Single Thin Films Research Articles

A new optimization approach for high efficiency of FTO/InS/CIS heterojunction solar cells

ABSTRACT In this work, a new approach is developed to optimize FTO/InS/CIS hetero-junction solar cell using the Slivaco-Atlas software. Each single thin film was prepared by spray pyrolysis method on glass substrates in order to characterize its proper material parameters. Structural and morphological analysis confirmed the deposition of F-doped SnO2, In2S3 and CuInS2 films with porous structures. The extracted physical properties such as thickness, optical, and electrical parameters are considered as input data for Silvaco-Atlas software simulation. It was found that thickness layers and carrier concentration of CIS-based solar cell play an important role in determining solar cell performances. The combination of the optimum parameters enables to obtain the efficiency of 38.20%. The overall investigation on CIS solar cell gives potential suggestions that may lead to the fabrication of the high-efficiency CIS-based solar cell.

Temperature-dependent periodicity halving of the in-plane angular magnetoresistance in La0.67Sr0.33MnO3 thin films on LaAlO3

Strain-engineering is used as a tool to alter electronic and magnetic properties like anisotropy energy. This study reports the different angle-dependent magnetoresistance properties of the strain-engineered La0.67Sr0.33MnO3 (LSMO) thin films, grown on LaAlO3, compared to their bulk analogs. Upon increasing temperature, a symmetry change from fourfold [cos(4θ)] to twofold [cos(2θ)] is observed in the angle-dependent resistance measurements. This systematic study with increasing temperature allows us to define three distinct temperature-dependent phases. The fourfold symmetric signal originates from magnetocrystalline anisotropy, whereas the twofold symmetric signal is believed to be the conventional anisotropic magnetoresistance. Our observations show that strain-engineering creates the possibility to manipulate the anisotropy, which, for example, can ultimately lead to observations of noncollinear quasi-particles like skyrmions in single layer thin films of LSMO.

Al2O3 and HfO2 Atomic Layers Deposited in Single and Multilayer Configurations on Titanium and on Stainless Steel for Biomedical Applications

Thin films of alumina and hafnia were prepared by atomic layer deposition, with the aim of investigating the use of such films in biomedical applications. Films were deposited on commercially pure titanium and on medical stainless steel. Two configurations were prepared: single alumina films, 20 nm and 60 nm thick, and a multilayer film, 60 nm thick, consisting of alumina/hafnia/alumina layers, each 20 nm thick. The morphology, structure and composition of the coated alloys were characterized using scanning electron microscopy with energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. In addition, ellipsometry and atomic force microscopy coupled with scanning Kelvin probe force microscopy, were used to study the thickness and the topography with surface potential properties. An improvised method, involving the Vickers hardness test, was applied to assess the delamination of the deposited films. Coated specimens, as well as bare substrates, were tested at 37 °C in simulated body fluid, using potentiodynamic polarization and electrochemical impedance spectroscopy as techniques for assessing corrosion susceptibility. In general, single and multilayer thin films possess excellent barrier properties and are worth investigating further for biomedical applications. The degree of protection is dependent mainly on film thickness and on the type of substrate, and less on configuration.

Investigation on Controllable Orientation Growth of BiFeO3 Thin Films Deposited by DC Magnetron Sputtering

Nanocrystalline BiFeO3 thin films were synthesized on single crystal SrTiO3(100) substrate by the magnetron sputtering method at a mixture of Ar/O2 gas discharge, structure and morphology were characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM). The miscut angle of 4° and 8° for substrate and the effect of deposition temperature of 650 °C, 700 °C, 750 °C and 800 °C were discussed, respectively. The other two different crystal orientations substrates of SrTiO3(110) and SrTiO3(111), different miscut angles substrate SrTiO3(100) were selected to characterize orientation growth of BiFeO3 thin films. The results showed single phase nanocrystalline BiFeO3 thin films were synthesized at 700 °C–800 °C. The best crystallinity of BiFeO3 thin films was obtained at 750 °C with the grain size of 50 nm approximately. Via optimizing controllable orientation growth through varing the miscut angle, the orientation of the film sample can be regulated by the crystal orientation of different substrates, further proved that possessed different electric domain directions with change of miscut angle for substrate.

Nondestructive Detection of Magnetic Contaminant in Aluminum Casting Using Thin Film Magnetic Sensor.

The thin film magneto-impedance sensor is useful for detecting a magnetic material nondestructively. The sensor made by single layer uniaxial amorphous thin film has a tolerance against surface normal magnetic field because of its demagnetizing force in the thickness direction. Our previous study proposed the sensitive driving circuit using 400 MHz high frequency current running through the sensor to detect the logarithmic amplifier. We also confirmed the sensitivity of the sensor within 0.3 T static normal magnetic field, which resulted in detection of 5 × 10−8 T of 5 Hz signal. This paper proposes a nondestructive inspection system for how detecting a contaminant of small tool steel chipping in aluminum casting specimen would be carried out. Three channel array sensors installed in the 30 mT static field detecting area were fabricated and experimentally showed a detection of low remanence magnetic contaminant in a bulk aluminum casing specimen.

BaBiO3—From single crystals towards oxide topological insulators

Abstract BaBiO3 is an oxide perovskite with a wide variety of interesting properties. It was expected that the compound would behave like a metal. However, experiments revealed that BaBiO3 is not metallic, which started an extensive debate about the mechanism responsible for this insulating behavior. The two most important conjectures in this debate are charge disproportionation of the Bi ion into 3+ and 5+ cations and bond hybridization of the Bi 6s and O 2p orbitals. Both mechanisms induce a breathing mode of the oxygen octahedra, which is experimentally observed in single crystals and thin films. Recently, ultra-thin BaBiO3 films were studied with the aim of suppressing the breathing mode, which was expected to result in re-emergence of metallicity. However, this expectation was not confirmed so far. Furthermore, theoretical calculations predict that BaBiO3 becomes a topological insulator (TI) when doped with electrons. Since high-temperature superconductivity was observed when doping the compound with holes, an interface between a superconductor and a TI can be established within the same parent compound. In this Review, we discuss the theoretical and experimental findings concerning the mechanism responsible for the unexpected insulating behavior of BaBiO3 for both single crystals and thin films. An overview is given of the current state of the art and the experimental challenges of achieving an oxide topological insulating state in BaBiO3.

Tribological and thermal characterization of electron beam physical vapor deposited single layer thin film for TBC application

Thin-film coatings have been commonly used in the automotive industry for a variety of applications. Thermal barrier coatings (TBCs) are designed to extend the life of combustors and turbine blades while mitigating high-temperature issues. In this study, an attempt has been made to develop a single-layer thin film as TBCs for engine applications. Yttria Stabilized Zirconia(YSZ) and Lanthanum Zirconate(LZ) were selected as the coating materials. The physical and chemical characteristics of target materials were studied using Scanning Electron Microscope (SEM), Energy Dispersive x-ray Spectroscopy (EDS), and x-ray Diffraction Analysis (XRD). FCD 400 has been taken as the substrates for this study. In general, TBCs thicknesses are usually about 100–300 μm, while in this work, a coating thickness of 750 nm is attempted using EB-PVD and its performance was evaluated. The mechanical, tribological, and thermal behaviors of the uncoated and coated substrates were characterized as per ASTM standards. Maximum hardness of 3.68 GPa was observed on the YSZ coated substrates. The average Coefficient of Friction (COF) and Coefficient of Thermal Expansion(CTE) values of YSZ coated substrates were 0.334 and 1.33 × 10–5 K−1, respectively, which were comparatively lower than LZ and uncoated substrates. On the contrary, the adhesive characteristics of YSZ and LZ coated substrates were enhanced, which was evident from their results of 6.28N and 6.19N respectively. The thermal conductivity of LZ coated substrates was found to be 3.2% lower than YSZ and 11% lower than uncoated substrates, respectively. From the results, it is observed that LZ thin film coating have better thermal properties than YSZ, which is best suited for TBCs application. Following evaluation of thin-film coatings, confirms that thin-film TBCs are a reliable approach for thermal and wear production as compared to thick TBCs, and their extended life could improve productivity and economic benefits for automotive industries.

Single crystal-like thin films of blue bronze

Pulsed laser deposition technique was employed to grow thin films of K0.3MoO3 on Al2O3 (1-102) and SrTiO3 (510) substrates. Structural and imaging characterization revealed good quality films with well oriented grains of few microns in length. Both non-selective (transport) and order-selective (femtosecond pump-probe spectroscopy) probes revealed charge density wave properties that are very close to those of the single crystals. The films exhibit metal-semiconductor phase transition in resistivity, pump-probe data show phase transition at the same temperature as the single crystal and the threshold for the photo-induced phase transition is approximately the same as in single crystal. We compare the properties of films with grains differing by an order of magnitude in length.

Effect of non-peripheral fluorosubstitution on the structure of metal phthalocyanines and their films

In this work, we study crystal structures and thin films of tetrasubstituted metal phthalocyanines with fluorine substituents in non-peripheral positions, MPcF4-np (M = Cu(II), Co(II), Pd(II), Fe(II), Pb(II), VO). The effect of fluorosubstitution in non-peripheral positions of the phthalocyanine macrocycle on the structure of single crystals and thin films, and intermolecular interactions is elucidated and compared with that of other fluorinated phthalocyanine derivatives. MPcF4-np (M = Cu(II), Pd(II), Fe(II)) are isostructural and crystallize in the monoclinic P21/c space group, while CoPcF4-np forms two polymorphs (P21 and P21/c). Monoclinic PbPcF4-np (P21/n) is packed in chains along the c axis, in which one PbPcF4-np molecule is oriented “up” and two neighboring molecules face “down”. Two triclinic (P-1) phases were obtained for VOPcF4-np. For the better visualization and comparison of intermolecular contacts in different MPcF4-np, the analysis of Hirshfeld surfaces (HS) was carried out. All investigated MPcF4-np derivatives form thin films with a strong preferred orientation. The effect of the positions of F-substituents on the electronic absorption spectra of MPcF4 solutions and thin films is also discussed.

Broadband angular color stability of dielectric thin film-coated pyramidal textured Si for photovoltaics

In this work we demonstrate the angular color stability of textured c-Si substrates colored by single layer thin film coatings of SiNx. These coatings show higher angular color stability on substrates with a random upright pyramidal surface texture compared to identical coatings on planar silicon substrates. Angle dependent reflectance measurements, supported by a modeling framework, display that the reflectance peaks originating from thin film interference of coated textured substrates only shift about 15 nm with an increasing angle of incidence from 10° to 80°, while the reflectance peaks of planar substrates with identical coatings shift about 120 nm at these angles. More specifically, reflectance peaks of planar substrates shift to shorter wavelengths, leading to a blue shift of the color appearance. The stable peak position of the textured samples is explained by a 2D representation of their surface texture and the primarily double interference interaction on it. While it is well known that a wide range of colors can be realized exhibiting low optical losses with thin film coatings, angular color stability was often not taken into account. However, for building integrated photovoltaics applications, a high angular color stability is desired, underlining the importance of using these textures. In most installed c-Si photovoltaics, similar substrate surface textures and dielectric thin film layers are already used. Therefore, this work envisions a route to facilitate large scale production of colored solar cells on textured c-Si substrates, colored by thin film SiNx layers, with minimized optical losses and improved angular color stability.

Magnetic Nanoparticle Detection Using Wheatstone Bridge Giant Magnetoresistance (GMR) Sensor with Double CoFeB Spin-Valve Thin Films

The Wheatstone bridge-giant magnetoresistance (GMR) sensor with single and double spin valve thin film was successfully developed for potential biomolecular detection. The GMR sensor with spin valves structure of [Ta (2nm)/IrMn (10nm)/CoFe (3nm)/Cu (2,2nm)/CoFeB (10nm)/Ta (5nm)] was fabricated using DC Magnetic Sputtering method. The Fe3O4magnetic nanoparticles were synthesized by the co-precipitation method as a magnetic label. The magnetic properties of the Fe3O4nanoparticles measured are the saturation magnetization (Ms) of 77.7 emu/g, remanence magnetization (Mr) of 7.7 emu/g, and coercivity (Hc) of 49 Oe. The X-ray diffraction pattern showed the inverse cubic spinel structure with an average crystal size of about 20.1 nm. Fe3O4magnetic nanoparticles with various concentrations were used to be detected using a GMR sensor. The output voltage of the GMR sensor with the single and double spin-valve increased from 1.7 to 3.9 mV and 2.9 to 5.3 mV with the increase of the Fe3O4concentration from 0 to 20 mg/mL, respectively.

Effect of bias voltage and carrier gas on the hydrogen gas-sensing properties of tungsten oxide nanobeads

We investigated the effect of bias voltage and carrier gas on the hydrogen sensing performance of tungsten oxide nanobeads. The tungsten oxide nanobeads were prepared by a template-assisted method followed by calcination. The porous single walled carbon nanotube thin film was used as sacrificed template for the deposition of tungsten, followed by thermal calcination at high temperature to oxidize W into WO3 and to burn out the template. The crystal structures and morphology of the synthesized materials were characterized by X-ray diffraction, field-emission scanning electron microscopy, high-resolution transmission electron microscopy and Raman spectra. Hydrogen gas sensing properties were tested in air and in N2 as refence for comparison. Our results indicated that Schottky junction was formed at the interface of WO3 and Pt electrodes. The sensor operated under revered bias voltage processed excellent hydrogen sensing performance. In addition, the H2 sensing performance of the WO3 nanobeads is higher when measured in N2 gas as reference.

Preparation of single crystalline AlN thin films on ZnO nanostructures by atomic layer deposition at low temperature

The growth of hetero-epitaxial ZnO-AlN core–shell nanowires (NWs) and single crystalline AlN films on non-polar ZnO substrate at temperature of 380 °C by atomic layer deposition (ALD) was investigated. Structural characterization shows that the AlN shells have excellent single-crystal properties. The epitaxial relationship of [0002]ZnO//[0002]AlN, and [10−10]ZnO//[10−10]AlN between ZnO core and AlN shell has been obtained. The ZnO NW templates were subsequently removed by annealing treatment in forming gas, resulting in ordered arrays of AlN single-crystal nanotubes. The impact factors on the epitaxial growth of AlN films are thoroughly investigated. It turned out that the growth parameters including lattice mismatch between substrate and AlN, growth temperature, and the polarity of ZnO substrate play important roles on the growth of single-crystal AlN films by ALD. Finally, non-polar AlN films with single-crystalline structure have been successfully grown on m-plane ZnO (10−10) single-crystal substrates. The as-grown hollow AlN nanotubes arrays and non-polar AlN films with single-crystalline structures are suggested to be highly promising for applications in nanoscale devices. Our research has developed a potential method to obtain other inorganic nanostructures and films with single-crystalline structure at fairly low temperature.

Semi analytical model for electrical transport in single wall carbon nanotube thin film transistors

With the recent advances in carbon nanotube (CNT) electronics, transistors made of thin films of single wall CNTs (SWNTs) are gaining great attention due to their high quality electrical characteristics. With such improvements it has become essential to develop suitable models to accurately predict the electrical transport in such devices which in the current scenario remains scarce. This work presents a numerical simulation of current transport in SWNT thin film-based transistors (TFTs). The developed model considers both Ohmic and Schottky type contacts that are exhibited by such field effect transistors based on which two separate modes of transport for electrons and holes are described. The electron transport is described through a tunneling transmission process while the hole transport is described by a thermionic transmission process where the model treats each SWNT individualistically and determines the overall current through a novel iterative process. The accuracy of the proposed model is verified by comparing it with multiple experimental data.

Analysis of HfO2 Charge Trapping Layer Characteristics After UV Treatment

The improvement in the charge storage characteristics in a non-volatile memory (NVM) device employing an ultraviolet (UV)-treated hafnium oxide (HfO2) layer as the charge-trapping layer is reported. X-ray photoelectron spectroscopy analysis was performed to characterize the Hf 4f and O 1s peaks. The defect densities corresponding to Hf and O after short-term UV treatment are 24.74% and 14.16%, respectively. The electrical characteristics, such as the interface trap density (Dit), dielectric constant, and flat band voltage (VFB), of single HfO2 thin films were determined via capacitance vs voltage (C–V) measurements of the fabricated metal–oxide–semiconductor (MOS) capacitors. Notably, this memory device has a maximum ΔVth of 4.10 V at 15 V, which corresponds to a 33.4% improvement in memory storage characteristics compared to those of an as-deposited HfO2 thin film-based memory. In addition, the charge retention after 10 years is 80.22%, which is superior to that of the as-deposited case. These results demonstrate the possibility of realizing high-efficiency TFT NVM devices using high-K materials, and are expected to enable further research on semiconductor devices using high-K materials as well as next-generation memory semiconductors using UV treatment.

Ditch and elevated organic thin film transistor‐based improved common source voltage amplifier: Frequency response characteristics and analytical modeling

AbstractIn this work, the frequency response of single gate organic thin film transistor (OTFT)‐based common source (CS) voltage amplifier is analyzed. Also, the contact‐channel resistance models are developed to validate the lower/upper cutoff frequency and mid‐band gain. The bandwidth of single gate bottom contact (BC) OTFT‐based amplifier is found to be 16 GHz, but the gain is quite low than the predicted due to its lower transconductance. Surprisingly, voltage gain is improved by four times (12.6 dB more) for dual gate TFT‐based amplifier. Moreover, the bandwidth (1 MHz) is also reasonably good. On applying top gate, biasing the gain is enhanced by 46%. Furthermore, two modified single gate BC structures, ditch and elevated source/drain (S/D) contacts, are incorporated to further augment the amplifier characteristics. Correspondingly, it shows a significant enhancement of 45% and 39% in the gain than that of normal BC. Additionally, the bandwidth is observed to be large and obtained as 100 and 96 MHz, which is also close to the expected analytically.

Fabrication of a rutile titanium dioxide thin film heterostructure using ion-implantation with Cu-Sn bonding

Single crystalline titanium dioxide thin film in the rutile phase (r-TiO2) is exfoliated from bulk material using a He+-implantation method, and is bonded onto SiO2 substrate to form a heterostructure using Cu-Sn bonding technology. The exfoliated r-TiO2 thin film was examined to be in good quality, and the exfoliation mechanism of ion-implanted r-TiO2 was analyzed. The obtained r-TiO2 thin film heterostructure with high refractive index contrast has a potential application in the fabrication of high-Q optical microcavities in visible wavelengths, which is useful in integrated photonic devices.

Chalcogenide perovskite BaZrS3 thin-film electronic and optoelectronic devices by low temperature processing

Owing to its superior visible light absorption and high chemical stability, chalcogenide perovskite barium zirconium sulfide has attracted significant attention in the past few years as a potential alternative to hybrid halide perovskites for optoelectronics. However, the high processing temperatures of BaZrS3 thin films at above 1000 C severely limits their potential for device applications. Herein, we report the synthesis of BaZrS3 thin films at temperatures as low as 500 C, by changing the chemical reaction pathway. The single phase BaZrS3 thin film was confirmed by X-ray diffraction and Raman spectroscopies. Atomic force microscopy and scanning electron microscopy show that crystalline size and surface roughness were consistently reduced with decreasing annealing temperature. The lower temperatures further eliminate sulfur vacancies and carbon contaminations associated with high temperature processing. The ability to synthesize chalcogenide perovskite thin films at lower temperatures removes a major hurdle for their device fabrication. The photodetectors demonstrate fast response and an on/off ratio of 80. The fabricated field effect transistors show an ambipolar behavior with electron and hole mobilities of 16.8 cm2/Vs and 2.6 cm2/Vs, respectively.

A diagnostic evaluation of single screen testing for malaria in the returning traveler: A large retrospective cohort study.

Screening for malaria in the returning traveler has often required repeat testing; however, audit data suggest that patients have not been reattending. We sought to ascertain if this was safe by examining the diagnostic efficacy of a single screen consisting of a rapid diagnostic test (RDT) and a thin film. We conducted a retrospective cohort study of patients with suspected malaria who attended in the past 5years from two large teaching hospitals. We assessed the diagnostic accuracy of a single screen, reporting measures of sensitivity and specificity. To establish a reference standard, we cross-linked data with the national malaria registry held at Public Health England and regional centers. The cohort consisted of 1365 patients, of whom 33 opted out of the research and one did not have a complete initial screen. Of those 1331 screens there were 74 cases of Plasmodium falciparum (prevalence of 5.6%) and 104 of any malaria species (prevalence of 7.8%). Sensitivity for the detection of P.falciparum was 100.00% (95% confidence interval [CI]= 95.1 to 100), with a specificity of 99.4% (95% CI= 98.9 to 99.8). For the detection of any species of malaria the sensitivity was slightly lower due to the presence of one false negative; sensitivity was 99.0% (95% CI= 94.8 to 100) and specificity was 99.5% (95% CI= 98.9 to 99.8). A single thin film and RDT is likely to be sufficient as a first screen for falciparum malaria in the returning traveler with important caveats. For those sent home from emergency departments, appropriate safety netting must be provided. Further prospective study is required to investigate this approach.

Enhanced Magneto-Optical Kerr Effect of GaAs-Based P-N Junctions in the Terahertz Range

We demonstrate that the magneto-optical Kerr effect at normal incidence in the terahertz (THz) frequency range is useful for evaluating carrier transport properties of particular layers of a p-n junction. Since a single p-type thin film only exhibits a small magneto-optical Kerr effect, magneto-optical Kerr spectroscopy cannot be used to determine the carrier densities of such a film with high sensitivity. However, because the electric field is enhanced at the p-layer in a p-n junction due to the interference between the THz waves that are reflected at the highly doped substrate and the p-layer at the surface, it is possible to conduct magneto-optical Kerr spectroscopy with a higher sensitivity. We numerically calculate and experimentally determine the spectra of the ellipticity and polarization rotation angles for single n- and p-GaAs epitaxial layers and GaAs-based photovoltaic devices with a p-i-n structure and evaluate the carrier densities of the n- and p-layers. At normal incidence, this method has a high spatial resolution, which is beneficial for imaging of large-area devices.