Indium oxide, tin oxide and indium tin oxide nanostructure growth by vapor deposition

Indium oxide, tin oxide and indium tin oxide nanowires have been grown by vapor deposition on Si and quartz substrates. Under the growth conditions used, pure SiO_x nanowires, a mixture of SiO_x and indium oxide, tin oxide or indium tin oxide nanostructures, or pure indium oxide, tin oxide or indium tin oxide nanostructures could be obtained at different substrate temperatures. The growth mechanism of the obtained nanostructures at different substrate temperatures is discussed. Optical and electrical properties of the deposited pure indium oxide, tin oxide or indium tin oxide nanostructures have been measured, and low sheet resistances on quartz substrates have been obtained for indium oxide and indium tin oxide nanostructures.     

Formation of lactose-mannitol molecular alloys by solid state vitrification

In this paper, we report the possibility to form glassy molecular alloys (α-lactose)_1−x(mannitol)_x for x<0.5 by co-milling two crystalline powders of pure α-lactose and pure mannitol β. The results have been established by differential scanning calorimetry and by powder X-ray diffraction. The concentration dependence of the glass transition temperature is found to obey the Gordon Taylor rule expected for regular solutions. It is also shown that the milling of pure mannitol β (x=1) leads to a polymorphic transformation towards the metastable form α of mannitol.     

Observation of negative photoconductivity in (ZnO)x(CdO)1−x films

In this study, (ZnO)_x(CdO)_1?x films were prepared by ultrasonic spray pyrolysis (USP) technique at a substrate temperature of 400 °C. X-ray diffraction patterns of the films indicate that the (ZnO)_x(CdO)_1?x films have hexagonal wurtzite and cubic structure for the constituent materials. A decrease in the average transmission with increasing quantity of the cadmium acetate dehydrate in the sprayed solution was observed. The photoconductivity transients were performed using UV light, which has 360 nm wavelength. After light cut off, conductivity changed slowly, and the decay time was thousands of seconds. The films with x=0.2 and 0 exhibited negative photoconductivity. Temperature-dependent photoconductivity and dark conductivity measurements were performed and negative photoconductivity was also observed for the same films (x=0.2 and 0). Photoluminescence measurements were performed and band-to-band excitation energies of (ZnO)_x(CdO)_1?x films were determined. Band gap of the pure CdO film was found as 3.11 eV, interestingly.     

Laser-induced congruent forward transfer of SiO x -layers

Laser-induced forward transfer of inorganic oxide films is demonstrated using the example of SiO _x -layers. SiO _x with x<2 is strongly UV-absorbing, so that excimer lasers are suited for inducing transfer. When the distance between donor and receiving substrate is reduced to zero, congruent transfer is possible; i.e. the deposited geometry corresponds exactly to the ablated spot. This zero-distance configuration is accomplished by using a polydimethylsiloxane (PDMS) film as the receiving substrate, which is cast directly on the SiO _x -coated fused silica donor substrate. After curing of the PDMS, the SiO _x -layer is irradiated by a single 25 ns-KrF-excimer laser pulse through the donor substrate. At a fluence of 300 to 600 mJ/cm² predefined areas of a 830 nm thick SiO _x -layer are cleanly transferred to the PDMS-substrate, i.e. the irradiated parts of the layer stick to the PDMS-surface after peeling it off. This way spot arrays or stripes with lateral dimensions of a few μm as well as free-standing grids can be generated. By multipulse exposure, the fabrication of stacks or bridges is possible.     

Growth of cubic MgxZn1−xO alloy films by electron beam evaporation

We report the growth of cubic Mg_xZn_1−xO alloy thin films on quartz by electron beam evaporation. It can be found that all the samples have sharp absorption edges by the absorption measurements. X-ray diffraction measurements indicate the Mg_xZn_1−xO films are cubic phase with preferred orientation along the (1 1 1) direction. Energy dispersive spectrometry (EDS) demonstrates that the Mg concentration in Mg_xZn_1−xO films is much higher than the ceramic target used, and the composition can be tuned in a small scope by varying the substrate temperature and the beam electric current. The reasons of this phenomenon are also discussed.     

Room-temperature ferromagnetism in Sn1−xMnxO2 nanocrystalline thin films prepared by ultrasonic spray pyrolysis

Sn_1−xMn_xO₂ (x=0.01-0.05) thin films were synthesized on quartz substrate using an inexpensive ultrasonic spray pyrolysis technique. The influence of doping concentration and substrate temperature on structural and magnetic properties of Sn_1−xMn_xO₂ thin films was systematically investigated. X-ray diffraction (XRD) studies of these films reflect that the Mn³⁺ ions have substituted Sn⁴⁺ ions without changing the tetragonal rutile structure of pure SnO₂. A linear increase in c-axis lattice constant has been observed with corresponding increase in Mn concentration. No impurity phase was detected in XRD patterns even after doping 5 at% of Mn. A systematic change in magnetic behavior from ferromagnetic to paramagnetic was observed with increase in substrate temperature from 500 to 700 °C for Sn_1−xMn_xO₂ (x=0.01) films. Magnetic studies reveal room-temperature ferromagnetism (RTFM) with 3.61×10⁻⁴ emu saturation magnetization and 92 Oe coercivity in case of Sn_1−xMn_xO₂ (x=0.01) films deposited at 500 °C. However, paramagnetic behavior was observed for the films deposited at a higher substrate temperature of 700 °C. The presence of room-temperature ferromagnetism in these films was observed to have an intrinsic origin and could be obtained by controlling the substrate temperature and Mn doping concentration.     

Effect of substrate annealing on the quality of pulsed laser deposited Zn1−xMgxO thin films

The annealing effects of sapphire substrate before deposition on the quality of epitaxial Zn_1−xMg_xO thin films grown by pulsed laser deposition are reported. Our Experimental results indicate that the surface quality of Zn_1−xMg_xO thin films and hexagonal columnar growth is improved on the annealed sapphire substrate at high temperatures due to formation of atomic terraces on the substrate surface. The photoluminescence signals also increases with the increasing annealing temperature of the substrate.     

Theory of band gap bowing of disordered substitutional II–VI and III–V semiconductor alloys

For a wide class of technologically relevant compound III?CV and II?CVI semiconductor materials AC and BC mixed crystals (alloys) of the type A _x B_1?x C can be realized. As the electronic properties like the bulk band gap vary continuously with x, any band gap in between that of the pure AC and BC systems can be obtained by choosing the appropriate concentration x, granted that the respective ratio is miscible and thermodynamically stable. In most cases the band gap does not vary linearly with x, but a pronounced bowing behavior as a function of the concentration is observed. In this paper we show that the electronic properties of such A _x B_1?x C semiconductors and, in particular, the band gap bowing can well be described and understood starting from empirical tight-binding models for the pure AC and BC systems. The electronic properties of the A _x B_1?x C system can be described by choosing the tight-binding parameters of the AC or BC system with probabilities x and 1 ? x, respectively. We demonstrate this by exact diagonalization of finite but large supercells and by means of calculations within the established coherent potential approximation (CPA) We apply this treatment to the II?CVI system Cd _x Zn_1?x Se, to the III?CV system In _x Ga_1?x As and to the III-nitride system Ga _x Al_1?x N.     

Annealing effects on the bonding structures, optical and mechanical properties for radio frequency reactive sputtered germanium carbide films

The effects of thermal annealing in vacuum on the bonding structures, optical and mechanical properties for germanium carbide (Ge_1−xC_x) thin films, deposited by radio frequency (RF) reactive sputtering of pure Ge(1 1 1) target in a CH₄/Ar mixture discharge, are investigated. We find that there are no significant changes in the bonding structure of the films annealed below 300 °C. The fraction of Ge-H bonds for the film annealed at temperatures (T_a) above 300 °C decreases, whereas that of C-H bonds show a decrease only when T_a exceeds 400 °C. The out-diffusion of hydrogen promotes the formation of Ge-C bonds at T_a above 400 °C and thus leads to a substantial increase in the compressive stress and hardness for the film. The refractive indices and optical gaps for Ge_1−xC_x films are almost constant against T_a, which can be ascribed to the unchanged ratios of Ge/C and sp²-C/sp³-C concentrations. Furthermore, we also find that the excellent optical transmission for an antireflection Ge_1−xC_x double-layer film on ZnS substrate is still maintained after annealing at 700 °C.     

Picosecond luminescence of excitons localized by disorder in CdSxSe1−x

We have investigated in CdS_xSe_1−x and in pure CdSe the temporal evolution of the excitonic luminescence with 20 ps time resolution. In CdSe and in alloys with x < 0.15 the onset and decay of the luminescence can be described by time constants which are independent of the photon energy in the region of the free and bound excitons. In contrast, the time constants vary strongly over the main emission band for x > 0.15, which is attributed to the relaxation of excitons localized by compositional disorder. A simplified hopping model is presented which accounts for the experimental findings.     

Decrease of superparamagnetic fraction at room temperature in ultrafine CoFe2O4 particles by Ag doping

Co_1???x Ag _x Fe₂O₄ nanoparticles have been prepared by the combustion route. The average crystallite sizes for compositions with x = 0 and 0.2 are found to be 36 and 33 nm respectively from the XRD line broadening. Compared to the pure CoFe₂O₄, Ag-doping reduces the intrinsic magnetization values (M, M _r), but enhances coercivity (H _c). Mössbauer spectra show two sextets, indicating occupancies of tetrahedral and octahedral sites by Fe^3?+?. Hyperfine fields of 505 and 477 kOe in pure CoFe₂O₄ have been found for octahedral and tetrahedral sites respectively at liquid nitrogen temperature. The hyperfine field decreases with Ag-doping which also corroborates the magnetization studies. EPR study confirms the room temperature ferromagnetic behavior for Co_1???x Ag _x Fe₂O₄ (x = 0.2). The room temperature Mössbauer studies on x?=?0.0 and 0.2 show the ferromagnetic sextets (95%) along with superparamagnetic doublet (5%). However, x = 0.6 sample shows the ferromagnetic sextets only at room temperature. Highly Ag doped samples could be useful for the fabrication of the high-density magnetic materials as well as magnetic drug delivery.     

Electronic structure of GaAs1−xNx under pressure

The electronic band structures of GaAs_1−xN_x for x=0.009, 0.016, 0.031 and 0.062 are calculated ab initio using a supercell approach in connection with the full-potential linear muffin-tin orbital method. Corrections for the ‘LDA gap errors’ are made by adding external potentials which are adjusted to yield correct gaps in pure GaAs. Even small amounts of nitrogen modify significantly the conduction bands, which become strongly non-parabolic. The effective mass in the lowest conduction band thus exhibits strong k-vector dependence. Calculated variations of gaps and effective masses with x and externally applied pressure are presented and compared to a variety of experimental data. There are significant error bars on our results due to the use of the supercell approach. These are estimated by examining the effects of varying the geometrical arrangement of the N-atoms substituting As. However, the calculations show that the electron mass for x>0.009 is much larger than that of pure GaAs, and that it decreases with x.     

Gas barrier properties of titanium oxynitride films deposited on polyethylene terephthalate substrates by reactive magnetron sputtering

Titanium oxynitride (TiN_xO_y) films were deposited on polyethylene terephthalate (PET) substrates by means of a reactive radio frequency (RF) magnetron sputtering system in which the power density and substrate bias were the varied parameters. Experimental results show that the deposited TiN_xO_y films exhibited an amorphous or a columnar structure with fine crystalline dependent on power density. The deposition rate increases significantly in conjunction as the power density increases from 2 W/cm² to 7 W/cm². The maximum deposition rate occurs, as the substrate bias is −40 V at a certain power densities chosen in this study. The film's roughness slightly decreases with increasing substrate bias. The TiN_xO_y films deposited at power densities above 4 W/cm² show a steady Ti:N:O ratio of about 1:1:0.8. The water vapor and oxygen transmission rates of the TiN_xO_y films reach values as low as 0.98 g/m²-day-atm and 0.60 cm³/m²-day-atm which are about 6 and 47 times lower than those of the uncoated PET substrate, respectively. These transmission rates are comparable to those of DLC, carbon-based and Al₂O₃ barrier films. Therefore, TiN_xO_y films are potential candidates to be used as a gas permeation barrier for PET substrate.     

Density and related thermophysical properties of metastable liquid Ni-Cu-Fe ternary alloys

The densities of liquid Ni-Cu-Fe ternary alloy system were investigated by molecular dynamics method in combination with a MEAM (Modified Embedded Atom Method) potential model. The temperature range is from 1000 to 2200 K, including both a broad superheating range and a large undercooled regime. The densities of six Ni100−2xCuxFex alloys (x=0,10,20,30,40,50) decrease linearly with the rise of temperature at the superheated and undercooled states, and increase with the enhancement of Ni content. Among the simulated alloys, the densities of only liquid pure Ni and Ni₆₀Cu₂₀Fe₂₀ alloy are available in literatures, which are in good agreement with the calculated values. According to the relationship between the excessive volume and the alloy composition, it can be deduced that Ni100−2xCuxFex alloys deviate from ideal solution. Moreover, a comparison was also performed between the calculated results and the approximated values by Neumann-Kopp's rule. Based on the obtained density data, the thermal expansion coefficients are also derived. It firstly decreases to a minimum value, and then displays a rise with the increase of Ni content.     

Ge1-xCx double-layer antireflection and protection coatings

The antireflection Germanium carbide (Ge_1-xC_x) coating, deposited using RF reactive sputtering, on both sides of ZnS substrate wafer has been developed. The infrared (IR) transmittance spectra show that the IR transmittance in the wavelength region between 8 and 12 μm for the designed system Ge_1-xC_x/ZnS/Ge_1-xC_x is greatly enhanced compared to that for ZnS substrate. In addition, the double-layer coated ZnS substrate is approximately four times as hard as uncoated ZnS substrate. This investigation indicates that a double-layer Ge_1-xC_x coating can be used as an effective antireflection and protection coating on ZnS infrared window.     

Hall effect in Al-W thin films

The Hall coefficient, R_H, electrical resistivity, ρ, and temperature coefficient of resistivity, α, of Al_xW_100−x (61≤x≤88) thin films and amorphous-like tungsten films are reported. The Al_xW_100−x films have been prepared by magnetron co-deposition of pure metals onto glass substrate. Films are X-ray amorphous for 63≤x≤86. Amorphous-like tungsten films (x=0) were obtained at sputtering conditions different from those applied for the preparation of Al-W alloys. The R_H value is strongly dependent upon the alloy composition: it changes sign from positive to negative at x≈78, and exhibits a maximum for x≈68 at.%. With the decrease of Al content, ρ steeply increases and exhibits a maximum at x≈80 at.%. The temperature coefficient of the resistivity exhibits large negative values, with a well-defined minimum at x≈80. The Hall coefficient of films with 67≤x≤80 has also been determined at liquid nitrogen temperature, and the values obtained were the same as the room temperature values. Since the value of electrical resistivity of the examined alloys in the temperature interval from 77 to 300 K noticeably changes (10%), a significant anomalous contribution to the Hall effect is thus excluded.     

Solution-processed high-k thin films as a resistive switching for ReRAM applications

Resistive switching characteristics of solution-processed high-k thin films (HfO_x and TaO_x) were investigated for ReRAM applications. The thickness of solution-processed high-k thin films can be easily controlled by simple spin coating. We optimized the critical thickness of solution-processed HfO_x and TaO_x thin films, for reliable ReRAM operations. A similar bipolar resistive switching behavior was observed from both solution-processed and sputter-processed HfO_x films. Furthermore, it was found that the solution-processed HfO_x and TaO_x films have a uniform resistive switching characteristic. The dominant conduction of these solution-processed films is described by Ohmic conduction in the low-resistance state. On the other hand, Ohmic conduction at low voltage and Poole–Frenkel emission at high voltage dominate in the high-resistance state. It was verified that the solution-processed HfO_x and TaO_x films have superior endurance and retention characteristics. Therefore, ReRAM devices based on solution-processed high-k materials are expected to be a promising candidate, for usage of resistive memory in glass substrate or flexible substrate based electronic devices.     

Luminescence of CsPbCl3 microcrystals in CsCl:Pb and PbCl2:Cs crystals under synchrotron excitation

This paper reports on a study of the luminescence kinetics in CsPbCl₃ microcrystals dispersed in a CsCl or PbCl₂ host matrix, which are excited by synchrotron radiation at energies E _exc=4–20 eV. The luminescence decay kinetics of CsPbCl₃ microcrystals is found to contain different time components generated by direct excitation of the microcrystals or reabsorption of the luminescence emitted by other centers. It is conjectured that the decreased luminescence decay constant of CsPbCl₃ microcrystals dispersed in these hosts as compared to its counterpart of CsPbCl₃ single crystals is accounted for by size quantization.     

Synthesis and structure of Mg(Fe0.8Ga0.2)2O4−δ film materials

Features of the preparation of magnetic semiconductor films with the composition Mg(Fe_0.8Ga_0.2)₂O_4?δ on a 200-nm-thick silicon substrate are presented. Both a pure substrate surface and one with protective TiO _x layers with a crystallization temperature of 900–1000°C for 30 min were used. The effect of the protective layers on the formation of the surface morphology of the films and their magnetic properties is shown.     

Structural and magnetic properties of Si1−xGex thin films implanted with Fe ions

A series of Si_1?xGe_x (x = 1, 0.848, 0.591, 0.382, 0.209, 0.064, 0) thin films prepared by ion beam sputtering were implanted with Fe ions to different doses using the metal vapor vacuum arc technique. X-ray absorption fine structure (XAFS) was used to characterize the local microstructure around the Fe atoms in Fe-doped Si_1?xGe_x samples. Structural analysis showed that for annealed samples of Ge-rich thin films (including pure Ge) implanted with low doses of Fe ions, almost all the Fe ions substituted at Ge sites. However, an anti-ferromagnetic Fe₆Ge₅ impurity phase existed in the annealed samples implanted with high doses of Fe. It was also found that the solubility of Fe ions was highest in pure Ge films and that with increasing Si concentration, the solubility decreased. Magnetic analysis showed that for the as-implanted and annealed samples of Ge-rich thin films implanted with Fe ions, room-temperature ferromagnetism was strongest in the pure Ge series of samples and that as the Ge concentration decreased, the ferromagnetism at room temperature weakened. In addition, annealing could increase the number of Fe ions at substitution sites, which resulted in the observed increase in the saturated magnetization after annealing. Experiment and theoretical analysis showed that the ferromagnetism of Fe-doped Ge-rich Si_1?xGe_x thin films samples originated from the s, p–d exchange interactions between the Si_1?xGe_x matrix and those Fe ions which substituted at Ge sites and that the ferromagnetism was mediated by carriers.