Transport Properties Of Films Research Articles

Polycrystalline GeSn Films Grown by Hot Wire Chemical Vapor Deposition on SiO2/Si(001) Substrates

The conditions for the growth of polycrystalline GeSn films on SiO2/Si(001) substrates by hot wire chemical vapor deposition are determined for the first time. The effect of the introduction of Sn into the Ge lattice on the morphology, structure, and transport properties of films is studied. GeSn films obtained at 300 °C have a uniform surface with a roughness of less than 1.0 nm. It is shown that the introduction of 5% Sn allows, without the use of recrystallization annealing, to significantly increase the hole mobility of polycrystalline GeSn films from 20 to 60 cm2 V−1 × s−1. despite the small grain size of 35 nm. Such films are of great interest for creating thin‐film transistors for active matrices’ liquid crystal displays.

Preparation and electrical transport properties of TiO thin films

Titanium monoxide has attracted great attention due to its unique superconducting characteristics and potential applications in microelectronics. In this work, a series of TiO thin films are prepared at room temperature by using the radio frequency magnetron sputtering method through changing the oxygen partial pressures. The crystal structures, valences of the elements, and electrical transport properties of the films are investigated systematically. X-ray diffraction results indicate that the films are epitaxially grown on MgO single crystal substrates along the [001] direction. After the surface of the TiO film is treated by ion etching, it is found that the Ti element mainly exists in a divalent form. For all films, the temperature coefficients of resistance are negative above superconducting transition temperature <i>T</i><sub>c</sub>. The films prepared under high oxygen partial pressures reveal insulator characteristics, and the temperature dependence of resistivity obeys the Mott-type variable-range-hopping law in low temperature regime. The films prepared under low oxygen partial pressures exhibit metallic properties, and enter into a superconducting state at low temperature. The superconducting transition temperature <i>T</i><sub>c</sub> in our film can be as high as 3.05 K. The carrier concentrations of the films are in the vicinity of ~2.0×10<sup>22</sup> cm<sup>–3</sup>, which is comparable to those for the typical metals. Interestingly, it is found that the main species of the charge carriers in the films transforms from electrons to holes with the oxygen partial pressure decreasing. The crossover of the species of the charge carriers could related to the changing of energy-band structure with the oxygen content in TiO film.

Structure, Morphology, Transport, and Mechanism of Oxygen Loss in YBa-=SUB=-2-=/SUB=-Cu-=SUB=-3-=/SUB=-O-=SUB=-7-delta-=/SUB=- Thin Films Obtained by Pulsed Laser Deposition with Velocity Filtration in Erosion Plume

We report the study of YBa2Cu3O7-delta films, synthesized on SrTiO3(100) substrates by pulsed laser deposition with velocity filtration, using X-ray diffractometry, transport measurements, and scanning electron microscopy. We have revealed the dependence of the structure of 100-200 nm thick YBa2Cu3O7-delta films on deposition time and velocity of particles in erosion plume, set by velocity filter. After deposition, the films, or their part, close to the substrate, consisted of 3-10-nm crystals with oxygen index delta=0.08, the same as in the target. For deposition time from 10 to 60 min, we observed the growth of regular pyramids with triangular and quadrangular bases from 20 to 500 nm in size at the base and spiral pyramids with polygonal bases on the film surface. The maximum oxygen loss up to delta=0.35 and T(R=0) up to 77.4 K coincided with the appearance of spiral pyramids up to 100 nm-high. These findings evidence in favor of oxygen depletion of the top layers of YBa2Cu3O7-delta thin films through the formation and growth of oxygen-deficient pyramids on their surface. The oxygen index in the range of delta=0.08-0.15 in both nanocrystals and regular pyramids of 20-300 nm in size provided T(R=0)=84-87 K and the width of superconducting transition Delta T=2.5-3.5 K. Keywords: pulsed laser deposition, surface morphology, film transport properties, film evolution, SrTiO3.

Harnessing Intramolecular Chalcogen-Chalcogen Bonding in Merocyanines for Utilization in High-Efficiency Photon-to-Current Conversion Optoelectronics.

A novel series of donor (D)-π-acceptor (A) merocyanine molecules harnessed with intramolecular chalcogen bonding (ChaB) is designed, synthesized, and characterized. ChaB comprises periodic chalcogen atoms, S, Se, and Te, and a neighboring oxygen atom of a carbonyl moiety. Compared to the D-π-A merocyanine dye with nontraditional intramolecular hydrogen bonding, the novel molecules with an intramolecular ChaB exhibit remarkably smaller absorption spectral widths and higher absorption coefficients attributed to their cyanine-like characteristics approaching the resonance parameter (c2) ∼0.5; furthermore, they exhibit better thermal stabilities and electrical charge-carrier transport properties in films. These novel D-π-A merocyanines harnessed with intramolecular ChaB networks are successfully utilized in high-performance color-selective organic photon-to-current conversion optoelectronic devices with excellent thermal stabilities. This study reports that the unique intramolecular ChaB plays an essential role in locking the molecular conformation of merocyanine molecules and enhancing the optical, thermal, and optoelectronic properties of high-performance and high-efficiency organic photon-to-current conversion devices.

Metalorganic Chemical Vapor Deposition Gallium Nitride with Fast Growth Rate for Vertical Power Device Applications

The development of high‐quality gallium nitride (GaN) epitaxy with thick drift layer, low controllable doping, and high mobility is key for vertical high‐power devices. Herein, the effect of increasing trimethylgallium (TMGa) molar flow rate on the growth rate, impurity incorporation, charge compensation, surface morphology, and carrier mobility is systematically studied. An optimized metalorganic chemical vapor deposition GaN growth condition with a typical growth rate of 2 μm h−1 is used as the baseline. With significant suppression of background Si, other impurity concentrations, and a precise control of the doping precursor SiH4 flow, an electron concentration as low as 4 × 1015 cm−3 in n−‐GaN is achieved. Through increasing the TMGa flow rate, the GaN growth rate is increased to 5.2 μm h−1. Secondary ion mass spectroscopy results show that the background H, O, and Mg remain below detection limit, but C level is increased to 2 × 1016 cm−3. GaN growth on Mn‐doped semi‐insulating GaN substrate is performed to probe the transport properties of film with low dislocation densities. Hall measurement shows that an electron mobility decreases from 852 to 604 cm2 V−1 s−1 as the growth rate increases. Results from this work reveal the challenge and guidance for achieving GaN vertical high power devices.

Precursor selection in hybrid molecular beam epitaxy of alkaline-earth stannates

One of the challenges of oxide molecular beam epitaxy (MBE) is the synthesis of oxides containing metals with high electronegativity (metals that are hard to oxidize). The use of reactive organometallic precursors can potentially address this issue. To investigate the formation of radicals in MBE, we explored three carefully chosen metal-organic precursors of tin for SnO2 and BaSnO3 growth: tetramethyltin (TMT), tetraethyltin (TET), and hexamethylditin (HMDT). All three precursors produced single-crystalline, atomically smooth, and epitaxial SnO2 (101) films on r-Al2O3 (101¯2) in the presence of oxygen plasma. The study of growth kinetics revealed reaction-limited and flux-limited regimes except for TET, which also exhibited a decrease in the deposition rate with increasing temperature above ∼800 °C. Contrary to these similarities, the performance of these precursors was dramatically different for BaSnO3 growth. TMT and TET were ineffective in supplying adequate tin, whereas HMDT yielded phase-pure, stoichiometric BaSnO3 films. Significantly, HMDT resulted in phase-pure and stoichiometric BaSnO3 films even without the use of an oxygen plasma (i.e., with molecular oxygen alone). These results are discussed using the ability of HMDT to form tin radicals and therefore assisting with Sn → Sn4+ oxidation reaction. Structural and electronic transport properties of films grown using HMDT with and without oxygen plasma are compared. This study provides guideline for the choice of precursors that will enable the synthesis of metal oxides containing hard-to-oxidize metals using reactive radicals in MBE.

The effect of electric transport properties of titanium dioxide nanostructures on their photocatalytic activity

Annotation. Films formed by nanoparticles, nanorods and nanotubes of titanium dioxide with a thickness of 3.9, 4.0 and 4.1 μm, respectively, with an area of 2 cm2 were obtained by various methods. Nanostructures were characterized by X-ray phase analysis, scanning electron microscopy (SEM), BET (Brunauer–Emmett– Teller), BJH (Barrett–Joyner–Halenda). The electric transport properties of the films were studied by impedance spectroscopy. The photocatalytic activity of the samples was evaluated by the photocurrent and degradation of the methylene blue dye under xenon lamp illumination. The concentration of hydrogen released per unit time was determined by gas chromatography in a standard quartz cuvette using a platinum electrode. The study of texture characteristics showed that the obtained isotherms belong to type IV isotherms with a hysteresis loop, reflecting the process of capillary condensation in mesopores. The diffraction peaks for the films of nanoparticles and nanotubes of titanium dioxide are identical and correspond to the tetragonal phase of anatase, for films of nanorods to the tetragonal phase of rutile. When studying the electric transport properties of films, it was found that films of titanium dioxide nanoparticles have a higher resistance associated with unformed bonds between nanoparticles. Despite the low specific surface area, titanium dioxide nanorods showed higher photocatalytic activity than nanotubes and nanoparticles. The results are confirmed by measurements of photocurrent, dye decomposition and the splitting of water molecules into hydrogen gas and oxygen.

Evolution of electrical and magnetotransport properties with lattice strain in La0.7Sr0.3MnO3 film**Project supported by the National Natural Science Foundation of China (Grant No. 10974105), the Double-Hundred Talent Plan, Shandong Province, China (Grant No. WST2018006), the Recruitment Program of High-end Foreign Experts, China (Grant Nos. GDW20163500110 and GDW20173500154), and the Top-notch Innovative Talent Program of Qingdao City, China (Grant No. 13-CX-8).

In this paper, we investigate the effects of lattice strain on the electrical and magnetotransport properties of La0.7Sr0.3MnO3 (LSMO) films by changing film thickness and substrate. For electrical properties, a resistivity upturn emerges in LSMO films, i.e., LSMO/STO and LSMO/LSAT with small lattice strain at a low temperature, which originates from the weak localization effect. Increasing film thickness weakens the weak localization effect, resulting in the disappearance of resistivity upturn. While in LSMO films with a large lattice strain (i.e., LSMO/LAO), an unexpected semiconductor behavior is observed due to the linear defects. For magnetotransport properties, an anomalous in-plane magnetoresistance peak (pMR) occurs at low temperatures in LSMO films with small lattice strain, which is caused by two-dimensional electron gas (2DEG). Increasing film thickness suppresses the 2DEG, which weakens the pMR. Besides, it is found that the film orientation has no influence on the formation of 2DEG. While in LSMO/LAO films, the 2DEG cannot form due to the existence of linear defects. This work can provide an efficient way to regulate the film transport properties.

Transport Properties of Film and Bulk Sr0.98Zr0.95Y0.05O3−δ Membranes

In electrode-supported solid oxide fuel cells (SOFCs) with a thin electrolyte, the electrolyte performance can be affected by its interaction with the electrode, therefore, it is particularly important to study the charge transport properties of thin electrode-supported electrolytes. The transport numbers of charged species in Ni-cermet supported Sr0.98Zr0.95Y0.05O3−δ (SZY) membranes were studied and compared to those of the bulk membrane. SZY films of 2.5 μm thickness were fabricated by the chemical solution deposition technique. It was shown that the surface layer of the films contained 1.5–2 at.% Ni due to Ni diffusion from the substrate. The Ni-cermet supported 2.5 μm-thick membrane operating in the fuel cell mode was found to possess the effective transport number of oxygen ions of 0.97 at 550 °C, close to that for the bulk SZY membrane (0.99). The high ionic transport numbers indicate that diffusional interaction between SZY films and Ni-cermet supporting electrodes does not entail electrolyte degradation. The relationship between SZY conductivity and oxygen partial pressure was derived from the data on effective conductivity and ionic transport numbers for the membrane operating under two different oxygen partial pressure gradients—in air/argon and air/hydrogen concentration cells.

Physicochemical and transport properties of biodegradable agar films impregnated with natural semiochemical based-on hydroalcoholic garlic extract

Biodegradable films based on agar with glycerol (GLY) as a plasticizer were developed by incorporating hydroalcoholic garlic extract (HGE) on the film surface. The effect of GLY content (0, 15, or 30 wt%) and different concentrations of HGE (0, 0.5, 1, or 1.5 μg/mL) on the physicochemical and transport properties of the films was evaluated. The optical (color and transparency), mechanical (tensile test), transport (diffusion and water vapor transmission rate), thermal (thermogravimetric analysis) structural (infrared spectroscopy and X-ray diffraction), and morphological (scanning electron microscope) properties were analyzed. The impregnation of HGE increased the transparency values and decreased the luminosity, tensile strength, elastic modulus, and crystallinity of the agar films. The formulation of 30 wt% GLY with 1.5 μg/mL HGE, identified as 30 GLY [1.5], showed a similar thermal stability that of a neat agar film. The agar films with 30 wt% GLY showed the lowest diffusion coefficient and water vapor transmission rate, indicating that volatile compounds are slowly released. From the results the formulation 30 GLY [1.5] could be used as a film to transport and to release HGE which is supported by a biodegradable matrix and this system has a potential use as insect semiochemical for plague control.

A patterned look into a mysterious phase

Solid-State Physics A thin superconducting film can become insulating by, for example, exposure to a sufficiently large magnetic field. In between the superconducting and insulating regimes, an intermediate metallic state has been observed whose nature remains unresolved. To study the superconductor–metal insulator transition, C. Yang et al. patterned a film of the high-temperature superconductor yttrium barium copper oxide (YBCO) into a network of triangular superconducting islands connected by bridges (see the Perspective by Phillips). The reactive ion-etching process used for patterning reduced the quality of the film in a controlled manner. By increasing the etching time, the film's transport properties could be tuned from superconducting, through metallic, to insulating. The metallic phase exhibited a bosonic character. Science , this issue p. [1505][1]; see also p. [1450][2] [1]: /lookup/doi/10.1126/science.aax5798 [2]: /lookup/doi/10.1126/science.aaz9902

Intermediate bosonic metallic state in the superconductor-insulator transition.

Whether a metallic ground state exists in a two-dimensional system beyond Anderson localization remains an unresolved question. We studied how quantum phase coherence evolves across superconductor-metal-insulator transitions through magnetoconductance quantum oscillations in nanopatterned high-temperature superconducting films. We tuned the degree of phase coherence by varying the etching time of our films. Between the superconducting and insulating regimes, we detected a robust intervening anomalous metallic state characterized by saturating resistance and oscillation amplitude at low temperatures. Our measurements suggest that the anomalous metallic state is bosonic and that the saturation of phase coherence plays a prominent role in its formation.

Electronic and vibrational signatures of ruthenium vacancies in Sr2RuO4 thin films

The synthesis of stoichiometric ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ thin films has been a challenge because of the high volatility of ruthenium oxide precursors, which gives rise to ruthenium vacancies in the films. Ru vacancies greatly affect the transport properties and electronic phase behavior of ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$, but their direct detection is difficult due to their atomic dimensions and low concentration. We applied polarized x-ray absorption spectroscopy at the oxygen $K$ edge and confocal Raman spectroscopy to ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ thin films synthesized under different conditions. The results show that these methods can serve as sensitive probes of the electronic and vibrational properties of Ru vacancies, respectively. The intensities of the vacancy-related spectroscopic features extracted from these measurements are well correlated with the transport properties of the films. The methodology introduced here can thus help one to understand and control the stoichiometry and transport properties in films of ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ and other ruthenates.

Manganese-vacancy complexes induced room temperature ferromagnetism in Mn/Mg co-doped In2O3 diluted magnetic semiconductors

Abstract The (In0.98-xMnxMg0.02)2O3 (x = 0, 0.02, 0.05, 0.07, 0.11) films were deposited on Si (001) and ultra-white glass substrates using the RF-magnetron sputtering technique. The effects of Mn doping on the structural, optical, magnetic and transport properties of films were systematically investigated. The XANES and EXAFS spectra at Mn K-edge as well as the corresponding multiple-scattering calculations of XANES spectra clearly indicate that the doped Mn ions replace In ions in the In2O3 matrix with +2 oxidation states and form Mn2+-VO complexs in the nearest coordination shell of Mn. The decreased film transmittance and red shift of the optical band gap are observed with increasing Mn concentration, which can be ascribed to sp-d exchange interaction associated with the Mn dopants. All the films exhibit intrinsic room-temperature ferromagnetic ordering and the semiconducting behavior with the transport mechanism of Mott variable range hopping (VRH). The ferromagnetic properties of the films can consider being due to the Mn2+-vacancy complexes induced magnetic interaction by the overlapping of bound magnetic polarons.

Surface Self-Assembly, Film Morphology, and Charge Transport Properties of Semiconducting Triazoloarenes.

Surface-assisted molecular self-assembly is a powerful strategy for forming molecular-scale architectures on surfaces. These molecular self-assemblies have potential applications in organic electronics, catalysis, photovoltaics, and many other technologies. Understanding the intermolecular interactions on a surface can help predict packing, stacking, and charge transport properties of films and allow for new molecular designs to be tailored for a required function. We have previously studied a molecular platform, tris( N-phenyltriazole) (TPT), that exhibits planar stacking through >20 molecular layers through donor-acceptor-type intermolecular π-π contacts between the electron-deficient tris(triazole) core and electron-rich peripheral phenyl units. Here, we investigate an expanded family of TPT-based molecules with variations made on the peripheral aryl groups to modulate the molecular electron distribution and examine the impact on molecular packing and charge transport properties. Molecular-resolution scanning tunneling microscopy was used to compare the molecular packing in the monolayer and to investigate the effects that the structural and electronic modifications have on the stacking in subsequent layers. Conductivity measurements were made using the four-point probe van der Pauw technique to demonstrate charge transport properties comparable to pentacene. Although molecular packing is clearly impacted by the chemical structure, we find that the charge transport efficiency is quite tolerant to small structural variations.

Unraveling the Morphology–Function Relationships of Polyamide Membranes Using Quantitative Electron Tomography

An understanding ofhow complex nanoscale morphologies emerge from synthesis would offer powerful strategies to construct soft materials with designed structures andfunctions. However, these kinds of morphologies have proven difficult to characterize, and therefore manipulate, because they are three-dimensional (3D), nanoscopic, and often highly irregular. Here, we studied polyamide (PA) membranes used in wastewater reclamation as a prime example of this challenge. Using electron tomography and quantitative morphometry, we reconstructed the nanoscale morphology of 3D crumples and voids in PA membranes for the first time. Various parameters governing film transport properties, such as surface-to-volume ratio and mass-per-area, were measured directly from the reconstructed membrane structure. In addition, we extracted information inaccessible by other means. For example, 3D reconstruction shows that membrane nanostructures are formed from PA layers 15-20 nm thick folding into 3D crumples which envelope up to 30% void by volume. Mapping local curvature and thickness in 3D quantitatively groups these crumples into three classes, "domes", "dimples", and "clusters", each being a distinct type of microenvironment. Elemental mapping of metal ion adsorption across the film demonstrates that these previously missed parameters are relevant to membrane performance. This imaging-morphometry platform can be applicable to other nanoscale soft materials and potentially suggests engineering strategies based directly on synthesis-morphology-function relationships.

Preparation of thulium iron garnet ceramics and investigation of spin transport properties in thin films

Compensated ferrimagnetic thulium iron garnet ceramics were prepared by the sol-gel method, which is significantly better than conventional solid-state reactions. Saturation magnetization yielded a maximum of 16.7 emu/g for specimens sintered at 900 °C. Subsequently, using the TmIG bulk as the target, an epitaxial film was grown by pulsed laser deposition. Furthermore, the spin transport properties of film with an attached 5 nm-thick platinum layer were studied in terms of longitudinal spin Seebeck effect (LSSE) and spin Hall magnetoresistance (SMR). The LSSE coefficient was as high as 0.38 μV/K and the SMR was 0.0072%. These results indicated that the bulk material and thin film presented excellent qualities, which are extremely important for the fundamental investigation of novel spin transport behaviour in compensated ferrimagnetic insulators. These results also provide more alternatives for spintronic materials.

Effect of structural disorder on transport properties of LaNiO3 thin films

We have deposited LaNiO3 thin films on LaAlO3 (001), SrTiO3 (001), and Si (001) substrates using the pulsed laser deposition technique. Depositions were carried out at various substrate temperatures ranging from 0 to 800 °C. The effects of lattice mismatch and structural disorder on the transport properties of films deposited on various substrates and at different substrate temperatures are reported. X-ray diffraction confirms a highly c-axis oriented growth of LaNiO3 films on all the substrates at substrate temperatures of 600 and 800 °C, while at lower substrate temperatures deposited films are amorphous. Emergence of a new Raman mode indicates symmetry lowering in all the deposited crystalline films. Hardening of the Eg(3) (∼400 cm−1) mode is also observed with the rise of in-plane compressive strain. Resistivity curves for films on Si show a semiconducting behaviour and follow a variable range hopping mechanism. Crystalline films on LaAlO3 and SrTiO3 exhibit a metallic character along with a low-temperature resistivity upturn, which is attributed to the contribution of self-localization to resistivity at low temperatures as indicated by magnetotransport measurements.

Thermomechanical and transport properties of LLDPE films impregnated with clove essential oil by high-pressure CO2

Clove essential oil (CEO) was impregnated in linear low-density polyethylene (LLDPE) films by high-pressure CO2 technique. Impregnations were performed at 150 bar, 25 and 32 °C for 2 h followed by depressurization at 10, 50 and 100 bar min−1. The influence of operational parameters was observed on impregnation, optical, topographic, morphological, thermomechanical and transport properties of films. Higher amounts of CEO were impregnated when reducing depressurization rate and increasing temperature, with a maximum of 26.83 mg CEO/g LLDPE. Diffusion mechanism governed CEO migration from LLDPE in 10% and 95% (v/v) ethanolic solutions. The effective diffusion coefficient of CEO in LLDPE ranged from 5.4 × 10−13 to 1.0 × 10−12 m2 s−1. Operational parameters can be adjusted to enhance CEO incorporation, presenting negligible effect over CEO diffusivity in LLDPE. The results suggest the potential for developing active food packaging materials by green processes, also aggregating value to compounds from natural sources.

Effect of Deposition Time on Polaron Hopping Conduction Parameters in Carbon Films Embedded by Nickel Nanoparticles

In this work, the electric properties of carbon films embedded by nickel nanoparticles deposited at different deposition times 50-600 sec were investigated. It can be seen that the deposition time affects on nanoparticle sizes and thicknesses of films. A detailed analysis in terms of phonon-assisted small polaron hopping model is used to correlate electrical transport properties of films in temperature range 150-300 K. With increasing deposition time from 50 to 180 sec the polaron radius (rp) decrease and then from 180 to 600 sec it increased. The polaron radius (rp) of films deposited at 180 sec has minimum value of 8.14 × 10−8cm. The polaron hopping energy (WH) of films deposited at 180 sec has minimum value 0.028 eV. With increasing deposition time from 50 to 180 sec the density of states N (EF) at the Fermi level increase and then from 180 to 600 sec it decreased. The density of states N (EF) at the Fermi level of films deposited at 180 sec has maximum value of 6.09 × 1020 eV−1cm−3.