For the first time, single crystalline GePb was formed using sputtering and laser induced epitaxy. The GePb alloy shows a good crystalline quality without Pb precipitation or clustering. No dislocation is observed at the interface between GePb and Ge. HRBS data indicates that substitutional Pb content of ~0.3% was obtained.

We have investigated the optical properties of Ge and GeSn alloys implanted with phosphorus ions at 400 °C by spectroscopic ellipsometry from far-infrared to ultraviolet. The dielectric response of heated GeSn implants displays structural and transport properties similar to those of heated Ge implants. The far-infrared dielectric function of as-implanted Ge and GeSn shows the typical free carrier response which can be described by a single Drude oscillator. Bulk Ge-like critical points E1, E1 + Δ1, E0', and E2 are observed in the visible-UV dielectric function of heated Ge and GeSn indicating single crystalline quality of the as-implanted layers. Although the implantation at 400 °C recovers crystallinity in both Ge and GeSn, an annealing step is necessary to enhance the carrier activation.

The search for oxide-based room-temperature ferromagnetism has been one of the holy grails in condensed matter physics. Room-temperature ferromagnetism observed in Nb-doped SrTiO3 single crystals is reported in this Rapid Communication. The ferromagnetism can be eliminated by air annealing (making the samples predominantly diamagnetic) and can be recovered by subsequent vacuum annealing. The temperature dependence of magnetic moment resembles the temperature dependence of carrier density, indicating that the magnetism is closely related to the free carriers. Our results suggest that the ferromagnetism is induced by oxygen vacancies. In addition, hysteretic magnetoresistance was observed for magnetic field parallel to current, indicating that the magnetic moments are in the plane of the samples. The x-ray photoemission spectroscopy, the static time-of-flight and the dynamic secondary ion mass spectroscopy and proton induced x-ray emission measurements were performed to examine magnetic impurities, showing that the observed ferromagnetism is unlikely due to any magnetic contaminant.

Transparent TiO2 nanotube arrays of micrometer lengths were prepared by anodization of titanium thin film RF sputtered on indium tin oxide (ITO) which was coated on glass substrate. The sputtering process took place at elevated temperature of 500 degrees C. The structures of the films were studied using scanning electron microscopy (SEM) and X-ray diffraction (XRD) while the optical properties of the films were investigated using UV-visible spectroscopy. Two types of electrolytes were used in this work: an aqueous mixture of acetic acid and HF solution and a mixture of NH4F and water dissolved in ethylene glycol. The concentration of NH4F, voltage and the thickness of the sputtered titanium film were varied to study their effect on the formation of TiO2 nanotube arrays. It is demonstrated in this work that the nanoporous layer is formed on top of the ordered array of TiO2 nanotubes. Furthermore, the optical transmittance of TiO2 nanotubes annealed at 450 degrees C is much lower than the non annealed TiO2 nanotubes in the visible wavelength region. (C) 2011 Elsevier B. V. All rights reserved.

CoFe2 nanowires with high aspect ratios were electrodeposited into the anodic aluminum oxide (AAO) template. The coercivities and remanence measured along the longitudinal axis of the nanowires are found to increase with the length of nanowires. The magnetostatic interaction between the nanowires is responsible for the decrease of coercivity and remanence of an array of nanowires as compared to an isolated single nanowire. By considering the magnetostatic interaction between the nanowires, a simple model as a function of length is used to calculate the coercivity in an array of the nanowire and this model shows good agreement with experimental data.

We report a nonvolatile, write-once-read-many-times (WORM) memory device based on a simple organic-inorganic heterojunction. The organic-based hybrid used is 9,9-dihexylfluorene and Eu-complexed benzoate, which contains both electron-donor (9,9"-dihexylfluorene) and electron-acceptor (europium complex) groups. Under current-voltage testing, the device is able to switch from one initial nonconducting state to a conducting state once a threshold voltage is reached. Diode rectifying characteristics, with a current ratio of four orders of magnitude, is also observed after the device is turned on, which is essential to address one memory cell in large passive matrix circuits.

A systematic investigation of the dependences of the exchange bias and the ferromagnetic resonance frequency on the pore size of the antidot arrays fabricated by depositing Permalloy-FeMn multilayer thin films onto self-organized porous anodic aluminum oxide membranes was carried out. The magnetic and microwave properties of the antidot arrays with different pore sizes ranging from 30 to 80 nm are characterized and compared with that of the continuous thin films. It was found that the exchange bias field and the ferromagnetic resonance frequency are increased with the increase of the pore size, which may tentatively be interpreted in the framework of the random field model. It was also found that by using the antidot arrays in the best condition (the FeNi thickness is 20 nm and the pore size is 80 nm), one can enhance the exchange bias field from 65 to 135 Oe and the ferromagnetic resonance frequency from 3.1 to 4.1 GHz accordingly.

The molecular conformation-dependent write-once read-many-times (WORM) memory based on an acrylate polymer containing pendant carbazole (donor) groups is transformed into a flash (rewritable) memory when acrylate units containing pendant oxadiazole (acceptor) groups are incorporated to form a copolymer. The as-fabricated device based on the acrylate copolymer containing carbazole-oxadiazole donor-acceptor pendant groups is in its low conductivity state and can be written to a high conductivity state at a threshold voltage of -1.8 V. The high conductivity state can be switched (erased) to the low conductivity state with a positive bias of 3.6 V. The device exhibits a high ON/OFF current ratio of 103 at a read voltage of -1 V. This rewritable polymer memory can be programmed and erased repeatedly with good accuracy. The copolymer is potentially useful for application in flash memory devices.

The half-metallic La0.67Sr0.33MnO3 (LSMO) thin film was fabricated by pulsed laser deposition on porous anodic aluminum oxide template. The mesh-like pattern was obtained with the lateral size of 30 - 50 nm. This laterally mesoscopic-patterned LSMO film exhibits typical low field magnetoresistance. The coercive field of 268 Oe is larger than that of the continuous polycrystalline film on Al2O3 substrate of 115 Oe, which is consistent with the larger coercive field of magnetic nanowires compared with magnetic bulk materials or thin films. This work provides a costeffective method to fabricate mesoscopic-pattern film with the lateral size down to several tens nanometers. (c) 2007 Elsevier B.V. All rights reserved.

We present an electrical-bistability device based on MIM-sandwiched structure. Poly(N-vinylcarbazole) (PVK) mixed with gold nanoparticles (GNPs) serve as the active layer between two metal electrodes. After applying a voltage, the as-fabricated device can transit from low conductivity state to high conductivity state. By simply using a reverse bias, the high conductivity state can return to the low conductivity state. An ON/OFF current ratio as high as 10(5) at room temperature has been achieved. The memory effect is attributed to electric-field-induced charge transfer complex formed between the PVK and the GNPs. The device shows a good stability under stress test for both states and exhibits a high potential on Flash-type memory applications.

CoAlO composite antidot arrays were fabricated on self-organized porous anodic aluminium oxide (AAO) membranes. The effects of pore size and film thickness on the magnetism and magnetotransport properties of the CoAlO films were investigated. On increasing the pore dimensions in the arrays, an anisotropic to isotropic magnetism transition was observed. The result is discussed based on the competitive contributions from the external field induced uniaxial anisotropy and the topology-induced shape anisotropy superimposed by the stray fields from the pore channels. Magnetoresistance showed corresponding variations with increasing pore sizes, as evidenced by a magnetoresistance variation from typically anisotropic to nearly isotropic behaviour. When deposited on large-pored AAO membranes, the antidot arrays showed no obvious anisotropy at different film thicknesses. It led to negligible magnetoresistive loops in the thick films of high structural continuity. The possible reasons for spin-independent electron scatterings are discussed.

We report a non-volatile, write-once-read-many times (WORM) memory device based on a simple organic-inorganic heterojunction. The organic film used is 9, 9-dihexylfluorene and Eu-complexed benzoate (PF6Eu (DBM)), which contains both electron-donor (9, 9-dihexylfluorene) and electron-acceptor (europium complex) groups. The inorganic n-type silicon substrate is used as the bottom electrode, while the Al is used as the top electrode. Under current-voltage testing, the device is able to switch from one initial non-conducting state (OFF) to a conducting state (ON) once a threshold voltage is reached under the first positive sweep. The “OFF” state is not recoverable with subsequent negative sweep after the device is turned “ON”. The ON/OFF current ratio is around 4×10 4 . Diode rectifying characteristics is also observed for the turned-on device with a current ratio of 7×10 4 , which is essential to address one memory cell in large passive matrix circuits. Reliability test is carried out and the device is able to sustain its “ON” state for at least 12 hours without any external bias.

Photo-induced reduction of gold and platinum metal salt solutions was carried out using viologen graft copolymerized on low-density polyethylene (LDPE) films and viologen-containing poly(vinylidene fluoride) (PVDF-PVBV) microporous membranes. The effects of the UV irradiation time and concentration of the metal salt solutions on the metal ion reduction process and the resultant metal deposition on the polymeric substrates were investigated. The metal-polymer composites were characterized using X-ray photoelectron spectroscopy (XPS), scanning and transmission electron microscopy (SEM and TEM), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and UV-visible absorption spectroscopy. The amount of metal uptake, the state of the metal, and the size of the metal particles were found to be strongly dependent on the UV irradiation time and the type and concentration of the metal salt solution. The microporous structure and the high viologen content of the PVDF-PVBV membrane constitute an effective matrix for metal ion reduction and preparation of metal nanoparticles.

Molecular modification of a fluorinated polyimide (FPI), 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride + 4,4‘-bis(4-aminophenoxy)diphenyl sulfone, via ozone pretreatment and thermally induced graft copolymerization with N-isopropylacrylamide (NIPAAm) in a N-methyl-2-pyrrolidone solution, was carried out. The resulting FPIs with grafted NIPAAm polymer side chains [FPI-g-P(NIPAAm) copolymers] were cast into microfiltration membranes by phase inversion in water at temperatures ranging from 4 to 55 °C. The surface composition of the membranes was characterized by X-ray photoelectron spectroscopy. The surface composition, mean pore size, and morphology of the membrane varied with the temperature of the aqueous coagulation bath. For the copolymer membrane cast below the lower critical solution temperature of the NIPAAm polymer (∼32 °C), the rate of water permeation increased substantially at a permeate temperature above 32 °C. For the flux of 2-propanol through the membrane cast above 32 °C, a rever...

High-resolution X-ray photoelectron spectroscopic (XPS) measurements of the various intrinsic redox states of polyaniline (PANI), using a monochromatized Al—Kα source, were carried out. The presence of the imine, amine and positively charged nitrogen species corresponding to a particular intrinsic redox state and protonation level of the polymer was resolved quantitatively and unambiguously. The result confirmed the peak assignments of former XPS core-level studies using the lower resolution non-monochromatized Mg—Kα X-ray source. Thus, the high-resolution XPS using a monochromatized Al—Kα X-ray source is a truly unique tool for the convenient and quantitative analysis of the various intrinsic redox states of PANI.

The oxygen ion-beam induced surface roughening observed during SIMS (secondary ion mass spectrometry) depth profiling of both the Si (001) and Si (111) surfaces has been studied by atomic force microscopy (AFM) as a function of both sputtered-depth and by varying the incident angles of the primary [Formula: see text] ion beam in the range of 44°–56°. Our result shows a surface orientation dependence of surface roughening whereby the transition roughening depth as well as the sputtering rate were observed to be greater in Si (111) than in Si (001). The orientation dependence was particularly obvious when increasing the incident angle of the [Formula: see text] ion beam from 44° to 56°. In addition, prominent elongated triangular and rectangular features are observed from sputtered Si (001) and Si (111) surfaces respectively at 56° incidence. These features may be associated with the formation of {111} and {001} facets on the sputtered Si (001) and Si (111) surfaces respectively.

“removed due to double publication”. The original paper: Journal: Semiconductor Science and Technology Create an alertIssue Volume 15, Number 6 Citation: L S Tan et al 2000 Semicond. Sci. Technol. 15 585 doi: 10.1088/0268-1242/15/6/317 can be accesses at IOP: http://iopscience.iop.org/0268-1242/15/6/317

Ohmic contacts have been fabricated on Si-doped GaN using Ti/Al by low temperature annealing at 500 °C. A contact resistivity of 8.6×10-6 ohm cm2 was obtained for n-GaN samples doped to 3.67×1018 cm-3. Secondary ion mass spectrometry (SIMS) analysis showed that Al diffused through the Ti layer after annealing. Furthermore, energy dispersive x-ray spectroscopy (EDS) analysis showed that reaction products of Al, Ti, Ga and N were present at the interface. Hence, a complex ternary or quaternary nitride as a possible low barrier height material to n-GaN may have resulted in good ohmic contact. Photoluminescence (PL) showed that there was no degradation in the epilayer quality of the film after annealing at 500 °C for 25 minutes.

Comparative ab initio restricted Hartree–Fock (RHF) and density functional theory (DFT) calculations were performed to investigate the geometric and electronic structures of various neutral aniline oligomers. These oligomers were selected to model polyaniline (PANI) in different intrinsic oxidation states, with an aim to study the applicability and extendibility of the theoretical methods to conjugated polymers. In general, we found that DFT calculations produce results that are in good agreement with observations from x-ray diffraction, ultraviolet-visible absorption, ultraviolet photoelectron and x-ray photoelectron spectroscopy. The DFT method has reproduced well the ∼4.0 eV π–π* transition of leucoemeraldine base and the ∼2.0 eV Peierls gap transition of pernigraniline base. The valence band structure and the ∼1.2 eV energy separation of nitrogen core levels of emeraldine base are also correctly predicted. On the other hand, large discrepancies with experimental measurements are predicted by the RHF method. Single-point MP2 calculations show that the DFT-optimized structures are all at lower energy than the RHF-optimized ones.

X-ray photoelectron spectroscopy was employed for the in situ study of interactions between thermally evaporated Mg atoms and electroactive polyaniline (PANI) films of various intrinsic oxidation states. Quantitative changes in the N1s core-level spectra and the Mg2p core-level spectra, as well as the changes in surface chemical stoichiometry of these films throughout the Mg evaporation process were carefully monitored. Although the nitrogen sites appeared to be more attractive to the in-coming Mg atoms and the emeraldine base (EB) and nigraniline base (NA) films underwent an apparent decrease in intrinsic oxidation state ([=N-]/[-NH-] ratio) as a result of Mg evaporation, there is no direct interaction between the two species. On the other hand, the adsorbed oxygen from the bulk of the polymer film played a dominant role in the interfacial interactions between the polymer and the metal. Characterization of the delaminated indium-tin-oxide (ITO) and polymer surfaces from EB film and its camphorsulfonic acid-doped counterpart cast on ITO substrates had also been carried out to evaluate the interaction of PANI with the high work function metal.