bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermopower, Electrical and Hall Conductivity of Undoped and Doped Iron Disilicide Single Crystals
Authors: Heinrich A. , Behr G. , Griessmann H. , Teichert S. , Lange H.
Published: April 2011

The electrical transport properties of β-FeSi2 single crystals have been investigated in dependence on the purity of the source material and on doping with 3d transition metals. The transport properties included are electrical conducticvity, Hall conductivity and thermopower mainly in the temperature range from 4K to 300K. The single crystals have been prepared by chemical transport reaction in a closed system with iodine as transport agent. In undoped single crystals prepared with 5N Fe both electrical conductivity and thermopower depend on the composition within the homogeinity range of β-FeSi2 which is explained by different intrinsic defects at the Sirich and Fe-rich phase boundaries. In both undoped and doped single crystals impurity band conduction is observed at low temperatures but above 100K extrinsic behaviour determined by shallow impurity states. The thermopower shows between 100K and 200K a significant phonon drag contribution which depends on intrinsic defects and additional doping. The Hall resistivity is considered mainly with respect to an anomalous contribution found in p-type and n-type single crystals and thin films. In addition doped single crystals show at temperatures below about 130K an hysteresis of the Hall voltage. These results make former mobility data uncertain. Comparison will be made between the transport properties of single crystals and polycrystalline material.
Overview of Industry Interest in New Thermoelectric Materials
Authors: Lyon H.B.
Published: April 2011

The technology base for air conditioning, refrigeration, component cooling below ambient temperatures and power generation will be required to meet several new challenges. The main lines of these challenges will be presented in a way which relates them to the several new thermoelectric materials and materials engineering options being pursued by the research community. The potential benefits of thermoelectric devices are only partially met by enhancing the figure of merit ZT, the nature of the design challenge and the resulting systems approach are presented. The research and the industry are entering into a new era.
Mapping Detector Response Over the Area of a CdZnTe-Multiple-Electrode Detector
Authors: Lingren C. L. , Apotovsky B. , Butler J. F. , Doty F. P. , Friesenhahn S. J. , Oganesyan A. , Pi B. , Zhao S.
Published: April 2011

Semiconductor multiple-electrode detectors have been developed for the purpose of reducing effects of hole trapping in room-temperature radiation detectors.1,2 Some reported geometries maintain a nearly-uniform electric field inside the detector, but others generate an electric field that is very non-uniform and highly-concentrated at the anode. This paper reports the results of mapping such a detector (having a non-uniform electric field) with a finely collimated gamma-ray beam to determine the detector response as a function of position.
PbTe(Ga) – New Multispectralir Photodetector
Authors: Belogorokhov A. I. , Ivanchik I. I. , Khokhlov D. R.
Published: April 2011

Doping of the lead telluride - narrow-gap semiconductor - with gallium results under certain conditions in the Fermi level pinning in the gap thus providing the semiinsulating state of material. Besides that, the persistent photoconductivity effect is observed at a temperatures T < T, = 80 K. The photoresponse kinetics consists of two parts: the slow one with the characteristic time tchar, going up to 104 s at T = 4.2 K, and the fast part with tchar of the order of 10 ms. We have measured the spectra of a fast part of the photoresponse using the Fouriertransform spectrometer “Bruker” IFS- 113v. The photoconductivity is observed in two spectral regions: in the middle- and far - infrared. Response in the middle-infrared consists of the ordinary fundamental band and a strong superimposed resonance-like structure just at the bandgap energy. The position of this spectral line may be tuned in a wide range (3.5–5.5) Pim by variation of temperature and/or composition of a lead telluride-based alloy. This middle-infrared photoresponse becomes considerable already at T = 160 K. The photoresponse in the far-infrared may be depending on the excitation conditions an analogous resonance-like structure at a wavelength 70 μm, or a broad band with the cutoff wavelength at least higher than 500 μm, which is the highest cutoff wavelength for the photon detectors observed up to date.
Reactive Ion Etching (RIE) Induced p- to n-Type Conversion in Extrinsically Doped p-Type HgCdTe
Authors: Musca C. A. , Smith E. P. G. , Siliquini J. F. , Dell J. M. , Antoszewski J. , Piotrowski J. , Faraone L.
Published: April 2011

Mercury annealing of reactive ion etching (RIE) induced p- to n-type conversion in extrinsically doped p-type epitaxial layers of HgCdTe (x=0.3 1) has been used to reconvert n-type conversion sustained during RIE processing. For the RIE processing conditions used (400mT, CH4/H2, 90 W) p- to n-type conversion was observed using laser beam induced current (LBIC) measurements. After a sealed tube mercury anneal at 200°C for 17 hours, LBIC measurements clearly indicated no n-type converted region remained. Subsequent Hall measurements confirmed that the material consisted of a p-type layer, with electrical properties equivalent to that of the initial as-grown wafer (NA-ND=2×1016 cm−3,.=350 cm2.V−1. S−1).
Dx-Like Centers and Photoconductivity Kinetics in PbTe-Based Alloys
Authors: Akimov B. A. , Bogoyavlenskiy V. A. , Vasil'kov V. N. , Ryabova L. I.
Published: April 2011

Results of the study of photoconductivity (PC) kinetics, thermally stimulated currents (TSC) and electrothermal instabilities in PbTe(Ga), Pb1−xMnxTe(In) (0<X<0. 11) single crystals and Pb1-x-ySnxGeyTe(In) (0.06<X<0.2; 0.06<Y<0.12) films are presented. The impurity states in these compounds exhibit a DX-like behavior. Reconstruction of the energy spectrum of solid solutions induced by the composition (X,Y) variation allows us to conclude that the metastable electronic states take par in PC kinetics and accelerate the relaxation process when the metastable levels appear inside the energy gap.
Reduced Al-Ga interdiffusion in GaAs/AlGaAs multiple quantum well structure by introducing low hydrogen content SiNx capping layer for dielectric cap quantum well disordering
Authors: Choi W. J. , Han S. M. , Shah S. I. , Choi S. G. , Woo D. H. , Lee S. , Kim H. J. , Han I. K. , Kim S. H. , Lee J. I. , Kang K. N. , Cho J.
Published: April 2011

Dielectric cap quantum well disordering (DCQWD) of GaAs/AlGaAs multiple quantum well (MQW) structure was carried out by using SiNx. capping layer grown by plasma enhanced chemical vapor deposition (PECVD). By varying the NH3 flow rate with fixed SiH4 flow rate during the SiNx. growth, the characteristics of the capping film were varied. There was an increase in the energy shift of quantum well photoluminescence (PL) peak after thermal treatment of the samples with rapid thermal annealing (RTA) as the NH3 flow rate was increased, although the thickness of SiNx decreased. This is thought to be due to the increase of hydrogen content in SiNx. film grown at higher NH3 flow rate.
Interdiffusion Mechanisms in GaAs/AlGaAs Quantum Well Heterostructures Induced by SiO2 Capping and Annealing
Authors: Pépin A. , Vieu C. , Schneider M. , Launois H. , Rao E. V. K.
Published: April 2011

We have investigated intermixing enhancement in GaAs/AlGaAs quantum well heterostructures achieved by SiO2 capping obtained by rapid thermal chemical vapor deposition. Evidence of fast Ga pumping inside the SiO2 layer during anneal and simultaneous generation of excess Ga vacancies under the SiO2/GaAs interface is presented. A simple model involving the thermal stress arising from the difference in thermal expansion coefficients between SiO2 and GaAs, is proposed to account for the abnormally fast Ga vacancy diffusion inside the heterostructure. A spatial control of the interdiffused areas can be achieved if a suitable stress field is imposed on the semiconductor surface by the capping layers. We show experimental evidence of this effect using a specific patterning of SiO2/Si3N4 bilayers.
Chemical Bonding on GaAs (001) Surfaces Passivated Using SeS2
Authors: Sun Jingxi , Seo Dong Ju , O'Brien W. L. , Himpsel F. J. , Kuech T. F.
Published: April 2011

Selenium disulfide has been demonstrated to be an effective passivant for GaAs (001) surfaces. This chemical treatment can be more robust and effective in reducing surface-states-based Fermi level pinning than other analogous chemical treatments. We have studied SeS2-passivated surfaces, formed by treatment of GaAs in SeS2:CS2 solution, with synchrotron radiation photoemission spectroscopy. The SeS2-treated surface consists of a chemically stratified structure of several atomic layers thickness. The As-based sulfides and selenides appear to reside on the outermost surface with the Ga-based compounds adjacent to the bulk GaAs substrate. The motion of the Fermi level within the band gap was monitored during controlled annealing conditions allowing for the specific chemical moieties responsible for the reduction in surface charge to be identified. As-based species are removed at low annealing conditions with little motion of the Fermi level. GaSe-based species, formed on the surface, are clearly shown to be associated with the unpinning of the Fermi level.
Surface and Interface Properties of InSb Epitaxial Thin Films Grown on Gaas by Low Pressure Metalorganic Chemical Vapor Deposition
Authors: Li K. , Tan K. L. , Pelczynski M. , Fenge Z. C. , Wee A. T. S. , Lin J. Y. , Ferguson I. , Stall R. A.
Published: April 2011

There is increasing interest in the epitaxial growth of high quality InSb thin films on GaAs substrates for many device applications such as infrared optoelectronics. The large lattice mismatch (14.6%) between InSb and GaAs has meant that both growth techniques and conditions have a large influence on the interface properties and consequently the film quality. A surface science study, by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) together with Nomarski microscopy, on the surface and interface properties of InSb/GaAs by metalorganic chemical vapor deposition is presented. It is found fromthe XPS data that the ambient surface is composed of InSb, In2O3, Sb2O3 and Sb2O5. The interdiffusion phenomena are studied by AES depth profiling; the width of interdiffusion region is determined to be 50±10 nm for all the samples grown at different V/III ratios. This is narrower than the data previously obtained for InSb/GaAs interfaces produced by metalorganic magnetron sputtering. The results also demonstrate that uniform and stoichiometric InSb films have been obtained, and that the reproducibility of the MOCVD technique is excellent.
Monolithic 1.55μm Surface Emitting Laser Structure With In0.53Al0.14Ga0.33As/In0.52Al0.48As Distributed Bragg Reflector and Single Cavity Active Layer Grown by Meatalorganic Chemical Vapor Deposition Method
Authors: Baek J.-H. , Lee B. , Han W. S. , Smith J. M. , Jeong B. S. , Lee E.-H.
Published: April 2011

Vertical cavity surface emitting laser (VCSEL) structure designed at 1.55 μm was grown by low pressure metalorganic chemical vapor deposition method. The VCSEL structure contains top and bottom distributed Bragg reflector (DBR) and single cavity active layer. The DBR was grown with In0.53Al0.14Ga0.33As and In0.52Al0.48As quarter lambda wavelength layer, alternatively. The growth temperature was as high as 750°C to prevent ordering and phase separation of the In0 52Al0.48As layer. The In0.52Al0.48As buffer layer was subsequently grown on the InP buffer layer in order to make an abrupt uniform interface. Unity reflectance was achieved at the center of 1.55 μm with 35.5 pairs undoped DBR layer. The reflectance spectrum of undoped DBR showed a wide flat-band region (greater than 50 nm) where the reflectivity was more than 99.5 %. The center wavelength of DBR was previously determined by an in-situ laser reflectometry technique during the growth of the whole structure. An infrared laser operating at 1.53 μm, which was the design wavelength of DBR layer was used as an in-situ measuring tool. The In0.53Ga0.47As multiple quantum well was used as a cavity layer. The reflectance spectrum of VCSEL structure, which included a single cavity active layer, showed excellent square shaped stop band and also showed an absorption region at the center of the flat band.
High Power Mid-Infrared Interband Cascade Lasers
Authors: Yang B. H. , Zhang D. , Yang Rui. Q. , Lin C.-H. , Murry S. J. , Wu H. , Pei S. S.
Published: April 2011

We have demonstrated 4-μm InAs/InGaSb/AlSb interband cascade lasers with optical output power close to 0.5 W per facet with 1-μs pulses at 1 kHz repetition rate. At 10% duty cycle, an average output power ∼20 mW was realized. External and internal quantum efficiencies exceeding 200% have been achieved at 80 K.
Influence Of Structural Defects And Zinc Composition Variation On The Device Response Of Cdl-xZnxTe Radiation Detectors
Authors: Yoon H. , Scyoc J. M. Van , Gilbert T. S. , Goorsky M. S. , Brunett B. A. , Lund J. C. , Hermon H. , Schiebert M. , James R. B.
Published: April 2011

Zinc composition variation and gross structural defects including grain and tilt boundaries, twins, and mechanical cracks in high pressure Bridgman Cd1−xZnxTe are characterized and correlated to various detector-related responses. Triple axis x-ray diffraction, double crystal x-ray topography, infrared microscopy, and etch pit density measurements are used to reveal and quantify the spatial distribution and the nature of the structural defects. Mechanical cracks in the material are found to act as conductive ‘shorting paths’, indicated by excessive leakage currents and reduced charge (electron) collection measured along these cracks. Reduced charge collection is also obtained across grain boundaries and in regions with poor crystallinity, indicating that they serve as carrier recombination sites. Finally, the effects of the zinc composition variation on the measured leakage current and the amount of electrons collected are found to be masked by gross structural defects. These characterization techniques provide a wealth of information which can be used not only to study the relationship between the structural and device properties of CdZnTe but also to screen production material for subsequent device fabrication.
Performance of Prototype Segmented CdZnTe Arrays
Authors: Parsons A. , Palmer D. M. , Kurczynski P. , Barbier L. , Barthelmy S. , Bartlett L. , Gehrels N. , Krizmanic J. , Stahle C. M. , Tueller J. , Teegarden B.
Published: April 2011

The Burst and All Sky Imaging Survey (BASIS) is a proposed mission to provide ∼3 arc second locations of approximately 90 Gamma-Ray Bursts (GRBs) per year. The BASIS coded aperture imaging system requires a segmented detector plane able to detect the interaction position of (10 - 150 keV) photons to less than 100 μm. To develop prototype detector arrays with such fine position resolution we have fabricated many 15 mm × 15 mm × 2 mm 100 μm pitch CdZnTe strip detectors. We have assembled these fine pitch CdZnTe strip detectors into prototype 2 × 2 and 6 × 6 element arrays read out by ASIC electronics. The assembly and electronics readout of the 6 × 6 flight prototype array will be discussed, and preliminary data illustrating the uniformity and efficiency of the array will be presented.
Effect Of Thermal Annealing In Bi And Zn Melts On Local Centers In Znse
Authors: Korotkov V. A. , Kovalev L. E. , Bruk L. I. , Gorea O. S. , Ketrush P. I. , Malikova L. V.
Published: April 2011

Time-resolved photoluminescence (TRPL) at T=4,2K, electron paramagnetic resonance (EPR) in the range of 4,2K–77K, and wavelength modulated transmittance (WMT) spectra for both undoped and annealed in Bi and Zn melts ZnSe single crystals have been investigated. It is found that the annealing in Bi melts leads to recovery of crystal structure. This supposition is based on the increase of fine and hype fine interaction of residual Mn2+, ions with the simultaneous decrease of the EPR signals line width and the decrease of the F-center line. Furthermore, the band with λmax=520 nm disappears, while exciton band I1 (λmax=445 nm) and edge band Q0 – DAP (λmax=460,2 nm), involving AlZn – LiZn, pairs, become more revealed. At the same time, band narrowing of the TRPL spectra was observed. The annealing in Zn melt causes the increase of the number of F-center. From WMT spectra the energy position of local centers and the dominant influence on impurities and defects of the crystal structure were investigated.
New Applications and Analysis of Avalanche Photodiodes as Detectors for Electrons Ranging from 10 KeV to 300 KeV
Authors: Kodama T. , Osakabe N. , Endo J. , Tonomura A. , Urakami T. , Ohsuka S. , Tsuchiya H. , Tsuchiya Y.
Published: April 2011

New applications of avalanche photodiodes as fast timing detectors for electrons ranging from 10 keV to 300 keV together with an analysis of the response of silicon avalanche photodiodes to the electrons are reported.
A Front End Readout Electronics ASIC Chip for Position Sensitive Solid State Detectors
Authors: Kravis S. D. , Tümer T. O. , Visser G. J. , Maeding D. G. , Yin S.
Published: April 2011

A mixed signal Application Specific Integrated Circuit (ASIC) chip for front end readout electronics of position sensitive solid state detectors has been manufactured. It is called RENA (Readout Electronics for Nuclear Applications). This chip can be used for both medical and industrial imaging of x-rays and gamma rays. The RENA chip is a monolithic integrated circuit and has 32 channels with low noise high input impedance charge sensitive amplifiers. It works in pulse counting mode with good energy resolution. It also has a self triggering output which is essential for nuclear applications when the incident radiation arrives at random. Different, externally selectable, operational modes that includes a sparse readout mode is available to increase data throughput. It also has externally selectable shaping (peaking) times.
Study on Deep Level Traps in P-Hgcdte With Dltfs
Authors: Kawata S. , Sugiyama I. , Kajihara N. , Miyamoto Y.
Published: April 2011

We studied the characteristics of deep-level traps in p-type HgCdTe diodes using the Deep Level Transient Fourier Spectroscopy (DLTFS) method. For both holes and electrons, two types of traps were observed. The DLTFS signal intensity of one type of trap increased with the carrier density in the HgCdTe, while the other did not exhibit a monotonic increase. While measuring the stability of these traps during cooling cycles, the DLTFS signal intensity of the first group was almost constant while that of the latter fluctuated with every cooling cycle. Stable traps originated from Hg vacancies, unstable traps are attributed to vacancy-impurity complex defects.
Multifunctional Hyper-Structured Molecules
Authors: Wada T. , Zhang Y. , Aoyama T. , Kubo Y. , Sasabe H.
Published: April 2011

To fill the gap between molecular design and the architecture of three-dimensional functional structures, we propose novel hyper-structured molecules (HSMs) based on welldefined and topologically controlled molecular systems. To this end we have developed carbazole dendrimers, trimers, cyclic oligomers and chromogenic calix[4]arenes as HSMs. Photorefractivity was selected as the primary target function of these HSMs. Oligomers developed in our laboratory exhibit intrinsic photocarrier generation, transport, electro-optic, film-forming and poling properties. These multifunctional properties allow us to demonstrate optical image processing using optical phase conjugation. The topological shapes of indoaniline-derived calix[4]arenes were studied by hyper-Rayleigh scattering. The two indoaniline moieties in calix[4]arene derivatives were pre-aligned so as to enhance the net molecular hyperpolarizability. Besides dendric oligomers, cyclic oligomers can be used as a molecular platform which allows molecular level tuning of shape, size and topology for superior opto-electronic functions.
Synthesis of a New Class of Polyphenylated Phthalocyanines and Metallophthalocyanines
Authors: Walsh Christopher J. , Mandal Braja K.
Published: April 2011

We wish to report the synthesis of a new class of peripherally modified, polyphenylated phthalocyanines (Pcs) and metallophthalocyanines (MPcs). These compounds were synthesized by cyclic tetramerization of functionalized pentaphenylbenzophthalonitriles. The phthalonitriles were made in several steps via Diels-Alder cycloaddition between phenylethynylphthalonitrile and substituted tetracyclones. The polyphenylated design leads to enhanced solubility. Thin films can be cast from solutions of the butoxy and dodecaoxy substituted polyphenylated Pcs and MPcs. Cyclodehydrogenation of the Pcs was studied in an attempt to produce planar systems. Preliminary results indicate the pentaphenyl substituent is too bulky to planarize under the conditions employed.
Optically and Electrically Excited Semiconducting polymer Structures
Authors: Becker H. , Burns S. E. , Denton G. J. , Harrison N. T. , Tessler N. , Wilkinson T. D. , Friend R. H.
Published: April 2011

We report recent advances in the development of conjugated polymer device structures. We have fabricated vertical microcavity structures in which the optical path distance is tunable through control of the orientation of a liquid crystal layer, and demonstrate cavity tuning over 59 nm. We show that this structure allows convenient matching of cavity modes to the freespace emission spectrum from poly(r henylene vinylene), PPV. We have investigated the operation of electrically-excited polymer LEDs with short pulse operation, and have achieved current densities above 103 A/cm2 and peak brightnesses of up to 5 × 106 cd/m 2. We have measured the optical absorption due to the injected carriers under these drive conditions, and find an absorption band near 1.6 eV which we attribute to the presence of polarons. This allows measurement of the injected charge density, from which we deduce that carrier mobilities are strongly enhanced at high fields, reaching values of 4 x 10−2 cm2/Vsec for PPV diodes.
Effect of Morphology on the Electrical Transport Properties of Polyaniline Films for Electronic Applications
Authors: Hardaker S. S. , Eaiprasertsak K. , Yon J. , Gregory R. V. , Tessema G. X.
Published: April 2011

Although it is well known that the oxidation state of polyaniline is an important characteristic, there are few reports of its influence on the development of morphology and electrical properties in fibers and films. In this work, differential scanning calorimentry is used in conjunction with measurements of temperature dependence of conductivity and thermoelectric power to elucidate the intimate relationship between structure and properties. By increasing the amount of chemical reduction of polyaniline solutions, films are prepared which exhibit a thermal transition between 300 and 385 °C, indicative of melting. Increasing the chemical reduction also increases the conductivity of iodine doped films. The most reduced film exhibited a semiconductor transport mechanism, while the other films could be modeled with a quasi-one dimensional variable range hopping mechanism. The temperature dependence of conductivity also showed increasing order for increasing reduction, consistent with the DSC results.
Molecular Self-Assembly Routes to Optically Functional Thin Films: Electroluminescent Multilayer Structures
Authors: Li W. , Malinsky J. E. , Chou H. , Ma W. , Geng L. , Marks T. J. , Jabbour G. E. , Shaheen S. E. , Kippelen B. , Peyghambarian N. , Andersont J. , Lee P. , Armstrong N.
Published: April 2011

This contribution describes the use of layer-by-layer self-limiting siloxane chemisorption processes to self-assemble structurally regular multilayer organic LED (OLED) devices. Topics discussed include: 1) the synthesis of silyl-functionalized precursor molecules for hole transport layer (HTL), emissive layer (EML), and electron transport layer (ETL) self-assembly, 2) the use of layer-by-layer self-assembly for ITO electrode modification/passivation/hole-electron balancing in a vapor-deposited device, 3) the microstructure/chemical characterization of HTL self-assembly using a prototype triarylamine precursor, 4) fabrication and properties of a hybrid self-assembled + vapor deposited two-layer LED, 4) fabrication and properties of a fully self-assembled two-layer OLED.
Controlling Materials Architecture on the Nanometer-Scale: PPV Nanocomposites Via Polymerizable Lyotropic Liquid Crystals
Authors: Smith Ryan C. , Deng Hai , Fischer Walter M. , Gin Douglas L.
Published: April 2011

We have developed a general strategy for the construction of ordered nanocomposites with hexagonal symmetry, using polymerizable lyotropic (i.e., amphiphilic) liquid crystals. In this approach, self-organizing lyotropic liquid-crystalline monomers are used to form an ordered template matrix in the presence of a reactive hydrophilic solution. Subsequent photopolymerization to lock-in the matrix architecture, followed by initiation of chemistry within the ordered hydrophilic domains to afford solid-state fillers, yields the anisotropic nanocomposites. Composites have been synthesized that have a regular hexagonal arrangement of extended poly(p-phenylenevinylene) (PPV) domains, with a regular interchannel spacing of 4 nm. The photoluminescence of these materials is significantly altered from that of bulk PPV. The dimensions of these nanocomposites can be tuned by varying the size of the hydrophobic tails and/or the nature of the counterion associated with the hydrophilic headgroup of the monomer.
Hexacyanodiazahexadiene (Hcdah) Dianion as a Component of Conducting Complexes
Authors: Yamochi Hideki , Tsutsumi Kiyohiko , Kawasaki Takeshi , Saito Gunzi
Published: April 2011

In the course of the preparation of conductive molecular crystals using ‘percyano anions’, the molecular structure of HCDAH2- was revealed to be a planar geometry having a long diagonal line (≈ 10.4 Å). In (TTF)2(HCDAH)(CH3CN) [block-shaped TTF complex] (triclinic, P1, a = 8.258(5), b = 9.572(6), c= 10.070(4) Å, α = 89.89(5), β = 70.76(4), γ = 80.76(5)°, V = 740.7(7) Å3, Z = 2, final R-value = 0.074), the face-to-face type overlap between the side-byside arranged HCDAH dianions was observed. The donor packing pattern in (BEDOTTF) 6(HCDAH) (monoclinic, P21/a, a = 20.243(3), b = 4.086(1), c = 16.820(4) Å, b = 99.45(1)°, V = 1372.4(5) Å3, Z = 2/3, final R-value = 0.048) was determined to be HCP-type which is the second example in BEDO-TTF complexes.
Thermally Stimulated Luminescence of Naphthylsubstituted Benzidine Derivative and Tris-8-(Hydroxyquinoline) Aluminum With and Without Metal Layers
Authors: Forsythe E. W. , Morton D. C. , Gao Y.
Published: April 2011

Multilayer organic light emitting devices based on tris-8-(hydroxyquinoline) aluminum (Alq3) and a naphthyl-substituted benzidine derivative (NPB) have demonstrated practical electroluminescence with a wide range of color. Trap states in these materials play an important role in the carrier transport as well as the light emission process. We report the first observation of thermally stimulated luminescence (TSL) from Alq3 and NPB. The TSL spectra from 8 K to 300 K were used to determine the trap states in Alq3 and NPB. The results for Alq3 show a significant trap distribution at 156 K, which corresponds to a mean trap depth ranging from 0.18 to 0.12 eV, whereas the trap states in NPB are centered from 0.15 eV to 0.01 eV. We have used TSL to study the trap state properties of thin metal layers in the Alq3 films. In addition, we report photoluminescence as a function of temperature for Alq3. TSL spectroscopy provides a technique to study the trap states in a specific layer of the device structure.
Structural Properties of Self-Assembled Poly(zinc-bisquinoline)
Authors: Thomsen D. L. , Phely-Bobin T. , Papadimitrakopoulos F.
Published: April 2011

Poly(zinc-bisquinoline) synthesized via a reactive self-assembly technique has been used as an active transport and emitting layer in light emitting diodes. This small molecule self-assembly, pioneered in our laboratory, was shown for the first time to produce pinhole-free films as thin as 400 Å. The ellipsometric trajectory and the refractive index of zinc bisquinoline self-assembled films on silicon were determined using spectroscopic ellipsometry. Psi and Del values were extrapolated at 633nm and 70 deg incidence for films ranging in thicknesses from 0 nm to 125 nm and plotted with model trajectories of 1.65, 1.70, and 1.75 refractive indices. Thin films over 20 nm followed a trajectory having similiar refractive indices between 1.65 and 1.70, indicative of homogenous films. A refractive index of 1.68 ± 0.01 at 633 nm was found to be among the highest reported values for a self-assembled metallorganic multilayer. Atomic force microscopy of a 90 Å film on silicon substrates with mean square roughness of c.a. 12 Å showed an approximate roughness of 14 - 17 Å.
Modification of Spontaneous Emission from Periodic Array of Spherical Polystyrene Particles Containing Fluorescent Molecules
Authors: Yamasaki T. , Tsutsui T.
Published: April 2011

Emissive behavior of dye molecules embedded in the systems with the size of visible wavelength were studied. The structures consisted of close-packed arrays of spherical dielectric particles with diameter of submicrometer were fabricated. Photoluminescence from selfassembled arrays of dye-doped polystyrene microspheres were examined. In this systems, partial suppression of spontaneous emission by ordered structures were observed. Electricallypumped emission from organic light emitting diodes with highly ordered arrays of silica microspheres were attempted.
Superconductivity of κ-(BEDT–TTF)2 Cu[N(CN) 2]Br: Isotope Effect Revisited
Authors: Tokumoto M. , Kinoshita N. , Tanaka Y. , Anzai H.
Published: April 2011

In 1991, we reported a normal isotope effect in organic superconductor κ-(BEDT–TTF)2Cu[N(CN)2]Br, when all the hydrogen atoms of BEDT – TTF were replaced with deuterium. In other words, Tc was depressed by as much as 0.9 K, in contrast to the “inverse isotope effect” commonly observed in 10K-class organic superconductors. Recently, it was reported that the deuterated κ-(BEDT–TTF)2Cu[N(CN)2]Br shows an insulating nature when cooled very rapidly. Therefore, it is necessary for us to reexamine the superconducting transition of both deuterated and undeuterated κ- (BEDT – TTF)2Cu[N(CN)2]Br by SQUID measurements with special attention to the cooling speed. We studied the effect of cooling rate ranging from 10 K/min down to as slow as 0.02 K/min, and observed a significant effect not only on the superconducting transition temperature Tc but also on the superconducting volume fraction.
Alternating-Current Light-Emitting Diodes and their Transient Characteristics: Response Time and Carrier Transport
Authors: Pal A. J. , öStergÅrd T. , österbacka R. , KÄllman K-M. , Stubb H.
Published: April 2011

We report the fabrication and characterization of alternating current light-emitting diodes (LEDs) with quinquethiophene as the emitting material. We have obtained equal electroluminescence intensity in both bias sections. From the frequency response of the LEDs, we have estimated the device response times and compared them with the response times obtained from the transient response of dc LEDs. Langmuir-Blodgett film deposition technique has been employed to control the thickness of the emitting layer on the molecular scale. We have shown that the response times originate from the accumulation rather than the transit of charge carriers. We have compared the photo- and electroluminescence spectra of QT LEDs.
Nonvolatile, Reversible Writing of Electronic Nanostructures in Epitaxial Ferroelectric / Metallic Oxide Heterostructures using a Field Effect
Authors: Ahn C. H. , Tybell T. , Antognazza L. , Char K. , Hammond R. H. , Beasley M. R. , Fischer Ø. , Triscone J.-M.
Published: April 2011

Using scanning probe microscopy, we have written nonvolatile electronic nanofeatures in the metallic perovskite oxide SrRuO3. The structures were written in epitaxial thin film Pb(Zr0.52Ti0.48)O3 (PZT) / SrRuO3 heterostructures by locally switching the polarization field of the ferroelectric PZT layer with an atomic force microscope (AFM). The resulting field effect changes the sheet resistance of the SrRuO3 layer by up to 300 ohms per square. Using the AFM as an electric field microscope, it is also possible to visualize the charge distribution of the written areas on the PZT surface. Large areas of up to 100 μm2 have been polarized and imaged with submicrometer resolution, with the smallest features having linewidths of 170 nm. This approach to local electronic doping is reversible and allows one to write nonvolatile submicron electronic features in two dimensions without lithographic steps or permanent electrical contacts required.
Suppression of the Tetragonal Distortion in Thin Pb(Zr,Ti)O3 Films Grown on MgO(001)
Authors: Kang H. C. , Noh D. Y. , Je J. H. , Kim H. K.
Published: April 2011

The paraelectric cubic to ferroelectric tetragonal phase transformation of thin Pb(Zr,Ti)O3/MgO(001) films was studied in synchrotron x-ray scattering experiments. As the thickness of the film decreases, the transition temperature and the amount of the tetragonal distortion were decreased continuously. The thinnest 250 Å thick film was purely composed of the c-type domains in the ferroelectric tetragonal phase. Based on this, we propose a model for the domain structure of the tetragonal PZT/MgO(001) film that is different from the ones suggested in literature. We attribute the suppression of the transition to the substrate effect that prefers the c-type domains near the interface, and reduces the tetragonal distortion to minimize the film-substrate lattice mismatch.
Correlation Between In Situ Optical Emission Spectroscopy in a Reactive O2 / AR RF Magnetron Sputtering Discharge and PZT Thin Film Composition
Authors: Ayguavives F. , Aubert P. , Ea-Kim B. , Agius B.
Published: April 2011

Lead zirconate titanate (PZT) thin films have been grown by rf magnetron sputtering on Si substrates from a metallic target of nominal composition Pb1.1(Zr0.4 Ti0.6 in a reactive argon / oxygen gas mixture. During plasma deposition, in situ Optical Emission Spectroscopy (OES) measurements show clearly a correlation between the evolution of characteristic atomic emission line intensities (Zr - 386.4 nm, Ti - 399.9 nm, Pb - 405.8 nm and O - 777.2 nm) and the thin-film composition determined by a simultaneous use of Rutherford Backscattering Spectroscopy (RBS) and Nuclear Reaction Analysis (NRA).
The Effects of High Temperature Annealing and Composition on the Dielectric Properties of Thin Films of BaxSrzTiO3
Authors: Carter Adriaan C. , Horwitz James S. , Chrisey Douglas B. , Pond Jeffrey M. , Kirchoefer Steven W. , Chang Wontae. , Loferski Patricia
Published: April 2011

Single phase, (100) oriented Ba0.5Sr0.5TiO3 films have been deposited by pulsed laser deposition onto (100) LaAIO3, SrTiO3, MgO substrates. The dielectric properties of these films were measured using interdigitated capacitors as a function of DC bias and temperature at 1 MHz and as a function of DC bias at 1 to 20 GHz at room temperature. Deposited films were annealed over a temperature range of 900 to 1350 C for 1 to 8 hours to observe its effect on dielectric properties. Chemical analysis on films deposited from stoichiometric targets showed the films to be up to 6% deficient in Ba and Sr under typical PLD deposition conditions. Optimal annealing conditions and target stoichiometries for minimizing dielectric loss and maximizing tuning are discussed.
Compositional Control of Ferroelectric Domain Structures in Eteroepitaxial PLZT Thin Films
Authors: Lee K. S. , Kang Y. M. , Baik S.
Published: April 2011

The mechanism and control of ferroelectric domain formation in heteroepitaxial (Pb1−xLax)(ZryTi1-y)O3 (PLZT) thin films grown on MgO(001) substrates have been investigated as a function of composition and temperature. Pulsed laser deposition and RF magnetron sputtering techniques were used and optimized to fabricate epitaxial thin films with varying La and/or Zr concentrations. Periodic 9° domain structures were developed when the film transformed from the cubic phase to the tetragonal phase during cooling after deposition. As a result of the tetragonality of the films, the domain formation induced slightly tilted twin structures. All films were grown highly c axis oriented and the degree of c axis orientation was improved with increasing La or Zr concentration. Experimental observations of the 90° domain evolution in films have been carried out in-situ and ex-situ using conventional and synchrotron X-ray diffraction and demonstrated that the most important parameter affecting the domain structure and its abundance is the transformation strain at the Curie temperature, which can be varied systematically by changing the concentration of La and/or Zr in the PLZT system.
(Mn, Sb) Doped-PZT/YBa2Cu3O7-y Heterostructure for IR Detector Array
Authors: Xu Y. Q. , Wu N. J. , Liu D. , Ignatiev A.
Published: April 2011

Mn and Sb doped-PZT (PMSZT)/YBa2Cu3O7−y (YBCO) heterostructures have been integrated with YSZ/Si substrates for fabrication of infrared (IR) detector arrays. PMSZT films with good epitaxy on c-oriented YBCO conducting oxide electrodes have been successfully grown by a pulsed laser ablation deposition. The ferroelectric properties of the PMSZT films show good hystersis loops with a coercive field Ec, of 70 kV/cm and a remnant polarization Pr, of 15μC/cm2. I-V curves show that the PMSZT films have high electrical field breakdown strength with values exceeding 400kV/cm. Doping Mn and Sb into PZT has been shown to not only decrease the Curie temperature Tc from 350°C for PZT to 175°C for PMSZT, but also to enhance the IR responsivity of the pyroelectric thin films. PMSZT detectors have a pyroelectric coefficient of 45nC/cm2K at 25°C and 148nC/cm2K at 88°C, and pyroelectric figures of merit, Fv of 15.5 × 10−11 C. cm/J and Fd of 9.5 × 10−9 C. cm/J at 25°C. The measured normalized detectivity D* in the 2.5μm--19.5μm wavelength range varies from 2.5×108cm. Hz1/2/W to 6.0×108cm. Hz1/2/W.
MOCVD of Alkaline Earth Titanates for Integrated RF Capacitors
Authors: Stauf G. T. , Seegel C. , Watts R. K. , O'Bryan H. M.
Published: April 2011

The high permittivity of BaSrTiO3 (BST) gives it the potential to replace discrete “passive” capacitors used in portable and wireless applications with integrated capacitors. Bringing thin film devices directly onto Si and GaAs chips shortens lead length and improves overall circuit Q values by reducing inductance, important at RF frequencies. A metalorganic chemical vapor deposition (MOCVD) process has been developed for this purpose. By modifying the basic BST stoichiometry, we have demonstrated charge storage densities up to 3,000 nF/cm2 with leakages below 10−8 A/cm2 at 3 V, and second order dielectric nonlinearities below 100 ppm/V2. For stoichiometric BST, Q factors are as high as 500 at kHz frequencies, and evidence suggests that low losses can be retained up through the L and S microwave bands (1 -4 GHz) in the modified titanates. These properties make alkaline earth titanate films suitable for use in decoupling and bypass capacitors, as well as switched capacitor filters.
Orientation Effects on Pyroelectric Properties of Solution - Derived Bismuth Titanate Films
Authors: Khang Tran D. , Buchanan Relva C.
Published: April 2011

Ferroelectric bismuth titanate (Bi4Ti3O12) thin films with controlled degree of c-orientation were fabricated on Pt/Si substrate by solution spin-casting technique. The degree of c-orientation of the films was characterized by XRD analysis and Raman spectroscopy. Film properties such as dielectric constant, dielectric loss factor, spontaneous polarization, and coercive field varied over the range of (119–87), (0.04–0.015), (8–4 μC/cm2), and (30-20 kV/cm), respectively as the degree of c- orientation of the films increased from 0.3 to 0.85. Values for the pyroelectric coefficient, voltage responsivity, and voltage figure of merit were also evaluated. These properties exhibited strong dependence on the degree of c-orientation of the films and, for highly oriented films, reached values of 9.5 nC/°C. cm2, 62 V/W, and 0.4×10−10 C. cm/J, respectively. The inter-correlation between degree of c-orientation, grain morphology, and pyroelectric properties of the films were explored in this study.
Epitaxial Ferroelectric Oxides for Electro-Optic and Non-Linear Optical Applications
Authors: Wessels B. W.
Published: April 2011

Ferroelectric oxide epitaxial thin films are potentially important for a variety of guided-wave electro-optic and non-linear optical applications. Metalorganic chemical vapor deposition has been used to synthesize epitaxial thin films of a number of ferroelectric oxides. The films now have sufficient optical quality to enable the fabrication of waveguide devices including electro-optic modulators and optical amplifiers for 1.54 microns.
Structure-Property Relationships of BaCeO Perovskites for the Oxidative Dehydrogenation of Alkanes
Authors: Nenoff T. M. , Jackson N. B. , Miller J. E. , Sault A. G. , Trudeil D.
Published: April 2011

The oxidative dehydrogenation (ODH) reactions for the formation of two important organic feedstocks ethylene and propylene are of great interest because of the potential in capital and energy savings associated with these reactions. Theoretically, ODH can achieve high conversions of the starting materials (ethane and propane) at lower temperatures than conventional dehydrogenation reactions. The important focus in our study of ODH catalysts is the development of a structure-property relationship for catalyst with respect to selectivity, so as to avoid the more thermodynamically favorable combustion reaction. Catalysts for the ODH reaction generally consist of mixed metal oxides. Since for the most selective catalyst lattice oxygen is known to participate in the reaction, catalysts are sought with surface oxygen atoms that are labile enough to perform dehydrogenation, but not so plentiful or weakly bound as to promote complete combustion. Also, catalysts must be able to replenish surface oxygen by transport from the bulk.

Perovskite materials are candidates to fulfill these requirements. We are studying BaCeO3 perovskites doped with elements such as Ca, Mg, and Sr. During the ODH of the alkanes at high temperatures, the perovskite structure is not retained and a mixture of carbonates and oxides is formed, as revealed by XRD. While the Ca doped materials showed enhanced total combustion activity below 600°C, they only showed enhanced alkene production at 700°C. Bulk structural and surface changes, as monitored by powder X-ray diffraction, and X-ray photoelectron spectroscopy are being correlated with activity in order to understand the factors affecting catalyst performance, and to modify catalyst formulations to improve conversion and selectivity.
Modeling of the Ion-Beam Growth of Covalently-Bonded Diamondlike Materials
Authors: Hofsäss H. C. , Sebastian M. , Feldermann H. , Merk R. , Ronning C.
Published: April 2011

A characteristic ion energy and substrate temperature dependence for the formation of tetra-hedral amorphous carbon (ta-C), cubic boron nitride (c-BN) and related diamondlike materials by ion deposition has been experimentally observed. We present an analytical model for diamondlike film growth that describes the transient modification of the film structure by successive individual ion impact events. Each ion impact is treated as a cylindrical thermal spike with a finite initial width, taking into account energy loss and energy dissipation processes. We show that rearrangement of atoms during a cylindrical spike is the dominant mechanism leading to the formation of the diamondlike phase. The model explains quantitatively the observed ion energy dependence of the sp3 bond fraction in ta-C, as well as the broad range of ion energies for which c-BN growth is observed.
High Rate Deposition of Ta-C:H Using an Electron Cyclotron Wave Resonance Plasma Source
Authors: Morrison N. A. , Muhl S. , Rodil S. E. , Milne W. I. , Robertson J. , Weiler M. , Wang P. Z. , Hutchings I. , Stolojan V. , Brown L. M.
Published: April 2011

A compact electron cyclotron wave resonance (ECWR) source has been developed for the high rate deposition of hydrogenated tetrahedral amorphous carbon (ta-C:H). The ECWR provides growth rates of up to 900 A/mm and an independent control of the deposition rate and ion energy. The ta-C:H was deposited using acetylene as the source gas and was characterized in terms of its bonding, stress and friction coefficient. The results indicated that the ta-C:H produced using this source fulfills the necessary requirements for applications requiring enhanced tribological performance.
Tribochemical Reactions of Si Incorporated Diamond-Like Carbon Films During the Initial Transient Period
Authors: Kim Myoung-Geun , Lee Kwang-Ryeol , Eun Kwang Yong
Published: April 2011

Tribochemical reactions between Si incorporated diamond-like carbon (Si–DLC) films and steel ball were investigated during initial stage of tribo-test. The films were deposited by r.f.–PACVD using mixtures of diluted silane (SiH4:H2=10:90) and benzene gases. Si concentration in the film was varied from 0 to 10 at.% by adjusting the diluted silane fraction in the reaction gases. A rotating type ball-on-disk wear rig was employed for the tribo-test in ambient atmosphere. When the Si concentration was less than 5 at.%, initial transient period of high friction coefficient was commonly observed. After the transient period, the friction coefficient becomes lower with increasing contact cycles. The initial transient period becomes shorter and the starting and maximum friction coefficients in transient period decreased with increasing Si concentration. Composition of the debris on the wear scar surface was analyzed by Auger spectroscopy at various stages in the initial transient period. We observed that when the friction coefficient increased in earlier stage of the transient period, iron and oxygen was observed in the debris. However, decrease in the friction coefficient in the later stage of the transient period was associated with the formation of silicon rich oxide debris. This result supports the friction mechanism of Si-DLC films that the formation of Si rich oxide debris results in low friction coefficient in ambient atmosphere.
Boron Nitride Coatings and Materials for use in Aggressive Environments
Authors: Besmann T. M. , Lee W. Y. , Young J. P. , Xiao H.
Published: April 2011

Boron nitride coatings and structures have demonstrated significant resistance to many corrosive environments. These coatings may have application in the protection of sensors needed for measuring a variety of properties such as temperature and chemistry. In addition, boron nitride materials may offer advantages as structural materials in high temperature materials processing. In this study, BN is assessed for use in aluminum smelting.
Structural Characterization of Crystalline Si-C-N Films
Authors: Wang E. G. , Wang Cheng-Zhang , Chen Changfeng , Chen Yan
Published: April 2011

High quality crystalline Si-C-N films on silicon substrate have been synthesized by bias-assisted hot filament chemical vapor deposition (CVD) using a gas mixture of nitrogen and methane. Scanning electron microscopy images show that the Si-C-N clusters are composed of many columnar crystals with hexagonal facets. X-ray diffraction and transmission electron microscopy analyses confirm the formation of Si-C-N crystals with lattice parameters a=7.06Å and c=2.72Å. First principles calculations are performed for β-Si3–nCnN4 (n=0,1,2,3). The calculated results support the experimental structural characterization and provide further insight into the property of the system. With increasing amount of C substitution, the bulk modulus progressively increases to 4.44 Mbar, comparable to that of diamond (4.43 Mbar), and both a and c are reduced but the ratio c/a shows little variation.