Thin Cover Layer Research Articles

Hybrid SERS substrate based on cotton swab for sensitive detection of organic molecules

For the last two decades, the development of substrates for Surface Enhanced Raman Spectroscopy (SERS) has been continuously pushed for better performances. In this research, we designed SERS substrates with better detection capability and more efficient sample collection. In particular, morphology-controlled Ag nanoparticles were deposited onto cotton swab (cotton Q-tip), followed by a thin cover layer of graphene oxide by the dip-coating method. The graphene oxide overlay was expected to not only protect Ag nanoparticles from degradation by the environment but also contribute to sample adsorption and signal enhancement. To demonstrate the performance of the SERS substrates, different concentrations of Rhodamine B as low as 10–10 M were successfully detected and the enhancement factors were estimated to be 3 × 1010–5 × 1010. It is our expectation that these cotton swab-based substrates will contribute to our ongoing efforts toward low-cost, high-efficiency and durable SERS substrate.

Gas-fed liquid-covered electrodes used for electrochemical reduction of dilute CO2 in a flue gas

Direct electrochemical reduction of dilute CO2 in a flue gas eliminates the energy-consuming preprocesses of capture and condensation for preparing 100% CO2 gas, and hence could decrease the total energy consumption for utilization of emitted CO2. However, it raises two major issues: (i) insufficient supply rate of CO2 to the cathode electrode and (ii) preferential reduction of O2; both lower the Faradaic efficiency of the target reaction of CO2 reduction. To solve these issues, we propose a new concept of gas-fed liquid-covered electrodes (GFLCEs). The reaction gas is fed to the catalyst layer across a thin liquid cover layer formed by a combination of hydrophilic and hydrophobic porous films. Owing to an extremely lower solubility of O2 in an aqueous electrolyte than that of CO2, the O2 concentration in the catalyst layer is sufficiently decreased while securing high CO2 concentration. In the GFLCE, the catalyst is entirely immersed in the electrolyte contrasting to those of conventional gas-diffusion electrodes. Therefore, a CO2 capture medium including monoethanolamine (MEA) added in the electrolyte increases the effective CO2 concentration. We applied the GFLCE concept with MEA to a Ru-complex-based electrocatalyst for formate production, and achieved high Faradaic efficiencies of around 70% under direct feeding of a simulated flue gas of 15% CO2 + 4% O2 + 81% N2 (v/v). The present concept proved here with the MEA additive is a versatile means applicable to existing electrocatalysts.

Stable white emission and color-tunable electroluminescence achieved from n-ZnO/p-GaN nano-heterojunction decorated with CsPbBr3 and CsPbI3 quantum dots

The development of wavelength adjustable electrically driven panchromatic display light-emitting devices (LEDs), a future direction for lighting sources, still seems necessary because of great development prospects and practical significance. Herein, perovskite quantum dots (QDs) of CsPbBr3 and CsPbI3 with multi-color luminescence feature were employed into n-ZnO/p-GaN nano-heterojunction LEDs. A thin polystyrene cover layer was intentionally inserted between CsPbBr3 and CsPbI3 to prevent the undesired halogen anion-exchange reaction. A color-tunable electroluminescence (EL) could be achieved by changing the molar ratio of these two types of perovskite QDs. By further optimizing the molar ratio between CsPbBr3 and CsPbI3, that is, the evolution of the share of red, green and blue-violet luminescence in EL spectra, a stable white light emission was obtained. The current research not only achieves multi-color EL emissions in a three-dimensional nano-architecture, but also proposes an effective and clever strategy for preparing and developing single-chip white LEDs.

Modelling of Irrigation Return Flow in Unconfined Aquifer of Dharoi Command in Mehsana District of Gujarat, India

Surface water flow and subsurface flow have traditionally been investigated separately and simulators have been developed over the years, to model each of these systems. Growing interest in conjunctive water management, and need for simulations of surface/subsurface flow and their interactions has lead to the linking of models of the respective domains. This study from Dharoi command area, using MODFLOW, showed pertaining to the second layer of the calibrated model. The first layer is a thin soil cover layer of about 3 m uniform thickness. Top layer is kept under unconfined water table condition, where as the next layer is given the scope of transforming between water table to confined state and vice versa depending upon the fluctuation of the computed water level with respect to the bottom boundary of the top layer. No recharge and discharge options other than a single boundary condition of average May water level in the extreme north-east grid has been allowed. This calibration is based upon matching the observed and computed average gradient of the water table (hydraulic gradient) and nothing to do with matching the point to point values of the observation wells as that could lead to misappropriation in respect of hydrologic condition. Over all gradient of the water table in the area of interest is computed as 0.23 m per km in comparison to an observed hydraulic gradient of 0.3 m per km. The rivers such as Sabarmati downstream of Dharoi dam and up to Bijapur, Rupen and Pushpawati are activated in the transient run. Conductance value is considered as 0.0001 m/sec for all the rivers. proximity of the second layer under unconfined state. Comparisons of water levels in selected locations. Overall match between the trends and the point values indicate that the calibrated model transient run can be considered as base case and various options can be studied with this model. Visual MODFLOW is very effective to know the present scenario of ground water flow, water level of aquifer, wells, also point values indicate that the calibrated model transient run can be considered as base case and various options can be studied with this model. Visual MODFLOW is very effective to know the present scenario of ground water flow, water level of aquifer, wells, also distribution of spatial recharge, specific yield distribution. It gives very close result to the observed value.

Quantifying the spreading currents over the circular contact region in a good conducting cover layer on a substrate

If a poorly conducting slab is covered with a good conducting cover layer, the resistance of the substrate with the cover layer might be considered to still be high. However, if the contact resistance is measured through a small circular region, the spreading currents conducting parallel to the cover layer surface could lower the resistance. We investigate theoretically the contact resistance of a circular spot and the electric field lines when a conducting substrate is covered with a good conducting thin film. Though an approximate expression of the contact resistance is derived when a metal slab is covered with a thin surface layer, which is easily able to be generalized for the semiconductor substrate, the validity of the approximate expressions of the contact resistance has not been fully understood. We present an accurate theoretical method for finding the correction terms to the approximate expressions and assess the validity of the approximation. We show that the approximate expressions give qualitatively correct results but a quantitatively large error is found for a thin cover layer on a poorly conducting substrate. The accurate theoretical results are useful to understand the dependence of the electrical spreading resistance on the conductivity of the layer and/or that of the substrate as well as the layer thickness. The results could also be used to detect the presence of the surface layer with a different electrical conductivity from that of the substrate through the measurement of the contact resistance with varying the contact area.

Skin Aging & Modern Edge Anti-Aging Strategies

Skin Aging & Modern Edge Anti-Aging Strategies

Skin Aging & Modern Age Anti-aging Strategies

As the most voluminous organ of the body that is exposed to the outer environment, the skin suffers from both intrinsic and extrinsic aging factors. Skin aging is characterized by features such as wrinkling, loss of elasticity, laxity, and rough-textured appearance. This aging process is accompanied with phenotypic changes in cutaneous cells as well as structural and functional changes in extracellular matrix components such as collagens and elastin. With intrinsic aging, structural changes occur in the skin as a natural consequence of the biological changes over time and produce a certain number of histological, physiological, and biochemical modifications. Intrinsic aging is determined genetically (influence of gender and ethnic group), variable in function of skin site, and also influenced by hormonal changes. Visually it is characterized by fine wrinkles. By comparison, “photoaging” is the term used to describe the changes occurring in the skin, resulting from repetitive exposure to sunlight. The histological, physiological, and biochemical changes in the different layers of the skin are much more drastic. From a mechanical point of view, human skin appears as a layered composite containing the stiff thin cover layer presented by the stratum corneum, below which are the more compliant layers of viable epidermis and dermis and further below the much more compliant adjacent layer of subcutaneous white adipose tissue.

Skin aging as a mechanical phenomenon: The main weak links.

From a mechanical point of view, human skin appears as a layered composite containing the stiff thin cover layer presented by the stratum corneum, below which are the more compliant layers of viable epidermis and dermis and further below the much more compliant adjacent layer of subcutaneous white adipose tissue (sWAT). Upon exposure to a strain, such a multi-layer system demonstrates structural instabilities in its stiffer layers, which in its simplest form is the wrinkling. These instabilities appear hierarchically when the mechanical strain in the skin exceeds some critical values. Their appearance is mainly dependent on the mismatch in mechanical properties between adjacent skin layers or between the skin and sWAT, on the adhesive strength and thickness ratios between the layers, on their bending and tensile stiffness as well as on the value of the stress existing in single layers. Gradual reduction of elastic fibers in aging significantly reduces the skin’s ability to bend, prompting an up to 4-fold reduction of its stability against wrinkling, thereby explaining the role of these fibers in skin aging. While chronological and extrinsic aging differently modify these parameters, they lead to the same end result, reducing the critical strain required for the onset of instabilities. Comparing of mechanical properties of the skin presented as a bi-, tri- or tetra-layer structure demonstrates the particular importance of the papillary dermis in skin aging and provides the arguments to consider the undulations on the dermal-epidermal and dermal-sWAT interfaces as the result of mechanical bifurcation, leading to structural instabilities inside of the skin. According to this model, anti-aging strategies should focus not as much on the reinforcement of the dermis, but rather aim to treat the elastic mismatch between different adjacent layers in the skin and sWAT as well as the adhesion between these layers.

Simple and inexpensive micromachined aluminum microfluidic devices for acoustic focusing of particles and cells

We introduce a new method to construct microfluidic devices especially useful for bulk acoustic wave (BAW)-based manipulation of cells and microparticles. To obtain efficient acoustic focusing, BAW devices require materials that have high acoustic impedance mismatch relative to the medium in which the cells/microparticles are suspended and materials with a high-quality factor. To date, silicon and glass have been the materials of choice for BAW-based acoustofluidic channel fabrication. Silicon- and glass-based fabrication is typically performed in clean room facilities, generates hazardous waste, and can take several hours to complete the microfabrication. To address some of the drawbacks in fabricating conventional BAW devices, we explored a new approach by micromachining microfluidic channels in aluminum substrates. Additionally, we demonstrate plasma bonding of poly(dimethylsiloxane) (PDMS) onto micromachined aluminum substrates. Our goal was to achieve an approach that is both low cost and effective in BAW applications. To this end, we micromachined aluminum 6061 plates and enclosed the systems with a thin PDMS cover layer. These aluminum/PDMS hybrid microfluidic devices use inexpensive materials and are simply constructed outside a clean room environment. Moreover, these devices demonstrate effectiveness in BAW applications as demonstrated by efficient acoustic focusing of polystyrene microspheres, bovine red blood cells, and Jurkat cells and the generation of multiple focused streams in flow-through systems. Graphical abstract The aluminum acoustofluidic device and the generation of multinode focusing of particles.

Soils in the bipartite sediments within the Moscow glacial limits of the Russian Plain: Sedimentary environment, pedogenesis, paleolandscape implication

The basal tills of the Late Moscow (MIS 6) Cryochrone form an important component of landscapes in northern Europe, including the center of the Russian Plain. The till is often covered only with a thin cover layer (30–50 cm as an average) – veneers of sands, sandy loams or silty loams, so that surface soils (Retisols) are formed in the bipartite sediments. The study of such soils allows identifying a set of pre-depositional, syn-depositional and post-depositional (pedogenic and cryogenic) features. An assemblage of (macro, meso and micro) morphological features together with analytical data confirmed that soils had been formed within several climatic cycles starting from the Late Moscow time till now, including the last Thermochrone, when the well-developed Argic horizon had been formed. Modern pedogenesis forms embedded profiles within the cover layer depending on the bioclimatic parameters (with Humic, Protospodic or Cambic horizons). The clear record of the final stages of sedimentation and ancient pedogenesis within profiles of soils in bipartite sediments may help to derive paleoclimatic interpretations from the last interglacial - glacial cycle till present. Correlation of these records with other archives in glacial and periglacial areas opens attractive research perspectives.

High-field domains in CdS adjacent to a junction of p-type solar cells

A thin cover layer (150 Å preferred) of copper-doped CdS, when applied on top of any p-type solar cell, can connect this cell directly to an electron-blocking electrode without a pn-junction and increases the open circuit voltage close to its theoretical value; in the example of a CdS/CdTe cell, it increases Voc to its extrapolated value at T = 0 K of the band gap of 1.45 eV. This is caused by a high-field domain that is attached to the junction and limits the field to below tunneling to prevent junction leakage and connects to the CdS that has turned p-type. The large Debye length exceeding the thickness of the CdS forces a direct connection to the electron-blocking cathode with holes tunneling into the metal. The difference of junction-attached high-field domains to the electrode-attached domains, which were described earlier, are given and the consequences are delineated by increasing the conversion efficiency from 8% to 16% in CdTe, while also causing some series resistance limitation. The effect of the added CdS layer is discussed by drawing a to-scale model of the CdS/CdTe solar cell from all experimentally available data and the assumption of the continuity of the hole current. A small jump of the valence band downward is caused by interface recombination. The assistance of high-field domains in CdS is also exemplified by the results of an extremely simple production procedure of the CdS/Cu2S solar cells.

Electroplating and magnetostructural characterization of multisegmented Co54Ni46/Co85Ni15 nanowires from single electrochemical bath in anodic alumina templates.

Highly hexagonally ordered hard anodic aluminum oxide membranes, which have been modified by a thin cover layer of SiO2 deposited by atomic layer deposition method, were used as templates for the synthesis of electrodeposited magnetic Co-Ni nanowire arrays having diameters of around 180 to 200 nm and made of tens of segments with alternating compositions of Co54Ni46 and Co85Ni15. Each Co-Ni single segment has a mean length of around 290 nm for the Co54Ni46 alloy, whereas the length of the Co85Ni15 segments was around 430 nm. The composition and crystalline structure of each Co-Ni nanowire segment were determined by transmission electron microscopy and selected area electron diffraction techniques. The employed single-bath electrochemical nanowire growth method allows for tuning both the composition and crystalline structure of each individual Co-Ni segment. The room temperature magnetic behavior of the multisegmented Co-Ni nanowire arrays is also studied and correlated with their structural and morphological properties.

Broadband anomalous reflection based on gradient low-Q meta-surface

Gradient–index metamaterial is crucial in the spatial manipulation of electromagnetic wave. Here we present an efficient approach to extend the bandwidth of phase modulation by utilizing the broadband characteristic of low-quality (Q) meta-surface in the reflection mode. The dispersion of the meta-surface is engineered to compensate the phase difference induced by frequency change. Meanwhile, a thin gradient index cover layer is added on the top of meta-surface to extend the phase modulation range to cover the entire [0, 360°]. As a proof of concept, anomalous nearly perfect reflection with relative bandwidth near 40% is demonstrated in the microwave regime.

Pyramid array substrates for biomedical studies

Cellular reactions to structured surfaces are the subject of intense studies in biomedical research, e.g., for implant technology. Substrates with well-defined structures in relevant materials such as titanium (Ti) are required for these investigations. The pyramidal arrays presented here offer very sharp edges and tips, which appeared to be the main adhesion spots in our earlier cell-surface-interaction studies. Using an etch process based on anisotropic etching of silicon in alkaline solution, the shape of the pyramids is strictly determined by the crystal structure of silicon, while the height as well as the pitch of the pyramids can be precisely controlled and, therefore, be varied in a systematic fashion. Being made from silicon nitride with a thin cover layer of titanium, they offer mechanical stiffness, inertness to all chemicals used in the cell experiments, and a high degree of biocompatibility.

Composition depth profile analysis of electrodeposited alloys and metal multilayers: the reverse approach

The reverse depth profile analysis is a recently developed method for the study of a deposit composition profile in the near-substrate zone. The sample preparation technique enables one to separate the deposit and a thin cover layer from its substrate, and the initial roughness of the sample is much smaller than in the conventional sputtering direction. This technique is particularly suitable to study the zones being formed in the early phase of the electrodeposition of alloys. It has been demonstrated with the reverse depth profile analysis that in many cases when one component of an alloy is preferentially deposited, an initial zone is formed that is rich in the preferentially deposited component. This phenomenon is demonstrated for Ni–Cd, Ni–Sn, Fe–Co–Ni, Co–Ni, and Co–Ni–Cu alloys. The composition change is confined to the initial 150-nm-thick deposit, and it is the result of the interplay of the deposition preference and the depletion of the electrolyte near the cathode with respect to the ion reduced preferentially. The reverse depth profile analysis made it possible to compare the measured and the calculated composition depth profile of electrodeposited multilayers. It has been shown that the decay in the composition oscillation intensity in Co/Cu multilayers with the increase of the sputtering depth can be derived from the roughness measured as a function of the deposit thickness.

Electro-optic long-period waveguide gratings in lithium niobate

We report electro-optic (EO) long-period waveguide gratings (LPWGs) fabricated in a special lithium-niobate (LiNbO3) waveguide structure. The waveguide consists of a clad core formed with a two-step proton-exchange process and a thin cover layer created by an additional reverse proton-exchange process for the restoration of the EO strength of the waveguide. Using several LPWG samples, we demonstrate experimentally the effects of using different cladding modes and waveguide parameters on the grating performance. One of our 10-mm long samples shows a 27-dB rejection band at a driving voltage of 95 V with a center wavelength tunable thermally at a sensitivity of -0.4 nm/degrees C. Our analysis of the theoretical limit of the efficiency of such an EO grating suggests room for significant further improvement by optimizing the waveguide and electrode designs. The LiNbO(3) LPWG provides an EO control of the grating strength and a thermo-optic control of the operating wavelength and thus opens up many new opportunities for high-speed applications, such as dynamic optical filtering and optical intensity modulation.

Polymer Lab-on-a-Chip System With Electrical Detection

Two important challenges of the rapid development of microfluidic chip systems are addressed in this paper: 1) new polymer materials and technologies for chip preparation and 2) a label-free method for analyte detection in microchannels. One of the general pacemakers in lab-on-a-chip concepts, capillary electrophoresis (CE) in chip format, was used as workhorse for demonstration. CE chips were fabricated and characterized using polymers such as PMMA, polystyrene and polycarbonate, cycloolefine copolymer, and for the first time, the outstanding high-performance polymer polyether ether ketone (PEEK). Especially for one of the most critical steps in microchannel preparation, bonding of the cover layer to the microstructured substrate, an advanced plasma preconditioning process has been developed. An electrical detection method, capacitively coupled contactless conductivity measurement (CCD), was transferred to the chip level. A high signal-to-noise ratio was obtained by using sputtered thin-film electrodes. It was additionally improved by the very thin channel cover layer thickness, which could be easily obtained by polymer technology. CCD was used for analyte detection near the outlet of the CE separation channel. Further, to demonstrate generally the benefit of CCD for microfluidic flow control, measurement electrodes were positioned at the CE chip injection cross to monitor the reliability of the sophisticated injection processes. A completely miniaturized CE device (ldquoMinCErdquo), was developed for low cost application. Potential applications were demonstrated on selected typical examples: for in situ food analysis, the determination of saccharides in beverages, for medical point-of-care diagnostics, the quantitative determination of antidepressant lithium in blood serum, and for bio analytics, the detection of proteinogenic amino acids. Biological macro molecules-in particular, for life sciences fundamental DNA-have not been in focus of contactless conductivity measurements until now. However, it was possible for the first time to detect DNA highly sensitive by conductivity measurement. The extremely low detection limits achieved are competitive with laser induced fluorescence (LIF) in commercial CE-chip-devices and could provide a highly cost-efficient alternative.

Low-loss terahertz transmission through curved metallic slit waveguides fabricated by spark erosion

Propagation characteristics of broadband terahertz pulses in straight and curved metallic slit (MS) waveguides fabricated using spark erosion technique are investigated in the 0.1–1.0THz frequency range. As the straight MS waveguides, the curved MS waveguides, having radii of curvature as small as 5mm, exhibit comparably undistorted terahertz pulse transmission. The observed bending loss is unexpectedly low, giving rise to the assumption that surface oxidization and roughness generated by the fabrication process are responsible for the improved signal routing behavior. Experimental results are compared with theoretical data from numerical field simulations incorporating the influence of a thin dielectric cover layer.

Fabrication of Microchannel with Thin Cover Layer for an Optical Waveguide MEMS Switch Based on Microfluidics

SUMMARY We propose and demonstrate a new fabrication process of a microchannel using the Damascene process. This process aims to integrate photonic circuits with microchannels fabricated in a glass film. The microchannel is fabricated by the removal of the sacrificial layer after a sacrificial layer is formed by the Damascene process and the cover is formed by sputter deposition. A thin cover layer can be formed by the sacrificial method, because the cover layer is supported by the sacrificial layer during film formation. The cover layer is hermetically sealed, since it is formed by radio frequency (RF) sputtering deposition. The thickness is 1 µ ma nd the width ranges from 3.5 to 8 µm. Using the proposed microchannel fabrication method, we prepared a microelectromechanical system (MEMS) optical switch using microfluidics, and we confirmed its functional operation. This optical switch actuates a minute droplet of liquid injected into the microchannel using Maxwell’s stresses. Light propagates straight through the waveguide so that the light passes through the microchannel when the droplet is in the microchannel, but the light rays are completely reflected into a crossed waveguide when the droplet is not in the microchannel. Since this fabrication method uses techniques common to those in the formation

Experimental Study of High-Density Rewritable Optical Disk Using a Blue-Laser Diode

The read-write characteristics of an optical disk utilizing a blue-laser diode are examined, applying land and groove recording and partial response and maximum likelihood (PRML) to two optical disk systems: 1) 0.85 numerical aperture (NA) optical disk system consisting of an objective lens with NA of 0.85 and a thin cover layer on a disk with a thickness of 0.1 mm and 2) 0.65 NA optical disk system consisting of an objective lens with NA of 0.65 and a 0.6-mm-thick disk substrate. In the 0.85 NA optical disk system, the track pitch and the data bit length employed for the experiment are 0.29 µm and 0.0987 µm, respectively. These parameters correspond to a capacity of 30 GB/side. In the 0.65 NA optical disk system, they are 0.37 µm and 0.155 µm, respectively, corresponding to a capacity of 15 GB/side. A bottom channel bit error rate (ch.bER) of less than 5.0×10-5 can be obtained in these systems, and it is confirmed experimentally that the ch.bER remains below 1.0×10-4 up to 1000 cross-write cycles.