Metal Alloy Films Research Articles

Stress evolution in sputtered vanadium-tungsten alloys

While metal alloy films are used in many applications, there remains a rather limited series of studies of their stress evolution during growth as compared to elemental films. Here, we provide measurements of the sputter deposition stress evolution of VxW1-x alloys, which is a system that forms a body centered cubic solid solution across all its compositions. By increasing either the tungsten content or the growth rate, we note an increasing trend towards a compressive stress state. Since the crystallite size is approximately the same for all alloys and growth rates, we conclude that the increasing tungsten content enhances the effect of energetic particle deposition (atomic peening) on the stress facilitating this change. The results suggest that stress can be understood in terms of the same physical processes that have been proposed previously to explain stress in elemental films. These mechanisms, described in the text include effects of non-energetic growth kinetics, microstructural evolution and energetic particle bombardment.

Controlled Growth of Semiconductor Alloy/Ferromagnetic Insulator (GeBi/Bi:Thulium Iron Garnet (TmIG)) Spin Heterojunction and Development of Quantum Logic Device

Replacing heavy metal and heavy metal alloy films with a semiconductor thin film, to form a semiconductor/ferromagnetic insulator spin heterojunction has always been an international research hotspot. This article reports on a Ge1–xBix/Bi:thulium iron garnet (TmIG) spin heterojunction. It was found that Ge1–xBix (x = 0.06–0.22) semiconductor alloy films and Bi3+-doped control Tm3–yBiyFe4.3Ga0.7O12 (Bi:TmIG, y = 0.2–1.0) films can enhance the spin–orbit coupling (SOC) strength, improving the abnormal spin Hall effect (ASHE) and the spin Hall magnetoresistance (RH) switch characteristics. As x varies from 0.06 to 0.22, it is noticed that the spin mixing conductance considerably increases. Because Bi ions have the ability to control the SOC strength, the 5–10 nm GeBi semiconductor thin film with the Bi-ion-doped Bi:TmIG film can realize a spin magnetic moment reversal and then drive the heterojunction magnetic moment switching effect, and the spin currents injected across this interface lead to deterministic magnetization reversal at an ultralow current density of 1.82 × 106 mA/cm2. This has significant practical applications in the design and implementation of spin quantum logic devices based on semiconductor processes, laying a material foundation for the development of quantum logic devices.

Electrochemical fabrication of mesoporous metal-alloy films

Electrochemical fabrication integrating templating strategies have paved the way for creating mesoporous metal alloy films with distinctive pores and functionalities for electrocatalysis, fuel cells, and sensor (bio) development.

Environmentally robust Ag–Cu based low-e coatings

Low emissivity (low-e) coatings minimise heat transmittance through the coating and emission of infrared light from hot surfaces. They are used in space applications to reduce overheating of the spacecraft, in architectural applications and automotive windows to block heat from entering a building or vehicle. Typically, in window applications the low-e coatings consist of a multilayer coating, which combine metallic films (approx. 10 nm); responsible for the heat reflection and dielectric films (approx. 40 nm); used to protect the metallic films and enhance their visible transmittance. Commercially available low-e coatings can contain more than 15 layers, with Ag typically used as the metallic layer. However, Ag is soft and tends to tarnish, making Ag-based low-e coatings vulnerable to degradation when exposed to environmental conditions. In this study we demonstrated environmentally durable low-e coatings based on Ag–Cu alloyed thin films. The thin film alloys showed higher level of scratch resistance than conventional pure Ag coatings with high level of transmittance of visible light. The multilayer coating consisting of a dielectric film, metal alloy film and a protective coating was demonstrated as robust, long-life, first surface low-e coating. • Ag–Cu thin films have been co-evaporated onto glass substrates. • 30 at.% Cu in Ag film exhibits the most neutral colour and good adhesion to TiO 2 . • Ag and Ag 70 Cu 30 based multilayer low-e coating have been grown on polycarbonate. • Cu in Ag film elevates the durability and barely compromising optical performance.

Laser-based, direct formation of thin copper–nickel alloy films with low thermal coefficient of resistivity

The growing market of printed electronics requires the development of new materials and processing technologies that enable the design of smart wearables, integrated sensors, and next-generation electronics. Against the backdrop of increasing material scarcity, these approaches must be resource-conserving and, at the same time, competitive with conventional technologies. As an alternative to nanoparticle-based inks currently used in printed electronics, another technology has been emerging in the last years that utilizes metal organic decomposition (MOD) inks, which are easy to fabricate and have a long shelf life. In this study, a method is presented that allows the direct formation of thin copper-nickel alloy films from a MOD ink. These alloys are preferably used for sensors like strain gauges as they exhibit a low thermal coefficient of resistivity (TCR). 250 nm thin alloy films are coated on glass substrates and thermally functionalized. In a conventional hot plate heat treatment under a nitrogen atmosphere, 10.2% bulk conductivity for a Cu55Ni45 alloy with a TCR of 8.3 × 10−5 K−1 is reached. X-ray diffraction analysis indicates the formation of a mixed crystal composed of nickel and copper atoms. A laser-based functionalization process is developed that allows the processing of Cu55Ni45 alloy films under ambient conditions without the formation of copper or nickel oxides. Laser-functionalized films exhibit 5.3% of the conductivity of bulk material. This study shows that metal alloy films can be fabricated directly from amine-based MOD inks.

Improving the electrical and structural stability of highly piezoresistive nickel–carbon sensor thin films

Abstract. The family of sputter deposited granular metal-based carbon-containing sensor films is known for their high sensitivity transforming force-dependent strain into electrical resistance change. Among them nickel–carbon thin films possess a gauge factor of up to 30, compared to only 2 for traditional sensor films of metal alloys. This high sensitivity is based on disordered interparticle tunneling through barriers of graphite-like carbon walls between metal–carbon particles of columnar shape. Force and pressure sensors would benefit a lot from the elevated piezoresistivity. A disadvantage, however, is a disturbing temporal creep and drift of the resistance under load and temperature. This contribution shows how to stabilize such sensor films. A significant stabilization is achieved by partially replacing nickel with chromium, albeit at the expense of sensitivity. The more chromium used in these NixCr1−x-C layers, the higher the optimum annealing temperature can be selected and the better the electrical stabilization. A good compromise while maintaining sensitivities well above the standard of 2 is identified for films with x=0.5 to 0.9, stabilized by optimized temperature treatments. The stabilizing effect of chromium is revealed by transmission electron microscopy with elemental analysis. The post-annealing drives segregation processes in the layer material. While the interior of the layer is depleted of chromium and carbon, boundary layers are formed. Chromium is enriched near the surface boundary, oxidized in air and forms chromium-rich oxide sub-layers, which are chemically very stable and protect against further reactions and corrosion. As a result, creep and drift errors are greatly reduced, so that the optimized sensor coatings are now suitable for widespread use.

Embedded Oxidized Ag-Pd-Cu Ultrathin Metal Alloy Film Prepared at Low Temperature with Excellent Electronic, Optical, and Mechanical Properties.

Most transparent conducting materials are based on Sn:In2O3 (ITO). When applied onto flexible substrates, ITO can be prepared in an oxide–metal–oxide (OMO) configuration, typically ITO/Ag/ITO, where the ductility of the embedded metal layer is intended to reduce the mechanical brittleness and improve the electrical conductivity of the OMO multilayer. Hitherto, the lower limit of the thickness of the Ag layer has been limited by the percolation threshold, which limits the Ag layer to be thicker than ∼10 nm to avoid agglomeration and to ensure conductivity and structural stability. Metal layers of thicknesses below 10 nm are, however, desirable for obtaining OMO coatings with better optical properties. It is known that agglomeration of the metal layer can, to some extent, be suppressed when substituting Ag by an Ag–Pd–Cu (APC) alloy. APC-based OMO films exhibit excellent optical and electrical properties, but still continuous APC films well below 10 nm thickness cannot be achieved. In this work we demonstrate that controlled oxidation of APC results in smooth, ultrathin APC:O continuous coatings (of thickness ∼5 nm) on ITO-coated PET substrates. Moderate oxidation yields superficial PdOx formation, which suppresses Ag agglomeration, while still maintaining excellent conductivity. On the other hand, extensive oxidation of APC leads to extensive Pd oxide nucleation deteriorating the conductivity of the film. The ITO/APC:O/ITO films exhibit low resistivity, attributed to a high Hall mobility associated with suppressed agglomeration, good stability in high humidity/temperature environments, superior transmittance in the visible and infrared region, and excellent mechanical bending properties, thus providing new opportunities for fabricating superior transparent conducting coatings on polymer substrates.

Noble metal alloy thin films by atomic layer deposition and rapid Joule heating

Metal alloys are usually fabricated by melting constituent metals together or sintering metal alloy particles made by high energy ball milling (mechanical alloying). All these methods only allow for bulk alloys to be formed. This manuscript details a new method of fabricating Rhodium–Iridium (Rh–Ir) metal alloy films using atomic layer deposition (ALD) and rapid Joule heating induced alloying that gives functional thin film alloys, enabling conformal thin films with high aspect ratios on 3D nanostructured substrate. In this work, ALD was used to deposit Rh thin film on an Al2O3 substrate, followed by an Ir overlayer on top of the Rh film. The multilayered structure was then alloyed/sintered using rapid Joule heating. We can precisely control the thickness of the resultant alloy films down to the atomic scale. The Rh–Ir alloy thin films were characterized using scanning and transmission electron microscopy (SEM/TEM) and energy dispersive spectroscopy (EDS) to study their microstructural characteristics which showed the morphology difference before and after rapid Joule heating and confirmed the interdiffusion between Rh and Ir during rapid Joule heating. The diffraction peak shift was observed by Grazing-incidence X-ray diffraction (GIXRD) indicating the formation of Rh–Ir thin film alloys after rapid Joule heating. X-ray photoelectron spectroscopy (XPS) was also carried out and implied the formation of Rh–Ir alloy. Molecular dynamics simulation experiments of Rh–Ir alloys using Large-Scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) were performed to elucidate the alloying mechanism during the rapid heating process, corroborating the experimental results.

(Invited) Precursors for the Thermal Atomic Layer Deposition of Cobalt Metal Films and Alloys Thereof

Herein, we will describe recent progress in our laboratory on the development of chemical precursors for the thermal atomic layer deposition (ALD) of cobalt metal, titanium metal, cobalt-titanium alloy, and other metal and metal alloy films. The nanoscale dimensions of current and future microelectronics devices now require alternative, ultrathin barrier materials for copper and other interconnect metals as well as new ultrathin liner materials. Sputtered cobalt-titanium alloys have been demonstrated to function as barrier materials and liners at dimensions as small as 1 nm. Hence, these materials may replace current barrier and liner materials such as TiN, TaN, and W metal. However, the narrow and deep nanoscale features require growth of cobalt-titanium alloy films by ALD to meet the strict conformality and thickness requirements. Moreover, thermal ALD is preferred over plasma-based processes, since recombination of atomic hydrogen on feature walls can afford poor conformal coverage. Thermal ALD processes for Co and Ti metal films are poorly developed, because the negative electrochemical potentials of the ions in precursors (Co2+ ↔ Co, E° = -0.280 V, Ti2+ ↔ Ti, E° = -1.628 V) require strong reducing co-reactants, which are not available. We will report new thermal ALD processes for cobalt metal films that employ various ligands, in combination with hydrazine-based co-reactants. These processes afford high purity cobalt metal films. We will also describe our efforts to develop new precursors for the thermal ALD of titanium metal films. Initial depositions of cobalt-titanium metal films will also be described.

Quantum Spin-Wave Materials, Interface Effects and Functional Devices for Information Applications

With the continuous miniaturization of electronic devices and the increasing speed of their operation, solving a series of technical issues caused by high power consumption has reached an unprecedented level of difficulty. Fortunately, magnons (the quanta of spin waves), which are the collective precession of spins in quantum magnetic materials, making it possible to replace the role of electrons in modern information applications. In the process of information transmission, nano-sized spin-wave devices do not transport any physical particles; therefore, the corresponding power consumption is extremely low. This review focuses on the emerging developments of the spin-wave materials, tunable effects, and functional devices applications. In the materials front, we summarize the magnetic properties and preparation characteristics of typical insulating single-crystalline garnet films or metallic alloy films, the development of new spin-wave material system is also introduced. Afterward, we introduce the emerging electric control of spin-wave effects originating from the interface transitions, physical or chemical, among these films including, voltage-controlled magnetic anisotropy, magneto-ionic transport, electric spin-torque, and magnon-torque. In the functional devices front, we summarize and elaborate on the low dispassion information processing devices and sensors that are realized based on spin waves.

The effect of stress on surface and interface segregation in thin alloy films on inert substrates

We employed a regular solution-type model to describe the equilibrium segregation of solute atoms on the external surface and at the film–substrate interface in the ultrathin single-crystalline films of binary metal alloys attached to an inert substrate. The finite size of the system, the interlayer interactions in the film and the heteroepitaxial strain in the film were taken into account. We demonstrated that the homogeneous heteroeptiaxial strain in the film affects the surface and interface segregation of solute atoms only in the case when the value of coherency strain parameter (describing the relative change of alloy lattice parameter upon addition of solutes) in the surface and interface layers is different from its value in the rest of the films. The developed model was applied to the Ni(Au) thin films deposited on sapphire substrate. The quantitative agreement between the model predictions and recent experimental data on interface segregation of Au could be achieved by assuming that the film is heteroepitaxially compressed.

Noble Metals Alloys Deposition from Non-Aqueous Solvents

Binary alloys of Pd and Pt were successfully deposited from 1-butyl-3-methyl imidazolium tetrafluoroborate (BMIM-BF4-Cl) ionic liquid and from a deep eutectic solvent (DES) based on a mixture of choline chloride and urea (ChCl-UA) at ambient atmosphere conditions. Ag, Ni and Sn were used as alloy components. Cyclic voltammetry experiments on glassy carbon electrode showed the reduction and dissolution of the alloys in the investigated solvents. Pulse plating and potentiostatic deposition techniques were used to deposit PdAg, PdNi, PdSn and PdPt alloys on cylindrical Cu substrate. The composition of the layers could be varied either by the concentration of the metals in the electrolyte solution or by changing the deposition mode (pulsed current or potentiostatic deposition). In order to determine the surface morphology and the thickness of the electrodeposited noble metal alloy films, a high resolution scanning electron microscope (SEM/EDX) and an energy dispersive X-ray fluorescence spectrometer (XRF) were used. The surface morphology of the layers was remarkable affected by the composition of the alloys. Scanning electron micrographs of the different electrodeposits showed that Pd alloys deposited by pulse current were generally nodular and relatively compact, whereas the films deposited by potentiostatic deposition were less dense and covered with dendrite-like and sharp-edged crystallites. The addition of a second metal (e.g. Ag+ or Sn2+) to a basic Pd or Pt electrolytes enhanced the overall metal deposition rate in comparison to solutions without alloying components and caused a remarkable increase of the layer thickness of the alloys. XRD measurements confirm that it was possible to deposit different binary metal alloys from both non-aqueous electrolytes by applying different deposition techniques. First adhesion tests and measurements of the microhardness of Pd-Ag deposits showed good properties of the produced alloy films. Also the hydrogen embrittlement of selected samples was proved by a hydrogen analyzer. These results confirmed that the quantity of hydrogen was negligible in the Pd alloy films produced from ionic liquids in comparison to films obtained from conventional aqueous solutions.

Accurate high-resolution depth profiling of magnetron sputtered transition metal alloy films containing light species: A multi-method approach

We present an assessment of a multi-method approach based on ion beam analysis to obtain high-resolution depth profiles of the total chemical composition of complex alloy systems. As a model system we employ an alloy based on several transition metals and containing light species. Samples have been investigated by a number of different ion-beam based techniques, i.e., Rutherford Backscattering Spectrometry, Particle-Induced X-ray Emission, Elastic Backscattering Spectrometry and Time-of-Flight/Energy Elastic Recoil Detection Analysis. Sets of spectra obtained from these different techniques were analyzed both independently and following an iterative and self-consistent approach yielding a more accurate depth profile of the sample, including both metallic heavy constituents (Cr, Fe and Ni) as well as the rather reactive light species (C, O) in the alloy. A quantitative comparison in terms of achievable precision and accuracy is made and the limitations of the single method approach are discussed for the different techniques. The multi-method approach is shown to yield significantly improved and accurate information on stoichiometry, depth distribution and thickness of the alloy with the improvements being decisive for a detailed correlation of composition to the material properties such as corrosion strength. The study also shows the increased relative importance of experimental statistics for the achievable accuracy in the multi-method approach.

Keynote Speakers

Keynote 1Prof. Ke Wang, East China University of Technology, Nanchang, ChinaSpeech Title:Magnetic and Perpendicular Exchange Coupling Properties of Rare-earth Transition Metal Alloy Films:In this talk, we will present some work we are carrying out on perpendicularly magnetized rare-earth transition metal alloy films (e.g., TbFeCo or Gd FeCo), which are currently attracting more attention for applications in low-power spintronic devices, ultrafast switching and logic memories. The perpendicular exchange coupling properties of TbFeCo/GdFeCo hard/soft bilayers are systematically investigated and some new results will be presented.Keynote 2Prof. Rangsu Liu, Hunan University, ChinaSpeech Title:Visualizing Study for Formation, Evolution and Hereditary Mechanisms of Nano-Clusters during Solidification Processes of Liquid Alloy under High Pressures:In recent years, we have deeply investigated the solidification processes of liquid metals of Al, Ag, Cu, Mg Na, Pb, Zn and alloys of Mg-Zn, Mg-Y, Al-Mg, Al-Zn, Ca-Zn by molecular dynamics simulation for the systems with different sizes of 100,000, 1,000,000 and 10.000,000 atoms, respectively. By using the visualizing method, the formation, evolution and hereditary mechanisms of nano-clusters, especially, under high pressures the large-scale microstructurel evolution, the crystallization and the hereditary mechanisms during their solidification processes have been clearly analyzed and described by the cluster type index method (CTIM) proposed by authors. Recently, many important results obtained. Highly interesting, for liquid alloy Mg-Y, it is found that all the simulation systems are directly solidified into crystal structures, and the crystallization temperature Tc is enhanced almost linearly with the increase of pressure. Highly interesting, there is an important phase transformation point from FCC to BCC structures between 15 ~ 20GPa during the solidification processes. And the structures formed at 20GPa possess the admirable microstructure configurations and excellent mechanical properties of materials.Keynote 3Prof. Chen Hsu, Lungwha University of Science and Technology, TaiwanSpeech Title:Small Molecular Sensing with Graphene, Zinc oxide, and Zinc Oxalate:Small molecules such as hydrogen and methane are able to be sensible using graphene, zinc oxide (ZnO), and zinc oxalate (ZnC2O4) via Van der Waals force. First of all, graphene is generally regarded as to have the function of adsorbing hydrogen molecules, but in really the adsorbing effect is not fit the demand. Graphene does not have the function of attracting hydrogen molecules. Graphene does not have the function of bullying hydrogen molecules. The main reason is that its plane is fully occupied by functional group. The graphene reduction exhibits many defect structures and residual oxidized groups, so even if many reduction methods are proposed, it is impossible to obtain a structure close to the perfect lattice of graphene. The basal plane and the edge of the reduced graphene oxide will contain a large number of oxygen functional groups; epoxy (C=O) and hydroxyl (hydroxyl, C)-OH is formed on the base surface, and carboxyl groups (COOH) and carbonyl groups (CO, CO) are distributed at the boundary.Keynote 4Prof. Chen-Kuei Chung, Department of Mechanical Engineering, National Cheng Kung University, TaiwanSpeech Title:Fabrication and Characteristics of Nanoporous Anodic Aluminum Oxide at High Temperature:The nanoporous anodic aluminum oxide (AAO) is one important nano-template used for synthesis of nanocomposite materials or as an etching mask for pattern transfer in a variety of applications. Conventional AAO templates were synthesized using two-step potentiostatic method of direct current anodization (DCA) at low temperature (0-10°C) to avoid dissolution effect. In this talk, an effective method of hybrid pulse anodization (HPA) with normal-positive and small-negative voltages has been proposed for AAO synthesis at relatively high temperature of 15-25°C for enhancing performance of AAO structure for both the cheap low-purity (99%) and costly high-purity (99.997%) aluminum foils. The pore size distribution and circularity of AAO by HPA is much better than DCA due to its effective cooling at relatively high temperature. The HPA not only merits manufacturing convenience and cost reduction but also promotes pore characteristics of AAO at severe conditions of cheap low-purity Al foils and high temperature. Moreover, the pore diameter can be enlarged by wet etching. A new finding of AAO pore diameter highly linked to the electrolyte anions contaminated AAO prepared by HPA at low-to-high concentrations (0.3~0.9 M) of oxalic acid at 25°C. The increase of widened diameter decreased with concentration due to AAO walls containing more anions high oxalic acid concentration to decrease etching rate during widening. Some application in humidity sensing and SERS will be presented.

Properties and Structure of Electroless Deposited Rhenium-Rich Re-Co Thin Films

Unique combination of rhenium (Re) mechanical and physical properties makes it very attractive material for variety of applications. Pure Re does not have a ductile-to-brittle transition temperature. Compared to other refractory metals, Re has the greatest tensile strength and excellent creep resistance over a wide range of temperatures (up to ~2000 °C). Moreover, Re does not form stable carbides. Thus, it is potentially attractive coating on different carbon materials. Re-based alloy coatings have been produced so far mainly by chemical vapor deposition (CVD) and electroplating. Electroless deposition is relatively simple and low cost method for thin metallic and metal alloy films preparation on conductive and nonconductive surfaces. The ability of electroless plating to coat the inside of holes and recesses without using external current source or vacuum technology equipment makes it an ideal coating technology for many uses. In this study, high Re content (more than 65 at.%) Re-Co coatings were prepared by electroless deposition on a functionalized SiO2 substrate and their morphology, composition, structure and properties were studied. The obtained films were characterized by HRSEM, AFM, XPS, XRD and EBSD methods. It was shown that as deposited films are amorphous with average microhardness of 620 HV that is higher than known in literature for binary Co-Re alloys. Crystalline hcp structure of Re-Co coating was detected only after annealing at 550 oC for 1 h in vacuum. Thin coatings (250-500 nm) have demonstrated good corrosion protection of copper in salt medium reducing corrosion current at list by one order of magnitude. The annealed deposits have shown improved mechanical and electrical properties. Such films exhibit ferromagnetism and could be applied in mobile magnetic components where soft-magnetic response combined with mechanical stability is required (MEMS devices).

Synthesizing amorphous Ni-P micro-/nano-composites with perfect roundness or embryo-like structures

The ability to manipulate the morphology and structure of core-shell materials on a micro/nano scale can further control their physical and chemical properties, leading to the wider applications. Herein, the conventional electroless deposition technique for metal alloy films on solid substrates was adapted to synthesize the Ni-P micro/nano-composites in solution under high temperature and high pressure through the hydrothermal method. The obtained amorphous Ni-P composites exhibit perfect roundness with the multilayer structure of concentric circle. By controlling the erosion condition in HNO3, the special embryo-like structure was obtained where a solid microsphere is encircled by a layer of hollow globular ultrathin film with the thickness smaller than 50 nm. A round hole opens on the surface of the embryo-like structure. The reaction or formation mechanism was tentatively discussed. The methods can be used to produce the special micro-/nano-structures of metal phosphide.

Nanotwinned metal MEMS films with unprecedented strength and stability.

Silicon-based microelectromechanical systems (MEMS) sensors have become ubiquitous in consumer-based products, but realization of an interconnected network of MEMS devices that allows components to be remotely monitored and controlled, a concept often described as the "Internet of Things," will require a suite of MEMS materials and properties that are not currently available. We report on the synthesis of metallic nickel-molybdenum-tungsten films with direct current sputter deposition, which results in fully dense crystallographically textured films that are filled with nanotwins. These films exhibit linear elastic mechanical behavior and tensile strengths exceeding 3 GPa, which is unprecedented for materials that are compatible with wafer-level device fabrication processes. The ultrahigh strength is attributed to a combination of solid solution strengthening and the presence of dense nanotwins. These films also have excellent thermal and mechanical stability, high density, and electrical properties that are attractive for next-generation metal MEMS applications.

Cu2ZnSnS4 films synthesized from co-electrodeposited Cu–Zn–Sn metallic alloy films

Cu2ZnSnS4 (CZTS) is a promising light absorber photovoltaic material due to its p-type conductivity, optimum direct band gap, high optical absorption coefficient, and the fact that it is composed from the abundant and non toxic elements. Among different preparation techniques, solution based routes are attractive due to their simplicity and low cost aspects. In this work the precursor Cu–Zn–Sn metallic alloy films were co-electrodeposited at the threshold cathode potential of −1.10 V (vs. Ag/AgCl reference electrode) on both molybdenum and ITO-coated glass substrates from the bath solutions containing 20 mM of copper, 10 mM of tin, 500 mM of tri-sodium citrate and different high zinc concentrations in the range of 200–600 mM. This approach of using high zinc concentrations in the bath solution and utilizing the least negative cathode potential in order to minimize the film porousity has not been adopted previously. The precursor films were converted to CZTS by a sulfurization process. We studied the effect of high Zn concentration in the bath solution on the composition, structure, morphology, and optical characteristics of the CZTS films using scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction, Raman spectroscopy, and optical transmittance spectroscopy. Non-porous and uniform near-stoichiometric and phase-pure stoichiometric CZTS films could be synthesized from the precursor films deposited from the 600-mM Zn-containing solution at 25 and 60 °C, respectively.

Chemical metallization of KMPR photoresist polymer in aqueous solutions

While conventional methods for preparing thin films of metals and metallic alloys on insulating substrates in the field of microelectromechanical systems (MEMS) include vapor deposition techniques, we demonstrate here that electroless deposition can be considered as an alternate efficient approach to metallize the surface of insulating substrates, such as KMPR epoxy photoresist polymer. In comparison with the physical and chemical vapor deposition methods, which are well-established for metallization of photoresist polymers, our electroless nickel plating requires only immersing the substrates into aqueous solutions in open air at low temperatures. Thin films of nickel alloy have been deposited electrolessly on KMPR surface, through a cost-effective and environmental chromium-free process, mediated through direct grafting of amine palladium complexes in aqueous medium. This covalent organic coating provides excellent adhesion between KMPR and the nickel film and allows better control of the palladium catalyst content. Covalent grafting and characterization of the deposited nickel film have been carried out by means of Fourier-transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy techniques.

Stress-induced surface instabilities and defects in thin films sputter deposited on compliant substrates.

Existing analyses predict that thin metal films deposited on compliant substrates are subject to a variety of surface instabilities, such as wrinkles, folds, creases, etc., that become more prominent with increased compressive residual stress. Under compressive stress, cracks have been assumed to form only when the interfacial strength is weak, allowing the film to detach from the substrate. In this work, we demonstrate that cracks also form on surfaces under compressive mismatch strain when the interface is strong. In particular, we consider metal alloy films sputter deposited under bias on elastomers with different thicknesses, curing temperatures or surface treatments. The deposition parameters created residual compressive strains and strong adhesion in the bilayers. Samples without surface treatment formed wrinkles and through-thickness cracks at 0.25-0.4% mismatch strains. Only through-thickness cracks were observed in UV treated samples. The crack spacing was found to decrease by a factor of 4 when the surface was UV treated and by a factor of 3 as the elastomer thickness decreased from 30 to 6 μm. Cracks penetrated through the elastomer, 15-30 times deeper than the film thickness, and formed in all samples with a brittle coating. A numerical model was developed to explain the formation of through-thickness cracks and wrinkles under applied compressive mismatch strains. The model suggests that cracks can initiate from the peak of wrinkles when the critical fracture strength of the coating is exceeded. For the UV treated samples, through-thickness cracks are possibly impacted by the formation of an embrittled near surface PDMS layer.