Film Profile Research Articles

Photophysical insights of highly transparent, flexible and re-emissive PVA @ WTR-CDs composite thin films: A next generation food packaging material for UV blocking applications

Herein, we have fabricated a highly transparent, flexible and re-emissive polyvinyl alcohol/waste tea residue carbon dots (PVA@WTR-CDs) composite thin films by simple solvent casting method. Incorporated WTR-CDs as a function of UV blocking (absorption of UV light and re-emission in the visible region) agent synthesized from waste tea residue powder as a sustainable material. The results revealed that, the WTR-CDs have the best compatibility with PVA. The incorporated fluorescent WTR-CDs impart fluorescence to the whole film and films are capable to not only block the UV region but also re-emit absorbed UV light into the visible region. The increased concentrations of WTR-CDs into PVA films enhances the UV blocking capability of the composite films. The composite, PVA@WTR-CDs-3 films were succeeded to block full (100%) of UV-C (230−280 nm) and UV-B (280−315 nm) region, while 20−60% of UV-A (315−400 nm). We achieved the maximum of UV blocking by PVA@WTR-CDs-5 composite films by controlling the transparency and thickness. By the successive addition of the UV blocking agent, there was no extreme changes observed in the intrinsic mechanical as well as tensile properties of PVA films. The thermal analysis study showed that, there was no adverse effect of WTR-CDs incorporation on the thermal stability and degradation profile of original PVA films. In detail, the possible mechanism of UV absorption and re-emission in the visible region by fabricated films is also discussed. Furthermore, practicability of the composite film was also investigated on a model (grape) fruit and thus can be used as a modern UV blocking material in packaging, pharmaceutical storage, wrapping, and coating etc.

Lithium-Doping Effects in Cu(In,Ga)Se2 Thin-Film and Photovoltaic Properties.

The beneficial effects of heavy alkali metals such as K, Rb, and Cs in enhancing Cu(In,Ga)Se2 (CIGS) photovoltaic efficiencies are widely known, though the detailed mechanism is still open for discussion. In the present work, the effects of the lightest alkali metal, Li, on CIGS thin-film and device properties are focused upon and compared to the effects of heavy alkali metals. Till date, the beneficial effects of elemental Li on Cu2ZnSnS4 photovoltaic devices in enhancing efficiencies have been reported. On the other hand, it is shown in the present work that the beneficial effects of Li on CIGS are not so significant. In contrast to the effects of Na or Rb in enhancing CIGS(112) growth orientation, Li was revealed not to affect CIGS growth orientation. The most distinctive feature observed between Li and other alkali metals was the elemental depth profile in CIGS films. Namely, Na and heavier alkali metals show a concentration peak near the surface (relatively Cu-poor) region of CIGS films, whereas elemental Li showed no such trend, suggesting that Li has no significant effect on CIGS surface modification. Nonetheless, Li was found to have some effect in enhancing the PL peak intensity and photovoltaic performance of CIGS, though the effect is relatively small in comparison to that obtained with other alkali metals.

Numerical study of purging of a gasoline direct injection nozzle at the end of injection

In gasoline direct injection engines, fuel injector nozzle is one of the vital components that determine the efficiency of fuel atomization which controls combustion and emission. There is an increased focus on developing better nozzles by studying the internal flow behavior especially during the needle transient phase and at the end of injection phase. Multiphase flow characteristics involving cavitation and hydraulic flip are observed inside the nozzle during its operation. At the end of injection, fuel inside the nozzle sac and nozzle holes is purged with the gas from the engine cylinder. The efficiency of this purging process is critical to prevent the carbon deposit formation on the wall of nozzle holes and on the surface of the nozzle tip. In this article, a numerical method is presented to predict the internal nozzle flow during the needle movement and during the end of injection to predict the purging capacity of a gasoline direct injection nozzle. Needle motion is accomplished using a moving mesh method via a user-defined function. The numerical model is compared with the X-ray measurements from the literature. Based on the validated model, the study is extended to analyze various parameters like injection pressure, nozzle hole location, number of nozzle holes and the inlet rounding of the nozzle hole which affects the effectiveness of nozzle purging. Fuel wetting at the nozzle tip after the end of injection is also numerically modeled to evaluate the thickness profile of the thin liquid film.

(Invited) Film Properties of Various Electroless Plated Co Alloy Films Formed on SiO2/Si Substrate and Its Interdiffusion Properties Against Cu

There is a serious problem of poor side wall coverage for the sputtered barrier metals in high aspect ratio TSVs. We have proposed electroless plated Co-alloy barrier metals for TSV. For this purpose, we prepared various CoB and CoWB alloys with different atomic compositions and crystalline structures. Furthermore, we evaluated interdiffusion properties of Cu/Co-alloy/Si stacked structure by SIMS analysis. It turned out that the electroless CoWB film containing larger amount of W has excellent diffusion barrier property than other CoWB films with smaller W content. We formed electroless barrier films of CoB and CoWB using Pd nanoparticle catalyst on SiO2/Si substrate [1]. For evaluation of Cu interdiffusion properties by SIMS, we deposited Cu and TiN thin films successively by sputtering on the barrier film. The ratio of the atomic composition was changed by adjusting the ratio of cobalt sulfate, tungstic acid, and some other contents of the plating bath. SIMS depth profiles of CoB (Fig.1-a) and CoWB films after annealing at 400 ℃ (Fig.1-b) are shown in Fig.1. There was a large interdiffusion between Cu and CoB after 400 ℃ annealing (Fig.1-a). Co-Silicide formation significantly occurred and Si atoms diffused into CoB layer. However, interdiffusion was significantly suppressed in the case of Co-20%W-B film (Fig.1-b). These results suggest that W atoms existed in CoWB have a strong effect of suppressing Cu diffusion in Co film, and CoWB with 20 atom % W showed a good diffusion barrier property. The present study suggests that the electroless plated CoWB having a larger W content has a high potential as a diffusion barrier film for the via last TSV process.[1] F. Inoue, T.Shimizu, F.Miyake, R.Arima, T.Ito, H.Seki, Y.Shinozaki, T.Yamamto, and S.Shingubara, Microelectronic Engineering, 106 (2013) 164–167.[2] T. Iseri, S.Shindo, Y.Miyachi, A.Hirate, S.Tanaka, T.Shimizu, T.Ito, S.Shingubara, Jpn. J. Appl. Phys. 57 (2018), 07MB02-1~6. Figure 1

Chroma-hue controllable color and thermocolor-added deoxyribonucleic acid films

Deoxyribonucleic acid (DNA) is a useful scaffolding material for the alignment of nanomaterials with specific functionalities. Here, we fabricated multi-layered (e.g., single, triple, and quintuple) color-added DNA films with a different color in each layer on substrates as well as a self-supported film with a mixture of different colors. A color-added DNA thin film on a substrate was prepared by either drop-casting or spin-coating, and a self-supporting DNA film was constructed by an oven-drying procedure. The optical characteristics of DNA films with various color dye concentrations were studied through transmittance and absorption. In addition, color profiles (i.e., chroma and hue angle) of the self-supporting DNA films were investigated by considering reflectance to obtain International Commission on Illumination LAB (CIELAB) values (where L, A, and B represent the brightness, x-axis (green-red), and y-axis (yellow-blue) in the CIE color space, respectively). Color profiles were obtained by L, A, and B. The chroma of the self-supporting DNA film with more colors were relatively small, indicating a dark achromatic characteristic of the samples. The hue angle of each film corresponded to the characteristic colors. Finally, the reversibility of the color change of DNA films embedded with thermochromatic dyes was demonstrated by varying the temperature to verify use in practical applications.

MRI-LINAC beam profile measurements using a plastic scintillation dosimeter.

Plastic scintillation dosimeters (PSDs) possess many desirable qualities for dosimetry with LINACs. These qualities are expected to make PSDs effective for MRI-LINAC dosimetry, however little research has been conducted investigating their dosimetric performance with MRI-LINACs. In this work, an in-house PSD was used to measure 8 beam profiles with an in-line MRI-LINAC, compared with film measurements. One dimensional global gamma indices (γ) and corresponding γ pass rates were calculated to compare PSD and film profiles for the 1%/1 mm, 2%/2 mm and 3%/3 mm criterion. The mean global pass rates were 85.8%, 97.5% and 99.4% for the 1%/1 mm, 2%/2 mm and 3%/3 mm criteria, respectively. The majority of the γ failures occurred in the penumbral regions. Penumbra widths were measured to be slightly narrower with the PSD compared to film, however, the uncertainties in the measured penumbra widths brought the PSD and film penumbra widths into agreement. Differences in dose were calculated between the PSD and film, and remained within 2.2% global agreement for the central regions and 1.5% global agreement for out of field regions. These values for range of agreement were similar to the those reported in the literature for other dosimeters which are trusted for relative MRI-LINAC dosimetry.

BIXS for tritium analysis with Ar gas and Al thin film as β-ray stopping layers and comparison with EBS

β-ray induced X-ray spectrometry (BIXS) and elastic backscattering spectrometry (EBS) were utilized in this study for the tritium analysis of samples of tritium/deuterium-containing titanium films with thick Mo substrates. Using the BIXS method which incorporates Monte Carlo simulated data, we used Ar gas filler (BIXS-Ar) or placed Al film (BIXS-Al), respectively, between the sample and X-ray detector as β-ray stopping layers. Using the EBS method to confirm whether or not the tritium will volatilize under the impact of the proton beams, we conducted two measurements at the same point of the sample surfaces. A TiH film sample with thick Mo substrate was used in our EBS experiment to remove the influence of the Mo spectrum on the EBS experimental spectra of tritium/deuterium-containing samples. We well fit using the SIMNRA code the tritium and deuterium EBS spectra that were obtained by removing the Mo spectra. The tritium content and depth profiles in the titanium films were obtained via these different methods and the results were compared. It was found that the total tritium content measured using the EBS, BIXS-Al, and BIXS-Ar methods were in agreement within the experimental uncertainties, and the BIXS-Al method may be better at measuring the tritium depth profiles than the BIXS-Ar method.

Interaction and instability of air films between bituminous coal surfaces and surfactant droplets

While the suppression of airborne coal particulates with water and surfactant sprays has been widely used in underground coal mines, the microscopic mechanism involved during the attachment process between water droplets and dust particles has not been well understood. In this work, both the interaction forces and instability of air films between aqueous droplets and coal surfaces are studied by monitoring the evolution of spatial and temporal thickness profiles of the air films. The measurements are conducted with both non-ionic and anionic surfactants. The results of this work show that the air film between the water droplet and the bituminous coal surface collapses at a critical rupture thickness of 104 nm, which is followed by a rapid spreading of the three-phase contact line. It has been found that both the critical rupture thickness and kinetics of film thinning increase with increasing surfactant concentrations regardless of the types of surfactants. An analysis of the spatiotemporal thickness profiles using the Reynolds equation shows that an attractive force is present across an air film. This force is found to be an electrostatic force. The force becomes more attractive with increasing surfactant concentrations of the aqueous solutions. The present work sheds new light on the capture of dust particles by water and surfactant sprays at a molecular level.

Inductively coupled plasma reactive ion etching of copper thin films using ethylenediamine/butanol/Ar plasma

The dry etching of copper thin films patterned with SiO2 hard masks was performed using an ethylenediamine (EDA)/butanol/Ar gas mixture. Ethylenediamine is an organic chelator that served as the main etching gas and butanol was used as an additive gas. As the concentrations of EDA and butanol in EDA/Ar and butanol/Ar increased, respectively, the etch rate of copper thin films decreased. The etch rate in EDA was less than that in butanol. However, a good etch profile of copper thin films was obtained with high EDA concentration in the EDA/Ar gas mixture, whereas high etch selectivity of copper was achieved from the butanol/Ar gas mixture. In the EDA/butanol/Ar gas mixture, the optimal ratio of EDA to butanol was investigated to increase the etch rate and improve the etch profile. The optical emission spectroscopy indicates that the main species in EDA were [CN] and [H], whereas in butanol, [H] was the main substance. The X-ray photoelectron spectroscopy reveals that copper reacted with [CN], [H], and [O] to form copper compounds that could be desorbed from the film surface by the sputtering of ions. The EDA/butanol/Ar gas mixture can be a good etch gas to dry-etch copper thin films.

Derivation of a heteroepitaxial thin-film model

A variational model for epitaxially-strained thin films on rigid substrates is derived both by \Gamma -convergence from a transition-layer setting, and by relaxation from a sharp-interface description available in the literature for regular configurations. The model is characterized by a configurational energy that accounts for both the competing mechanisms responsible for the film shape. On the one hand, the lattice mismatch between the film and the substrate generate large stresses, and corrugations may be present because film atoms move to release the elastic energy. On the other hand, flatter profiles may be preferable to minimize the surface energy. Some first regularity results are presented for energetically-optimal film profiles.

Multi-Stimuli-Responsive Field-Effect Transistor with Conjugated Polymer Entailing Spiropyran in the Side Chains

Multi-stimuli-responsive field-effect transistors (FETs) with organic/polymeric semiconductors have received increasing attention. Herein, we report a novel strategy for fabricating multi-stimuli-r...

Modulation of the Visible Absorption and Reflection Profiles of ITO Nanocrystal Thin Films by Plasmon Excitation

Heavily doped metal oxide nanocrystals (NCs) possess tunable infrared localized surface plasmon resonances (LSPRs) that give them utility for several potential applications, including photothermal ...

Iron-Based Mixed Phosphate Na4Fe3(PO4)2P2O7 Thin Films for Sodium-Ion Microbatteries.

Iron-based polyanionic materials can be exploited to realize low cost, durable, and safe cathodes for both bulk and thin film sodium-ion batteries. Herein, we report pulsed laser deposited mixed phosphate Na4Fe3(PO4)2P2O7 as a positive electrode for thin film sodium-ion microbatteries. The bulk material and thin films of Na4Fe3(PO4)2P2O7 are employed by solution combustion synthesis (SCS) and the pulsed laser deposition (PLD) technique, respectively. Phase purity and the nature of the crystallinity of the thin films were confirmed by grazing incidence X-ray diffraction and transmission electron microscopy. Identification of surface roughness and morphology was obtained from atomic force microscopy and scanning electron microscopy, respectively. Emerging electrochemical properties were observed from charge–discharge profiles of the thin films, which are well comparable to bulk material properties. The Na4Fe3(PO4)2P2O7 thin film electrodes delivered a highly reversible Na+ storage capacity of ∼120 mAh g–1 with an excellent stability of over 500 cycles. Electrochemical analysis results revealed that the thickness of the film affects the storage capacity.

Modulated and monotonic monolayer-magnetism in hetero-epitaxial Fe on Cu(001)

We have combined two complementary techniques, element sensitive ex situ X-ray magnetic circular dichroism (XMCD) and in situ polarized neutron reflectivity (i-PNR), to determine the values of evolving magnetic moments obtained from a low symmetry system of hetero-epitaxial Fe monolayers (MLs), as a function of thickness. The samples were grown by magnetron sputtering on face-centered-cubic (fcc) Cu(001)/Si(001). Within experimental errors, we found a corroboration of the modulated moments from the XMCD and of the magnetic anisotropies from magnetization measurements with those obtained earlier from layer-by-layer i-PNR measurements. The modulation was attributed to initial island-like growth morphology assisted monolayer-magnetism during sputtering. Furthermore, analyzing the depth sensitive i-PNR profile of a bulk-like film, we developed a model characterized by monotonic magnetism involving collinear spins. The model is further described by a higher magnetization for the deeper layers, which decreases gradually for the upper layers before attaining saturation at its bulk value within a few MLs. This model contradicts the earlier proposed non-collinear model involving antiferromagnetic units, thus clarifying the long standing ambiguity in the coverage regime. The results have been compared with those existing, following the theoretical parameterized tight-binding model with satisfactory agreement. This study distinguishes the variation of monolayer-magnetism owing to the growth morphology from the layer-by-layer investigation vis-à-vis depth-profiling of bulk-like film. At the same time, it also promises the general possibility of depth-profiling using i-PNR in other complex multilayered systems on high flux neutron sources.

Studies on the Drug Loading and Release Profiles of Degradable Chitosan-Based Multilayer Films for Anticancer Treatment.

This study demonstrates the possibility of developing a rapidly degradable chitosan-based multilayer film for controlled drug release. The chitosan (CHI)-based multilayer nanofilms were prepared with three different types of anions, hyaluronic acid (HA), alginic acid (ALG) and tannic acid (TA). Taking advantage of the Layer-by-Layer (LBL) assembly, each multilayer film has different morphology, porosity and thickness depending on their ionic density, molecular structure and the polymer functionality of the building blocks. We loaded drug models such as doxorubicin hydrochloride (DOX), fluorescein isothiocyanate (FITC) and ovalbumin (Ova) into multilayer films and analyzed the drug loading and release profiles in phosphate-buffered saline (PBS) buffer with the same osmolarity and temperature as the human body. Despite the rapid degradation of the multilayer film in a high pH and salt solution, the drug release profile can be controlled by increasing the functional group density, which results in interaction with the drug. In particular, the abundant carboxylate groups in the CHI/HA film increased the loading amount of DOX and decreased rapid drug release. The TA interaction with DOX via electrostatic interaction, hydrogen bonding and hydrophobic interaction showed a sustained drug release profile. These results serve as principles for fabricating a tailored multilayer film for drug delivery application.

Novel imaging technique for non-destructive metrology and characterization of ultraviolet-sensitive polymeric microstructures.

The negative photoresist SU-8 has attracted much research interest as a structural material for creating complex three-dimensional (3D) microstructures incorporating hidden features such as microchannels and microwells for a variety of lab-on-a-chip and biomedical applications. Achieving desired topological and dimensional accuracy in such SU-8 microstructures is crucial for most applications, but existing methods for their metrology, such as scanning electron microscopy (SEM) and optical profilometry, are not practical for non-destructive measurement of hidden features. This paper introduces an alternative imaging modality for non-destructively characterizing the features and dimensions of SU-8 microstructures by measuring their transmittance of 365 nm ultraviolet (UV) light. Here, depth profiles of SU-8 3D microstructures and thin films are determined by relating UV transmittance and the thicknesses of SU-8 samples imaged in the UV spectrum through the Beer-Lambert law applied to the images on a pixel-by-pixel basis. This technique is validated by imaging the UV transmittance of several prototype SU-8 3D microstructures, including those comprising hidden hollow subsurface features, as well as SU-8 thin-films, and verifying the measured data through SEM. These results suggest that UV transmittance imaging offers a cost-effective, non-destructive technique to quickly measure and identify SU-8 microstructures with surface and hidden subsurface features unlike existing techniques.

Planar dynamics of inclined curved flexible riser carrying slug liquid–gas flows

Flexible risers transporting hydrocarbon liquid–gas flows may be subject to internal dynamic fluctuations of multiphase densities, velocities and pressure changes. Previous studies have mostly focused on single-phase flows in oscillating pipes or multiphase flows in static pipes whereas understanding of multiphase flow effects on oscillating pipes with variable curvatures is still lacking. The present study aims to numerically investigate fundamental planar dynamics of a long flexible catenary riser carrying slug liquid–gas flows and to analyse the mechanical effects of slug flow characteristics including the slug unit length, translational velocity and fluctuation frequencies leading to resonances. A two-dimensional continuum model, describing the coupled horizontal and vertical motions of an inclined flexible/extensible curved riser subject to the space–time varying fluid weights, flow centrifugal momenta and Coriolis effects, is presented. Steady slug flows are considered and modelled by accounting for the mass–momentum balances of liquid–gas phases within an idealized slug unit cell comprising the slug liquid (containing small gas bubbles) and elongated gas bubble (interfacing with the liquid film) parts. A nonlinear hydrodynamic film profile is described, depending on the pipe diameter, inclination, liquid–gas phase properties, superficial velocities and empirical correlations. These enable the approximation of phase fractions, local velocities and pressure variations which are employed as the time-varying, distributed parameters leading to the slug flow-induced vibration (SIV) of catenary riser. Several key SIV features are numerically investigated, highlighting the slug flow-induced transient drifts due to the travelling masses, amplified mean displacements due to the combined slug weights and flow momenta, extensibility or tension changes due to a reconfiguration of pipe equilibrium, oscillation amplitudes and resonant frequencies. Single- and multi-modal patterns of riser dynamic profiles are determined, enabling the evaluation of associated bending/axial stresses. Parametric studies reveal the individual effect of the slug unit length and the translational velocity on SIV response regardless of the slug characteristic frequency being a function of these two parameters. This key observation is practically useful for the identification of critical maximum response.

Multiscale plasma and feature profile simulations of plasma-enhanced chemical vapor deposition and atomic layer deposition processes for titanium thin film fabrication

Mechanisms of titanium (Ti) thin films deposited in plasma-enhanced (PE) chemical vapor deposition (CVD) and atomic layer deposition (ALD) processes have been elucidated via multiscale plasma and feature profile simulations. Firstly, by iterating a 2D reactor-scale plasma simulation and a feature-scale deposition profile simulation, a shared surface reaction model has been determined for PECVD processes. Ti film thicknesses and profiles consistently computed both along a wafer surface and inside a test structure agreed very well with the experimental data. Then, another multiscale simulation, with the same plasma model and the surface reaction model to which the Eley–Rideal surface kinetics is added, has been applied to a PEALD process. The simulation succeeded again in reproducing and explaining the non-conformal Ti film deposition observed in experiments, while conformal Ti films are obtained in PECVD processes. Through the simulation work, comprehensive mechanisms of Ti film deposition, which cover both PECVD and PEALD processes, have been discussed and proposed in this study.

Comparative study of optimised molybdenum back-contact deposition with different barriers (Ti, ZnO) on stainless steel substrate for flexible solar cell application

In this study, we optimised the molybdenum (Mo) back-contact layer for solar cell applications on stainless steel substrates using direct-current (dc) sputtering with varying sputtering powers (100 W to 500 W) and pressures (5 mTorr to 20 mTorr). We comparatively analysed the effectiveness of titanium (Ti) layer deposited using e-beam evaporation deposition and zinc oxide (ZnO) layer deposited using radio-frequency (RF) sputtering for barrier application with Mo. Structural characterisation of the optimised Mo films was carried out using XRD studies confirmed the (110) plane corresponding to the body-centred cubic (bcc) structure. Estimated Mo film parameters for films deposited on barrier layers were compared against films deposited on SS substrate without any barriers as these properties influence the prospective diffusion of Fe and Cr into the absorber layer. Surface characterisation of the deposited films was carried out using a scanning electron microscopy (SEM) to study the morphology of films, and energy-dispersive X-ray (EDX) to identify elemental presence to confirm the blockage of the impurities atoms through the film. Secondary ion mass spectroscopy (SIMS) was employed to study the depth profiles of films while atomic force microscopy (AFM) was used to characterise the topographical properties from the sputtered Mo film and analyse the grain properties of the films. A low resistivity value of 0.511 × 10–6 Ω m for Mo films on the reference glass substrate and 0.625 × 10–6 Ω m for the Mo film on ZnO barrier was measured using the four-point probe. We observed a further 40% reduction in impurities using annealed ZnO barrier combined with an optimised Mo layer.

Preparation of wide optical spectrum and high antireflection MgF2 thin film with SF6 as reactive gas

In order to suppress F-deficiency, SF6 was added into the working gas Ar2 as the reaction gas to deposit MgF2 thin film on quartz glass substrate with radio frequency (RF) magnetron sputtering, and the effects of working pressure on the chemical compositions, microstructure and property of MgF2 thin film were investigated. The results show that with the working pressure increase from 1.0 to 2.5 Pa, the atomic ratio of F: Mg decreased continuously, and reached 2.02 at 2.0 Pa, very close to the ideal stoichiometric ratio of 2:1; the crystallinity of MgF2 film improved first then decreased, and finally changed into amorphous state; the particles’ profile of MgF2 film became clearer and their size increased significantly at first, but finally their profile became blurred. The refractive index of MgF2 film decreased first and then increased, and got the lowest value at 2.0 Pa, 1.384, almost equal to that of MgF2 bulk crystal. The transmittance of the coated glass within 300–1100 nm (hereinafter referred to as the transmittance of the thin film) increased first and then decreased. The transmittance of all films was higher than that of the bare glass substrate (93.2%), that is to say, all films had antireflection effect. The film transmittance reached 94.99% at 2.0 Pa, higher than that of the bare glass substrate by 1.79%, and higher than the simulated value calculated with G-Solver software by about 0.5%.