degenerate dispersive (Fe,Co)-Sb band, which by itself would not be favorable for TE. However, very flat transition metal derived bands occur in close proximity and become active as the doping level is increased, giving a non-trivial dependence of the properties on carrier concentration and explaining the favorable TE properties.
Structural and Optical Properties of β-FeSi2/Si(100) Prepared by Laser Ablation Method
Authors: Kakemoto H. , Makita Y. , Obara A. , Tsai Y. , Sakuragi S. , Ando S. , Tsukamoto T.
Published: April 2011

β-FeSi2 is a promising material for the application of various electronic, optoelectronic and energy devices. We present here the semiconducting properties of β-FeSi2 films on Si(100) substrate prepared by laser ablation method. Samples were grown using poly-crystalline bulk β-FeSi2 prepared by horizontal gradient freeze method. For the monitoring of growth, in-situ observation of ablation plume was made through fluorescence spectroscopy. Reflection of highenergy electron beam diffraction (RHEED) was also made in-situ to see the surface morphology. Characterization of the films by X-ray diffraction presented purely P3(220) orientation. Raman scattering measurements at room temperature also indicated that the grown films are semiconducting β-FeSi2. Optical absorption spectra at room temperature showed absorption coefficient higher than 105 cm−1 above the band-gap (˜1.2 eV). It was revealed that high quality semiconducting β-FeSi2 films can be fabricated by laser ablation method without post-annealing.
Thermoelectric Applications as Related to Biomedical Engineering for Nasa Johnson Space Center
Authors: Kramer C. D. , P.E.
Published: April 2011

This paper presents current NASA biomedical developments and applications using thermoelectrics. Discussion will include future technology enhancements that would be most beneficial to the application of thermoelectric technology.

A great deal of thermoelectric applications have focused on electronic cooling. As with all technological developments within NASA, if the application cannot be related to the average consumer, the technology will not be mass-produced and widely available to the public (a key to research and development expenditures and thermoelectric companies). Included are discussions of thermoelectric applications to cool astronauts during launch and reentry. The earth-based applications, or spin-offs, include such innovations as tank and race car driver cooling, to cooling infants with high temperatures, as well as, the prevention of hair loss during chemotherapy. In order to preserve the scientific value of metabolic samples during long-term space missions, cooling is required to enable scientific studies. Results of one such study should provide a better understanding of osteoporosis and may lead to a possible cure for the disease.

In the space environment, noise has to be kept to a minimum. In long-term space applications such as the International Space Station, thermoelectric technology provides the acoustic relief and the reliability for food, as well as, scientific refrigeration/freezers. Applications and future needs are discussed as NASA moves closer to a continued space presence in Mir, International Space Station, and Lunar-Mars Exploration.
Prospects for High Thermoelectric Figures of Merit in 2D Systems
Authors: Dresselhaus M. S. , Sun X. , Cronin S. B. , Koga T. , Dresselhaus G. , Wang K. L.
Published: April 2011

Enhanced ZT has been predicted theoretically and observed experimentally in 2D quantum wells, with good agreement between theory and experiment. Advantages of low dimensional systems for thermoelectric applications are described and prospects for further enhancement of ZT are discussed.
Thermoelectric Power of Bi And Bi1−xSbx Alloy Thin Films And Superlattices Grown by MBE
Authors: Cho Sunglae , DiVenere Antonio , Wong George K. , Ketterson John B. , Meyer Jerry R. , Hoffmian Craig A.
Published: April 2011

We have measured the thermoelectric power (TEP) of MBE-grown epitaxial Bi and Bi1−xSbx alloy thin films and superlattices as a function of temperature in the range 20–300 K. We have observed that the TEP of a Bi thin film of 1 μm thickness is in good agreement with the bulk single crystal value and that the TEPs for superlattices with 400 Å and 800 Å Bi well thicknesses are enhanced over the bulk values. For x=0.072 and 0.088 in Bi1−xSbx thin films showing semiconducting behavior, TEP enhancement was observed by a factor of two. However as Bi or Bi1−xSbx well thickness decreases in superlattice geometry, the TEP decreases, which may be due to unintentional p-type doping.
Enhancement in Figure-Of-Merit with Superlattice Structures for Thin-Film Thermoelectric Devices
Authors: Venkatasubramanian R. , Colpitts T.
Published: April 2011

Thin-film superlattice (SL) structures in thermoelectric materials are shown to be a promising approach to obtaining an enhanced figure-of-merit, ZT, compared to conventional, state-of-the-art bulk alloyed materials. In this paper we describe experimental results on Bi2Te3/Sb2Te3 and Si/Ge SL structures, relevant to thermoelectric cooling and power conversion, respectively. The short-period Bi2Te3/Sb2Te3 and Si/Ge SL structures appear to indicate reduced thermal conductivities compared to alloys of these materials. From the observed behavior of thermal conductivity values in the Bi2Te3/Sb2Te3 SL structures, a distinction is made where certain types of periodic structures may correspond to an ordered alloy rather than an SL, and therefore, do not offer a significant reduction in thermal conductivity values. Our study also indicates that SL structures, with little or weak quantum-confinement, also offer an improvement in thermoelectric power factor over conventional alloys. We present power factor and electrical transport data in the plane of the SL interfaces to provide preliminary support for our arguments on reduced alloy scattering and impurity scattering in Bi2Te3/Sb2Te3 and Si/Ge SL structures. These results, though tentative due to the possible role of the substrate and the developmental nature of the 3-ω method used to determine thermal conductivity values, suggest that the short-period SL structures potentially offer factorial improvements in the three-dimensional figure-of-merit (ZT3D) compared to current state-of-the-art bulk alloys. An approach to a thin-film thermoelectric device called a Bipolarity-Assembled, Series-Inter-Connected Thin- Film Thermoelectric Device (BASIC-TFTD) is introduced to take advantage of these thin-film SL structures.
3.2 AND 3.8 μm Emission and Lasing in AlGaAsSb/InGaAsSb Double Heterostructures with Asymmetric Band Offset Confinements
Authors: Mikhailova M. P. , Zhurtanov B. E. , Moiseev K. D. , Imenkov A. N. , Ershov O. G. , Yakovlev Yu. P.
Published: April 2011

We report the first observations of electroluminescence (EL) and lasing in laser structures with high Al-content (x=0.64, Eg=1.474 eV) cladding layers and a narrow-gap InGaAsSb active layer (Eg=0.326 eV at T=77K). The structures are LPE-grown lattice-matched to GaSb substrate. Band energy diagrams of the laser structures had strongly asymmetric band offsets. The heterojunction between high Al-content layer and InGaAsSb narrow-gap active layer has a type II broken-gap alignment at 300K. In this laser structure spontaneous emission was obtained at λ=3.8μm at T=77K and λ=4.25 μm at T=300K. Full width at half maximum (FWHM) of emission band was 34 meV. Emission intensity decreased by a factor of 30 from T=77K to 300K. Lasing with single dominant mode was achieved at λ=3.774 μm (T=80K) in pulsed mode. Threshold current as low as 60 mA and characteristic temperature T0=26K were obtained at T=80–120K.
Non-Equilibrium InSb/InAISb Diodes Grown by MBE
Authors: Johnson A D , Smout A B J , Cairns J W , Pryce G J , Pidduck A J , Jefferies R , Ashley T , Elliott C T
Published: April 2011

The application of non-equilibrium transport techniques to Molecular Beam Epitaxy (MBE) grown InSb/InAlSb heterostructure diodes has produced practical devices such as midinfrared LED's and negative luminescent sources that operate at room temperature. By extending the epitaxial growth to vicinal InSb substrates it has been demonstrated that the temperature window for high quality epitaxy can be lowered by ∼12°C, giving greatly improved epilayer morphology. The degree of misorientation needed for given growth temperatures is shown from Atomic Force Microscope (AFM) measurements to be only ∼2°. In addition, the lower growth temperature gives improved dopant activation, lower trap densities and lower reverse bias leakage currents, with consequent benefits to device performance.
GaAs/AlGaAs Intersubband MID-Infrared Emitter
Authors: Strasser G. , Gianordoli S. , Hvozdara L. , Bichl H. , Unterrainer K. , Gornik E. , Kruck P. , Helm M. , Heyman J. N.
Published: April 2011

We report here the growth and characterization of intersubband quantum well structures based on the GaAs/AlGaAs material system, designed to emit radiation at approximately 7 micrometers. We present transport behavior, infrared photocurrent spectra, and electroluminescence data. First attempts to fabricate a laser structure from this devices encountered difficulties with the electrical properties of the AIGaAs waveguide cladding layers. Thus, we present measurements with different waveguide concepts as doped AlAs cladding layers and doped superlattice cladding structures.
Germanium Far Infrared Blocked Impurity Band Detectors
Authors: Olsen C. S. , Beeman J. W. , Hansen W. L. , Hallerab E. E.
Published: April 2011

We report on the development of Germanium Blocked Impurity Band (BIB) photoconductors for long wavelength infrared detection in the 100 to 250.μm region. Liquid Phase Epitaxy (LPE) was used to grow the high purity blocking layer, and in some cases, the heavily doped infrared absorbing layer that comprise theses detectors. To achieve the stringent demands on purity and crystalline perfection we have developed a high purity LPE process which can be used for the growth of high purity as well as purely doped Ge epilayers. The low melting point, high purity metal, Pb, was used as a solvent. Pb has a negligible solubility <1017 cm−3 in Ge at 650°C and is isoelectronic with Ge. We have identified the residual impurities Bi, P, and Sb in the Ge epilayers and have determined that the Pb solvent is the source. Experiments are in progress to purify the Pb. The first tests of BIB structures with the purely doped absorbing layer grown on high purity substrates look very promising. The detectors exhibit extended wavelength cutoff when compared to standard Ge:Ga photoconductors (155 μm vs. 120 μm) and show the expected asymmetric current-voltage dependencies. We are currently optimizing doping and layer thickness to achieve the optimum responsivity, Noise Equivalent Power (NEP), and dark current in our devices.
Modular 64×64 CdZnTe Arrays With Multiplexer Readout for High-Resolution Nuclear Medicine Imaging
Authors: Woolfenden J. M. , Barber H. B. , Barrett H. H. , Dereniak E. L. , Eskin J. D. , Marks D. G. , Matherson K. J. , Young E. T. , Augustine F. L.
Published: April 2011

We are developing modular arrays of CdZnTe radiation detectors for high-resolution nuclear medicine imaging. Each detector is delineated into a 64×64 array of pixels; the pixel pitch is 380 ptm. Each pixel is connected to a corresponding pad on a multiplexer readout circuit. The imaging system is controlled by a personal computer. We obtained images of standard nuclear medicine phantoms in which the spatial resolution of approximately 1.5 mm was limited by the collimator that was used. Significant improvements in spatial resolution should be possible with different collimator designs. These results are promising for high-resolution nuclear medicine imaging.
Current Issues of High-Pressure Bridgman Growth of Semi-Insulating CdZnTe
Authors: Szeles Csaba , Eissler Elgin E.
Published: April 2011

The availability of large-size, detector-grade CdZnTe crystals in large volume and at affordable cost is a key to the further development of radiation-detector applications based on this II-VI compound. The high pressure Bridgman technique that supplies the bulk of semiinsulating CdZnTe crystals used in X-ray, γ-ray detector and imaging devices at present is hampered by material issues that limit the yield of large-size and high-quality crystals. These include ingot cracking, formation of pipes, material homogeneity and the reproducibility of the material from growth to growth. The incorporation of macro defects in the material during crystal growth poses both material quality limitations and technological problems for detector fabrication. The effects of macro defects such as Te inclusions and pipes on the charge-transport properties of CdZnTe are discussed in this paper. Growth experiments designed to study the origin and formation of large defects are described. The importance of material-crucible interactions and control of thermodynamic parameters during crystal growth are also addressed. Opportunities for growth improvements and yield increases are identified.
Dopants in HgCdTe
Authors: Berding M. A. , Sher A.
Published: April 2011

In this paper we discuss our ab initio calculations of native point defect and impurity densities in HgCdTe. Our calculations have explained the experimental finding in general, and in particular have explained the in-active incorporation of the group VII elements under mercury-deficient conditions; have shown that the group I elements have a large fraction of interstitial incorporation, thereby explaining their fast diffusion; and have described a microscopic mechanism for the amphoteric behavior of the group V elements. We discuss the trends found among the compounds in terms of the underlying bond strengths to understand why the various elements behave the way they do.
Substrate Misorientation Effects on Epitaxial GaInAsSb
Authors: Wang C. A. , Choi H. K. , Oakley D. C. , Charache G. W.
Published: April 2011

The effect of substrate misorientation on the growth of GaInAsSb was studied for epilayers grown lattice matched to GaSb substrates by low-pressure organometallic vapor phase epitaxy. The substrates were (100) misoriented 2 or 6° toward (110), (111)A, or (111)B. The surface is mirror-like and featureless for layers grown with a 6° toward (111)B misorientation, while a slight texture was observed for layers grown on all other misorientations. The optical quality of layers, as determined by the full width at half-maximum of photoluminescence spectra measured at 4K, is significantly better for layers grown on substrates with a 6° toward (111)B misorientation. The incorporation of Zn as a p-type dopant in GaInAsSb is about 1.5 times more efficient on substrates with 60 toward (111)B misorientation compared to 2° toward (110) misorientation. The external quantum efficiency of thermophotovoltaic devices is not, however, significantly affected by substrate misorientation.
Dark Soliton Formation for Light-Induced Waveguiding in Photorefractive inP:Fe
Authors: Chauvet M. , Hawkins S. A. , Salamo G. J. , Segev M. , Bliss D. F. , Bryant G.
Published: April 2011

We present experimental evidence for the observation of steady-state dark photorefractive screening solitons trapped in bulk InP:Fe.
Photoacoustic Study of The Effect of 0.9 eV Light Illumination in Semi-Insulating GaAs
Authors: Fukuyama Atsuhiko , Akashi Yoshito , Yoshino Kenji , Maeda Kouji , Ikari Tetsuo
Published: April 2011

The effect of the secondary light illumination of hv = 0.9 eV on the photoquenched and the enhanced states in semi-insulating GaAs are investigated by using piezoelectric photoacoustic (PPA) measurements at 80 K. It is found that the secondary light causes an optical recovery from EL2* to EL2° and this is in agrezment with the result reported by using infrared optical absorption measurements. We observed a broad peak around 0.9 eV after the secondary light illumination for the first time. The most important finding is that the PPA spectra after the secondary light illumination on the quenched and the enhanced states are the same in the whole photon energy region. We concluded that the secondary light of hv = 0.9 eV induces both an optical recovery and generation of metastable state of the EL6 level. The difference of the transformation rates of these two processes explains well the observed complex natures of the PPA signal under the secondary light illumination.
High Resolution X-Ray Reflectometry and Diffraction of CaF2/Si(111) Structures Grown by Molecular Beam Epitaxy
Authors: Abramof E. , Ferreira S. O. , Rappl P. H. O , Ueta A. Y. , Boschetti C. , Closs H. , Motisuke P. , Bandeira I. N.
Published: April 2011

CaF2 layers were grown by molecular beam epitaxy on differently prepared Si(111) substrates. X-ray reflectivity spectra were measured and fitted. From the fitting process, the thickness of the CaF2 layer was precisely (within 1 Å) determined and the CaF2/Si interface roughness was also obtained. This roughness was used as an evaluation parameter for the quality of the layers. The CaF2/Si sample from which the intentional oxide was desorpted at 800°C inside the growth chamber exhibited the most clear x-ray reflectivity spectrum with very well resolved interference fringes. The epitaxial relations of the CaF2/Si samples grown at temperatures between 250 and 700°C were determined from x-ray diffraction analysis.
Auger Recombination in Antimony-Based, Strain-Balanced, Narrow-Band-Gap Superlattics
Authors: Olesberg J. T. , Boggess Thomas F. , Anson S. A. , Jan D.-J. , Flatté M. E. , Hasenberg T. C. , Grein C. H.
Published: April 2011

Time-resolved all-optical techniques are used to measure the density and temperature dependence of electron-hole recombination in an InAs/GaInSb/InAs/AlGaInAsSb strain-balanced superlattice grown by molecular beam expitaxy on GaSb. This 4 μm bandgap structure, which has been designed for suppressed Auger recombination, is a candidate material for the active region of mid-infrared lasers. While carrier lifetime measurements at room temperature show unambiguous evidence of Auger recombination, the extracted Auger recombination rates are considerably lower than those reported for bulk materials of comparable bandgap energy. We find that the Auger rate saturates at carrier densities comparable to those required for degeneracy of the valence band, illustrating the impact of Fermi statistics on the Auger process. The measured results are compared with theoretical Auger rates computed using a band structure obtained from a semi-empirical 8-band K.p model. We find excellent agreement between theoretical and experimental results when Umklapp processes in the growth direction are included in the calculation. Measured recombination rates from 50 to 300 K are combined with calculated threshold carrier densities to determine a material To value for the superlattice.
Metal Oxide / Silicon Heterostructures: New Solutions for Different Optoelectronic Applications
Authors: Malik A. , Martins R.
Published: April 2011

In this paper we report the success in fabricating FTO/Si surface-barrier photodiodes produced by spray pyrolysis deposition technique, under ambient conditions. Three types of photodetectors for low-voltage-bias operation were developed based on high-resistivity silicon: 1. X-Ray detectors with energy resolution of 16.5% at 661.5 keV (137Cs source), consisting of surface-barrier PIN photodiode with an active area of 50 mm2 operating at 5V reverse bias, scintillator based on monocrystalline Bi4Ge3O12 and preamplifier (noise of 250 e− RMS.); 2. Fastresponse surface-barrier FTO/I n−-n+ silicon epitaxial photodiodes, operating at 10 V bias with rise times of 2 ns at λ = 0.85 μm; 3. Radiation-resistant drift epitaxial surface-barrier PIN photodiodes for unbiased operating conditions, with an exponential impurity distribution in a 8 μm thick epitaxial layer. A built-in electrical field due to the carrier concentration distribution in the epitaxial layer provides a considerable improvement in the “critical fluence” value (3× 1014 cm−2 ) for neutron irradiation.
Scintillator - Photodiode Linear Arrays for X-Ray Inspection System
Authors: Ignatov S. M. , Potapov V.N. , Fedin A. V. , Chirkin V. M. , Urutskoev L. I. , Gostilo V. V. , Kondrashov V. V. , Sokolov A. D.
Published: April 2011

The evaluations of the following performances of detectors for design of the radiographic system were carried out by mathematical simulation method and experimentally: sensitivity to absorbed energy, noise level, form of apparatus function for spatial resolution of detectors array.

The results of calculations were used for designing of CdWO4-Si arrays with optimal sizes of scintillator and photodiode for resolution ability. At the given stage the quality of radiation detectors was evaluated by spectroscopic methods. At the bias voltage on photodiode 24 V, the sensitivity of detectors has made up (0,95–1,00) × 10−21 C / eV, noise level - (1,50–1,75) ×10−16 C together with electronic noise. Dynamic range at absorbed energy by separate detector is more than 105, what is sufficient to get required image contrast.
Photochromic Liquid Hydrogels as Hosts for Holographic Materials
Authors: White R. L. , Hsu Y. Y. , Cooper T. M. , Gresser J. D. , Wise D. L. , Trantolo D. J.
Published: April 2011

The goal of this project is to develop, fabricate, and test advanced optical materials for potential applications to real-time holography based on liquid crystalline polymer hydrogels. In this project, we are investigating the feasibility of increasing holographic capacity and lifetime by coupling a photochromic spyropyran dye to in a liquid crystalline polymer in which cholesteric order has been ‘captured.’ ‘Capture’ is being approached using a unique in-plane poling process with the helical polypeptide poly(α-benzyl-L-glutamate), PBLG, a biopolymer which is capable of maintaining cholesteric order in a liquid crystalline state. Subsequent in situ crosslinking of this aligned biopolymer is projected to offer increased birefringence of the host in the writing of a hologram. Given that a key issue is the magnitude of the real component of the refractive index, increasing the bireflingence may be a useful approach. In writing the hologram, the liquid crystals (LC's) go from isotropic to an ordered dispersion, a property which can be captured via crosslinking to improve holographic lifetime. In the following, the characterization of an aligned host LC system based on the biopolymer poly(α-benzyl-L-glutamate), PBLG, is presented. Inplane alignment is shown to depend on a number of variables, most notably the choice of solvent, polymer molecular weight, and field strength. The results show that optimal alignment of the PBLG LC is achieved with a 2.5% (w/w) concentration of a 118kD biopolymer in methylene chloride in an applied field of 10 kV/cm. Subsequent work will exploit this system as a host for a spiropyran dye for improved holographics.
Synthesis and Electroluminescence Study of a Novel Copolymer:Poly(Phenylene Vinylene-Co-Quinoline Vinylene)
Authors: Kasim Ramesh K. , Derecskei Bela , Pomerantz Martin , Elsenbaumer Ronald L.
Published: April 2011

High-efficiency polymer light-emitting diodes (LEDs) are often fabricated using multilayered structures with separate carrier transport and light emission layers. Recently, we reported on the synthesis and electroluminescence (EL) characteristics of poly(2,6-quinoline vinylene) (PQV) and its potential for use as an electron transport layer in poly(phenylene vinylene) (PPV) LEDs. To take advantage of the high emission efficiency of PPV and electron accepting ability of PQV, a copolymer of PPV and PQV, poly(phenylene vinylene-co-quinoline vinylene) (PPVQV) was synthesized via the precursor polymer route and converted to the conjugated form by thermal elimination. When used as the emissive layer with Indium-Tin Oxide (ITO) and aluminum as positive and negative electrodes respectively, PPVQV emitted blue light at an onset electric field of 1.05x 106 V/cm and emission efficiency of 0.08%. Improved efficiencies of the order of 0.15% were obtained when blends of copolymer with PPV were used in conjunction with PPV in a multi-layered structure. Along with copolymer chemical characterization data, results from EL studies on single and multi-layered devices are discussed. We also report on a simple and costeffective chemical deposition of silver for the negative electrode in polymer LEDs.