Properties Of Thin Metal Films Research Articles

Electrophysical properties of Cu/Cr and Fe/Cr film systems within elastic and plastic deformation range

We have investigated the electrophysical properties of metallic thin films based on Cu/Cr and Fe/Cr systems. We find that the longitudinal gauge factor of two-layer films is significantly greater as compared with one-layer films, which have the same thickness as the total thickness of a two-layer film. Interface and intensive grain–boundary electron scattering explain such an increase in the longitudinal gauge factor. We find that the longitudinal gauge factor increases in transition from elastic to plastic zone.

Phase Relations Associated with One-Dimensional Shell Effects in Thin Metal Films

The physical and chemical properties of thin metal films show damped oscillations as a function of film thickness (one-dimensional shell effects). While the oscillation period, determined by subband crossings of the Fermi level, is the same for all properties, the phases can be different. Specifically, oscillations in the work function and surface energy are offset by 1/4 of a period. For Pb(111) films, this offset is approximately 0.18 monolayers, a seemingly very small effect. However, aliasing caused by the discrete atomic layer structure leads to striking out-of-phase beating patterns displayed by these two quantities.

The fragmentation test applied to adhesion measurements and microstructural characterization in plasma pre‐treated metallized plastic webs

AbstractA theoretical and experimental approach based on cracking analysis of stressed films (fragmentation test) has been applied to the study of interface dominant properties of metallized plastic flexible films. The test was found to be accurate for quantitative aluminium adhesion measurements and was used for an evaluation of the effect of different plasma pre‐treatments on the final properties of the metallized poly(ethylene) films. The test proved to be a powerful method for better understanding both the adhesion and the mechanical and microstructural properties of thin metal films. A clear improvement of aluminium adhesion was demonstrated for increasing plasma pre‐treatment times up to 0.8 s, and microstructural features were deduced from the test data. Copyright © 2009 John Wiley & Sons, Ltd

Quantum oscillations in surface properties

Many properties of metallic thin films have been shown to oscillate with film thickness due to quantum size effects, i.e. the confinement of electrons inside epitaxial metal overlayers which causes quantization of the electronic states. This is a very general phenomenon and it affects both bulk properties of the films, such as resistivity or superconducting transition temperatures, and surface properties, such as chemical reactivity, diffusivity, thermal stability, i.e surface roughening transitions. In this paper we describe some of these thickness-dependent properties which affect the stability of nanostructures and allow us to tailor their properties. We shall concentrate in the paradigmatic example of thin films of Pb grown on metallic and semiconducting substrates and how one can achieve the growth of highly perfect, atomically flat, epitaxial films on different substrates, due to the kinetic constrains imposed by the presence of QSE, a topic increasingly important in the production of nanoscale quantum devices.

Temperature- and frequency-dependent optical properties of ultrathin Au films

While the optical properties of thin metal films are well understood in the visible and near-infrared range, little has been done in the midinfrared and far-infrared region. Here we investigate ultrathin gold films prepared on $\text{Si}(111)(7\ifmmode\times\else\texttimes\fi{}7)$ in UHV by measuring in the frequency range between 500 and $7000\text{ }{\text{cm}}^{\ensuremath{-}1}$ and for temperatures between 300 and 5 K. The nominal thickness of the gold layers ranges between one monolayer and 9 nm. The frequency and temperature dependences of the thicker films can be well described by the Drude model of a metal when taking into account classical size effects due to surface scattering. The films below the percolation threshold exhibit a nonmetallic behavior; the reflection increases with frequency and decreases with temperature. The frequency dependence can partly be described by a generalized Drude model. The temperature dependence does not follow a simple activation process. For monolayers we observe a transition between surface states around $1100\text{ }{\text{cm}}^{\ensuremath{-}1}$.

Molecular Dynamics Simulation on the Nanoindentation Behavior of a Copper Bilayered Thin Film

Abstract Understanding the mechanical properties of multilayered metal thin films is very important for their applications in nanoscale devices. Nanoindentation is one of the widely used tools for examining the mechanical properties of metal thin films. In the present study, molecular dynamics simulation was employed to investigate the nanoindentation behavior of a Cu(100)/Cu(110) bilayered thin film. The load-displacement response and the detailed deformation structure of the copper thin film during the nanoindentation were inspected and compared with those of Cu(100) and Cu(110) thin films. It was found that at the indenting stage the maximum indentation load of the bi-layered thin film is lower than that of its ingredients, however, they have nearly the same maximum indentation load. At the retracting stage, the maximum attractive force of the bilayered thin film was found near that of its ingredients but occurred much earlier than the ingredients. The detailed deformation structure of the bilayered thin film was observed to be similar to that of the ingredients and correlated very well with the load-displacement response.

Some considerations on the transmissivity of thin metal films

As interest in plasmonics grows the optical properties of thin metal films becomes increasingly significant. Here we explore the transmissivity of thin metal films at normal incidence, from the ultraviolet to microwaves, and show how, contrary to simplistic treatments, the microwave transmissivity may be much less than the optical transmissivity for films which are well below the skin depth in thickness. This arises because the film is acting as a zero order Fabry-Perot with very high reflectivity at each interface. The skin depth then becomes irrelevant for thin metal films at microwave frequencies. We also note in passing that the expected exponential dependence on thickness at higher thicknesses has an asymptotic limit at zero thickness which may be as high as four times the input intensity.

Editorial for Biointerphases in focus: Surface plasmon resonance-plasmonics

Optical characterization of ultrathin films and interfaces using surface plasmon polariton or surface plasmon resonance (SPR) excitation in “free-electron-like” metals of gold and silver was pioneered by two research groups from Germany in the late 1960s.1,2 They showed that the SPR phenomenon could be excited optically by the method of attenuated total reflection (ATR) either via a very thin air gap-“the Otto configuration”-or by a route where the thin metal film was deposited directly on the base of a glass prism-“the Kretschmann configuration.” Both methods were extensively used to study fundamental optical properties of thin metal films and inorganic/organic coatings deposited on top of the metal film surface. In the following years the SPR-ATR approach became very popular for studies of monomolecular assemblies of Langmuir-Blodgett films on metals3 and later for the determination of molecular orientation4 in such assemblies as well as for measurement of refractive index changes occurring during phase transitions in liquid crystals.5

Thermoplasmonic shift and dispersion in thin metal films

In 2004, the authors reported two coupling schemes based on the thermo-optic properties of thin metallic films and their associated sub- and superstrates, by utilizing surface plasmons. These studies showed a potential for all-optical modulation at low rates that may be used for sensing purposes. In this article, they continue by investigating thermal processes involved in thin metallic films with different approaches. They first experimentally imaged the shift of the surface plasmon dispersion relation in the visible spectrum, as the thin film temperature is externally varied. They then reinforce the previous observations by collecting the absorption curves at selected visible photon energies of excitation, as the film temperature in the excitation region increases. Utilizing the absorption measurements, they briefly address how one may obtain the real and imaginary parts of the index of refraction of the thin film as a function of temperature for each involved wavelength. Finally, they investigate the local physical state of the film by optically profiling the surface plasmon excitation region.

Microstructural Design of Advanced Architectures in Titanium/Platinum Thin Films by Laser Interference Metallurgy

Laser Interference Metallurgy has been used to modify locally microstructure and mechanical properties of metallic thin films with spatial periodicity. Irradiating Platinum films using a Nd:YAG pulsed laser enables the fabrication of three different microstructural architectures. Texture analyses have proven the corresponding impact on the microstructure and the anisotropy of periodic structures. Nanoindentation tests demonstrate an increase of hardness in the microcrystalline region according to the inverse Hall-Petch effect.

Investigation on methods for dealing with pile-up errors in evaluating the mechanical properties of thin metal films at sub-micron scale on hard substrates by nanoindentation technique

Two quantitative approaches are proposed in this paper in order to deal with the significant errors produced during evaluating the mechanical properties of soft metal films on hard substrates by using nanoindention technique, which depend on calculating actual contact area (CACA: area) and correcting contact depth errors (CCDE: depth). The hardness and elastic modulus of films-only for two elastically matching systems with film thickness of about 500 nm, Au/glass-ceramic and Al/7059 glass, are then obtained by using the methods. The above parameters are also determined by the Oliver and Pharr method and the constant modulus assumption analysis (CMAA: modulus) for comparisons. In CMAA: modulus, the values are assumed to be independent of the contact area and contact depth. The results indicate that the two methods are both able to correct severe pile-up errors in the Oliver and Pharr analysis and produce a relative high accuracy.

Effects of thin film properties on metallic pattern formation by direct nanoimprint

Abstract In this paper, the relation between properties of metallic thin films and the formability for metal direct imprinting method is discussed. In order to obtain a better formability of thin films, aluminum thin films with different grain sizes were prepared first. Nanoindentation test was applied to measure and confirm the material properties such as the hardness and elastic modulus of the thin film. It was found that the larger grain size is, the lower hardness is. This is called the Hall–Petch effect, which was confirmed by the former paper. To measure the surface topology, roughness, and height of the transferred pattern of the aluminum thin films, atomic force microscope (AFM) was employed. After the metal direct imprinting experiments, it was found the smaller grain size with the lower pattern transfer ratio. According to the results of indentation and imprint experiments, these indicate that the bigger grain size could have better formability, because of the effects from grain boundary. The formability of the metallic thin films can be improved through the thin film fabrication process for a suitable grain size and thickness control. Base on this method, valuable guidelines for the direct metallic imprinting process in nano/microscale pattern transfer could be provided.

Electrical conductance at initial stage in epitaxial growth of Pb, Ag, Au and In on modified Si(1 1 1) surface

The electronic properties of thin metallic films of Pb, Ag, Au and In atoms deposited at 105 K on well defined metallic surface, i.e. Si(1 1 1)-(6 × 6)Au surface with 10 ML of annealed Pb, were investigated using four-point probe method in UHV condition. The structure of the substrate and deposited metals were monitored by the RHEED system. The electrical conductance, measured during the deposition of In and Pb atoms, shows the local minimum for the coverage equals about 0.3 ML whereas for Au and Ag atoms the conductance decreases during the first monolayer growth. For Au atoms the local maximum in the conductance was observed for the coverage about 0.55 ML, which can be connected with localized states. To describe theoretically the conductance behavior the tight-binding Hamiltonian and equation of motion for the Green’s function were used and good qualitative agreement was obtained.

A MEMS-Based Evaluation of the Mechanical Properties of Metallic Thin Films

Characterizing the mechanical properties of metal thin films is critical for the design and fabrication of metal microelectromechanical systems and integrated circuit devices. This paper focuses on wafer-level determination of the mechanical behavior of sputtered aluminum and nickel thin films, using a variety of measurement techniques. Elastic moduli have been determined in devices fabricated with standard micromachining techniques using bulge testing of square diaphragms and lateral resonator structures. We find a Young's modulus of ~70 GPa for Al and ~200 GPa for Ni, in agreement with data for the bulk metals. Using pressurize/depressurize cycles, the load-deflection curves of the membranes have also been determined, and in conjunction with finite element simulations, were used to determine the yield strength and fracture strength of these films. Residual stresses in the films have also been investigated using wafer curvature, bulge testing, and X-ray diffraction. The merits of each measurement technique are discussed.

Fatigue and thermal fatigue damage analysis of thin metal films

In this paper, we summarize several testing methods that are currently available for the characterization of fatigue properties of thin metal films. Using these testing methods, a number of experimental investigations of the fatigue and thermal fatigue of metal films with thicknesses ranging from micrometers to sub-micrometers are described. Extensive experimental observations as well as theoretical analyses reveal that the damage behavior, i.e. typical fatigue extrusions and cracking, are quite different from that of bulk materials, and are controlled by the length scales of the materials. Due to the high surface to volume ratio of thin films interface-induced and diffusion-related damage are prevalent in these small length scale materials. As a result, interfaces pose a serious threat to the reliability of thin films.

Electroless deposition and electrical resistivity of sub-100 nm Cu films on SAMs: State of the art

Self-assembled organic monolayers (SAMs) of silanes with –SH, –NH 2 and –C 5H 4N functional groups have been shown recently to act as ultra-thin, robust diffusion barriers at the Cu/SiO 2 and Cu/ultra low- k dielectric interfaces. More generally, SAMs with their tunable surface chemistry are essential elements of future all-wet ULSI metallization with Cu deposited by electroless (ELD) over SAM-functionalized dielectrics. Far too small is known however on the electrical properties of thin metal films formed onto SAM/dielectric substrates. In this paper, we give first a brief literature survey of what is known about Cu films deposited by electroless over dielectrics modified by SAMs. Second, we present our observations of electrical resistivity ρ of sub-100 nm ELD Cu films deposited over the surface of amino-silane SAM/SiO 2 activated by Au monodispersed nano-particles and show that this techniques helps to obtain considerably smaller ρ compared to the previously reported data.

Refractive index and extinction coefficient dependence of thin Al and Ir films on deposition technique and thickness

We show that the optical properties of thin metallic films depend on the thickness of the film as well as on the deposition technique. Several thicknesses of electron-beam-gun-evaporated aluminium films were measured and the refractive index and the extinction coefficient defined using ellipsometry. In addition, the refractive indexes and the extinction coefficients of atomic-layer-deposited iridium were compared with those of evaporated iridium samples.

Strains, Stresses and Elastic Properties in Polycrystalline Metallic Thin Films: In Situ Deformation Combined with X-Ray Diffraction and Simulation Experiments

X-ray diffraction is used in combination with tensile testing for measuring elastic properties of metallic thin films. Size effect, elastic anisotropy and grain morphologies are considered in all these experiments and supported by different kind of numerical simulations operating at different length scales. Such instrumental studies are time consuming even if synchrotron sources are used. New experiments are under progress for reducing acquisition data and improving precision on strain measurements. After introducing briefly the main principles and results of our techniques, first promising measurements on nanometric W/Cu multilayers using 2D CCD detectors and high monochromatic flux at the Advanced Light Source Berkeley (USA) on beam line 11.3.1 are presented. In addition, simulation experiments for analyzing elasticity in textured gold film are discussed.

Thermomechanical Properties of Thin α-Fe Films Above the Brittle to Ductile Transition Temperature

ABSTRACTThe mechanical properties of thin metal films as compared to their bulk counterparts have been in the focus of materials science in the recent years. Owing to their technological importance, almost only metals with a face centered cubic structure like copper and aluminum have attracted scientific interest. Thin films made of bcc metals, on the other hand, have been largely neglected.However, from a scientific point of view, the mechanical properties of bcc metals are of special interest. As an example, the yield stress of bcc metals is strongly temperature dependent for low temperatures, while it shows a behavior similar to fcc metals for higher temperatures. This is often referred to as the brittle to ductile transition (BDT). Despite intense research the underlying mechanisms leading to this phenomenon are still not understood in full detail. A major problem is the understanding of dislocation dynamics on the microscopic scale, which is different from that of fcc metals because of the special symmetry of the crystal system.A first step is to verify in thin films that for temperatures above the BDT the thermomechanical behavior of bcc metals resembles that of fcc metals. As a model system we chose iron with a BDT temperature slightly above room temperature. We deposited iron by means of an MBE system on sapphire substrates. The so-produced epitaxial thin iron films with thicknesses above 50 nm were then thermally cycled from room temperature to 540°C in a vacuum substrate curvature apparatus to test their thermomechanical behavior.We will present the results of substrate curvature measurements performed with iron films of different thicknesses and discuss similarities and differences to results obtained for metals with fcc crystal structures.

Development of a Depth-resolved XMCD Method and Its Application to the Study of Surface and Interface Magnetic Properties of Metal Thin Films

X-ray magnetic circular dichroism (XMCD) is a powerful method to study the magnetic properties of magnetic thin films. However it provides depth-averaged information. Recently, we have developed a simple but effective depth-resolved technique in XMCD by using an imaging type microchannel plate detector. The performance of this method is demonstrated by applying to the depth-resolved analyses of Ni/Cu(100) and the effect of CO adsorption on Ni/Cu(100), Fe/Cu(100) and Fe/Ni/Cu(100) magnetic thin films. For Ni/Cu(100), magnetic orbital moments of the surface and internal layers are extracted to give deep insight for the spin reorientation transitions. For 7 ML Fe/Cu(100), the surface two layers are ferromagnetically coupled, while the inner layers are non-magnetic at 200 K and are in the spin density wave (SDW) state at 130 K. For Fe/Ni/Cu(100), magnetically live surface layers and some thickness-dependent magnetic coupling between the Fe surface and Ni film have been observed.