Optical Field Emission Research Articles

Dynamics of electron-emission currents in plasmonic gaps induced by strong fields.

The dynamics of ultrafast electron currents triggered by femtosecond laser pulse irradiation of narrow gaps in a plasmonic dimer is studied using quantum mechanical Time-Dependent Density Functional Theory (TDDFT). The electrons are injected into the gap due to the optical field emission from the surfaces of the metal nanoparticles across the junction. Further evolution of the electron currents in the gap is governed by the locally enhanced electric fields. The combination of TDDFT and classical modelling of the electron trajectories allows us to study the quiver motion of the electrons in the gap region as a function of the Carrier Envelope Phase (CEP) of the incident pulse. In particular, we demonstrate the role of the quiver motion in establishing the CEP-sensitive net electric transport between nanoparticles.

Ionic Liquid Stabilized Gelatin-Lignin Films: A Potential UV-Shielding Material with Excellent Mechanical and Antimicrobial Properties.

Significant research is currently underway to develop environmentally friendly UV-shielding materials. Herein, we have constructed choline citrate (a biobased ionic liquid, IL) stabilized homogeneous gelatin-lignin UV-shielding films with excellent antimicrobial and mechanical properties. The synthesis procedure of the films is less energy demanding, one pot, and sustainable in nature. Prepared films were characterized by mechanical and thermal analysis using UTM and TGA, respectively. ATR-IR and PXRD was employed to explore the possible formation of H-bonding between biopolymers and the IL and the change in crystallinity in films after addition of IL to the gelatin-lignin matrix. Surface morphology of prepared films has been studied using optical microscope, AFM, and field emission SEM (FE-SEM). Optical properties of prepared films were measured using UV/Vis spectroscopy. Antimicrobial activity of the prepared films was tested against Bacillus subtilis. Prepared biofilms showed a sun-protection factor (SPF) of up to ≈45.0, large elongation ≈200 %, and tensile strength ≈70 MPa, which are as good as those values exhibited by organic polymeric films, indicating a promising renewable-resources-based material for UV light blocking.

Effect of heat input in pulsed Nd:YAG laser welding of titanium alloy (Ti6Al4V) on microstructure and mechanical properties

In the present investigation, titanium alloy Ti6Al4V of 1.4 mm thickness has been laser-welded in butt joint configuration using pulsed Nd:YAG laser system. The effects of heat input on weld bead shape, fusion zone width (top, middle, and bottom), heat-affected zone (HAZ) width (top, middle, and bottom), and fusion zone area have been studied. The microstructure and mechanical properties of laser-welded specimens at various heat inputs (43.7–103.5 J/mm) have also been investigated. Microstructures of the fusion zone, HAZ, and parent material have been compared at various heat inputs using optical microscope and field emission scanning electron microscope (FESEM). The mechanical properties such as microhardness and tensile strength of the welded joints at varying heat inputs have been studied. Tensile tests of the welded specimen and base metal have been conducted for analyzing ultimate tensile strength and percentage elongation. Surface topography of the tensile fractured specimen of the welded joints and base metal has been examined to analyze the ductile and brittle behavior. EDS analyses of base metal and fusion zone of the welded specimen have been studied. XRD of the as-received base metal and welded specimen have been measured in the range of 30 to 85° to study the crystallographic structure.

Patterned bacterial cellulose wound dressing for hypertrophic scar inhibition behavior

Hypertrophic scar (HS) is a kind of fibroproliferative disorder with gross and inordinate fiber bundles twisted in the deep scar and it often occurs after deep dermal injury. In this paper, bacterial cellulose (BC), a good candidate for wound dressing, was modified with a stripe pattern by a simple static culture method using patterned PDMS templates in order to investigate the inhibition of cicatricial contractions. The obtained patterned bacterial celluloses (pBC) with different sizes were characterized by optical microscopy and field emission scanning electron microscopy. Different nanofiber structures were observed in bulges and depressions, indicating different cell behaviors on the pBC. In vitro experiments demonstrated that L929 cells showed a clear stripe distribution. Moreover, pBC had an obvious inhibitory effect on L929 cells proliferation, especially pBC with 10 μm stripes which was close to the size of the cells. Furthermore, in vivo experiments of injury model demonstrated that pBC effectively inhibited inflammatory response, reduced accumulation of fibroblasts, and significantly decreased the scar contraction compared to the control and standard groups, indicating its good HS inhibition effect. Compared with that for unmodified BC, the scar thickness for the pBC wound dressing significantly decreased from 428.7 ± 61.9 to 261.5 ± 89.6 µm, which was at least two times less than that of the standard and blank control groups. Excitingly, it was found that if the width of the stripes matched the size of the cell, the pBC had better anti-scar effect, which can also be extended to other dressings.

Microstructure and corrosion characterization of the nugget region in dissimilar friction-stir-welded AA5083 and AA1050

Metallurgical structure, mechanical properties and electrochemical behavior of dissimilar friction stir welding (FSW) between structural AA5083 and AA1050 alloys were investigated in this study. Optical microscopy and field emission scanning electron microscopy observations showed that the nugget zone (NZ) possesses equiaxed recrystallized grains of the two alloys with a flowing shape. Energy-dispersive spectroscopy analysis revealed that NZ is mainly composed of the advancing side alloy. The ultimate tensile and yield strengths of the dissimilar FSW joint were higher than those of AA1050 and lower than those of AA5083. Consequently, fracture occurred on AA1050 side during the tensile tests. The potentiodynamic polarization (PDP) results revealed that the passive current density of the FSW joint was in between that of AA1050 and AA5083. A modified Randles equivalent circuit was used to simulate the obtained experimental data of electrochemical impedance spectroscopy measurements. The acquired impedance parameters were in good agreement with the PDP measurements.

Dry Sliding Wear Behavior of (Cr, Fe)7C3-γ(Cr, Fe) Metal Matrix Composite (MMC) Coatings: The Influence of High Volume Fraction (Cr, Fe)7C3 Carbide

The high volume fraction (Cr, Fe)7C3 carbide particle-reinforced metal matrix composite (MMC) coatings with different Cr/C ratios were produced by flux-cored arc welding (FCAW). The in situ synthesized effectiveness of (Cr, Fe)7C3 carbide in the coatings was studied by the aid of CALPHAD and differential scanning calorimeter. The microstructure of the coatings was observed by optical microscope and field emission scanning electron microscope, and their phases were determined by the X-ray diffraction. Meanwhile, the hardness and wear resistance of the coatings were measured. The results show that the (Cr, Fe)7C3 carbide can be in situ synthesized in the coatings. With decreased Cr/C ratio, the in situ synthesized effectiveness of (Cr, Fe)7C3 carbide is improved and the mass fraction of the (Cr, Fe)7C3 carbide is increased. The microstructure of the coatings consists of in situ synthesized (Cr, Fe)7C3 carbide and eutectic (Cr, Fe)7C3/ γ (Cr, Fe) matrix. The hexagonal-rod-form (Cr, Fe)7C3 carbide can be fractured and segregated from austenite-matrix under a relatively high load force (50 N), and transforms the wear state from two-body-abrasion to three-body-abrasion, which facilitates the coating be seriously abraded and even adhered. The wear resistance of the MMC coatings can be effectively improved by the formation of high volume fraction of (Cr, Fe)7C3 carbide.

Influence of vanadium, cobalt-codoping on electrochemical performance of titanium dioxide bronze nanobelts used as lithium ion battery anodes

In this work, V, Co-codoped TiO2(B) samples are synthesized through a hydrothermal method, and used as negative electrode materials for lithium ion batteries. The amount of dopants is varied in order to investigate their influence on electrochemical properties. The formation of V, Co-codoped TiO2(B) nanobelts with widths of 20 and 60 nm is demonstrated using X-ray diffraction, X-ray photoelectron spectroscopy, inductively coupled plasma–optical emission spectrometry and field-emission scanning electron microscopy analyses. In addition, the electrochemical properties of the samples are tested by cyclic voltammetry, charging/discharging, and cyclic performance techniques. Compared to other samples, TiO2(B) nanobelts codoped with 2.5 wt% Co–2.5 wt% V, shows the best cycling performance, and exhibits the first high capacity of 264.86 mAh g−1 [x = 0.79, LiXTiO2(B)] at a rate of 0.5 C due to the improved Li+ diffusion and electronic conductivity, induced by crystal defects and oxygen vacancy. This electrode demonstrates excellent cyclability and has more than 96% capacity even after 50 cycles. It is concluded that the concentration of dopants in the TiO2(B) structure plays an effective role in improving the electrochemical performance of electrodes.

Manufacture and characterization of a novel agro-waste based low cost metal matrix composite (MMC) by compocasting

Fabrication of low cost composites with enhanced properties has been of great interest for researchers across the globe. In line with this, the present work deals with a low cost production technique for an aluminium alloy composite using a cheaper and easily available reinforcement. The fabrication and mechanical characterization of Al6061 alloy reinforced with Lemon Grass Ash (LGA) particles are dealt in the present investigation. The metal matrix composites (MMCs) were prepared by the addition of 3, 5 and 7 wt% reinforcing particulates through compo-casting technique. Optical microscopy and Field Emission Scanning Electron Microscopy (FESEM) were used for metallurgical characterization exhibiting a homogeneous distribution of the LGA particles. Mechanical properties viz. tensile strength and hardness were found to be significant for these low cost composites. It was observed that the tensile property and the microhardness of the composites showed a linear improvement i.e. 160 MPa and 155 HV respectively at the optimum addition of LGA as reinforcement. Such improvement can be attributed to the fine dispersion of LGA particles offering resistance to the motion of dislocations in the matrix alloy.

Antibacterial Functionalization of PVD Coatings on Ceramics

The application of surface treatments that incorporate silver or copper as antibacterial elements has become a common practice for a wide variety of medical devices and materials because of their effective activity against nosocomial infections. Ceramic tiles are choice materials for cladding the floors and walls of operation rooms and other hospital spaces. This study is focused on the deposition of biocide physical vapor deposition (PVD) coatings on glazed ceramic tiles. The objective was to provide antibacterial activity to the surfaces without worsening their mechanical properties. Silver and copper-doped chromium nitride (CrN) and titanium nitride (TiN) coatings were deposited on samples of tiles. A complete characterization was carried out in order to determine the composition and structure of the coatings, as well as their topographical and mechanical properties. The distribution of Ag and Cu within the coating was analyzed using glow discharge optical emission spectrometry (GD-OES) and field emission scanning electron microscope (FE-SEM). Roughness, microhardness, and scratch resistance were measured for all of the combinations of coatings and dopants, as well as their wettability. Finally, tests of antibacterial efficacy against Staphylococcus aureus and Escherichia coli were carried out, showing that all of the doped coatings had pronounced biocide activity.

Experimental Study of Surface Hardening of AISI 420 Martensitic Stainless Steel Using High Power Diode Laser

In this paper laser surface hardening of martensitic stainless steel AISI 420 was conducted using a 1600 W semiconductor diode laser. Focal plane position, laser power and scanning speed were considered as process variables. Microhardness was measured in depth and surface of the hardened layer and metallography of samples were conducted in order to study the microstructure of the hardened zone. Macrography was also performed to measure the geometrical dimensions of hardened zone (width and depth). Microstructure evaluation was investigated through optical microscopy and field emission scanning electron microscopy. Microstructure observation of laser treated zone indicated that the higher surface hardness created the finer and more uniform martensitic phase. Results showed that by increasing the laser power and decreasing the focal plane position, depth of penetration and microhardness of hardened zone increased. By increasing the scanning speed and focal plane position, penetration depth decreased while width of hardened zone increased. Under desired conditions resulting from this research (laser power 1400 W, scanning speed 5 mm/s and focal plane position 65 mm), surface hardness of AISI 420 martensitic steel increased to 720 from 210 Vickers. The dimension of hardened layer was 1.2 mm in depth and 6.1 mm in width. Comparing the results with the furnace hardening heat treatment showed that the laser hardening process was more effective and precise than conventional processes.

Texturization of as-cut p-type monocrystalline silicon wafer using different wet chemical solutions

Implementing texturization process on the monocrystalline silicon substrate reduces reflection and enhances light absorption of the substrate. Thus texturization is one of the key elements to increase the efficiency of solar cell. Considering as-cut monocrystalline silicon wafer as base substrate, in this work different concentrations of Na2CO3 and NaHCO3 solution, KOH–IPA (isopropyl alcohol) solution and tetramethylammonium hydroxide solution with different time intervals have been investigated for texturization process. Furthermore, saw damage removal process was conducted with 10% NaOH solution, 20 wt% KOH–13.33 wt% IPA solution and HF/nitric/acetic acid solution. The surface morphology of saw damage, saw damage removed surface and textured wafer were observed using optical microscope and field emission scanning electron microscopy. Texturization causes pyramidal micro structures on the surface of (100) oriented monocrystalline silicon wafer. The height of the pyramid on the silicon surface varies from 1.5 to 3.2 µm and the inclined planes of the pyramids are acute angle. Contact angle value indicates that the textured wafer’s surface fall in between near-hydrophobic to hydrophobic range. With respect to base material absolute reflectance 1.049–0.75% within 250–800 nm wavelength region, 0.1–0.026% has been achieved within the same wavelength region when textured with 0.76 wt% KOH–4 wt% IPA solution for 20 min. Furthermore, an alternative route of using 1 wt% Na2CO3–0.2 wt% NaHCO3 solution for 50 min has been exploited in the texturization process.

Effects of conventional, severe, over, and re-shot peening processes on the fatigue behavior of mild carbon steel

The present study investigates experimentally the effects of different shot peening treatments, including conventional, severe, over, and re-shot peening on microstructure, mechanical properties, and fatigue behavior of AISI 1050 mild carbon steel. Different shot peening treatments were performed using various effective parameters by considering the influences of increasing Almen intensity and coverage. Optical microscopy and field emission scanning electron microscopy observations and X-Ray diffraction measurements were carried out to analyze grains refinement in each shot peening treatment. Microhardness and residual stress measurements were taken from shot peened surfaces to the core material to investigate the mechanical properties. The fatigue behaviors of the specimens were examined by using the axial fatigue test. The results indicated that post-grinding, re-shot peening, and severe shot peening processes have significant effects on fatigue life improvement.

Microstructure evolution and micro-mechanical behavior of secondary carbides at grain boundary in a Fe–Cr–W–Mo–V–C alloy

The microstructure evolution and micro-mechanical behavior of secondary carbides at grain boundary in a Fe–Cr–W–Mo–V–C alloy for cold work roll were systematically investigated in this study. The typical microstructures at the characteristic temperature of 1240°C, 1200°C and 1150°C were observed by Optical Microscope and Field Emission Scanning Electron Microscope. The hardness values of secondary carbides were predicted and measured by first-principles calculation, Vickers hardness tester and nanoindentation technique. The fracture toughness (KC) values were calculated by a method known as Indentation Microfracture. Single-pass scratch tests were carried out to investigate the micro-scale wear behavior of secondary carbides. The macroscopic pin-on-disk test was also performed. The results show that the secondary carbide at grain boundary contains secondary MC, M2C and M7C3. The formation of secondary MC and M7C3 belongs to the precipitation and growth process, while secondary M2C is the result from the growth of eutectic M2C. In the studied alloy, M7C3 is a dominant carbide in quantity, and has higher hardness than secondary M2C and the matrix, and processes the better toughness than secondary MC, whose hardness almost reaches 30GPa, and can also effectively resist the crack initiation and propagation, which therefore makes a significant contribution to the wear resistance of the alloy.

A Comparative Study of Microstructure and Mechanical Properties of 21-4-N Steel Weld Joints Using Different Filler Materials

The present study leads to the selection of matching filler materials to weld nitrogen alloyed austenitic stainless steel 21-4-N with the desired combination of properties. 7 mm thick 21-4-N hot rolled steel plates were butt welded by Gas Tungsten Arc Welding (GTAW) with ER2209 (nitrogen alloyed) and E309LMo stainless steel filler wire. Microstructure and mechanical properties of weld joint were studied. The various zones of weld joint were carried out using optical microscopy and field emission electron microscopy (FESEM). It was observed that the weld zone exhibited higher nitrogen content with ER2209 filler resulting in higher tensile strength and hardness.

Micro friction stir lap welding of AISI 430 ferritic stainless steel: a study on the mechanical properties, microstructure, texture and magnetic properties

In this study, the effect of friction stir welding of AISI 430 (X6Cr17, material number 1.4016) ferritic stainless steel is examined. Two thin sheets with dimensions of 0.4 × 50 × 200 mm3 are joined in lap configuration. Optical microscopy and field emission electron microscopy were used in order to microstructural evaluations and fracture analysis, respectively. Tensile test and microhardness measurements are employed in order to study the mechanical behaviors of welds. Also, vibrational sample magnetometry (VSM) is employed for characterizing magnetic properties of welded samples. Texture analysis is carried out in order to clarify the change mechanism of magnetic properties in the welded area. The results show that AISI 430 sheets are successfully joined considering both, the appearance of the welding bead and the strength of the welded joint. It is found that by friction stir welding of AISI 430 sheets, texture components with easy axes magnetization have been replaced by texture components with harder magnetization axes. VSM analysis showed that friction stir welding leads to increase in residual induction (Br) and coercivity (Hc). This increase is attributed to the grain refining due the friction stir welding and formation of texture components with harder axes of magnetizations.

Effect of UV-induce ozone treatment on physics and morphological properties of hydrothermally grown Ga-F-codoped ZnO nanostructure

The effects of ultraviolet ozone treatment (UVO treatment) on the physical and morphological structure of Ga/F co-doped Zn Onanorods. The ZnO seeding layers were prepared by sol-gel dip coating method based on zinc acetate dehydrate (CH3COO)2Zn•2H2O and diethanolamine ((HOCH2CH2)2NH, DEA) into absolute ethanol (C2H5OH) with concentration of 0.5 M. The seeding solution was dip-coated onto the cleaned glass substrates. The G/F co-doped ZnO nanorods were synthesized by hydrothermal process. The G/F co-doped ZnO nanorods were grown on seed layer with varied ultraviolet ozone treatment at 2, 4, 6, 8, 10, 12, 14, 16 and18 min. The influence of ultraviolet ozone treatment on physical, optical and morphological of G/F co-doped ZnO nanorods have been extensively scrutinized by X-ray diffraction (XRD) and optical spectroscopy, UV-Visible Spectrophotometer (UV-vis) and Field emission scanning electron microscope (FE-SEM). The effects of ultraviolet ozone treatment on different density of Ga/F co-doped ZnO nanorods were obtained as different ultraviolet ozone treatment were introduced.

The Petrography, Mineralogy and Geochemistry of Some Cu- and Pb-Enriched Coals from Jungar Coalfield, Northwestern China

The petrological, geochemical, and mineralogical composition of the Carboniferous-Permian coal deposit in the Jungar coalfield of inner Mongolia, Northwestern China, were investigated using optical microscopy and field emission scanning electron microscopy in conjunction with an energy-dispersive X-ray spectrometer (SEM-EDX), as well as X-ray powder diffraction, X-ray fluorescence, and inductively coupled plasma mass spectrometry. The Jungar coal is of high volatile C/B bituminous quality with 0.58% vitrinite reflectance and has a low sulfur content of 0.70% on average. Inertinite (mineral-free basis) generally dominates in coal from the lower part of the Shanxi formation, and vitrinite is the major maceral assemblage in the coal from the Taiyuan formation, which exhibits forms suggesting variation in the sedimentary environment. The Jungar coal is characterized by higher concentrations of copper (Cu) in No. 6 coal, at 55 μg/g, and lead (Pb) in No. 4 coal at 42 μg/g. Relative to the upper continental crust, the rare earth elements (REE) in the coal are characterized by light and medium–heavy REE enrichment. The minerals in the Jungar coal are mainly kaolinite, dickite, pyrite, calcite, siderite, quartz, and, to a lesser extent, gypsum and K-feldspar. The enrichment and occurrence of the trace elements, and of the minerals in the coal, are attributed to the fragmental parent rock during diagenesis and coalification. The main elements with high enrichment factors, Cu and Pb, overall exhibit a notably inorganic sulfide affinity and a weak organic affinity. Primary and epigenetic sedimentary environment and the lithology of the terrigenous parent rock are the key factors that influence the occurrence and formation of Cu and Pb in coal. The depositional environment is more influential in the formation of Cu than Pb in coal. Lead is more easily affected by the terrigenous factors than Cu when they are under a similar depositional environment.

Improving the wetting and dissolution of ibuprofen using solventless co-milling

The wetting and dissolution of a BCS class II drug (Ibuprofen) is enhanced by solventless solid dispersion technique using co-milling. The co-milling is performed in a planetary ball mill using 1:1wt. ratio of Ibuprofen (drug) and Microcrystalline cellulose, MCC (excipient). The improvement in wettability and dissolution after co-milling are compared with the raw ibuprofen, ball-milled ibuprofen without any excipient and v-blend mixture of ibuprofen with an excipient. The changes in crystal level properties and reduction in crystallinity due to co-milling are measured using Powder X-ray diffraction (P-XRD) and Differential Scanning Calorimetry (DSC) respectively. The increased interaction between ibuprofen and MCC as well as hydrogen bond formation is confirmed by Fourier Transform Infrared Spectroscopy (FTIR). The morphological changes are observed by optical microscopy and Field Emission Scanning Electron Microscopy (FESEM). The miscibility of drug and excipient and evidence of formation of glassy solutions are demonstrated by Modulated Temperature Differential Scanning Calorimetry (MTDSC) and Raman microscopy. The surface energy and wetting properties are determined using Inverse Gas Chromatography (IGC) and sessile drop method respectively. The results show that co-milling generates defects, strain, and reduction in crystallite size (changes in crystal level properties) which are responsible for the improvement of wetting and dissolution (96% in 90min). Also, with increase in co-milling time, the polar surface energy increases and the hydrophobic ibuprofen drug surface transforms into hydrophilic surface due to increase in OH groups of MCC on the ibuprofen surface. The present work quantified all the above-mentioned parameters including the acidic and basic parameters of co-milled ibuprofen using IGC. The technique improves the wetting and dissolution of hydrophobic drugs. It can be very well extended to BCS class II and IV drugs in the presence of different hydrophilic excipients.

Surface modification and characterization of zirconium carbide particulate reinforced C70600 CuNi composite fabricated via friction stir processing

In the present research work, Friction stir processing (FSP) technique has been applied to develop a C70600 graded copper-nickel (CuNi) Surface metal matrix composite (SMMC) reinforced with and without addition of ZrCp. Rotational and traverse speeds were set as 1200 rpm and 30 mm/min, respectively. The fabricated SMMC were metallurgically characterized by using Optical microscope (OM) and Field emission scanning electron microscope (FESEM). The homogeneous distribution of ZrC particles and good interfacial bonding between matrix/reinforcement were observed via OM and FESEM microscopes. The microhardness of the CuNi/ZrC surface composite was observed by using microhardness tester at the cross section of the sample. The average higher microhardness of 148 Hv at CuNi/ZrC SMMC and lower microhardness of 115 Hv at FSPed CuNi was found. The Ultimate tensile strength (UTS) value was measured by using micro tensile testing machine. The UTS value of CuNi/ZrC composite and FSPed CuNi were observed to be 310 MPa and 302 MPa, respectively. The mode of fracture was also observed via FESEM. The X-ray diffraction (XRD) test was carried out to confirm the presence of CuNi & ZrC in the SMMC layer.

Effect of Austempering Time on the Microstructure and Carbon Partitioning of Ultrahigh Strength Steel 56NiCrMoV7

Ultrahigh strength steel 56NiCrMoV7 was austempered at 270 °C for different durations in order to investigate the microstructure evolution, carbon partitioning behaviour and hardness property. Detailed microstructure has been characterised using optical microscopy and field emission gun scanning electron microscopy. A newly developed X-ray diffraction method has been employed to dissolve the bainitic/martensitic ferrite phase as two sub-phases of different tetragonal ratios, which provides quantitative analyses of the carbon partitioning between the resultant ferrites and the retained austenite. The results show that, a short-term austempering treatment was in the incubation period of the bainite transformation, which resulted in maximum hardness being equivalent to the oil-quenching treatment. The associated microstructure comprises fine carbide-free martensitic and bainitic ferrites of supersaturated carbon contents as well as carbon-rich retained austenite. In particular, the short-term austempering treatment helped prevent the formation of lengthy martensitic laths as those being found in the microstructure of oil-quenched sample. When the austempering time was increased from 20 to 80 min, progressive decrease of the hardness was associated with the evolution of the microstructure, including progressive coarsening of bainitic ferrite, carbide precipitating inside high-carbon bainitic ferrite and its subsequent decarbonisation.