Changes In Surface State Research Articles

A Fully Integrated Flexible Tunable Chemical Sensor Based on Gold-Modified Indium Selenide Nanosheets.

In this work, a novel light-modulated bifunctional gas sensor based on Au nanoparticles-modified 2D InSe nanosheets was demonstrated. The prepared sensor displayed a reversible and extremely high response for recognition of nitrogen dioxide (NO2) under visible-light illumination. The sensitivity (1192%) was about 10 times higher than that under dark condition, and the limit of detection (LOD) was 0.17 ppb. In contrast, when sensing ammonia (NH3), higher sensitivity and selectivity were obtained in darkness rather than in light, with sensitivity and LOD of 11% and 0.2 ppm. Furthermore, the sensor possesses decent stability, repeatability, and anti-interference ability. The tunable sensing behavior with light modulation has been clearly studied with the help of density functional theory. A new principle called "carrier storage box" of Au nanoparticles was proposed to explain the change in surface state of InSe under light modulation. Finally, the prepared sensor has been successfully applied to construct a fully integrated wearable device to measure NH3 and NO2 in ambient environment. In all, this work provides a highly competitive gas detection method and paves the way for designing 2D materials-based optoelectronic devices with tunable and multifunctional features.

Using Granulate Composites with Calcined Phosphogypsum and Pet Additive in Asphalting

The paper discusses the change of phosphogypsum surface state produced by Apatit (Cherepovetsky branch, Vologda region) during calcination at 298-1173 K. The authors have determined the average size of its crystallites and studied the atomic composition of raw materials and finished composites that include crushed rock fraction (5-10 mm), oil bitumen, and polyethylene terephthalate additive (1.0-1.2 wt. %). The compounds present in calcined phosphogypsum have been analyzed by X-ray diffraction. The granulate was obtained by pelletizing phosphogypsum with a mixture of the above components. The paper presents the assessment of its physical and chemical properties. The granulated composites based on the specified samples of calcined phosphogypsum, bitumen, and melted polyethylene terephthalate waste show great promise for construction road works in European countries in summer and winter, as well as countries with tropical climates.

Discriminative intracellular and extracellular ATP detection based on magnetically controlled antimicrobial peptide

Extracellular free adenosine triphosphate (ATP) is often encountered as an interferent in the detection of intracellular ATP, especially in biofilm systems. To resolve this problem, in this study, a novel impedimetric aptasensor was designed for the discriminative detection of intracellular and extracellular ATP using antimicrobial peptide-functionalized magnetic particles (M-AMPs). Successive fabrication of reduced graphene sheets (rGSs) and gold nano-clusters (Au NCs) on a glassy carbon electrode was conducted by simple electrodeposition methods to achieve improved detection sensitivity. Single-stranded aptamers were attached to the surface of Au NCs for selective ATP binding, and electrochemical impedance spectroscopy was conducted to analyze the change of surface state induced by ATP binding. For discriminative intracellular and extracellular ATP detection, magnetically controlled M-AMPs were introduced into the detection system for mild and rapid bacterial disintegration. In bacterial samples, the M-AMPs were firstly constrained by a magnetic field, and extracellular ATP was selectively bound to the prepared aptasensor, leading to increased impedance response. Thereafter, the magnetic field was shut down to liberate the M-AMPs for cell disruption, and the released intracellular ATP was determined by the further impedance increasement. The results demonstrated that the proposed aptasensor exhibited excellent sensitivity and selectivity, with a wide linear range from 1 nM to 100 nM and a detection limit of 0.65 nM. Remarkably, this electrochemical aptasensor provided a convenient and label-free approach for discriminative intracellular and extracellular ATP detection, and the detection reliability was verified in various bacterial samples and E. coli biofilms.

Simultaneous increase in electrical conductivity and fatigue strength of Cu-Ni-Si alloy by utilizing discontinuous precipitates

Cu-6Ni-1.5Si alloy having fully fiber-shaped discontinuous precipitates was fabricated by overaging (DP specimen), and subsequently cold-rolled down to 80% reduction in area (CR-DP specimen). The tensile and fatigue strengths of DP and CR-DP specimens were compared to those of CP specimen with nano-sized continuous precipitates by normal aging. The CR-DP specimen showed the highest tensile and fatigue strengths among the specimens tested, and comparable electrical conductivity to the DP specimen. The reason for such an excellent combination of tensile strength, fatigue strength and electrical conductivity was discussed based on the change in microstructure and surface states during stressing.

Construction of a novel photoelectrochemical sensor for detecting trace amount of copper (II) ion

A photoelectrochemical (PEC) sensor for determination of copper (II) ion has been developed. The indium tin oxide (ITO) electrode modified by ZnS quantum dots (QDs) was used as working electrode and dopamine (DA) as detection solution. When different amounts of Cu2+ were added, the polydopamine-copper (II) complex (PDA-Cu (II)) was in suit formed and attached tightly to the surface of ITO electrode based on the interaction between copper (II) and dopamine (DA) under weakly alkaline (pH 8.00) solution. The detection of Cu2+ was achieved by means of the decreasing photocurrent. The linear range of 1 - 1000 pM and sensitivity of 0.45 pM were obtained. In addition, the formation of PDA-Cu (II) was characterized by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). Thus, a PEC sensor based on the change of electrode surface state can realize the sensitive detection of Cu2+.

Temperature-dependence on the optical properties of chitosan carbon dots in the solid state.

We report the synthesis of chitosan-derived aminated carbon dots with dual fluorescence bands and their influence on the morphology, absorption and emission spectral profiles as well as on the band gap energy in relation to thermal treatment after synthesis. To unravel these changes, we performed spectroscopic measurements in the solid state on two stages at temperatures ranging from 303 to 453 K. For the first heating stage, the emission spectrum showed a 20 nm red shift and a new absorption band at 350 nm, possibly related to new bonds and/or nitrogenous molecular fractions. For the second heating stage in the same temperature range, no displacements in the emission spectrum were observed and both the energy gap and bandwidths for the two emission bands are practically constant, indicating a change nitrogen moiety exposed on the surface. Furthermore, through atomic force microscopy it was noted that the morphology and size of the CDs were not significantly affected by the increase in temperature. It is noteworthy that the values of the Huang–Rhys factor, respectively, 2.584 × 10−10 and 2.315 × 10−9 for band I and II emission after the second heating indicate a mechanism of weak electron–phonon interactions. This work may open a novel perspective for the development of new surface modulation strategies for carbon dots subjected to thermal treatment in the solid state.

Получение атомарно-чистых и структурно-упорядоченных поверхностей эпитаксиальных пленок CdTe для последующей эпитаксии

In this work, atomically clean and structurally ordered surface of CdTe epitaxial layer after storage in air by treatment in isopropyl alcohol saturated with vapors of hydrochloric acid, and further temperature heating in an ultrahigh vacuum, was obtained. CdTe surface chemical treatment results in the removal of native oxides and surface enrichment with elemental tellurium. Heating in vacuum leads to the tellurium desorption and the appearance of a Te-stabilized CdTe surface. During heating in vacuum, two stages of surface state change are observed (~125°С and ≤250°С). At Т>250°С, elemental tellurium is desorbed and a Te-stabilized structure (1x1) CdTe(013) is formed.

Na+-functionalized carbon dots with aggregation-induced and enhanced cyan emission

A new type of carbon dots that emit blue emission in aqueous state while cyan emission in solid state was synthesized by a simple hydrothermal method. The photoluminescence quantum yield of the carbon dots in aqueous state and solid state is 7.6% and 29.2%, respectively. The enhanced and red-shifted emission observed in solid state carbon dots is ascribed to surface state change caused by aggregation. The occurrence of surface state change in solid state carbon dots has been evidenced by concentration dependent steady-state photoluminecence spectra and time-resolved luminescence decay. Surface functionalization by Na+ is beneficial for carbon dots to resist luminescence quenching in solid state. A proof-of-concept study was performed to demonstrate the potential application of the obtained carbon dots as inks for anti-counterfeiting and printing high quality fluorescent images.

Change of the topological surface states induced by ferromagnetic metals deposited on BiSbTeSe2

The energy gap was revealed in the Dirac cone of the BiSbTeSe2 topological insulator after the submonolayer deposition of a ferromagnetic metal. As a ferromagnet, cobalt and manganese were used. Such way of the energy gap opening is novel in comparison to the bulk ferromagnetic doping of topological insulators.

EFFECT OF SOIL SURFACE SLOPE AND SOME HYDRAULIC PARAMETERS FOR DRIP IRRIGATION SYSTEM ON GROWTH AND YIELD OF TOMATO (Lycopersicon esculentum mill)

A field experiment was conducted in AL-Ramadi desert – Al-Bufaraj region in spring season 2018, North of AL-Ramadi city Far away about 110 km west of Baghdad, aimed to study the influence of the level and slope of the soil and some hydraulic parameters of drip irrigation system on growth and yield of tomato, the texture of soil is Silty loam. The experiment was designed with Split-Split plots according to "RCBD" with three replicates. The experiment included three factors : the first: soil surface(S) at two levels: flat land(S0) and land with slope (S1), the second: Emitter’s discharge (D) with two discharge, emitters type GR, whose discharge 4 Lh-1 (D4), and emitters type GR with discharge of 8 Lh-1 (D8), the last factor: lateral line (L), with two lengths, the first length lateral line with a diameter 16mm, 30m (L30) and length 60m (L60). The results of the study showed that the operational pressure 70 KPa is optimal of the operation of the irrigation system, the decrease in leaf area was 7.12%, 3.56%, 3.87% and 10.34% While the percentage of increase in depth roots was 7.50%, 7.14%, 4.55% and 4.17%, but the decrease in the early yield was 6.58%, 23.57%, 20.72% and 29.35%, while the results showed decreased values of total yield, 6.72%,9.85%, 9.71% and 20.10% due to change of soil surface state from flat to slope and increased emitters' discharge and lateral lines, respectively.

Ambient-Environment Effect on the Polished Surfaces of OF4 and STK19 Optical Glasses

Environmentally induced changes in the state of polished surfaces of STK19 and OF4 optical glasses were studied by means of ellipsometry and IR-spectroscopy as well as by measuring the roughness of the samples. It is shown that the surface state changes immediately on completion of polishing and does not change during the entire holding period. Changes in the temperature and humidity bring about subsequent changes in the state of the surfaces. Surface treatment of optical glasses in HMDS (hexamethyldisilazane) vapor impedes corrosion from occurring in the glass bulk and prevents roughness from increasing.

Hexene passivation on a p-type Zn-doped InGaAs surface

Indium gallium arsenide (InGaAs) is a promising candidate for high-performance complementary metal-oxide-semiconductor (CMOS) channel materials. In this study, self-assembled monolayer passivation was performed on the surface of p-type Zn-doped InGaAs to improve the semiconductor/dielectric interfacial electrical properties. In particular, the oxidation behavior and surface state change that occurred with hexene passivation were analyzed. A relatively thin oxide was formed on the hexene-passivated InGaAs surface and compared to the unpassivated surface after exposure to air over time. It was observed that oxidation was effectively suppressed for all the In, Ga, and As elements. It is considered from the relationship between the oxidation time and the oxide thickness change that the initial oxidation surface reaction is hindered by hexene passivation. In addition, the depletion depth was reduced from 28.2 to 24.4 nm and the interface trapped charge density of InGaAs MOS capacitor was decreased from 4.29 × 1013 to 2.24 × 1013 cm−2eV−1 after hexene passivation. The improvement in the interfacial electrical performance of the MOS capacitor may result from the suppressed oxidation caused by the passivation with hexene on the InGaAs surface.

Fluoride ion batteries: Designing flexible M2CH2 (M=Ti or V) MXenes as high-capacity cathode materials

Abstract The new concept of rechargeable fluoride ion batteries (FIBs) could potentially be safer, cheaper and higher energy density than those of traditional batteries. However, due to the higher working temperature (~340 K) and the choice of electrolytes and electrodes with excellent electrochemical performance, FIBs are not utilized in daily life yet. In our work, we have systematically investigated several critical parameters of M2CH2 (M = Ti or V) MXenes to assess their performances as cathode materials for rechargeable FIBs, including energetic stability and thermal dynamic stability, electronic property, strain-driven ionic mobility, average open circuit voltage and theoretical specific capacity. Specifically, the ground state structures of M2CH2 are firstly confirmed and then F ion adsorption behavior on the substrate is investigated. Sequentially, F− microscopic diffusion path and migration barrier are identified with and without driven by strain. It reveals that Ti2CH2 displays a lower F− diffusion energy barrier than that of V2CH2 monolayer in a large strain span. Besides, an appropriate control of compression strain could effectively increase the F− mobility due to the change of surface state on Ti2CH2. Importantly, the obtained results show that the F− intercalation into Ti2CH2 exhibits a larger storage capacity (488 mA h g−1) and higher open circuit voltage (4.62 V) than these into V2CH2 monolayer. Moreover, ab initio molecular dynamics (AIMD) calculations prove F2Ti2CH2 is thermo-dynamically stable at 500 K, while, HF compound emerges on F2V2CH2 monolayer at 300 K, implying that Ti2CH2 cathode is possible to work at harshest environment. A combination of these key parameters, we demonstrate that Ti2CH2 monolayer has potential to be a flexible and strain-controllable cathode material for rechargeable FIBs. We hope our detailed investigations could serve as a motivation and provide valuable insights for future experiments to design flexible and dynamically stable cathode materials of high-performance FIBs.

Stability analysis of silver nanoparticle suspensions by cyclic voltammetry.

We report the application of cyclic voltammetry and absorption spectroscopy to the characterization and study of the stability of silver colloids in water. The samples are prepared via chemical reduction and the reactions are catalyzed by irradiation with white light. The electrochemical response is related to the characteristic sample surface plasmon resonance (SPR) in the UV-visible absorption spectra. Cyclic voltammetry shows a characteristic reduction peak whose position is specific to each analyzed sample. Optical analysis of a colloid precursor during a 12 h time span, under low-power white-light irradiation, shows that nanoparticles undergo change in size and surface state (absorption bands splitting and inversion) to attain the "stable" colloidal form. While the absorption spectrum bands of the precursor return almost periodically to similar positions, the cyclic voltammogram characteristic reduction peak is displaced as a function of time. Finally, we follow the SPR changes of one "stable" colloid being subjected to electrolysis, heating, and sunlight irradiation, for environmental remediation purposes. Sunlight exposure produces the most significant SPR intensity drop, but the electrochemical technique shows itself promising as well.

Heat-Resistant Properties of a SiO<sub>2</sub>-Coated PET Film Prepared by Irradiating a Polysilazane-Coated Film with Excimer Light

Flexible electronics have been recently paid much attention. A flexible substrate (Organic resin film) is indispensable component for flexible devices. Though PET film is low-cost organic film, low heat-resistance of PET film limits its application as a flexible device substrate. We have developed heat-resistant PET which does not deteriorate even at 190°C heat treatment for one hour. An excimer light was irradiated onto a polysi-lazane (PHPS: perhydropolysilane)-coated film to form a dense silicon-dioxide (SiO2) layer on a PET film, and the heat-resistance property of the formed film was examined. Changes of surface state and cross-sectional structure of the formed film due to heat treatment were investigated by scanning electron microscope (SEM) and transmission electron microscope (TEM). Compared to normal PET, which is deteriorated and whitened by heat treatment of about 110°C - 120°C, the SiO2-coated PET film maintains transparency and does not deteriorate after heat treatment at 180°C - 190°C for one hour. This high heat resistance is due to a dense SiO2 film formed on the surface that prevents surface precipitation and crystallization of low-molecular-weight oligomers (which are the cause of thermal degradation of PET). It is expected that enhancing the heat resistance of PET—which has high versatility and low cost—to about 180°C to 190°C will allow SiO2-film-coated PET to be developed as a film substrate for flexible devices.

Metal Nano Networks by Potential-Controlled In Situ Assembling of Gold/Silver Nanoparticles.

Non‐spherical Au/Ag nanoparticles can be generated by chemical reduction of silver ions in the presence of preformed gold nanoparticles. The process of particle formation can be controlled by concentrations of ligands and reducing agent. The formation of ellipsoidal, nanorod‐ and peanut‐shaped nanoparticles as well as of more complex fractal nanoassemblies can be explained by changes in particle surface state, electrochemical potential formation and particle‐internal self‐polarization effects. It is possible to create highly fractal nanoassemblies with sizes between the mid‐nanometer and the lower micrometer range. The assemblies are marked by high optical absorption and complex nano‐networks of very high surface‐to‐volume ratios and a granular base structure.

Theory of the Josephson current on a magnetically doped topological insulator

Proximity induced superconducting states in the surface of magnetically doped topological insulators can host chiral Majorana modes. We consider a Josephson junction in that system with changing the chemical potential, which drives a topological phase transition in the induced superconducting states as well as a metal-insulator transition in the surface states. The local density of states and the Josephson current are analytically calculated by McMillan's Green's function method in terms of the Andreev reflection coefficient. We show that although the magnitude of the Josephson current is greatly enhanced when the surface state changes from insulating to metallic, its temperature dependence drastically changes at the topological phase transition point, reflecting the appearance of the chiral Majorana modes

Search method for changes of the earth’s surface state through multi-temporal satellite images

Subject of Research. We study the approach to the underlying surface interpretation automation for satellite images obtained by the onboard optical-electronic equipment of the Earth remote sensing systems. The topicality of research is determined by the necessity of introduction of computer vision methods aimed at solving the search problem of the earth’s surface state changes through multi-temporal satellite monitoring data. The goal of research is reducing of the time spent on processing of large area satellite images. Method. The method is based on the idea of comparing the contrast of different-time satellite images. For method implementation, a mathematical apparatus is formed for calculating the contrast values of the analyzed images in the normalized interval from 0 to 1. The effectiveness of automated processing of satellite images is ensured by their pre- segmentation and zoning. Segmentation parameters are selected taking into account the size of the objects to be detected. The efficiency of the proposed method is confirmed by the high correlation of the automated processing results with the results of visual analysis of test satellite images. Main Results. The results of calculating the contrast of test images using the formulated mathematical apparatus are presented. The necessity of image segmentation is proved to solve the problem of detecting changes in the terrain on the example of processing images consisting of different number of fragments. An approach is developed for reducing the redundancy of data on terrain changes by performing a preliminary zoning procedure. The essence of this procedure is to determine the researched area boundaries in order to limit the zones for search of changes. Practical Relevance. The proposed method of data processing on the Earth remote sensing provides interpretation of the underlying surface images in an automated mode without operator participation. At that, the interpretation of images, when observing large areas, can be accelerated.

Synthesis of phosphate functionalized highly porous activated carbon and its utilization as an efficient copper (II) adsorbent

Hollow silica microspheres were prepared by emulsion/extraction method, where the changes of particle size distribution and surface state of the final microspheres were examined considering the effects of a number of processing variables. First, silica sols were emulsified by 2-ethyl-1-hexanol and then the formed droplets were water extracted to form the gelled hollow microspheres. Average particle size of the final microspheres decreased with increasing stirring speed in emulsion formation step and decreasing colloid concentration. Higher colloid sol concentration gives smaller hollowness of the final microspheres. Solid microspheres formed at colloidal silica sol concentration over 60wt%. In addition, average particle size of the final microspheres decreases with increasing percentage of Span80, but aggregation of the final microspheres occurred in the excessive addition. Moderate volume ratio of silica sol to dispersing agent was 1:5, where silica sol were completely used to from liquid droplets. Also the effects of sintering temperature and the volume of dehydrating liquid were examined.

Methylamine Treated Mn3O4 Nanoparticles for Efficient Water Oxidation Catalyst at Neutral Condition

Developing alternatives to replace fossil fuels is an important issue for maintaining sustainable energy system in the future. Hydrogen fuel is an attractive alternative owing to its high energy density and environmentally friendly by-products. Electrical water splitting powered by a renewable energy source is a promising way to produce hydrogen fuel. However, anodic water oxidation is considered to be a bottleneck due to its high overpotential. Therefore, designing efficient catalyst for water splitting is regarded as an important issue. Previously, Ir and Ru-based catalysts have been shown to exhibit remarkable catalytic activity toward oxygen evolving reaction (OER) under acidic condition. Despite their high activity, it is difficult to use noble-metal-based catalysts for commercial applications because of the scarcity of precious metals and their costs. Therefore, non-precious transition metal oxide electrocatalysts were investigated for water oxidation reaction such as cobalt oxides, nickel oxides, iron oxides and manganese oxides.1,2 Their activities were only retained under basic conditions and advancement in electrocatalysts that show moderate activity at neutral pH has been relatively insufficient. Nature has highly efficient OER catalysts in photosystem II which is Mn4CaO5 cluster also called as oxygen evolving complex. Inspired by unique structure and catalytic mechanism of this cluster, Mn-based catalysts have been actively studied. Among various manganese oxide, nanoparticle system showed superior catalytic activity due to its totally different reaction mechanism compared to the bulk counterparts.3,4 However, after synthesis of manganese oxide nanoparticles, long alkyl organic ligands are attached on the surface of nanoparticles interrupting the approach of water molecules, which inhibits water oxidation. Previously, hydrophobic organic ligands were removed by thermal decomposition with sufficient annealing process. Alternative way to remove alkyl ligands is replacing it with different ligands through surface ligand treatment such as BF4 -, PF6 -, OH-, thiol, SCN- and PbCl3 -. Surface ligand exchange is beneficial in that it does not need high temperature annealing and possibility of fine surface control. We have successfully synthesized 6 nm Mn3O4 nanoparticles (NPs) and used for further surface treatments. Mn3O4 NPs were OH ligand exchanged as a first step and followed by methylamine treatment in aqueous solution. Identical TEM images and XRD patterns showed that the size of NPs was unchanged and the phase of NPs was maintained as Mn3O4. Electrokinetic study of the OER was analyzed by cyclic voltammetry (CV) at pH 7 and compared between OH ligand exchanged Mn3O4 NPs and further methylamine treated Mn3O4 NPs. Methylamine treatment reduced the overpotential for OER by nearly 100 mV at the current density 5 mA cm-2. Tafel slopes was also decreased after methylamine treatment to 83.1 mV dec-1. To understand the phenomenon of increased catalytic activity after methylamine treatment, further analysis of the surface of NPs were conducted using spectroscopic measurement. In the XPS O 1s spectra, surface hydroxyl group (Mn-OH) was increased up to 57.3 % after OH ligand exchange. Also, FTIR spectra showed increased ratio of Mn-OH to lattice oxygen (Mn-O-Mn) for OH ligand exchanged Mn3O4 NPs compared to Mn3O4 NPs which indicates successful OH ligand exchange on the surface of Mn3O4 NPs. After methylamine treatment of OH ligand exchanged Mn3O4 NPs, methylamine was not attached to the surface of NPs. XPS N 1s spectra did not show characteristic methylamine peak, FTIR did not show C-N vibration mode and elemental analysis indicates that N does not exist in the NPs. To figure out the role of methylamine on the surface of OH ligand exchanged Mn3O4 NPs, titration and zeta potential was measured. After methylamine treatment surface was more deprotonated. Deprotonation resulted in loss of positively charged proton which induced negative charge on the surface of Mn3O4 NPs and showed negative zeta potential. On the basis of nonexistence of methylamine on the surface and surface deprotonation after methylamine treatment, we hypothesized that methylamine work as Brønsted-Lowry base. Methylamine was replaced by ethylamine, ethylenediamine, dimethylamine, trimethylamine and ammonia water, then after reaction with different amines, overpotential was decreased for all cases. Interestingly, amines with larger pK a showed larger decrease in overpotential. Based on these results, we first proposed correlation between the surface charge and oxygen evolving activity. Deprotonating the surface of the catalyst through simple acid-base reaction induced a change in the surface state followed by catalytic activity improvement. This understanding can be applied for developing efficient nano-catalysts by deprotonating the nanoparticle surface to induce surface state change. [1] J. Am. Chem. Soc., 2014, 136, 4201-4211 [2] J. Am. Chem. Soc., 2014, 136, 7435-7443 [3] Sci. Rep., 2015, 5, 10279 [4] J. Am. Chem. Soc., 2017, 139, 2277-2285 Figure 1