Dependence of the laser-induced voltages on the oxygen content in normal state YBa2Cu3O7−δ films

Our investigation on the relation between oxygen content and the laser-induced voltages of the YBa₂Cu₃O_7−δ films in normal-state shows that deoxygenation of the superconducting films reduces the laser-induced voltages greatly, even reverses the sign of the signals at large oxygen deficiency. The absolute value of the negative signal at large oxygen deficiency can be greater than that of the positive signal.     

Thickness transitions in thin films: The equilibrium

The thermodynamic and thickness equilibria of planar solid, liquid or gaseous thin films are described in terms of the film excess chemical potential μ_ex. A general formula is given which relates μ_ex to the short- and/or long-range surface forces associated with the two film surfaces and the dependence of the film specific surface free energy σ on the film thickness h is expressed through μ_ex. The conditions under which the thin films are in stable or metastable thermodynamic equilibrium are analyzed and it is shown that the metastable thin films are subject to thickness transitions involving abrupt changes of h. The thin film thickness equilibrium, i.e. the coexistence between two films of different thickness, is also considered and the film equilibrium chemical potential characterizing this equilibrium is determined by means of μ_ex and σ.     

Silanation and stability of 3-aminopropyl triethoxy silane on nanosized superparamagnetic particles: I. Direct silanation

The direct silanation of nanosized superparamagnetic particles (γ-Fe₂O₃) using 3-aminopropyl triethoxy silane is described. The silanized films are characterized using X-ray photoelectron spectroscopy, diffuse-reflectance Fourier transform infrared spectroscopy and electrokinetics. The silanation is conducted in both organic (toluene) and water solutions to examine the solvent effect on the molecular orientation and packing density of the silanized films. Depending on the solvent, about 74 to 83% of amine groups are found to be un-protonated and remain reactive on the particles. In acidic environment, the films silanized in toluene are more stable than that in water, but both are unstable in basic environment.     

Study of the effect of manganese impurities on dielectric characteristics of BSTO films

Capacitance voltage and current voltage characteristics of BSTO ferroelectric films containing a manganese dioxide impurity (～1.5–2 mol%) are compared to those of impurity-free samples. It is shown that in Mn-doped samples tan δ drops to 10^?3, and the dependence of tan δ on the applied voltage changes as well. IVCs of these samples are strictly ohmic and do not show a nonlinearity at high voltages. A mechanism is proposed of the effect of Mn on the charge state of the defects comprising oxygen vacancies in BSTO films.     

溅射粒子能量对金属Mo薄膜表面特性的影响

利用原子力显微镜研究了不同溅射离子能量对Mo薄膜表面形貌的影响.利用特殊设计的夹具，在同一真空内完成所有薄膜样品的制备，减少了多次沉积过程对薄膜生长特性的影响 .对原子力显微镜测量得到的表面高度数据进行相关运算，从统计角度定量地研究了不同沉积能量下Mo薄膜表面特性.结果表明，薄膜表面具有典型的分形特征，在相关运算的基础上给出表面的分形维数、水平相关长度、界面宽度等参数.其中，屏栅电压为500V时制备 的薄膜样品与300和700?V时制备的薄膜样品表面的界面宽度及水平相关长度具有倍数差别，但三种溅射电压下薄 关键词： 离子束溅射 钼 薄膜 分形     

Zinc Oxide Thin Films for Memristive Devices: A Review

Zinc Oxide (ZnO) thin films have been addressed as promising candidates for the fabrication of Resistive Random Access Memory devices, which are alternative to conventional charge-based flash memories. According to the filamentary conducting model and charge trapping/detrapping theory developed in the last decade, the memristive behavior of ZnO thin films is explained in terms of conducting filaments formed by metallic ions and/or oxygen vacancies, and their breaking through electrochemical redox reactions and/or recombination of oxygen vacancies/ions. A comparative review of the memristive properties of ZnO thin films grown by sputtering, atomic layer deposition (ALD), pulsed laser deposition (PLD), and sol-gel methods is here proposed. Sputtered ZnO thin films show promising resistive switching behaviors, showing high on/off ratios (10–10⁴), good endurance, and low operating voltages. ALD is also indicated to be useful for growing conformal ZnO layers with atomic thickness control, resulting in important resistive switching characteristics, such as relatively high on/off ratios and low operating voltages. High insulating epitaxial ZnO thin films can be obtained by PLD, showing reliable switching properties at low voltages and with good retention. On the contrary, the sol-gel approach generally results in ZnO thin films with poor resistive switching behaviors. Nevertheless, thin films derived from ZnO NPs show improved switching performances, with higher on/off ratios and lower operating voltages. Independently of the synthetic approach, doped ZnO thin films exhibit better resistive switching behaviors than pristine ones, coupling a strong increase of the on/off ratio with a more stable switching response.     

Physics of non-adiabatic transport and field-domain effect in quantum-well infrared photodetectors

A previous theory for studying the distribution of non-uniform fields in multiple-quantum-well photodetectors under an ac voltage is generalized by including non-adiabatic space-charge-field effects. Numerical calculations indicate that field-domain effects are only important at high temperatures or high voltages when both injection and sequential-tunneling currents are significant. On the other hand, it is found that the non-adiabatic effects included in this generalized theory become significant at low temperatures and low voltages when field-domain effects are negligible. In order to explain the non-adiabatic charge-density fluctuations quantum-statistically, a non-adiabatic differential equation is derived based on the self-consistent Hartree model by using a shifted Fermi–Dirac model for the local fluctuation of electron distributions. The non-adiabatic effect is found to cause an “equilibrium” state variation with time under an ac voltage.     

Structural and electrical properties of the α-form of metal-free phthalocyanine (α-H2Pc) semiconducting thin films

An X-ray structural study of thermally evaporated metal-free phthalocyanine thin films with various film thicknesses was performed. All samples studied had polycrystalline structure and the unit cell was found to be of the α-form. Variation of the deposition rate from 0.5 to 1 nm s⁻¹ had little effect on the structure. The films exhibit preferential orientation at low thickness; however, at higher thickness they become less orientated as additional peaks appear in the spectrum. The increase in the intensity of the first significant low angle peak with increasing thickness is attributed to the increased volume of the crystal probed during the X-ray exposure.The current density–voltage (J–V) characteristics of α-H₂Pc films sandwiched between two aluminum electrodes showed ohmic behavior at low voltages and space–charge-limited conduction (SCLC) at higher voltages. For comparison, similar measurements of the current density as a function of voltage were performed on zinc phthalocyanine, ZnPc, thin films using aluminum electrodes. The J–V characteristics showed ohmic behavior at low voltages followed by SCLC dominated by an exponential trap distribution at higher voltages. Consequently, in both H₂Pc and ZnPc films, aluminum electrodes act as if they are ohmic contacts. The implied provision of ohmic contacts using aluminum in this case is attributed to the formation of a thin Al₂O₃ layer during the deposition process.     

Growth of Ni-Mn-Ga high-temperature shape memory alloy thin films by magnetron sputtering technique

Ni-Mn-Ga thin films have been fabricated by using magnetron sputtering technique under various substrate negative bias voltages. The effect of substrate negative bias voltage on the compositions and surface morphology of Ni-Mn-Ga thin films was systematically investigated by energy dispersive X-ray spectrum and atomic force microscopy, respectively. The results show that the Ni contents of the thin films increase with the increase of the substrate negative bias voltages, whereas the Mn contents and Ga contents decrease with the increase of substrate negative bias voltages. It was also found that the surface roughness and average particle size of the thin films remarkably decrease with the increase of substrate negative bias voltages. Based on the influence of bias voltages on film compositions, a Ni₅₆Mn₂₇Ga₁₇ thin film was obtained at the substrate negative bias voltage of 30 V. Further investigations indicate that the martensitic transformation start temperature of this film is up to 584 K, much higher than room temperature, and the film has a non-modulated tetragonal martensitic structure at room temperature. Transmission electron microscopy observations reveal that microstructure of the thin film exhibits an internally (1 1 1) type twinned substructure. The fabrication of Ni₅₆Mn₂₇Ga₁₇ high-temperature shape memory alloy thin film will contribute to the successful development of microactuators.     

Effect of Bias Voltage on Microstructure and Mechanical Properties of Nanocomposite ZrCN Films Deposited by Filtered Cathodic Vacuum Arc

Nanocomposite ZrCN films consisting of nanocrystalline ZrCN grains embedded in nitrogen-doped amorphous carbon film are deposited by filtered cathodic vacuum arc technology under different bias voltages ranging from 50to 400 V.The influence of bias voltage on the characterization and the mechanical properties of the ZrCN films are investigated by x-ray diffraction,x-ray photoelectron spectroscopy,scanning electron microscopy,transmission electron microscopy,Raman spectroscopy and nano-indentation.The bias voltage has a subtle effect on the ZrCN grain size,which is around 9.5 nm and keeps almost constant.A slight increase of the bias voltage induces a relatively high sp~3 fraction about 40%in N-doped amorphous C films but leads to the graphitization of the films under a higher voltage.The best mechanical property of the ZrCN film with the hardness of 41 GPa is obtained under the bias voltage of 200 V,indicating the positive effect of slight increase of ion bombardment on the hardness of the films.     

The real-time gamma radiation dosimetry with TeO2 thin films

A detailed study of the effect of gamma radiation on the current–voltage characteristics of the TeO₂ thin films of different thicknesses, prepared by thermal evaporation in a vacuum, has been carried out for a much wider range of the gamma radiation doses than made here-to-fore. Subsequently, for the thin films of different thicknesses at different applied voltages, the variations of the current density with dose have been obtained. The current density increases near linearly with the gamma radiation dose up to a critical radiation dose, a dose value higher for the thicker films and decreases thereafter. The sensitivities of these TeO₂ thin films at different applied voltages have been found to be in the range 1.2–37.0 nA/cm²/μGy. Correspondingly, the detection limits have also been estimated and have been found to be in the range 0.22–2.16 mGy. Clearly, the TeO₂ thin films have high potential for their use as real-time gamma radiation dosimeters in monitoring the gamma radiation doses under a variety of practical situations involving low level to high level of the doses.     

The fabrication and photoresponse of ZnO/diamond film heterojunction diode

Boron-doped p-type freestanding diamond (FSD) films were prepared by hot filament chemical vapor deposition (HFCVD) method. The effect of B/C ratio on the electrical properties of FSD films was investigated by Hall effect measurement system. A ZnO/diamond heterojunction diode was fabricated successfully by depositing n-type ZnO films on the p-type FSD substrate by radio-frequency (RF) magnetron sputtering method. The wavelength dependent photoresponse properties of the heterojunction diode were investigated by studying the effect of light illumination on current-voltage (I-V) characteristics and photocurrent spectra at room temperature. The diode showed a significant discrimination between ultraviolet (UV) and the visible light under reverse bias conditions and photoresponse of the device was approximately linear related to the increasing reverse bias voltages.     

Optical characterization of amorphous Ga50Se45S5 films

The transmission spectra of thermally evaporated Ga₅₀Se₄₅S₅ films were measured over the wavelength range 300–900 nm. A simple method, suggested by Swanepoel, was used for the determination of the optical constants and thickness of the films. Increasing the thickness of the film beyond 450 nm does not affect the optical constants. The dependence of the absorption coefficient on the photon energy (hν) at the edge of the absorption band is well described by the relation hν=β(hν−E_opt)² with an optical gap equals 2.4 eV. A good fit of the experimental points with Tauc relation indicates that non-direct transition is the most probable mechanism responsible for the photon absorption inside the investigated film.     

Crystal structure of YBa2Cu3O7−x thin films prepared by pulsed laser deposition with substrate bias voltage

The crystal structure of YBa₂Cu₃O_7−x thin films has been investigated by cross-section transmission electron microscopy. The samples were deposited on MgO (100) substrates at 670°C with substrate bias voltages of ±300 V. For the unbiased case, c-axis, a-axis and (103) oriented domains normal to the substrate surface were observed. In this film, the c-axis oriented domains are dominant, but the crystal often exhibits a longer c-lattice constant than that of the YBa₂Cu₃O_7−x system, so extra cationic layers are inserted in the YBa₂Cu₃O_7−x intrinsic stacking sequence. For the case of −300 V, rotated domains were dominant in the entire film; however, c-axis oriented domains also grow from the substrate surface. Small-angle semicoherent grain boundaries between them were observed. In the case of +300 V, all the grains show c-axis oriented YBa₂Cu₃O_7−x. The degree of preferential orientation of the grains is reduced at negative bias voltage of −300 V and the structure defects are reduced by applying a positive bias of +300 V.     

A step towards nanoionics

The interaction of finely focused 20–100 keV electron beam at 10–1000 A/cm² current densities with 30–150 nm films of the RbAg₄I₅-family solid electrolytes has been studied. The results obtained show that it is possible to form arrays of electrochemical devices with single elements ≈ 10 nm in size in the films. Arrays of 100×100 nm structures consisting of a solid electrolyte film on C-, Au-and Ag-thin supports are demonstrated.     

FePt nano-stripes fabricated on anodic aluminum oxide templates

A new Fe Pt nanostructure with stripe-like patterns has been prepared by direct current(DC) magnetron sputtering on anodic aluminum oxide(AAO) templates. AAO templates anodized under low voltages(7 V) demonstrate self-organized,maze-like patterns, different from the conventional porous structures obtained at high voltages. Fe Pt thin films deposited on such templates tend to replicate the morphology of the templates. Although there is no obvious spatial ordering, the dimensions of the Fe Pt nano-stripes are highly uniform, due to the constrained growth along the transverse direction of the AAO pattern. The magnetic properties are strongly influenced by this unique morphology. While continuous films demonstrate strong exchange coupling, the dominant interaction in Fe Pt nano-stripes with the same nominal thickness is magnetostatic. The morphology also dictates the magnetization reversal behaviors, with thin films dominated by domain nucleation; while nano-stripes incline to reverse their magnetization by spin rotation. Our work demonstrates that selforganized AAO templates can be used to control the morphology and magnetic behavior of Fe Pt materials.     

Microwave acoustic delay lines

The established technology for making evaporated thin film piezoelectric transducers has made the construction of delay lines at microwave frequencies possible. Thin films of CdS on sapphire delay media have been used to make c.w. and pulsed delay lines from 1–11GHz, with delays from 1–14μs operating at 77°K and 300°K. The performance of some of these lines is described. The parameters governing the choice of delay media, transducer material and electrode structure are discussed and the importance of careful electrical matching of transducer to generator is emphasised.     

Investigation of diffusion and crystallization processes in thin ITO films by temperature and time resolved grazing incidence X-ray diffractometry

Oxygen diffusion into metallic In/Sn films and crystallite growth of thin indium tin oxide (ITO) films were investigated by in situ high temperature grazing incidence X-ray diffractometry (HT-GIXRD) at temperatures ranging from 100 to 300 °C. The investigated films were deposited by dc magnetron sputtering from a metallic target at different oxygen flows and bias voltages. The deposition process influences not only the film properties but also the film reactions during the post-deposition annealing process.

The ITO formation is determined by two processes: the diffusion of oxygen into the metallic grains and a fast crystallization process. Kinetic parameters for both processes were derived. A model was developed which allows the determination of the diffusion coefficient D from the time dependence of the integral intensity of the ITO X-ray reflection. Diffusion coefficients as well as the activation energies are influenced by the bias voltage but not by the oxygen flow.

According to the Johnson–Mehl–Avrami theory, the crystallization can be described as a two-dimensional process.     

Applications of surface polaritons for detection and vibrational spectral analysis of thin films on metals and dielectrics

Phonon-polaritons interactions with molecular vibrations of thin films were used for the detection of film oscillator spectral positions. The gap in the polariton branch was proportional to √ ℓ,ℓ being the thickness of the film on dielectric support. The ATR method in the Otto configuration was used for measurements as well as thermal stimulated emission. The vibrational spectra (infrared absorption) of monomolecular films were detected by surface electromagnetic waves (SEW) - surface plasmon-polaritons propagating along the metallic substrate. A comparison of the reflection-absorption method with the SEW broadband (650-2500cm⁻¹) FT-IR method of thin films detection is made. The better sensitivity of the last one is shown. The prism, grating and edge methods of SEW excitations in IR are discussed.     

Memory Effect in the Charge Transport in Strongly Disordered Antimony Films

We study conductivity of strongly disordered amorphous antimony films under high bias voltages. We observe non-linear current-voltage characteristic, where the conductivity value at zero bias is one of two distinct values, being determined by the sign of previously applied voltage. Relaxation curves demonstrate high stability of these conductivity values on a large timescale. Investigations of the antimony film structure allows to determine the percolation character of electron transport in strongly disordered films. We connect the memory effect in conductivity with modification of the percolation pattern due to recharging of some film regions at high bias voltages.