Formation of ordered nanostructures in liquid-crystalline block copolymers with side-chain semiconductor materials

ABSTRACT

We developed a novel block copolymer composed of poly(ethylene oxide) (PEO) and polymethacrylate functionalized with liquid–cryst-alline oligothiophene by using the atom transfer radical polymerization (ATRP), aiming at application to organic photovoltaic (OPV) cells. Thermal investigation showed that the resultant polymer exhibits liquid–crystalline phases both on heating and cooling. Morphologies of the thin films of the block copolymer were investigated by atomic force microscopy (AFM). Microphase separation with a small size of almost 10 nm (nano-phase-separated structures) was observed upon annealing.     

Synthesis and properties of PbGeO3 nanostructures

PbGeO₃ nanostructures including nanofibers and nanobelts, have been synthesized via a facile hydrothermal method by the reaction between GeO₂ and Pb(CH₃COO)₂·3H₂O in the absence of any surfactant. The influences of synthetic parameters, such as reaction time, reaction temperature, and the concentration of ethylenediamine, on the morphologies and sizes of PbGeO₃ nanostructures have been investigated. It is found that an evolution of PbGeO₃ nanostructures from nanobelts to nanofibers is observed for the first time with the reaction time increased from 1 h to 6 h. The diameters of PbGeO₃ nanofibers can be controled from 300–900 nm to 80–120 nm by adjusting the concentration of ethylenediamine. Under similar conditions, PbGeO₃: Eu³⁺ nanofibers with rough surfaces can also be obtained. The photoluminescent spectra of PbGeO₃: Eu³⁺ nanofibers exhibits two fluorescence emission peaks centered at around 591 and 614 nm as the excitation wavelength is 395 nm. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electron optical identification of precipitations in silicon semiconductor devices

In silicon MOS semiconductor devices precipitations were observed by TEM in the boron-diffused regions. They were identified by using selected area diffraction, high resolution lattice plane imaging, Auger spectroscopy and microanalysis of X-rays. The results lead to the conclusion that these particles consist of polycrystalline silicon and that oxygen and nitrogen, probably carbon too are concentrated inside the particles. The formation of these precipitations is only due to the technological process of the device manufactoring and does not depend on the silicon starting material.     

Numerical modeling of frequency influence on the electromagnetic stirring of semiconductor melts

Alternating magnetic fields can be used in order to increase the level of convection and to mix the doped semiconductor alloys. A numerical analysis of the electromagnetic induced convection in GaInSb semiconductor melts is performed by using the software package CrysVUn. The magnetic field parameters are varied in order to obtain a maximum efficiency of the induced convection with a minimum quantity of the heat released in the melt. The influence of the electrical current frequency on the convection intensity is analyzed for samples with various radii (R = 0.5 – 3cm). Numerical procedure is validated by comparing the numerical results obtained in mercury samples with the experimental data given from the literature, which show a maximum stirring for a magnetic skin depth δ = 0.2R , in the case of a mercury sample with the radius R = 10 cm. This maximum corresponds to a shielding parameter R _ω = 40. Our numerical results show that the value of the shielding parameter for which the convection intensity reaches the maximum depends on the sample radius and increases when the sample radius increases. The results of this analysis are important in the case of samples with small radius, when a good mixing of the melt can be obtained for frequencies much lower than those corresponding to a shielding parameter R_ω = 40. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Hydrothermal synthesis and electrochemical properties of MnO2 nanostructures

Manganese oxide (MnO₂) nanowires with diameters of 40–50 nm and lengths up to several micrometers have been successfully synthesized through a simply hydrothermal route. The influences of synthetic parameters, such as reaction time, and reaction temperature, on the growth and morphologies of MnO₂ nanowires have been investigated. It is found that MnO₂ nanowires can be evolved into MnO₂ microrods with the reaction time/temperature increased. The electrochemical characterization of MnO₂ nanostructures was carried out in 1 M Na₂SO₄ aqueous electrolyte at the scan rate of 10 mV s^‐1. The results indicate that the MnO₂ microrods obtained when the reaction performed at 200 °C for 24 h showed the best performance for supercapacitor. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ordered gold nanostructures on sapphire surfaces: Fabrication and optical investigations

The possibilities of obtaining ordered gold nanoarrays on sapphire surfaces with oriented nanorelief are demonstrated. The structures are morphologically described using atomic force microscopy data. A study of the angular dependence of the reflectivity in the visible range of electromagnetic waves has revealed some features which are likely to indicate surface plasmon-polariton excitation at the air-gold interface under exposure to p-polarized radiation. The experimental results are found to be in good agreement with the theoretical calculations.     

Numerical modeling of optical properties of a system of two zone plates for focusing hard synchrotron radiation

Results of numerical experiments on focusing of a monochromatic spherical wave by a system of two linear zone plates are reported. Calculations were performed for a photon energy of 12.3985 keV and zone plates with a radius of the first zone of 5 μm, a number of zones of 628, and an aperture of 250 μm. To calculate the Kirchhoff integrals, the double Fourier transform method was used and the fast Fourier transform procedure on a grid with a number of points 65 536 = 2¹⁶ was applied. On the basis of the calculation results, a conclusion was drawn that two zone plates operate as one with a doubled phase shift in zones with a material if the longitudinal distance between them is smaller than 1/3 of the focus depth and the transverse displacement is smaller than 1/3 of the outermost zone width (the focus size). If the distance (displacement) exceeds the focus depth (size), the two zone plates operate independently, similar to refracting lenses with a set of different focusing orders, including the zero order. The nature of the moiré pattern at a transverse displacement of the zone plates is discussed.     

Fabrication of cobalt ferrite nanostructures and comparison of their electrochemical properties

Cobalt Ferrite (CoFe₂O₄) nanorods and nanorings have been successfully controllable synthesized by solvothermal method. The specific characteristics were confirmed by X‐ray diffraction studies (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The measurement of their electrochemical properties as supercapacitor electrode materials indicate different morphological characterizations have various capacitive effects, and CoFe₂O₄ nanorings generally have larger specific capacitances than nanorods at different scan rates and current densities in 1.0 M KOH solution.     

Structural and optical properties of the gadolinium-lead-germanate glasses

Glasses in the system xGd₂O₃(100 − x)[7GeO₂·3PbO] with 0 ≤ x ≤ 40 mol% have been prepared from melt quenching method. The influence of gadolinium ions on structural behavior in lead-germanate glasses has been investigated using FTIR, UV-VIS and EPR spectroscopy. The structural changes have been analyzed with increasing rare earth concentration.FTIR data suggest that the glass network modifications has taken place mainly in the germanate part whereas the lead part remained unmodified and its network consists mainly from the [GeO₄], [GeO₆], [Ge₂O₇] structural units and with interconnected through Ge-O-Ge bridges in [GeO₄] structural units. The changes in amplitude and bandwidth of the UV-VIS bands ranging from 200 nm to 350 nm depend on the content of Gd₂O₃.By increasing the Gd₂O₃ content in the glass matrix, the optical band gap energy increases, indicating changes of the lattice parameters and that no non-bridging-oxygens form upon the addition of gadolinium oxide. The decreasing trend has been observed both in optical gap band energy and refractive index of oxide glasses at x = 10 mol% Gd₂O₃ indicating breaks up the [GeO₄] tetrahedral units bonds and create of non-bridging oxygen atoms. For sample with x ≥ 20 mol%, the gadolinium ions having a behavior of network formers (g ≈ 4.8) will coordinate more with the excess of oxygen. Accordingly, the gadolinium ions are generally suspected to improve their environment of network formers.     

Growth and photoluminescence properties of CdS solid solution semiconductor

Photoluminescence (PL) emitted from Cd_1‐xZn_xS and CdS_1‐ySe_y solid solution semiconductor was significantly stronger than PL from the pure CdS and CdSe semiconductor. The samples were prepared using an improved Se‐S‐Na₂S flux route. Photoluminescence in Cd_1‐xZn_xS crystal was brightly yellow at the room temperature under VU radiation. The phase and composition of the solid solution was measured by the XRD and was confirmed by UV‐NIS spectrum as x of 0.3 and y of 0.2. The enhanced photoluminescence was presumably due to the introduction of extra defect (vacancies) by solid solution action and consequently the increasing of luminescence center concentration. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Microscopic properties of silicon dihydride bonding in a-Si:H

We use proton nuclear magnetic resonance to probe stable silicon dihydride existing in high defect density hydrogenated amorphous silicon. The silicon dihydride line shape exhibits the well-known ‘Pake’ doublet form resulting from a dipole interaction between two protons. We simulate the line shape using the relevant Hamiltonian and broadening effects known to occur in this amorphous system and discuss the sets of simulation parameters that reproduce the experimental data. The sets share a common feature – they require the proton–proton separation to be approximately 1.8 Å, not the 2.4 Å determined by recent theoretical calculations.     

Linear and nonlinear optical properties of the optical fiber doped with silicon nano-particles

We report for the first time the realization of the optical fiber doped with silicon nano-particles. Silica glass optical fibers incorporated with silicon nano-particles were fabricated by the modified chemical vapor deposition and the solution doping technique. We found that a broadband absorption appeared at 450–1300 nm and a photoluminescence band appeared at 600–1100 nm upon pumping with the Ar-ion laser, indicating that silicon nano-particles were successfully incorporated in the fiber core. We also estimated the third-order optical nonlinearity of the optical fibers by measuring the fringe shift obtained from the long-period gratings upon pumping with the Ar-ion laser from 477 to 512 nm. Importantly the optical nonlinearity at 1550 nm was found to be ～1.5 × 10^?15 m²/W and we believe that this large optical nonlinearity is caused by the exciton absorption of the silicon particles.     

Studies of the optical properties of sodium copolyphosphate glasses

A number of samples of glassy sodium polyphosphate and copolyphosphates of sodium — cobalt, sodium — copper, sodium — nickel, sodium-manganese and sodium — calcium were prepared and their optical properties were investigated. The ultraviolet and visible spectra of these glasses were recorded at the room temperature. It was found that the fundamental absorption edge of these glasses usually occurs in the ultraviolet — visible region. The optical absorption edges (E₀) were calculated by using the relation h ν = B (hν − E₀)² where B is constant. The linear variation of (hν)^1/2 with hν where is the absorption coefficient and hν is the incident photon energy, is taken as evidence of non-direct interband transitions. The E₀ values obtained for copolyphosphate glasses appeared to depend on the size of the counter cation. The infrared spectra of all these glasses appeared to be almost the same, indicating the presence of characteristic P --- O --- P linkages of linear polyphosphate chains and two non bridging oxygen atoms bonded to phosphorus atoms O --- P --- O (PO₂) units in the polyphosphate tetrahedra.     

The preparation and electrical properties of thin chalcogenide semiconductor films

Thin chalcogenide films from the GeTeAsSi system have been prepared using electron beam evaporation and R.F. sputtering techniques. The techniques are described in some details as it is believed that the deposition procedure has a significant on subsequent electrical switching behaviour.     

Growth,structure, electrical and optical properties of transition metal chalcogenide crystals synthesized by improved chemical vapor transport technique for semiconductor technologies

Low dimensional structures, including bulk crystals, thin films, nanowires and nanotubes, have received remarkable attention due to their novel functionality and potential applications in various areas of optics, electronics, photonics, and sensing devices and photovoltaic field. Recently, remarkable progress and modification have been achieved in the synthesis process of crystalline material by vapor transport technique. In this review, we introduce an improved concept of the closed tube Chemical Vapor Transport (CVT) technique for the single crystal growth of ZrSTe, TiSTe and TiSeTe. A modified reverse temperature profile has reported the growth of ZrSTe, TiSTe and TiSeTe results show the good crystalline quality of synthesized materials. The single-crystal X-ray diffraction data reveals all three samples have trigonal unit cell structure with a space group of P31. The Semiconducting behavior of grown crystals of ZrSTe, TiSTe and TiSeTe was verified by two probe resistivity measurements, Hall Effect measurements and optical absorption at room temperature in the spectral range of 200 nm - 2200 nm. In this review, we highlight the recent progress in the transition of metal chalcogenides for their advanced application in solar energy conversion, thin-film electronics, optoelectronic devices and quantum communication devices. Moreover, different experimental challenges within the described growth technique are probed. Additionally, a survey was done for the possible enhancement of Transition Metal Chalcogenide (TMC) crystalline materials grown by the Chemical Vapor Transport technique based on various growth parameters.     

Anisotropic optical properties of crystals with the Ca-gallogermanate structure

The optical properties of inactivated and activated crystals with the structure of Ca-gallogermanate have been studied. The components of the gyration pseudotensor for Sr₃Ga₂Ge₄O₁₄ crystals are determined. In the ultraviolet range of the spectra of all the crystals studied, the bands of circular and linear dichroism and the anomalous behavior of the linear birefringence are observed irrespective of the activating dopant. The formation of these bands is not associated with the electron transitions of doping ions and can be caused by structural defects formed in the growth process.     

Controllable synthesis and field emission properties of In2O3 nanostructures

Large‐scale In₂O₃ nanorods, nanocubes and nanowires have been successfully synthesized by chemical vapor deposition route under atmospheric pressure. The structures and morphologies were characterized by x‐ray diffraction (XRD), scanning election microscopy (SEM) and high‐resolution transmission electron microscopy (HRTEM). The growth mechanisms of these In₂O₃ nanostructures were analyzed in detail based on the experimental results. Field‐emission measurements of these nanostructures demonstrated that nanorods with rectangular cross‐section possessed good performance with a turn‐on field of 2.47 Vμm^–1 and a field enhancement factor of 4597. The room‐temperature photoluminescence (PL) spectrum of the In₂O₃ nanostructure showed UV emission centered at about 396 nm and visible emissions located at 541 and 623 nm. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Some ways to solve the problem of controllable chalcogenide semiconductor thin film properties

The possibilities of guided change of chalcogenide semiconductors (ChS) electrical and photoelectrical properties are revealed. These possibilities are based on the contact metal influence and on diffusion of some metals in the ChS films.     

Simulation of the optical properties of Tm:ZBLAN glass

The optical properties of Tm:ZBLAN glass have been simulated. The simulated optical spectra agreed substantially with the observed spectra. The population of the energy levels of the Tm³⁺ ion under dual-wavelength excitation for upconversion emission and amplification was evaluated by solving the rate equation with the simulated transition probabilities and spectral shapes of the transitions of which the initial levels were from the ³H₆ to ³P₂ levels. The large population of the ¹G₄ level, which is the upper level for 480 nm laser oscillation, was estimated for the conditions of laser oscillation at room temperature. We also proposed new combinations of the excitation wavelengths for the amplification of the 1470 nm signal.