Plane Of Thin Film Research Articles

High-temperature superconductor quantum flux parametron for energy efficient logic

We report the fabrication and measurement of quantum flux parametron logic from high-transition-temperature Josephson junctions operating at 25 K, above the temperature of liquid helium. The circuits are written directly into the plane of a single-layer thin film of YBa2Cu3O7 using a focused helium ion beam. A single-cell quantum flux parametron was constructed and correct logic operation was verified by using an on-chip superconducting quantum interference device for readout. A three-cell shift register was also fabricated and tested using a three-phase clock cycle. We estimate the average bit energy to be about 1×10−20 J at 1 GHz.

Synthesis of AZO-Coated ZnO Core-Shell Nanorods by Mist Chemical Vapor Deposition for Wastewater Treatment Applications.

AZO-coated ZnO core-shell nanorods were successfully fabricated using the mist chemical vapor deposition method. The influence of coating time on the structural, optical, and photocatalytic properties of zinc oxide nanorods was investigated. It was observed that the surface area of AZO-coated ZnO core-shell nanorods increased with an increase in coating time. The growth orientation along the (0001) crystal plane of the AZO thin film coating was the same as that of zinc oxide nanorods. The crystallinity of AZO-coated ZnO core-shell nanorods was significantly improved as well. The optical transmittance of AZO-coated ZnO core-shell nanorods was greater than 55% in the visible region. The degradation efficiency for methyl red dye solution increased with an increase in coating time. The highest degradation efficiency was achieved by AZO-coated ZnO core-shell nanorods with a coating duration of 20 min, exhibiting a degradation rate of 0.0053 min-1. The photodegradation mechanism of AZO-coated ZnO core-shell nanorods under ultraviolet irradiation was revealed.

Ethanol formation via CO2 electroreduction at low overvoltage over exposed (111) plane of CuO thin film

In this study, we fabricated CuO thin films using the sol-gel spin coating method. The fabricated thin films were utilized for electrocatalytic reduction of CO2 (CO2ER). Fabrication of thin film is vital to provide a large surface area and a more exposed (111) crystal plane for ethanol selectivity. This is verified by comparing it with bulk powder material which does not give such activity. CO2ER over thin film electrode specifically forms CO(g) and Ethanol(l), 2 and 12 electron reduction products, and eliminates the possibility of unwanted HER as a side reaction in the CO2 saturated NaHCO3 electrolyte. We achieved significant product selectivity and faradaic efficiency, utilizing the very low potential for both CO and ethanol. Specific formation of only CO and ethanol makes the process efficient as the separation of gas and liquid is easy. Results based on density functional theory calculations suggest that CuO (111) and CuO (-111) surfaces promote CO2 adsorption and subsequent formation of CO. However, a direct CO-dimerization is observed only on the CuO (111) surface that facilitates the formation of ethanol as the C2 product. This comparative study of bulk and thin-film opens new insight and highlights the importance of catalyst fabrication for the specific product formation utilizing significantly less energy.

Forward volume magnetoacoustic spin wave excitation with micron-scale spatial resolution

The interaction between surface acoustic waves (SAWs) and spin waves (SWs) in a piezoelectric-magnetic thin film heterostructure yields potential for the realization of novel microwave devices and applications in magnonics. In the present work, we characterize magnetoacoustic waves in three adjacent magnetic micro-stripes made from CoFe + Ga, CoFe, and CoFe + Pt with a single pair of tapered interdigital transducers (TIDTs). The magnetic micro-stripes were deposited by focused electron beam-induced deposition and focused ion beam-induced deposition direct-writing techniques. The transmission characteristics of the TIDTs are leveraged to selectively address the individual micro-stripes. Here, the external magnetic field is continuously rotated out of the plane of the magnetic thin film and the forward volume SW geometry is probed with the external magnetic field along the film normal. Our experimental findings are well explained by an extended phenomenological model based on a modified Landau–Lifshitz–Gilbert approach that considers SWs with nonzero wave vectors. Magnetoelastic excitation of forward volume SWs is possible because of the vertical shear strain ɛxz of the Rayleigh-type SAW.

Unraveling hausmannite (Mn3O4) thin films surface structure by X ray linear dichroism

There is an urgent need to understand the relationship between oxide thin-film surface plane and its electronic properties because of its key role in molecular adsorption and surface reactivity as requested in optimal applications of magnetism to catalysis. The present work intends to resolve this open issue by investigating the surface structure and electronic properties of Mn3O4 thin films. To this end, well-defined Mn3O4 (110) and (001) surfaces were prepared and their electronic properties were explored by X-ray linear dichroism, XLD (the search light effect). The Mn3O4 thin films were extensively prepared on distinct noble metal substrates (Au(111), Cu (111), Ag (001)) with the aim of disentangling the film’s electronic structure and their corresponding film strain from their free surface, bulk, and interface contribution. Our experiments revealed the sensitivity of the 3d orbital occupancy and their intensity ratio (dx2−y2/d3z2−r2) to the surface orientation. The variation of relative 3d occupation as a function of strain was quantified by using the XLD sum rules. These results reveal important aspects for the identification and further engineering of well-defined crystallographic surfaces in several fields of applications.

Angular dependence of Hall effect and magnetoresistance in SrRuO3−SrIrO3 heterostructures

Perovskite SrRuO$_3$ is a prototypical itinerant ferromagnet which allows interface engineering of its electronic and magnetic properties. We report synthesis and investigation of atomically flat artificial multilayers of SrRuO$_3$ with the spin-orbit semimetal SrIrO$_3$ in combination with band-structure calculations with a Hubbard $U$ term and topological analysis. They reveal an electronic reconstruction and emergence of flat Ru-4d$_{xz}$ bands near the interface, ferromagnetic interlayer coupling and negative Berry-curvature contribution to the anomalous Hall effect. We analyze the Hall effect and magnetoresistance measurements as a function of the field angle from out of plane towards in-plane orientation (either parallel or perpendicular to the current direction) by a two-channel model. The magnetic easy direction is tilted by about $20^\circ$ from the sample normal for low magnetic fields, rotating towards the out-of-plane direction by increasing fields. Fully strained epitaxial growth enables a strong anisotropy of magnetoresistance. An additional Hall effect contribution, not accounted for by the two-channel model is compatible with stable skyrmions only up to a critical angle of roughly $45^\circ$ from the sample normal. Within about $20^\circ$ from the thin film plane an additional peak-like contribution to the Hall effect suggests the formation of a non-trivial spin structure.

Influence of cobalt doping on the structural, optical, topographical and sensing properties of spray deposited zinc oxide thin films

Structural, optical and gas sensing properties of spray deposited undoped and cobalt doped ZnO thin films have been carried out and reported. Hexagonal wurtzite structure of the investigated thin films is confirmed using X-ray diffraction technique. Interestingly, crystallite sizes are found to decrease with increasing Co concentration with 0.003 M having least size of 40 nm. The growth orientation plane of ZnO thin films are found to vary with Co doping. Atomic force micrographs reveal spherical grains with compact structure for both the films. The optical band gap values at higher doping concentrations were found to be increased. The Co doped (0.003 M) film gained less band gap (3.36 eV) which is beneficial for ammonia sensing application. The sensing characteristics of doped (Co-0.003 M) ZnO (0.1 M) film at various ammonia vapour concentrations at room temperature were studied.

Study on Preparation and Properties of InN Films on Self-Supporting Diamond Substrates Under Different Nitrogen Flows

Several InN film samples with superb properties were prepared on a self-supporting diamond substrate for different nitrogen flow rates using an electron cyclotron resonance plasma-enhanced metal-organic chemical vapor deposition (ECR-PEMOCVD) system. After the InN film samples were obtained, the samples were characterized via reflected high-energy electron diffraction (RHEED), X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscope (AFM), and electron probe micro-analysis (EPMA) to study the effect of the nitrogen flow on the quality of the InN films. The experimental results show that the variation in the nitrogen flow has a great impact on the preferential growth of the (0002) crystal plane of the InN thin-film. By increasing the nitrogen flow moderately, the crystal quality of the film is improved. Under the growth condition of appropriate nitrogen flow, InN thin-films with a preferred orientation along the c-axis can be obtained, and the surface of the resulting InN thin-films is relatively flat. However, a high nitrogen flow does not improve the film crystal quality. The results of the experiment and of the analysis show that the InN films prepared with a nitrogen flow rate of 80 sccm have an excellent preferential orientation. The result of the EPMA test shows that the percentages of the In and N atoms in the prepared film samples are close to a ratio of 1:1, and a small amount of metal In droplets is present. In addition, the InN thin-films prepared in such condition have an excellent surface morphology and composition.

Experimental Study of the Thermal Conductivity of Single-Walled Carbon Nanotube-Based Thin Films

The single-walled carbon nanotube-based thin films with a thickness from 11 ± 3 to 157 ± 18 nm have been formed using vacuum filtration. The thermal conductivity of the thin films as a function of thickness and temperature up to 450 K has been studied by the 3ω technique. It has been found that, in the region of 49 nm, the supplied heat from a gold strip started propagating with the high efficiency to the thin film plane. The thermal conductivity of the thin films with a thickness of 49 ± 8 nm was measured using the 3ω technique for bulk samples. It has been found that the thermal conductivity of the single-walled carbon nanotube-based thin films strongly depends on their thickness and temperature. The thermal conductivity sharply (by a factor of ~60) increases with an increase in thickness from 11 ± 3 to 65 ± 4 nm. In addition, it has been observed that the thermal conductivity of the thin film with a thickness of 157 ± 18 nm rapidly decreases from 211 ± 11 to 27.5 ± 1.4 W m–1 K–1 at 300 and 450 K, respectively.

Large-area implementation and critical evaluation of the material and fabrication aspects of a thin-film thermoelectric generator based on aluminum-doped zinc oxide

A large-area thermoelectric generator (TEG) utilizing a folded thin-film concept is implemented and the performance evaluated for near room temperature applications having modest temperature gradients (<50 K). The TEGs with the area of ∼0.33 m2 are shown capable of powering a wireless sensor node of multiple sensors suitable e.g. for monitoring environmental variables in buildings. The TEGs are based on a transparent, non-toxic and abundant thermoelectric material, i.e. aluminium-doped zinc oxide (AZO), deposited on flexible substrates. After folding, both the electrical current and heat flux are in the plane of the thermoelectric thin-film. Heat leakage in the folded TEG is shown to be minimal (close to that of air), enabling sufficient temperature gradients without efficient heat sinks, contrary to the conventional TEGs having the thermal flux and electrical current perpendicular to the plane of the thermoelectric films. The long-term stability studies reveal that there are no significant changes in the electrical or thermoelectric properties of AZO over several months, while the contact resistance between AZO and silver ink is an issue exhibiting a continuous increase over time. The performance of the TEGs and technological implications in relation to a state-of-the-art thermoelectric material are further assessed via a computational study.

FMR and Magnetic Studies of RF-Sputtered Mn-Zn Ferrite Thin Films

The Manganese–Zinc ferrite (MZF) thin films were deposited on quartz substrates by radio frequency (RF) magnetron sputtering at 10 mTorr of argon gas pressure. The FMR and magnetization measurement were carried out to understand magnetic properties of the as-deposited and annealed MZF films. The resonance field (Hr) of the FMR spectra shifts towards higher magnetic field when angle between applied field and thin film plane is changed from 0 to 90° indicating the existence of uniaxial anisotropy in the film. Whereas, Hr shifts towards lower magnetic field with decrease in temperature of the film. This is due to ferrimagnetic ordering in the films at low temperatures. The magnetization versus field (M-H) plots reveal the soft ferrimagnetic behavior of the films. The post-deposition annealing of the film leads to increase in crystallite size with more uniform film surface and dense columnar growth compared to the as-deposited film. The increase in magnetization and decreases in Hr-values compared to that of as-deposited film are observed for annealed film. The optical band gap of the film is also found to increase with annealing.

Information Content in Nuclear Medicine Imaging

The aim of the present study was to investigate the information content of positron emission tomography (PET) images. We used the GATE Monte Carlo package (GEANT4 application for tomographic emission) and reconstructed images, obtained using the software for tomographic image reconstruction (STIR). The case study for the investigation of the PET images information content was the General Electric Discovery-ST (USA) PET scanner. A thin film plane source aluminum (Al) foil, coated with a thin layer of silica and a fluorodeoxyglucose (18F-FDG) bath distribution of (1 MBq) was used in the simulation for the image signal to noise ratio assessment. The influence of the maximum likelihood estimation ordered subsets maximum a posteriori one step late (MLE)-OS-MAP-OSL algorithm, using various subsets (1 to 21) and iterations (1 to 20) was examined. The image information content was assessed in terms of the information capacity (IC). Results showed that the single index information capacity maximized for the range of 8-20 iterations and 3 subsets. In conclusion, our study showed that the image information content of PET scanners can be fully characterized and further improved by investigation of the imaging chain components through Monte Carlo methods. Moreover, new perspectives are created by using the suggested techniques in the context of a global cloud service that could serve as an online quality evaluation metric for the PET scanners and other medical imaging systems.

Information Capacity of Positron Emission Tomography Scanners

Background: The aim of the present study was to assess the upper information content bound of positron emission tomography (PET) images, by means of the information capacity (IC). Methods: The Geant4 Application for the Tomographic Emission (GATE) Monte Carlo (MC) package was used, and reconstructed images were obtained by using the software for tomographic image reconstruction (STIR). The case study for the assessment of the information content was the General Electric (GE) Discovery-ST PET scanner. A thin-film plane source aluminum (Al) foil, coated with a thin layer of silica and with a 18F-fludeoxyglucose (FDG) bath distribution of 1 MBq was used. The influence of the (a) maximum likelihood estimation-ordered subsets-maximum a posteriori probability-one step late (MLE-OS-MAP-OSL) algorithm, using various subsets (1 to 21) and iterations (1 to 20) and (b) different scintillating crystals on PET scanner’s performance, was examined. The study was focused on the noise equivalent quanta (NEQ) and on the single index IC. Images of configurations by using different crystals were obtained after the commonly used 2-dimensional filtered back projection (FBP2D), 3-dimensional filtered back projection re-projection (FPB3DRP) and the (MLE)-OS-MAP-OSL algorithms. Results: Results shown that the images obtained with one subset and various iterations provided maximum NEQ values, however with a steep drop-off after 0.045 cycles/mm. The single index IC data were maximized for the range of 8–20 iterations and three subsets. The PET scanner configuration incorporating lutetium orthoaluminate perovskite (LuAP) crystals provided the highest NEQ values in 2D FBP for spatial frequencies higher than 0.028 cycles/mm. Bismuth germanium oxide (BGO) shows clear dominance against all other examined crystals across the spatial frequency range, in both 3D FBP and OS-MAP-OSL. The particular PET scanner provided optimum IC values using FBP3DRP and BGO crystals (2.4829 bits/mm2). Conclusions: The upper bound of the image information content of PET scanners can be fully characterized and further improved by investigating the imaging chain components through MC methods.

Fresnel diffraction of spin waves

The propagation of magnetostatic forward volume waves excited by a constricted coplanar waveguide is studied via inductive spectroscopy techniques. A series of devices consisting of pairs of sub-micrometer size antennae is used to perform a discrete mapping of the spin wave amplitude in the plane of a 30-nm thin YIG film. We found that the spin wave propagation remains well focused in a beam shape of width comparable to the constriction length and that the amplitude within the constriction displays oscillations, two features which are explained in terms of near-field Fresnel diffraction theory.

Magnetic properties of L10 FePt thin film influenced by recoverable strains stemmed from the polarization of Pb(Mg1/3Nb2/3)O3–PbTiO3 substrate**Project supported by the National Natural Science Foundation of China (Grant Nos. 11474167, 51701091, and 11504020) and the Start-up Funds of NUIST, China (Grant Nos. 2243141601035 and 2243141601018).

The magnetic properties and magnetization reversible processes of L10 FePt (3 nm)/Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN–PT) heterostructure were investigated by using the phase field model. The simulation results show that the magnetic coercivities and magnetic domains evolution in the L10 FePt thin film are significantly influenced by the compressive strains stemming from the polarization of single crystal PMN–PT substrate under an applied electric field. It is found that the magnetic coercivities increase with increasing of the compressive strain. A large compressive strain is beneficial to aligning the magnetic moments along the out-of-plane direction and to the enhancement of perpendicular magnetic anisotropy. The variations of magnetic energy densities show that when compressive strains are different at the magnetization reversible processes, the magnetic anisotropy energies and the magnetic exchange energies firstly increase and then decrease, the negative demagnetization energy peaks appear at coercivities fields, and the magnetoelastic energies are invariable at large external magnetic field with the energy maximum appearing at coercivities fields. The variations of the magnetoelastic energies bring about the perpendicular magnetic anisotropy so that the magnetoelastic energy is lower at the large external magnetic fields, whereas the appearance of magnetoelastic energy peaks is due to the magnetization-altered direction from the normal direction of the plane of the L10 FePt thin film at coercivities fields.

A numerical study on the design trade-offs of a thin-film thermoelectric generator for large-area applications

Thin-film thermoelectric generators with a novel folding scheme are proposed for large-area, low energy-density applications. Both the electrical current and heat transfer are in the plane of the thermoelectric thin-film, yet the heat transfer is across the plane of the module - similar to conventional bulk thermoelectric modules. With such designs, the heat leakage through the module itself can be minimized and the available temperature gradient maximized. Different from the previously reported corrugated thermoelectric generators, the proposed folding scheme enables high packing densities without compromising the thermal contact area to the heat source and sink. The significance of various thermal transport, or leakage, mechanisms in relation to power production is demonstrated for different packing densities and thicknesses of the module under heat sink-limited conditions. It is shown that the power factor is more important than ZT for predicting the power output of such thin-film devices. As very thin thermoelectric films are employed with modest temperature gradients, high aspect-ratio elements are needed to meet the - usually ignored - requirements of practical applications for the current. With the design trade-offs considered, the proposed devices may enable the exploitation of thermoelectric energy harvesting in new - large-area - applications at reasonable cost.

Influence of ion implantation parameters on the perpendicular magnetic anisotropy of Fe-N thin films with stripe domains

Nitrogen-martensite thin films are known to present a perpendicular magnetic anisotropy (PMA) depending on the nitrogen content. Additionally, weak magnetic stripe domains have been studied in Fe-N samples made by ion implantation. In this work, ion implantation proves to be a good technique to make nitrogen-martensite thin films presenting both tunable PMA and stripe domains. We report on the changes in magnetic and structural properties of nitrogen-implanted iron thin films, resulting from various implantation conditions. Fluences from 1.8 × 1016 N2+/cm2 to 3.5 × 1016 N2+/cm2 at 26 keV and 5.3 × 1016 N2+/cm2 at 40 keV were used to implant iron thin films epitaxially grown on ZnSe/GaAs(001). X-ray diffraction measurements disclosed the presence of body-centered tetragonal nitrogen-martensite whose c-axis is perpendicular to the thin film plane and the c-parameter increases with fluence. Vibrating sample magnetometer measurements revealed that nitrogen implantation induced strong changes in magnetic properties such as an increasing PMA with fluence. Therefore, this PMA may originate from the magnetocrystalline anisotropy of nitrogen-martensite and stress-induced anisotropy. Magnetic stripe domains are notably observed by magnetic force microscopy for the highest fluences. Furthermore, ferromagnetic resonance measurements lead to the magnetic anisotropy constants calculation. The results show a significant increase of the PMA, related to the presence of nitrogen-martensite whose c-parameter is close to that of α′-Fe8N, which reaches a maximum value of 4.9 × 106 erg/cm3. In addition, an interesting comparison is done between the anisotropy constants of Fe-N and Fe-Ga samples. Fe-Ga thin films are also well known to present PMA and stripe domains.

Perpendicular Magnetic Anisotropy in Fe–N Thin Films: Threshold Field for Irreversible Magnetic Stripe Domain Rotation

The magnetic properties of an iron nitride thin film obtained by ion implantation have been investigated. N[Formula: see text] ions were implanted in a pristine iron layer epitaxially grown on ZnSe/GaAs(001). X-ray diffraction measurements revealed the formation of body-centered tetragonal N-martensite whose [Formula: see text]-axis is perpendicular to the thin film plane and [Formula: see text]-parameter is close to that of [Formula: see text]-Fe8N. Magnetic measurements disclosed a weak perpendicular magnetic anisotropy (PMA) whose energy density [Formula: see text] was assessed to about 105[Formula: see text]J/m3. A sharp decline of the in-plane magnetocrystalline anisotropy (MCA) was also observed, in comparison with the body-centered cubic iron. The origin of the PMA is attributed to the MCA of N-martensite and/or stress-induced anisotropy. As a result of the PMA, weak magnetic stripe domains with a period of about 130[Formula: see text]nm aligned along the last saturating magnetic field direction were observed at remanence by magnetic force microscopy. The application of an increasing in-plane magnetic field transverse to the stripes [Formula: see text] highlighted a threshold value ([Formula: see text][Formula: see text]T) above which these magnetic domains irreversibly rotated. Interestingly, below this threshold, the stripes do not rotate, leading to a zero remanent magnetization along the direction of the applied field. The interest of this system for magnetization dynamics is discussed.

Digital polarization holography advancing geometrical phase optics.

Geometrical phase or the fourth generation (4G) optics enables realization of optical components (lenses, prisms, gratings, spiral phase plates, etc.) by patterning the optical axis orientation in the plane of thin anisotropic films. Such components exhibit near 100% diffraction efficiency over a broadband of wavelengths. The films are obtained by coating liquid crystalline (LC) materials over substrates with patterned alignment conditions. Photo-anisotropic materials are used for producing desired alignment conditions at the substrate surface. We present and discuss here an opportunity of producing the widest variety of "free-form" 4G optical components with arbitrary spatial patterns of the optical anisotropy axis orientation with the aid of a digital spatial light polarization converter (DSLPC). The DSLPC is based on a reflective, high resolution spatial light modulator (SLM) combined with an "ad hoc" optical setup. The most attractive feature of the use of a DSLPC for photoalignment of nanometer thin photo-anisotropic coatings is that the orientation of the alignment layer, and therefore of the fabricated LC or LC polymer (LCP) components can be specified on a pixel-by-pixel basis with high spatial resolution. By varying the optical magnification or de-magnification the spatial resolution of the photoaligned layer can be adjusted to an optimum for each application. With a simple "click" it is possible to record different optical components as well as arbitrary patterns ranging from lenses to invisible labels and other transparent labels that reveal different images depending on the side from which they are viewed.

In situ crystallization of highly conducting and transparent ITO thin films deposited by RF magnetron sputtering

ITO thin films are prepared on glass substrates by radio frequency magnetron sputtering at sputtering powers varying from 50W to 200W. Structural and morphological investigation by X-ray diffraction and scanning electron microscopy of the films reveals them to have progressively undergone in situ crystallization with increasing sputtering power, without any need of intentional substrate heating. This result is highly useful in applications where ITO film coatings are to be fabricated on substrates which cannot withstand high temperature. Further, the preferential orientation of the thin film planes along [100] direction is found to produce drastic enhancements in the carrier mobility and electrical conductivity without much affecting the transparency of the thin films.