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We report fabrication of reduced graphene oxide (rGO) films using chemical reduction by hydrazine hydrate and rGO paper-like samples using low temperature treatment reduction. Structural analysis confirms the formation of the rGO structure for both samples. Current-voltage (I-V) measurements of the rGO film reveal semiconductor behavior with the maximum current value of ~3×10-4A. The current for the rGO paper sample is found to be, at least, one order of magnitude higher. Moreover, bipolar resistance switching, corresponding to memristive behavior of type II, is observed in the I-V data of the rGO paper. Although precise values of the rGO film conductivity and the Seebeck coefficient could not be measured, rGO paper shows an electrical conductivity of 6.7×102S/m and Seebeck coefficient of -6μV/°C. Thus, we demonstrate a simplified way for the fabrication of rGO paper that possesses better and easier measurable macroscopic electrical properties than that of rGO thin film. [ABSTRACT FROM AUTHOR]

In this paper, a paper-based ultracapacitors were fabricated by the rod-rolling method with the ink of carbon nanomaterials, which were synthesized by arc discharge under various magnetic conditions. Composites of carbon nanostructures, including high-purity single-walled carbon nanotubes (SWCNTs) and graphene flakes were synthesized simultaneously in a magnetically enhanced arc. These two nanostructures have promising electrical properties and synergistic effects in the application of ultracapacitors. Scanning electron microscope, transmission electron microscope, and Raman spectroscopy were employed to characterize the properties of carbon nanostructures and their thin films. The sheet resistance of the SWCNT and composite thin films was also evaluated by four-point probe from room temperature to the cryogenic temperature as low as 90 K. In addition, measurements of cyclic voltammetery and galvanostatic charging/discharging showed the ultracapacitor based on composites possessed a superior specific capacitance of up to 100 F/g, which is around three times higher than the ultracapacitor entirely fabricated with SWCNT. [ABSTRACT FROM AUTHOR]

We report carbon nanotube thin film-based supercapacitors fabricated with printing methods, where electrodes and separators are integrated into single sheets of commercial paper. Carbon nanotube films are easily printed with Meyer rod coating or ink-jet printing onto a paper substrate due to the excellent ink absorption of paper. A specific capacity of 33 F/g at a high specific power of 250 000 W/kg is achieved with an organic electrolyte. Such a lightweight paper-based supercapacitor could be used to power paper electronics such as transistors or displays. [ABSTRACT FROM AUTHOR]

This paper focused on developing a methodology and metrology using a differential photoacoustic (PA) system to determine the effective water vapor diffusion coefficient (D e f f ) and the effective permeability coefficient (Π) in thin films as a piece of paper and standard polystyrene for a controlled relative humidity. The methodology proposes a new differential photoacoustic system, including the water reservoir, relative humidity, and temperature detectors. Two cells, reference/sample, were used to obtain the instrumental function to reduce the electronic and environmental noises. A method based on the study of ln [ 1 − (S − S 0) / Δ S ] = t / τ D and the behaviors of R2 as a function of the number of data was proposed to assess the region in which the photoacoustic signal should be processed to determine each effective coefficient. S is the amplitude of the PA signal, S 0 is the initial amplitude value, Δ S is the change, t (time), and τ D is the water vapor diffusion time. The effective water diffusion coefficient (D e f f ) for water and polystyrene was 1.90 × 10−11 m2/s and 3.09 × 10−11 m2/s, respectively. The permeability coefficient value for the piece of paper was 4.18 × 10−9 mol kg−1 cm−2 s−1 Pa−1, while for polystyrene, it was 6.80 × 10−9 mol kg−1 cm−2 s−1 Pa−1 for 70% of relative humidity. This methodology can be extended by changing the moisture content on the chamber to obtain the dependence of D e f f as a function of relative humidity. [ABSTRACT FROM AUTHOR]

We have fabricated bottom-gate amorphous (α-) indium-gallium-zinc-oxide (InGaZnO4) thin film transistors (TFTs) on both paper and glass substrates at low processing temperature (≤100 °C). As a water and solvent barrier layer, cyclotene (BCB 3022–35 from Dow Chemical) was spin-coated on the entire paper substrate. TFTs on the paper substrates exhibited saturation mobility (μsat) of 1.2 cm2 V-1 s-1, threshold voltage (VTH) of 1.9 V, subthreshold gate-voltage swing (S) of 0.65 V decade-1, and drain current on-to-off ratio (ION/IOFF) of ∼104. These values were only slightly inferior to those obtained from devices on glass substrates (μsat∼2.1 cm2 V-1 s-1, VTH∼0 V, S∼0.74 V decade-1, and ION/IOFF=105–106). The uneven surface of the paper sheet led to relatively poor contact resistance between source-drain electrodes and channel layer. The ability to achieve InGaZnO TFTs on cyclotene-coated paper substrates demonstrates the enormous potential for applications such as low-cost and large area electronics. [ABSTRACT FROM AUTHOR]

There is no consensus among researchers regarding how phase transitions occur in antiferroelectric (AFE) epitaxial heterostructures, in particular, in heterostructures based on model AFE lead zirconate. The questions about the number of phase transitions in such films and by what mechanism they occur remain controversial. This paper presents a look at the phase transition scenario in two types of epitaxial heterostructures: PbZrO 3 /Ba[La–Sn]O 3 /MgO (001) thin films with thicknesses from 25 to 1000 nm and PbZrO 3 /SrRuO 3 /SrTiO 3 (001) thin film 100 nm thick using the diffuse x-ray scattering in the grazing incidence setup. We register the characteristic butterfly-shaped diffuse scattering (DS) intensity distribution in the H K pseudocubic planes, which corresponds to the anisotropic ferroelectric soft mode. No incommensurate soft mode was observed in the cuts of reciprocal space parallel to the film surface by diffuse scattering. We reproduce the shape of DS distribution at different temperatures by the model based on the dielectric stiffness and the electric polarization correlation tensor in the cubic approximation. Such modeling allows not only to characterize the DS parameters from the challengingly low signal-to-background data set, but also to extract experimentally the sensitivity of the materials with respect to inhomogeneous polarization. While the observed temperature evolution of DS is consistent with the dielectric measurements, the correlation between the DS and the phase transition sequence observed by superstructure reflections is yet to be understood better. [ABSTRACT FROM AUTHOR]

Wrinkling, creasing, and folding are frequent phenomena encountered in biological and man-made bilayers made by thin films bonded to thicker and softer substrates often containing fibers. Paradigmatic examples of the latter are the skin, the brain, and arterial walls, for which wiggly cross sections are detected. Although experimental investigations on corrugation of these and analog bilayers would greatly benefit from scaling laws for prompt comparison of the wrinkling features, neither are they available nor have systematic approaches yielding to such laws ever been provided before. This gap is filled in this paper, where a uniaxially compressed bilayer formed by a thin elastic film bonded on a hyperelastic fiber-reinforced substrate is considered. The force balance at the film–substrate interface is here analytically and numerically investigated for highly mismatched film–substrates. The onset of wrinkling is then characterized in terms of both the critical strain and its corresponding wavenumber. Inspired by the asymptotic laws available for neo-Hookean bilayers, the paper then provides a systematic way to achieve novel scaling laws for the wrinkling features for fiber-reinforced highly mismatched hyperelastic bilayers. Such novel scaling laws shed light on the key contributions defining the response of the bilayer, as it is characterized by a fiber-induced complex anisotropy. Results are compared with finite element analyses and also with outcomes of both existing linear models and available ad hoc scalings. Furthermore, the amplitude, the global maximum and minimum of ruga occurring under increasing compression spanning the wrinkling, period doubling, and folding regimes are also obtained. [ABSTRACT FROM AUTHOR]

Thin films deposited on wafers show, in some cases, large variations in stress. The local curvature is often used in the Stoney equation [G. G. Stoney, Proc. R. Soc. London, Ser. A 82, 172 (1909)] to calculate the local stress. This practice leads to false stress results. A general method for the calculation of the film stress, for films with isotropic stress, is presented here. The stress is calculated from both the local and overall shape of the substrate. Simple examples of isotropic stress were simulated and the substrate deformation calculated. The film stress was calculated back from the substrate shape with good agreement with the initial stress distribution. The substrate shape under films with centrosymmetric stress distribution can be analytically calculated. The current method successfully calculates the stress distribution from the substrate shape. Some guidelines for the deviation of the calculated stress from that of Stoney’s are given. Finally, the case of nonisotropic stressed film cannot be generally solved since there is no unique stress distribution for any given substrate shape. [ABSTRACT FROM AUTHOR]

HfO 2 -based thin films have raised considerable interest in ferroelectric memory devices due to their thickness scalability and process compatibility with CMOS. Stress exhibits a significant influence on ferroelectric polarization in HfO 2 -based films. However, the effect of stress has yet to be clarified despite numerous efforts, and there has been a lack of systematic review to collate and discuss this effect. This paper briefly introduces how stress is characterized in HfO 2 -based polycrystalline films as basis. Then, the process in which stress affects ferroelectricity is carefully discussed. The paper subsequently elaborates both the effects of out of plane stress and in plane stress. Furthermore, the interaction between stress and other factors is presented. Finally, the up-to-date research on the effect of stress are summarized, and several further research challenges for researchers are provided. Given the ubiquitous stress during the chip manufacturing process, a detailed summary of the stress effect has technological implications for processing and applications of HfO 2 -based thin films. [ABSTRACT FROM AUTHOR]

Recently, lithium niobate thin film laterally excited bulk wave resonators (XBARs) have attracted much attention because of their advantage of high frequency and outstanding electromechanical coupling factor (K2) enabling wide filter bandwidths. These can satisfy the increasing 5G communication demand. However, their large temperature coefficient limits their development to some extent. To improve their temperature stability with little K2 reduction, this paper has proposed a sandwiched structure for temperature compensated XBARs (TC XBARs). This structure includes the top silicon dioxide (SiO2) layer and the bottom SiO2 layer. One layer can improve temperature stability, and the other layer can increase K2. The optimized XBARs have a temperature coefficient of frequency (TCF) of −90.77 ppm⁄°C. The common two-layer TC XBARs can achieve a TCF of −22 ppm⁄°C sacrificing K2 to 8%. However, the proposed sandwiched TC XBARs can achieve a K2 of 12.15 and a TCF of −28.94 ppm⁄°C simultaneously, with a large FoM. Meanwhile, spurious modes can be suppressed in the sandwiched structure. Thus, this sandwiched structure can provide a good solution for the high performance of XBARs. [ABSTRACT FROM AUTHOR]

In this paper, we explored the resistivity behavior of Sb7Se3 thin films on flexible mica. The films maintained their resistance characteristics through various thicknesses and bending cycles. With increasing bends, resistivity and phase transition temperature of both amorphous and crystalline states rose, while the resistance drift coefficient gradually increased. Raman and near infrared experiments confirmed the internal structural changes and bandgap enhancement after bending. Transmission electron microscopy showed enhanced crystallization and uniform element distribution after annealing. Atomic force microscopy observed cracks, explaining the property changes. Additionally, we developed a flexible Sb7Se3 thin-film resistive device with swift reversibility (∼10 ns) regardless of bending, opening new avenues for flexible information storage. [ABSTRACT FROM AUTHOR]

The holy grail of achieving efficient operation of infrared (IR) rectennas continues to be the realization of a high performance rectifier. In this paper, we have fabricated metal–insulator–metal (MIM) diodes based on TiO2, ZnO, and NiO thin films using shadow mask evaporation, photolithography, and sputtering. The electron affinities of oxides have been measured by a combination of variable angle spectroscopic ellipsometry and x-ray photoelectron spectroscopy, as well as deduction from the extraction of metal/oxide barrier heights of Fowler–Nordheim tunneling plots. Our results confirm a low value for the electron affinity of NiOx of ∼2.1–2.5 eV, which correlates with the high zero-bias dynamic resistance (RD0) of ∼500 kΩ of an associated MIM diode. These values render NiOx to be unsuitable for use in a rectenna device. Better performance has been observed from diodes based on TiO2 and ZnOx films. The best rectification performance was achieved for a Au/2.6 nm ZnOx/Cr diode, scaled down to 1 μm2 device area, showing a zero-bias dynamic resistance of RD0 = 71 kΩ, zero-bias responsivity β0 = 0.28 A/W, and a coupling efficiency of ηc = 2.4 × 10−5% for rectification at 28.3 THz. The main significance of this study is that it employs a methodology whereby key parameters of the MIM stack are derived from physical measurements, which are then used to assist in the fitting of electrical current–voltage data to produce a reliable appraisal of diode performance in an IR rectenna. [ABSTRACT FROM AUTHOR]

This paper reports a strategy for more reliably obtaining sputtered thin yttrium–iron–garnet (YIG) films possessing both low magnetic damping (α) and a highly spin transparent surface, which represent two of the most important properties for YIG films applied in spintronic devices. The two key points of this strategy, concluded from our systematical studies, are as follows: oxygen reactive sputtering of a slight Y-rich YIG target to avoid the over-stoichiometry of the Fe component and at the same time minimize oxygen vacancy density; and employing phosphoric acid wet etching to remove the inevitable thin magnetic dead layer formed on the surface. The feasibility of this strategy was proved by the achievement of a high quality 30 nm-thick YIG film. It possesses a ferromagnetic resonance linewidth of only 3.4 Oe at 8 GHz, α of only 4.6 × 10−4, and a very spin-transparent surface, as proved by the measured extremely large spin pumping voltage of 650.1 µV after depositing a 3 nm Pt layer. [ABSTRACT FROM AUTHOR]

To study the effect of large area uniform garnet film on the consistency of image quality of a magneto-optical imaging system, the effect of lattice mismatch on a large area uniform domain structure of magneto-optical materials was studied. In this paper, (BiTm)3(GaFe)5O12 thin garnet films with different stress were prepared on the surface of gadolinium gallium garnet by liquid phase epitaxy. The results show that the magnetic hysteresis mechanism exists in the (BiTm)3(GaFe)5O12 thin films with tensile stress, and the domains can preferentially respond to magnetic signals in very small regions. This is mainly the phenomenon of magnetic domain partitioning caused by cracks. In addition, the non-uniform distribution of coercive force in a large range is the main cause of hysteresis. The thin films with weak compressive stress (BiTm)3(GaFe)5O12 are uniformly distributed over a large area. [ABSTRACT FROM AUTHOR]

We discuss the structure of threading dislocations in α-Ga2O3 thin films grown on c- and m-plane sapphire substrates. The thickness-dependent threading dislocation density in both films directly affects the electrical properties of the films including carrier concentration and mobility. Two distinct types of threading dislocations are identified for each of the c- and m-plane α-Ga2O3 thin films. The c-plane α-Ga2O3 thin film shows Burgers vectors of 1 / 3 [ 1 1 ¯ 01 ] and 1 / 3 [ 11 2 ¯ 0 ] , while the m-plane α-Ga2O3 thin film displays Burgers vectors of 1 / 3 [ 2 1 ¯ 1 ¯ 0 ] and 1 / 3 [ 1 1 ¯ 01 ]. This paper presents a detailed structure of the threading dislocations in α-Ga2O3, which has been little disclosed thus far mainly due to the difficulty in synthesizing the metastable α-Ga2O3. [ABSTRACT FROM AUTHOR]

One of the main methods for obtaining information about the generation of sound pulses in metals is to measure the reflection coefficient of a probe wave. Various theoretical models are used to interpret the results of measuring the contribution to reflection coefficient Δ R (t) due to sound-generated displacements of lattice atoms. The purpose of this paper is to establish the degree of accuracy of models used in the case of sound generation in thin films exposed to a femtosecond pulse. It is shown below that the assumption of uniform heating used for thin films is justified if the film thickness is less than the film heating depth and for thicker films at times greater than the film heating time over the entire thickness. For optically thick films, a relatively simple expression for the field can be used. If the film thickness is less than the skin layer depth of the pump field, then it is necessary to consider the field reflection from a substrate. In this case, depending on the optical properties of the metal and the substrate, taking into account reflection can lead to either an increase or a decrease in Δ R (t). It has been established that if the skin layer at the frequency of probe radiation is less than the film heating depth, then taking into account temperature gradients in the equation for the displacement of lattice atoms leads to small changes in Δ R (t). This makes it possible to significantly simplify calculations of the displacement of lattice atoms. [ABSTRACT FROM AUTHOR]

Magnetic materials with high negative spin polarization have been sought as a building block to increase the design freedom and performance of spintronics devices. In this paper, we investigate negative spin polarization of Mn2VGa Heusler alloy in current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices. We fabricated an epitaxial CPP-GMR stack consisting of Mn2VGa/Ag/CoFe with L21 ordering in the Mn2VGa layer and observed negative magnetoresistance (MR), which provided evidence of negative spin polarization. The MR ratio depended on thermal treatments (deposition at an elevated temperature and post-annealing), because these processes affected the ordering, roughness, and magnetic properties of Mn2VGa. The maximum MR ratio reached −1.8% at room temperature and −3.0% at low temperatures, representing the highest among the negative MR values in pseudo-spin-valve CPP-GMR devices despite the underestimation due to an incomplete antiparallel magnetization configuration. These findings demonstrate the potential of Mn2VGa for a material with high negative spin polarization. [ABSTRACT FROM AUTHOR]

Among the numerous advantages of the high-power impulse magnetron sputtering (HiPIMS) technique, the most important is the enhanced ionization degree of sputtered species contributing to the film growth. Consequently, the quality of deposited thin films is highly improved. Still, the optimization process is challenging due to the complexity associated with the intricate transport of the sputtered species, ionized or neutrals. The scarce knowledge available on the spatial distribution of these species when operating a HiPIMS discharge makes the quantitative prediction of any deposition feature particularly difficult. In this paper, we discuss the influence of experimentally controllable quantities, such as gas pressure and target current density, on the transport of sputtered titanium in non-reactive (argon) HiPIMS, namely, on the behavior of metal atoms and metal ion fluxes intercepting the substrate. Systematic quantitative measurements were performed in a diameter normal plane on a circular planar target. Hence, the 2D spatial distribution of the ionized flux fraction (IFF) and the total flux of titanium sputtered particles (deposition rate) are evaluated by biasing a quartz crystal microbalance equipped with an electron magnetic filter. The wide range of parameters we examined allows us to predict and optimize the flux of sputtered species based on complete mapping of the IFF of sputtered particles. [ABSTRACT FROM AUTHOR]

Polycrystalline thin films are widely used for devices and energy-related applications, such as power electronics, solar cells, and thermal management of devices. In many cases, large-scale crystallization during thin-film growth is challenging, so columnar grains are often found in metal and semiconductor thin films. These rough columnar grain boundaries may also have different phonon specularities from that for typically smoother top/bottom film surfaces. A simple analytical model to separately treat these boundaries and interfaces for phonon scattering is currently unavailable, although the in-plane thermal transport is critical to heat spreading within thin-film devices. In this paper, we extend the effective medium formulation from three-dimensional polycrystalline bulk materials to columnar-grained thin films. The model predictions agree well with those given by frequency-dependent phonon Monte Carlo simulations, considering varied phonon specularity at top/bottom film surfaces and grain-boundary phonon transmissivity. The analytical model is further used to analyze the existing data on polycrystalline ZnO thin films with columnar grains. [ABSTRACT FROM AUTHOR]

Nanostructured topological insulators (TIs) have the potential to impact a wide array of condensed matter physics topics, ranging from Majorana physics to spintronics. However, the most common TI materials, the B i 2 S e 3 family, are easily damaged during nanofabrication of devices. In this paper, we show that electron beam lithography performed with a 30 or 50 kV accelerating voltage—common for nanopatterning in academic facilities—damages both nonmagnetic TIs and their magnetically doped counterparts at unacceptable levels. We additionally demonstrate that electron beam lithography with a 10 kV accelerating voltage produces minimal damage detectable through low-temperature electronic transport. Although reduced accelerating voltages present challenges in creating fine features, we show that with careful choice of processing parameters, particularly the resist, 100 nm features are reliably achievable. [ABSTRACT FROM AUTHOR]

Herein, a prototype nonvolatile bent ferroelastic domain wall (DW) memory based on extension–retraction of DWs in a top electrode/bent ferroelastic DWs/bottom electrode architecture is demonstrated and the effects of mechanical condition, electrical condition, and the material parameter on ferroelastic DWs in PbTiO3 ferroelectric thin films are studied by phase field modeling. Misfit strain can be used to drive the bend of DWs in PbTiO3 thin film, resulting in a change of ferroelastic domain size, bending degree, and conductivity. Stable and reversible switching of DWs between the extendible state with high conductivity and the retractile state with low conductivity can be realized, resulting in an apparent resistance change with a large ON/OFF ratio of >102 and an excellent retention characteristic. The extension and retraction speed, corresponding to data writing speed, can be adjusted by the electric field magnitude and distributions. The memory speed increases by 5% under a homogeneous electric field and 6% under an inhomogeneous probing electric field, after the buildup of space charges in a ferroelectric thin film, and the fastest memory speed is obtained at tip potential φ = 1.8. Moreover, polarization orientations of a and c domains separated by bent ferroelastic DWs do not affect memory performance. This paper can guide the development of new ferroelectric domain wall memory. [ABSTRACT FROM AUTHOR]

In this paper, we investigated the dependence of dynamic hysteresis on the electric field amplitude E0 and the frequency f in organic ferroelectric copolymer polyvinylidene fluoride-trifluoroethylene [P(VDF-TrFE)] thin films prepared by a spin-coating method on fluorine-doped tin oxide conductive glass. Three stages can be observed of the hysteresis area vs the field strength E0. In stage I of low E0 values, the area ⟨ A ⟩ dependent on E0 follows the law of ⟨ A ⟩ ∝ E 0 1.92795 , whereas the diverse distribution of the area ⟨ A ⟩ with frequency f is found. In stage II of the intermediate E0 values, ⟨ A ⟩ ∝ E 0 β is not applicable owing to collective contributions between 180° domain and chiral domain, while a relation of ⟨ A ⟩ ∝ f − 0.18636 can be deduced, a fascinating characteristic distinguishing from the nonlinear relations of the inorganics in this section. In stage III of high E0 values, the scaling law is ⟨ A ⟩ ∝ f 0.08447 E 0 0.49394 where the chiral domain is active. The positive β in the law of ⟨ A ⟩ ∝ f α E 0 β illustrates that a growing number of chiral domains in P(VDF-TrFE) can keep pace with the variation of E0. Especially, the negative α in the transition zone, resembling some inorganics under low electric fields, probably indicates 180° domain reversal failing to follow with the alternating velocity of the increasing periodic electric field. [ABSTRACT FROM AUTHOR]

In this paper, the field-induced residual ferroelectricity in antiferroelectric lead zirconate thin films has been studied by impedance measurements together with a hyperbolic law analysis, which permits us to extract the different contributions to the material's complex permittivity. By measuring the Rayleigh coefficient α r , it appears that the residual ferroelectricity is considerably enhanced when the sample has been previously exposed to an electric field close to the antiferroelectric to ferroelectric transition field. This indicates that a part of the material remains ferroelectric after the antiferroelectric–ferroelectric backward transition, which constitutes an additional contribution to polarization. Consequently, a higher domain wall density and mobility can be observed. Measurements after exposition to thermal treatment show that this ferroelectric response is metastable. [ABSTRACT FROM AUTHOR]

In this paper, we proposed and numerically demonstrated a giant enhancement up to in both fo 10 8 rward and backward propagation of the second harmonic generation by combining the high-quality factor cavities of the bound states in the continuum and the excellent nonlinear optical crystal of lithium niobate. The enhancement factor is defined as the ratio of the second harmonic signal generated by the structure (lithium niobate membrane with Si grating) divided by the signal generated by the lithium niobate membrane alone. Furthermore, a minimum interaction time of 350 ps is achieved despite the etching less lithium niobate membrane with a conversion efficiency of 4.77 × 10−6. The origin of the enhancements is linked to the excitation of a Fano-like shape symmetry-protected mode that is revealed by finite-difference time-domain simulations. The proposed platform opens the way to a new generation of efficient integrated optical sources compatible with nano-photonic devices for classical and quantum applications. [ABSTRACT FROM AUTHOR]

The process of quasi-isothermal dehydration of thin films of pure water and aqueous sugar solutions is investigated with a dual experimental and theoretical approach. A nanoporous paper disk with a homogeneous internal structure was used as a substrate. This experimental set-up makes it possible to gather thermodynamic data under well-defined conditions, develop a numerical model, and extract needed information about the dehydration process, in particular the water activity. It is found that the temperature evolution of the pure water film is not strictly isothermal during the drying process, possibly due to the influence of water diffusion through the cellulose web of the substrate. The role of sugar is clearly detectable and its influence on the dehydration process can be identified. At the end of the drying process, trehalose molecules slow down the diffusion of water molecules through the substrate in a more pronounced way than do the glucose molecules. [ABSTRACT FROM AUTHOR]

The current focus in Autonomous Experimentation (AE) is on developing robust workflows to conduct the AE effectively. This entails the need for well-defined approaches to guide the AE process, including strategies for hyperparameter tuning and high-level human interventions within the workflow loop. This paper presents a comprehensive analysis of the influence of initial experimental conditions and in-loop interventions on the learning dynamics of Deep Kernel Learning (DKL) within the realm of AE in scanning probe microscopy. We explore the concept of the "seed effect," where the initial experiment setup has a substantial impact on the subsequent learning trajectory. Additionally, we introduce an approach of the seed point interventions in AE allowing the operator to influence the exploration process. Using a dataset from Piezoresponse Force Microscopy on PbTiO3 thin films, we illustrate the impact of the "seed effect" and in-loop seed interventions on the effectiveness of DKL in predicting material properties. The study highlights the importance of initial choices and adaptive interventions in optimizing learning rates and enhancing the efficiency of automated material characterization. This work offers valuable insights into designing more robust and effective AE workflows in microscopy with potential applications across various characterization techniques. [ABSTRACT FROM AUTHOR]

In this paper, we have studied the effect on the structure and magnetic properties of partial Pd substitution by Gd in Fe–Pd thin films of nominal composition Fe56Pd44−xGdx (x = 1, 3, 5, and 7), deposited onto Si(100) and Si(100)/SiO2 substrates by thermal evaporation. Several techniques contribute to the characterization of their microstructure and magnetic properties, such as x-ray diffraction (XRD), scanning electron microscopy, alternating gradient field magnetometry, and magnetic force microscopy (MFM). X-ray diffraction shows that the as-deposited films are either amorphous or contain a disordered FePd phase, depending on the film thickness. The transformation of disordered fcc-FePd into ordered fct-FePd has been induced by a heat treatment at 530 °C for 4 h. The addition of gadolinium leads to a reduction in the coercivity as a consequence of the emergence of soft phases and of the progressive reduction of the fct-FePd phase, which is primarily responsible for the observed maze magnetic domains. The exchange coupling between the soft phase and the hard fct-FePd phase is demonstrated by first-order reversal curves (FORCs). [ABSTRACT FROM AUTHOR]

A novel elastomer-based composite material with enhanced piezoelectric performances is proposed in this paper, which is composed of the top and bottom polytetrafluoroethylene (PTFE) solid films with the middle PTFE nanoparticle–polydimethylsiloxane (PDMS) sponge layer. To enhance the charge retention capability of elastomers, PTFE nanoparticles are introduced to form PTFE–PDMS interfaces, which can trap charges with longevity. Besides, PTFE solid films take on the role of the charge blocking layers to further improve the piezoelectric performances. As a result, the PTFE–PDMS sandwich structure shows the advantages of remarkable sensitivity (1053 pC/N), high stability, and flexibility. After a 6 h of annealing treatment at the temperature of 100 °C, no significant deterioration of the piezoelectric properties can be observed, which reveals the great thermal stability of the sandwich structure. In addition, the sandwich structure can be immersed in water for 24 h without any loss of piezoelectric activity. Finally, the experiment of lighting one LED by hand pressing successfully demonstrates that the sandwich structure has good applicability in the field of energy harvesting. Considering the excellent electrical and mechanical features, the PTFE–PDMS sandwich structure has promising applications in sensing, energy harvesting, and actuation. [ABSTRACT FROM AUTHOR]

Two-dimensional transition metal dichalcogenides (TMDCs) are demonstrated to be appealing semiconductors for optoelectronic applications, thanks to their remarkable properties in the ultraviolet-visible spectral range. Interestingly, TMDCs have not yet been characterized when exposed to x rays, although they would be ideal candidates for optoelectronic applications in this spectral range. They benefit from the high cross section of the constituent heavy atoms, while keeping the absorption very low, due to the ultrathin structure of the film. This encourages the development of photodetectors based on TMDCs for several applications dealing with x rays, such as radioprotection, medical treatments, and diagnosis. Given the atomic thickness of TMDCs, they can be expected to perform well at low dose measurements with minimal perturbation of the radiation beam, which is required for in vivo applications. In this paper, the use of TMDCs as active materials for direct x-ray detection is demonstrated, using a photodetector based on a MoS2 monolayer (1L-MoS2). The detector shows a response to x rays in the range of 101–102 keV, at dose rates as low as fractions of mGy/s. The sensitivity of 1L-MoS2 reaches values in the range of 108–109µC Gy−1 cm−3, overcoming the values reported for most of the organic and inorganic materials. To improve the x-ray photoresponse even further, the 1L-MoS2 was coupled with a polymeric film integrating a scintillator based on terbium-doped gadolinium oxysulfide (Gd2O2S:Tb). The resulting signal was three times larger, enabled by the indirect x ray to visible photoconversion mechanism. This paper might pave the way toward the production of ultrathin real-time dosimeters for in vivo applications. [ABSTRACT FROM AUTHOR]

In this (Paper II) and the preceding companion paper (Paper I; R. May, R. Smith, and B. Kay, J. Chem. Phys. 138, 104501 (2013)), we investigate the mechanisms for the release of trapped gases from underneath amorphous solid water (ASW) films. In Paper I, we focused on the low coverage regime where the release mechanism is controlled by crystallization-induced cracks formed in the ASW overlayer. In that regime, the results were largely independent of the particular gas underlayer. Here in Paper II, we focus on the high coverage regime where new desorption pathways become accessible prior to ASW crystallization. In contrast to the results for the low coverage regime (Paper I), the release mechanism is a function of the multilayer thickness and composition, displaying dramatically different behavior between Ar, Kr, Xe, CH4, N2, O2, and CO. Two primary desorption pathways are observed. The first occurs between 100 and 150 K and manifests itself as sharp, extremely narrow desorption peaks. Temperature programmed desorption is utilized to show that these abrupt desorption bursts are due to pressure induced structural failure of the ASW overlayer. The second pathway occurs at low temperature (typically <100 K) where broad desorption peaks are observed. Desorption through this pathway is attributed to diffusion through pores formed during ASW deposition. The extent of desorption and the line shape of the low temperature desorption peak are dependent on the substrate on which the gas underlayer is deposited. Angle dependent ballistic deposition of ASW is used to vary the porosity of the overlayer and strongly supports the hypothesis that the low temperature desorption pathway is due to porosity that is templated into the ASW overlayer by the underlayer during deposition. [ABSTRACT FROM AUTHOR]

In a recently published paper [S. Sivaramakrishnan et al., Appl. Phys. Lett. 103, 132904 (2013)], the electrode-size dependence of the longitudinal effective piezoelectric coefficient (d33,f) of piezoelectric thin films measured by double beam laser interferometry was shown to be due to the substrate clamping effects. It was also shown that the true d33,f is measured when the ratio of the electrode size to the substrate thickness is approximately unity, in the case of a substrate with isotropic elastic properties and a Poisson's ratio of ~0.3. In this paper, we further investigate the dependence of the critical ratio (rc) of the electrode size to the substrate thickness at which the true d33,f is measured on the substrate Poisson's ratio for isotopic substrates and for the important case of the anisotropic Si substrate. It turns out that it is the out-of-plane Poisson's ratio (-s13/s11) that is relevant for this measurement technique and not the in-plane Poisson's ratio which is highly anisotropic for the (001) oriented Si. Furthermore, we show that the transverse effective piezoelectric coefficient (e31,f) can also be determined from the same measurement of the electrode size dependence of d33,f. This provides a convenient non-destructive wafer-level measurement technique for the determination of both the piezoelectric coefficients simultaneously. Moreover, this technique is also capable of measuring e31,f under varying electric field excitation which is important for many applications such as actuators. [ABSTRACT FROM AUTHOR]

In this paper, nanostructured tungsten oxide (WO3) thin films are deposited using the RF-magnetron sputtering technique in Glancing Angle (GLAD) arrangement. Variation in the structural, morphological, optical, and resistive switching (RS) characteristics of nanostructured WO3 film is investigated as a function of GLAD angle (60°–80°). Electrical studies on nanostructured WO3 films deposited at room temperature are found to exhibit enhanced bipolar resistive-switching properties in metal–insulator–metal pattern [Au/WO3/ITO]. The RON/ROFF ratio between high and low resistance states was noted to be about 190 besides a minimum set voltage of ∼2.22 V in the case of the WO3 thin film deposited at the 70° glancing angle. A detailed current transport mechanism analysis indicates the existence of ohmic-behavior and trap-assisted space charge limited conduction as the governing mechanisms at the state of low and high applied bias, respectively. Good data-retention characteristics coupled with reproducible and fast RS capabilities obtained with Au/WO3/ITO device structure promise scope of rapid development in future RS-based novel memory device applications. [ABSTRACT FROM AUTHOR]

Lift-off processes have been developed as the enabling technology to free the epitaxial III-nitride thin film from a conventional growth substrate such as sapphire and silicon in order to realize a variety of novel device designs and structures not otherwise possible. An epitaxial lift-off (ELO) process can be adopted to transfer the entire film to an arbitrary foreign substrate to achieve various functions, including enhancement of device performance, improvement of thermal management, and to enable flexibility among others. On the other hand, partial ELO techniques, whereby only a portion of the thin-film is detached from the substrate, can be employed to realize unconventional device structures or geometries, such as apertured, pivoted, and flexible devices, which may be exploited for various photonic structures or optical cavities. This paper reviews the development of different lift-off strategies and processes for III-nitride materials and devices, followed by a perspective on the future directions of this technology. [ABSTRACT FROM AUTHOR]

Double perovskite ferroelectric thin films are completely new material systems derived from single perovskite. Their diversity of composition and structure and the tendency for spontaneous atomic ordering broaden the path for the development of ferroelectric thin films. The ordered double perovskite ferroelectric thin films lead to excellent ferroelectric, dielectric, magnetic, and optical properties, promising further applications in photovoltaic cells, information memory, and spintronic and photoelectric devices, where the intrinsic coupling and tuning of multiple properties could also push it into multifunctional intersecting devices. However, complex internal physical mechanisms and difficult preparation conditions have prevented its further development. Based on ordered/disordered ferroelectric thin films of double perovskites, this paper first discusses ordered characterization methods such as superstructure reflection/diffraction peaks, especially for epitaxial thin films, saturation magnetization (macroscopic), and scanning transmission electron microscopy (microscopic). In response to the generally poor ordering of present systems, the paper also reviews the internal structure of the material and the external synthesis conditions that affect the ordering, including the valence and radii of the cations, preparation methods, element substitution and strain engineering, in the hope of triggering further research into ordered double perovskite ferroelectrics. Combined with the current state of research on existing double perovskite ferroelectricity thin film systems, advances in the fields of ferroelectric photovoltaics, magnetoelectric coupling, dielectric tunability, resistive switching, and photoelectric coupling have been presented. Finally, the challenges facing the material system are discussed and an outlook is provided for the development of the field. [ABSTRACT FROM AUTHOR]

Lead-free piezoelectric (K, Na)NbO3 (KNN) is considered one of the promising candidates for the replacement of Pb(ZrxTi1−x)O3. Several studies underlined the issue of K and Na volatility with increasing deposition temperatures, leading to high leakage currents in thin films, which still represents a major drawback for applications. This paper shows how epitaxial growth with concomitant preferred orientation of KNN films on niobium-doped strontium titanate (Nb:STO) depends on growth temperature and substrate strain. A preferred out-of-plane polar (001) orientation of KNN is obtained at high temperatures (>600 °C), while (100) orientation is dominant for lower ones. The (001) orientation is forced out-of-plane due to the sizeable in-plane stress derived from a negative lattice mismatch of pseudo-cubic KNN with respect to the underlying cubic (001) Nb:STO substrate. Moreover, we show that K-Na deficiency and high leakage of epitaxial KNN films deposited at high temperatures are accompanied by the appearance of a pattern of orthogonal spontaneous ferroelectric domains aligned to the [100] and [010] directions of Nb:STO. This pattern, visible in secondary electron microscopy, piezoforce response microscopy, and conductive atomic force microscopy images, is uncorrelated to the surface morphology. Supported by reciprocal space mapping by x-ray diffraction, this phenomenon is interpreted as the result of strain relaxation via ferroelectric domain formation related to K-Na deficient films displaying a sizable and increasing compressive strain when grown on Nb:SrTiO3. Our findings suggest that strain engineering strategies in thin films could be used to stabilize specific configurations of piezo- and ferroelectric domains. [ABSTRACT FROM AUTHOR]

Proton irradiation of lithium fluoride (LiF) crystals and thin films causes the formation of electronic defects, known as color centers, in the crystal lattice, some of which show photoluminescence in the visible range under blue-light excitation. With a suitable irradiation geometry, the energy density that protons deposit in the material can be recorded as a spatial distribution of these light-emitting color centers, from which a luminous replica of the proton Bragg curve can be thereafter extracted and analyzed in a fluorescence microscope. In this paper, the cases of two LiF thin films deposited on silicon substrates and of a LiF crystal, all of them transversally irradiated with a nominal 35 MeV proton beam, are considered. A comparison of the measured photoluminescent Bragg curves with Monte Carlo simulations demonstrates (i) that the Bragg peaks in the films are located at the very same positions that would be expected in the underlying silicon substrates rather than in LiF and (ii) that an even small grazing angle of the impinging proton beam is able to significantly modify the shape of the Bragg curve in the films. Both of these findings are ascribed to the effects of multiple Coulomb scattering in both the film and the substrate. The coincidence of the Bragg peak positions with those expected in the silicon substrates and the possibility of visualizing such peaks in the Bragg curves stored as latent fluorescence images in the LiF films allow one to regard them as information transducers for proton beam diagnostics and dosimetry. [ABSTRACT FROM AUTHOR]

Previous studies reported that the drying time of a respiratory droplet on an impermeable surface along with a residual film left on it is correlated with the coronavirus survival time. Notably, earlier virus titer measurements revealed that the survival time is surprisingly less on porous surfaces such as paper and cloth than that on impermeable surfaces. Previous studies could not capture this distinct aspect of the porous media. We demonstrate how the mass loss of a respiratory droplet and the evaporation mechanism of a thin liquid film are modified for the porous media, which leads to a faster decay of the coronavirus on such media. While diffusion-limited evaporation governs the mass loss from the bulk droplet for the impermeable surface, a much faster capillary imbibition process dominates the mass loss for the porous material. After the bulk droplet vanishes, a thin liquid film remaining on the exposed solid area serves as a medium for the virus survival. However, the thin film evaporates much faster on porous surfaces than on impermeable surfaces. The aforesaid faster film evaporation is attributed to droplet spreading due to the capillary action between the contact line and fibers present on the porous surface and the modified effective wetted area due to the voids of porous materials, which leads to an enhanced disjoining pressure within the film, thereby accelerating the film evaporation. Therefore, the porous materials are less susceptible to virus survival. The findings have been compared with the previous virus titer measurements. [ABSTRACT FROM AUTHOR]

This paper reports the onset of ferroelectricity in NiO by breaking the crystallographic symmetry with oxygen vacancies created by N doping. Nitrogen-doped NiO was grown at room temperature by RF sputtering of Ni target in Ar–O2–N2 plasma on silicon and fused silica substrates. The impact of the nitrogen doping of NiO on microstructural, optical, and electrical properties has been investigated. According to x-ray diffraction investigations, by increasing the N doping level in NiO, a transition from (002) to a (111) preferential orientation for the cubic NiO phase was observed, as well as a lattice strain relaxation, that is usually ascribed to structural defect formation in crystal. The x-ray diffraction pole figures the presence of a distorted cubic structure in NiO and supports the Rietveld refinement findings related to the strain, which pointed out that nitrogen doping fosters lattice imperfections formation. These findings were found to be in agreement with our far-infrared measurements that revealed that upon nitrogen doping a structural distortion of the NiO cubic phase appears. X-ray photoemission spectroscopy measurements reveal the presence of oxygen vacancies in the NiO film following nitrogen doping. Evidence of ferroelectricity in nitrogen-doped NiO thin films has been provided by using the well-established Sawyer–Tower method. The results reported here provide the first insights on oxygen-vacancy induced ferroelectricity in nitrogen-doped nickel oxide thin films. [ABSTRACT FROM AUTHOR]

In the past two decades, there have been huge developments in the understanding of damping in multilayered thin films and, more generally, in spin-transport in spintronic systems. In multilayered ferromagnetic (FM)/non-magnetic (NM) thin-film systems, observations of ferromagnetic resonant precession show a strong increase in the fundamental damping when the FM thin films are layered with heavy metals, such as Pt. These observations led to significant theoretical developments, dominated by the "spin-pumping" formalism, which describes the enhancement of damping in terms of the propagation or "pumping" of spin-current across the interface from the precessing magnetization into the heavy metal. This paper presents a perspective that introduces the key early experimental damping results in FM/NM systems and outlines the theoretical models developed to explain the enhanced damping observed in these systems. This is followed by a wider discussion of a range of experimental results in the context of the theoretical models, highlighting agreement between the theory and experiment, and more recent observations that have required further theoretical consideration, in particular, with respect to the role of the interfaces and proximity-induced magnetism in the heavy metal layer. The Perspective concludes with an outline discussion of spinpumping in the broader context of spin-transport. [ABSTRACT FROM AUTHOR]

MEMS electric energy utilization rate is the key parameter affecting firing performance. It has important relationship with its preparation technology, microscale and structure morphology. In order to improve the theory of energy exchange element design for MEMS pyrotechnics, reduce the design error of transducer parameters at microscale. To ensure the performance of MEMS pyrotechnics, in this paper, the influence of the central line of the thin film transducer element on the electrothermal conversion is simulated and analyzed. The electrothermal conversion and temperature characterization of different central lines in the transducer bridge area are calculated by the finite element method. The influence of the central line on the thermal efficiency under microscale is revealed. The corresponding data are obtained. [ABSTRACT FROM AUTHOR]

In this (Paper I) and the companion paper (Paper II; R. May, R. Smith, and B. Kay, J. Chem. Phys. 138, 104502 (2013)), we investigate the mechanisms for the release of trapped gases from underneath amorphous solid water (ASW) films. In prior work, we reported the episodic release of trapped gases in concert with the crystallization of ASW, a phenomenon that we termed the 'molecular volcano.' The observed abrupt desorption is due to the formation of cracks that span the film to form a connected pathway for release. In this paper, we utilize the 'molecular volcano' desorption peak to characterize the formation of crystallization-induced cracks. We find that the crack length distribution is independent of the trapped gas (Ar, Kr, Xe, CH4, N2, O2, or CO). Selective placement of the inert gas layer is used to show that cracks form near the top of the film and propagate downward into the film. Isothermal experiments reveal that, after some induction time, cracks propagate linearly in time with an Arrhenius dependent velocity corresponding to an activation energy of 54 kJ/mol. This value is consistent with the crystallization growth rates reported by others and establishes a direct connection between crystallization growth rate and the crack propagation rate. A two-step model in which nucleation and crystallization occurs in an induction zone near the top of the film followed by the propagation of a crystallization/crack front into the film is in good agreement with the temperature programmed desorption results. [ABSTRACT FROM AUTHOR]

We present an experimental technique to measure the diffusivity of supercooled liquids at temperatures near their Tg. The approach uses the permeation of inert gases through supercooled liquid overlayers as a measure of the diffusivity of the supercooled liquid itself. The desorption spectra of the probe gas are used to extract the low temperature supercooled liquid diffusivities. In the preceding companion paper, we derived equations using ideal model simulations from which the diffusivity could be extracted using the desorption peak times for isothermal or peak temperatures for temperature programmed desorption experiments. Here, we discuss the experimental conditions for which these equations are valid and demonstrate their utility using amorphous methanol with Ar, Kr, Xe, and CH4 as probe gases. The approach offers a new method by which the diffusivities of supercooled liquids can be measured in the experimentally challenging temperature regime near the glass transition temperature. [ABSTRACT FROM AUTHOR]

The flash methods, which are the most popular transient methods for measuring the thermal diffusivity of solid materials, have evolved into ultrafast laser flash methods by using picosecond or nanosecond pulse lasers as a heating source and a thermo-reflectance technique such as high-speed thermometry. In conventional ultrafast laser flash methods, thermal diffusivity is determined by fitting an analytical equation after single pulse heating to observe thermo-reflectance signals, although actual thermo-reflectance signals are observed after periodic pulse heating. This paper presents an exact analytical solution of the temperature response expressed by Fourier series for one-dimensional heat diffusion after periodic pulse heating. These Fourier coefficients are directly related to the Laplace transformation of the temperature response after single pulse heating. The signal observed for a 100 nm thick platinum thin film on a fused quartz substrate was analyzed by this Fourier expansion analysis and fitted by analytical equations with three parameters: heat diffusion time across thin film, the ratio of heat effusion of the substrate to thin film, and the amplitude of the signal over the entire range of pulse interval in the time domain. Robustness in determining the thermal diffusivity of the thin film by the ultrafast laser flash method can be improved by this new analysis approach. [ABSTRACT FROM AUTHOR]