Chromium Thin Films Research Articles

Morphological and multifractal properties of Cr thin films deposited onto different substrates.

In this study, the morphological properties and micro-roughness of chromium thin film prepared by thermal evaporation technique and confirmed via EDS analysis are examined on different substrates of BK7, Silicon (Si), and glass using atomic force microscope analysis (AFM). Analysis of amplitude parameters, Minkowski functionals, and films' spatial microtexture extracted from AFM analysis showed the difference between glass substrate and the other two (BK7 and Si) substrates for the growth of chromium thin films. In addition, we observed robust signatures of multifractality of the Cr thin films deposited on all substrates we studied. Moreover, we highlight that the Glass substrates displayed the strongest multifractality indicating that such samples present space filling properties distributed over more spatial scales than the samples of BK7 and Si.

Effects of Multilayer Structure on the Microstructure and Optical Properties of the DC Sputtered Chromium Thin Films for Selective Solar Absorber Applications

Chromium thin films exhibit several properties that make them potential for solar thermal applications. In this work the effect of film thickness and sputtering power based multilayer structure on the optical properties of DC sputtered chromium thin films is reported. The structural, topological, and optical properties of these films were determined by X-ray diffractometer, Atomic Force Microscopy, and Ultraviolet-Visible-Near Infrared spectrophotometer, respectively. XRD spectra revealed a single peak with preferential orientation of (200) and (210) for single layer and multilayer chromium films, respectively. The grain size and roughness were relatively higher for the multilayer compared to single layer Chromium films. Spectral transmittance showed very high sensitivity to film thickness with average peak of 69% and 5% at a wavelength range of 250-2500 nm for the film thickness of 12 nm and 94 nm, respectively. Spectral transmittance was also found to be higher in single layered films than multi-layered films. Findings from this study suggest that multilayer structure have the potential of tuning the microstructure and optical properties of low thickness Cr films, hence, extending its potential applications in selective solar absorber applications.
 Keywords: Multilayer, Chromium, Sputtering, Optical constants

Surface exciton polariton resonances (SEPR)–based sensors

A new type of resonance in the development of sensors using long-range surface exciton polariton (LRSEP) phenomena has been coined: surface exciton polariton resonance (SEPR). The resonance was obtained in the reflected spectrum of a Kretschmann-Raether setup with a two-coupled-interface structure composed of 412 nm magnesium fluoride and 50 nm chromium thin films. The roles of different parameters such as thicknesses of the films and the incidence angles have been simulated. Some preliminary experimental results show a promising performance with a shift of the resonance central wavelength with changes in the incidence angle of -136.52 nm/° and a sensitivity of 23,221 nm/refractive index unit.

Formation of periodic relief structures in thin chromium films using laser interference lithography

Subject of study. The formation process of contact masks in thin films of photoresist and chromium using laser interference lithography was investigated. Hence, the photoresist films were structured by exposure in the interference field followed by the transfer of the formed microrelief to the chromium film using a plasma method. Method. The investigation is based on the use of laser interference lithography for the formation of protective masks in the layer of high-resolution photoresist. The photoresist was deposited via spin coating and subsequently dried. Lloyd’s interference scheme was used for photoresist exposure. After exposure, the photoresist was developed in a standard base developer specified by the manufacturer. The distribution nonuniformity of thickness of the photoresist film with microrelief over the substrate surface after development was determined as a ratio of difference in photoresist thicknesses at the substrate edges obtained using profilometry to the maximum thickness. Microrelief in the photoresist layer and chromium film was investigated via scanning probe microscopy. The etching uniformity and process of the microrelief transfer to the chromium film via the protective mask in the photoresist layer were investigated using a setup for reactive ion etching in inductively coupled plasma. Main results. The periodic relief structures in chromium films were obtained for the first time via laser interference lithography for photoresist structuring and transfer of microrelief by reactive ion etching. The obtained depth of microrelief in the photoresist layer corresponded to 350 nm. This depth is sufficient for microrelief transfer to the metal film. We established that the interference field in the recording area enables the formation of the microrelief in the photoresist layer with a coefficient of film thickness nonuniformity of 5% over the surface of the substrate with a diameter of 25 mm. Practical significance. The conducted investigation is initial and the aim involved identifying the principal possibility of formation of contact masks in metal films using laser interference lithography. If the lithographic setup is modified, this method can be applied to form contact masks for diffractive optical elements on substrates with sizes exceeding 25×25mm.

Spectral analysis and correction of the structure of computer-generated fan-out Dammann gratings at their fabrication

A technique for quickly finding the optimal time of liquid etching the amplitude masks of two-dimensional Dammann gratings, the structure of which is synthesized by direct laser writing in a polar coordinate system, is studied theoretically and experimentally. Thin chromium films are used as the recording material for laser writing, which are oxidized during laser writing and form an amplitude mask during their liquid etching (when using the thermochemical technology for their processing). The change in the etching time here occurs in the form of etching and displacement of the edges of the exposed zones. To find the optimal etching time for chromium films, it is proposed to use a procedure of measuring the spectra of amplitude gratings, by quick operational measurement and analysis of the intensity distribution of high diffraction orders, and by minimization of the root-mean-square deviation of these intensities. It is shown that higher diffraction orders in the spectra of binary-amplitude structures correlate well with the same orders of binary-phase structures. This conclusion can be effectively used to determine the moment when the optimum zone size is reached during liquid etching.

Analysis of errors and correction of topology of computer-generated two-dimensional fan-out gratings

A procedure is proposed and investigated for correction of direct laser writing of the topology of two-dimensional diffraction fan-out gratings with the use of a laser-lithographic system DWL66+ operating in the Cartesian system. Thin films of photoresist and chromium on a quartz substrate were used as recording materials. The required binary-phase structures were obtained by subsequent ion-plasma etching of the amplitude structures recorded by the system. The minimum feature size of the binary zones of synthesized structures was 1500´1500 nm. It has been found that, in order to obtain the stability of the reproduction of the synthesized structures and to approach these structures to the calculated ones, it is necessary to use a regime with partial overexposure of photoresist and correction of position of transition boundaries of exposed zones. The specified correction of position of transition boundaries was experimentally implemented by software, with a modification of the topology of written structures and with experimental founding the optimal diffraction fan-out gratings accounting for their response, with the maximization of efficiency in useful diffraction orders and minimization of the root-mean-square deviation between intensity maxima in useful orders. Taking into account the size of a focused spot (about 550 nm), as well as the recording materials and the regime of photoresist overexposure, it was found that the optimal correction for the displacement of the boundaries of the exposed zones amounts to 200 nm, with the boundaries being shifted to the centers (inside) of the zones.

The Synergistic Effect of the Laser Beam on the Thermionic Vacuum Arc Method for Titanium-Doped Chromium Thin Film Deposition

Laser-Induced Thermionic Vacuum Arc (LTVA) provides a better way to produce uniform metallic thin films than the classical Thermionic Vacuum Arc (TVA) method. In Ti-doped chromium thin films produced using LTVA, the amorphous chromium is superimposed with small bcc chromium nanoparticles. These amorphous/crystalline structures with small crystallites induce lower roughness and electrical resistivity, reducing electron–phonon scattering and increasing charge transport across LTVA thin films. A significant shift in resistivity for the LTVA samples is observed due to electron scattering on the phonon–crystalline structures in the TVA samples which exhibit larger crystallites. Meanwhile, the wettability measurements reveal a higher contact angle, resulting in a lower surface free energy and consecutively lower dissociation energy for the LTVA-produced thin films than the TVA samples.

Negative spin Hall angle and large spin-charge conversion in thermally evaporated chromium thin films

Spin-to-charge conversion and the reverse process are now critically important physical processes for a wide range of fundamental and applied studies in spintronics. Here, we experimentally demonstrate effective spin-to-charge conversion in thermally evaporated chromium thin films using the longitudinal spin Seebeck effect (LSSE). We present LSSE results measured near room temperature for Cr films with thicknesses from 2 to 11 nm, deposited at room temperature on bulk polycrystalline yttrium-iron-garnet (YIG) substrates. Comparison of the measured LSSE voltage, VLSSE, in Cr to a sputtered Pt film at the same nominal thickness grown on a matched YIG substrate shows that both films show comparably large spin-to-charge conversion. As previously shown for other forms of Cr, the LSSE signal for evaporated Cr/YIG shows the opposite sign compared to Pt, indicating that Cr has a negative spin Hall angle, θsh. We also present measured charge resistivity, ρ, of the same evaporated Cr films on YIG. These values are large compared to Pt and comparable to β-W at a similar thickness. Non-monotonic behavior of both ρ and VLSSE with film thickness suggests that spin-to-charge conversion in evaporated Cr, which we expect has a different strain state than previously investigated sputtered films, could be modified by spin density wave antiferromagnetism in Cr.

Electron Irradiation of Titanium-Doped Chromium Nanostructured Thin Films for Higher Conductive Electrodes

The low-energy electron irradiation improves the electrical properties of the Ti-doped chromium thin films obtained by Laser-assisted Thermionic Vacuum Arc (LTVA). The irradiation doses, between 0.6 C/m2 and 326.4 C/m2, operate as a nanozonal melting effect, decreasing the metallic alloy's roughness, and increasing the electrical conductivity at a depth up to 8 nm. Therefore, the grain sizes of the surface nanostructures are increased after irradiation, but the surface roughness is substantially improved. By tailoring the surface parameters like crystallinity and roughness of the metallic thin films used as electrodes in the OLED technologies, a reduction of the Schottky contacts between the metal and semiconductor contact is expected. This fact minimizes the contact resistance between the metallic and semiconductor thin films and increases the charge injection across the OLED sandwich structures

Examination of Film Thickness Dependence on Acoustic Impedance of Gold and Chromium Thin Films by Scanning Acoustic Microscopy

Thickness induced changes in acoustic impedance of gold (Au) and chromium (Cr) thin films are studied with scanning acoustic microscopy (SAM). Thin films are produced by thermal evaporation technique on BK7 glass substrates with varying thicknesses between 40 nm to 200 nm. In acoustic impedance (AI) mode, the microscope generates two-dimensional acoustic impedance maps of the thin films and micrometer resolution helps determining the surface defects on these films. On the other hand, acoustic impedance value is found to increase as thickness increases for both Au and Cr thin films indicating increased elasticity, therefore, hardness. The mean and standard deviation values of acoustic impedance of Cr thin films were found as 1.901 ± 0.050 MRayl for 40 nm, 1.905 ± 0.045 MRayl for 80 nm, 1.943 ± 0.049 MRayl for 120 nm, 1.964 ± 0.049 MRayl for 160 nm and 1.987 ± 0.052 MRayl for 200 nm. The mean and standard deviation values of acoustic impedance of Au thin films were found as 1.725 ± 0.026 MRayl for 80 nm and 1.954 ± 0.047 MRayl for 200 nm. This success achieved by SAM, demonstrates its potential in monitoring thin film surfaces even with very small thicknesses.

Anomalous Hall effect in antiferromagnetic Cr thin films

Bulk chromium is the simplest antiferromagnet in our general material database, which has been firmly believed to exhibit a collinear spin structure and a consequent vanishing anomalous Hall effect (AHE). In this work, we report an unexpected weak AHE in polycrystalline thin films of chromium. We attribute this phenomenon to the noncollinear spin textures induced by the local spin frustration and rearrangement in certain areas with high residual strain and defect densities. Moreover, a dominant underlying mechanism of intrinsic Berry phase is speculated. This could be a general feature for all the collinear antiferromagnetic thin-film materials with moderately high defect concentrations, making them promising candidates for emergent antiferromagnetic spintronics.

Effect of thermally grown Al2O3 on electrical insulation properties of thin film sensors for high temperature environments

NiCrAlY thin films are employed as buffer layers for high temperature thin film sensors, and thermally grown alumina (TG Al2O3) scales are formed by vacuum segregation and oxidation of Al processes at high temperature, which could synergistically enhance the insulation properties of the thin film sensors. In this work, nickel-22% chromium-10% aluminum-1% yttrium (NiCrAlY) thin films were deposited on GH3536 Ni-based superalloys by direct current (DC) magnetron sputtering. The samples were vacuum heat-treated at 1050 °C for 6 h and then subjected to isothermal oxidation at 1050 °C for different time. The morphological and electrical insulation properties of the TG Al2O3 scales were then investigated. The X-ray diffraction peaks of TG Al2O3 gradually increased with increasing oxidation time, while the surface became compact, as confirmed by scanning electron microscopy. The gradual structure from metal alloy to oxide was tailored. Several creaks were observed in the cross-section of TG Al2O3 after prolonged oxidation; thermal mismatch stress is mainly responsible for this phenomenon, which is detrimental to the adhesion of thin film sensors. Furthermore, the results of insulation resistance tests on the TG Al2O3 scales showed that the insulation resistance increased by an order of magnitude with increasing oxidation time, reaching a maximum of ~5 kΩ at 800 °C. Finally, a layer of Al2O3 was deposited by electron beam evaporation to form a multilayer insulating structure, in which the TG Al2O3 was oxidized for 6 h. A favorable insulation resistance (>2 MΩ) was obtained at 800 °C; the electrical insulation properties were assessed using a palladium chromium (PdCr) thin film strain gauge, which exhibited excellent repeatability over four thermal cycles from 25 °C to 800 °C.

On the Use of Chromium Coating for Inner-Side Fuel Cladding Protection: Thickness Identification Based on Fission Fragments Implantation and Damage Profile

Inner-side coatings have been proposed as a complementary solution within the accident tolerant fuel (ATF) framework, to provide enhanced protection for the nuclear fuel cladding. Unlike external surface, the degradation of irradiated internal cladding surface has not been studied extensively. Fission fragments produced during the fission of nuclear fuel is one of the key players in this degradation. This study aimed to estimate the minimum thickness of the thin chromium film, required to protect the inner side of the nuclear fuel cladding. The approach used is based on a set of calculations, of Ion ranges and damage profiles, for a group fission fragments, using the TRIM code. The calculation results were verified by comparison with the experimental data associated with the phenomena of the inner cladding degradation of thermo-releasing elements. The recommended minimum thickness for such a film was found to be 9 microns. Calculations also showed that chromium metal has a greater stopping power compared to the zirconium-based alloy E110, which indicates an increased ability of chromium to withstand exposure to energetic fission fragments during reactor operation.

Crack Programming: From Chaos to Control: Programmable Crack Patterning with Molecular Order in Polymer Substrates (Adv. Mater. 22/2021)

Cracking is typically an uncontrolled material failure process. In article number 2008434, Hyun Kim, Taylor H. Ware, and co-workers describe a process that enables unprecedented control of crack formation. By depositing thin-film chromium on photoaligned liquid-crystal polymer networks, patterns of cracks on the surface of a polymer can be freely programmed in a high-resolution and high-throughput manner. This crack programming process provides new opportunities for unconventional microfabrication. The image depicts light transmitted through a polymer film coated with chromium with azimuthally patterned cracks.

Kinematics and kinetics of alternating electric field induced liquid mass transport on chromium thin films

Long range mass transport driven by an electric field has many applications in the fields of nanoscience and technology. Liquid-phase mass transport ranging from the micrometer to the millimeter scale and its application to nanopatterning have been demonstrated on chromium (Cr) thin films using a DC electric field. Under the influence of an electric field, the metal seems to undergo a chemical reaction, and the resulting liquid material flows out radially in all directions. In this study, we have explored the effect of an alternating (AC) electric field on this kind of liquid-phase material transport. Within the scope of this work, mass transport has been studied on Cr films 30 nm thick using an alternating square waveform with frequencies ranging from 100 Hz to 1000 Hz in steps of 50 Hz. The dependence of the material’s formation, flow distance, and flow velocity on frequency, for a constant applied root mean square (RMS) voltage, was studied in detail. An analytical model is presented to explain the experimental results. This study, in particular the frequency parameter and the intermittent nature of the applied bias, will help us get a better control over the mass flow process, will lead to better resolutions for the electrolithography process.

Rapid development of the photoresponse and oxygen evolution of TiO2 nanotubes sputtered with Cr thin films realized via laser annealing

Recently, earth abundant transition metal oxides have gained particular attention as potential catalyst candidates due to their availability and low-cost comparing to substrates containing precious Pt or Au species. Herein, we present characterization of morphology, structure and electrochemical properties of pulsed 532 nm laser treated TiO2 nanotubes (NT) sputtered by the thin film of chromium. Scanning electron microscopy enables verification of the diameter and length of titania while Raman and X-ray photoelectron spectroscopies were used to evaluate crystalline phase and the oxidation state of elements, respectively. The recorded polarization curves clearly indicate that the optimized laser-treatment enhances activity towards oxygen evolution reaction (OER) of the TiO2 NT decorated with very small amount of Cr species. The analysis of Mott-Schottky plot shows significant increment in donor density (Nd) for the laser irradiated sample comparing to the one before annealing and pristine titania resulting from the effective manipulation of the electrode/electrolyte interface. Moreover, the impact of the processing parameters including energy fluence of laser beam and the thickness of sputtered Cr layer on the current density was evaluated by the electrochemical measurements performed under vis and UV–vis light. The results show promising application of direct interaction of laser beam with the surface of material exhibiting initially both poor OER activity and visible light response.

Multi-parameter coupling study of magnetron sputtering nickel–chromium thin film based on Taguchi-gray correlation method

In this study, a nickel–chromium film for detecting strain stress was deposited on 304 stainless steel substrates by the magnetron sputtering technique. The sputtering process parameters were optimized to obtain a better nickel–chromium film. Orthogonal array L16(44) design, signal-to-noise ratio calculation, and variance analysis were performed on the experimental data by the Taguchi method. The influence of the coupling of process parameters such as power, pressure, bias, and substrate temperature on the surface roughness, deposition rate, and resistivity of the film was studied. The power is the most significant influence factor affecting the film’s performance indicators, and the contribution rates of each process parameter to the response variables and the regression equation of each response variable are obtained. Finally, the gray correlation analysis results of the response variables show that at conditions of 200 W power, 1.6 Pa pressure, −100 V bias, and 400 °C substrate temperature, the surface roughness of the nickel–chromium film is 55 nm, the deposition rate is 110 nm/min, and the resistivity is 1.10 × 10−4 Ω cm. It can be seen that the best film performance parameter group can be obtained using the Taguchi gray correlation method under the multi-parameter coupling of the nickel–chromium thin-film.

Epitaxy and controlled oxidation of chromium ultrathin films on ferroelectric BaTiO3 templates

Interfaces play a crucial role in the study of novel phenomena emerging at heterostructures comprising metals and functional oxides. In this work, we consider Cr/BaTiO3 heterostructures grown on Nb:SrTiO3 (001) substrates. Chromium thin films with 2 nm nominal thickness are deposited by molecular beam epitaxy on the BaTiO3 layer, and subsequently annealed in vacuum at temperatures ranging from 800 K to 970 K, and finally exposed to 10−7 torr of molecular oxygen for 300 s. Highly ordered films are obtained for each of this condition, ranging from metallic Cr to insulating Cr2O3 with tetragonal structure. Quite unexpectedly, an intermediate – fully ordered – case exists, with the co-presence of Cr and Cr2O3 compounds, each one with its proper crystal orientation. These results show the opportunity of controlling the metal/oxide state of crystalline Cr films grown onto the ferroelectric template BaTiO3/Nb:SrTiO3.

Admittance analysis of broadband omnidirectional near-perfect absorber in epsilon-near-zero mode.

In this paper, we propose a broadband omnidirectional near-perfect absorber that transforms light energy into heat. In contrast to previous research on structural metamaterials, this study focuses on light absorption in the epsilon-near-zero (ENZ) layers without any structural patterns. Chromium (Cr) thin films were applied as ENZ layers. Using the admittance method, we found the proper thicknesses of SiO2 layers to match the incident medium and achieve perfect absorption. Also, the absorber is angular insensitive up to 60°. The temperature of the absorber increases from room temperature to 42°C, which is 4°C higher than the uncoated substrate at 38°C, after exposure to sunlight for 20 min.

The effect of annealing process on the performance of strain nickel–chromium thin film sensor

In order to reduce the resistance value of the sputtering thin film resistor grid and improve the adhesion of the film, a thin film sensor with the NiCr film as a sensitive layer on a 304 stainless steel substrate is annealed in the N2 environment. During the experiment, it is found that the different annealing temperatures (300 °C, 350 °C, 400 °C, 450 °C, and 500 °C) can effectively reduce the resistance value of the thin film resistor grid; the decrease is the largest at 450 °C, and the resistance value change is 1.77 kΩ. The small resistance value enables the thin film sensor to detect smaller strain and has higher measurement accuracy. The thin film has the strongest adhesion on the substrate at 350 °C and 30 min, which is about 37.5% higher than that of the sputtering state. The increase in adhesion makes the thin film less likely to crack and fall off prematurely, which can expand the measuring force range. In addition, the atomic force microscopy results demonstrate that the thin film annealed at a higher annealing temperature has higher surface roughness, which may be caused by the phenomenon of original grain clusters after annealing. In addition, the temperature coefficient of resistance value and strain sensitivity coefficient (kn) increase with the increase in the annealing temperature, with kn increasing only slightly.