Effect of Plasmonic Ag Nanoparticles on Emission Properties of Planar GaN Nanowires.

The combination of plasmonic nanoparticles and semiconductor substrates changes the properties of hybrid structures that can be used for various applications in optoelectronics, photonics, and sensing. Structures formed by colloidal Ag nanoparticles (NPs) with a size of 60 nm and planar GaN nanowires (NWs) have been studied by optical spectroscopy. GaN NWs have been grown using selective-area metalorganic vapor phase epitaxy. A modification of the emission spectra of hybrid structures has been observed. In the vicinity of the Ag NPs, a new emission line appears at 3.36 eV. To explain the experimental results, a model considering the Fröhlich resonance approximation is suggested. The effective medium approach is used to describe the enhancement of emission features near the GaN band gap.

Fragmented graphene synthesized on a dielectric substrate for THz applications.

Fragmented multi-layered graphene films were directly synthesized via chemical vapor deposition (CVD) on dielectric substrates with a pre-deposited copper catalyst. We demonstrate that the thickness of the sacrificial copper film, process temperature, and growth time essentially influence the integrity, quality, and disorder of the synthesized graphene. Atomic force microscopy and Kelvin probe force microscopy measurements revealed the presence of nano-agglomerates and charge puddles. The potential gradients measured over the sample surface confirmed that the deposited graphene film possessed a multilayered structure, which was modelled as an ensemble of randomly oriented conductive prolate ellipsoids. THz time domain spectroscopy measurements gave theacconductivity of the graphene flakes and homogenized graphitic films as being around 1200 S cm-1and 1000 S cm-1, respectively. Our approach offers a scalable fabrication of graphene structures composed of graphene flakes, which have effective conductivity sufficient for a wide variety of THz applications.

Mechanical relaxation of functionalized carbosilane dendrimer melts.

Functionalizing the internal structure of classical dendrimers is a new way of tailoring their properties. Using atomistic molecular dynamics simulations, we investigate the rheological behavior of functionalized dendrimer (FD) melts obtained by modifying the branching of carbosilane dendrimers (CSD). The time (relaxation modulus G(t)) and frequency (storage G' and loss G'' moduli) dependencies of the dynamic modulus are obtained. Fourth generation FD melts present a region where G' > G''. In contrast, their non-functionalized counterparts (i.e., classical dendrimers with regular branching) do not show such a region. The comparative analysis of FD and CSD suggests that the internal densification due to functionalization prevents the penetration of branches and causes FD to behave like colloidal particles in a crowded environment. Since CSD have no special interactions, we expect that this effect will be common for other dendrimer macromolecules.

Dual-center co-doped and mixed ratiometric LuVO4:Nd3+/Yb3+nanothermometers.

During last decade luminescence thermometry has become a widely studied research field due to its potential applications for real time contactless temperature sensing where usual thermometers cannot be used. Special attention is paid to the development of accurate and reliable thermal sensors with simple reading. To address existing problems of ratiometric thermometers based on thermally-coupled levels, LuVO4:Nd3+/Yb3+thermal sensors were studied as a proof-of-concept of dual-center thermometer obtained by co-doping or mixture. Both approaches to create a dual-center sensor were compared in terms of energy transfer efficiency, relative sensitivity, and temperature resolution. Effect of excitation mechanism and Yb3+doping concentration on thermometric performances was also investigated. The best characteristics ofSr = 0.34% K-1@298 K and ΔT = 0.2 K were obtained for mixed phosphors upon host excitation.

Upconverting NIR-to-NIR LuVO4:Nd3+/Yb3+ Nanophosphors for High-Sensitivity Optical Thermometry.

Accurate contactless thermometry is required in many rapidly developing modern applications such as biomedicine, micro- and nanoelectronics, and integrated optics. Ratiometric luminescence thermal sensing attracts a lot of attention due to its robustness toward systematic errors. Herein, a phonon-assisted upconversion in LuVO4:Nd3+/Yb3+ nanophosphors was successfully applied for temperature measurements within the 323-873 K range via the luminescence intensity ratio technique. Dual-activating samples were obtained by codoping and mixing single-doped nanopowders. The effect of the type of dispersion system and the Yb3+ doping concentration was studied in terms of thermometric performances. The relative thermal sensitivity reached a value of 2.6% K-1, while the best temperature resolution was 0.2 K. The presented findings show the way to enhance the thermometric characteristics of contactless optical sensors.

Al3+ solvation in solutions of aluminum nitrate in a protic ionic liquid: Nuclear magnetic resonance verification of the solvation shell composition.

The closest environment of Al3+ cations was analyzed in detail in solutions of aluminum nitrate in the prototypical protic ionic liquid ethyl ammonium nitrate (EAN) using 1 H and 14 N nuclear magnetic resonance (NMR) spectra. For Al (NO3 )3 -EAN mixtures with different water content, a quantitative analysis of the integral intensities of the 1 H and 14 N signals was carried out and the composition of the first solvation shell of the aluminum cation was refined.

Effect of crystal structure on the Young's modulus of GaP nanowires.

Young's modulus of tapered mixed composition (zinc-blende with a high density of twins and wurtzite with a high density of stacking faults) gallium phosphide (GaP) nanowires (NWs) was investigated by atomic force microscopy. Experimental measurements were performed by obtaining bending profiles of as-grown inclined GaP NWs deformed by applying a constant force to a series of NW surface locations at various distances from the NW/substrate interface. Numerical modeling of experimental data on bending profiles was done by applying Euler-Bernoulli beam theory. Measurements of the nano-local stiffness at different distances from the NW/substrate interface revealed NWs with a non-ideal mechanical fixation at the NW/substrate interface. Analysis of the NWs with ideally fixed base resulted in experimentally measured Young's modulus of 155 ± 20 GPa for ZB NWs, and 157 ± 20 GPa for WZ NWs, respectively, which are in consistence with a theoretically predicted bulk value of 167 GPa. Thus, impacts of the crystal structure (WZ/ZB) and crystal defects on Young's modulus of GaP NWs were found to be negligible.

Modification Approaches to Enhance Dehydration Properties of Sodium Alginate-Based Pervaporation Membranes.

Transport characteristics of sodium alginate (SA) membranes cross-linked with CaCl2 and modified with fullerenol and fullerene derivative with L-arginine for pervaporation dehydration were improved applying various approaches, including the selection of a porous substrate for the creation of a thin selective SA-based layer, and the deposition of nano-sized polyelectrolyte (PEL) layers through the use of a layer-by-layer (Lbl) method. The impacts of commercial porous substrates made of polyacrylonitrile (PAN), regenerated cellulose, and aromatic polysulfone amide were investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), standard porosimetry method, and water filtration. The effects of PEL combinations (such as poly(sodium 4-styrene sulfonate) (PSS)/SA, PSS/chitosan, PSS/polyacrylic acid, PSS/poly(allylamine hydrochloride)) and the number of PEL bilayers deposited with the Lbl technique on the properties of the SA and SA/fullerene derivative membranes were studied by SEM, AFM, and contact angle measurements. The best characteristics were exhibited by a cross-linked PAN-supported SA/fullerenol (5%) membrane with five PSS/SA bilayers: permeation flux of 0.68-1.38 kg/(m2h), 0.18-1.55 kg/(m2h), and 0.50-1.15 kg/(m2h), and over 99.7, 99.0, and 89.0 wt.% water in the permeate for the pervaporation dehydration of isopropanol (12-70 wt.% water), ethanol (4-70 wt.% water), and tetrahydrofuran (5.7-70 wt.% water), respectively. It was demonstrated that the mutual application of bulk and surface modifications essentially improved the membrane's characteristics in pervaporation dehydration.

Gd3+-Doping Effect on Upconversion Emission of NaYF4: Yb3+, Er3+/Tm3+ Microparticles.

ß-NaYF4 microcrystals co-doped with Yb3+, Er3+/Tm3+, and Gd3+ ions were synthesized via a hydrothermal method using rare-earth chlorides as the precursors. The SEM and XRD data show that the doped ß-NaYF4 form uniform hexagonal prisms with an approximate size of 600-800 nm. The partial substitution of Y by Gd results in size reduction of microcrystals. Upconversion luminescence spectra of microcrystals upon 980 nm excitation contain characteristic intra-configurational ff bands of Er3+/Tm3+ ions. An addition of Gd3+ ions leads to a significant enhancement of upconversion luminescence intensity with maxima at 5 mol % of dopant.

Novel Mixed Matrix Sodium Alginate-Fullerenol Membranes: Development, Characterization, and Study in Pervaporation Dehydration of Isopropanol.

Novel mixed matrix dense and supported membranes based on biopolymer sodium alginate (SA) modified by fullerenol were developed. Two kinds of SA-fullerenol membranes were investigated: untreated and cross-linked by immersing the dry membranes in 1.25 wt % calcium chloride (CaCl2) in water for 10 min. The structural and physicochemical characteristics features of the SA-fullerenol composite were investigated by Fourier-transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopic methods, scanning electron (SEM) and atomic force (AFM) microscopies, thermogravimetric analysis (TGA), and swelling experiments. Transport properties were evaluated in pervaporation dehydration of isopropanol in a wide concentration range. It was found that the developed supported cross-linked SA-5/PANCaCl2 membrane (modified by 5 wt % fullerenol) possessed the best transport properties (the highest permeation fluxes 0.64-2.9 kg/(m2 h) and separation factors 26-73,326) for the pervaporation separation of the water-isopropanol mixture in the wide concentration range (12-90 wt % water) at 22 °C and is suitable for the promising application in industry.

Construction of efficient dual activating ratiometric YVO4:Nd3+/Eu3+ nanothermometers using co-doped and mixed phosphors.

The development of new contactless thermal nanosensors based on a ratiometric approach is of significant interest. To overcome the intrinsic limitations of thermally coupled levels, a dual activation strategy was applied. Dual activation was performed using co-doped single nanoparticles and a binary mixture of single-doped nanoparticles. Co-doped and mixed YVO4:Nd3+/Eu3+ nanoparticles were successfully demonstrated as luminescent nanothermometers and their thermometric performance, in terms of thermal sensitivity, temperature resolution and repeatability, was studied and compared.

Local dynamics in LiCl-CsCl-D2O water-in-salt solutions according to NMR relaxation.

The main purpose of this study was to investigate the local structure and dynamics in 'water-in-salt' solutions, namely the ternary concentrated LiCl-CsCl-D2O electrolytes. Water based electrolyte solutions are components of natural waters, they are very widespread and possess many practical abilities. NMR was applied as the main technique to study the local structure of the solutions as well as ion and solvent dynamics. The characteristic reorientation times (τc) were calculated from spin-lattice relaxation times for 2H, 7Li, and 133Cs nuclei. The diffusion coefficients (D) for 1H, 7Li, and 133Cs nuclei were also obtained. We have confirmed that most of the molecules and ions are combined into dynamic clusters, 'cybotactic groups', with lifetimes long enough for them to diffuse as a whole unit. Thus, the results provide direct experimental confirmation of the existence of 'cybotactic groups' predicted earlier for concentrated electrolyte solutions. The precise self-diffusion coefficients show the state of ions in the system and can be used as a reference for modelling of such systems.

Stable Deuterium Labeling of Histidine-Rich Lysine-Based Dendrimers.

Peptide dendrimers, due to their biocompatibility and low toxicity, are highly promising candidates as nanocarriers for drugs and genes. The development of this kind of delivery system requires reliable monitoring of their metabolic and biological pathways. In this respect, hydrogen isotope labeling has tremendous importance, being a safe tool for detection of the labeled nanocarriers. In this work, we have synthesized new histidine-rich lysine-based dendrimers (Lys-2His dendrimer) with two linear histidine (His) residues in every inner segment. The presence of His residues has enabled us to perform controlled deuteration of Lys-2His dendrimers. The high deuteration degree (around 70%) does not practically change after redissolving the samples in H2O and heating them at 40 °C, which indicates the isotopic label stability.

Lysine-based dendrimer with double arginine residues.

Due to their well-defined structure, multivalency, biocompatibility, and low toxicity, lysine dendrimers can be used as safe and efficient nanocarriers for drug and gene delivery. One useful strategy for improving the gene delivery properties of dendrimers is modification with arginine amino acid (Arg) residues. Incorporation of Arg residues could be favorable for the enhancement in transfection efficiency of lysine based dendrimers. In this work, we have synthesized a new second-generation poly-l-lysine dendrimer with repeating units containing two linear Arg residues between neighboring lysine branching points (Lys-2Arg dendrimer) and studied its physicochemical properties. We confirmed the structure of Lys-2Arg dendrimer using various one- and two-dimensional 1H and 13C NMR spectroscopy methods. Comparison of T 1H relaxation data for Lys-2Arg and Lys-2Lys dendrimers showed that the replacement of double Lys residues with double Arg residues resulted in a sharp decrease in the mobility of methylene groups in side segments and in the main chain of ε-Lys inner segments. We suggest that this unexpected effect is caused by a guanidine-guanidine pairing effect in water, which leads to entanglements between dendrimer branches.

Magnetotransport and conductivity mechanisms in Cu2ZnSnxGe1-xS4 single crystals.

Resistivity, ρ(T), and magnetoresistance (MR) are investigated in the Cu2ZnSnxGe1-xS4 single crystals, obtained by the chemical vapor transport method, between x = 0-0.70, in the temperature range of T ~ 50-300 K in pulsed magnetic field of B up to 20 T. The Mott variable-range hopping (VRH) conductivity is observed within broad temperature intervals, lying inside that of T ~ 80-180 K for different x. The nearest-neighbor hopping conductivity and the charge transfer, connected to activation of holes into the delocalized states of the acceptor band, are identified above and below the Mott VRH conduction domain, respectively. The microscopic electronic parameters, including width of the acceptor band, the localization radius and the density of the localized states at the Fermi level, as well as the acceptor concentration and the critical concentration of the metal-insulator transition, are obtained with the analysis of the ρ(T) and MR data. All the parameters above exhibit extremums near x = 0.13, which are attributable mainly to the transition from the stannite crystal structure at x = 0 to the kesterite-like structure near x = 0.13. The detailed analysis of the activation energy in the low-temperature interval permitted estimations of contributions from different crystal phases of the border compounds into the alloy structure at different compositions.

High-temperature magnetism and microstructure of a semiconducting ferromagnetic (GaSb)1-x (MnSb) x alloy.

We have studied the properties of relatively thick (about 120 nm) magnetic composite films grown by pulsed laser deposition using the eutectic compound (GaSb)0.59(MnSb)0.41 as target for sputtering. For the studied films we have observed ferromagnetism and an anomalous Hall effect above room temperature, confirming the presence of spin-polarized carriers. Electron microscopy, atomic and magnetic force microscopy results suggest that the films under study have a homogenous columnar structure in the bulk while MnSb inclusions accumulate near the surface. This is in good agreement with the high mobility values of charge carriers. Based on our data we conclude that the magnetic and magnetotransport properties of the films at room temperature are defined by the MnSb inclusions.

Plasticizing of chitosan films with deep eutectic mixture of malonic acid and choline chloride.

Chitosan (CS) films containing deep eutectic solvent (DES) based on malonic acid (MA) and choline chloride (ChCl) were successfully prepared by solution casting method by using DES content ranging from 0 to 82 wt%. A strong interaction of CS with the components of DES was demonstrated by analyses of water sorption isotherms, atomic force microscopy and FTIR results. The plasticizing effect of the MA and ChCl mixture on the CS matrix was shown by static bulk mechanical measurements, thermal analysis and quantitative nanomechanical mapping (QNM). Elongation at break increased from 3 to 62% at increase of DES content from 0 to 67 wt%, while further increase of DES content led to the decreasing of maximal elongation. Introduction of DES into CS films led to the appearance of glass transition temperature in the region +2 - -2.3 °C. QNM results indicated homogeneity of the films containing up to 75 wt% of DES.

NMR studies of excluded volume interactions in peptide dendrimers.

Peptide dendrimers are good candidates for diverse biomedical applications due to their biocompatibility and low toxicity. The local orientational mobility of groups with different radial localization inside dendrimers is important characteristic for drug and gene delivery, synthesis of nanoparticles, and other specific purposes. In this paper we focus on the validation of two theoretical assumptions for dendrimers: (i) independence of NMR relaxations on excluded volume effects and (ii) similarity of mobilities of side and terminal segments of dendrimers. For this purpose we study 1H NMR spin-lattice relaxation time, T1H, of two similar peptide dendrimers of the second generation, with and without side fragments in their inner segments. Temperature dependences of 1/T1H in the temperature range from 283 to 343 K were measured for inner and terminal groups of the dendrimers dissolved in deuterated water. We have shown that the 1/T1H temperature dependences of inner groups for both dendrimers (with and without side fragments) practically coincide despite different densities of atoms inside these dendrimers. This result confirms the first theoretical assumption. The second assumption is confirmed by the 1/T1H temperature dependences of terminal groups which are similar for both dendrimers.

Effect of Domain Structure of Segmented Poly(urethane-imide) Membranes with Polycaprolactone Soft Blocks on Dehydration of n-Propanol via Pervaporation.

Segmented poly(urethane-imide)s (PUIs) were synthesized by polyaddition reaction and applied for preparation of membranes. Tolylene-2,4-diisocyanate, pyromellitic dianhydride, and m-phenylenediamine for chain extension were used to form hard aromatic blocks. Polycaprolactone diols with molecular weights equal to 530 and 2000 g mol-1 were chosen as soft segments. The effect of the length of soft segments on the structure, morphology, and transport properties of segmented poly(urethane-imide) membranes were studied using atomic force microscopy, small-angle and wide-angle X-ray scattering, and pervaporation experiments. It was found that a copolymer with a shorter soft segment (530 g mol-1) consists of soft domains in a hard matrix, while the introduction of polycaprolactone blocks with higher molecular weight (2000 g mol-1) leads to the formation of hard domains in a soft matrix. Additionally, the introduction of hard segments prevents crystallization of polycaprolactone. Transport properties of membranes based on segmented PUIs containing soft segments of different length were tested for pervaporation of a model mixture of propanol/water with 20 wt % H2O content. It was found that a membrane based on segmented PUIs containing longer soft segments demonstrates higher flux (8.8 kg µm m-2 h-1) and selectivity (179) toward water in comparison with results for pure polycaprolactone reported in literature. The membrane based on segmented PUIs with 530 g mol-1 soft segment has a lower flux (5.1 kg µm m-2 h-1) and higher selectivity (437).

Molecular mobility in several imidazolium-based ionic liquids according to data of 1 H and 13 C NMR relaxation.

Temperature dependences are compared for 1 H and 13 C NMR 1/T1 curves relaxation rates in three imidazolium-based ionic liquids (ILs), namely, in [bmim]PF6 , [bmim]BF4 , and [emim]CH3 COO. 13 C curves show alike behavior for all three ILs and follow a well-known Bloembergen-Pound-Purcell (BPP) equation. On the contrary, an essential part of 1 H curves differ strongly from corresponding 13 C ones and also have different shapes for different ILs. For the first time, we have detected the specific, two-maximum shape of 1 H relaxation curve for hydrogen atom of C(2)H group of the [emim]CH3 COO. Assuming that this maximum reflects the correlated rotation of several adjoining ion pairs, we have tried to destroy this rotation by addition of glycerol to the [emim]CH3 COO. The second, high-temperature maximum has disappeared in the [emim]CH3 COO-glycerol mixture, and this fact confirms our assumption. Copyright © 2017 John Wiley & Sons, Ltd.