Chromium Thin Films Research Articles

A thin chromium film formation monitoring method: Monitoring of the early stages

A method to monitor thin film deposition on insulating and semiconductive substrates based on the surface conductivity measurements is proposed. This method differs from previous thin film conductivity measurement methods by the absence of an external power source. Instead, it employs natural charges carried by ions and electrons that are present in a vapor that is deposited. The ability to monitor thin film conductivity, starting with early nucleation stages up to the formation of the integrally conductive film is shown by a comparison of in-situ recorded voltage changes and ex-situ by X-Ray photoelectron spectroscopy and atomic force microscopy analysis of the stepwise covered samples. Repeatability of the experimental data was within a ± 25% interval at the experimental parameter region where an integrally conductive film starts to form.

Simple MEMS-based Incandescent Microlamps

In this work, the fabrication and operation of micro-incandescent lamps is presented. Two types of microlamps are fabricated using micro-cantilevers and micro-bridges of silicon oxynitride (SiOxNy) deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) at low temperatures (320{degree sign}C) with embedded chromium thin film resistors. In both cases, the chromium resistor is sandwiched between layers of SiOxNy that isolates it from the atmosphere, while electric current heats the resistor to incandescent temperatures. Front-side bulk micromachining of the silicon substrate in KOH solution is used to fabricate the cantilevers and bridges that thermally isolate the resistors from the substrate, thus reducing the heat transfer and current required to light the lamp. Finally, arrays of bridges are used to fabricate arrays of microlamps that can be polarized as a micro-display.

Nanoscale thermoelastic probing of megahertz thermal diffusion

The authors demonstrate a method to probe thermal diffusion at megahertz frequencies with nanometer lateral resolution in a thin opaque film on a transparent substrate. They map photothermally induced megahertz surface vibrations in an atomic force microscope using tightly focused optical illumination from the substrate side. By comparison with a theoretical model of the surface displacement field, the authors derive the thermal diffusivity of a thin chromium film on a silica substrate.

Thermal loading of laser induced plasma shockwaves on thin films in nanoparticle removal

Damage concerns, such as substrate/film material alterations, damage, and delamination of thin films, have become a central problem in sub-100 nm particle removal applications. In the laser induced plasma (LIP) removal technique both LIP shockwave and radiation heating are potential sources of thermomechanical damage. The specific objective of current study is to conduct a computational investigation of the LIP shockwave effect on the thermoelastic response of a thin chromium (Cr) film deposited on a quartz substrate and to identify the conditions leading to the onset of plastic film deformations. The experimentally characterized shockwave pressure and temperature (approximated from gas dynamic relations) were prescribed as boundary conditions in the computational analysis. From the shockwave arrival times for different travel distances, the shockwave radius as well as the velocity were obtained as a function of the shockwave propagation time. Radial (and circumferential) stresses, caused by thermal expansion of the Cr film, were most dominant and, hence, of damage concern. It is determined that the resultant temperature rise utilizing a 1064 nm Nd:yttrium-aluminum-garnet (YAG) laser (450 mJ) due to the film-shockwave interactions was not sufficiently high to initiate film and/or substrate damage. No material alteration/damage of the Cr film is predicted due to the temperature and pressure of LIP shockwaves at the firing distance of 2 mm, with a high strain rate gain factor of two (minimum), though damage was observed experimentally for 1064 nm Nd:YAG laser at the pulse energy of 370 mJ. Reported results indicate that the leading cause of observed thin film damage during nanoparticle removal is almost certainly radiation heating from the LIP core.

Fabrication and characterization of sub-45 nm multiple linewidth samples

A method of fabricating nanometre scale multiple linewidth standards based on multilayer thin film deposition techniques is presented. Three layers of chromium (Cr) thin films and three layers of silicon nitride (Si3N4) thin films were alternately deposited on a silicon substrate in the radio frequency (RF) magnetron sputtering system and the low-temperature plasma enhanced chemical vapour deposition (PECVD) system. The deposition thicknesses of the Cr thin films are equal to the desired linewidths. The silicon substrate was then cut into small pieces, and the cross-section of each piece was metallographically polished. Perpendicular to the cross-section Si3N4 was etched with reactive ion etching (RIE) and nanometre scale multiple linewidth samples with nominal linewidths of 20 nm, 25 nm and 35 nm were fabricated. The fabricated samples were characterized with a scanning electron microscope (SEM). The line edge roughness (LER) and the linewidth roughness (LWR) of the lines of the fabricated samples were evaluated by an offline image analysis algorithm. The lines of the fabricated samples have uniform attributes and good linearity over hundreds of microns. The results show that the presented method is a promising method for the fabrication of nanometre scale multiple linewidth standards.

Pulsed laser deposition of metal films and nanoparticles in vacuum using subnanosecond laser pulses

A study of silver, chromium, stainless-steel, and indium thin films prepared by subnanosecond laser deposition in vacuum is reported. We compare the laser ablation in vacuum at the weak- and tight-focusing conditions of a Ti:sapphire laser beam and analyze the nanoparticles synthesized in the latter case using absorption spectroscopy, x-ray fluorescence, atomic force microscopy, and scanning electron microscopy. Our results show that the nanoparticle formation can be accomplished using long laser pulses under tight-focusing conditions.

Glancing angle deposition to control microstructure and roughness of chromium thin films

Glancing angle deposition (GLAD) was used to sculpt chromium thin films sputter deposited by dc magnetron sputtering into the desired zigzag microstructure. The flux angle of incident species α was systematically varied from 0 to 50° and periodically changed from α to − α. The total film thickness was kept constant at 1 μm and the number of periods ranged from 0.5 to 10. In order to improve the film adhesion, a substrate heating (350 °C) was added during the sputtering. Our results show that the zigzag microstructure of chromium thin films influences the microstructure and the surface properties of the coatings. The relationships between the Ra roughness, the flux angle and the number of periods were successfully demonstrated. This allows the deposition of films with controlled roughness. It was shown that the regularity of the surface morphology is improved for the flux angles α > 20°. Microstructure of the films was investigated by SEM, AFM and X-ray diffraction and the mechanical properties were determined by nanoindentation.

Ripple formation in the chromium thin film during laser ablation

The beam of a nanosecond pulse laser tightly focused to a line was applied for the back-side ablation of the chromium thin film on a glass substrate. The stripe ablated with a single laser pulse had sharp edges on both sides and ridges of the melted metal around it. The partially overlapping pulses formed a wide cleaned area with a complicated structure made of the metal remaining from the ridges. Regular structures, ripples, were developed when laser fluence was slightly above the single-pulse removal threshold and the shift between pulses was less than half width of the line ablated with a single laser pulse. The ripples were located periodically (∼4 μm) and were orientated perpendicularly to the long axis of the beam spot. Their orientation did not depend on the laser beam polarization. Different models of the ripple formation in the thin metal film were considered, and instability of the moving vapor–liquid–solid contact line during evaporation of thin liquid films appears to be the most probable process responsible for the observed phenomena. Formation of regular gratings with the unlimited line length was experimentally implemented by using the above-mentioned technique.

Propagation of high amplitude strain pulses in sapphire

The propagation of acoustic pulses in sapphire has been investigated using bolometric time-of-flight techniques. Excitation of a thin chromium film by an amplified Ti:sapphire laser pulse resulted in the generation of high-amplitude acoustic pulses. The propagation time of these across the 1-cm-thick sapphire crystal was measured using a superconducting aluminum bolometer. By increasing the excitation power, the growth of an intense fast pulse on the leading edge of the longitudinal heat pulse was observed. This was detected as an additional, separate, signal component, with a propagation time shorter than the heat pulse. This pulse is attributed to the formation and propagation of a high-amplitude coherent strain pulse. The bolometric detection technique allows high resolution images of the acoustic flux over macroscopic propagation distances, and measurements show the strain pulse propagates as a strongly collimated beam. These results demonstrate the applicability of bolometric detection techniques, in addition to Brillouin scattering and pump-probe measurements, to study the propagation of ultrashort strain pulses in crystals.

Plasmonic effects in near-field optical transmission enhancement through a single bowtie-shaped aperture

In this paper, the enhanced optical transmission through a special type of aperture of a bowtie shape is investigated through near-field imaging and finite-difference numerical analysis. Under linear polarizations in two orthogonal directions, the optical near fields of the bowtie aperture and comparable square and rectangular apertures made in gold and chromium thin films are measured and compared. The bowtie aperture is able to provide a nanometer-sized optical spot when the incident light is polarized across the bowtie gap and delivers a considerable amount of light. Localized surface plasmons are clearly observed in the near-field images for both bowtie and rectangular apertures in gold, but invisible in chromium. Finite-difference time-domain calculations reveal that, depending on the polarization of the incident light, the unique optical properties of the bowtie aperture are a result of either the optical waveguide and the coupled surface plasmon polariton modes existing in the bowtie gap or the coupling between the two open arms of the bowtie aperture.

X-ray reflectometry analyses of chromium thin films

A series of thin (less than 100 nm) chromium films on Si and SiO2/Si substrates has been examined using X-ray reflectometry (XRR) and cross-section scanning electron microscopy. Comparisons of the measured film thicknesses from the two disparate methods were in good agreement. Because of this accord, it was possible to use these chromium thin films as model systems in order to probe the impact of both random and systematic errors on quantitative XRR measurements. In general, the errors associated with common XRR operations such as sample placement, system alignment, and choice of an instrumental broadening characteristic were much smaller than the statistical error obtained from a genetic algorithm fitting process to the experimental XRR curve.

Modeling of Young's modulus, hardness and stiffness of chromium zigzag multilayers sputter deposited

Sculptured thin films exhibiting a zigzag microstructure behave as a field of “microsprings”. Two theoretical approaches are presented to predict hardness, Young's modulus and stiffness of these coatings taking into account the film's geometry (zigzag) and the bulk material properties. Both models are based on the deformation of a single zigzag period caused by a normal force. In the first model (simple model), the column diameter is neglected during the deformation (no difference between the curvature radius of internal and external fibre). These differences are taken into account in the second model (enhanced model). The column section is not perfectly circular and so, both models are developed for circular and square sections. Models are tested on chromium zigzag multilayers sputter deposited with a constant thickness close to 1 μm and with half-period thickness Λ/2 ranging from 50 to 1000 nm. Geometrical parameters are determined from Scanning Electron Microscopy observations. These parameters are used to calculate the theoretical values of Young's modulus, hardness, and stiffness. Experimental values of Young's modulus (ranging from 86 GPa for single layers up to 250 GPa for the film composed of 10 periods 100 nm thick) and hardness (ranging from 2 GPa for single layers up to 14 GPa for the film composed of 10 periods 100 nm thick) of chromium thin films are measured by nanoindentation. A quite good agreement is obtained between experimental and computed values. Such comparison proves that the proposed models are valuable to predict some mechanical properties of multilayers with a zigzag microstructure.

Microstructural and corrosivity changes induced by nitrogen ion implantation on chromium films

The chromium thin films were prepared using ion beam deposition on stainless steel 304. The chromium films were implanted by nitrogen ions after deposition at doses in the range of 4.5 × 10 17 to 2.7 × 10 18 N +/cm 2 and energy of 30 keV. The formation of nitride phases and corrosion behavior after nitrogen implantation were characterized by XRD and corrosion test, respectively. The results show that corrosion resistance rise, reach to a maximum at dose of 1.8 × 10 18, and then fall down at higher doses. In addition, the effect of corrosion tests was analyzed using scanning electron microscopy (SEM).

Investigations on the influence of process parameters on the structural evolution of ion beam sputter deposited chromium thin films

Chromium thin films are technologically important as underlayers for the deposition of cobalt-based magnetic films because of their good lattice match and adhesion. The structural orientation and morphology of the chromium under layers control the magnetic properties of the cobalt-based films deposited on them. Hence, optimization of the structure and properties of chromium under layers is essential for realizing magnetic thin films with desired properties. In this paper, we report the structural variation observed in chromium thin films deposited on silicon(1 0 0) substrates deposited using Ion Beam Sputter Deposition (IBSD) technique. The influence of process parameters, such as ion beam current density, substrate temperature and the angle of incidence of the condensing species, on the structural transformation from (1 1 0) orientation to (2 0 0) orientation has been presented. The structural variation and morphological variations observed have been discussed based on the growth models and the energetics involved in the process.

Chromium enrichment of AISI 304 stainless steel surface after nitrogen ion recoil bombardment of chromium film

When performing nitriding of stainless steels, there is a decrease or even complete depletion of chromium in the nitrogen rich region just beneath the surface, inhibiting the formation of passivated Cr oxide layer, beneficial to withstand corrosive attacks and Cr/Fe nitrides, responsible for hardness enhancement. To overcome this problem, a hybrid technique was used, consisting of depositing a thin chromium film on steel surface and then bombarding it with nitrogen ions. By a complex recoil process, chromium atoms are implanted into the steel matrix. Plasma immersion ion implantation (PIII) was used in this bombardment. The new Cr-rich layer allows the formation of Cr oxides and nitrides. Treated surfaces were characterized by Auger electron spectroscopy (AES) and conversion electron Mössbauer spectroscopy (CEMS), showing formation of a new Cr-rich layer.

Sputter-deposited ultra-low catalyst loadings for PEM fuel cells

Sputter-deposited Pt thin film layers are employed as catalyst material for polymer electrolyte membrane (PEM) fuel cells. An ultra-low catalyst loading of 5 μ g cm −2 platinum results in a maximum power density of 124–132 mW cm −2 depending on the gas diffusion layer substrate when feeding H 2/O 2 at ambient temperature and pressure. By using the sputter deposition process less catalyst is needed for comparable cell performance to contemporary standard electrodes loaded with 1 mg cm −2 Pt that have been used for reference. Catalyst layers sputter-deposited onto different porous electrodes are investigated with respect to their effect on characteristic fuel cell performance which improves by 8% after adding chromium or palladium thin film layers.

Nanoindentation of chromium zigzag thin films sputter deposited

Chromium thin films exhibiting a columnar microstructure were prepared by dc magnetron sputtering. The glancing angle deposition technique (GLAD) combined with the periodical changing of the incidence flux angle from α to −α was used to sculpt chromium thin films following a zigzag microstructure. The zigzag microstructure was systematically modified varying the flux angle α from 0 to 50° and the half-period thickness λ from 50 to 1000 nm. The changes in the microstructure were correlated with the evolution of the film's hardness and reduced Young's modulus obtained by nanoindentation. The drop of the film's hardness from H=10 to 1.4 GPa and the reduced Young's modulus from Er=245 to 91 GPa was noted with increasing flux angle α and half-period thickness λ. In agreement with the Hall–Petch effect, the diminution of the half-period thickness of chromium zigzag thin films led to an improvement of the nanohardness of chromium thin films deposited at the normal incidence up to 160%. The surface roughness and film's porosity depend strongly on the microstructure of the zigzag thin films. The influence of these parameters on the indentation of the zigzag thin films was also discussed. It was shown, that the Young's modulus depends on the films porosity. Correcting the films porosity using the mixing rule, the contribution of the flux angle and the number of layers could be easily demonstrated. For the small half-period thicknesses, values of Young's modulus of the coatings tend to be that of the bulk chromium.

Chromium multilayered thin films with orientated microstructure

Chromium thin films exhibiting a columnar microstructure have been prepared by dc magnetron sputtering. The glancing angle deposition (GLAD) technique and the substrate motion have been implemented to sculpt this typical columnar microstructure into desired zigzag shapes. By changing the direction of the incident flux of the species impinging on the substrate surface, the deposited films led to columns that are tilted with respect to the substrate normal. A systematic and periodic variation of the angle of incidence α from -50 to 50° allowed to achieve chromium multilayered thin films with a controlled zigzag microstructure. The growth mechanisms and the morphology of such films have been investigated by scanning electron microscopy. The effect of the angle of incidence and the half-period (one layer thickness) λ(50 < X < 1000 nm) on porosity, film microstructure, deposition rate, and surface properties have mainly been studied.

Light transmission assisted by Brewster-Zennek modes in chromium films carrying a subwavelength hole array

This work confirms that not only surface plasmons but many other kinds of electromagnetic eigenmodes should be considered in explaining the values of the transmittivity through a slab bearing a two-dimensional periodic corrugation. Specifically, the role of Brewster-Zennek modes appearing in metallic films exhibiting regions of weak positive dielectric constant. It is proposed that these modes play a significant role in the light transmission in a thin chromium film perforated with normal cylindrical holes, for appropriate lattice parameters.

Fabrication and Composition Control of NiTi Shape Memory Thin Films for Microactuators

AbstractMicroactuators fabricated with NiTi thin films take advantage of the shape memory effect's large energy density (∼5-10 joules/cm3) and high strain recovery (∼8%). Microelectromechanical Systems (MEMS) designed with these actuators can serve as biosensors, micro-fluidic pumps or optical switches. However, the fundamental mechanical properties of these shape memory NiTi films have not been fully characterized with micro-scale test structures. Equiatomic NiTi thin films were deposited by co-sputtering NiTi and Ti targets with the intension of fabricating such test structures. Dual cathodes allowed direct control of the film composition by adjusting the Ti cathode power. Energy Dispersive Spectroscopy (EDS) quantified the film composition relative to pure standards. A thin (∼50 nm) chromium film on a pure silicon substrate created excellent film adhesion. Oxidized Si wafers did not bond with the Cr and NiTi films. This deposition method enabled control of film composition and the necessary adhesion.