Cr Films Research Articles

Super-regular femtosecond laser nanolithography based on dual-interface plasmons coupling

Abstract Advances in femtosecond laser-material interaction facilitate the extension of maskless optical processing to the high efficiency and deep-subwavelength scale. Here, a hybrid plasmon lithography technique has been demonstrated by irradiating near-infrared femtosecond laser pulses onto the Si material coated with thin Cr films in a vacuum chamber, and superior nanograting structures are found to deeply penetrate through the thin Cr film into the underlying Si substrate. In stark contrast to the common ripple structures formed on the Si surface, the Cr-layer mediated Si nanograting structures not only exhibit the spatially super-regular arrangements with a deep-subwavelength period of 355 nm but also present the nonsinusoidal sharp-edged groove geometry with a large depth-to-width aspect ratio of 2.1. Theoretical analyses and calculations reveal that the anomalous structure characterizations are physically ascribed to the excitation of dual-interface coupled plasmons in the thin metal layer, which possess the squeezed spatial wavelength and the periodic columnar intensity distributions. Moreover, the further deepening of periodic nanostructures into the Si substrate is also elucidated by the simulation of electric field enhancements at the bottom of shallow grooves under irradiation of subsequent laser pulses. In combination with a wet etching process, the Si nanograting structures can be modified into the smooth and narrow-mouthed V-profiles, whose optical measurements show a near omnidirectional antireflection especially in the visible range of 565–750 nm, which is expected for the design of advanced photonic devices.

Introducing Water Electrolithography.

High-resolution patterning with remarkable customizability has stimulated the invention of numerous scanning probe lithography (SPL) techniques. However, frequent tip damage, substrate-film deterioration, low throughput, and debris amassing in the patterned region are the inherent impediments that have precluded obtaining patterns with high repeatability using SPL. Hence, SPL still has not got wider acceptance for industrial fabrication and technological applications. Here, we introduce a novel SPL technique, named water electrolithography (W-ELG), for patterning at the microscale and potentially at the nanoscale also. The technique operates in the non-contact mode and is based on the selective etching, via an electrochemical process, of a metallic film (e.g., Cr) submerged into water. Here, the working of W-ELG is demonstrated by scribing a pattern into the Cr film by a traversing cathode tip along a preset locus. A numerical analysis establishing the working principles and optimization strategies of W-ELG is also presented. The tip-sample distance and tip-diameter are identified as the critical parameters controlling the pattern creation. W-ELG achieved a throughput of 1.5 × 107 μm2/h, which is the highest among the existing SPL techniques, while drawing 4 μm wide lines, and is also immune to deleterious issues of tip damage, debris amassment, etc. Therefore, the resolution of these inherent impediments of SPL in W-ELG sets the stage for a paradigm shift that may now translate the SPL from academic exploration to industrial fabrications.

Ultrabroadband and ultrathin absorber based on an encapsulated T-shaped metasurface.

Ultrabroadband absorbers are vital for applications such as solar energy harvesting and integrated optoelectronic devices. Herein, we design, fabricate and characterize a novel ultrabroadband and ultrathin absorber based on the encapsulated T-shaped metasurface (ETM). The ETM consists of a 20 nm Cr film and a Cr substrate sandwiched by the T-shaped polymethyl methacrylate (PMMA) arrays. The Cr film provides a robust absorptive surface with improved impedance matching, and ultrabroadband absorption can be achieved via the excitation of the localized surface plasmon (LSP) of this ultrathin film. The average absorption of simulated and experimental results of the ETM in the visible range of 400-800 nm for the TM (TE) polarization are 96.4% (96.3%) and 90.6% (89.4%), respectively. Three-dimensional (3D) power dissipation density distributions of the proposed structure have been investigated, which indicates that the synergistic absorption effect of different parts of the T-shaped ultrathin Cr film contributes to the major absorption enhancement. The absorption of the ETM is very robust to the changes of geometrical parameters and the symmetry of the structure, and it can be maintained almost the same even if T-shaped profiles are changed to L-shaped profiles. Moreover, the absorption performance of the ETM exhibits polarization-insensitive and wide-angle features, which has advantages for many potential applications.

Highly oriented MIL-101(Cr) continuous films grown on carbon cloth as efficient polysulfide barrier for lithium-sulfur batteries

The development of lithium-sulfur (Li-S) batteries is obstructed by polysulfide-shuttling and sluggish conversion kinetics during the process of charge and discharge. Herein, a highly oriented MIL-101(Cr) continuous film is developed on carbon cloth and utilized as trustworthy interlayer for lithium-sulfur batteries. This interlayer possesses a unique hierarchical porous structure and abundant active sites, providing efficient confinement of polysulfides through strong physical/chemical adsorption. Specially, the Lewis acidic Cr(III) centers of MIL-101(Cr) films are able to coordinate with polysulfides through Lewis acid-base interactions. Moreover, MIL-101(Cr) films also have the electrocatalytic effect of promoting the conversion of polysulfides. Benefiting from these features, this composite interlayer establishes an efficient barrier to inhibit the shuttling of polysulfides. Consequently, the as-prepared multifunctional interlayer exhibits a remarkable rate performance of 635 mAh g−1 at 3 C, a superior cycle stability with a low-capacity decay of 0.039% per cycle over 500 cycles at 1 C and high areal specific capacity of 4.3 mAh cm−2 under raised sulfur loading (5.1 mg cm−2).

Ellipsometric investigation of AlN thin films - Effect of temperature and doping with Ti,Cr

Spectroscopic Ellipsometer is employed to study the optical properties (including complex refractive index and bandgap) of pristine and doped AlN (Ti and Cr) films as a function of doping concentration and temperature (273 K–573 K). Pristine AlN, Al1−xTixN (x = 1.5, 3 and 4 at%) and Al1−xCrxN (x = 2, 4 and 6 at%) films are grown on Si(100) substrates using magnetron sputtering technique. The crystal structure and chemical composition of the as grown films are analyzed using Grazing Incidence X-ray Diffraction (GIXRD) and X-ray Photoelectron Spectroscopy (XPS) techniques, respectively. The optical properties of Ti, Cr doped AlN films at a wider range of energies as well as different ambient temperatures are reported. To determine the complex refractive indices, the measured ellipsometric parameters Is and Ic are fitted using a five layer model with Lorentz oscillator dispersion relation. As far as the bandgap region is concerned, both the real and imaginary parts of the refractive index show significant changes near the bandgap. It is observed that, the real part of refractive index of AlN increases monotonically with the increase in Ti doping and opposite in Cr doping. The extinction coefficient is relatively larger for Cr-doped AlN compared to Ti-doped AlN films. With the increase in doping concentration, the bandgap is found to decrease rapidly for Cr-doped AlN in comparison to Ti-doped AlN films. Additionally, a significant change in the complex refractive index of doped AlN films is observed with temperature.

Influence of RF-power on the optical, structural, and morphological properties of ZnS:Cr thin films

ABSTRACT In this work, the morphological, optical, and structural properties of ZnS:Cr films deposited by RF-sputtering are examined for different RF-powers. For this, thin films (ZnS) and (ZnS:Cr) were deposited on glass and Si substrates. The deposition time was set at 90 min, and the RF power varied in the range of 100–200 W. X-ray indicated that all the ZnS films were single-phase with apreferred growth orientation along the (111) plane of the (ZB) phase. The Cr-doped ZnS, and showed the (111) (2 20) and (311) peaks of the same phase. The ZnS films showed acrystallite size of 25.45 nm for RF power of 200 W. While in the case of ZnS:Cr, the crystallite size increased from 16.6 nm to 28.5 nm. The strain was shown to decrease from 2.2 × 10−3 to 1.45 × 10−3. SEM observations revealed smooth film surfaces. (EDS) revealed that the Cr rate is smaller than the Zn and Srates. UV- measurements revealed that the ZnS films exhibit an average transmittance on the order of 70% whilst that the ZnS:Cr was less than 60% in the visible wavelength region. Moreover, the optical bandgap of the ZnS films was found to be equal to 3.57 eV, and decreases for ZnS:Cr.

Pervaporation of dichloromethane‐cyclopentane and methylal‐cyclopentane mixtures through membranes from chloroprene rubber

AbstractChloroprene rubber (CR) has been commonly applied in various branches of the industry but its application in selective layers of pervaporation membranes remains overseen. To survey its applicability, we report on the pervaporation of two close‐boiling azeotrope‐forming systems of common solvents, blowing agents, adjuvants, and refrigerants, namely, dichloromethane‐cyclopentane (DCM‐CP) and methylal‐cyclopentane (ML‐CP). Vulcanizates having the form of thin films (66 ± 5 μm) have been prepared from the crystallization‐resistant (WRT) polychloroprene by using nanoparticles of ZnO and MgO. Mechanical and thermal properties have been characterized using dynamic mechanical analysis (DMA) and thermogravimetry analysis, spectral properties using ATR‐FTIR. Plasticization has been assessed by measuring DMA characteristics for the CR films exposed to vapors of the studied compounds. The CR films are preferentially permeable to DCM and ML over CP, break the respective azeotropes, and show comparable selectivity ranging from 1.1 to 1.7 for DCM‐CP and from 1.0 to 1.8 for ML‐CP. Importantly, plasticization of the CR membranes by DCM and ML enhances the selectivity and, simultaneously, the transmembrane flux. Overall, we show that membranes from CR enable selective and intensive pervaporative recovery of halogenated hydrocarbons from their mixtures with hydrocarbons, which is relevant, for instance, for the recycling of blowing agents.

Properties of CrSi2 Layers Obtained by Rapid Heat Treatment of Cr Film on Silicon.

The changes in the morphology and the electrophysical properties of the Cr/n-Si (111) structure depending on the rapid thermal treatment were considered in this study. The chromium films of about 30 nm thickness were deposited via magnetron sputtering. The rapid thermal treatment was performed by the irradiation of the substrate’s back side with the incoherent light flux of the quartz halogen lamps in nitrogen medium up to 200–550 °C. The surface morphology was investigated, including the grain size, the roughness parameters and the specific surface energy using atomic force microscopy. The resistivity value of the chromium films on silicon was determined by means of the four-probe method. It was established that at the temperatures of the rapid thermal treatment up to 350 °C one can observe re-crystallization of the chromium films with preservation of the fine grain morphology of the surface, accompanied by a reduction in the grain sizes, specific surface energy and the value of specific resistivity. At the temperatures of the rapid thermal treatment from 400 to 550 °C there originates the diffusion synthesis of the chromium disilicide CrSi2 with the wave-like surface morphology, followed by an increase in the grain sizes, roughness parameters, the specific surface energy and the specific resistivity value.

The estimation of residual stresses by the brittle thin film’s initial cracks on a ductile substrate subjected to tensile stresses

Thin metal films in the nanometer range are extensively used for electronic and optoelectronic devices. However, the residual stress has a profound impact on the durability of the devices during their lifetime. This paper developed a two-dimensional (2D) elastic model to study the residual stress and opening-mode fractures (OMFs) in a film/substrate assembly. The fracture strength expressed by crack length is derived by the strength criterion. This paper also studies fragmentation of 100–400 nm thin Cr films on 125 μm polyimide substrates. The residual stress in the coating process is estimated based on the onset strains of fragmentation. For films with thicknesses of 100 nm, 200 nm, and 400 nm, the estimated residual stresses are −1.204 GPa, −0.889 GPa, and −0.305 GPa respectively. This method shows more convenient than some traditional methods (including the use of X-ray diffraction technique or other methods of determining curvature). The tensile fragmentation tests would provide data to verify the accuracy of the estimation during crack accumulation; a good agreement is found between the experimental results and those predicted using the estimated residual stresses.

Layered structure enhances the hardness of Cu-48at.%Cr film prepared by co-sputtering deposition technique

The Cu-48at.%Cr film was prepared by magnetron co-sputtering deposition technique with working pressure from 0.2 Pa to 1.5 Pa. The microstructure and nanoindentation hardness were investigated. When the working pressure decreased to 0.2 Pa, the consecutive layered structure formed. The formation of layered structure was attributed to the diffusion barrier ability of Cr element and the uphill diffusion of Cu atoms. While at higher working pressure, the sputtering particles energy near the substrate was not enough to promote the Cu diffusion. Therefore, the layered structure became indistinct as the working pressure increased. Owing to the interface strengthen, this layered structure made the nanoindentation hardness increase markedly from 4.2 GPa to 9.3 GPa as the working pressure decreased from 1.5 Pa to 0.2 Pa. This study could provide a good basis for preparing the film with specific microstructure in Cu–Cr system, even in other immiscible systems.

An In Situ and Real-Time Plasmonic Approach of Seed/Adhesion Layers: Chromium Buffer Effect at the Zinc/Alumina Interface

The effect of additives on metal/oxide interfaces is explored in situ and in real time on evaporated films by a combination of surface science techniques, among which a very flexible optical method shows a unique ability to scrutinize the growth and wetting properties of supported clusters that involve several elements. The study focuses on Cr at the Zn/α-Al2O3(0001) interface at 300 K. A particular interest of the present interface is that Zn does not stick at all on bare alumina. The sticking and morphology of both Cr and Zn films during their growth are analyzed from sub-monolayer to multilayer thicknesses. After an initial oxidation reaction with residual OH groups, shown to be detrimental to Zn adhesion, Cr growth proceeds through the formation of high aspect ratio particles that percolate around an average thickness of 10 Å. With regard to Zn growth on a Cr deposit, two very distinct stages can be distinguished. In the sub-monolayer thickness range, Cr forms a seed layer that drastically increases the Zn sticking coefficient from 0 to nearly 1 due to a diffusion length of physisorbed Zn adatoms before desorption larger than Cr island separation; Zn clusters are anchored on the Cr seeds that they encapsulate, but their wetting behavior is dictated by the interaction with alumina. In a second stage, as soon as the Cr film percolates, it forms an adhesion layer on which Zn grows in a nearly two-dimensional mode. In all cases, Cr films are stable upon annealing. On Cr-covered alumina, the Zn desorption energy is enhanced as compared to bare surfaces, which, in line with atomistic simulations, is assigned to the formation of more favorable Cr–Al2O3 and Cr–Zn than Zn–Al2O3 bonds. Generally speaking, the ability demonstrated herein of small amounts of additives to dramatically increase the adhesion of films is of great practical interest. It shows that noncontinuous and partially oxidized films of additives, closer to realistic cases of application, can strongly enhance the sticking of films. Also, anchoring a functional film by discrete predeposited seeds can keep its properties intact.

Influence of Metal Substitution and Ion Energy on Microstructure Evolution of High-Entropy Nitride (TiZrTaMe)N1–x (Me = Hf, Nb, Mo, or Cr) Films

Multicomponent or high-entropy ceramics show unique combinations of mechanical, electrical, and chemical properties of importance in coating applications. However, generalizing controllable thin-film processes for these complex materials remains a challenge. Here, understoichiometric (TiZrTaMe)N1–x (Me = Hf, Nb, Mo, or Cr, 0.12 ≤ x ≤ 0.30) films were deposited on Si(100) substrates at 400 °C by reactive magnetron sputtering using single elemental targets. The influence of ion energy during film growth was investigated by varying the negative substrate bias voltage from ∼10 V (floating potential) to 130 V. The nitrogen content for the samples determined by elastic recoil detection analysis varied from 34.9 to 43.8 at. % (0.12 ≤ x ≤ 0.30), and the metal components were near-equimolar and not affected by the bias voltage. On increasing the substrate bias, the phase structures of (TiZrTaMe)N1–x (Me = Hf, Nb, or Mo) films evolved from a polycrystalline fcc phase to a (002) preferred orientation along with a change in surface morphology from faceted triangular features to a dense and smooth structure with nodular mounds. All the four series of (TiZrTaMe)N1–x (Me = Hf, Nb, Mo, or Cr) films exhibited increasing intrinsic stress with increasing negative bias. The maximum compressive stress reached ∼3.1 GPa in Hf- and Cr-containing films deposited at −130 V. The hardness reached a maximum value of 28.0 ± 1.0 GPa at a negative bias ≥100 V for all the four series of films. The effect of bias on the mechanical properties of (TiNbZrMe)N1–x films can thus guide the design of protective high-entropy nitride films.

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.

High vacuum arc ion plating Cr films: Self-ion bombarding effect and oxidation behavior

High vacuum arc ion plating gas-free Cr films under self-ion bombarding and their oxidation behaviours were investigated. Ultrafine column-grained Cr films were obtained, which showed stronger crystallographic orientation of (200) as the bombarding energy increased from 50 eV to 250 eV. Oxidation of the Cr films at 900 °C revealed that the thickness of the chromia scale decreased with enhanced bombarding energy. The thickness decreases over 56 % due to the elimination of gas inclusion but only around 18 % further by introducing orientation in the film, demonstrating the key role of high vacuum for depositing advanced Cr films.

Ag@MIL-101(Cr) Film Substrate with High SERS Enhancement Effect and Uniformity

Surface-enhanced Raman scattering (SERS), owing to its high sensitivity and rapid response, has been widely used in various fields. However, it is still a challenge to prepare SERS substrates with ...

Changes in the chemical state of metallic Cr during deposition on a polyimide substrate: Full soft XPS and ToF-SIMS depth profiles

We demonstrate the effectiveness of the combination of depth profile analyses based on soft X-ray photoelectron spectroscopy (XPS) with Ar+ sputtering and time-of-flight secondary ion mass spectrometry (ToF–SIMS) with Cs+ sputtering, to determine the changes in the chemical states of Cr nanofilms during deposition on a polyimide (PI) substrate, with nanoscale-depth resolution. The XPS and ToF-SIMS depth profiles obtained show evidence of preferential oxygen sputtering during Ar+ and Cs+ bombardment. Therefore, detailed analyses of the depth profiles and spectra were performed with consideration of the results of cross-sectional electron energy loss spectroscopy and non-destructive hard XPS for the same sample. As a result, the depth profiles for Cr, Cr2O, Cr2O3, Cr(OH)3, and CrO3 in the Cr film were successfully differentiated with nanoscale resolution. At the deeper area, the ratio of Cr2O3, Cr(OH)3, and CrO3 decreases, while that of Cr metal and Cr2O increases, which was caused by Ar+ and Cs+ sputtering. The presence of the Cr2O phase in the Cr film was revealed, regardless of the preferential sputtering. These results are very useful for optimization of the Cr/PI bilayer fabrication process, which is one of the most important components in flexible electronics.

High-efficient photoacoustic generation with an ultrathin metallic multilayer broadband absorber.

Metal nanomaterials have been widely used to generate photoacoustic (PA) signals because of their high optical absorption characteristics. However, the PA conversion efficiency of metal nanomaterials is limited by the single-wavelength absorption at the resonant peak. To mitigate this issue, a three-layer ultrathin film containing a thin PDMS layer sandwiched between two ultrathin chromium films is proposed. This kind of film structure can attain high optical absorbance (>80%) through the visible light range (450-850 nm). The optical absorption characteristics can be easily modulated by varying the thickness of the PDMS layer. Under the same excitation condition, the PA signal generated by this film structure is twice that of an only Cr film and three times that of an only Au film. This film structure is easily fabricated and can operate with lasers having different central wavelengths or even white light sources, leading to its applications in many fields, including photoacoustic communications and audio transducers.

Odd spin frustration in Cr(001) films thinner than three nanometers revealed by spin-polarized scanning tunneling microscopy

We have studied the surface structure and morphology of epitaxial Cr films on Au(001) substrate with Cr thickness (${d}_{\mathrm{Cr}}$) below 3 nm. We have characterized the films prepared under various growth conditions by using scanning tunneling microscopy and spectroscopy (STM/STS), low-energy electron diffraction, and Auger electron spectroscopy. The good growth conditions of the Cr(001) films, which have atomically flat terraces without surface segregation of Au and with distinct surface states, are obtained by the following two methods. (I) ${d}_{\mathrm{Cr}}=3$ nm film realized by two-step growth, i.e., first 1.5 nm of Cr deposited at room temperature ($\ensuremath{\sim}290$ K) and an additional 1.5 nm Cr deposition at 570 K and (II) ${d}_{\mathrm{Cr}}=1.5$ nm film by room temperature growth and subsequently post-annealing at 470 K. The magnetic imaging of (I) ${d}_{\mathrm{Cr}}=3$ nm Cr(001) film was performed by means of spin-polarized STM/STS. The observed magnetic image indicates that the topological antiferromagnetic (AF) order appears in a series of adjacent terraces and two types of spin frustration caused by screw dislocations lead to modifications of the topological AF order. One type of spin frustration is accompanied by narrow domain walls between two screw dislocations. The other type is a complex spin frustration caused by a cluster of an odd number of screw dislocations. The difference of the two types of spin frustration is explained through a micromagnetic simulation. We have also identified a large spin-frustrated area, consisting of a cluster of multiple number of screw dislocations.

Application of the MTSVD method in the experimental x-ray spectrum unfolding in the diagnostic energy range using CR film and Plexiglas wedge

Obtaining the quality of the beam is considered one of the most important quality control issues for X-ray tubes. X-ray spectrum is a very important aspect of quality control of medical imaging devices. However it may not be measured directly due to the very high photon flux, increasing the problems of the dead time and the Pile-up effect. The purpose of this study is to use a simple, and indirect method to unfold the primary X-ray spectrum. In this investigation, a system composing of a PMMA wedge, and a CR film was designed and constructed. The absorbed dose by the film is related to the primary spectrum by response matrix which was obtained using the MCNP Monte Carlo code exactly. The response matrix was used to unfold the spectrum, from the reading of the CR film. However, as the response matrix is ill-conditioned, it is not possible to solve the equation system in the normal way. Therefore the MTSVD regularization method in MATLAB software was used for unfolding the primary spectrum. The shape of the spectrum and the beam quality was compared with the IPEM 78 report catalog. The results indicate that the X-ray spectrum may be unfolded using this indirect method with sufficient accuracy.

Characteristics by deposition and heat treatment of Cr and Al thin film on stainless steel

Characteristics by deposition and heat treatment of Cr and Al thin film on stainless steel