Characteristic Length of Metallic Nanorods under Physical Vapor Deposition

By using physical vapor deposition(PVD)to grow metallic nanorods,the characteristic length is controllable,which can be identified by two different growth modes:Mode I and Mode II.In Mode I,the growth of metallic nanorods is dominated by the monolayer surface steps.Whereas in Mode II,the growth mechanism is mainly determined by the multilayer surface steps.In this work,we focused on the analysis of the physical process of Mode I,in which the adatoms diffuse on the monolayer surface at beginning,then diffuse down to the next monolayer surface,and finally result in the metallic nanorods growth.Based on the physical process,both the variations of the characteristic length and the numerical solutions were theoretically proposed.In addition,the twodimensional(2 D)lattice kinetic Monte Carlo simulations were employed to verify the theoretical derivation of the metallic nanorods growth.Our results pay a new way for modifying the performance of metallic nanorods-based applications and devices.

Achieving highly uniform two-dimensional PbI2 flakes for photodetectors via space confined physical vapor deposition

Two-dimensional(2D) PbI_2 flakes have been attracting intensive attention as one potential candidate for the modern optoelectronics. However, suffered from the instability of kinetics-driven growth, the fabricated 2D PbI_2 flakes have a wide dimensional distribution even under the same conditions. Herein, a novel facile space confined physical vapor deposition(PVD) process is provided to synthesize uniform triangle PbI_2 flakes with high quality. The confined space provides a relatively stable growth environment that renders more control on the growth kinetics, leading to highly uniform triangle PbI_2 flakes with the average size of 5 mm and thickness of 17 nm. Moreover, as-fabricated PbI_2-based photodetectors show promising stable and flexible optoelectronic performances to 470 nm light, including high responsivity(0.72 AW^(-1)), large on/off ratio up to 900, fast photoresponse speed(rise time of 13.5 ms and decay time of 20 ms) and high detectivity(1.04×10^(10) Jones). The well-controllable growth of the uniform triangle PbI_2 flakes and the detailed exploration of their optoelectronic properties are particularly valuable for their further practical applications.

Plasma spray-physical vapor deposition toward advanced thermal barrier coatings:a review

Plasma spray–physical vapor deposition(PS–PVD)is a unique technology that enables highly tailorable functional films and coatings with various rare metal elements to be processed.This technology bridges the gap between conventional thermal spray and vapor deposition and provides a variety of coating microstructures composed of vapor,liquid,and solid deposition units.The PS–PVD technique serves a broad range of applications in the fields of thermal barrier coatings(TBCs),environmental barrier coatings(EBCs),oxygen permeable films,and electrode films.It also represents the development direction of high-performance TBC/EBC preparation technologies.With the PS–PVD technique,the composition of the deposition unit determines the microstructure of the coating and its performance.When coating materials are injected into a nozzle and transported into the plasma jet,the deposition unit generated by a coating material is affected by the plasma jet characteristics.However,there is no direct in situ measurement method of material transfer and deposition processes in the PS–PVD plasma jet,because of the extreme conditions of PS–PVD such as a low operating pressure of*100 Pa,temperatures of thousands of degrees,and a thin and high-velocity jet.Despite the difficulties,the transport and transformation behaviors of the deposition units were also researched by optical emission spectroscopy,observation of the coating microstructure and other methods.This paper reviews the progress of PS–PVD technologies considering the preparation of advanced thermal barrier coatings from the perspective of the transport and transformation behaviors of the deposition units.The development prospects of new high-performance TBCs using the PS–PVD technique are also discussed.

^(60)Co Gamma Irradiation and Annealing Effects on Transport Properties of Antimony Telluride Platelets Grown by Physical Vapor Deposition

Physical vapor deposition method was employed to deposit antimony telluride （Sb2Te3） crystals in a dual-zone furnace. The microstructure, surface topography and composition of samples were characterized using X-ray diffraction, atomic force and scanning electron microscopy. Seebeck coefficient （Sic）, electrical conductivity （σ⊥c） as well as power factor （PF） were enhanced for pure Sb2Te3 samples upon annealing, and the samples annealed at 473 K exhibited the highest PF of 3.16 × 10^-3 W m-1K-2 with an enhancement of 22% in the figure of merit （Z）. When the delivered dose of 60Co gamma radiation was increased from 0 to 30 kGy in the stoichiometric crystals, σ⊥c decreased due to the decrease in mobility. As a result of the increase in S, PF and Z improved by 12.11 and 13.7%, respectively, in the 30 kGy gamma- irradiated crystals. Both RH （BIIc） and S⊥c were positive, suggesting that the prepared Sb2Te3 crystals retained the p-type semiconductivity after these treatments.

A perspective of microplasma oxidation (MPO) and vapor deposition coatings in surface engineering of aluminum alloys

Over the past years, great achievements have been made in the development of coating technologies for surface improvement of aluminum alloys. Despite these achievements, the role in the market strongly depends on the ability of surface coating technology under technical and economic considerations to meet the increased demands for heavy tribological applications of aluminum alloys. Microplasma oxidation (MPO) technology has recently been studied as a novel and effective means to provide thick and hard ceramic coating with improved properties such as excellent load-bearing and wear resistance properties on aluminum alloys. The present work covers the evaluation of the performances of current single and duplex coatings combining MPO, physical vapor deposition (PVD), and plasma assisted chemical vapor deposition (PACVD) coatings on aluminum alloys. It suggests that the MPO coating is a promising candidate for design engineers to apply aluminum alloys to heavy load-bearing applications. The prospective future for the research on MPO coatings is introduced as well.

Influence of Deposition Temperature on the Electrical and Electrochemical Properties of Carbon-Based Coatings for Metallic Bipolar Plates, Prepared by Cathodic Arc Evaporation

Cathodic arc evaporation is a well-established physical vapor deposition technique which is characterized by a high degree of ionization and high deposition rate. So far, this technique has been mainly used for the deposition of tribological coatings. In this study, anti-corrosive and electrical conductive carbon-based coatings with a metallic interlayer were prepared on stainless steel substrates as surface modification for metallic bipolar plates. Hereby, the influence of the deposition temperature during the deposition of the carbon top layer was investigated. Raman spectroscopy revealed differences in the microstructure at 200°C compared to 300°C and 100°C. Measurements of the interfacial contact resistance showed that the deposited coatings significantly improve the electrical conductivity. There are only minor differences between the different carbon top layers. The corrosion resistance of the coatings was studied via potentiodynamic polarization at room temperature and 80°C. Experiments showed that the coating with a carbon top layer deposited at 200°C, considerably reduces the current density and thus corrosion of the substrate is suppressed.

Fabrication of Gd_(2)O_(3)-doped CeO_(2)thin films through DC reactive sputtering and their application in solid oxide fuel cells

Physical vapor deposition(PVD)can be used to produce high-quality Gd_(2)O_(3)-doped CeO2(GDC)films.Among various PVD methods,reactive sputtering provides unique benefits,such as high deposition rates and easy upscaling for industrial applications.GDC thin films were successfully fabricated through reactive sputtering using a Gd_(0.2)Ce_(0.8)(at%)metallic target,and their application in solid oxide fuel cells,such as buffer layers between yttria-stabilized zirconia(YSZ)/La0.6Sr0.4Co0.2Fe0.8O_(3−δ)and as sublayers in the steel/coating system,was evaluated.First,the direct current(DC)reactive-sputtering behavior of the GdCe metallic target was determined.Then,the GDC films were deposited on NiO-YSZ/YSZ half-cells to investigate the influence of oxygen flow rate on the quality of annealed GDC films.The results demonstrated that reactive sputtering can be used to prepare thin and dense GDC buffer layers without high-temperature sintering.Furthermore,the cells with a sputtered GDC buffer layer showed better electrochemical performance than those with a screen-printed GDC buffer layer.In addition,the insertion of a GDC sublayer between the SUS441 interconnects and the Mn-Co spinel coatings contributed to the reduction of the oxidation rate for SUS441 at operating temperatures,according to the area-specific resistance tests.

Effect of heat treatment on microstructure and tensile strength of NiCoCrAl alloy sheet fabricated by EB-PVD

The NiCoCrAl alloy sheet was fabricated by electron beam physical vapor deposition technique and the effects of the heat treatment on the microstructure and tensile strength of the NiCoCrAl alloy sheet were investigated. The heat treatment at 1050 °C is favorable to improve the interface bonding between the columnar structures due to the disappearance of the intergranular gaps. Comparing with the thin NiCoCrAl alloy sheet before heat treatment, the Ni3Al phase appears in the NiCoCrAl alloy sheet after heat treatment, which is favorable to improve the interface bonding between the columnar structures. The increase in the tensile strength and elongation is attributed to the improvement of the interface bonding between the columnar structures. The residual stress in the NiCoCrAl alloy sheet after heat treatment is reduced significantly, which also confirms that the interface bonding is improved by the heat treatment.

Ferromagnetic MnSb Films Consisting of Nanorods and Nanoleaves

Ferromagnetic MnSb films were synthesized on Si wafers by physical vapor deposition. X-ray diffraction revealed that the films primarily consisted of MnSb alloy. Nanorods and nanoleaves were observed in the MnSb films by field-emission scanning electron microscopy. These nanorods had an average diameter of 20nm and a length of up to hundreds of nanometers. The nanoleaves had a width and thickness of about 100 and 20nm, respectively. Magnetic hysteresis loops were measured by an alternative gradient magnetometer, and the loops showed strong geometrical anisotropy.

Comparison of TiAlN, AlCrN, and AlCrN/TiAlN coatings for cutting-tool applications

Monolayer and bilayer coatings of TiAlN, AlCrN, and AlCrN/TiAlN were deposited onto tungsten carbide inserts using the plasma enhanced physical vapor deposition process. The microstructures of the coatings were characterized using scanning electron microscopy （SEM） and atomic force microscopy （AFM）. The SEM micrographs revealed that the AlrN and AlCrN/TiAlN coatings were uniform and highly dense and contained only a limited number of microvoids. The TiAIN coating was non-uniform and highly porous and contained more micro droplets. The hardness and scratch resistance of the specimens were measured using a nanoindentation tester and scratch tester, respectively. Different phases formed in the coatings were analyzed by X-ray diffraction （XRD）. The AlCrN/TiAlN coating exhibited a higher hardness （32.75 GPa）, a higher Young＇s modulus （561.97 GPa）, and superior scratch resistance （LcN = 46 N） compared to conventional coatings such as TiAlN, A1CrN, and TiN.

Effects of heat treatment on mechanical properties of ODS nickel-based superalloy sheets prepared by EB-PVD

A Y2O3 dispersion strengthened nickel-based superalloy sheet（0.15 mm thick） was prepared by electron beam physical vapor deposition（EB-PVD） technology.Different heat treatments were used to improve the mechanical properties of the alloy sheet.Differential thermal analysis（DTA） was used to examine the thermal stability of the as-deposited sheet.Element contents,phase composition and microstructure investigations on as-deposited and heat treated specimens were performed by X-ray fluorescence spectrometer（XRF）,X-ray diffraction（XRD） and scanning electron microscopy（SEM）.Tensile tests were conducted at room temperature on specimens as-deposited and heat treated.The results show that the as-deposited sheet is composed of equiaxed grains on the substrate side and columnar grains on the evaporation side.The as-deposited sheet shows poor ductility due to micropores between columnar grains.The strength and ductility can be improved effectively by annealing at 800°C for 3 h.For samples treated at 1100°C,the strength drops down due to the precipitates of Y3Al5O12（YAG）.

Preparation of a Novel Micro/nano Tubes via Electrospun Fiber as a Template

Poly (para-xylylene) hollow fibers with inner diameters can be prepared via template fibers electrospun from solutions. The PPX is deposited from the vapor phase and the template fiber is selectively removed by heat treatment or solvent extraction. The PPX is partially crystalline and the crystal modification depending on the route is used to extract the template fiber. The thermal stability of the hollow fibers is only slightly reduced relative to the bulk material and the same holds for the UV-stability.

Electrochemical evaluation of zinc and magnesium alloy coatings deposited on electrogalvanized steel by PVD

Zinc alloy coating attracted much attention due to its high anti-corrosive properties.Particularly,zinc alloy coatings containing magnesium was considered a promising metallic alloy due to a remarkable improvement of corrosion resistance.The proper magnesium content for Zn-Mg alloy coatings was studied.The samples were prepared using thermal evaporation method.The influence of Zn-Mg alloy coating on corrosion resistance was evaluated using immersion test,potentiodynamic test,and galvanic test in 3% NaCl solution at room temperature.The results show that the corrosion resistance of Zn-Mg alloy coatings is strongly dependent on magnesium content.Corrosion potential decreases with increasing magnesium content,whereas current density increases up to 15% magnesium content,and passivity region was found only in Zn-Mg coatings.

Effect of pulsed bias on the properties of ZrN/TiZrN films deposited by a cathodic vacuum arc

ZrN/TiZrN multilayers are deposited by using the cathodic vacuum arc method with different substrate bias（from 0 to 800 V）,using Ti and Zr plasma flows in residual N 2 atmosphere,combined with ion bombardment of sample surfaces.The effect of pulsed bias on the structure and properties of films is investigated.Microstructure of the coating is analyzed by X-ray diffraction（XRD）,and scanning electron microscopy（SEM）.In addition,nanohardness,Young＇s modulus,and scratch tests are performed.The experimental results show that the films exhibit a nanoscale multilayer structure consisting of TiZrN and ZrN phases.Solid solutions are formed for component TiZrN films.The dominant preferred orientation of TiZrN films is（111） and（220）.At a pulsed bias of 200 V,the nanohardness and the adhesion strength of the ZrN/TiZrN multilayer reach a maximum of 38 GPa,and 78 N,respectively.The ZrN/TiZrN multilayer demonstrates an enhanced nanohardness compared with binary TiN and ZrN films deposited under equivalent conditions.

Fabrication and characterization of rugate structures composed of SiO_(2) and Nb_(2)O_(5)

Gradient index layers and rugate structures were fabricated on a Leybold Syrus pro deposition system by plasma-assisted coevaporation of the low index material silica and the high index material niobium pentoxide.To obtain information about the compositional profiles of the produced layers,cross sectional transmission electron microscopy was used in assistance to deposition rate data recorded by two independent crystal monitors during the film preparation.The depth dependent concentration profiles were transformed to refractive index gradients by means of effective medium approximation.Based on the refractive index gradients the corresponding samples`transmission and reflection spectra could be calculated by utilizing matrix formalism.The relevance of the established refractive index profiles could be verified by comparison of the calculated spectra with the measured ones.

Oxidation and Hot Corrosion of Gradient Thermal Barrier Coatings Prepared by EB-PVD

The performances of gradient thermal barrier coatings (GTBCs) produced by EB-PVD were evaluated by isothermal oxidation and cyclic hot corrosion (HTHC) tests. Compared with conventional two-layered TBCs, the GTBCs exhibite better resistance to not only oxidation but also hot-corrosion. A dense Al2O3 layer in the GTBCs effectively prohibites inward diffusion of O and S and outward diffusion of Al and Cr during the tests. On the other hand, an "inlaid" interface, resulting from oxidation of the Al along the columnar grains of the bond coat, enhances the adherence of AI2O3 layer. Failure of the GTBC finally occurred by cracking at the interface between the bond coat and AI2O3 layer, due to the combined effect of sulfidation of the bond coat and thermal cvcling.

Residual stress of physical vapor-deposited polycrystalline multilayers

An extended one-dimensional stress model for the deposition of multilayer films is built based on the existing stress model by considering the influence of deposition conditions. Both thermal stress and intrinsic stress are considered to constitute the final residual stress in the model. The deposition process conditions such as deposition temperature, oxygen pressure, and film growth rate are correlated to the full stress model to analyze the final residual stress distribution, and thus the deformation of the deposited multilayer system under different process conditions. Also, the model is numerically realized with in-house built code. A deposition of Ag-Cu multilayer system is simulated with the as-built extended stress model, and the final residual stresses under different deposition conditions are discussed with part of the results compared with experiment from other literature.

Structural, Optical and Electrical Properties of Li-doped ZnO Thin Films Influenced by Annealing Temperature

Li-doped ZnO thin films had been grown by radio frequency magnetron sputtering and then annealed under various annealing temperatures. The characteristics of ZnO films were examined by XRD, FESEM, Hall measurement and optical transmission spectra. Results showed that p type conduction was observed in Li doped ZnO films annealed at 500-600 ℃ and thep type ZnO films possessed a good crystalline with c-axis orientation, dense surface, and average transmission of about 85% in visible spectral region.

Promising Electrode and Electrolyte Materials for High-Energy-Density Thin-Film Lithium Batteries

All-solid-state thin-film lithium batteries(TFLBs)are the ideal wireless power sources for on-chip micro/nanodevices due to the significant advantages of safety,portability,and integration.As the bottleneck for increasing the energy density of TFLBs,the key components of cathode,electrolyte,and anode are still underway to be improved.In this review,a brief history of TFLBs is first outlined by presenting several TFLB configurations.Based on the state-of-the-art materials developed for lithium-ion batteries(LIBs),the challenges and related strategies for the application of those potential electrode and electrolyte materials in TFLBs are discussed.Given the advanced manufacture and characterization techniques,the recent advances of TFLBs are reviewed for pursuing the high-energy-density and long-termdurability demands,which could guide the development of future TFLBs and analogous all-solid-state lithium batteries.

Characterization of EBPVD micro-layer composites and simulation of its internal stress state

Based on the basic operating principal and the technology characteristic of electron beam physical vapor deposition(EBPVD) technique, EBPVD was used to prepare the micro-layer composites. The effect on the substrate preheating temperature was taken into accounts and the finite element analysis package ANSYS was used to simulate the internal stress field and the potential displacement changing tendency. The results show that one of the most important quality factors on the judgment of micro-layer composites is the adhesion between the substrate and the deposition layers as well as among the different deposition layers. Besides the existance of temperature gradient through the thickness of layers, the main reason for the internal stress in micro-layer composites is the mismatch of various properties of the layer and the substrate of different thermal expansions and crystal lattice types. With the increase of substrate preheating temperature, the inter-laminar shear stress also takes on a tendency of increase but the axial residual stress decrease.