Tribological behavior of CrAlSiN/W2N multilayer coatings deposited by DC magnetron sputtering

The CrAlSiN/W₂N multilayer coatings were fabricated by DC magnetron sputtering. The bilayer periods of multilayer films were controlled in the range from 3 to 20 nm. The cross-sectional structure of multilayer and monolayer coatings was evaluated by transmission electron microscopy (TEM). The wear behavior of monolayer and multilayer coatings was investigated by a pin-on-disc tribometer. The nano-scratch tester was employed to study the crack propagation of scratched coatings. The images of wear scars were observed by optical microscopy (OM). The cross-sectional image of scratched films was analyzed by transmission electron microscopy (TEM). Owing to the nano-layered structure and higher hardness (or H/E ratio), the multilayer coatings exhibited better wear resistance than homogeneous films. The coefficient of friction of CrAlSiN/W₂N multilayer coating with a bilayer period of 8 nm was around 0.6, and that of CrAlSiN homogeneous film was about 0.8. Different crack propagation mechanisms of CrAlSiN/W₂N multilayer and CrAlSiN monolayer coatings were proposed and discussed.     

Phase effects owing to multilayer coatings in a two-mirror extreme-ultraviolet schwarzschild objective

The aberrations of a multilayer-coated reflective Schwarzschild objective, which are influenced both by mirror surface profiles and by multilayer coatings, are evaluated with a phase-shifting point diffraction interferometer operating in the extreme ultraviolet. Using wave-front measurements at multiple wavelengths near 13.4 nm, we observed chromatic aberrations and wavelength-dependent transmission changes that were due to molybdenum-silicon multilayer coatings. The effects of chromatic vignetting due to limited multilayer reflection passbands on the imaging performance of the Schwarzschild optic are considered. The coating characteristics extracted from the interferometry data on the two-mirror optical system are compared with previously reported coating properties measured on individual mirror substrates.     

Characterization of a multilayer highly reflecting mirror by spectroscopic phase-modulated ellipsometry

The characterization of optical multilayer coatings has been a challenging task for thin-film scientists and engineers because of the various complex, interdependent layer parameters that exist in the system. Spectroscopic phase-modulated ellipsometry has some advantages in the postanalysis of the layer parameters of such multilayer coatings because it suitably models the layer structure with respect to the ellipsometric measurements. An algorithm to characterize multilayer optical coatings with large numbers of layers has been described by spectroscopic ellipsometry by use of a discrete spectral zone fitting approach. A 23-layer multilayer highly reflecting mirror has been characterized by this technique in the wavelength range 280-1000 nm. The ellipsometric spectra (? and D versus wavelength) have been fitted separately in three wavelength regimes. Fitting the ellipsometric spectra in the wavelength regime of 700-1000 nm permitted the sample structure to be determined. The data were then fitted in the wavelength range 280-340 nm, i.e., near the fundamental absorption edge of TiO(2), to yield the dispersion relation for the optical constants of TiO(2). Finally, the data were fitted in the wavelength range 340-700 nm, and the true dispersion of the refractive index of TiO(2), along with the best-fitting sample structure, was obtained.     

Anisotropic protective coating for brewster angle windows

We propose what we believe is a new type of dielectric anisotropic coating of arbitrary thickness that can protect Brewster angle windows without degrading their optical quality. Such a coating may be fabricated as a multilayer two-component structure. The parameters of the structure, i.e., the dielectric permittivities of the components and their concentrations, are calculated. For ZnSe windows two examples of anisotropic coatings are presented. The optical quality of the multilayer films does not depend on their precise thickness, which makes them less sensitive to surface damage.     

Fabrication of mitigation pits for improving laser damage resistance in dielectric mirrors by femtosecond laser machining

Femtosecond laser machining is used to create mitigation pits to stabilize nanosecond laser-induced damage in multilayer dielectric mirror coatings on BK7 substrates. In this paper, we characterize features and the artifacts associated with mitigation pits and further investigate the impact of pulse energy and pulse duration on pit quality and damage resistance. Our results show that these mitigation features can double the fluence-handling capability of large-aperture optical multilayer mirror coatings and further demonstrate that femtosecond laser macromachining is a promising means for fabricating mitigation geometry in multilayer coatings to increase mirror performance under high-power laser irradiation.     

Deposition of nano-scaled CrTiAlN multilayer coatings with different negative bias voltage on Mg alloy by unbalanced magnetron sputtering

In a magnetron sputtering system, the negative substrate bias voltage has been used as a basic process parameter to modify the deposition structure and properties of coatings. In this paper we report the effect of bias voltage ranging from −40 V to −90 V on nano-scaled CrN/TiN/CrN/AlN (CrTiAlN) multilayer coatings synthesized on a Mg alloy by a closed-field unbalanced magnetron sputtering ion plating system in a gas mixture of Ar + N₂. The technological temperature and atomic concentration in the multilayer coatings were controlled by adjusting the current density of different metal magnetron targets and the plasma optical emission monitor. The composition, crystallographic structure, deposition model and friction coefficient of multilayer coatings were characterized by X-ray photoelectron spectrometry (XPS), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and ball-on-disc testing. The experimental results show that the deposition model and friction coefficient of nano-scaled CrTiAlN multilayer coatings were significantly affected by the negative bias voltage (V_b). The nitride species in multilayer coatings mainly involve CrN, AlN and TiN, and XRD analysis shows that the crystallographic structure was face-centered cubic. Under different bias voltage conditions, the multilayer coating composition shows a fluctuation, and the Al and Cr concentrations respond in the opposite sense to the bias voltage, attaining their greatest values at V_b = −70 V. The surface and cross-sectional morphology shows deposition model change from a columnar model into non-columnar model with the increase in negative bias voltage. The friction coefficient of the nano-scaled multilayer coatings at V_b = −55 V stabilize after 10 000 cycles.     

Reflectance enhancement in the extreme ultraviolet and soft x rays by means of multilayers with more than two materials

Sub-quarterwave multilayer coatings with more than two different materials are shown to provide a reflectance enhancement compared with the standard two-material multilayer coatings when reflectance is limited by material absorption. A remarkable reflectance enhancement is obtained when the materials in the multilayer are moderately absorbing. A simple rule based on the material optical constants is provided to select the most suitable materials for the multilayer and to arrange the materials in the correct sequence in order to obtain the highest possible reflectance. It is shown that sub-quarterwave multilayers generalize the concept of multilayers, of which the standard two-material multilayers are a particular case. Various examples illustrate the benefit of sub-quarter-wave multilayer coatings for highest reflectance in the extreme ultraviolet. Applications for sub-quarterwave multilayer coatings are envisaged for astronomy in the extreme ultraviolet (EUV) and soft x rays and also for future EUY lithography.     

Investigation of conductive and transparent Al-doped ZnO/Ag/Al-doped ZnO multilayer coatings by electron beam evaporation

Multilayer coatings consisting of thin silver layer sandwiched between layers of Al-doped ZnO (AZO) were prepared by electron beam evaporation. The optical and electrical performances of AZO/Ag/AZO multilayers were investigated. Optimization of the multilayer coatings resulted with low sheet resistance of 7.7 Ω/sq and transmittance of 85%. The influence of thickness of each layer on the optic and electrical performance was analyzed. The sheet resistance of the multilayer was reduced to 5.34 Ω/sq. and the average transmittance was improved to 90% by the thermal treatment. The coatings had satisfactory properties of low resistance, high transmittance and thermal stability.     

Design and plasma deposition of dispersion-corrected multiband rugate filters

Inverse Fourier transform method has been commonly used for designing complex inhomogeneous optical coatings. Since it assumes dispersion-free optical constants, introducing real optical materials induces shifts in the position of reflectance bands in multiband inhomogeneous minus (rugate) filters. We propose a simple method for considering optical dispersion in the synthesis of multiband rugate filter designs. Model filters designed with this method were fabricated on glass and polycarbonate substrates by plasma-enhanced chemical vapor deposition of silicon oxynitrides and SiO2/TiO2 mixtures with precisely controlled composition gradients.     

Comparison of algorithms used for optical characterization of multilayer optical coatings

Two algorithms used for the on-line and off-line characterization of multilayer optical coatings are experimentally compared using test samples produced by two different deposition processes and different monitoring approaches. One of these algorithms, called the triangular algorithm, demonstrates its superiority in all considered situations. We performed experiments with multilayer samples formed by high-density thin films, which allowed us to neglect possible errors in the film refractive indices and concentrate only on errors in the thicknesses of the layers of the produced coatings.     

脉冲偏压幅值对TiN／TiAlN多层薄膜微观结构和性能的影响

采用电弧离子镀的方法,通过改变脉冲偏压幅值在M2高速钢表面制备了TiN／TiAlN多层薄膜,研究了脉冲电压幅值TiN／TiAlN多层薄膜微观结构和性能的变化。随着脉冲偏压幅值的增加,薄膜表面的大颗粒数目明显减少。EDX结果表明,脉冲偏压幅值的增加还引起Al／Ti原子比的降低。TiN／TiAlN多层薄膜主要以（111）晶...     

Photothermal deflection in multilayer coatings: modeling and experiment

A model of the photothermal deflection signal in multilayer coatings is presented that takes into account optical interference effects and heat flow within the stack. Measurements are then taken of high-reflectivity HfO2/SiO2 ultraviolet mirrors made by plasma ion assisted deposition and compared to calculations. Good agreement is found between the experimental results and the model. Using this model for the calibration and the setup described, one can measure absorption in multilayer coatings accurately down to 10(-7) of the incident power.     

Alte Faustregeln für das Design optischer Schichtsysteme

Old rules useful to the designer of optical coatings Optical coatings are usually composed of multilayer film structures which are used to obtain a desired transmittance, reflectance and absorptance from a surface. The spectral characteristic may be due to the intrinsic property of the material (e.g. metal reflectors) or due to interference effects arising from the multilayer stack. The following is a set of guidelines (“old rules”) useful to the designer of optical systems of which coated surfaces are an integral part.     

Crystal phase transition of HfO2 films evaporated by plasma-ion-assisted deposition

HfO(2) is a well-known high-refractive-index material for optical interference coatings from the infrared down to the ultraviolet (UV). Dense, homogeneous, and stoichiometric HfO(2) film is critical for low-loss UV optics where the spectral region is close to its fundamental absorption edge. We prepare HfO(2) films by plasma-ion-assisted deposition with various amounts of plasma-ion momentum transfer. The correlation between the HfO(2) film structure and the optical properties are evaluated by a variable-angle spectroscopic ellipsometry, indicating inhomogeneous to homogeneous to inhomogeneous film structural evolution with increasing momentum transfer during deposition. The HfO(2) film inhomogeneity, surface roughness, and crystal phase are confirmed by scanning electron microscopy cross-sectional, atomic force microscopy, and x-ray diffraction measurements. The results suggest that the HfO(2) film structural evolution corresponds to crystal phase transition from weak monocline amorphous to strong monocline depending on the amount of plasma-ion momentum transfer during film deposition.     

Microstructure-related properties at 193 nm of MgF2 and GdF3 films deposited by a resistive-heating boat

MgF2 and GdF3 materials, used for a single-layer coating at 193 nm, are deposited by a resistive-heating boat at specific substrate temperatures. Optical characteristics (transmittance, refractive index, extinction coefficient, and optical loss) and microstructures (morphology and crystalline structure) are investigated and discussed. Furthermore, MgF2 is used as a low-index material, and GdF3 is used as a high-index material for multilayer coatings. Reflectance, stress, and the laser-induced damage threshold (LIDT) are studied. It is shown that MgF2 and GdF3 thin films, deposited on the substrate at a temperature of 300 degrees C, obtain good quality thin films with high transmittance and little optical loss at 193 nm. For multilayer coatings, the stress mainly comes from MgF2, and the absorption comes from GdF3. Among those coatings, the sixteen-layer design, sub/(1.4L 0.6H)8/air, shows the largest LIDT.     

Microstructure and properties of zirconia-alumina nanolaminate sol-gel coatings

Zirconia-alumina multilayer nanolaminate coatings were applied on stainless steel 316 substrates by a sol-gel dipping method. The coatings were characterised using X-ray diffraction, optical and scanning electron microscopy. The hardness and elastic modulus, the wear resistance and the oxidation resistance of the coatings were measured and assessed. It was observed that the coatings possessed fine grains, fine pores and high retention of tetragonal zirconia phase. The coatings exhibited high hardness and elastic modulus as well as good resistance to oxidation at high temperatures. However, these properties may be influenced by the interactions at the coating/substrate interface.     

Manufacture and characterization of optical coatings with incorporated copper island films

Copper island films have been prepared by thermal evaporation in vacuum and characterized by in situ as well as ex situ spectrophotometry. The parallel investigation of the island morphology by means of transmission electron microscopy allowed us to establish a clear correlation between film structure and optical properties. The effective optical constants of the copper island films could be determined by means of a fit of their ex situ transmission and reflection spectra. The effective optical constants have been used for designing and preparing optical multilayer coatings applicable for attenuator or color filter specifications. Measured characteristics of the multilayer coatings are in very good agreement with the calculated spectra.     

TiN/Ti多层膜调制比对摩擦磨损行为影响的研究

考察了TiN/Ti多层膜调制比对其摩擦磨损行为的影响. 采用磁过滤阴极弧沉积的方法制备了具有不同调制比的TiN/Ti多层膜, 用扫描电镜和透射电镜对其层状结构及子层结构进行了观察和分析. 用纳米压痕和SRV摩擦磨损试验的方法, 对多层膜进行了纳米硬度和弹性模量测试以及摩擦磨损实验. 结果表明, 所制备的TiN/Ti多层膜层状结构清晰, 与基底结合良好, 调制比对多层膜的硬度和磨损特性影响较大, 而对摩擦系数的影响却不明显. 结合实验结果, 讨论了硬度与弹性模量的比值(H/E值)对TiN/Ti多层膜耐磨性的影响.