Shoulder Peak Research Articles

Self-limiting CVD of a passivating SiOx control layer on InGaAs(001)-(2x4) with the prevention of III-V oxidation

A thin passivating SiOx control layer has been deposited via self-limiting CVD on the InGaAs(001)-(2x4) surface by first depositing 2 monolayers of silicon with –Clx termination using Si2Cl6,and then subsequently oxidizing the silicon seed layer by employing anhydrous HOOH(g) at a substrate temperature of 350°C. After HOOH(g)) dosing, XPS spectra show a higher binding energy shoulder peak on Si2p indicative of SiOx bonding, while an unshifted Si 2p component remains, and In 3d, Ga 2p, and As 2p peaks show no higher binding energy components consistent with the prevention of III-V oxidation. Scanning tunneling spectroscopy (STS) measurements show after SiOx deposition on the InGaAs(001)-(2x4) surface, the bandgap broadens towards that of SiO2, with the electronic structure free of states in the bandgap leaving the surface ready for subsequent gate oxide ALD. Density functional theory calculations support the experimental STS data following TMA dosing, which shows TMA nucleates directly on the SiOx/InGaAs(001) surface and leaves an electrically passive interface with the bandgap free of defect states and the surface ready for high-K gate oxide nucleation.

Low temperature thermal ALD of a SiNx interfacial diffusion barrier and interface passivation layer on SixGe1− x(001) and SixGe1− x(110)

Atomic layer deposition of a silicon rich SiNx layer on Si0.7Ge0.3(001), Si0.5Ge0.5(001), and Si0.5Ge0.5(110) surfaces has been achieved by sequential pulsing of Si2Cl6 and N2H4 precursors at a substrate temperature of 285 °C. XPS spectra show a higher binding energy shoulder peak on Si 2p indicative of SiOxNyClz bonding while Ge 2p and Ge 3d peaks show only a small amount of higher binding energy components consistent with only interfacial bonds, indicating the growth of SiOxNy on the SiGe surface with negligible subsurface reactions. Scanning tunneling spectroscopy measurements confirm that the SiNx interfacial layer forms an electrically passive surface on p-type Si0.70Ge0.30(001), Si0.50Ge0.50(110), and Si0.50Ge0.50(001) substrates as the surface Fermi level is unpinned and the electronic structure is free of states in the band gap. DFT calculations show that a Si rich a-SiO0.4N0,4 interlayer can produce lower interfacial defect density than stoichiometric a-SiO0.8N0.8, substoichiometric a-Si3N2, or stoichiometric a-Si3N4 interlayers by minimizing strain and bond breaking in the SiGe by the interlayer. Metal-oxide-semiconductor capacitors devices were fabricated on p-type Si0.7Ge0.3(001) and Si0.5Ge0.5(001) substrates with and without the insertion of an ALD SiOxNy interfacial layer, and the SiOxNy layer resulted in a decrease in interface state density near midgap with a comparable Cmax value.

Luminescence Spectroscopical Properties of Plagioclase Particles from the Hayabusa Sample Return Mission: An Implication for Study of Space Weathering Processes in the Asteroid Itokawa.

We report a systematic spectroscopical investigation of three plagioclase particles (RB-QD04-0022, RA-QD02-0025-01, and RA-QD02-0025-02) returned by the Hayabusa spacecraft from the asteroid Itokawa, by means of scanning electron microscopy, cathodoluminescence microscopy/spectroscopy, and micro-Raman spectroscopy. The cathodoluminescence properties are used to evaluate the crystallization effects and the degree of space weathering processes, especially the shock-wave history of Itokawa. They provide new insights regarding spectral changes of asteroidal bodies due to space weathering processes. The cathodoluminescence spectra of the plagioclase particles from Itokawa show a defect-related broad band centered at around 450 nm, with a shoulder peak at 425 nm in the blue region, but there are no Mn- or Fe-related emission peaks. The absence of these crystal field-related activators indicates that the plagioclase was formed during thermal metamorphism at subsolidus temperature and extreme low oxygen fugacity. Luminescence characteristics of the selected samples do not show any signatures of the shock-induced microstructures or amorphization, indicating that these plagioclase samples suffered no (or low-shock pressure regime) shock metamorphism. Cathodoluminescence can play a key role as a powerful tool to determine mineralogy of fine-grained astromaterials.

Efficient Synthesis of Fluorinated Phenanthrene Monomers Using Mallory Reaction and Their Copolymerization

The Mallory reaction of 1,2-diarylhexafluorocyclopentene (1, aryl = 3-bromophenyl; 2, aryl = 4-bromophenyl) under light irradiation (λ = 365 nm) in the presence of iodide proceeded to give dibromophenanthrene derivatives, 3 and 4. Polycondensation of 9,9-dioctylfluorene-2,7-diboronic acid bis(1,3-propanediol)ester with the obtained monomers by Suzuki–Miyaura coupling afforded the phenanthrene-type copolymers Poly-3 and Poly-4 in high yields. For comparison, diphenylethene-type copolymers (Poly-1 and Poly-2) were also prepared analogously. UV–vis spectra of Poly-3 and Poly-4 in CHCl3 showed π–π* transition peaks at 380 and 354 nm, respectively, and additional shoulder peaks appeared at a longer wavelength in the film, suggesting the molecular assembly of the polymer molecules. In contrast, the spectra of Poly-1 and Poly-2 in solution were essentially unchanged as measured in the film, presumably owing to partial interruption of the π-conjugation system in polymer main chains. The copolymers showed photolum...

Interplay of bifurcated hydrogen bonds in making of inclusion/pseudo-inclusion complexes of Ni(II), Cu(II) and Zn(II) of a salophen type ligand: Crystal structures and spectral aspects

Three novel photoluminescent materials were synthesized by treating Ni(II), Cu(II) and Zn(II) acetate salts with a Schiff base prepared from 3-ethoxysalicylaldehyde and 2-aminobenzylamine. Among the prepared complexes, Ni(II) and Cu(II) complexes are inclusion compounds while Zn(II) complex is a pseudo-inclusion compound. They were characterized by elemental analysis, IR, UV–visible and EPR spectra. Single crystal XRD studies of these complexes suggest that Ni(II) and Cu(II) are in a distorted square planar environment while the spatial arrangement of donor atoms in Zn(II) complex is best described as distorted square based pyramid although significant distortion towards trigonal bipyramid is noticed. Stabilized crystal packing of the complexes is established via supramolecular interactions. The metal chelate rings as the π system for C–H···π interactions found in Cu(II) and Zn(II) complexes explicit the concept of metalloaromaticity. TG-DTG studies reveal that all the complexes are thermally stable. Both ligand and complexes exhibit intense photoluminescence in near UV region. However, Zn(II) complex giving an intense blue-green emission spectrum at maximum wavelength of 518 nm with shoulder peaks, could be used for optoelectronic applications.

Effects of Mg doping content and annealing temperature on the structural properties of Zn1-x Mg x O thin films prepared by radio-frequency magnetron sputtering

The doping content of Mg plays an important role in the crystalline structure and morphology properties of Zn1-x Mg x O thin films. Here, using radio-frequency magnetron sputtering method, we prepared Zn1-x Mg x O thin films on single crystalline Si(100) substrates with a series of x values. By means of X-ray diffraction (XRD) and scanning electron microscope (SEM), the crystalline structure and morphology of Zn1-x Mg x O thin films with different x values are investigated. The crystalline structure of Zn1-x Mg x O thin film is single phase with x 0.3, and hexagonal and cubic structures will coexist in Zn1-x Mg x O thin films with higher x values. Especially with lower x values, a shoulder peak of 35.1° appearing in the XRD pattern indicates a double-crystalline structure of Zn1-x Mg x O thin film. The crystalline quality has been improved and the inner stress has been released, after the Zn1-x Mg x O thin films were annealed at 600 °C in vacuum condition.

Novel Dual BODIPY-Carbazole Conjugates with Various Linkers

Four dual BODIPY-carbazole conjugates (BDPa–d, BODIPY is 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene), with various π bridges, including none, phenyl, thiophene, and furan, were designed and synthesized. The results suggest that the π bridges have significant effect on the thermal, photophysical, and electrochemical properties of the conjugates. BDPc and BDPd, with a five-membered heterocycle as a π bridge possessing more coplanar molecular geometry, exhibit broader and red-shifted absorption with an obvious charge transfer shoulder peak, as well as red-shifted emission. UV-visible absorption spectroscopy and cyclic voltammetry results show that the extension of the π-conjugated system leads to a reduction in the optical gap with a decrease of the LUMO level. All conjugates display remarkable Stokes shifts (107–216 nm) and low fluorescence quantum yields. BDPc and BDPd, which essentially possess broad and intense absorption, and suitable HOMO–LUMO energy levels, are potential candidates for light-harvesting and photovoltaic applications.

Synthesis and characterization of gold – silver alloy nanoparticles

Gold–Silver alloy nanoparticles were synthesized by microwave assisted redution and polyol reactions, where trisodium citrate (TSC) and poly vinyl pyrollidone (PVP, Mn=1,000,000) played as protective agents, process includes two steps: (i) first, gold nanoparticles were synthesized, (ii) then silver nanoparticles were developed on gold nanoparticles surfaces to form alloy nanoscale. The results of the analysis from UV-Vis, XRD, TEM spectrums showed that gold – silver alloy nanoparticles mostly had core–shell structure and gold was proposed as the core. The particle size of alloy nanoparticles was 30–35 nm, and developed if the amount of silver has increased. UV-Vis spectrum showed this solution has a shoulder peak beside maximum absorbent peak. Trisodium citrate kept an important role to form gold–silver alloy nanoparticles in ethylene glycol.

Gamma radiation-induced thermoluminescence, trace element and paramagnetic defect of quartz from the Sambagawa metamorphic belt, Central Shikoku, Japan

This study analyzes the Thermoluminescence (TL) emissions for five emission bands, trace element concentrations and defects in quartz grains extracted from metamorphic rocks and quartz veins in the Sambagawa metamorphic belt, central Shikoku. An emission of 500nm with 195, 245, and 320–325°C glow peaks are observed through the lowest to highest grade samples. A 450nm emission band with intense 195 and 245°C glow peaks and a 320–325°C shoulder peak is found in the higher grade samples. A 570nm emission band with a 170°C glow peak is observed in the samples derived from the lower grade zones. These characteristics of TL emissions of quartz suggest that they can be an indicator for the identification of rock derived from different metamorphic grades. The higher metamorphic grade samples with 450nm emission bands in particular show higher intensities of the E1′ center. This relation indicates that the activation of the E1′ center in higher metamorphic conditions possibly contributed to the 450nm emission band. Also, the 500nm emission band is generally observed in the samples with the signal intensities of the Aluminum hole center, suggesting that the center is the source of this emission band. We also observed that the lower metamorphic grade samples contain lower signal intensities of the Aluminum hole center, despite higher aluminum concentrations. This inconsistency indicates that the formation of interstitial aluminum ions cause local lattice distortion regions, where self-trapped excitons can be formed and presumably provide the 570nm emissions.

Spectro-Electrochemical of Detection Anthracene at Electrodeposited Polyamic Acid Thin Films

Polyamic acid (PAA) thin films were prepared by electrodepositing PAA onto indium tin oxide (ITO) electrode and characterized using electrochemical methods (cyclic voltammetry, square wave voltammetry), Ultraviolet Visible spectroscopy and Ultraviolet Visible/Spectro-electrochemistry (UV/vis Spectro-electrochemistry). The electrodeposited PAA thin films were observed to have two redox couples with a formal of 118 mV and 274 mV. The diffusion coefficient (De) determined from cyclic voltammetry was found to be 7.9x10-6 cm2/s and provide a measure of how fast charge is transported through the thin film. PAA showed a broad absorption peak at 214 nm due to the carbonyl chromophores within the polymer and shoulder peak at 293 nm from a quinoid-type chromophore. The calculated band gap of 4.23 eV suggested the polymer was optically transparent between 300 nm to 800 nm. This indicated that the PAA thin films has emerged as a very promising and cost effective alternative material to ITO with good transparent and conductive properties. PAA thin films were further applied for the detection of anthracene. The analytical response of anthracene was studied at the ITO/PAA using spectro-electrochemistry. The characteristic analytical absorbance signal for anthracene was clearly identified at 375 nm when ITO/PAA electrode was polarised at -800 mV (vs Ag/AgCl). The calibration curve for anthracene showed a linear response from 4.95x10-4 to 1.15x10-2 M. The ITO/PAA showed a low detection limit of (0.0068 g/L) and high sensitivity for anthracene, making it a suitable platform for spectro-electrochemical analysis of polycyclic aromatic hydrocarbons.

Reconstruction of facial and napex scar with expanded cervico-acromial flap

Objective To discuss the feasibility of transferring neck- shoulder peak area expanded skin flap to facial and napex area of removed scar tissue, and to observe the therapeutic effect of expanded cervico-acromial flaps for facial and napex scar. Methods In the first stage, the soft tissue expanders (ranging from 600 ml to 800 ml in volume) were implanted under the deep fascia of the cervio-acromion region. The blood vessle that located at the base of the flap were protected. In the second stage, the expanded flap, pedicled by the lateral neck (supraclavicular artery), was elevated and rotated by 90-180 degree to the facial or napex defects. The donor site of the flap was closed primarily or by free skin graft. Results A lot of 28 patients, with napex scar in 5 cases, facial scar in 23 cases, were treated by the expanded cervico-acromial flaps, the length of which ranged from 5-10 cm, the width 15-20 cm. All flaps survived with color and texture matched well with the surrounding skin tissue. Conclusions The blood supply of the cervico-acromial flap is stable and abundant with constant perforators. It is a reliable technique for facial and napex reconstruction. Key words: Facial scar; Neck scar; Cervico-acromial flap; Expand flap

Photoluminescence enhancement from GaN by beryllium doping

High quality Be-doped (Be = 0.19 at.%) GaN powder has been grown by reacting high purity Ga diluted alloys (Be-Ga) with ultra high purity ammonia in a horizontal quartz tube reactor at 1200 °C. An initial low-temperature treatment to dissolve ammonia into the Ga melt produced GaN powders with 100% reaction efficiency. Doping was achieved by dissolving beryllium into the gallium metal. The powders synthesized by this method regularly consist of two particle size distributions: large hollow columns with lengths between 5 and 10 μm and small platelets in a range of diameters among 1 and 3 μm. The GaN:Be powders present a high quality polycrystalline profile with preferential growth on the [101¯1] plane, observed by means of X-ray diffraction. The three characteristics growth planes of the GaN crystalline phase were found by using high resolution TEM microscopy. The optical enhancing of the emission in the GaN powder is attributed to defects created with the beryllium doping. The room temperature photoluminescence emission spectra of GaN:Be powders, revealed the presence of beryllium on a shoulder peak at 3.39 eV and an unusual Y6 emission at 3.32eV related to surface donor-acceptor pairs. Also, a donor-acceptor-pair transition at 3.17 eV and a phonon replica transition at 3.1 eV were observed at low temperature (10 K). The well-known yellow luminescence band coming from defects was observed in both spectra at room and low temperature. Cathodoluminescence emission from GaN:Be powders presents two main peaks associated with an ultraviolet band emission and the yellow emission known from defects. To study the trapping levels related with the defects formed in the GaN:Be, thermoluminescence glow curves were obtained using UV and β radiation in the range of 50 and 150 °C.

CdS@SiO2 Core-Shell Electroluminescent Nanorod Arrays Based on a Metal-Insulator-Semiconductor Structure.

Enormous advancement has been achieved in the field of one-dimensional (1D) semiconductor light-emitting devices (LEDs), however, LEDs based on 1D CdS nanostructures have been rarely reported. The fabrication of CdS@SiO2 core-shell nanorod array LEDs based on a Au-SiO2 -CdS metal-insulator-semiconductor (MIS) structure is presented. The MIS LEDs exhibit strong yellow emission with a low threshold voltage of 2.7 V. Electroluminescence with a broad emission ranging from 450 nm to 800 nm and a shoulder peak at 700 nm is observed, which is related to the defects and surface states of the CdS nanorods. The influence of the SiO2 shell thickness on the electroluminescence intensity is systematically investigated. The devices have a high light-emitting spatial resolution of 1.5 μm and maintain an excellent emission property even after shelving at room temperature for at least three months. Moreover, the fabrication process is simple and cost effective and the MIS device could be fabricated on a flexible substrate, which holds great potential for application as a flexible light source. This prototype is expected to open up a new route towards the development of large-scale light-emitting devices with excellent attributes, such as high resolution, low cost, and good stability.

Synthesis, characterization and photovoltaic properties of low band gap donor-acceptor polymers containing benzodithiophene donor unit with fluorenylthiophene as 2D-conjugated side for organic solar cell application

ABSTRACTTwo donor−acceptor low band gap polymers P1 (octyl as solubilizing group) and P2 (ethylhexyl as solubilizing group) containing fluorenylthiophene-substituted benzoditihiophene as an electron-rich unit and 3,6-bis(5-bromothiophen-2-yl)-2,5-bis(2-ethylhexyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione as an electron-deficient unit are designed and synthesized for polymer solar cells application. Compared with P2 based on ethyl hexyl group, P1 with octyl group displays well resolved vibronic shoulder peak in absorption spectra, stronger intermolecular interactions, and higher hole mobility. Polymer solar cells based on P1 and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) exhibit a maximum power conversion efficiency of 1.78% under AM 1.5G illumination (100 mW/cm2).

A taxonomy of fronto-parietal P3-like positivities based on information theoretic models of cognitive control

Phyto-sequestration of heavy metals originating from urban runoff entering into wetland systems is one of the ways to mitigate the pollution. Due to the chemical environment of runoff wetlands, the plants and especially their roots are often stressed. While growing on contaminated environment, wetland plants undergo a number of physio-chemical changes in their roots, stems and leaves in the form of ecological adaptations. In this study, the three category samples of the macrophyte Cyperus vaginatus R.Br. growing in a wetland, near to the wetland (<20 m) and far from the wetland (>100 m) were collected to determine heavy metals and organic matter status in roots. This study revealed hyperaccumulation of metals in plants growing in the wetland compared to nearby and far from the wetland. Statistical analysis showed metals accumulating pattern to be distinct for each sampling category based on location. The UV spectra of C. vaginatus root produced a distinct shoulder peak at 324 nm whereas the plants growing far from the wetland showed a spectroscopic shoulder at 267 nm. The plant root growing near to wetland showed both shoulders at 324 nm and 267 nm but with reduced peak height. Statistical analysis of UV spectra also followed location specificity pattern. UV spectral result was further validated by FTIR analysis where plants growing in wetland and near to wetland possessed spectra similar to UV spectral results. This observation leads us to conclude that C. vaginatus R.Br. exhibited changes in root chemical composition to tolerate metal toxicity and perform phytoaccumulation.

Isolation and Characterization of Nanocrystalline Cellulose from Totally Chlorine Free Oil Palm Empty Fruit Bunch Pulp

Nanocrystalline cellulose (NCC) was isolated from a totally chlorine free (TCF) bleached oil palm empty fruit bunch (OPEFB) pulp via acid hydrolysis using a 58 % sulfuric acid concentration and ultrasonic treatment. The effects of acid concentration and hydrolysis time were investigated. Characterization of OPEFB–NCC was carried out using TEM, FTIR, 13C-NMR, XRD, zeta potential and TGA. The optimal hydrolysis time was 80 min as indicated by the leveling off of the OPEFB–NCC dimensions (length 150 nm and diameter 6.5 nm) with no significant loss of crystallinity at this point. The presence of a shoulder peak at 1231 cm−1 (assigned to a sulfate group) in the FTIR spectrum of NCC is indicative of a successful esterification. This is further corroborated by the 13C-NMR analysis whereby the distinct C4 amorphous and crystalline peaks present in OPEFB–TCF pulp had almost disappeared and the cluster of signals for C2, C3, C5, and a well separated signal of C6 had merged into one single peak in the OPEFB–NCC sample. These observations allude to most of the amorphous region having been removed and to the strong possibility of sulfonation having not only occurred on the C6, but also on C2 and C3. OPEFB–NCC isolated over shorter hydrolysis time was more thermally stable; however, the char fraction decreases with hydrolysis time despite having a higher zeta potential. The results of this investigation demonstrate that NCC can be produced from pulp made by chlorine free environmentally benign processes with ensuing savings in energy and chemicals.

Dual Strong Couplings Between TPPS J-Aggregates and Aluminum Plasmonic States.

We report on the spectral properties of strong coupling between the localized surface plasmon resonances (LSPRs) of aluminum (Al) nanostructures and tetraphenylporphyrin tetrasulfonic acid hydrate (TPPS) J-aggregates. Because of their wide spectral range of LSPR bands from ultraviolet to near-infrared wavelengths by controlling structural size, Al nanodisks can realize strong coupling with different excitons of TPPS J-aggregates. The Rabi splitting energies of the excitons based on Soret and Q bands are 300 and 180 meV, respectively. In addition to extinction spectrum, we have also measured an excitation spectrum to determine the essential absorption of the hybrid states and successfully confirmed a shoulder peak corresponding to a lower branch of hybrid states. In Al nanorod systems, strong coupling with two excitons can also be selectively induced by merely rotating the polarization of the incident light, which constituted a simple platform for the dynamic control of exciton/plasmon coupling states.

Room temperature blue LED based on p-ZnO/(CdZnO/ZnO) MQWs/ n-ZnO

Blue multiple quantum well light-emitting diodes comprising of p-ZnO/(Cd0.12Zn0.88O/ZnO) multiple quantum wells/n-ZnO were grown on n-Si substrates using dual ion-beam sputtering deposition technique. X-ray diffraction of individual thin films revealed growth preferentially in c-axis direction perpendicular to the substrate. Photoluminescence studies indicated blue emission ~ 440nm from CdZnO and UV emission ~384nm arising from ZnO thin films. The LED showed a rectifying current–voltage behavior with a turn-on voltage of ~4.69V at room temperature. It emanated a room-temperature electroluminescence peak centered at 442nm, along with shoulder peak at 380nm in ultra-violet region associated with the recombination in ZnO layers of structure. It was found that with the increase in injection current the blue EL intensity increased and UV emission decreased, leading to improvement in successful radiative recombination in quantum wells. The results indicate prospects of fabrication of ZnO-based blue multiple quantum well LEDs.

Structural Characterization and Pyrolysis Behavior of Cellulose and Hemicellulose Isolated from Softwood Pinus armandii Franch

Cellulose and hemicellulose were isolated directly from softwood Pinus armandii Franch by the alkali method for pyrolysis mechanism study. Structural characterization based on FTIR, 1H NMR, and 13C NMR showed that the hemicellulose was mainly composed of galactoglucomannan and arabinoxylan with abundant branches, while the cellulose was mainly composed of β-1,4-glucan with a few residual hemicellulose fragments. Pyrolysis of extracted cellulose showed high char yield due to the lower crystallinity. Hemicellulose pyrolysis showed a shoulder peak at low temperature and high char yield because of its abundant branches. A double-Gaussian distributed activation energy model was introduced for pyrolysis kinetics analysis. The devolatilization process for both cellulose and hemicellulose was dominated by a parallel decomposition reaction pathway. The distributions of their pyrolysis products were analyzed by Py-GC/MS. It is suggested that the utilization of isolated sample as model compound could give a better u...

Deciphering lead and cadmium stripping peaks for porous antimony deposited electrodes

AbstractCadmium and lead are generally taken as model heavy metal ions in water to scale the detection limit of various electrode sensors, using electrochemical sensing techniques. These ions interact with the electrochemically deposited antimony electrodes depending on the diffusion limitations. The phenomenon acts differently for thein-situandex-situdeposition as well as for porous and non-porous electrodes. A method has been adopted in this study to discourage the stripping and deposition of the working ions (antimony) to understand the principle of heavy metal ion detection. X-ray photoelectron spectroscopy (XPS) technique was used to establish the interaction between the working and dissolved ions. In addition to the distinct peaks for each analyte, researchers also observed a shoulder peak. A possible reason for the presence of this peak was provided. Different electrochemical tests were performed to ascertain the theory on the basis of the experimental observations.