Bimetallic Silver-Gold Film Waveguide Surface Plasmon Resonance Sensor

It is desirable that a surface plasmon resonance (SPR) sensor is highly sensitive to binding interactions within the sensing region, generate evanescent fields with long penetration depths, and utilize a metal film that is very stable even in extreme environmental conditions. In this study, we present the first example of a wavelength-modulated waveguide SPR sensor with a bimetallic silver-gold film for surface plasmon excitation. The underlying silver yields better evanescent field enhancement of the sensing surface, while the overlying gold ensures that the stability of the metallic film is not compromised. It is shown experimentally that in terms of dλ/dn, the bimetallic film waveguide SPR configuration has a sensitivity of 1232 nm/RIU, greater than two times improvement from the 594 nm/RIU achievable with single gold film waveguide SPR sensor. The higher sensitivity, compact nature, and better evanescent field enhancement of this configuration provides the potential to biosensing applications.     

The effect of residual fibres on the micro-topography of cellulose nanopaper

Nanopaper is a new material concept composed of nanocellulose, which has been proposed for a series of applications. Recently, the surface of nanopapers has also been emphasized as an important structure to control. This is due to the potential of nanopaper structures as a substrate for printing functionality, which could expand the applicability of nanopaper as a functionalized biomaterial. In this study, we demonstrate how the roughness of nanopaper is affected by the fraction of residual fibres that were not fibrillated into nanofibrils after a homogenization procedure. The topography and morphology were assessed with laser profilometry, atomic force microscopy and scanning (transmission) electron microscopy. The results show a linear correlation between the estimated fraction of residual fibres and the roughness of the assessed nanopapers. Furthermore, the fraction of residual fibres can be reduced by fractionating the nanocellulose, which is demonstrated in the present work. Such knowledge will be valuable for designing nanopaper surfaces with specific structural characteristics.     

Fluorine, chlorine and iodine adsorption on the Ge(0 0 1) surface: Comparative study for the coverage of 0.75 and 1 monolayer

Theoretical study of the adsorption of 0.75 and 1 monolayer of F, Cl, and I on the Ge(0 0 1)-p(1×2) surface is presented. Various stable atomic configurations are considered, their surface electronic properties are discussed by means of the density-of-states analysis, and the corresponding STM images are simulated. While the results obtained for Cl and I are similar to those known for Br, the F-covered surfaces exhibit noticeably different features.     

响应曲面法提取水松总黄酮的工艺研究

采用响应曲面法,优化了提取水松总黄酮的提取工艺条件为:微波时间3.8min,乙醇浓度69%,固液比1∶31,在此条件下,水松总黄酮的产率为1.88%。     

Simple laser vision sensor calibration for surface profiling applications

Due to the relatively large structures in the Oil and Gas industry, original equipment manufacturers (OEMs) have been implementing custom-designed laser vision sensor (LVS) surface profiling systems as part of quality control in their manufacturing processes. The rough manufacturing environment and the continuous movement and misalignment of these custom-designed tools adversely affect the accuracy of laser-based vision surface profiling applications. Accordingly, Oil and Gas businesses have been raising the demand from the OEMs to implement practical and robust LVS calibration techniques prior to running any visual inspections. This effort introduces an LVS calibration technique representing a simplified version of two known calibration techniques, which are commonly implemented to obtain a calibrated LVS system for surface profiling applications. Both calibration techniques are implemented virtually and experimentally to scan simulated and three-dimensional (3D) printed features of known profiles, respectively. Scanned data is transformed from the camera frame to points in the world coordinate system and compared with the input profiles to validate the introduced calibration technique capability against the more complex approach and preliminarily assess the measurement technique for weld profiling applications. Moreover, the sensitivity to stand-off distances is analyzed to illustrate the practicality of the presented technique.     

On the photon-drag effect of photocurrent of surface states of topological insulators

The photocurrent of surface states of topological insulator due to photon-drag effect is computed, being based on pure Dirac model of surface states. The scattering by disorder is taken into account to provide a relaxation mechanism for the photocurrent. The Keldysh–Schwinger formalism has been employed for the systematic calculation of photocurrent. The helicity dependent photocurrent of sizable magnitude transverse to the in-plane photon momentum is found, which is consistent with experimental data. Other helicity independent photocurrents with various polarization states are also calculated.     

Theoretical study of surface plasmons coupling in transition metallic alloy 2D binary grating

The excitation of a surface plasmon polariton (SPP) wave on a metal–air interface by a 2D diffraction grating is numerically investigated. The grating consists of homogeneous alloys of two metals of a formula A_xB_1−x, or three metals of a formula A_xB_yC_z, where A, B and C could be silver (Ag), copper (Cu), gold (Au) or aluminum (Al).It is observed that all the alloys of two metals present a very small change of surface plasmon resonance (SPR) irrespective of composition x. Moreover, the addition of 25% of Al to two metals alloy is insufficient to change the SPR curves. The influence of the different grating parameters is discussed in details using rigorous coupled-wave analysis (RCWA) method. Furthermore, the SPR is highly dependent on grating periods (d_x and d_y) and the height of the grating h. The results reveal that d_x= d_y= 700 nm, h=40 nm and duty cycle w=0.5 are the optimal parameters for exciting SPP.     

Controllable growth and characterizations of hybrid spiral-like atomically thin molybdenum disulfide

Monolayer MoS₂ is an emerging two-dimensional semiconductor with wide-ranging potential applications in novel electronic and optoelectronic devices. Here, we reported controlled vapor phase growth of hybrid spiral-like MoS₂ crystals investigated by multiple means of X-Ray photoemission spectroscopy, scanning electron microscopy, atomic force microscopy, kelvin probe force microscopy, Raman and Photoluminescence techniques. Morphological characterizations reveal an intriguing hybrid spiral-like MoS₂ feature whose lower planes are AB Bernal stacking and upper structure is spiral. We ascribe the hybrid spiral-like structure to a screw dislocation drive growth mechanism owing to lower supersaturation and layer-by-layer growth mode. In addition, the electrostatic properties of MoS₂ microflakes with hybrid spiral structures are obvious inhomogeneous and dependent on morphology manifested by kelvin probe force microscopy. Our work deepens the understanding of growth mechanisms of CVD-grown MoS₂, which is also adoptable to other TMDC materials.     

Gain-assisted indented plasmonic waveguide for low-threshold nanolaser applications

A subwavelength plasmonic indented waveguide with an active InGaAsP core is proposed.The characteristics of the gap plasmon mode and gain required for lossless propagation are investigated and analyzed by the finite element method.We numerically calculate the normalized mode areas and percentages of energy confined in InGaAsP and metal for plasmonic nanolaser applications.It is shown that the indentation of the sidewalls has an optimal value for which the lasing threshold gain is minimal.The structure could enable low-threshold subwavelength lasing and applications for optoelectronic integrated circuits.     

Simultaneous determination of cation exchange capacity and surface area of acid activated bentonite powders by methylene blue sorption

To distinguish the ion exchanged and physically adsorbed methylene blue cations (MB⁺) on ionic surfaces, acid activated bentonite samples were used as porous adsorbents. A natural calcium bentonite (CaB) sample from Enez/Edirne, Turkey, was acid activated at 90 °C for 16 h with various HCl/CaB ratios. The irreversible exchange and physical adsorption of MB⁺ cations on the ionic solids have simultaneously occurred. The ion exchanged (m_ex) and physically adsorbed (m_ad) MB⁺ contents were obtained as the values of sorption capacity at c = 0 and the increase to a plateaus of adsorption isotherms, respectively. The m_ad value was taken to be monolayer adsorption capacity. Cation exchange capacity (CEC) and specific surface area (S_MB) for each sample were calculated from the m_ex and m_ad values, respectively. Also, the BET specific surface areas (S_BET) and pore size distribution were determined from low temperature nitrogen adsorption/desorption data. A linear correlation between the S_MB and S_BET values was found.