The effect of magnetic impurity scattering in Au films

The magnetic impurity scattering plays an important role in the phase coherence behavior of thin films.By using the thickness and disorder dependences of the low temperature logarithmic anomaly in resistivity we are able to determine the concentration of magnetic impurities in Au films and demonstrate that the low temperature saturation or plateau in phase decoherence time is closely related with the Kondo effect.     

Nanostructuring of thin films by ns pulsed laser interference

We show that nanosecond pulsed laser interference can be used to structure surfaces on a nanoscale. With this method, we are able to create hollow structures on various thin films like Ta, Ni, Au, Cu, Co, and NiTi. We find that the structuring mechanism is related to the mechanical effect of thermal expansion upon melting. To corroborate this model, we study materials with an abnormal behavior at the melting point like Si, Ge, or Bi, as they contract upon melting.     

On the theory of thermodynamic properties of geometrically confined disordered ferroelectrics

We propose a theoretical approach to calculate the thermodynamic properties of thin films fabricated from disordered ferroelectrics. To calculate the above thermodynamic properties, we use so-called random field method, modified for the case of thin films. The essence of modification is the altering of the interaction between impurity dipoles by geometrical confinement. We show that in thin films the ferroelectric phase transition is inhibited as compared to the case of bulk samples. Our theory is generalizable to ferroelectrics of other shapes as well as magnets and multiferroics.     

Phase transition behavior of highly (100) textured sol-gel-derived Ba<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript> thin films

We have investigated the relations between microstructure and dielectric properties in order to fabricate sol-gel-derived highly (100) oriented Ba_0.5Sr_0.5TiO₃ (BST 50/50) thin films with properties comparable to those of the bulk material. For the first time, we were able to fabricate BST thin films which exhibited the orthorhombic-to-tetragonal transition in addition to the commonly observed tetragonal-to-cubic transition. We were successful in explaining the commonly observed degradation of the dielectric behavior of BST thin films, when compared to that of the bulk material, in terms of grain size, compositional inhomogeneity (measured in terms of Sr/Ba ratio) between the grain bulk and grain boundary, and mechanical stresses. PACS 77.55.+f; 77.22Gm; 77.80.Bh; 77.80.Dj     

Editorial: Special issue on Properties of Thin Polymer Films

The behavior of polymers in thin films or close to interfaces is far from being understood. Many observations, encompassing both structural and dynamical behavior, indicate that the properties of polymers in thin films deviate from what we know from the bulk. Questions about the density (irreversible and reversible changes after annealing even above the bulk glass transition temperature), film stability and dewetting, glass transition temperature, diffusion coefficient and chain conformation and relaxation are intensively debated. In particular, it is not yet clear how the size of such chain-like molecules (their molecular weight) comes into play, especially if the thickness of the film is less than the radius of gyration of these macromolecules. In addition, due to the high surface-to-volume ratio the influence of surface and interfacial properties becomes important if not dominant. This interfacial sensitivity highlights the importance of the properties of the near surface region in polymer films; a topic whose importance is beginning to be recognized. This special issue presents experimental and theoretical works on a variety of questions related to polymers at interfaces and in thin films, ranging from space-averaged properties like adhesion to surface ordering or dynamic molecular (segmental) motion in confining geometries. Since the first reports of anomalous dynamics in thin polymer films almost a decade ago, the subject of dynamics in thin films has gained considerable momentum. Until very recently, this body of work focused almost solely on measurements of the thermodynamic signature of the kinetic glass transition. Such measurements are, at best, a very indirect probe of the microscopic dynamics and convolute the temperature dependence, time dependence and sometimes even the thermal history into a single measured value. The articles focusing on dynamics in thin films published in this special issue illustrate an important shift in this rapidly evolving field. There is now a strong focus on many different fronts. Measurements of dynamics are more varied, ranging from indirect studies such as adhesion to direct measurement of the segmental relaxation using dielectric spectroscopy. There is a concerted effort now to draw analogies to bulk systems in order to learn about what effects may contribute to the observation made in thin films. There is also a strong effort using numerical simulations to make quite direct comparisons to measured values in thin films. Finally, in a way that signals a new maturity to this field, a significant fraction of literature being currently published concerns ideas as to why the dynamics in thin films behave the way they do. In this special issue we have aimed at capturing a cross-section of problems of high current interest. While all contributions definitely provide highly valuable insight in the behavior of polymers in thin films, many questions are still unanswered and await further in-depth-going studies. We just want to note a few of these questions, also highlighted in several commentaries published in this issue: Can polymers in experimental studies on thin films ever be fully equilibrated? What is the relaxation behavior of macromolecules in confining geometries with interacting boundaries? How does the relaxation behavior depend on the length scale over which it is measured? What are the mechanical properties of thin polymer films? We tried to assemble different approaches and opinions from various viewpoints. We hope that such a complementary presentation is helpful and stimulates further discussions in order to dissolve some of the confusion in this area, leading eventually to a clear understanding of thin-film properties of polymers. The European Physical Journal E - Soft Matter will continue to provide a forum for the discussion of such questions and a place for the publication of future work on properties of polymers in thin films for all colleagues interested in these questions. Günter Reiter (Editor) James Forrest (Guest Editor)     

Polar dependent in-plane electric transport of epitaxial ZnO thin films on SrTiO(3) substrates

Polar (001) and nonpolar (110) ZnO epitaxial thin films were grown on SrTiO(3) substrates by the pulsed laser deposition method and the in-plane electric transport was investigated. Both films display semiconducting behavior. The polar thin films have linear I-V relations with mobility increasing almost linearly with temperature. In contrast, for nonpolar ZnO thin films, the I-V curves are symmetric and nonlinear with room temperature resistivity 30 times larger than that of polar thin films. We conclude that in nonpolar ZnO thin films the bound polarization charge induced barrier limits the carrier transport. Instead, for polar thin films, the polar effect on the in-plane transport is negligible, and the charged dislocation scattering is dominant. Our observations suggest the polar effect should be considered in the design of ZnO related devices.     

Au/PZT/BIT/p-Si异质结的制备与性能研究

采用脉冲激光沉积(PLD)工艺,制备了以Bi₄Ti₃O₁₂(BIT)为过渡阻挡层的Au/PZT/BIT/p-Si异质结.研究了BIT铁电层对Pb(Zr_0.52Ti_0.48)O₃(PZT)薄膜晶相结构、铁电及介电性能的影响,对Au/PZT/BIT/p-Si异质结的导电机制进行了讨论.氧气氛530℃淀积的PZT为多晶铁电薄膜,与直接淀积在Si基片上相比,加入BIT铁电层后PZT铁 关键词： 铁电薄膜 异质结构 脉冲激光沉积(PLD)     

Shear response of molecularly thin liquid films to an applied air stress

The shear response of molecularly thin liquid films on solid substrates when subjected to an applied air stress has been measured. The response corresponds to viscous friction while the same films sheared between two solid surfaces display static friction. These results show that molecularly thin liquid films partially confined by a single solid surface do not solidify as when confined between two solid surfaces. We are also able to observe several novel properties for liquid films on single solid surfaces not previously observed or expected.     

Impact of thermal annealing on physical properties of vacuum evaporated polycrystalline CdTe thin films for solar cell applications

A study on impact of post-deposition thermal annealing on the physical properties of CdTe thin films is undertaken in this paper. The thin films of thickness 500 nm were grown on ITO and glass substrates employing thermal vacuum evaporation followed by post-deposition thermal annealing in air atmosphere within low temperature range 150–350 °C. These films were subjected to the XRD, UV‐Vis NIR spectrophotometer, source meter, SEM coupled with EDS and AFM for structural, optical, electrical and surface topographical analysis respectively. The diffraction patterns reveal that the films are having zinc-blende cubic structure with preferred orientation along (111) and polycrystalline in nature. The crystallographic parameters are calculated and discussed in detail. The optical band gap is found in the range 1.48–1.64 eV and observed to decrease with thermal annealing. The current–voltage characteristics show that the CdTe films exhibit linear ohmic behavior. The SEM studies show that the as-grown films are homogeneous, uniform and free from defects. The AFM studies reveal that the surface roughness of films is observed to increase with annealing. The experimental results reveal that the thermal annealing has significant impact on the physical properties of CdTe thin films and may be used as absorber layer to the CdTe/CdS thin films solar cells.     

Aging phenomena in polystyrene thin films

The aging behavior is investigated for thin films of atactic polystyrene through measurements of complex electric capacitance. During isothermal aging process the real part of the electric capacitance increases with aging time, while the imaginary part decreases with aging time. This result suggests that the aging time dependence of the real and imaginary parts are mainly associated with change in thickness and dielectric permittivity, respectively. In thin films, the thickness depends on thermal history of aging even above the glass transition. Memory and `rejuvenation' effects are also observed in the thin films.     

Growth dynamics of ZnPc and TiOPc thin films: Effect of crystallinity on anomalous scaling behavior

The surface morphology evolution and scaling behavior of zinc phthalocyanine (ZnPc) and titanyl phthalocyanine (TiOPc) thin films have been studied using atomic force microscopy, X-ray diffraction and height difference correlation function analysis. In contrast to the large growth exponent (β) values and anomalous scaling behavior previously reported for other crystalline molecular thin films, significantly small β and anomaly values were observed for amorphous TiOPc thin films. The relatively small anomaly value of ZnPc thin films, though larger than that of TiOPc thin films, is also rationalized by the lack of crystallographic ordering at the initial stage of growth.     

Low temperature crystallization behavior of multi-walled carbon nanotubes/Pb(Zr0.52Ti0.48)O3 nanocomposite thin films through annealing in various atmosphere and duration control

We report a successful fabrication of 300 nm thick carbon nanotubes and Pb(Zr_0.52Ti_0.48)O₃ (CNT–PZT) nanocomposite thin films with annealing temperature as low as 500 °C in H₂/N₂ atmosphere. Realizing the thickness of CNT–PZT nanocomposite thin films down to few hundred nanometers is one way to reduce the operating voltage of its application to micro- or nano-electromechanical system. The field emission scanning electron microscopic and atomic microscopic analysis revealed that the nanocomposite thin films annealed in H₂/N₂ atmosphere exhibits the most favorable surface morphology with adequate perovskite (111) reflection of PZT based on X-ray diffraction analysis. The measured dielectric constant and loss tangent of the nanocomposite thin films show that the annealing duration of 30 min promotes the optimum dielectric properties of the nanocomposite thin films. Our observations suggest that the annealing atmosphere and duration are important parameters in controlling the crystallization behavior hence the dielectric properties of the nanocomposite thin films, which can be readily applicable to other nanocomposite thin films.     

Effect of thickness on physical properties of electron beam vacuum evaporated CdZnTe thin films for tandem solar cells

The thickness and physical properties of electron beam vacuum evaporated CdZnTe thin films have been optimized in the present work. The films of thickness 300 nm and 400 nm were deposited on ITO coated glass substrates and subjected to different characterization tools like X-ray diffraction (XRD), UV‐Vis spectrophotometer, source meter and scanning electron microscopy (SEM) to investigate the structural, optical, electrical and surface morphological properties respectively. The XRD results show that the as-deposited CdZnTe thin films have zinc blende cubic structure and polycrystalline in nature with preferred orientation (111). Different structural parameters are also evaluated and discussed. The optical study reveals that the optical transition is found to be direct and energy band gap is decreased for higher thickness. The transmittance is found to increase with thickness and red shift observed which is suitable for CdZnTe films as an absorber layer in tandem solar cells. The current-voltage characteristics of deposited films show linear behavior in both forward and reverse directions as well as the conductivity is increased for higher film thickness. The SEM studies show that the as-deposited CdZnTe thin films are found to be homogeneous, uniform, small circle-shaped grains and free from crystal defects. The experimental results confirm that the film thickness plays an important role to optimize the physical properties of CdZnTe thin films for tandem solar cell applications as an absorber layer.     

Low-field vortex dynamics in various high-T c thin films

We present a novel ac susceptibility technique for the study of vortex creep in superconducting thin films. With this technique we study the dynamics of dilute vortices in c-axis oriented Y-123, Hg-1212, and Tl-1212 thin films, as well as a axis oriented Hg-1212 thin films. Results on the Hg-1212 and Tl-1212 thin films indicate that dislocation-mediated plastic flux creep of single vortices dominates at low temperatures and fields. As the temperature (or the field) is increased, the increasing vortex-vortex interactions promote a collective behavior, which can be characterized by elastic creep with a non-zero μ exponent. Also, in some of these samples effects of thermally assisted quantum creep are visible up to 45 K in some of these samples. In Y-123 thin films, creep is found to be collective down to the lowest temperatures and fields investigated, while the quantum creep persists only up to 10–11 K.     

Sr-doping effects on conductivity,charge transport,and ferroelectricity of Ba_(0.7)La_(0.3)TiO_3 epitaxial thin films

Sr-doped Ba_0.7La_0.3TiO₃(BSLTO)thin films are deposited by pulsed laser deposition,and their microstructure,conductivity,carrier transport mechanism,and ferroelectricity are systematically investigated.The x-ray diffraction measurements demonstrate that Sr-doping reduces the lattice constant of BSLTO thin films,resulting in the enhanced phonon energy in the films as evidenced by the Raman measurements.Resistivity-temperature and Hall effect measurements demonstrate that Sr can gradually reduce electrical resistivity while the electron concentration remains almost unchanged at high temperatures.For the films with semiconducting behavior,the charge transport model transforms from variable range hopping to small polaron hopping as the measurement temperature increases.The metalic conductive behaviors in the films with Sr=0.30,0.40 conform to thermal phonon scattering mode.The difference in charge transport behavior dependent on the A-site cation doping,is clarified.It is revealed that the increasing of phonon energy by Sr doping is responsible for lower activation energy of small polaron hopping,higher carrier mobility,and lower electrical resistivity.Interestingly,the piezoelectric force microscopy(PFM)results demonstrate that all the BSLTO films can exhibit ferroelectricity,especially for the room temperature metallic conduction film with Sr=0.40.These results imply that Sr-doping could be a potential way to explore ferroelectric metal materials for other perovskite oxides.     

溶胶-凝胶ZrO_2/SiO_2薄膜的激光损伤研究

采用溶胶-凝胶工艺分别制备了SiO2和ZrO2单层薄膜、ZrO2/SiO2双层膜以及ZrO2/SiO2多层高反膜。用输出波长为1064nm、脉宽为6.3ns的YAG激光器对薄膜进行了激光损伤实验。观察了薄膜经强激光辐照后的损伤情况,讨论了薄膜的激光损伤行为,并从理论上分析了产生这些损伤的原因,为进一步镀制高质量的ZrO2/SiO2多层高反膜提供了依据。     

Selective electroplating of copper lines on pre-patterned tantalum oxide thin films

Direct selective metal deposition on semiconductors is of interest to electronic device technology, in particular for interconnects and Schottky devices. In this study, we investigate selective copper electrodeposition on patterned tantalum oxide thin films. Cyclic voltammetry studies show that thick tantalum oxide thin films have insulating properties while oxide films thinner than a critical value are semiconductors. Copper films electrodeposited on tantalum oxide thin films are known to form Schottky contacts. We demonstrate the formation of copper patterns on pre-patterned tantalum oxide films by a simple process: an insulating tantalum oxide film was grown electrochemically, the film was then mechanically scratched followed by mild oxidation to produce a thin tantalum oxide film inside the scratch. Based on the differential behavior of thin and thick tantalum oxide films, metal lines were electrodeposited selectively under formation of Schottky junctions. The process demonstrated in this paper is compatible to standard processes for semiconductor device fabrication while permitting flexible prototyping for research at small scales.     

Ferroelectric domain structures and polarization switching characteristics of polycrystalline BiFeO3 thin films on glass substrates

We investigated ferroelectric characteristics of BiFeO₃ (BFO) thin films on SrRuO₃ (SRO)/yttria-stabilized zirconia (YSZ)/glass substrates grown by pulsed laser deposition. YSZ buffer layers were employed to grow highly crystallized BFO thin films as well as SRO bottom electrodes on glass substrates. The BFO thin films exhibited good ferroelectric properties with a remanent polarization of 2P_r = 59.6 μC/cm² and fast switching behavior within about 125 ns. Piezoelectric force microscopy (PFM) study revealed that the BFO thin films have much smaller mosaic ferroelectric domain patterns than epitaxial BFO thin films on Nb:SrTiO₃ substrates. Presumably these small domain widths which originated from smaller domain energy give rise to the faster electrical switching behavior in comparison with the epitaxial BFO thin films on Nb:SrTiO₃ substrates.     

Tribological properties of chemically bonded polyimide films on silicon with polyglycidyl methacrylate brush as adhesive layer

Polyimide thin films, which possess good stability and film uniformity, are successfully fabricated on single crystal silicon wafers coated with a thin polymer brush by suface-initiated polymerization (SIP) as an adhesive layer. The growth kinetic of polyglycidyl methacrylate (PGMA) brush was studied by the means of ellipsometry. The nano-scale morphology and chemical composition of PGMA brush and polyimide film were studied with atomic force microscopy (AFM), Fourier transform infrared spectrum (FT-IR), and X-ray photoelectron spectroscopy (XPS). The tribological behaviors of the thin films sliding against AISI-52100 steel ball were examined on a static-dynamic friction precision measurement apparatus and UMT-2MT tribometer. The worn surface of the polyimide thin films was investigated with scanning electron microscopy (SEM). The results indicated that the chemically bonded polyimide films exhibited better friction reduction and antiwear behavior compared to the polymide films on bare silicon surface. At a load of 0.5 N and sliding speed of 20 mm s⁻¹, the durability life of the polyimide thin films is over 25,000 sliding cycles and the friction coefficient is about 0.08.     

Effects of oxygen partial pressure on resistive switching characteristics of ZnO thin films by DC reactive magnetron sputtering

Cu/ZnO/n⁺-Si structures were prepared by magnetron sputtering of a layer of ZnO thin film onto heavily doped silicon substrate, followed by thermal evaporation of a thin layer of metallic Cu. The resistive switching characteristics of Cu/ZnO/n⁺-Si structures were investigated as a function of oxygen partial pressure during ZnO deposition. Reproducible resistive switching characteristics were observed in ZnO thin films deposited at 20%, 33% and 50% oxygen partial pressure ratios while ZnO thin film deposited at 10% oxygen partial pressure ratio did not show resistive switching behavior. The conduction mechanisms in high and low resistance states are dominated by space-charge-limited conduction and ohmic behavior respectively, which suggests that resistive switching behaviors in such structures are related to filament formation and rupture. It is also found that the reset current decreases as oxygen partial pressure increases, due to the variation of oxygen vacancy concentration in the ZnO thin films.