bluuebunny/crossref_metadata_2025 huggingface dataset:
Tackling problems in the growth of ZnS/Se through precursor design
Authors: Foster Douglas F. , Patterson Ian L. J. , James Linda D. , Cole‐Hamilton David J. , Armitage David N. , Yates Heather M. , Wright Andrew C. , Williams John O.
Published: May 2005

A variety of problems in the growth of wide band gap II/VI materials by MOVPE has been addressed by the use of alternative precursors. The quality of grown layers of ZnSe has been greatly improved by adduct purification of Me2Zn. Using 4,4′‐bipyridyl, the recovery of Me2Zn is variable because of the insolubility of 4,4′‐bipyridyl in diethylether. Higher yields can be obtained using the ether‐soluble base 1,3‐bis(4‐pyridyl)propane.tBuSH has been introduced for the growth of ZnS. Being a liquid, this compound is easy to handle and it allows growth of high‐quality ZnS at temperatures down to 325°C with very little gas phase pre‐reaction with Me2Zn. Growth of ZnSxSe1 − x at atmospheric pressure using H2S and Et2Se as the group 16 precursors allows excellent stoichiometric control, since the ratio of S : Se in the grown solid is similar to that of H2S : Et2Se in the gas phase for all compositions. Finally, multilayer structures have been grown at low pressure with excellent interface abruptness and goodquality material. However, the ternary layers are all much higher in sulphur than expected from the gas phase composition and the composition of the ternary appears to be influenced by the nature of the surface on which it is growing.
Mixed alkyl zinc or cadmium complexes with dialkyl thio‐ or selenocarbamates: Precursors for cadmium chalcogenides
Authors: Malik M. Azad , O'Brien Paul
Published: May 2005

A series of new compounds [RME2CNR′2]2 (R and R′ are various alkyl groups, e.g. M  Zn or Cd, R  Me, R′  Et) have been synthesised and characterised. The compounds can be used as single molecular precursors for the deposition of the corresponding binary chalcogenides. In the present paper the range of compounds synthesised and their uses are reviewed. Preliminary observations on the deposition of thin films on glass and GaAs(100) substrates are reported.
Effects of rapid thermal annealing on the electrical properties of Hg1 − xCdxTe bulk crystals
Authors: Rubio J. A. López , Sangrador J. , Rodríguez T.
Published: May 2005

This paper reports the change in the bulk transport properties of p‐type MCT samples induced by a rapid thermal annealing (RTA) process. This change is produced homogeneously within the crystal without interchange of mercury with the surrounding atmosphere. The carrier concentration varies towards an equilibrium value that depends only on the annealing temperature. For the material and temperatures investigated (250–420°C) the equilibrium carrier concentration depends exponentially on the inverse of the temperature, its value ranges between 1 × 1017 and 4 × 1017 cm−3. The time needed to reach equilibrium is a function of the temperature, varying from 10 s at 420°C to 200 s at 250°C. The hole mobility is also affected by the RTA process, its evolution being a function of the process temperature and time. A model is proposed to explain these modifications based on a reaction of generation‐annhilitation of mercury vacancies and interstitials that would take place within the crystal with no external interaction.
High‐resolution scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) of ZnSxSe1 − x/ZnSe Quantum Wells
Authors: Bollig B. , Geyzers K. P. , Heuken M.
Published: May 2005

Epitaxial growth techniques for ZnSxSe1 − x/ZnSe heterostructures have already achieved a high degree of development. Further improvements strongly require characterisation techniques with high compositional sensitivity and high spatial resolution. Therefore in this work high‐resolution Z‐contrast, which provides compositional information down to the atomic scale, has been used for the first time to characterise ZnSxSe1 − x/ZnSe quantum well structures. The influence of structural defects on Z‐contrast is demonstrated by comparison of scanning transmission electron microscopy (STEM) bright field images and STEM Z‐contrast micrographs of planar defects and dislocations. The compositional abruptness of ZnSxSe1 − x/ZnSe interfaces in MOVPE‐grown quantum well (QW) structures is judged from high‐resolution Z‐contrast micrographs. Electron energy loss spectroscopy (EELS) measurements were performed for the first time in ZnSxSe1 − x/ZnSe QW structures in order to obtain quantitative compositional information with nanometre spatial resolution. From EELS line scans, which monitor the selenium concentration across ZnSe QWs, the obtainable spatial resolution is estimated to be about 1–2 nm. The problems that have prevented quantitative analysis of the selenium concentration up to now are discussed.
Radiative efficiencies and deep levels in zinc selenide
Authors: Allen J. W.
Published: May 2005

Although zinc selenide and related materials are promising for blue light‐emitting diodes and lasers, present performance is unsatisfactory. The blue radiative efficiency at room temperature is low and the decay time of luminescence is correspondingly short. It is argued that the problem is non‐radiative recombination by the Hall–Shockley–Read mechanism at deep levels and that the concentration of these levels must be high. Experimental evidence for the existence of such levels is presented. Characterisation and control of deep levels will be essential for progress in this area.
Plasma‐enhanced MOVPE and nitrogen doping of ZnSe
Authors: Taudt W. , Hermans J. , Schneider A. , Woitok J. , Geurts J. , Heuken M.
Published: May 2005

In order to obtain high quality Znse epilayers on GaAs which can be intentionally P‐ and n‐type doped growth at a reduced temperature is highly desirable. Therefore in this work the suitability of diallylselenide and the influrnce of plasma precracking have ben investigated. Photoluminesscence, Raman spectroscopy, scanning electron microscopy, X‐ray, SIMS and Hall measurements were used to anaylse the samples. The selenium precursor was fully decomposed at temperatures above 360°C if it was precracked by a plasma. Bound excitions could be resolved with negligible donor–acceptor pair (DAP) and copper green emission in the PL spectra form films which were grown with a plasma at temperatures beyond 530°C. Clearly the hpe for reduction in the deposition temperature was not achieved. Raman spectra also revealed strong crystalline quality variations. For the doping experiments nitrogen was used as the carrier gasa instead of hydrogen. Plasma cracking of the selenium precursor was still necessary. Thye substitution of the H2 carrier gas by nitrogen reduced the growth rate by a factor of 2.6 but enhanced the crystalline properties of the samples as shown by the Raman measurements. Strong DAP emission at 2.7eV in the (PL) spectra was observed. SIMS measurements showed a nitrogend concertration of about 3 × 1017 cm−3. An additional nirtogen plasama (0–7W) had a begligible effect on the nitrogen concentration in the sample. The samples were semi‐insulating, whichmight be a conswquence of the crystalline quality of ZnSe grown with DASe as selenium precursor.
A comparison of the diffusion of copper, gallium and cadmium in cadmium telluride
Authors: Jones E. D. , Stewart N. M. , Mullin J. B.
Published: May 2005

The rates of diffusion of both Ga and Cu in CdTe have been measured over the temperature ranges 350–820 and 200–400°C respectively and the results are compared with the self‐diffusion of Cd (350–920°C).

In the case of the Cd self‐diffusion the Arrhenius graph showed two active diffusion mechanisms, one dominating above 500°C and the other below. It suggested that in the temperature range 500–800°C the main defect responsible for diffusion was Cd, with a significant contribution at lower temperatures from the associated defect of the form (CdiVcd)x Below 500°C another mechanism predominated which was possibly due to residual impurities.

The results for the diffusions were in close agreement with those obtained by other workers. The Ga diffusions showed a complex behaviour which suggested that two mechanisms were active simultaneously, one independent of Cd partial pressure and the other decreasing with increasing Cd partial pressure.

It was concluded that CdTe would be suitable as a diffusion barrier to protect HgxCd1 − xTe devices from Ga contamination from GaAs substrates but would not be efficient at reducing Cu contamination from the substrate in the device.
Recombination dynamics of dense elctron–hole plasma in CdS‐doped glasses
Authors: Juršėnas S. , Žukauskas A. , Strumskis M. , Ekimov A. I.
Published: May 2005

Time‐resolved luminescence spectra of highly excited CdS‐microcrystallites are studied at room temperature in relation to the hot electron–hole plasma (EHP) effect. When the EHP thermalization is complete the luminescence kinetics shows a steady increase in the recombination rate with decreasing microcrystallite average radius (from 1000 Å to 54 Å). The obtained size dpendence is attributed to surface recombination.
Electrical and optical properties of the transition metal iron in ZnTe and CdTe
Authors: Lechner H. , Hofmann D. M. , Meyer B. K. , Azoulay M. , Krambrock K. , Spaeth J.‐M. , Döornen A. , Kaufmann B. , Omling P. , Salk M. , Benz K. W.
Published: May 2005

We present results of electron paramagnetic resonance (EPR) and optical spectroscopy on different charge states of the transition metal impurity iron in ZnTe and CdTe. We identify the energy level position of the Fe+ acceptor in ZnTe at Ev + 1.7eV and estimate its position in CdTe. Ionisation transitions from Fe+to the conduction and valence bands ar found in both absorption spectroscopy and photo‐EPR. Optical intra‐defect tracsitions from Fe+ to crystalfield‐split excited states ar resolved for the first time. This assignment to Fe2+ is based on optically detected EPR. Application of both far‐infrared Fourier transform and EPR spectroscopy allows the determination of the total iron concentration in all charge states.
Comparison of two approaches to forced convection in crystal growth of II–VI compounds by THM
Authors: Bloedner R. U. , Presia M. , Gille P.
Published: May 2005

Hg1 − xCdxTe and Cd1 − xZnxTe single crystals were grown by the tracwelling heater method (THM), applying two different techniques of artificially stirring the solution zone. Accelerated crucible rotation (ACRT) was used in a vertical growth arrangement and compared a technique with constant rotation around the horizontal axis of the ampoule. The dominant hydrodynamic mechanisms of noth methods are discribed by the rotating disc model and are suggested to be almost identical with respect to the growth conditions at the interface. Convective flow is effectively enhanced adhacent to the growing crystal, where the matter transport is regarded as the rate‐limiting step of solution growth. Inclusion density analysis by IR microscopy was used to characterise the crystals of Cd1 − xZnxTe grown at different rates. It was shown that forced convection allows an increase in the crystal growth rate from a few mm day−1 with ACRT or horizontally rotating THM.
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

After 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

Znse: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

In 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

A 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

We 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

Ca1 − 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

A 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

In 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

Reaction 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

Treatment 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

A 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

The 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

Polydiheteroarylenemethines 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

Complexes 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

The 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

The 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.
Liquid crystalline hydrogen‐bonded complexes formed between alkoxystibazoles and phenols
Authors: Bruce Duncan W. , Price Daniel J.
Published: May 2005

Mesomorphic materials formed by hydrogen bonding between 4‐alkoxystillbazoles and some phenols are described.
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

We 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

1H 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

The 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

Molecular 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

Oxide 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.
Themal spray and adhesive bonding of optical fibres to high‐temperature compsie materials
Authors: Henkel Daniel P.
Published: May 2005

Microstructural characteristic were identified for three surface‐mounted optical fibre sensors which were thermal spray bonded to high‐temperature composite materials. The primary objective was to determine the defect generation mechanisms that occur during thermal cycling and to make processing and testing recommendations that would optimise the sensor performance. A second objective was to identify areas of microstructural research that would have the most significant impact on the development of high‐temperature smart materials.

The smart material systems of the present study were comprised of (1) silica optical fibre sessors bonded to titanium matrix composites (TMCs) using a nickel‐based thermal spray, (2) silica optical fibre sensors bonded to TMCs using ceramic cement and (3) sapphire optical fibre sensors bonded to titanium matrix composites (TMCs) using a nickel‐based thermal spray, (2) silica optical fibre sensors bonded to TMCs using ceramic cement and (3) saphire optical fibre sensors bonded to carbon–carbon composites (CCCs) using ceramic cement. The thermal and prior to any thermal stresscycling. In combination with the non‐metallic spheroidal inclusions of the titanium matrix, the microcracking provided a mechanism for disbonding the optical fibres with a subsequent loss of sensor performance. A high degree of kporosity in both systems containing ceramic cements significantly reduced the interfacial bonding area. This, combined with the inherent ceramic brittleness, caused disbonding of the optical fibres in the cemented systems.
Growth of chromium‐doped alumina thin films by metal‐organic chemical vapour deposition
Authors: Chiu Hsin‐Tien , Lin Been‐Hon
Published: May 2005

Amorphous thin films of chromium‐doped alumina were grown from Al(OiPr)3 (iPr, Isopropyl) and Cr(CO)6 on silicon and quartz substrates by chemical vapour deposition at 673 K. The films were annealed at 1223 and 1473 K to form chromium‐doped γ‐Al2O3 and γ‐Al2O3respectively. The lattice constant a of the γ‐Al2O3thin films enlarged with increasing Cr Concentration. The lattice constant a (=b) of the α‐Al2O3 thin films increased while the lattice constant c decreased with increasing Cr concentration. UV‐visible spectra of the annealed films showed maximum absorptions near 380, 500 and 690 nm.
p‐Doping of GaAs and AlGaAs using the triethylamine adduct of dimethylzinc
Authors: Jones Anthony C. , Rushworth Simon A. , O'Brien Paul , Walsh John R. , Meaton Clive
Published: May 2005

The adduct between dimethylzinc and triethylamine has been used as a p‐dopant source in the growth of GaAs and Al0.3Ga0.7As alloys by metalorganic vapour phase epitaxy (MOVPE). The dopling efficiency of this adduct in these alloys and in InP is lower than that of dimethyl zinc.
Two‐Wavelength switching of luciferase activity using caged compounds
Authors: Chittock R. S. , Wharton C. W. , Jackson J. B. , Lidzey D. G. , Berovic N. , Beynon T. D.
Published: May 2005

Firefly luciferase, luciferin, 1‐(3,4‐dimethoxy‐6‐nitrophenyl) elthyl ATP and 1‐(2‐nitrophenyl) ethyl acetic acid were immobilised in an agarose gel matrix. By illuminating the gel with 350 nm light through a mask, a positive bioluminescent pattern was written on to the gel by releasing ATP in the illuminated areas. The gel was then illuminated with a brpadbnand UV light through a second mask to release acetic acid, lowering the local pH and deactivating the enzyme. This produced a negative image of the second mask superimposed on the positive image of the first mask.

The system represents a two‐wavelength switch in which one wavelength of light activates the enzyme while a second deactivates it. This demonstrates the feasibility of using biological molecules as logic element in future devices.
Dynamic displacement anisotropy of atoms, streamer discharges and phonon focusing in BeO and CdSe crystals and I–VII compounds
Authors: Zubritskii V. V. , Zaitsev A. M.
Published: May 2005

Streamer discharges at 77 K and crytallographically oriented surface spark breakdown at 295 K have been obtained in BeO crystals. An inverted temperature dependence has been found for the breakdown anisotropy compared with that in CdSe crystals. It is shown that the temperature dependences of the excitation thresholds of the incomplete electric breakdown at different crystallographic orientations in dielectrics as well as those of the streamer discharges in hexagonal semiconductors are controlled by the anisotroply of ionic dynamic displacements. The directions of maximum phonon focusing have been calculated in the localoisation planes of the incomplete breakdown in NaCl, KBr and LiF crystals at room temperature in accordance with well‐known breakdown model along phonon streams. It is shown that the alkali halide breakdown data do not agree with this model. An anisotropy is predicted of the dynamic displacement of atoms in alkali halide crystals as well as in the basis plane and mirrorsymmetric directions of planes containing the crystallographic c‐axis in hexagonal II–VI compounds, which allows us to explain the observable particularities of the discharge anisotropy in both cubic and hexagonal crystals.
Electron‐beam‐pumped laser emitters with microrelief mirrors based on II–VI semiconductors
Authors: Gribkovskii V. P. , Gurskii A. L. , Kulak I. I. , Lutsenko E. V. , Mitcovets A. I. , Yablonskii G. P.
Published: May 2005

The power characteristics of electron‐beam‐pumped emitters based on II–VI compounds have been stukdied. The use of a microrelief with direction‐selective reflective properties instead of a totally reflecting miror has made it possible to provide effective sukppression of closed non‐characteristics and efficiency of lasers and to make them suitable for obtaining generation with high efficiency in a number of media, in particular YAG:Nd3+, KGW:Nd3+ and Lif:F (OH), at room temperature.
Crystallographic orientation and light emission of streamer discharges in II–VI semiconductors
Authors: Gribkovskii V. P. , Gurskii A. L. , Lutsenko E. V. , Yablonskii G. P.
Published: May 2005

Some results of Investigations on the crystallographic orientation, luminescence and stimulated emission of streamer discharges in monocrystals of hexagonal CdS, CdSe and ZnO and cubic Znsand Snseare presented.
Growth of yttrium oxide thin films from β‐diketonate precursor
Authors: Mölsä Heini , Niinistö Lauri , Utriainen Mikko
Published: May 2005

Yttrium oxide thin films were deposited in a flow‐type ALE reactor from Y(thd)3 (Hthd  2,2,6,6‐tetramethyl‐3,5‐heptanedione) and either ozone or oxygen. The influence of the substrate and source temperatures, pressure and pulse durations on the film growth on soda‐lime and silicon substrates was studied. Films were also grown on Corning glass, sapphire and Si/CeO2 substrates to study the effect of the substrate on the growth rate and crystallinity of the films. Spectrophotometry, XRD and AFM were used to determine the optical properties, thickness, crystallinity and surface morphology of the films. All the films deposited with ozone were crystalline, but differences in preferential orientation depending on the substrate were observed. The growth rate with ozone was about 0.8 Å cycle−1 on all substrates except sapphire where it was higher. The films deposited with oxygen were less crystalline and the growth rate was significantly lower than in depositions with ozone under the same growth conditions.
Identification of the impurity phase in chemically deposited CdS thin films
Authors: Sebastian P. J. , Hu Hailin
Published: May 2005

Identification of the impurity phase present in chemically deposited CdS thin films and in the precipitate used for screen printing CdS/CdTe solar cells is reported in this paper. X‐ray diffraction (XRD) studies of the films and the precipitate showed that the impurity phase is a mixture of cadmium oxide sulphate (Cd3O2SO4) and cadmium oxide (CdO). Analysis of the films and the powders obtained using thiourea (TU) and thioacetamide (TA) as sulphursing agents showed that the impurity phase is predominantly present when TU is used in the chemical bath. The high conductivity shown by chemically deposited CdS films (using TU) when annealed at higher temperatures in air is attributed to the predominance of the conducting CdO phase in the film.
Nearly resonant third‐order optical non‐linearity in c60 cast films
Authors: Henari Fryad Z. , Blau Werner J. , Seldon Declan N.
Published: May 2005

We have carried out measurements of the third‐order optical non‐linearityX(3) of C60 cast films using the z‐scan technique. The measurements have shown that two‐photon absorption is the dominant non‐linear process around the 3.76 eV absorption region. The real and imaginary parts of X(3) of C60 films have been measured at 665 nm are found to be 2.8 × 10−8 and −3.2 × 10−8 esu respectively.
Optically stimulated intersubband absorption in undoped amorphous Si/SiO2 qiantum well
Authors: Keller Ole , Zayats Anatoly , Vinogradov E. A.
Published: May 2005

Intersubband absorption has been observed in undoped amorphous multiple‐quantum‐well (MQW) strucctures under interband excitation. The transitions take place between the first and second subbands of the conduction band and involve non‐equilibrium electrons excited into the first subband by optical pumping. The absorption band FWHM of 0.1 eV is much larger than for crystalline MQWs, a fact which reflects the relaxation of the electron momentum conservation in the QW plane. The high joint density of states and oscillator strength for the intersubband transitions in amorphous QWs allow one to observe the absorption at low electron concentrations (Ne ≈ 1013 cm−3) in the ground conduction subband.
A comparative study of pulsed laser deposition and flash evaporation of Culn0.75Ga0.25Se2 thin films
Authors: Ahmed E. , Hill A. E. , Pilkington R. D. , Tomlinson R. D. , Levoska J. , Kusmartseva O. , Leppävuori J.
Published: May 2005

In this paper initial results are presented for the growth and characterisation of polycrystalline Culn0.75Ga0.25Se2 thin films prepared by pulsed laser deposition and flash evaporation. Analogies are drawn between these two important deposition technologies. The deposited films were characterised using a veriety of analytical techniques, including energy‐dispersive analysis of X‐rays and Rutherford‐backscattering spectroscopy for compositional evaluation, X‐ray diffreaction and Raman spectroscopy for structural evaluation, scanning electron microscopy for surface examination and the four‐point and hot‐point probe techniques for electrical characterisation. The comparison of films produced by these two deposition methods revealed that, in terms of their stochiometry, electrical and physical characteristics, good‐quality GIGS thin films could be produced by both techniques.
The X‐ray crystal and molecular structure of [Ba(TDFND)2.tetraglyme], the first molten barium precursor for MOCVD applications
Authors: Nash Jason A. P. , Barnes John C. , Cole‐Hamilton David J. , Richards Barbara C. , Cook Stephen L. , Hitchman Michael L.
Published: May 2005

At 150 K [Ba(TDFND)2, tetraglyme] crystallises in the P1/c space group with a = 17.15(2) Å b = 10.735(5) Å, c = 22.830(7) A, β = 97.56 (7)°, V = 4165 (5) Å3, Z=4. R1 = 0.0435, wR2 = 0.1079. The barium atom is nine‐co‐ordinate, with binding to all the O atoms. The two BaTDFND rings are planar but tilted by 26° from being co‐planar. The five O atoms of the tetraglyme ligand are also essentially co‐planar, but this plane subtends angles of 88.8(1)° and 67.4(1)° to the two BaTDFND planes. The BaO (TDFND) bond lengths are longer than for other related compounds, but the BaO (tetraglyme) bond lengths are similar to those in [Ba(HFA)2.tetraglyme] (HFA  CF3C(O)CHC(O)CF3). The low melting point and the fact that [Ba(TDFND)2.tetraglyme], alone of barium complexes of this kind, can be evaporated without decomposition at 1 atm are attributed to lower intermolecular forces for this compound and to its greater thermal stability.
IR and UV laser‐assisted deposition from titanium tetrachloride: A comparative study
Authors: Alexandrescu R. , Cireasa R. , Dragnea B. , Morjan I. , Voicu I. , Andrei A. , Vasiliu F. , Popescu C.
Published: May 2005

Laser‐induced TiCl4 decomposition at vapour pressure was performed and comparative study of the composition and structure of thermally (at 10.6 μm) and photolytically (at 248 nm) deposited Ti‐based films is presented. Emphasis was given to the less explored titanium deposition process by CO2 laser pyrolysis of TiCl4. The detailed structure of films deposited on quartz substrates was examined by scanning electron microscopy and X‐ray photoelectron spectroscopy. The influence of the incident laser energy on the chemical content of the films as well as on the film growth rate was demonstrated. The results indicate that in the thermal IR decomposition of TiCl4 a multilayer structure is formed with unsaturated TiSix at the interface and oxidized phases at the surface. The photolytic process leads to films with increased purity and a specific growth morphology.
Electrical conductivity of 1,4‐dihydroxyanthraquinone and the complex silver/dihydroxyanthraquinone
Authors: Nasrallah T. Ben , Bernède J. C. , Jamali M.
Published: May 2005

Quinizarin (1,4‐DHAQ) and Ag/I,4‐DHAQ thin films deposited under vacuum were investigated by I–V measurements at various temperatures. It is shown that when submitted to an electric field of 5 × 105 V cm−1 or less, the I‐V characteristics of AI/DHAQ/AI sandwich structures are ohmic. The temperature dependence is I ∝ exp(‐ΔE/kT). The measured activation energy is 0.3 eV in the case of pure DHAQ and 30meV in the case of Ag/DHAQ. Therefore we can imagine that in the former case the conductivity is controlled by thermally activated hopping above intermolecular barriers, while in the latter case the conductivity can be attributed to tunnelling between silver grains.