Investigations of Droplet‐Plasma Interaction using Multi‐Dimensional Coupled Model

Recently developed multi‐dimensional coupled fluid‐droplet model is used to investigate the behavior of complex interaction between the liquid precursor droplets and atmospheric pressure plasma (APP). The significance of this droplet‐plasma interaction is not well understood under diverse realm of working conditions in two‐phase flow. In this study, we explain the implication of vaporization of liquid droplets in APP which are subsequently responsible to control major characteristics of surface coating depositions. Coalescence of water droplets is more dominant than Hexamethyldisiloxane (HMDSO) droplets because of its sluggish rate of evaporation. A disparity in the performance of evaporation is identified in two independent mediums, such as gas mixture and discharge plasma using HMDSO precursor. The length of evaporation of droplets is amplified by an increment of gas flow rate indicating with a reduction in the gas temperature and electron mean energy. In particular, the spatio‐temporal density distributions of charged particles show a clear pattern in which the typical nitrogen impurity ions are primarily effective as compared to other helium ionic species along the pulse of droplets in APP. Finally, we contrast the behavior of discharge species in the pure helium and He‐N2 gas mixtures revealing the importance of stepwise and Penning ionization processes. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Two‐dimensional correlation Raman spectroscopy for characterizing protein structure and dynamics

Since the initial introduction of the basic concept almost twenty years ago, two‐dimensional correlation spectroscopy (2DCoS) has become a popular analytical tool applicable to a broad range of science problems. Vibrational spectroscopy remains the major area of 2DCoS applications where infrared spectroscopy is the most popular technique followed by Raman and Near Infrared spectroscopies. An increasing number of publications over the past few years have established Raman 2DCoS as a powerful problem solving technique in protein studies. In this review we provide a critical survey of recent protein studies using the 2DCoS Raman approach. We also analyze common misconceptions and potential pitfalls in the interpretation of 2D correlation data. Over the past decade, there have been a number of publications pointing to artifacts associated with visualization and interpretation of 2D correlation maps. We demonstrate here how some of the ‘artifacts’ of the 2DCoS approach in ‐ reality turn into the strength of the method. Copyright © 2009 John Wiley & Sons, Ltd.     

Two‐dimensional stimulated ultraviolet resonance Raman spectra of tyrosine and tryptophan: a simulation study

We report an ab initio simulation study of the ultrafast broad bandwidth ultraviolet stimulated resonance Raman spectra (SRRS) of l ‐tyrosine, l ‐tryptophan, and trans‐l ‐tryptophan‐l ‐tyrosine (WY) dipeptide. Two‐pulse one‐dimensional SRRS and three‐pulse two‐dimensional SRRS that reveal inter‐residue and intra‐residue vibrational correlations are simulated using electronically resonant or pre‐resonant pulse configurations that select the Raman signal and discriminate against excited state pathways. Multimode effects are incorporated via the cumulant expansion. The two‐dimensional SRRS technique is more sensitive to residue couplings than spontaneous Raman. Copyright © 2013 John Wiley & Sons, Ltd.     

Low‐temperature photoluminescence of oxide‐covered single‐layer MoS2

We present a photoluminescence study of single‐layer MoS₂ flakes on SiO₂ surfaces. We demonstrate that the luminescence peak position of flakes prepared from natural MoS₂, which varies by up to 25 meV between individual flakes, can be homogenized by annealing in vacuum. We use HfO₂ and Al₂O₃ layers prepared by atomic layer deposition to cover some of our flakes. In these flakes, we observe a suppression of the low‐energy luminescence peak which appears in asprepared flakes at low temperatures. We infer that this peak originates from excitons bound to surface adsorbates. We also observe different temperature‐induced shifts of the luminescence peaks for the oxide‐covered flakes. This effect stems from the different thermal expansion coefficients of the oxide layers and the MoS₂ flakes. It indicates that the single‐layer MoS₂ flakes strongly adhere to the oxide layers and are therefore strained. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Mobility Enhancement of P3HT‐Based OTFTs upon Blending with Au Nanorods

The mobility enhancement of organic thin‐film transistors based on poly(3‐hexylthiophene) (P3HT) by incorporating gold nanorods (Au NRs) is reported. Through varying the doping concentration and surface modifier of the Au NRs in P3HT matrix, the P3HT/Au composite with 0.5 mg mL^?1 pyridine‐capped Au NRs exhibits a hole mobility of 0.059 cm² V^?1 s^?1, this value is seven times higher than that of pristine P3HT. This remarkable improvement of mobility originates from the enhanced crystallinity and optimized orientation of P3HT after doping with Au NRs. In addition, the appropriate surface modification can produce more‐efficient hole conduction of Au NRs.     

Spin–orbit stiffness of the spin‐polarized electron gas

In a spin‐polarized electron gas, Coulomb interaction couples the spin and motion degrees of freedom to build propagating spin waves. The spin wave stiffness S_sw quantifies the energy cost to trigger such excitation by perturbing the kinetic energy of the electron gas (i.e. putting it in motion). Here we introduce the concept of spin–orbit stiffness, S_so, as the energy necessary to excite a spin wave with a spin polarization induced by spin–orbit coupling. This quantity governs the Coulombic enhancement of the spin–orbit field acting of the spin wave. First‐principles calculations and electronic Raman scattering experiments carried out on a model spin‐polarized electron gas, embedded in a CdMnTe quantum well, demonstrate that S_so = S_sw. Through optical gating of the structure, we demonstrate the reproducible tuning of S_so by a factor of 3, highlighting the great potential of spin–orbit control of spin waves in view of spintronics applications. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Resonant two‐magnon Raman scattering in high‐Tc cuprates

Resonance enhancement of one‐phonon, two‐phonon, and two‐magnon Raman scattering in a general, exactly solvable, multiband model is explained in a way that is in accordance with the general analytical properties of the total optical conductivity tensor. Using this approach, the charge‐transfer limit of the Emery three‐band model is examined to explain resonance enhancement of the two‐magnon Raman spectra of high‐T_c cuprates, which is found in experiments to be of 3 orders of magnitude. While previous Raman and optical conductivity analyzes of the cuprates, based on the single‐band Hubbard model, are found to be consistent with the picture where one hole per one CuO₂ unit is localized on the Cu ion, the present three‐band approach allows the study of the opposite, strong copper‐oxygen hybridization limit, which is found to be in agreement with the results of nuclear magnetic resonance (NMR) and one‐phonon Raman scattering experiments. Copyright © 2010 John Wiley & Sons, Ltd.     

Surface Plasmon Mediated Controllable Spin‐Resolved Transmission in Meta‐Hole Structures

Chiral responses are optical responses involving circular polarizations. Controlling the chiral response in a flexible way is very important in optical manipulations. Chiral metamaterials have thus drawn enormous interest due to their flexible designing feature. However, most of the previous studies are mainly realized by designing the structure of the individual meta‐atom. Meanwhile, to enhance the response, complex design and fabrication processes are typically required. Here, by introducing spin‐dependent propagating surface plasmons and spin‐selective interference, giant spin‐resolved transmission is achieved in a simple meta‐hole structure. In this interaction process, spin‐orbital angular momentum conversion plays an essential role. By controlling the phase difference between the interference components, controllable spin‐resolved transmission is achieved. Furthermore, such method can also be applied to realize spin‐resolved excitation of surface plasmons. The proposed controlling strategy offers a versatile platform for a variety of promising applications, such as polarization control, asymmetric transmission, surface plasmon excitation, and on‐chip chiral manipulation.     

Inter‐ and intramolecular hydrogen bonds in polyamines: variable‐concentration 1H‐NMR studies

Inter‐ and intramolecular hydrogen bonding play an important role in determining the arrangement, physical properties, and reactivity of a great diversity of structures in chemical and biological systems. Several aromatic nucleophilic substitutions (ANS) in nonpolar aprotic, (non‐HBD), solvents recently studied in our laboratory have demonstrated the importance of self‐association of amines by hydrogen‐bond interactions. In this paper, we describe ¹H‐NMR studies carried out at room temperature on bi‐ and polyfunctionalized amines, namely: N‐(3‐amino‐1‐propyl)morpholine (3‐APMo), histamine, 2‐guanidinobenzimidazole (2‐GB), 1,2‐diaminoethane (EDA), 3‐dimethylamino‐l‐propylamine (DMPA), and 1‐(2‐aminoethyl)piperidine (2‐AEPip). By ¹H‐NMR measurements of amine solutions at variable concentrations we have shown that 3‐APMo, histamine and 2‐GB are able to form a six‐membered ring by intramolecular hydrogen bonding, while EDA, DMPA, and 2‐AEPip form dimers by intermolecular hydrogen bonds. Likewise, variable concentration ¹H‐NMR studies allowed estimation of the corresponding equilibrium constants for the dimerization. These results are correlated with experimental kinetic results of ANS, confirming hereto the relevance of the “dimer mechanism” in reactions involving these amines. Copyright © 2011 John Wiley & Sons, Ltd.