Electron-beam Sputtering Research Articles

Effect of separated layer thickness on magnetoresistance and magnetic properties of Co/Dy/Co and Ni/Dy/Ni film systems

Co(5 nm)/Dy(t[Formula: see text])/Co(20 nm)/S and Ni(5 nm)/Dy(t[Formula: see text])/Ni(20 nm)/S trilayer films are prepared by electron-beam sputtering to investigate the influence of dysprosium layer thickness (t[Formula: see text]) and thermal annealing on the crystal structure, magnetoresistance (MR) and magnetic properties of thin films. The thickness of Dy layer changed in the range from 1 nm to 20 nm. The samples annealed for 20 min at 700 K. Electron diffraction patterns reveal that the as-deposited and annealed systems Co/Dy/Co and Ni/Dy/Ni had fcc-Co + hcp-Dy and fcc-Ni + hcp-Dy phase state, respectively. It is also shown that at the t[Formula: see text] = 15 nm the transition from amorphous to crystalline structures of Dy layer is observed. An increase in the Dy layer thickness results in changes in the MR and magnetic properties of the trilayer systems. It is shown that MR is most thermally stable against annealing to 700 K at t[Formula: see text] = 15 nm for Co/Dy/Co as well as for Ni/Dy/Ni. For t[Formula: see text] = 15 nm the, value of MR for both system increases by two times compared to those of pure ferromagnetic (FM) samples. The coercivity (B[Formula: see text]), remanent (M[Formula: see text]) and saturation (M[Formula: see text]) magnetization of the in-plain magnetization hysteresis loops are related to the Dy layer thickness too. The coercivity depends on the FM materials type and diffusion processes at the layer boundary. Accordingly, M[Formula: see text] and M[Formula: see text] are reduced with t[Formula: see text] increasing before and after annealing for both trilayer systems.

Morphology and Contact Properties of Polytetrafluoroethylene-Like Films Deposited onto Track-Etched Membrane Surface in Vacuum

The surface morphology and wettability of nanoscale polytetrafluoroethylene-like films deposited onto the surface of the poly(ethylene terephthalate) track-etched membrane by RF-magnetron and electron-beam sputtering of polytetrafluoroethylene in vacuum have been studied. It was shown that the morphology of films formed with the use of these coating techniques varies considerably. This is due to the size of the deposited polymer nanostructures. The nanostructures produced by the electron-beam sputtering of polytetrafluoroethylene are much bigger in size. Investigation of the surface properties of the composite membranes obtained in these processes showns that the deposition of the polytetrafluoroethylene-like film onto track-etched membrane leads to hydrophobization of its surface. The water contact angle for the composite membranes significantly increases.<br /><br />

Peculiarity of magnetoresistance of discontinuous ferromagnetic thin films

The magnetoresistive properties of discontinuous ferromagnetic Fe and Co thin films deposited by electron-beam sputtering onto glass substrates at room temperature were investigated. Tunnel magnetoresistance (MR) was observed for all of the as-deposited samples. The maximum MR was observed for Fe thin films with an effective thickness of 17 nm. In the case of the Co thin films, the annealing process led to a change of the type of MR to anisotropic at Co film thicknesses (dCo) of 15 ≤ dCo ≤ 25 nm and to positive isotropic at thicknesses of dCo < 15 nm. By contrast, the MR type of Fe thin films did not change.

Optical Properties of TiO2 Films Deposited by Reactive Electron Beam Sputtering

Titanium dioxide (anatase, a-TiO2) films have been prepared by electron beam sputtering of a TiO2 target in reactive atmosphere and their structural, microstructural, and optical properties were evaluated by reflection high- energy electron diffraction (RHEED) and x-ray diffraction (XRD) analyses, atomic force microscopy (AFM), and spectroscopic ellipsometry (SE). Different reflection models for determination of film optical parameters were tested and compared. The dispersive optical parameters were defined using the Tauc–Lorentz model by SE in the photon energy range of E = 1.12–4.96 eV. The films were transparent at E 3 eV. The bandgap was estimated at the level of Eg ≈ 3.44 eV.

Silicon and III-V Solar Cells: From Modus Vivendi to Modus Operandi

In the present paper, some novel opportunities for the development of high-efficient Si and III-V-based solar cells are considered: energy-saving environment friendly low-temperature technology of forming p-n junctions in Si (1), elaboration of structurally perfect GaAs/Ge/Si epitaxial substrates (2) and application of protective antireflecting coatings based on cubic zirconia (3). As a result: 1) New technique of forming p-n junctions in silicon has been elaborated. The technique provided easy and comparatively cheap process of production of semiconductor devices such as solar cells. The essence of the technique under the study is comprised in formation p-n junctions in silicon by a change of conductivity in the bulk of the sample occurring as a result of redistribution of the impurities, which already exists in the sample before its processing by ions. It differs from the techniques of diffusion and ion doping where change of conductivity and formation of p-n junction in the sample occur as a result of introduction of atoms of the other dopants from the outside; 2) The conditions for synthesis of GaAs/Ge/Si epitaxial substrates with a thin (200 nm) Ge buffer layer featured with (1 - 2) × 105 cm-2 density of the threading dislocation in the GaAs layer. Ge buffer was obtained by chemical vapor deposition with a hot wire and GaAs layer of 1 μm thick was grown by the metal organic chemical vapor deposition. Root mean square surface roughness of GaAs layers of the less than 1 nm and good photoluminescence properties along with their high uniformity were obtained; 3) The conditions ensuring the synthesis of uniform functional (buffer, insulating and protective) fianite layers on Si and GaAs substrates by means of magnetron and electron-beam sputtering have been determined. Fianite films have been shown to be suitable for the use as an ideal anti-reflecting material with high protective and anticorrosive properties.

Spall behavior of copper under ultra-high strain rate loading

The spall behavior of copper at ultra-high strain rate is studied by molecular dynamics simulation combined with an experimental analysis of laser ablation of a bulk copper target by femtosecond laser pulses. In the molecular dynamics simulation, two-temperature model is used, shock wave and spallation characteristics of copper shock-loaded by femtosecond laser are analyzed in detail. It is concluded that the evolution of pressure indicates a triangular waveform of the shock wave, and the spall strength of copper is about 19 GPa at strain rates ranging from 109 s-1 to 1010 s-1, while higher pressure would melt the sample and the spall strength decreases to 14.89 GPa. Normally, the spallation is characterized by the sample free-surface undergoing alternately acceleration and deceleration, and the spallation mechanism could be explained by void nucleation, growth, coalescence that leads to the final fracture. An experiment is conducted to achieve high strain rate load on copper. The driving laser has a pulse width of 25 fs and central wavelength of 800 nm, the thickness values of the shocked copper foils are (5025) nm, fabricated by electron beam sputtering deposition onto 180 upm cover slip substrates. The driving laser beam with maximum intensity 5.51013 W/cm2, is focused on the front surface of the copper through the transparent substrate. Movements of the free rear surfaces of the copper foils are detected by chirped pulse spectral interferometry, and the theoretical time resolution is 1.3 ps. As a result, the free surface displacement and velocity evolution profile of the shocked area are obtained in a single measurement, and the results directly show that the maximum free surface velocity is 0.43 km/s and no alternately acceleration and deceleration appears. According to the shock wave relations, the maximum pressure near free-surface is 8.18 GPa. Meanwhile, derived from the velocity evolution profile, the strain rate is 7.3109 s-1. Combining with the above molecular dynamics simulation results, it is concluded that there is no spallation in the copper foil. Furthermore, we recover the sample targets and observe the microstructures by using scanning electron microscope. The copper foils are peeled off, but no spall scab is observed, indicating that the internal stress is between the copper spall strength and the bonding strength of copper foil with the transparent substrate. Ripple structure on copper surface demonstrates the femtosecond pulsed laser has ablated the copper film, and the propagation of the shock in fs regime is sensitive to microscopic defects.

Formation of composite membranes containing hydrophobic polymer layers by electron-beam sputter deposition

The chemical structure and the contact and morphological properties of composite membranes prepared by electron-beam sputter deposition of a polytetrafluoroethylene layer on the surface of track-etched polypropylene membrane have been studied. It has been found that the application of such layers results in bilayer composite membranes with both the layers having hydrophobic properties. It has been shown that an increase in the thickness of the deposited polytetrafluoroethylene layer leads to development of its roughness, resulting in the formation of a polymer with superhydrophobic properties on the surface of the initial membrane.

Liquid-Cell Transmission Electron Microscopy of Localized Corrosion of Aluminum

While the growth of pits in passive metals exposed to chloride solutions is well understood, the processes associated with the initiation and propagation of stable pits, versus pits that form and then re-passivate, are still a matter of conjecture. This study uses potentiostatic polarization to determine the pitting potential of aluminum as a function of chloride activity at constant pH. In contrast to earlier studies there is a departure from linearity as the solution becomes increasingly dilute, suggesting a new mechanism for the initiation of pits in less aggressive environments. This is shown in Figure 1, where a line has been fit both to the entire dataset, and two lines have been fit to their respective high and low portions of the dataset. The data at low chloride concentrations do not agree with the formulation developed by McCafferty [1] unless fit separately as two lines of different slope. Pitting corrosion is directly observed in situ in a liquid cell transmission electron microscope (TEM) [2]. Figure 2 shows a schematic of our corrosion cell design that we incorporate into this holder. The sample is created using standard electron beam evaporation, sputter deposition, and shadow mask methods. Current is supplied with titanium leads to the aluminum. This configuration allows pitting corrosion to be randomly distributed over the entire aluminum field. The influence of the microscope induced electron dose on the corrosion properties has been investigated and found to be controllable and consistent. We have characterized the thin film aluminum electrochemical behavior by generating Tafel curves within the liquid cell, and found the observations in situ to be largely representative of the bulk behavior. In Figure 3 this comparison is shown for nominally pure aluminum in the bulk case, versus the thin film samples, both in and out of the TEM. At low chloride concentration the curves have similar characteristics, such as similar anodic current slope, but are translated to more noble potentials and higher current densities for pitting behavior. Changes in the open circuit potential between the two thin film samples; in the microscope and external to it, are partially explained by the bias applied by the goniometer. The difference between open circuit potential in the bulk and thin film cases is consistent over several measurements, but the reason for the shift is a topic of further research. Current work is probing the relationship between thickness of the thin film and behavior compared to the bulk. In all cases we observed current transients representative of metastable pitting. We were able to relate crystalline features found in situ with topographic features using atomic force microscopy (AFM), as seen in this group’s earlier work [3]. Coupled with a depth profile from Auger Electron Spectroscopy of the pit this suggests that the ridges observed around the pit cusp in AFM are metallic aluminum. Pit growth is observed in situ, as seen in Figure 4, and suggests a redeposition of aluminum from the pit anolyte as seen in the red-circled features. Redeposition could result in conditions for repassivation by depriving the system of the critical concentration of aluminum ions [4]. Future work will include oxidation of the aluminum film in situ to examine changes from radiolysis by the beam, and effects of chloride on a fully oxidized aluminum film (no remaining underlying aluminum metal). It is expected this will reveal the influence of chloride on the surface-oxide interface and lead to greater detailed understanding of the oxide film’s role in passivation. This work is funded by NSF, under NSF-DMR 1309509. We acknowledge See Wee Chee and Brent Engler for collaboration, R. Dove and R. Planty for technical assistance and facilities within the Nanoscale Characterization Core operated by the Center for Materials Devices and Integrated Systems at RPI.

Technique for forming ITO films with a controlled refractive index

A new method for fabricating transparent conducting coatings based on indium-tin oxide (ITO) with a controlled refractive index is proposed. This method implies the successive deposition of material by electron-beam evaporation and magnetron sputtering. Sputtered coatings with different densities (and, correspondingly, different refractive indices) can be obtained by varying the ratio of the mass fractions of material deposited by different methods. As an example, films with effective refractive indices of 1.2, 1.4, and 1.7 in the wavelength range of 440–460 nm are fabricated. Two-layer ITO coatings with controlled refractive indices of the layers are also formed by the proposed method. Thus, multilayer transparent conducting coatings with desired optical parameters can be produced.

Migration mechanism of a GaN bicrystalline grain boundary as a model system

Using in situ high-resolution transmission electron microscopy, we have explored migration mechanism of a grain boundary in a GaN bicrystal as a model system. During annealing at 500 °C, the grain-boundary region underwent a decrease in thickness, which occurred by decomposition or sublimation of GaN during annealing at 500 °C coupled with electron-beam sputtering. The decrease in thickness corresponds to an increase in the driving force for migration, because the migration of the grain boundary was driven by the surface energy difference. As the driving force increased with annealing time, the grain-boundary morphology turned from atomically smooth to rough, which is characterized by kinetic roughening. The observations indicate that a grain boundary exhibits a nonlinear relationship between driving force for migration and migration velocity, in discord with the general presumption that a grain boundary follows a linear relationship.

A versatile platform for magnetostriction measurements in thin films

We present a versatile nanomechanical sensing platform for the investigation of magnetostriction in thin films. It is based on a doubly clamped silicon nitride nanobeam resonator covered with a thin magnetostrictive film. Changing the magnetization direction within the film plane by an applied magnetic field generates a magnetoelastic stress and thus changes the resonance frequency of the nanobeam. A measurement of the resulting resonance frequency shift, e.g., by optical interferometry, allows to quantitatively determine the magnetostriction constants of the thin film. In a proof-of-principle experiment, we determine the magnetostriction constants of a 10 nm thick polycrystalline cobalt film, showing very good agreement with literature values. The presented technique aims, in particular, for the precise measurement of magnetostriction in a variety of (conducting and insulating) thin films, which can be deposited by, e.g., electron beam deposition, thermal evaporation, or sputtering.

Application of nanostructured silver film in multilayer contact system of Ti/Mo/Ag silicon photoconverters

In this article we have synthesized multilayer contact systems Ti/Ag and Ti/Mo/Ag with nanostructured silver films using two vacuum methods, namely the method of electron-beam evaporation and HF magnetron sputtering. Using the data of atomic force microscopy, X-ray diffraction and mass spectroscopy of the secondary neutrals in the paper we have investigated the influence of the application method and of the annealing conditions on the grain formation processes in silver thin films and mass transfer between the metal layers of the contact system. The decrease of surface resistivity of the developed contacts and, respectively, the increase of short-circuit current of the heterojunction silicon solar cells have been determined.

GaAs structures with a gate dielectric based on aluminum-oxide layers

Different types of dielectrics obtained by low-temperature electron-beam sputtering are studied; these dielectrics include Al2O3 layers and Al2O3/SiO2/Al2O3 three-layer compositions. The dependence of the electrical strength of Al2O3 layers on their thickness is determined. It is established that formation of the three-layer dielectric Al2O3/SiO2/Al2O3 makes it possible to increase the range of operating voltages up to 60 V for structures with a gate electrode. It is shown that it is possible to control the density of charge carriers (holes) in the two-dimensional conduction channel of GaAs structures by changing the gate voltage when the Al2O3/SiO2/Al2O3 structure is used as a gate dielectric.

Experiment research on dynamic response of copper film at high strain rate by chirped pulse spectral interferometry

That the femtosecond laser pulses irradiate metallic materials thereby inducing ultrahigh strain rates, is an important experimental approach to studying the material behavior under extreme conditions. Femtosecond laser-generated shock waves in metal films have rise times of several picoseconds, the corresponding diagnostic technique is required to work with a higher time resolution, which makes the experimental measurements difficult. Chirped pulse spectral interferometry (CPSI) possesses capabilities of ultrafast time resolution and continuous measurement, thus it provides a diagnostic technique for studying the ultrashort shock wave. In this article, we carry out an experiment on femtosecond laser driven shock wave in copper film and the measurement by CPSI. Laser pulse of 25 fs duration at the central wavelength 800 nm is used, the tested samples are copper films of (5025) nm in thickness fabricated by electron beam sputtering deposition onto cover slip substrate of 180 m in thickness, pump beam focuses onto front surface of the copper film through the transparent substrate and this laser intensity is 2.31013 W/cm2. Chirped pulse spectral interferometry is used to detect the movements of the free rear surfaces of the copper films with temporal and spatial resolution. In the spectral interferometry, linearly chirped pulse is required and obtained by stretching the femtosecond laser pulse with a pair of gratings. The relation between frequency and time of the chirped pulse is accurately measured using asymmetric spectral interference method, which is required for explaining the experimental data. Since CPSI is a single shot diagnostic technique, we obtain the displacement and velocity history of the free rear surface with picosecond time resolution in a single measurement. From the results, the average shock velocity is calculated to be (5.60.2) km/s and the shock wave rise time is determined to be 6.9 ps. According to the shock wave relations, impact pressure and strain rate in the copper film are (57.18.8) GPa and 8109 s-1 respectively, the strain rate is so high that it is hard to achieve by long-pulse laser driven or other loading approaches. Additionally, experimental results also show that the free rear surface alternately experiences acceleration and deceleration, which indicates the spallation in the copper target. It is obvious that chirped pulse spectral interferometry is a reliable approach to studying ultrashort shock waves in metal films.

Micro- and nanofluidic diodes based on track-etched poly(ethylene terephthalate) membrane

The work is devoted to fabrication of micro- and nanofluidic diodes, devices that are polymer composite membranes with asymmetric conductivity. To this end, a polytetrafluoroethylene layer has been applied by electron beam sputter deposition on one side of a poly(ethylene terephthalate) track-etched membrane used as a porous substrate. It has been shown that the resulting effect of conductivity asymmetry is due to not only a significant decrease of the diameter of pores and a change in their geometry in the deposited polytetrafluoroethylene layer, but also the existence of an interface between the initial membrane and the hydrophobic polymer layer in the pores. Devices of this kind can be used for directional ion transport.

Vacuum-Plasma Synthesis of Functional Coatings Using Targets Obtained by the Sol-Gel Method

To prepare coatings by electron-beam sputtering, targets have been designed and synthesized by a sol-gel method, based on SiO2 and TiO2 materials. The optimum basic compounds for the synthesis of stable silica sol and titanium are reported. Spectroscopic studies have been conducted for the coatings aiming at the characterization in terms of optical characteristics, such as refractive index, reflectance, transmission and absorption coefficients. The morphology of the layers was investigated by atomic force (AFM) and scanning electron (SEM) microscopies.

Vacuum deposition of chitosan thin films by electron beam sputtering

Vacuum deposition of chitosan thin films by electron beam sputtering

Influence of deposition process and substrate on the phase transition of vanadium dioxide thin films

The abrupt changes in structural, electronic and optical properties that accompany the vanadium dioxide (VO2) phase transition make it a promising material for a wide range of thin-film applications in electronics,photonics and plasmonics. Several physical vapor-deposition techniques are used by various research groups, but until now there has been no systematic comparison of the three most common methods – electron beam evaporation, pulsed-laser deposition and sputtering – covering the most common substrates. Here we explore the influence of substrate, deposition process and annealing time at 450°C on the phase transition properties and morphology of thin VO2 films. Films deposited by rf magnetron sputtering have the same structure on glass, silicon and sapphire substrates and are stable for 90min of annealing. In contrast, the structure of films deposited by electron beam evaporation and pulsed laser deposition depends heavily on the substrate. Dewetting plays a prominent role in the evolution of film structure and the phase transition properties for films deposited on silicon and glass are unstable for 90min annealing. The epitaxial relationship between VO2 and sapphire stabilizes the phase transition contrast for all deposition processes and annealing times. Performance as measured by switching contrast is maximized for all deposition processes with 10min of annealing.

Note: development of a volume-limited dot target for a high brightness extreme ultraviolet microplasma source.

We report on production of volume-limited dot targets based on electron beam lithographic and sputtering technologies for use in efficient high brightness extreme ultraviolet microplasma sources. We successfully produced cylindrical tin (Sn) targets with diameters of 10, 15, and 20 μm and a height of 150 nm. The calculated spectrum around 13.5 nm was in good agreement with that obtained experimentally.

Radio frequency-H2O plasma treatment on indium tin oxide films produced by electron beam and radio frequency magnetron sputtering methods

Electron beam and radio frequency (RF: 13.56MHz) magnetron sputtering methods were used to obtain a highly transparent and conductive indium tin oxide (ITO) films. The coated thin films were treated by RF-H2O plasma in order to improve optical and electrical properties. RF-H2O plasma characteristics were investigated by optical emission spectroscopy during surface treatments. X-ray photoelectron spectroscopy results on O 1s core levels indicated the activated oxygen species in both amorphous and crystalline ITO structures. The structural, electrical and optical properties of ITO film were characterized by scanning electron microscopy, X-ray diffraction, and four-probe techniques. After the RF-H2O plasma treatment, the ITO films exhibited lower resistivity and better transparency due to the formation of radical species.