bluuebunny/crossref_metadata_2025_split huggingface dataset:
GaAs substrates for the MOVPE growth of (Hg,Cd)Te layers
Authors: Triboulet R. , Tromson‐Carli A. , Patriarche G. , Lorans D. , Duy T. Nguyen 
Published: May 2005

AbstractAfter a review of the structural properties of (Hg,Cd)Te layers grown by MOVPE on GaAs substrates, topical questions such as out‐diffusion of Ga and As from the substrate into the layers, monolithic integration of signal procesing into the substrate and the presence of pyramidal defects in (100) layers will be discussed. In order to solve the last problem, a systematic study of the influence of the (h11) GaAs substrate orientation and polarity on the structrual properties and surface morphology of CdTe layers grown by MOVPE has ben carried out. Twin‐free layers are obtained on (211)A, (311)B and (511)B GaAs surface orientations as ezplained by a model taking into accountthe type of dangling bonds at the interface. The performance of photoconductors fabricated on(Hg,Cd)Te layers of various orientations confirms these results. Particularly good results have been obtained for the (311)B orientation.
Vapour growth, EPR and optical study of Znse:Ti single crystals
Authors: Klimakow A. , Dziesiaty J. , Korostelin J. , Lehr M. U. , Peka P. , Schulz H.‐J. 
Published: May 2005

AbstractZnse:Ti crystals were grown by seeded chemical vapour transport (SCVT) in a hydrogen atmosphere. In situ doping with titanium was carried out from an additional TiSe source in the quartz ampoule at 1460 K. The Good homogeneity of the Ti distribution and the presence of only a few defects have been demonstrated by etch pit and X‐ray topography studies. For the frist time, Ti3+ (3d1) centres in a II–VI semiconductor compund are detected. The concentration of localized centres of Ti2+ and Ti3+ in high‐resistivity material determined by EPR is about 5 × 1016 cm−3. Fe3+, Ni2+ and traces of Mn2+ are additionally observed. Below 77K an anisotropic EPR spectrum of Ti3+ (d1) is recorded, indicating both a dynamic and a static Jahn–Teller effect of the 2E(D) ground state. At lower temperatures clear evidence of the static Jahn–Teller effect is observed. The frist emission and excitation spectra of Ti impurities in II–VI compounds are presented. An emission near 3400 cm−1 is assigned to the 3T2(F) → 3A2(F) transition of Ti2+ (d2). Its excitation structures coincide with the known absorption bands to 3T1(P) and 3T1(F). A further structured luminescence band at 4700 cm−1 is related to 2T2 → 2E(D) transition of Ti3+ (d1). Ti ions form a deep donor level Ti2+/Ti3+ situated approximately 14,100 cm−1 above the valence band. This photo‐ionization threshold is derived from the excitation measurements in accordance with previous photoconductivity experiments.
Photoluminescence spectroscopy as a tool to assess extrinsic impurities and quality of ZnSe and ZnSxSeI − x grown by MOVPE
Authors: Schneider A. , Geyzers K.‐P. , Guimarães F. E. G. , Heuken M. 
Published: May 2005

AbstractIn this paper we report new results concerning the cause of impurities responsible for the Ix, and I2‐peaks in photoluminescence (PL) spectra of ZnSe grown by MOVPE. An improvement in ZnSe epilayer quality is obtained by using a metal organic selenium precursor with reduced chlorine concentration. The PL spectrum of such a layer shows typical excitonic transitions, but compared with samples grown with a more contaminated source, the intensity of the Ix, and the I2 peaks decreases relative to the free exciton transition. A Gaussian fitting of the donor‐bound exciton peaks taking the background of other structures into account shows that the ratio between the Ix and I2 peaks does not differ significantly between two samples. Both the decrease in donor‐bound exciton transitions and the unchangeability of the ratio Ix/I2lead to the conclusion that only chlorine impurities are responsible for Ixand Ix. In order to verify the homogeneity of impurity uptake across a 2 inch wafer, we performed PL mapping of ZnSxSe1 − x layers. Mapping of a 2 inch ZnSe wafer shows that the FWHM of Ix across a wafer does not vary significantly (1.55 ± 0.21 meV). On mapping a 2 inch ZnS0.3Se0.7 wafer fabricated with H2S as the sulphur source at TD = 480°C, we found a rotational symmetric dstribution of sulphur in the layer. The sulphur content x at the centre is nearly constant. The difference in x between the centre and the boundary of a bad surface region at the edge of the wafer is less than Δx = 0.045. The FWHM of the band edge luminescence follows the same tendency across the wafer. The dependence of homogeneity on the reactor design as well as the uptake of unintentional impurities from the precursor is discussed in detail.
Analysis of photoinduced current transient spectroscopy (PICTS) data by a regularisation method: Application of compensation defects in CdTe
Authors: Eiche C. , Maier D. , Weese J. , Benz K. W. 
Published: May 2005

AbstractA detailed analysis of photoinduced current transients of differntly grown CdTe:Cl samples was performed in the 100–130 K range in order to investigate the influence of the different growth techniques (sublimation, Bridgman method and travelling heater method (THM)) on the compensation defects. The transients were evaluated using a regularisation method (fast Tikhonov regularisation) as implimented in the program FTIKREG. The advantages of the regularisation method in comparison with the customary two‐gate technique are demonstrated by the analysis of simulated data. It can be shown that the different growth techniques have only one level in common. Furthermore, the superposition of different traps can lead to wrong results using the conventional two‐gate technigque. The temperature dependence of the relaxation times is evaluated and the corresponding trap parameters are determined.
Far‐infrared and Raman spectroscopy of Zn(Se,S) layers
Authors: Geurts J. , Hermans J. 
Published: May 2005

AbstractWe discuss the optical analysis of Zn(Se,S) layers by the application of far‐infrared (FIR) and Raman spectroscopy. First a summary is presented of the principles of FIR and Raman Spectroscopy with regard to the relevant epilayer properties which can be investigated by these methods. Subsequently we treat some selected results of FIR and Raman analysis of epilayers grown on GaAs(100) by metal organic vapour phase epitaxy (MOVPE). The main points of interest are crystalline quality, free carrier concentration and interface sharpness. It is shown that n‐type conductivty is achieved by Ga implantation in ZnSe but the annealing process (870°C, 30 s) leads to a p‐type interface layer in the GaAs due to Zn diffusion. Furthermore, the beneficial effect of growth interruptions to the sharpness of ZnS/ZnSe multiquantum‐well interfaces is demonstrated.
Phosphorescent spectral and decay studies of CaI − xSrxS:Ce solid solutions
Authors: Fritz U. , Ray B. , Viney I. V. F. , Arterton B. W. , Brightwell J. W. 
Published: May 2005

AbstractCa1 − xSrxS Solid Solutions at 10 m/o intervals have been prepared by coprecipitation of sulphates from aqueous solution followed by reduction at 1000°C with hydrogen. Phosphorescence emission spectra have been determined for these solid solutions doped with 0.1 m/o cerium and show a blue shift with increasing strontium content from 2.46 to 2.59 eV. Hyperbolic phosphorescent decay curves were observed at both room and liquid nitrogen temperatures across the composition range and have been broken down into three exponential components by graphical and computer‐programme‐based methods. At room temperature trap depth values of 0.366, 0.316 and 0.282 eV with measured lifetimes of 1.9, 0.26 and 0.07 ms respectively were determined with little dependence on composition. At liquid nitrogen temperature shallower traps were observed at 0.103, 0.086 and 0.076 eV with respective decay times of 5, 0.4 and 0.09 ms having little sensitivity to changes in the host compostion. These traps are related to intrinsic defects, some of which may be surface in character. The blue shift in emission peak energy with the decrease in band gap from CaS to SrS is discussed.
Control of composition and substitutional acceptor density during crystal growth of CdTe
Authors: Rudolph P. , Schröter H. , Rinas U. , Zimmermann H. , Boyn R. 
Published: May 2005

AbstractA correlation between carrier concentration and the concentration of important substitutional acceptors (AgCd, CuCd, PTe) determined from photoluminescence analysis is reported for p‐and n‐type CdTe crystals grown by various Bridgman techniques. We consider that the results show that the concentrations and distribution coefficients are controlled by the densities of Cd(Te) vacancies which are present under crystal growth conditions.
Depth‐resolved cathodoluminescence of ZnSe epilayers
Authors: Trager‐Cowan Carol , Yang F. , O'Donnell K. P. 
Published: May 2005

AbstractIn This paper we illustrate the use of an electron beam of variable energy to get depth information on the strain, impurity and defect distribution in ZnSe epilayers. From the increase in splitting of the free light and heavy hole exciton bands with increasing electron beam energy we deduce that the strain increases with depth. From the increase in the luminescence intensity of the impurity and defect bands compared with the luminescene intensity of the free heavy hole exciton band with increasing electron beam energy we deduce that the impurity and defect densities also increase as a function of depth.
Encapsulated alkaline earth metallocenes. 3: Structural influences on phase transformations alkaline earth complexes
Authors: Burkey David J. , Hanusa Timothy P. , Huffman John C. 
Published: May 2005

AbstractReaction of two equivalents of KCp3i (Cp3i ≡ 1,2,4‐(i‐Pr)3C5H2) with MgBr2 in Et2O produces the base‐free metallocene (Cp3i)2Mg in high yield; the similarly prepared organocalcium complex (Cp3i)2Ca, although initally isolated as an oil, forms a crystalline solid on standing for several months. Crystals of (Cp3i)2 CA are tetragonal, space group P42/n, with a = 18.147(4), c = 15.996(4) Å, Å and Dcalc = 1.066 g cm−3 for Z = 8. Lease‐squares refinement based on 2044 reflections led to a final R‐value of 0.072. The complex possesses a metallocene geometry that is slightly bent; the average Ca–C distance is 2.62(2) Å and the right centroid–Ca–ring centroid angle is 169.7°. Comparison of these complexes with previously reported alkaline earth metallocenes suggests that the volatility of the metallocenses depends primarily on the degree of aggregation in the solid state, whereas the melting point of the nonomeric compounds varies with the asymmetry and ligan flexibility in the complex.
A new, thermally efficient route to crystalline BaTiO3 from monodispersed rutile powder
Authors: Rees Willam S. , Carris Michael W. 
Published: May 2005

AbstractTreatment of monodispersed rutile (TiO2) powder with an ammonlacial solution of elemental barium gives a uniformly coated precursor to BaTiO3. Thermolysis at about 900 °C for 6 h gives crystalline (by XRS) material with an average particle size of less than 0.1 μm (as determined by SEM).
Neural network analysis of molecular hyperpolarisabilities
Authors: Munn R. W. , Munn N. S. , Hardie K. J. 
Published: May 2005

AbstractA standard back‐propagation neural netwrok is trained to predict the hyperpolarisability β of substituted nitrobenzenses as reported from EFISH experiments. Learning is faster with 13C NMR chemical shifts as input than with standard substituent constants and the predictions are somewhat better. The dipole moments μ can be predicted at the same time as β, but training to high precision is then much slower. Developments of this approach may be useful in screening out molecules of high β for synthesis and experimental study.
Langmuir–Blodgett films of indandione‐l,3 pyridinium betaine. II: Molecular structure and properties of monolayers; simulation and optical absorption data
Authors: Rutkis M. A. , Lindquist S. E. , Wistus E. , Almgren M. , Klimkans A. B. , Larsson S. , Silinsh E. A. 
Published: May 2005

AbstractThe molecular structure and optical properties of a monolayer at the air/water interface of novel amphiphilic derivatives of indandione‐1,3 pyridinium betaine (IPB) with different lengths of the aliphatic tail, namely C1lIPB and C17IPB, have been studied using optical absorption techniques and computer simulation approaches.The compression π‐A isotherm of the C17IPB monolayer and computer simulation of its molecular structure show that there may exist two energetically stable molecular configurations, one with antiparallel orientation of the dipole moments of the C17IP ‘heads’ in the low‐pressure region at π = 5–32 mN m−1 and the second (after a distinct phase transition at π = 33 mN m−1) with parallel orientation of the dipoles, with different tilt angles and areas per molecule. For C11IPB only the first structural phase is observable.The compression‐induced changes in spectral characteristics of the two structural phases go in diametrically opposite directions. In the low‐pressure phase compression induces a red shift and an increase in intensity of the S1 absorption band, while in the high pressure phase a blue shift and a decrease in the intensity of this band are observed. These spectral changes correlate reproducibly with the compression π‐A isotherms. Measurements of absorption dichroism confirm the change in the tilt angle at the phase transition pressure. The compression‐induced spectral changes have been substantiated by the results of quantum chemical calculations.
Electronic properties of polydiheteroarylenemethines: Electrical conductivity
Authors: Bourdin E. , Curran S. , Davey A. , Blau W. , Blöchl G. , Becker R. , Bräunling H. 
Published: May 2005

AbstractPolydiheteroarylenemethines show a relatively high electrical conductivity. Two‐coplanar‐electrode measurements give a high surface conductivity of 10−9 S/□ and a high mobility up to 1 cm2 V−1. Depending on the type of side group, doping with iodine served to raise the conductivity by five orders of magnitude. Optical absorption analysed with DC and AC conductivity data revealed two components in the transport process: A VHR (variable range hopping) process shifting to a band tail polaronic process as the degree of polymerisation increases, corresponding to a very characteristic transition in the AC conductivity. The hopping process corresponds to an AC conductivity frequency power law dependence of ω0.66, whereas the polaronic process corresponds to a power law dependence of ω0.1.
Langmuir‐blodgett films of stilbazole complexes of iridium(I) and rhodium(I)
Authors: Richardson Tim , Topacli Arzu , Majid Wan Haliza Abd. , Greenwood Michael B. , Bruce Duncan W. , Thornton Anna , Marsden Julian R. 
Published: May 2005

AbstractComplexes of 4‐alkoxystilbazoles with iridium and rhodium form stable Langmuir layers at the air‐water interface even when the alkoxy chain is relatively short (C5–C12). The surface pressure‐area isotherms indicate that condensed molecular monolayers are obtained. The area per molecule of each compound in its monolayer form is typically 0.60 nm2, which agrees well with the cross‐sectional area of the [Ir(CO)2CI] or [Rh(CO)2CI] head group predicated using molecular models. This suggests that the molecules are oriented with the metal moiety close to the water surface and their alkoxystilbazole ‘rod’ protruding from the plane of the water surface. Such floating monolayers have been transferred on to solid substrates such as glass, aluminium (AI2O3/AI/Glass) and silicon (SiO2/Si) at relatively high speed (10 mm min −1) to form Y‐type LB assemblies. The UV–Visible absorption properties of these materials in solution and LB film form have been studied. LB films of these complexes yield bathochromically shifted spectra relative to the LB film spectrum of the uncomplexed stilbazole. Additionally, these spectra are often broader and hypsochromically shifted relative to their corresponding solution spectra as a result of the close molecular packing within the LB film and the associated dipole–dipole interactions.The electrically polar nature of the molecules described in this paper suggest that they may be suitable candidates for new pyroelectric materials. Thus the pyroelectric coefficient (the rate of change of electric polarisation with respect to temperature) has been measured for a polar multilayer LB film containing an iridium complex. A pyroelectric coefficient of 3.5 μCm−2K−1 (at 30 °C) has been measured, which is one of the highest reported valued for an LB film. Additionally, a low dielectric loss of around 0.01 has been found over the frequency range 50 Hz–1 kHz, indicating that such LB films may be usfeul materials for pyroelectric sensors.
Electrical characteristics of polypyrrole composites at microwave frequencies
Authors: Wright P. V. , Wong T. C. P. , Chambers B. , Anderson A. P. 
Published: May 2005

AbstractThe microwave absorption and reflection characteristics of composites of polypyrrole with paper, cotton cloth and polyester fabrics have been evaluated. Refiectivity measurements in the range 2–18 GHz and plane wave modelling have revealed impedance charateristics with a common transition rgion. Relationships between substrate material, polymer loading and electrical performacne have been explored. Polarisation characteristics have alos been measured. The electrical model has been successful in predicting the performance of both Salisbury screen and Jaumann multilayer designs of radar‐absorbing material.
Isomorphous mixing of mesogenic anions and uncharged analogues in organised poly(ehtylene oxide)‐alkali salt complexes
Authors: Patel Jayesh P. , Wright Peter V. , Dunmur David A. , Tajbakhsh Ali R. 
Published: May 2005

AbstractThe preparation and characterisation of novel ionic polymer liquid crystal complexes of poly(ethylene oxide)–Na+ with mesogenic anions and their uncharged structural analogues in homogeneous mixtures are described. The systems discused most fully are the anion of the phenolic mesogen 4‐n‐hexyloxybenzylidene‐4‐hydroxy aniline (1) with its uncharged analogue 4‐n‐hexyloxybenzylidene aniline (1a) and the anion of 5‐(4‐n‐octyloxy‐2,3‐dicyanophenyleneoxycarbonyl)benzimidazo‐le (2) and its uncharged analogue 4‐octyloxy‐2,3‐dicyanophenyloxybenzoyl (2). Differential scanning calorimetry, wide angle x‐ray diffraction and polarised light microscopy show that PEO–Na1/1a and PEO–Na2/2a are homogeneous mesogenic phases when Na1 or Na2 are present at 50% or less of the stoichiometric composition in complexes (EO : salt = 3 : 1) and the shortfall is made up from 1a or 2a uncharged analogues of 1a and related systems substituted by methoxy rather than hydrogen do not form homogeneous mixtures.
Quadratic electro‐optic non‐linearity of a conjugated porphyrin polymer measured in the Q‐band one‐photon resonance region
Authors: Martin Simon J. , Anderson Harry L. , Bradley Donal D. C. 
Published: May 2005

AbstractWe reprot linear and non‐liner optical experiments on a new edge‐linked porphyrin polymer that is soluble in pyridine/chlorinated solvent mixtures and that produces optical quality thin films by spin coating. This linear absorption properties of the polymer indicate that it posseses an extended intermacrocycle π‐conjugation. This results in a strong red shift of the macrocycle‐derived Q‐band with the polymer peak at 874 nm (1.42 eV) in solution and 838 nm (1.48 eV) in solid films compared with a monomer solution peak at 642 nm (1.93 eV). The polymer possesses a large Stark‐shift‐related DC Kerr electro‐optic non‐linearity with peak responses in the real and imaginary part of X(3) (−ω; 0, 0, ω) of ReX(3) = −7.2 × 10 −8 esu at 849 nm (1.46 eV) and lmX(3) = 6.7 × 10−8 esu at 855 nm (1.45 eV). This response is 3–10 tiems larger that that reported for quasi‐one‐dimesional conjugated polymers and enhancements can be anticipated. Detailed examination of the electro‐optic response spectra shows several interesting features which indicated that the usual phenomenological models of molecular Stark shifts do not provide a full description of the abserved behaviour. Future studies are planned to look more closely at the nature of the electro‐optic response.
Cleavage of silicon‐carbon bonds and relative rates of hydrolysis of ormosil precursors for optical materials
Authors: Seddon Angela B. , Hunt Suzane , Rourke Jonathan P. , Bruce Duncan W. 
Published: May 2005

Abstract1H NMR spectroscopy of methyltrimethoxysilane (MTMS) has revealed that cleavage of the Si—C bond occur during hydrolysis in the presence of HCI. A mechanism is suggested involving nuleophillic attack by CI− with electrophilic promotion. Optical materials based on tetramethoxysilane (TMOS) and MTMS are vsually transparent and 1H NMR reveals the similarity of the hydrolysis rates of these precursors under acid catalysis. 1H NMR indicates that residual unhydrolysed methoxide groups in the finished optical materials are a possibility.
Macroscopic non‐linearities of some stilbazolium derivatives and the calculatium derivatives and the calculation of their molecular hyperpolarisability
Authors: Bruce Duncan W. , Grayson Martin , Lagadec Ronan Le , Pickup Barry T. , Thornton Anna , Denning Robert G. , Lai Kai K. 
Published: May 2005

AbstractThe synthesis of some optically non‐linear stilbazolium salts is described. Since their solid state non‐linearities were small, MOPAC5 was used to compare their relative molecular non‐linearities.
Structure and conductivity of liquid crystal channel‐like linic complexes of taper‐shaped compounds
Authors: Ungar G. , Batty S. V. , Percec V. , Heck J. , Johansson G. 
Published: May 2005

AbstractMolecular packing and electrical conductivity were studied in complexes of alkali trifluoromethanesulphonates with low‐molar or polymeric compounds containing both taper‐shaped mesogens were esters of either 3,4,5‐tris [p‐(n‐dodecan‐l‐yloxy) benzyloxy] benzoic acid (I) or 3, 4, 5‐tris (n‐dodecan‐l‐yloxy) benzoic acid (II). In the hexagonal columnar liquid crystal phase the tapered mesogens fan out from the centre of the column, with the ionic receptors forming the central channel and the aliphatic tails constituting the continuum matrix. In the case of side‐chain polymethacrylates the column core also contains the backbone chain. The DC conductivity σ of unoriented samples increases greatly at the crystal‐columnar transition, with only a minor further change upon columnar‐isotropic transition. σ was in the range 10−9 − 10−6 in the columnar phase 40–90 °C, whilst the activation energies for conduction were between 28 kcal mol−1 for the crown ether and only 2 kcal mo−1 for the complex of LiCf3SO3 with the non‐polymeric ester of tri(ethylene oxide) with I.
Oxide removal from the GaSb surface and fabrication of MBE GaSb photodiodes and Au–GaSb schottky diodes
Authors: Kodama Mitsuru 
Published: May 2005

AbstractOxide removal from GaSb surfaces by several wet chemical treatments and subsequent thermal annealing was investigated. Preferable wet chemical treatments by which surface oxides could be removed effectively at room temperature were evaluated in the experiments. This method can be effectively applied to fabrication processing of MBE GaSb photodoides and Au–GaSb Schottky doides. Low‐reverse‐leakage GaSb photodiodes and near ideal Au–GaSb Schottky diodes were thus obtianed.