Cr Films Research Articles

Inexpensive Home-Made Single Wavelength Ellipsometer (λ = 633 nm) for Measuring the Optical Constant of Nanostructured Materials

Inexpensive home-made Single wavelength Ellipsometry with RAE (Rotating Analyser Ellipsometer) configuration has been developed. Spectroscopic ellipsometry (SE) is an optical measurement technique which is based on the measurement of the change of the phase difference (Δ) and the amplitude ratio (ψ) between p and s linear polarized of reflected (or transmitted) light. Our RAE configuration system composed of polarizer, sample, analyzer, detector, and He-Ne laser (λ = 633 nm) that acted as the monochromatic light source. To test the reliability of our SE system, we measure the optical constant of Au bulk and Cr (30 nm thick) film. The optical constant and the thickness were extracted by employing the pseudo-dielectric function and numerical inversion which is based on the secant method, the ψ and Δ of our SE data which is modelled by Fresnel equation. From the extraction using the secant method we obtain the optical constant of the Au bulk sample with n = 0.11 to 0.22 and k = 3.26 to 3.37 which is close to that of using pseudo-dielectric method. We obtain the same result for Cr film with n = 3.66 to 3.81 and k = 5.32 to 5.38 which is close to the result from reference. These results show that our inexpensive home-made Single wavelength Ellipsometry instrument and the extraction method are reliable for determining the optical constant of nanostructured materials.

Improvement in Cr Nanoparticle Content in Ni–Cr Film by Co-deposition with Combined Surfactant HPB and CTAB

The effects of single surfactant hexadecylpyridinium bromide (HPB) and cetyltrimethylammonium bromide (CTAB) and the combination of HPB and CTAB on the Cr nanoparticle content in the Ni–Cr film prepared by co-deposition were investigated. Single HPB/CTAB addition inhibited the oxidation and amorphous transformation of the Cr nanoparticles in the plating bath and effectively stabilized the Cr nanoparticles content at approximately 10 mass% as a function of time. Moreover, the combination of HPB and CTAB formed a cylindrical micelle structure on the Cr nanoparticle surface, which prompted the formation of a layer of NiCr2O4. As a result, the Cr nanoparticle content increased sharply to 20 mass%.

A comparative study on the properties of chromium coatings deposited by magnetron sputtering with hot and cooled target

This article reports on the analysis of energy flux density to the substrate and results of the detailed study of properties of Cr coatings deposited by magnetron sputtering with hot and cooled Cr targets. It was demonstrated that deposition rates of Cr films increase and particle flow density on the substrate changes by target sublimation. Heat radiation of the hot target leads to more rapid heating of the substrate and this energy flux has a main contribution in enhancement of total energy flux density on the substrate (from 0.06 to 0.43 W/cm2). As consequence, energy per deposited atom increases in 5.8 times for the hot Cr target sputtering even taking into account higher deposition rates. Cr films deposited by the cooled target sputtering have a (110) crystal texture, columnar microstructure, low surface roughness (∼2.66 nm) and hardness from 13.8 to 14.2 GPa. In the case of the hot target sputtering, the competitive crystal growth of (110) and (200) directions is observed, microstructure of the Cr films is denser and homogeneous, grain size increases up to 200–300 nm and film surface becomes coarse (Ra ∼11.75 nm), hardness of the Cr films drops by a factor of about 2.

A review of chromium(VI) use in chlorate electrolysis: Functions, challenges and suggested alternatives

Sodium chlorate is industrially produced by electrolysis of an aqueous salt solution, in which chromium(VI) constitutes an important excipient component. It is added to a concentration of a few grams Na2Cr2O7/liter to the electrolyte and has several functions in the process, the most important being to increase the Faradaic efficiency for hydrogen evolution in the undivided electrochemical cells. A thin film of Cr(OH)3×nH2O formed by reductive deposition on the cathodes decreases the rate of unwanted side reactions, while still enabling hydrogen evolution to occur. In addition chromium(VI) buffers the electrolyte at the optimum pH for operation and promotes the desired homogeneous reactions in the electrolyte bulk. Chromium species also affect the rates of hydrogen and oxygen evolution at the electrodes and are said to protect the steel cathodes from corrosion.Although chromium(VI) stays in a closed loop during chlorate production, chromate is a highly toxic compound and new REACH legislation therefore intends to phase out its use in Europe from 2017. A production without chromium(VI), with no other process modifications is not possible, and today there are no commercially available alternatives to its addition. Thus, there is an urgent need for European chlorate producers to find solutions to this problem. It is expected that chromium-free production will be a requirement also in other parts of the world, following the European example.As the chromium(VI) addition affects the chlorate process in many ways its replacement might require a combination of solutions targeting each function separately. The aim of this paper is to explain the role and importance of chromium(VI) in the chlorate manufacturing process. Previous achievements in its replacement are summarized and critically evaluated to expose the current state of the field, and to highlight the most promising avenues to be followed. An attempt is also made to reveal connections with other research fields (e.g. photochemical water splitting, corrosion science) facing similar problems. Allied effort of these different communities is expected to open up research avenues to the mutual benefit of these fields.

Picosecond laser registration of interference pattern by oxidation of thin Cr films

The laser oxidation of thin metallic films followed by its selective chemical etching is a promising method for the formation of binary metal structures on the glass substrates. It is important to confirm that even a single ultrashort laser pulse irradiation is able to create the protective oxide layer that makes possible to imprint the thermochemical image.Results of the thermo-chemical treatment of thin chromium films irradiated by picosecond laser pulse utilizing two and four beam interference combined with the chemical etching are presented. The spatial resolution of this method can be high enough due to thermo-chemical sharpening and can be close to the diffraction limit. Micro-Raman spectroscopy was applied for characterization of the chemical composition of the protective oxide layers formed under atmospheric conditions on the surface of thin chromium films.

CNS 表面の作製と潤滑特性

We fabricated contoured nanostripe (CNS) surface consisting of Cr and Cu multilayer films having a contour like grooves by wet blasting. Depth of nanoscale grooves (nanogrooves) on the substrate is 60 to180 nm. The friction tests at a constant load were carried out using an Al ball under a lubricating condition. The CNS substrate having dense nano-grooves showed the lowest wear. The substrate having nano-grooves showed good lubricating properties. Durability of CNS surface probably depended on interfacial strength between films. The friction loop showed that the CNS surface had locally friction reduction properties.

Investigation of Na2SO4 Deposit Induced Corrosion of Cr, Al, C Binary and Ternary Thin Film Coatings on Ni-201

Al-C, Cr-C, Al-Cr and Al-Cr-C thin film coatings were sputtered onto Ni-201 substrates. Samples were deposited with 1.0 ± 0.3 mg cm−2 Na2SO4 and exposed to dry air/2 ppm SO2 gas atmosphere, at 700°C for 250 hours. Coated samples had reduced corrosion rates relative to uncoated samples. Al–C and Cr–C coatings were not effective since NiO was the only compound detected on the surfaces; in contrast Cr–Al and Cr–Al–C developed protective layers of Al2O3 and Cr2O3 with Cr–Al–C coated samples having the least corrosion rate.

Nanostructured thin film coatings with different strengthening effects

A number of articles on strengthening thin film coatings were analyzed and a lot of unusual strengthening effects, such as super high hardness and plasticity simultaneously, ultra low friction coefficient, high wear-resistance, curve rigidity increasing of drills with small diameter, associated with process formation of nanostructured coatings by the different thin film deposition methods were detected. Vacuum coater with RF magnetron sputtering system and ion-beam source and arc evaporator for nanostructured thin film coating manufacture are represented. Diamond Like Carbon and MoS 2 thin film coatings, Ti, Al, Nb, Cr, nitride, carbide, and carbo-nitride thin film materials are described as strengthening coatings.

Microwave Cooled Microbolometers Based on Cermet Si–Cr Films

We present the results of creating a cooled microbolometer based on the cermet films of the silicon and chromium mixture. This material is used for manufacturing the freely hanging high-resistive microbolometers for the first time. The details of fabricating such microbolometers and the prospects for using cermet films to construct microbolometers are discussed. The first estimates of sensitivity of the fabricated microbolometers are given.

Influence of Doping Element Crystal Structure on the Microstructure of Cr Films by Magnetron Sputtering

Cr films with different doping elements were deposited onto silicon wafer by magnetron sputtering. The microstructure and preferred orientation of Cr films were analyzed by TEM and XRD. The results show that the doping element W with bcc structure can strongly inhibit preferred orientation growth trend along (110) crystal plane of Cr film. A nano-multilayer structure is easily formed in the film, which is composed of Cr and W single layer. The doping element Al with fcc structure can strongly inhibit preferred orientation growth trend along all crystal planes of Cr film. The average grain size of Al (Ce) doped Cr film decreased significantly and the crystallization degree improved with the rare earth element Ce added. Both the doping element Zn with hcp structure and the doping element C with hexagonal structure can inhibit preferred orientation growth trend along (110) crystal plane of Cr film. The mechanism is to form the replacement solid solution and interstitial solid solution with Cr atoms, respectively. Nano-multilayer structure composed of Cr and Zn (or C) single layer formed in the films.

Effects of Cr interlayer thickness on adhesive, structural, and thermoelectric properties of antimony telluride thin films deposited by radio-frequency magnetron sputtering

We investigated the effects of Cr interlayer thickness on adhesive, structural, and thermoelectric properties of p-type antimony telluride (Sb2Te3) thin films. Prior to depositing Sb2Te3 films with a thickness of 1μm using radio-frequency magnetron sputtering, a Cr film with a thickness ranging from 0 to 216nm was deposited on a glass substrate using the same sputtering equipment. The obtained samples were thermally annealed at 300°C for 1h. Adhesiveness of the films was examined by a cross-cut method. Adhesion of Sb2Te3 thin films could be improved by incorporating the Cr interlayer, independent of the thickness of the interlayer. The surface morphology of the Sb2Te3 thin films became flat with a dense structure as the thickness of the Cr interlayer increased. Atomic composition analysis indicated that Te atoms might be diffused into the Cr interlayer and formed Cr-based alloys when the Cr interlayer thickness was increased to >100nm. X-ray diffraction analyses indicated that the crystal orientation, crystallite size, and strain of the films reached their maximum values at Cr interlayer thicknesses of 46–70nm. Thermoelectric properties of the films were improved by incorporating the Cr interlayer of appropriate thickness. In particular, a power factor of 18.7μW/(cmK2) was achieved at a Cr interlayer thickness of 46nm, which was approximately 4 times larger than that of the film with no Cr interlayer.

Experiments for improving fabrication, recovery and surface-protection of Cs3Sb photocathode

We examined 1) the photocurrent from Cs3Sb photocathode as a function of anode voltage below 200V, 2) the relationship between the quantum efficiency of photoemission and the conditions for fabrication by the sandwich method, 3) recovery of the photoemission by additional Cs deposition, and 4) the effects of surface protection of Cs3Sb photocathodes by WO3 and Cr2O3 films in the passive state. The photocurrent had a maximum at approximately 68V except when we increased the anode voltage extraordinarily slowly. Cs3Sb photocathodes were fabricated by increasing the temperature of sandwiched layers of Sb, Cs and Sb deposited on the fine tips of eight cathodes at less than −12°C. Cs3Sb photocathodes having higher quantum efficiency were fabricated by smoothly increasing the temperature of the layers quickly after we deposited the second Sb layer. The photocurrent from the Cs3Sb photocathodes was significantly higher when Cs was deposited at temperatures of 50–70°C. Deposition of a one- to three- atomic-layer W or Cr film extended the photoemission lifetime after the layers were oxidized to WO3 or Cr2O3 in the passive state due to oxidation. The WO3 or Cr2O3 in the passive state provided more surface protection as their thickness increased.

Internal stress analysis of electroplated films based on electron theory

Cu films on Fe, Ni and Ag substrates, Ni films on Fe and Ag substrates, Ag film on Cu substrate, Cr film on Fe substrate, Ag film on Ag substrate, Ni film on Ni substrate and Cu film on Cu substrate were deposited by electroplating. The average internal stress in all films, except Cr, was in-situ measured by the cantilever beam test. The interfacial stress is very large in the films with different materials with substrates and is zero in the films with the same material with substrates. The interfacial stress character obtained from the cantilever beam bending direction is consistent with that obtained from the modified Thomas-Fermi-Dirac electron theory.

Improvement of Oxidation Behavior in Cr(N,O) By Increasing the Oxygen Content

Chromium oxynitride(Cr(N,O)) thin films have been developed by controlling the oxygen partial pressure during the deposition 1). The Cr(N,O) thin films show superior properties not only the hardness but also the oxidation behavior than those of CrN, which are suitable for machining tool applications. However, the reason of the oxidation improvement was not known because of the presence of grain boundaries. Recently, we have succeeded in preparation of epitaxially grown Cr(N,O) on MgO and other single crystal substrates to reduce the density of grain boundaries2). In this work, oxidation behavior of the epitaxially grown Cr(N,O) thin films was investigated from crosssectional transmission electron microscope (TEM) observations. Thin films of Cr(N,O) were epitaxially grown by a pulsed laser deposition method. In the deposition chamber, oxygen gas with a partial pressure of 2x10-5Pa and N radicals from an RF radical source were introduced. A plate of Cr was rotated in the deposition chamber was irradiated by a Nd:YAG pulsed laser with a wavelength of 355 nm. Thin films were deposited on MgO (100) single crystal substrates kept at 973 K in the deposition chamber. After the deposition, oxidation tests were carried out in a furnace at 673-1173 K in air for one hour. After the oxidation tests, powder X-ray diffraction (XRD), crosssectional TEM and electron energy loss spectroscopy (EELS) observations/analyses were conducted for precise phase, microstructure and composition analysis. From the XRD and TEM analyses, the as-deposited thin films were of epitaxially grown Cr(N,O) on the substrates. After the oxidation tests, from XRD patterns, peaks for Cr2O3were seen from samples heated above 873 K. On the other hand, peaks for Cr(N,O) remained up to 1073 K. From TEM and EELS analyses of the sample heated at 1073K, on the existing Cr(N,O) epitaxially grown thin film, a polycrystalline oxide layer was covering. It was found that the oxide layer works as an oxygen diffusion barrier from the surface. References 1) T. Suzuki, J. Inoue, H. Saito, M. Hirai, H. Suematsu, W. Jiang, and K. Yatsui, Thin Solid Films 515, 2161 (2006). 2) K. Suzuki, T. Endo, A. Sato, T. Suzuki, T. Nakayama, H. Suematsu, and K. Niihara, Mater. Trans. 54, 1957 (2013).

High-rate magnetron sputtering with hot target

Chromium films were deposited by cooled and hot target magnetron sputtering techniques with unbalanced magnetic field configuration at equal target power density. The dependence of deposition rates of Cr films by the hot target magnetron sputtering on the power density was a non-linear at 27.5–31.5W/cm2. The optical emission studies indicated the enhancement of deposition rates due to the evaporation of the hot Cr target. The chromium film structure was strongly depended on the factor of «hot target» and the target power density. Cr films were structured to (110) direction in the case of the hot target sputtering, for cooled target configuration – the preferred orientation was changed from (110) to (200) with the power density. Cr+ to Cr ratio and heat flow from the cathode to the substrate influenced on the coating hardness and adhesion. The Cr films with 9.84–12.79GPa and the non-cracking behavior (up to 15N) were obtained.

Optical and structural properties of Cr and Ag thin films deposited on glass substrate

Most of the rotating or noting patterns are being developed by using silver plating through chemical coating. Silver layers deteriorate with the passage of time and become less reflective while undergo through cleaning process due to its softness and the results become unpredictable. In this paper an alternate method for development of above mentioned pattern has been demonstrated. Chromium (Cr) and Silver (Ag) thin films of 200nm and 160nm thick respectively have been realized using electron beam evaporation (PVD technique) on quartz substrate. Structural analysis has been carried out by XRD and SEM while optical transmission/reflection has been studied using spectrophotometer. XRD analysis shows that Ag coated thin films exhibit FCC structure while Cr coated thin films reveals a BCC structure. SEM analysis shows almost smooth and uniform surfaces in both cases. After passing through high and low temperature cycles it was found that the results of pattern structures developed by chromium coating were more reliable than obtained through silver platting process.

Contact Metal–MoS2 Interfacial Reactions and Potential Implications on MoS2-Based Device Performance

Thin films of contact metals, specifically Au, Ir, Cr, and Sc, are deposited on exfoliated, bulk MoS2 using electron beam deposition under two different reactor base pressures to determine the contact metal–MoS2 interface chemistry and its dependence on the reactor ambient. The high work function metal Au does not react with MoS2 regardless of reactor ambient. In contrast, interfacial reactions between MoS2 and another high work function metal, Ir, are observed when it is deposited under both high vacuum (HV, ∼ 1 × 10–6 mbar) and ultrahigh vacuum (UHV, ∼ 1 × 10–9 mbar). Interfacial reactions occur between metals with low work functions (Cr, Sc) near the electron affinity of MoS2 when the contact metal is deposited under UHV conditions. In addition, Sc is rapidly oxidized on the MoS2 surface, whereas Cr is only partially oxidized when deposited under HV conditions. This indicates that deposition chamber ambient can affect the contact metal chemistry in addition to the chemistry present at the contact metal...

Gap and spin texture engineering of Dirac topological states at theCr−Bi2Se3interface

The presence of an exchange field in topological insulators reveals novel spin related phenomena derived from the combination of topology and magnetism. In the present work we show the controlled occurrence of either metallic or gapped topological Dirac states at the interface between ultrathin Cr films and the Bi$_2$Se$_3$ surface. The opening and closing of the gap at the Dirac point is caused by the spin reorientation transitions arising in the Cr films. We find that atom thin layers of Cr adhered to Bi$_2$Se$_3$ surfaces present a magnetic ground state with ferromagnetic planes coupled antiferromagnetically. As the thickness of the Cr film increases stepwise from one to three atomic layers, the direction of the magnetization changes twice from out-of-plane to in-plane and to out-of-plane again. The out of plane magnetization drives the gap opening and the topological surface states acquire a circular meron spin structure. Therefore, the Cr spin reorientation leads to the metal/insulator transition in the Bi$_2$Se$_3$ surface and to the correlated modification of the surface state spin texture. Consequently, the thickness of the Cr film provides an effective and controllable mechanism to modify the metallic or gapped nature, as well as the spin texture of the topological Dirac states.

Thin film wrinkling by strain mismatch on 3D surfaces

Wrinkling of thin films in micro- and nanoscale has found wide applications in stretchable electronics, optical gratings, material characterization, and biology. However, most wrinkling work is in planar fashion and only limited work on 3D wrinkling has been reported. In this paper, we present experimental demonstration of 3D Cr film wrinkling on PDMS micro-ridges induced by strain mismatch. We first fabricated PDMS micro-ridges using replication from a silicon mold, prepared by conventional microfabrication processes. While pre-stretching the PDMS specimen along the ridge direction, thin Cr film was deposited through physical sputtering. After releasing the prestrain, two wrinkling waves formed on the two inclined surfaces of the PDMS ridges with the same wavelength but opposite phases. These two wrinkling waves twist the top of the ridge into a wavy shape, forming wrinkling waves oscillating in the direction parallel to the substrate plane. In contrast, 2D wrinkling waves oscillate in the direction perpendicular to the substrate plane. Using finite element simulations, we demonstrate that the 180° phase shift between the two sides is favored by the dominant buckling modes. While the 3D wrinkling wavelength is consistent with 2D theoretical prediction, wrinkles on the ridge feature non-uniform wrinkling wave amplitude along the width of the inclined surface. This 3D wrinkling work opens new opportunities in manufacturing curved-shape mold for contact printing and increases surface to volume ratio for wetting and battery applications.

The properties of self-formed diffusion barrier layer in Cu(Cr) alloy

The properties of Cu(Cr) alloy films were measured to evaluate its potential application as self-formed diffusion barrier in copper interconnect. Pure Cu and Cu(4.5 at%Cr) alloy films were deposited on SiO2/Si substrates using magnetron sputtering and subsequently annealed in vacuum (2 × 10−4 Pa) at the temperature of 350°C–550 °C. After annealing, the film properties were examined using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and four-point probe (FPP) method. The results indicate that there was no intermetallic compound (copper–silicide) detected at the interface after annealing. A 7 nm Cr rich layer was self-formed at the interface between Cu(Cr) and SiO2/Si after annealing which acted as a thermally stable barrier against the diffusion of Cu into SiO2. The resistivity of the films decreased with increasing the annealing temperature. After annealing at 550 °C for 1 h, the resistivity of the studied alloy films was 6.9 μΩ cm, which is comparable to that of Cu films (5.17 μΩ cm). These evidences suggest that Cu(Cr) films with excellent thermal stability and low sheet resistance would become a promising material for future advanced barrierless Cu interconnects.