Microstructure evolution and mechanical properties of Ti-B-N coatings deposited by plasma-enhanced chemical vapor deposition

Ternary Ti-B-N coatings were synthesized on AISI 304 and Si wafer by plasma-enhanced chemical vapor deposition (PECVD) technique using a gaseous mixture of TiCl4,BCl3,H2,N2,and Ar.By virtue of X-ray diffraction analysis,X-ray photoelectron spectroscopy,scanning electron microscope,and high-resolution transmission electron microscope,the influences of B content on the microstructure and properties of Ti B N coatings were investigated systematically.The results indicated that the microstructure and mechanical properties of Ti-B-N coatings largely depend on the transformation from FCC-TiN phase to HCP-TiB2 phase.With increasing B content and decreasing N content in the coatings,the coating microstructure evolves gradually from FCC-TiN/a-BN to HCP-TiB2 /a-BN via FCC-TiN+HCP-TiB2/a-BN.The highest microhardness of about 34 GPa is achieved,which corresponds to the nanocomposite Ti-63%B-N (mole fraction) coating consisting of the HCP-TiB2 nano-crystallites and amorphous BN phase.The lowest friction-coefficient was observed for the nanocomposite Ti-41%B-N (mole fraction) coating consisting of the FCC-TiN nanocrystallites and amorphous BN

Influence of Annealing on Properties of ZnO Films Grown via Plasma-enhanced MOCVD

The structural and the optical properties of ZnO films with high quality grown via plasma-enhanced metal\|organic chemical vapour deposition(MOCVD) on C-plane sapphire substrate were studied. The crystallinity and the optical properties of the films are greatly improved having been annealed in oxygen plasma atmosphere. The structure, the band gap and the binding energy of O 1s electrons, and the molar ratio of O to Zn were determined by X-ray diffraction(XRD), photoluminescence(PL) and X-ray photoelectron scan methods. For both the annealed and the as-grown films, the exciton peak features were observed at room temperature. The band-edge photoluminescence of the annealed film is much stronger than that of the as-grown film, and the exciton peak relating to the deep level at 439 nm disappears. The molar ratio of O to Zn in the annealed film is 0 91, while it is 0 78 for the as-grown film.

Influence of oxygen on the growth of cubic boron nitride thin films by plasma-enhanced chemical vapour deposition

Cubic boron nitride thin films were deposited on silicon substrates by low-pressure inductively coupled plasmaenhanced chemical vapour deposition. It was found that the introduction of 02 into the deposition system suppresses both nucleation and growth of cubic boron nitride. At a B2H6 concentration of 2.5% during film deposition, the critical O2 concentration allowed for the nucleation of cubic boron nitride was found to be less than 1.4%, while that for the growth of cubic boron nitride was higher than 2.1%. Moreover, the infrared absorption peak observed at around 1230- 1280 cm^-1, frequently detected for cubic boron nitride films prepared using non-ultrahigh vacuum systems, appears to be due to the absorption of boron oxide, a contaminant formed as a result of the oxygen impurity. Therefore, the existence of trace oxygen contamination in boron nitride films can be evaluated qualitatively by this infrared absorption peak.

Effects of various substrate materials on structural and optical properties of amorphous silicon nitride thin films deposited by plasma-enhanced chemical vapor deposition

The plasma-enhanced chemical vapor deposition(PECVD)technique is well suited for fabricating optical filters with continuously variable refractive index profiles;however,it is not clear how the optical and structural properties of thin films differ when deposited on different substrates.Herein,silicon nitride films were deposited on silicon,fused silica,and glass substrates by PECVD,using silane and ammonia,to investigate the effects of the substrate used on the optical properties and structures of the films.All of the deposited films were amorphous.Further,the types and amounts of Si-centered tetrahedral Si–SivN4-v bonds formed were based upon the substrates used;Si–N4 bonds with higher elemental nitrogen content were formed on Si substrates,which lead to obtaining higher refractive indices,and the Si–SiN3 bonds were mainly formed on glass and fused silica substrates.The refractive indices of the films formed on the different substrates had a maximum difference of0.05(at 550 nm),the refractive index of SiNx films formed on silicon substrates was 1.83,and the refractive indices of films formed on glass were very close to those formed on fused silica.The deposition rates of these SiNx films are similar,and the extinction coefficients of all the films were lower than 10-4.

Growth of Gallium Nitride Films on Multilayer Graphene Template Using Plasma-Enhanced Atomic Layer Deposition

In this work,the GaN thin films were directly deposited on multilayer graphene(MLG)by plasma-enhanced atomic layer deposition.The deposition was carried out at a low temperature using triethylgallium(TEGa)precursor and Ar/N2/H2 plasma.Chemical properties of the bulk GaN and GaN-graphene interface were analyzed using X-ray photoelectron spectroscopy.The sharp interface between GaN and graphene was verified via X-ray reflectivity and transmission electron microscope.The microstructures and the nucleation behaviors of the GaN grown on graphene have been also studied.The results of grazing incidence X-ray diffraction and Raman spectrum indicate that the as-deposited sample is polycrystalline with wurtzite structure and has a weakly tensile stress.Optical properties of the sample were investigated by photoluminescence(PL)at room temperature.The successful growth of GaN on MLG at a low temperature opens up the possibility of ameliorating the performance of electronic and optical devices based on GaN/graphene heterojunction.

From Amorphous Carbon to Carbon Nanobelts and Vertically Oriented Graphene Nanosheets Synthesized by Plasma-enhanced Chemical Vapor Deposition

Carbon materials with various structures were produced via plasma-enhanced chemical vapor deposition by controlling substrate temperature and mixed gases in the atmosphere. Scanning electron microscopy（SEM）, transmission electron microscopy（TEM）, high resolution transmission electron microscopy（HRTEM） and Raman spectroscopy were employed to investigate the morphology and structure of the materials. The results show that at a low substrate temperature（100 ~C） in CHa：Ar（flow rate ratio was 100 cm3/min：10 cm3/min）, amorphous carbon formed on Si（100） that could act as a support for the growth of carbon nanobelt and layer graphene at 800 ~C. Vertically oriented multi-layer graphene nanosheets（GNs） were catalyst-free synthesized on Si and Ni foam at 800 ~C in a mixture of CHa：Ar（20 cm3/min：60, 80 and 100 cm3/min）. The capacitor character investigated by cyclic voltammetry and galvanostatic charge/discharge indicates that for the as-synthesized GNs, the electrochemical capacitance is very small（16 F/g at current density of 16 A/g）. However, having been treated in acidic solution, the GNs exhibited good capacitive behavior, with a capacitance of 166 F/g, and after 800 charge/discharge cycles at 32 A/g, the capacitance could retain about 88.4%. The enhancement of specific capacitance is attributed to the increase of specific surface area after etching treatment of them.

Electrical and Corrosion Properties of Titanium Aluminum Nitride Thin Films Prepared by Plasma-Enhanced Atomic Layer Deposition

Titanium-aluminum-nitride（TiAlN） films were grown by plasma-enhanced atomic layer deposition（PEALD）on 316 L stainless steel at a deposition temperature of 200 °C. A supercycle, consisting of one AlN and ten TiN subcycles, was used to prepare TiAlN films with a chemical composition of Ti（0.25）Al（0.25）N（0.50）. The addition of AlN to TiN resulted in an increased electrical resistivity of TiAlN films of 2800 μΩ cm, compared with 475 μΩ cm of TiN films, mainly due to the high electrical resistivity of AlN and the amorphous structure of TiAlN. However, potentiostatic polarization measurements showed that amorphous TiAlN films exhibited excellent corrosion resistance with a corrosion current density of 0.12 μA/cm^2, about three times higher than that of TiN films, and about 12.5 times higher than that of 316 L stainless steel.

Effect of trace oxygen on plasma nitriding of titanium foil

Titanium nitride films are prepared by plasma enhanced chemical vapor deposition method on titanium foil using N_(2) as precursor. In order to evaluate the effect of oxygen on the growth of titanium nitride films, a small amount of O_(2) is introduced into the preparation process. The study indicates that trace O_(2) addition into the reaction chamber gives rise to significant changes on the color and micro-morphology of the foil, featuring dense and long nano-wires. The as-synthesized nanostructures are characterized by various methods and identified as TiN, Ti_(2) N, and TiO_(2) respectively. Moreover, the experiment results show that oxide nanowire has a high degree of crystallinity and the nitrides present specific orientation relationships with the titanium matrix.

Confining TiO_2 Nanotubes in PECVD-Enabled Graphene Capsules Toward Ultrafast K-Ion Storage: In Situ TEM/XRD Study and DFT Analysis

Titanium dioxide(TiO2) has gained burgeoning attention for potassium-ion storage because of its large theoretical capacity,wide availability,and environmental benignity.Nevertheless,the inherently poor conductivity gives rise to its sluggish reaction kinetics and inferior rate capability.Here,we report the direct graphene growth over TiO2 nanotubes by virtue of chemical vapor deposition.Such conformal graphene coatings effectively enhance the conductive environment and well accommodate the volume change of TiO2 upon potassiation/depotassiation.When paired with an activated carbon cathode,the graphene-armored TiO2 nanotubes allow the potassium-ion hybrid capacitor full cells to harvest an energy/power density of 81.2 Wh kg-1/3746.6 W kg-1.We further employ in situ transmis sion electron microscopy and ope rando X-ray diffraction to probe the potassium-ion storage behavior.This work offers a viable and versatile solution to the anode design and in situ probing of potassium storage technologies that is readily promising for practical applications.

Simple method to rapidly fabricate chain-like carbon nanotube films and its field emission properties

A simple process to fabricate chain-like carbon nanotube （CNT） films by microwave plasma-enhanced chemical vapor deposition （MPCVD） was developed successfully. Prior to deposition, the Ti/Al2O3 substrates were ground with Fe-doped SiO2 powder. The nano-structure of the deposited films was analyzed by scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, and Raman spectroscopy. The field electron emission characteristics of the chain-like carbon nanotube films were measured under the vacuum of 10-5 Pa. The low turn-on field of 0.80 V/μm and the emission current density of 8.5 mA/cm2 at the electric field of 3.0 V/μm are obtained. Based on the above results, chain-like carbon nanotube films probably have important applications in cold cathode materials and electrode materials.

In-Situ Nitrogen Doping of the TiO2 Photocatalyst Deposited by PEALD for Visible Light Activity

In this paper, an N-doped titanium oxide （TiO2） photocatalyst is deposited by a plasma-enhanced atomic layer deposition （PEALD） system through the in-situ doping method. X-ray photoelectron spectroscopy （XPS） analysis indicates that substitutional nitrogen atoms （-395.9 eV） with 1 atom% are effectively doped into TiO2 films. UV-VIS spectrometry shows that the in-situ nitrogen doping method indeed enhances the visible-activity of TiO2 films in the 425-550 nm range, and the results of the performance tests of the N-doped TiO2 films also imply that the photocatalysis activity is improved by in-situ doping. The in-situ doping mechanism of the N-doped TiO2 film is suggested according to the XPS results and the typical atomic layer deposition process.

Roll-to-roll fabrication of large-scale polyorgansiloxane thin film with high flexibility and ultra-efficient atomic oxygen resistance

One of the most widely used and well-established atomic oxygen(AO)protection solutions for low Earth orbit(LEO)satellites is the deposition of protective coatings on polymeric materials.However,manufacturing extensive expanses of these coating materials with good transparency,flexibility,smoothness,ultra-thinness,and exceptional AO resistance remains a critical issue.Herein,we successfully deposited a 400 nm thick polyorgansiloxane(SiO_(x)C_(y)H_(z))coating with high optical transparency and uniform good adherence on to a 1.2 m wide polyimide surface,by optimizing the distribution of hexamethyldisiloxane and oxygen as precursors in the roll-to-roll compatible plasmaenhanced chemical vapor deposition process.After AO irradiation with the fluence of 7.9×10^(20)atoms·cm^(–2),the erosion yield of the SiO_(x)C_(y)H_(z)-coated Kapton was less than 2.30×10^(–26)cm^3·atom^(–1),which was less than 0.77%of that of the Kapton.It indicates that the SiO_(x)C_(y)H_(z)coating can well prevent the erosion of Kapton by AO.In addition,it was also clarified that a SiO_(2) passivation layer was formed on the surface of the SiO_(x)C_(y)H_(z)coating during AO irradiation,which exhibited a‘self-reinforcing’defense mechanism.The entire preparation process of the SiO_(x)C_(y)H_(z)coating was highly efficient and low-cost,and it has shown great potential for applications in LEO.

Effects of SiN_x on two-dimensional electron gas and current collapse of AlGaN/GaN high electron mobility transistors

SiNx is commonly used as a passivation material for AlGaN/GaN high electron mobility transistors （HEMTs）. In this paper, the effects of SiNx passivation film on both two-dimensional electron gas characteristics and current collapse of A1GaN/GaN HEMTs are investigated. The SiNx films are deposited by high- and low-frequency plasma-enhanced chemical vapour deposition, and they display different strains on the AlGaN/GaN heterostructure, which can explain the experiment results.

Effects of the Fabrication Processes of NC-Si:H Films on Their Mechanical Properties

Studies of nanoindentation were performed on nc-Si：H films to evaluate the effects of the fabrication processes on their mechanical properties. It is observed that with the decrease of the SiH4 contents, the grain size of the films increases gradually, and as does the crystalline volume fraction. The smaller the grains become, the more homogeneous the films, and the more even the hardness as well as the modulus will be. The hardness and the modulus will increase with the substrate＇s temperature rising. The hardness and the modulus of the nc-Si：H films on the Si substrate prove to be higher than those on the glass substrate given the same technology parameters. How- ever, the films on the glass substrate appear to be more homogeneous.

SUBSTRATE EFFECT ON HYDROGENATED MICROCRYSTALLINE SILICON FILMS DEPOSITED WITH VHF-PECVD TECHNIQUE

Raman spectra and scanning electron microscope （SEM） techniques were used to determine the structural properties of microcrb＇stalline silicon （μc-Si：H） films deposited on different substrates with the very high frequency plasma-enhanced chemical vapor deposition （VHF-PECVD） technique. Using the Raman spectra, the values of crystalline volume fraction Xc and average grain size d are 86%, 12.3nm; 65%, 5.45nm; and 38%, 4.05nm, for single crystalline silicon wafer, coming 7059 glass, and general optical glass substrates, respectively. The SEM images further demonstrate the substrate effect on the film surface roughness. For the single crystalline silicon wafer and Coming 7059 glass, the surfaces of the μc-Si：H films are fairly smooth because of the homogenous growth or h＇ttle lattice mismatch. But for general optical glass, the surface of the μ-Si： H film is very rough, thus the growing surface roughness affects the crystallization process and determines the average grain size of the deposited material. Moreover, with the measurements of thickness, photo and dark conductivity, photosensitivity and activation energy, the substrate effect on the deposition rate, optical and electrical properties of the μc-Si：H thin films have also been investigated. On the basis of the above results, it can be concluded that the substrates affect the initial growing layers acting as a seed for the formation of a crystalline-like material and then the deposition rates, optical and electrical properties are also strongly influenced, hence, deposition parameter optimization is the key method that can be used to obtain a good initial growing layer, to realize the deposition of μc-Si：H films with device-grade quality on cheap substrates such as general glass.

Neural network modeling and prediction of HfO2 thin film properties tuned by thermal annealing

Plasma-enhanced atomic layer deposition (PEALD) is gaining interest in thin films for laser applications, and post-annealing treatments are often used to improve thin film properties. However, research to improve thin film properties is often based on an expensive and time-consuming trial-and-error process. In this study, PEALD-HfO2 thin film samples were deposited and treated under different annealing atmospheres and temperatures. The samples were characterized in terms of their refractive indices, layer thicknesses and O/Hf ratios. The collected data were split into training and validation sets and fed to multiple back-propagation neural networks with different hidden layers to determine the best way to construct the process–performance relationship. The results showed that the three-hidden-layer back-propagation neural network (THL-BPNN) achieved stable and accurate fitting. For the refractive index, layer thickness and O/Hf ratio, the THL-BPNN model achieved accuracy values of 0.99, 0.94 and 0.94, respectively, on the training set and 0.99, 0.91 and 0.90, respectively, on the validation set. The THL-BPNN model was further used to predict the laser-induced damage threshold of PEALD-HfO2 thin films and the properties of the PEALD-SiO2 thin films, both showing high accuracy. This study not only provides quantitative guidance for the improvement of thin film properties but also proposes a general model that can be applied to predict the properties of different types of laser thin films, saving experimental costs for process optimization.

Global optimization of process parameters for low-temperature SiN_(x) based on orthogonal experiments

Low-temperature silicon nitride(SiNx)films deposited by plasma-enhanced chemical vapor deposition(PECVD)have huge application potential in the flexible display.However,the applicability of SiNx largely depends on the film’s general properties,including flexibility,deposition rate,residual stress,elastic modulus,fracture strain,dielectric constant,refraction index,etc.Process optimization towards specific application by conventional experiment design needs lots of work due to the interaction of muti quality and process parameters.Therefore,an efficient global optimization approach for the process technology was proposed based on the Taguchi orthogonal experiment method considering muti-factor muti-responses.First of all,the Taguchi orthogonal experiment design and analysis was used to rank the influences of main process parameters on the quality characteristics,including radio frequency(RF)power,pressure,silane flow rate,ammonia flow rate and nitrogen flow rate.Then,the global optimization approach was carried out utilizing the multi-response optimizer considering the combination target of film formation rate,residual stress,dielectric constant,elastic modulus,fracture strain,refractive index.Finally,the optimal solution of the SiNx film was finally obtained and verified.

Confining MOF-derived SnSe nanoplatelets in nitrogen-doped graphene cages via direct CVD for durable sodium ion storage

Tin-based compounds are deemed as suitable anode candidates affording promising sodium-ion storages for rechargeable batteries andhybrid capacitors.However,synergistically tailoring the electrical conductivity and structural stability of tin-based anodes to attain durablesodium-ion storages remains challenging to date for its practical applications.Herein,metal-organic framework(MOF)derived SnSe/C wrappedwithin nitrogen-doped graphene(NG@SnSe/C)is designed targeting durable sodium-ion storage.NG@SnSe/C possesses favorable electricalconductivity and structure stability due to the"inner"carbon framework from the MOF thermal treatment and"outer"graphitic cage from thedirect chemical vapor deposition synthesis.Consequently,NG@SnSe/C electrode can obtain a high reversible capacity of 650 mAh·g^-1 at 0.05 A·g^1,a favorable rate performance of 287.8 mAh·g^1 at 5 A·g^1 and a superior cycle stability with a negligible capacity decay of 0.016%percycle over 3,200 cycles at 0.4 A·g^1.Theoretical calculations reveal that the nitrogen-doping in graphene can stabilize the NG@SnSe/Cstructure and improve the electrical conductivity.The reversible Na-ion storage mechanism of SnSe is further investigated by in-situ X-raydiffraction/ex-s/tu transmission electron microscopy.Furthermore,assembled sodium-ion hybrid capacitor full-cells comprising our NG@SnSe/Canode and an active carbon cathode harvest a high energy/power density of 115.5 Wh·kg^-1/5,742 W·kg^-1,holding promise for next-generationen ergy storages.

Property mapping of polycrystalline diamond coatings over large area

Large-area polycrystalline diamond(PCD)coatings are important for fields such as thermal management,optical windows,tribological moving mechanical assemblies,harsh chemical environments,biological sensors,etc.Microwave plasma chemical vapor deposition(MPCVD)is a standard technique to grow high-quality PCD films over large area due to the absence of contact between the reactive species and the filament or the chamber wall.However,the existence of temperature gradients during growth may compromise the desired uniformity of the final diamond coatings.In the present work,a thick PCD coating was deposited on a 100-mm silicon substrate inside a 915-MHz reactor;the temperature gradient resulted in a non-uniform diamond coating.An attempt was made to relate the local temperature variation during deposition and the different properties of the final coating.It was found that there was large instability inside the system,in terms of substrate temperature(as high asΔT=212℃),that resulted in a large dispersion of the diamond coating’s final properties:residual stress(-15.8 GPa to+6.2 GPa),surface morphology(octahedral pyramids with(111)planes to cubo-octahedrals with(100)flat top surfaces),thickness(190μm to 245μm),columnar growth of diamond(with appearance of variety of nanostructures),nucleation side hardness(17 GPa to 48 GPa),quality(Raman peak FWHM varying from 5.1 cm^(-1) to 12.4 cm^(-1) with occasional splitting).This random variation in properties over large-area PCD coating may hamper reproducible diamond growth for any meaningful technological application.