Electron-beam Vapor Deposition Research Articles

Vanadium Oxide Device with Tunable Oxygen Vacancy Concentration for Neuromorphic Computing

Analog, non-volatile memories that can enable in-memory data processing are attractive for exploring non-von-Neumann architectures to realize substantially more efficient computing for AI applications. Among the various device concepts, NVMs based on tuning of point defects via insertion of ions such as alkali metals, protons, or oxygen vacancies are attractive due to the ability to finely tune the electronic conductivity by controlling the defect concentration. Previously, oxygen vacancy concentration in vanadium oxide (VO2-x) has been linked to electronic conductivity and the insulator-to-metal transition temperature. However, while previous studies have mainly concentrated on single crystal epitaxial films of VO2, polycrystalline films deposited by technique compatible with Si back end of the line (BEOL) fabrication scheme are considerably easier to integrate with CMOS circuitry. We employ two distinct approaches for device integration of VO2-x thin films: (1) an electron beam evaporation deposition of bulk vanadium (V) precursor followed by annealing in an oxygen (O2) environment, and (2) reactive sputtering of vanadium oxide followed by annealing in air. Raman spectroscopy reveals the presence of VO2 and V2O5 phases, with differing ratios indicative of device conductance states [Figure 1b].1 Previous research has demonstrated that the characteristics of VO2 insulator to metal transition (IMT) can be adjusted by manipulating oxygen vacancy concentration using an electrolyte.2 However, the presence of the electrolyte interface can introduce noise due to uncontrolled parasitic reactions. To mitigate this issue, our study utilized electron beam irradiation to deliberately induce vacancies in the VO2 without relying on an electrolyte. This controlled alteration of the device state was found to lead to a significant change in noise levels, particularly when the device was in proximity to the IMT transition temperature.The analysis of our films provides detailed structural and compositional dynamics of VO2-x and V2O5 phases which exhibit analog synaptic and threshold tunability with remarkable state retention2 [Figure 1cd]. This abstract provides a comparative analysis of these approaches, focusing on their respective advantages and disadvantages in the context of vanadium oxide based analog device fabrication.

Performance and Degradation of Electrolyte Supported SOECs with Advanced Thin-Film Gadolinium Doped Ceria Barrier Layers in Long-Term Stack Test

Electrolyte supported Solid Oxide Cells (ESCs) with advanced thin-film Gd-doped ceria diffusion barrier layers between electrolyte and electrodes were assembled and electrochemically investigated in steam electrolysis mode in a so-called “rainbow” stack with 30 repeat units (RUs). The barrier layers were deposited onto the electrolyte supports via electron-beam physical evaporation deposition (EB-PVD) method at 600 °C. In this paper, the investigation mainly focuses on the electrochemical characteristics of RUs containing the EB-PVD thin-film GDC layers. At the initial stage of the SOEC operation, the stack reached a high performance with an electrical efficiency of 99.65% at 75% steam conversion and a total power input of 1.98 kW. A long-term stack test was performed in SOEC mode for over 5000 h and demonstrated a low voltage degradation of approx. +11.3 mV·kh–1 per RU (+0.9% kh–1). The RUs with EB-PVD GDC thin-films revealed similar initial performance and degradation rate to the state-of-the-art cells with screen printed GDC layers.

Enhanced field emission characteristics of WS2 nano-films by diamond film and Mo film

WS2 is a type of transition metal chalcogenide materials (TMDCs) that exhibits exceptional photoelectric properties. Due to its atomically sharp edges, WS2 has the capability to enhance the electric field around its edges, thus presenting significant potential in field emission applications. In this study, the electron beam vapor deposition (EBVD) system and microwave plasma chemical vapor deposition (MPCVD) system were used to prepare a series of single-layer WS2 films，single-layer diamond films and diamond/WS2 nano-composite films on N-type highly doped Si substrate, and Mo/WS2 nano-composite films were prepared on Al2O3 ceramic substrate. Based on the characterization and analysis of the microstructure and chemical composition of each thin film layer in the above film devices, the field emission (FE) characteristics of each thin film device are compared and studied. The results demonstrate that the maximum FE current density of diamond/WS2 nano-composite film device is 912 μA/cm2, which is 2.7 times of the maximum FE current density of Mo/WS2 nano-composite film device 330 μA/cm2, and 3.4 times of the maximum FE current density of the single-layer diamond thin film device 267 μA/cm2. The single layer WS2 film did not exhibit measurable FE performance. The working principles of thin film field emission devices with various structures are introduced. It is considered that the diamond layer plays the role of electron accelerating layer, which not only effectively improves the FE characteristics of diamond/WS2 nanocomposite film, but also improves the repeatability and long-term stability of diamond/WS2 nanocomposite film FE devices.

Study on field emission performance of SrTiO3 film enhanced by LiF film

A series of monolayer SrTiO3 films and LiF/SrTiO3 bilayer films were prepared on n-Si substrates by using vacuum electron beam vapor deposition (EBVD) technology. The morphologies and thicknesses of the SrTiO3 film and LiF film were controlled through adjustments and optimization of the growth conditions as well as deposition time. The experimental results show that the field emission performance of SrTiO3 film is significantly improved after LiF film is added. Under the research conditions in our laboratory, a large number of LiF/SrTiO3 bilayer film field emission devices have been tested and analyzed in the wide range of LiF film thickness (10–300 nm), and the effective field emission LiF film thickness (50–90 nm) was initially determined. Further study shows that the LiF/SrTiO3 bilayer film has the best field emission performance when the optimal LiF film thickness is 70 nm, and its maximum field emission current density can reach 305.48 μA/cm2. The field emission current density of the LiF/SrTiO3 bilayer thin film device is nearly 4 times compared to that of the monolayer SrTiO3 film when the applied electric field intensity reaches 9.05 V/μm. All the field emission devices exhibit excellent functioning stability and experimental reproducibility.

Photocatalytic Oxidization Based on TiO2/Au Nanocomposite Film for the Pretreatment of Total Phosphorus (TP)

Phosphorus, an essential rare element in aquatic ecosystems, plays a key role in maintaining ecosystem balance. However, excess phosphorus leads to eutrophication and algal proliferation. To prevent eutrophication, the pretreatment and measuring of the concentration of total phosphorus (TP) is crucial. Compared to conventional TP pretreatment equipment (autoclave), a lab-on-a-chip detection device fabricated using micro-electromechanical system technology and titania (TiO2) as a photocatalyst is more convenient, efficient, and cost-effective. However, the wide bandgap of TiO2 (3.2 eV) limits photocatalytic activity. To address this problem, this paper describes the preparation of a TiO2/Au nanocomposite film using electron-beam evaporation and atomic-layer deposition, based on the introduction of gold film and TiO2 to a quartz substrate. The photocatalytic degradation properties of TiO2/Au nanocomposite films with thicknesses of 1, 2, 3, and 4 nm were assessed using rhodamine B as a pollutant. The experimental results demonstrate that the deposition of gold films with different thicknesses can enhance photocatalytic degradation efficiency through synergetic reactions in the charge separation process on the surface. The optimal photocatalytic efficiency is achieved when the deposition thickness is 2 nm, and it decreases with further increase in the thickness. When the photocatalytic reaction time is 15 min, the lab-on-a-chip (LOC) device with a 2-nm-thick gold layer and autoclave exhibits a similar TP pretreatment performance. Therefore, the proposed LOC device based on photocatalytic technology can address the limitations of conventional autoclave equipment, such as large volumes, long processing times, and high costs, thereby satisfying the growing demand for on-site evaluation.

ALUMINUM OXIDE IN VACUUM CONDENSATES BASED ON COPPER

Strengthening of copper and copper alloys with aluminum oxide particles is an important technological technique. Composite materials based on copper strengthened with aluminum oxide particles have a significant operating temperature range and better mechanical properties at elevated temperatures than age-hardening alloys. However, at moderate operating temperatures, the use of age-hardening alloys remains more economically justified. The main direction in the development of composites strengthened with oxide particles is the dispersion of the strengthening phase to sizes of several or one nanometer, which will bring their mechanical properties to the level of age-hardening alloys. However, dispersion leads to a significant increase not only in strength, but also in electrical resistance. The adverse effect on the electrical conductivity of dispersed particles will decrease with a decrease in the volume fraction of oxide, bringing the electrical conductivity closer to the level of copper. Based on an analysis of the materials of scientific research devoted to the production of dispersion-strengthened Cu–Al2O3 composites, it was concluded that the most significant progress in the dispersion of oxide particles with uniform distribution in the copper matrix of the composite was achieved using the method of electron beam evaporation and simultaneous deposition (condensation) of vapors of components in vacuum (EB–PVD). Structural studies of the morphology of aluminum oxide particles in dispersion-strengthened copper composites were carried out using methods such as: X-ray fluorescence analysis, transmission electron microscopy, and energy-dispersive X-ray spectroscopy (EDS). The average size of aluminum oxide particles in the studied dispersion-strengthened composites was in the range from 1.8 to 3 nm. In the work, the dependence of the specific electrical resistance of composites (ρ) on the oxide content was investigated. It was found that a decrease in the size of oxide particles leads to an increase in the electrical resistance of the dispersion-strengthened composite. The studies of the method of electron beam evaporation and subsequent condensation in vacuum, presented in the work, confirm the possibility of further dispersion of aluminum oxide particles with simultaneous narrowing of the distribution histogram. This opens up prospects for further improvement of vacuum dispersion-strengthened copper-based composites.

Performance and Degradation of Electrolyte Supported SOECs with Advanced GDC Thin-film Layers in Long-term Stack Test

Solid oxide electrolyser (SOE) based on electrolyte-supported cell (ESC) architecture is proven to be highly efficient and reliable technology for green hydrogen production via high temperature electrolysis. Operating under industrial conditions, the performance, lifetime and robustness of the cells and stacks belong to the most important factors for an up-scaled penetration of the SOE technology into energy and chemistry sectors. A typical ESC consists of scandia- or yttria-stabilized zirconia electrolyte, Ni-cermet fuel electrode, lanthanum strontium cobalt ferrite (LSCF) oxygen electrode and either one or two Gd-doped ceria (GDC) layers with a thickness of 5-7 µm between electrolyte and electrodes. At the oxygen electrode side, the GDC layer prevents interdiffusion (mainly of Sr), whereas at the fuel electrode side, the GDC layer may improve the electrode adherence to electrolyte and reduce the interfacial resistance. State-of-the-art fabrication route of the GDC layers is screen-printing followed by partially sintering at high temperature between 1200 °C to 1300 °C. This fabrication process usually results in porous structure in the GDC layers and residual stresses which reduce the mechanical strength of the cells.Aiming to improve the mechanical strength of ESCs and the properties (e.g. porosity and electrical conductivity) of GDC layers, the conventional screen-printed GDC layers either only at the oxygen electrode or at both electrodes were replaced by 0.5 µm thick thin-film GDC layers fabricated by electron-beam physical evaporation deposition (EB-PVD) method at 600 °C. These EB-PVD-fabricated thin-film GDC layers were electrochemically characterized in a so-called “rainbow” stack with 30 repeat units (RUs), including 4 RUs with EB-PVD GDC layers at the oxygen electrode and screen-printed GDC at fuel electrode, 3 RUs with EB-PVD GDC layers at both electrodes and 23 RUs with state-of-the-art screen-printed GDC layers at both electrodes. The stack was operated for over 5000 h in SOEC mode under a current density of -410 mA cm−2 and 75 % steam conversion, with a feed gas composition of 80 % steam + 10 % H2 + 10 % N2 on the fuel electrode and air on oxygen electrode.In this paper, the investigation focuses on the electrochemical characteristics of RUs containing the EB-PVD thin-film GDC layers during the SOEC stack testing. The performance and degradation behavior of the stack and representative RUs were investigated and compared by means of current-voltage curves and electrochemical impedance spectroscopy (EIS). The initial performance and the degradation of the voltage and resistances of the stack and the RUs with EB-PVD GDC thin-film layers were determined and discussed in order to evaluate the effectiveness of the modifications in the scenario of long-term SOEC stack testing.The German Federal Ministry for Education and Research (BMBF) is acknowledged for the financial supports within the project H2GiGa-HTEL (grant no. 03HY124E).

White electroluminescence of diamond/boron/diamond/SrTiO3 composite film

Diamond/boron/diamond/SrTiO3 composite film (BDDSCF) electroluminescent (EL) devices were deposited by microwave plasma chemical vapor deposition (MPCVD) technology and vacuum electron beam vapor deposition (EBVD) technology. The samples were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDXS). The current-voltage (I–V) characteristic of the sample was measured by an adjustable direct current power supply. The EL spectra of the samples obviously exhibit three emission peaks, which are centered at 440 nm (blue area), 592 nm (yellow area) and 736 nm (red area). In the indoor environment, it can be observed by the naked eye that the surface of the sample will emit uniform and high brightness white light. The blue peak is from the recombination of the conduction band electron in SrTiO3 film and the quasi-acceptor (trapped hole) associated with oxygen vacancy, the yellow peak is caused by the self-trapping exciton (STE) recombination caused by oxygen vacancies in SrTiO3, and the red peak is attributed to the silicon impurity centers or carbon neutral vacancy in diamond films.

Memristors Based on Many-Layer Non-Stoichiometric Germanosilicate Glass Films

Nonstoichiometric GeSixOy glass films and many-layer structures based on them were obtained by high-vacuum electron beam vapor deposition (EBVD). Using EBVD, the GeO2, SiO, SiO2, or Ge powders were co-evaporated and deposited onto a cold (100 °C) p+-Si(001) substrate with resistivity ρ = 0.0016 ± 0.0001 Ohm·cm. The as-deposited samples were studied by Fourier-transformed infrared spectroscopy, atomic force microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. A transparent indium–tin–oxide (ITO) contact was deposited as the top electrode, and memristor metal–insulator–semiconductor (MIS) structures were fabricated. The current–voltage characteristics (I–V), as well as the resistive switching cycles of the MIS, have been studied. Reversible resistive switching (memristor effect) was observed for one-layer GeSi0.9O2.8, two-layer GeSi0.9O1.8/GeSi0.9O2.8 and GeSi0.9O1.8/SiO, and three-layer SiO2/a–Ge/GeSi0.9O2.8 MIS structures. For a one-layer MIS structure, the number of rewriting cycles reached several thousand, while the memory window (the ratio of currents in the ON and OFF states) remained at 1–2 orders of magnitude. Intermediate resistance states were observed in many-layer structures. These states may be promising for use in multi-bit memristors and for simulating neural networks. In the three-layer MIS structure, resistive switching took place quite smoothly, and hysteresis was observed in the I–V characteristics; such a structure can be used as an “analog” memristor.

LiF film enhanced high brightness blue electroluminescence of diamond /CeF3 composite film

Diamond/CeF3 composite film (DCCF) and diamond/CeF3/LiF composite film (DCLCF) electroluminescent(EL)devices were deposited on n-type heavy-doped silicon substrates by using microwave plasma chemical vapor deposition system (MPCVD) and vacuum electron beam vapor deposition system (EBVD). A series of corresponding tests characterized the composition, microstructure, and EL characteristics of the devices. The experimental results show that the LiF layer can effectively enhance the blue light emission intensity of the composite film device. Blue light emission can be observed in the two types of devices when the forward bias is applied, and the EL spectra of both devices show a strong wide peak at 440 nm. Meanwhile there is no significant difference in the maximum luminous intensity between them. However, when the reverse bias voltage is applied to the two devices, it is found that DCCF device hardly observes visible light emission, while the blue light emission of DCLCF device is very strong. And the EL spectrum of DCLCF device still shows a strong wide peak at 440 nm, and the blue light emission can reach the maximum at 350 V reverse bias voltage. Its maximum luminous intensity is 3.5 times that of DCCF devices, and its brightness can reach 35 cd/m2.

A novel catalyst derived from Co-ZIFs to grow N-doped carbon nanotubes for all-solid-state supercapacitors with high performance.

Carbon nanotubes (CNTs) have been widely used as electrode materials for electrochemical energy storage devices (e.g., supercapacitors) due to their excellent chemical and physical properties. However, conventional approaches (e.g., electron-beam vapor deposition and atomic layer deposition) to fabricate catalysts for the growth of CNTs are complex and demand high energy consumption. Herein, we report a facile method to synthesize catalysts derived from cobalt-containing zeolitic imidazolate frameworks (Co-ZIFs), which is exploited to in situ construct the three-dimensional (3D) CNT hybrid materials for all-solid-state supercapacitors. In brief, Co-ZIFs with a controllable structure is first grown on the inner porous surface of carbon foams pyrolyzed from commercial melamine foams, followed by thermal annealing and chemical vapor deposition to grow CNTs, achieving 3D free-standing CNT-based hybrids. The well-distributed Co-ZIFs in the carbon foam enable the grown CNTs with uniform structures and morphologies. Using the fabricated CNT-based hybrid as electrodes, the assembled all-solid-state supercapacitors show a high specific capacitance of 19.4 mF cm-2 at a current density of 0.5 mA cm-2, which could be further optimized to as high as 871.8 mF cm-2 by incorporating the pseudocapacitive material of manganese dioxide in CNT-based hybrids. This study provides a facile solution approach to fabricate the catalyst for the growth of a CNT inner porous substrate; the resultant 3D free-standing hybrids could be used as efficient electrodes for high-performance energy storage devices beyond supercapacitors.

Влияние шероховатости барьерного слоя на формирования наночастиц катализатора роста углеродных нанотрубок

This article compares TiN layers produced by electron beam evaporation (EBE) and atomic layer deposition (ALD) for the effect of barrier layer deposition technology on the formation of carbon nanotube (CNT) growth catalyst nanoparticles. The layers obtained by EBE have a roughness 1.5 times higher than the layers deposited by the ALD method (Ra = 1 nm and Ra = 0.6 nm). Nanoparticles formed on the surface of the EBE layer are characterized by a large average size (about 30 nm) and a 1.3 times greater dispersion of the distribution compared to nanoparticles formed on the ALD layer. TiN layers obtained by EBE are characterized by better surface wettability in comparison with ALD layers. The contact angle for catalyst nanoparticles on the surface of the EBE layer of TiN is about 30 degrees and approaches 90 degrees for ALD layers. Catalyst spreading is due to the Wenzel model. It is shown that the higher surface roughness of the EBE samples is associated with the crystallization of TiN, since the layer formation process proceeds at a higher temperature compared to the ALD process. For this reason, the use of barrier layers obtained by the ALD method is preferable for the formation of CNT growth catalyst nanoparticles on their surface.

Effect of Barrier Layer Roughness on the Formation of Nanoparticles of the Carbon Nanotube Growth Catalyst

This article compares TiN layers produced by electron beam evaporation (EBE) and atomic layer deposition (ALD) for the effect of barrier layer deposition technology on the formation of carbon nanotube (CNT) growth catalyst nanoparticles. The layers obtained by EBE have a roughness 1.5 times higher than the layers deposited by the ALD method (R a =1 nm and R a =0.6 nm). Nanoparticles formed on the surface of the EBE layer are characterized by a large average size (about 30 nm) and a 1.3 times greater dispersion of the distribution compared to nanoparticles formed on the ALD layer. TiN layers obtained by EBE are characterized by better surface wettability in comparison with ALD layers. The contact angle for catalyst nanoparticles on the surface of the EBE layer of TiN is about 30 degrees and approaches 90 degrees for ALD layers. Catalyst spreading is due to the Wenzel model. It is shown that the higher surface roughness of the EBE samples is associated with the crystallization of TiN, since the layer formation process proceeds at a higher temperature compared to the ALD process. For this reason, the use of barrier layers obtained by the ALD method is preferable for the formation of CNT growth catalyst nanoparticles on their surface. Keywords: electron beam evaporation, atomic layer deposition, roughness, wetting, catalyst nanoparticles.

Influence of the roughness of the barrier layer on the formation of nanoparticles of the catalyst for the growth of carbon nanotubes

Usually, the synthesis of carbon nanotubes arrays for use in nanoelectronics is carried out on a two-layer catalyst. The lower layer is a barrier for the interaction of the upper catalyst layer with the substrate. When heated to the synthesis temperature, the upper layer 2–4 nm thick melts and catalyst nanoparticles are formed on the surface of the barrier layer. The novelty of the presented research is the search for a technology that provides a smaller spread in the size of catalyst nanoparticles and, accordingly, a higher quality vertical array of carbon nanotubes during subsequent synthesis. To this end, the paper compares two methods of forming a TiN barrier layer, electron beam evaporation (EBE) and atomic layer deposition (ALD), to obtain Ni catalyst nanoparticles with the smallest average diameter and narrow distribution dispersion. The layers obtained by EBE have a roughness 1.5 times higher than the layers deposited by ALD (Ra = 1 nm and Ra = 0.6 nm respectively). The roughness of the barrier layer affects the dispersion of the size distribution of nanoparticles. Thus, the average size of nanoparticles on the EBE layer is about 30 nm, and the distribution dispersion is 1.3 times larger compared to the ALD layer. Wetting of the surface of the TiN barrier layer for EBE samples is better than for ALD samples. The contact angle for the catalyst nanoparticle on the surface of the TiN layer is about 30° for EBE samples and approaches 80° for ALD samples. In this case, the surface relief is filled with metal, which corresponds to the Wenzel model. It is assumed that the higher surface roughness of the EBE samples is associated with a higher temperature of titanium nitride film formation compared to ALD. ALD deposition of TiN barrier layers is preferable for the formation of catalytic nanoparticles on their surface for the growth of carbon nanotubes.

A Mini Review on Thin Film Superconductors

Thin superconducting films have been a significant part of superconductivity research for more than six decades. They have had a significant impact on the existing consensus on the microscopic and macroscopic nature of the superconducting state. Thin-film superconductors have properties that are very different and superior to bulk material. Amongst the various classification criteria, thin-film superconductors can be classified into Fe based thin-film superconductors, layered titanium compound thin-film superconductors, intercalation compounds of layered and cage-like structures, and other thin-film superconductors that do not fall into these groups. There are various techniques of manufacturing thin films, which include atomic layer deposition (ALD), chemical vapour deposition (CVD), physical vapour deposition (PVD), molecular beam epitaxy (MBE), sputtering, electron beam evaporation, laser ablation, cathodic arc, and pulsed laser deposition (PLD). Thin film technology offers a lucrative scheme of creating engineered surfaces and opens a wide exploration of prospects to modify material properties for specific applications, such as those that depend on surfaces. This review paper reports on the different types and groups of superconductors, fabrication of thin-film superconductors by MBE, PLD, and ALD, their applications, and various challenges faced by superconductor technologies. Amongst all the thin film manufacturing techniques, more focus is put on the fabrication of thin film superconductors by atomic layer deposition because of the growing popularity the process has gained in the past decade.

Green electroluminescence of Al2O3 film

Silicon-based Al2O3 film electroluminescent devices were fabricated by using vacuum electron beam vapor deposition technique. The thin films were characterized by field emission scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS) and UV–visible grating spectrometer. The electroluminescence spectrum of the device shows two emission peaks in the visible region, the main peak in the green region (503 nm) and the sub-peak in the red region (680 nm). When a forward bias voltage of about 10V is applied, the luminescence of the device is clearly visible to the naked eye in a dark room. And when the forward bias voltage increases to 30V, the luminescence intensity reaches the maximum. In addition, the experiment found that when the annealing temperature of the Al2O3 film is higher than 600 °C, the electroluminescent intensity of the Al2O3 film device gradually deteriorates, until the annealing temperature is higher than 800 °C, the electroluminescence of Al2O3 film devices disappears completely. This work provides a basis for the application of Al2O3 thin film in the field of electroluminescence.

Thin Film Deposition and Characterization Techniques

Thin films are everywhere in the modern world, with many of the technologies we depend upon in daily life being, in turn, dependent upon thin film technology. Chemical bath deposition includes principles of chemical bath deposition (CBD) and concept of solubility product, nucleation and film growth, thin film deposition mechanism in chemical bath deposition. The non-metallic ion source (anions) and metal ion source (cations) then react to form the compound. The nucleation process plays an important role in determining the crystallinity and microstructure of the resultant film. From the discussion of deposition techniques which are physical and chemical deposition methods. Physical deposition techniques contains sputtering deposition, electron beam evaporation and physical vapour deposition (PVD) process have been known for over 100 years and also fabrication films on the substrate, as well as the increasement of the pressure in the chamber due to operation of the sources indicates directly that gases or vapors are desorbed. Chemical deposition process is economically effective and has been industrially exploited to large scale. It can be summarized that thin film characterization techniques include X-ray diffraction (XRD), UV-Vis spectrophotometer, scanning electron microscopy, energy dispersive x-ray diffraction, transmission electron microscopy (TEM). X-rays diffraction (XRD) is a rapid and a powerful technique used to study the phase of a crystalline material, information on unit cell lattice parameters, crystal structure, crystal orientation and crystalline size.

Comparative Study of Tribological Behavior of TiN Hard Coatings Deposited by Various PVD Deposition Techniques

In this paper, we present a comparative study of tribological properties of TiN coatings deposited by low-voltage electron beam evaporation, magnetron sputtering and cathodic arc deposition. The correlation of tribological behavior of these coatings with their intrinsic properties and friction condition was studied. The influence of surface topography and the surrounding atmosphere was analyzed in more detail. We limited ourselves to the investigation of tribological processes that take place in the initial phase of the sliding test (the first 1000 cycles). A significant difference in the initial phase of the sliding test of three types of TiN coatings was observed. We found that nodular defects on the coating surface have an important role in this stage of the sliding test. The tribological response of TiN coatings, prepared by cathodic arc deposition, is also affected by the metal droplets on the coating surface, as well as those incorporated in the coating itself. Namely, the soft metal droplets increase the adhesion component of friction. The wear rates increased with the surface roughness of TiN coatings, the most for coatings prepared by cathodic arc deposition. The influences of post-polishing of the coating and the surrounding atmosphere were also investigated. The sliding tests on different types of TiN coatings were conducted in ambient air, oxygen and nitrogen. While oxygen promotes tribo-chemical reactions at the contact surface of the coating, nitrogen suppresses them. We found that the wear rate measured in ambient air, compared with that in an oxygen atmosphere, was lower. The difference is probably due to the influence of humidity in the ambient air. On the other hand, wear rates measured in a nitrogen atmosphere were much lower in comparison with those measured in an oxygen or ambient air atmosphere.

The Influence of Ion Beam Bombardment on the Properties of High Laser-Induced Damage Threshold HfO2 Thin Films

HfO2 thin films were deposited on BK-7 glass substrates using an electron beam evaporation deposition (EBD) technique and then post-treated with argon and oxygen ions at an ion energy ranging from 800 to 1200 eV. The optical properties, laser damage resistance, and surface morphology of the thin films exposed to Ar ions and O2 ions at various energies were studied. It was found that the two ion post-treatment methods after deposition were effective for improving the LIDT of HfO2 thin films, but the mechanism for the improvement differs. The dense thin films highly resistant to laser damage can be obtained through Ar ion post-treatment at a certain ion energy. The laser-induced damage threshold (LIDT) of thin films after O2 ion post-treatment was higher in comparison to those irradiated with Ar ion at the same ion energy.

Investigation of UV, ns-laser damage resistance of hafnia films produced by electron beam evaporation and ion beam sputtering deposition methods

Laser-induced damage in coating materials with a high index of refraction, such as hafnia, limits the performance of high power and high energy laser systems. Understanding the underlying physics responsible for laser damage holds the key for developing damage-resistant optical films. Previous studies have reported a substantial difference in laser damage onset for hafnia films produced by different deposition methods, yet the underlying mechanisms for the observed difference remain elusive. We combined laser damage testing with analytical characterizations and theoretical simulations to investigate the response of hafnia films produced by electron (e-) beam evaporation vs ion beam sputtering (IBS) methods upon UV ns-laser exposure. We found that e-beam produced hafnia films were overall more damage resistant; in addition, we observed a polarization anisotropy associated with the onset of damage in the e-beam films, while this effect was absent in the latter films. The observed differences can be attributed to the stark contrast in the pressure inside the pores inherent in both films. The high pressure inside the IBS-induced nanobubbles has been shown to reduce the threshold for laser-induced plasma breakdown leading to film damage. The polarization effects in the e-beam coatings can be related to the asymmetric electric field intensification induced by the columnar void structure. Our findings provide a fundamental basis for developing strategies to produce laser damage-resistant coatings for UV pulsed laser applications.