Nanometer Thin Films Research Articles

Energy storage performance of thin film nanocrystalline vanadium oxide with fluorinated tin oxide current carrier electrode for solid-state transparent supercapacitors based on ionic liquid gel electrolyte

Energy-power performance of transparent supercapacitors based on sol gel processed nanometer thin nanocrystalline vanadium oxide film composite with fluorinated tin oxide (FTO) thin film electrode as current collector is investigated. The symmetric supercapacitor device configured in the solid-state form using the BMIMBF4 ionic liquid with LiClO4 dopant gel electrolyte shows high areal capacitance of 310 mFcm−2 attributed to pseudocapacitive energy storage mechanism with minimal ion kinetics limitation. The vanadium oxide electrode forms in the stoichiometric V2O5 and in the multivalent phases depending on the annealing process in film synthesis which impacts the specific energy-power performance. The supercapacitor based on V2O5 with distorted [VO5] pyramids alongside phases with V4+ and mixed V oxidation states exhibited high specific energy 7.7 μWhcm−2 at corresponding specific power of 64.7 μWcm−2 and significantly large specific power of 363.8 μWcm−2 at 1.5 V. High capacitance and energy-power is attributed to simultaneous redox reactions storing charges in the specific potential range to contribute to the pseudocapacitance. The stoichiometric V2O5 films in V5+ valence state show minimum loss of specific energy (1.20–0.89 μWhcm−2) at high power (40–132 μWcm−2) and much stable 75 ± 2% charge-discharge performance for 2000 cycles. The single valent V2O5 electrodes show sequential V5+/V4+ and V4+/V3+ redox processes and lesser stored charge but high cyclic stability. The significantly improved capacitive and specific energy-power parameters pertaining to a high >77% transmittance at 590 nm show the applicability of the V2O5 solid-state ionic liquid electrolyte based supercapacitor energy storage devices in futuristic transparent electronics.

Terahertz sensing of 7 nm dielectric film with bound states in the continuum metasurfaces

The fingerprint spectral response of several materials with terahertz electromagnetic radiation indicates that terahertz technology is an effective tool for sensing applications. However, sensing few nanometer thin-films of dielectrics with much longer terahertz waves (1 THz = 0.3 mm) is challenging. Here, we demonstrate a quasibound state in the continuum (BIC) resonance for sensing of a nanometer scale thin analyte deposited on a flexible metasurface. The large sensitivity originates from the strong local field confinement of the quasi-BIC Fano resonance state and extremely low absorption loss of a low-index cyclic olefin copolymer substrate. A minimum thickness of 7 nm thin-film of germanium is sensed on the metasurface, which corresponds to a deep subwavelength scale of λ/43 000, where λ is the resonance wavelength. The low-loss, flexible, and large mechanical strength of the quasi-BIC microstructured metamaterial sensor could be an ideal platform for developing ultrasensitive wearable terahertz sensors.

Water Confined in Hydrophobic Cup-Stacked Carbon Nanotubes beyond Surface-Tension Dominance.

Water confined in carbon nanotubes (CNTs) can exhibit distinctly different behaviors from the bulk. We report transmission electron microscopy (TEM) observation of water phases inside hydrophobic cup-stacked CNTs exposed to high vacuum. Unexpectedly, we observed stable water morphologies beyond surface-tension dominance, including nanometer thin free water films, complex water-bubble structures, and zigzag-shaped liquid-gas interface. The menisci of the water phases are complex and inflected, where we measured the contact angles on the CNT inner wall to be 68-104°. The superstability of the suspended ultrathin water films is attributed to the strong hydrogen-bonded network among water molecules and adsorption of water molecules on the cup-structured inner wall. The complex water-bubble structure is a result of the stability of free water films and interfacial nanobubbles, and the zigzag edge of the liquid-gas interface is explained by the pinning effect. These experimental findings provide valuable knowledge for the research on fluids under nanoscale confinement.

Demonstration of a picosecond Bragg switch for hard X-rays in a synchrotron-based pump-probe experiment.

A benchmark experiment is reported that demonstrates the shortening of hard X-ray pulses in a synchrotron-based optical pump-X-ray probe measurement. The pulse-shortening device is a photoacoustic Bragg switch that reduces the temporal resolution of an incident X-ray pulse to approximately 7.5 ps. The Bragg switch is employed to monitor propagating sound waves in nanometer thin epitaxial films. From the experimental data, the pulse duration, diffraction efficiency and switching contrast of the device can be inferred. A detailed efficiency analysis shows that the switch can deliver up to 109 photons s-1 in high-repetition-rate synchrotron experiments.

Kossel interferences of proton-induced X-ray emission lines to study thin film waveguides

PIXE combined in Kossel geometry was developed as a non-destructive structural characterization method of nanometer thin films deposited on Si. The method is applied to study Pt/Fe/Pt and Ta/Cr/Pt thin films designed as X-ray planar waveguides. The intensities of characteristic X-ray emissions versus the detection angle (grazing exit), called Kossel curves, were measured by an energy dispersive X-ray camera. It is found that an interfacial compound is formed in Pt/Fe/Pt waveguide, whereas oxidation and mixing occur in the Ta/Cr/Pt system. It was not possible to obtain the description of the successive layers when considering only grazing incidence x-ray reflectivity. When PIXE-Kossel experiments are considered, supplementary constraints have to be fulfilled when fitting the values of the stack parameters (number, composition, thickness, roughness and density of the layers) which restrict the possible descriptions of waveguides. Thus PIXE-Kossel is suitable to characterize stacks of nanometer thin films designed as an x-ray waveguide.

Bulklike behavior of magnetoelasticity in epitaxial Fe1−xGax thin films

Bulk ${\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Ga}}_{x}$ alloys present a strong sensitivity of the magnetostrictive properties with Ga content with maximum magnetostriction near $x=0.19$. Here, we present magnetoelastic coefficients measured by the cantilever method on ${\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Ga}}_{x}$ thin films grown by molecular beam epitaxy on GaAs(001). We find that Ga-dependent magnetoelastic coefficients in nanometer thin films are comparable in magnitude to the respective bulk values. Moreover, we compare thin films with a tetragonal structure due to a slightly preferential alignment of Ga pairs along the growth direction with and a cubic structure. It turns out that magnetoelastic coefficients are unaffected by a preferential alignment of Ga pairs along the growth direction.

Quasi-Ballistic Thermal Transport Across MoS2 Thin Films.

Layered two-dimensional (2D) materials have highly anisotropic thermal properties between the in-plane and cross-plane directions. Conventionally, it is thought that cross-plane thermal conductivities (κ z) are low, and therefore c-axis phonon mean free paths (MFPs) are small. Here, we measure κ z across MoS2 films of varying thickness (20-240 nm) and uncover evidence of very long c-axis phonon MFPs at room temperature in these layered semiconductors. Experimental data obtained using time-domain thermoreflectance (TDTR) are in good agreement with first-principles density functional theory (DFT). These calculations suggest that ∼50% of the heat is carried by phonons with MFP > 200 nm, exceeding kinetic theory estimates by nearly 2 orders of magnitude. Because of quasi-ballistic effects, the κ z of nanometer-thin films of MoS2 scales with theirthickness and the volumetric thermal resistance asymptotes to a nonzero value, ∼10 m2 K GW-1. This contributes as much as 30% to the total thermal resistance of a 20 nm thick film, the rest being limited by thermal interface resistance with the SiO2 substrate and top-side aluminum transducer. These findings are essential for understanding heat flow across nanometer-thin films of MoS2 for optoelectronic and thermoelectric applications.

Segmental α-Relaxation for the First Step and Sub-Rouse Modes for the Second Step in Enthalpy Recovery in the Glassy State of Polystyrene

Cangialosi and co-workers found two steps in the enthalpy recovery deep in the glassy state of high and low molecular weight bulk polystyrene (PS). We attribute the first step to the segmental α-relaxation and the second step to the sub-Rouse modes and explain the two-step enthalpy recovery by the dynamic properties of the two processes in bulk PS by the coupling model (CM). The two-step enthalpy recovery was found in nanometer thin films of polystyrene (PS). On decreasing film thickness h, the first step was shifted to much lower temperature than the second step, and the effect is explained by the segmental α-relaxation shifting to lower temperature much more than the sub-Rouse modes, as predicted by the CM. Furthermore, the dependences of the faster and slower processes of the two-step enthalpy relaxation on film thickness are analogues of two effects observed on decreasing h of freestanding polystyrene films. One effect is the observation of two transitions by ellipsometry. We associated the lower transition at Tgl(h) with the segmental α-relaxation and the upper transition at Tgu(h) with the sub-Rouse modes and explained the experimentally observation of Tgl(h) decreasing more rapidly than Tgu(h) on decreasing h also by the CM. The other effect is the rubbery stiffening observed by creep compliance measurements on decreasing h of freestanding films in polymers including PS. This effect was explained by the more rapid decrease of the segmental α-relaxation time τα(T,h) with decreasing h than the sub-Rouse relaxation time τsR(T,h), again using the CM. These two analogues of the two-step enthalpy recovery in bulk and nanometer PS thin films strengthen the common CM explanation of the first step by the segmental α-relaxation and the second step by the sub-Rouse modes in enthalpy recovery.

Low Reversible Capacity of Nitridated Titanium Electrical Terminals

The currently preferred manufacturing method for Lithium-ion battery (LIB) electrodes is via the slurry route. While such an approach is appealing, the complexity of the electrode layers containing the active materials, conductivity helpers, and binders, has hampered detailed investigations of the active materials. As an alternative, an active material can be deposited as a thin film on a planar substrate, which enables a more robust and detailed analysis. However, due to the small areal capacity of nanometric thin films, the electrochemical activity of the cell casing must be negligible or at least well determined. We reported on the capacity and the differential capacity metrics of several materials used in the construction of the electrical terminals in LIBs. Among these materials, Ti was revealed to have the minimum reversible capacity for lithium-ion storage. The mechanical and electrochemical properties of the Ti–based materials were further improved through surface nitridation with thermal treatment in an ammonia-rich atmosphere. The nitridated Ti electrical terminal achieved a reversible capacity that was at least fifteen times lower than that of stainless steel, with a featureless differential capacity representation creating quasi-ideal experimental conditions for a detailed investigation of electroactive thin films.

Enhanced Second Harmonic Generation from Ferroelectric HfO2-Based Hybrid Metasurfaces.

Integrated nonlinear metasurfaces leading to high-efficiency optical second harmonic generation (SHG) are highly desirable for optical sensing, imaging, and quantum photonic systems. Compared to traditional metal-only metasurfaces, their hybrid counterparts, where a noncentrosymmetric nonlinear photonic material is incorporated in the near-field of a metasurface, can significantly boost SHG efficiency. However, it is difficult to integrate such devices on-chip due to material incompatibilities, thickness scaling challenges, and the narrow band gaps of nonlinear optical materials. Here, we demonstrate significantly enhanced SHG in on-chip integrated metasurfaces by using nanometer thin films of ferroelectric Y:HfO2. This material has the merit of CMOS compatibility, ultraviolet transparency up to 250 nm, and significant scalability down to sub-10 nm when deposited on silicon. We observe a 20-fold magnitude enhancement of the SHG intensity from the hybrid metasurface compared to a bare ferroelectric HfO2 thin film. Moreover, a 3-fold SHG enhancement is observed from the hybrid metasurface compared to a control structure using nonferroelectric HfO2, demonstrating a major contribution to the SHG signal from ferroelectric Y:HfO2. The effective second-order nonlinear optical coefficient χ(2) of Y:HfO2 is determined to be 6.0 ± 0.5 pm/V, which is comparable to other complex nonlinear photonic oxide materials. Our work provides a general pathway to build an efficient on-chip nanophotonic nonlinear light source for SHG using ferroelectric HfO2 thin films.

Effect of thermal annealing and irradiation damage on the superconducting critical temperature of nanocrystalline γ-Mo2N thin films

We report on the influence of the disorder and stoichiometry in the resulting superconducting critical temperature of γ-Mo2N thin films. Initially, three films (with Tc values of 7.6 K, 6.8 K and 6 K) were grown at room temperature by reactive sputtering, on Si (1 0 0) using different N2/(Ar+N2) mixtures. The influence of the thermal annealing up to 973 K and irradiation damage produced by 1 MeV Zr+(fluence up 2 × 1014 cm−2) is analyzed. The Tc of pristine films remains unchanged for increasing irradiation doses up 2 × 1014 cm−2. The Tc for annealed films decreases close to the value expected for bulk samples (≈5 K) for increasing the annealing temperature. Successive irradiations of the annealed films tend to increase their Tc up to its initial values (before annealing). The results indicate that the Tc in nanometric grain size γ-Mo2N thin films is affected by both nitrogen stoichiometry and disorder at the atomic scale.

Numerical tool for estimating the dielectric constant, the thickness, and the coverage of immobilized inhomogeneous protein films on gold in aqueous solution.

A numerical simulation tool is reported for nanometer thin and inhomogeneous immobilized protein films on gold in aqueous solution. It allows for the first time, to the best of our knowledge, the simultaneous assessment of refractive index, film thickness, and surface coverage. The model relies on and combines the convective diffusion equation, the Langmuir adsorption isotherm, and the Helmholtz equation, with appropriate boundary conditions. These three differential equations were jointly solved using a multiphysics software. The physical film parameters were extracted employing an optimization procedure for immobilized bovine serum albumin, hemoglobin, and neutravidin films. The relatively good agreement between the extracted values for the refractive index, film thickness, and surface coverage and the corresponding values reported in the open literature show the correctness of the proposed methodology.

Preparation of Tin Oxide Nanometer Thin Films by Hydrothermal Method

Given the shortage of energy reserves, new energy sources must be identified. In this regard, improving the efficiency of solar cell conversion and simplifying the solar cell technology have become the focus of research. In this study, tin oxide nanometer thin film was fabricated on FTO conductive glass as photocathode through hydrothermal method. The synthesis condition was regulated, and performance test was also conducted. Results show that the crystallization driving force, crystallization rate, and grain size of tin dioxide crystal increase with increasing alkali ratio, leading to disorganized accumulation of tin oxide. Under prolonged holding time, tin oxide crystal became complete, and the surface area of the crystal increased. The crystallization driving force and rate also increased with increasing salt concentration and accompanied by clutter of tin oxide. The optimized process condition included 1:4 molar ratio of salt to alkali, 0.05 mol/L salt concentration, 200 °C reaction temperature, and 8 days of reaction. The highest specific surface area of the tin oxide nanometer film was obtained under the optimized condition.

Effect of Carbon Surface on Nafion Thin Film Hygro-Expansion and Thermal-Expansion

Polymer electrolyte fuel cell (PEFC) catalyst layers consist of carbon, platinum, and ionomer. Carbon is necessary to provide a high surface area to support catalytic platinum nanoparticles and facilitate electron transport to the reaction sites whereas ionomer is required to supply protons to the reaction site. In addition, together they contribute to the structural strength of a catalyst layer. Since ionomer and carbon make up a majority of the catalyst layer volume, the ionomer in catalyst layer mostly interfaces with carbon support. Studies have shown the suppression of ionomer properties in thin film form especially below 50 nm and is also highly dependent on the substrate. For example, Key et. al measured higher water content in 19 nm thick Nafion coated on Pt than ionomer on SiO2 [1]. Recently, Orfanidi et. al, showed that the functionalization of carbon with NHx group assists in better distribution of ionomer within catalyst layer and restructure the ionomer in such a way that oxygen transport resistance across the ionomer drops [2]. Hence, from the fuel cell application perspective, it is important to study the effect of different carbon substrates on ionomer properties. There is lack of data available on fundamental properties such as hygro-expansion and thermal-expansion of nanometer thin film Nafion on carbon in general and the effect of carbon surface characteristics, in particular on these properties. This presentation will share the effect of hydrophobic carbon and functionalized hydrophilic surfaces on the hygro- and thermal-expansion of 20 and 70 nm thick Nafion films.

Perturbing the spin crossover transition activation energies in Fe(H2B(pz)2)2(bipy) with zwitterionic additions

A thermal component to the soft x-ray induced spin crossover transition exists in the switching of a spin crossover compound (complex [Fe{H2B(pz)2}2(bipy)] (pz = pyrazol-1-yl, bipy = 2,2′-bipyridine) combined with the dipolar molecular additives (zwitterionic p-benzoquinonemonoimine C6H2()2()2). The addition of the zwitterionic molecule locks the Fe(II) complex in a largely low spin state configuration over an unusually broad temperature range that includes temperatures well above the thermal spin crossover temperature of 160 K. It is demonstrated here that the process of exciting the [Fe{H2B(pz)2}2(bipy)] moiety, in the presence of with C6H2()2()2, to an electronic state characteristic of the high spin state though incident x-ray fluences, has a thermal activation energies are determined to 14–18 meV for a range of mixing ratios from 1:2 to 1:10. Those activation energies are also significantly reduced as compared to values of 60–80 meV found for nanometer thin films of [Fe{H2B(pz)2}2(bipy)] on SiO2.

Smart Window Based on Electric Unfolding of Microwrinkled TiO2 Nanometric Films

Flat glass is clear while frosted glass with a microrough surface appears translucent by light scattering. Motivated by this optical surface scatterer, a transparent soft media with electrically tunable surface roughness could make a low-cost smart window. Recently, a dielectric elastomer actuator with microwrinkled transparent compliant electrodes was proposed to make such a smart window, but its active microwrinkled area occupied only a small fraction of the window device, as it needs room for large-strain unfolding. To solve this issue, this paper first shows transparent-to-translucent switching by a low-strain-induced microwrinkling and the reverse by electric-field-induced unfolding. This is possible by using an electrically tunable optical surface scatterer that consists of a TiO2 nanometric thin film of high modulus and high refractive index that is sandwiched between a nanometric conductive overcoat of transparent conductive polymer, that is, poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)...

Nanometric thin films of non-doped diamond-like carbon grown on n-type (P-doped) silicon substrates as electrochemical electrodes

The electrochemical response of thin non-doped diamond-like carbon films grown by pulsed laser deposition onto n-type (P-doped) silicon substrates was studied using different redox-active couples. The experiments were conducted as a function of the film thickness which can be controlled by the deposition time. It could be demonstrated that the film thickness greatly influences the electrochemical response and the electron transference rate at the surface, thus reaching an optimal response for films with a thickness of around 35 nm. This holds true for all redox couples studied. Those films show rather similar properties compared to boron-doped diamond electrodes, thus becoming an interesting coating to be studied as electrochemical electrode.

Thin films in partial wetting: stability, dewetting and coarsening

A uniform nanometric thin liquid film on a solid substrate can become unstable due to the action of van der Waals (vdW) forces. The instability leads to dewetting of the uniform film and the formation of drops. To minimize the total free energy of the system, these drops coarsen over time until one single drop remains. Here, using a thermodynamically consistent framework, we derive a new model for thin films in partial wetting with a free energy that resembles the Cahn–Hilliard form with a height-dependent surface tension that leads to a generalized disjoining pressure, and revisit the dewetting problem. Using both linear stability analysis and nonlinear simulations we show that the new model predicts a slightly smaller critical instability wavelength and a significantly (up to six-fold) faster growth rate than the classical model in the spinodal regime; this faster growth rate brings the theoretical predictions closer to published experimental observations. During coarsening at intermediate times, the dynamics become self-similar and model-independent; we therefore observe the same scalings in both the classical (with and without thermal noise) and new models. Both models also lead to a mean-field Lifshitz–Slyozov–Wagner (LSW)-type droplet-size distribution at intermediate times for small drop sizes. We, however, observe a skewed drop-size distribution for larger drops in the new model; while the tail of the distribution follows a Smoluchowski equation, it is not associated with a coalescence-dominated coarsening, calling into question the association made in some earlier experiments. Our observations point to the importance of the height dependence of surface tension in the early and late stages of dewetting of nanometric films and motivate new high-resolution experimental observations to guide the development of improved models of interfacial flows at the nanoscale.

Plasmonic Nanopore Fabrication for Single Molecule Bio Sensor By Using Electron Beam Irradation

Recently the portable device called MINion for single molecule analysis was developed by Oxford Nanopore Technology. The electrical detection technique for the solid state device was utilized for single molecule detection . However, the large error rates were reported by several journals, even though the significant error reduction was developed after the invention of the portable nanopore device. In this report, we introduce the optical nanopore fabrication by using plasmonic optical enhancement effect. First, the Au thin films were vacuum-deposited on the nanometer thin SiN film, followed by removal of SiN film and by drilling Au apertures by using focused ion beam (FIB) technique. Then, electron beam irradiations on the specimens either by using low energy field emission electron beam microscopy (FESEM) or high energy Transmission electron beam microscopy (TEM). In addition, the periodic grooves, or the periodic Au aperture array were fabricated on the Au sample in order to provide strong plamonic optical enhancements. During the electron irradiation on the fabricated Au surface, we observed the diffused binary Au-C membrane due to Ostwald ripening and also the unstable Au-C mixed phase change via spinodal decomposition. We also found that the Au cluster diffusion would depend upon the electron beam fluence. However, the exact understanding of this phenomenon is still on-going investigation. Figure 1

“Rubbery Stiffening” and Rupture Behavior of Freely Standing Nanometric Thin PIB Films

Prior bubble inflation studies have shown strong evidence of rubbery-like stiffening behaviors for several organic and inorganic thin films. The possible origin is still unclear, but recently Ngai et al. [J. Polym. Sci., Part B: Polym. Phys. 2013, 51 (3), 214−224] and Li and McKenna [Macromolecules 2015, 48 (17), 6329−6336] proposed that the separation of molecular motions and dynamic fragility are closely related to the observed rubber-like stiffening behavior. In the present work, we report observations from bubble inflation measurements on nanometric thin polyisobutylene (PIB) films that test the correlations suggested by the Ngai coupling model (stiffening is related to the shape parameter describing the α-relaxation) and Li and McKenna (the rubbery stiffening correlates with the dynamic fragility). Mechanical properties and surface tension of nanometric thin PIB films were investigated through strain–stress measurements for film thicknesses ranging from 13 to 126 nm. The tests were performed at room ...