Beam Deposition Research Articles

Study of the microstructure and surface morphology of silver nanolayers obtained by ion-beam deposition

The aim of this research is to fabricate Ag nanoparticle assemblies forming nanolayers with different thicknesses in order to evaluate their physical properties and their 3-D (three-dimensional) surface micromorphology. Such Ag nanolayers were deposited by physical vapor deposition methods under ion-beam irradiation in argon atmosphere at room temperature. X-ray diffraction (XRD) characterizations confirmed the formation of silver nanocrystals. Using surface field parameters, which were derived from atomic force microscopy (AFM) analysis, the surface morphology of the nanolayers were described according ISO 25178-2:2012. The height and slope distribution functions, together with the autocorrelation (ACF), the height–height correlation (HHCF) and the power spectral density (PSDF) functions were determined for the different analyzed samples using linear interpolation in the horizontal direction. All samples had a fractal character with a fractal dimension of 2.54 ± 0.01 independent of the film thickness.

Positioning of cobalt atoms in amorphous carbon films by pre-selecting the hydrogen concentration

Amorphous carbon and hydrogenated amorphous carbon layers were implanted at room temperature with Co ions to investigate the role of hydrogen on the Co distribution. Amorphous carbon (a:C) and hydrogenated amorphous carbon (a:C–H) films were prepared by mass selective ion beam deposition with a 5kV acceleration voltage using C+ and C3H6+ ions, respectively. The typically 100nm thin films were implanted with Co using a 30kV acceleration voltage to a fluence of 4×1016cm−2. Raman measurements showed that Co implantation in hydrogenated amorphous carbon causes increased sp2 clustering while in amorphous carbon there is significant rehybridisation of carbon from sp3 to sp2 bonding. High resolution Rutherford backscattering measurements indicated that in the absence of hydrogen in the base matrix, the implantation profile assumes a unimodal distribution as predicted by simulations. However, in the presence of hydrogen the effects of collision cascade enhanced diffusion are significant in altering the implantation profile resulting in a bimodal distribution. The difference in the Co depth distribution between a:C and a:C–H films is explained by the change in thermal conductivity of the carbon matrix in the presence of hydrogen. The ability to position Co (magnetic atoms) in the surface region of diamond-like carbon films offers great advantages for applications in novel magnetic devices.

Ion mass and energy selective hyperthermal ion-beam assisted deposition setup.

For the synthesis of high-quality thin films, ion-beam assisted deposition (IBAD) is a frequently used technique providing precise control over several substantial film properties. IBAD typically relies on the use of a broad-beam ion source. Such ion sources suffer from the limitation that they deliver a blend of ions with different ion masses, each of them possessing a certain distribution of kinetic energy. In this paper, a compact experimental setup is presented that enables the separate control of ion mass and ion kinetic energy in the region of hyperthermal energies (few 1 eV - few 100 eV). This ion energy region is of increasing interest not only for ion-assisted film growth but also for the wide field of preparative mass spectrometry. The setup consists of a constricted glow-discharge plasma beam source and a tailor-made, compact quadrupole system equipped with entry and exit ion optics. It is demonstrated that the separation of monoatomic and polyatomic nitrogen ions (N+ and N2+) is accomplished. For both ion species, the kinetic energy is shown to be selectable in the region of hyperthermal energies. At the sample position, ion current densities are found to be in the order of 1 μA/cm2 and the full width at half maximum of the ion beam profile is in the order of 10 mm. Thus, the requirements for homogeneous deposition processes in sufficiently short periods of time are fulfilled. Finally, employing the described setup, for the first time in practice epitaxial GaN films were deposited. This opens up the opportunity to fundamentally study the influence of the simultaneous irradiation with hyperthermal ions on the thin film growth in IBAD processes and to increase the flexibility of the technique.

Functional fatigue of submicrometer NiTi shape memory alloy thin films

Submicrometer NiTi alloy thin films prepared using biased target ion beam deposition (BTIBD) recently revealed ultranarrow thermal hysteresis and a B2 ⇌ R-phase transformation path. Here, the authors investigate the influence of thermal cycles on the phase transformation characteristics of near-equiatomic NiTi alloy films with 800 nm thicknesses deposited using BTIBD. Evolution of transformation temperatures, thermal hysteresis, and recovery stress over thermal cycles is tracked using the wafer curvature method, and changes in atomic crystal structures are detected using x-ray diffraction. The authors find that the submicrometer thin films exhibit stabilized transformation temperatures, consistent recovery stresses, and reproducible narrow thermal hysteresis over up to 100 cycles although Ni49.7Ti50.3 films undergo two-stage phase transformation B2 → R-phase → B19′ while Ni50.3Ti49.7 films have one-stage transformation between the B2 and R-phases. The inherent deposition mechanism and transformation-path-related lattice distortion can be responsible for the reduced fatigue of functional characteristics in submicrometer NiTi alloy thin films.

Extension of the T-bridge method for measuring the thermal conductivity of two-dimensional materials.

In this paper, the T-bridge method is extended to measure the thermal properties of two-dimensional nanomaterials. We present an analysis of the measureable positions, width, and thermal resistance of two-dimensional materials. For verification purposes, the thermal conductivity of a SiO2 nanoribbon was measured. To enhance the thermal contact between the nanoribbon and the heater in the setup, the nanoribbon was dipped into either isopropanol or water in order to promote a sticking force. Also, focused ion beam deposition was used to deposit the nanoribbon onto the contact. The thermal conductivities of all three cases were identical, showing that water dipping could be used to enhance the thermal contact. Due to the simple structure of this method and the analysis provided herein, the T-bridge method can be widely used for measuring the thermal conductivity of two-dimensional materials.

Oxygen-assisted purification of platinum structures deposited by ion and electron beam induced processes

Purification in the presence of O2 flux is investigated in platinum structures grown by ion and electron beam induced deposition processes using a standard precursor, MeCpPtMe3. Two different room temperature purification processes are evaluated. In the first process, the purification is obtained by simultaneously supplying oxygen and precursor gas during the deposition. In the second process, an in situ post-treatment is performed on deposited structures by electron irradiation in the presence of oxygen. The first process applied to electron beam deposition requires a high flux of oxygen to improve the purification efficiency, while application to ion beam deposition requires a lower oxygen flux to enhance purification while avoiding an additional increase of the milling process. Both purification processes result in high purity Pt depositions and a reduction of deposition yields. For the ion beam, the electrical resistivity only drops for the first purification process: deposition supplying simultaneously oxygen and gas precursor. The second process of electron post irradiation does result in compositional changes, including reduced amounts of carbon but does not result in improvements in resistivity. For the electron beam, the resistivity shows a significant reduction applying both purification processes in sequence: in this way a resistivity of 22.5 µΩ cm has been obtained which is only twice the bulk value for Pt.

Self-assembly of magnetic nanoclusters in diamond-like carbon by diffusion processes enhanced by collision cascades

Mono-energetic cobalt implantation into hydrogenated diamond-like carbon at room temperature results in a bimodal distribution of implanted atoms without any thermal treatment. The ∼100 nm thin films were synthesised by mass selective ion beam deposition. The films were implanted with cobalt at an energy of 30 keV and an ion current density of ∼5 μA cm−2. Simulations suggest the implantation profile to be single Gaussian with a projected range of ∼37 nm. High resolution Rutherford backscattering measurements reveal that a bimodal distribution evolves from a single near-Gaussian distribution as the fluence increases from 1.2 to 7 × 1016 cm−2. Cross-sectional transmission electron microscopy further reveals that the implanted atoms cluster into nanoparticles. At high implantation doses, the nanoparticles assemble primarily in two bands: one near the surface with nanoparticle diameters of up to 5 nm and the other beyond the projected range with ∼2 nm nanoparticles. The bimodal distribution along with the nanoparticle formation is explained with diffusion enhanced by energy deposited during collision cascades, relaxation of thermal spikes, and defects formed during ion implantation. This unique distribution of magnetic nanoparticles with the bimodal size and range is of significant interest to magnetic semiconductor and sensor applications.

Electronic Transport on W-Rich Films Deposited by Focused Ion Beam

The electrical transport properties of W films obtained through focused ion beam deposition reveal a transition from weakly insulating to metallic behavior for increasing film thickness. At low temperatures, all the films make a transition to the superconducting state. The observed stochastic distribution of the critical superconducting current is related to the occurrence of phase slip processes as documented by the statistical distribution of the depairing current and its temperature dependence according to the thermally activated model of the superconducting phase in a tilted washboard potential.

Micro 3D measurement applied to interfacial deformation of bilayer thin film/substrate structure under thermal cycling loads

Abstract Failures resulting from thermal mismatch between the layers in a multilayer thin Film/Substrate structure (F/S) are fatal for the reliability of F/S-based electron devices. In this paper, a bilayer F/S consisting of a silicon substrate, a chromium film layer and a copper film layer is investigated under external thermal cycling loads. Grid method combining with the stereovision model in a Scanning Electron Microscope (SEM) system is developed to realize the measurement of three-dimensional deformation at microscale. The Focused Ion Beam (FIB) deposition technology is employed to fabricate micro-scale grid pattern with the spatial frequency of 1000 lines/mm on the test sample surface. The thermal fatigue mismatch between the film layers gives rise to intense 3D deformation near the interface area. The out-of-plane deformation as well as the in-plane deformation of the interface area is measured to achieve the genuine 3D deformation characterization. The accuracy analysis validates the feasibility of the proposed method.

Ion-beam formation of electrocatalysts for fuel cells with polymer membrane electrolyte

Active layers of electrocatalysts are prepared by the ion-beam assisted deposition (IBAD) of platinum onto carbon-based AVCarb® Carbon Fiber Paper P50 and Toray Carbon Fiber Paper TGP-H-060 T supports and Nafion® N 115 polymer membrane electrolyte in the mode where the deposited metal ions are used as ions assisting the deposition process. Metal deposition and mixing of the deposited layer with the substrate under an accelerating voltage of 10 kV by the same metal ions are carried out from a neutral fraction of metal vapor and the ionized plasma of a pulsed vacuum-arc discharge, respectively. The composition and microstructure of the surface layers obtained are studied by Rutherford backscattering spectrometry (RBS), scanning electron microscopy (SEM), electron-probe microanalysis (EPMA), and X-ray fluorescence (XRF) analysis. The platinum concentration in the layers is (0.5–1.5) × 1016 at/cm2. The prepared electrocatalysts exhibit activity in the process of the electrochemical oxidation of methanol and ethanol, which form the basis for the principle of operation of low temperature fuel cells (direct methanol fuel cells (DMFC) and direct ethanol fuel cells (DEFC)).

Two-Dimensional Folding of Polypeptides into Molecular Nanostructures at Surfaces.

Herein we report the fabrication of molecular nanostructures on surfaces via two-dimensional (2D) folding of the nine amino acid peptide bradykinin. Soft-landing electrospray ion beam deposition in conjunction with high-resolution imaging by scanning tunneling microscopy is used to fabricate and investigate the molecular nanostructures. Subnanometer resolved images evidence the large conformational freedom of the molecules if thermal motion is inhibited and the formation of stable uniform dimers of only one specific conformation when diffusion can take place. Molecular dynamics modeling supported by density functional theory calculations give atomically precise insight into the induced-fit binding scheme when the folded dimer is formed. In the absence of solvent, we find a hierarchy of binding strength from polar to nonpolar, manifested in an inverted polar-nonpolar segregation which suppresses unspecific interactions at the rim of the nanostructure. The demonstrated 2D-folding scheme resembles many key properties of its native 3D counterpart and shows that functional, molecular nanostructures on surfaces fabricated by folding could be just as versatile and specific.

Analysis of sub-bandgap losses in TiO2 coating deposited via single and dual ion beam deposition

We present a detailed study of sub-bandgap losses in TiO2 optical coatings prepared by using a single and a dual ion beam deposition. By extracting high-precision spectra of the losses in the TiO2 layers deposited under varied parameters we were able to study the losses in great detail. We were able to identify several spectral features and discuss their origin. Additional experiments allowed us to determine the contribution of absorption and scattering to the losses, as well as to discern whether the observed losses have volume or interface character. The results reveal that the dominant source of absorption in the high-quality samples is volume absorption originating from the so-called Urbach tail. We discuss the limitations imposed by the Urbach tail.

Imaging proteins at the single-molecule level

Imaging single proteins has been a long-standing ambition for advancing various fields in natural science, as for instance structural biology, biophysics, and molecular nanotechnology. In particular, revealing the distinct conformations of an individual protein is of utmost importance. Here, we show the imaging of individual proteins and protein complexes by low-energy electron holography. Samples of individual proteins and protein complexes on ultraclean freestanding graphene were prepared by soft-landing electrospray ion beam deposition, which allows chemical- and conformational-specific selection and gentle deposition. Low-energy electrons do not induce radiation damage, which enables acquiring subnanometer resolution images of individual proteins (cytochrome C and BSA) as well as of protein complexes (hemoglobin), which are not the result of an averaging process.

Influence of metastable Al9Ni2 phase on the sequence of phase transformations initiated by heating of Al/Ni multilayer foils produced by EBPVD method

Al/Ni multilayer foils (MF) undergo a cascade of phase transformations at heating, initiated by diffusion interaction of Al and Ni layers. It is found that phase transformations sequence at initial stages depends on the method of producing MF: at sputtering or ion-beam deposition of elements, metastable Al9Ni2 phase forms at phase transformations initial stages, and in the case of MF produced by electron-beam physical vapour deposition (EBPVD) method or cold rolling of laminates, this is Al3Ni phase. Such a difference in phase transformations sequence is associated with the influence of the method of MF production on the possibility of intermixed zone (IZ) formation on layer interfaces. In the study it was suggested that such anomalously high diffusion mobility of atoms can be achieved in the presence of excess vacancies in MF structure. With this purpose, MF structure was produced by high-rate (up to 30 nm/s) layer-by-layer deposition of elements by EBPVD method. Phase transformations and MF were studied by the method of X-ray diffraction (XRD) and differential-thermal analysis (DTA). It is shown that irrespective of MF composition and modulation period, at their heating phase transformations start with formation of metastable Al9Ni2 phase. At further MF heating, a stable Al3Ni phase forms alongside Al9Ni2 phase. Later on, Al9Ni2 and Al3Ni phases turn into stable intermetallics characteristic of MF chemical composition.

The Effect of Stress in the Density of States of Amorphous Carbon Films Determined by X-Ray Excited Auger Electron Spectroscopy

Amorphous carbon films can be prepared with a large variety of structure and have been used in a number of technological applications. Many of their properties have been determined, but very little is known concerning the effect of pressure on their properties. In this work we investigate the influence of pressure of graphite-like amorphous carbon films on the density of states (DOS) using X-ray Excited Auger Electron Spectroscopy (XAES) and the second derivate method of the XAES. The films were deposited by ion beam deposition and simultaneously bombarded with argon, which is responsible for the variation of the film stress, reaching extremely high values (4.5 GPa). Marked variations of the density of states of the pπ, pσ, sp, and s components were observed with increasing stress.

Effect of heat treatment on the structure and the thermoelectric properties of Sb0.9Bi1.1Te2.9Se0.1 thin films and composites based on them

This work considers the effect of vacuum annealing on the thermoelectric properties of Sb0.9Bi1.1Te2.9Se0.1 thin film and Sb0.9Bi1.1Te2.9Se0.1–C composites with various carbon contents produced by ion-beam deposition in an argon atmosphere. The electrical resistivity and the thermopower of Sb0.9Bi1.1Te2.9Se0.1–C nanocomposites are found to be dependent on not only the carbon concentration but also the type and the concentration of intrinsic point defects of the Sb0.9Bi1.1Te2.9Se0.1 solid solution, which determine the type of conductivity of Sb0.9Bi1.1Te2.9Se0.1 granules. The power factors are estimated for films of Sb0.9Bi1.1Te2.9Se0.1 solid solution and films of Sb0.9Bi1.1Te2.9Se0.1–C composites and found to have values comparable with the values for nanostructured materials on the basis of (Bi,Sb)2(Te,Se)3 solid solutions.

Nanocrystalline Porous Hydrogen Storage Based on Vanadium and Titanium Nitrides

This review summarizes results of our study of the application of ion-beam assisted deposition (IBAD) technology for creation of nanoporous thin-film structures that can absorb more than 6 wt.% of hydrogen. Data of mathematical modeling are presented highlighting the structure formation and component creation of the films during their deposition at the time of simultaneous bombardment by mixed beam of nitrogen and helium ions with energy of 30 keV. Results of high-resolution transmission electron microscopy revealed that VNxfilms consist of 150–200 nm particles, boundaries of which contain nanopores of 10–15 nm diameters. Particles themselves consist of randomly oriented 10–20 nm nanograins. Grain boundaries also contain nanopores (3–8 nm). Examination of the absorption characteristics of VNx, TiNx, and(V,Ti)Nxfilms showed that the amount of absorbed hydrogen depends very little on the chemical composition of films, but it is determined by the structure pore. The amount of absorbed hydrogen at 0.3 MPa and 20°C is 6-7 wt.%, whereas the bulk of hydrogen is accumulated in the grain boundaries and pores. Films begin to release hydrogen even at 50°C, and it is desorbed completely at the temperature range of 50–250°C. It was found that the electrical resistance of films during the hydrogen desorption increases 104times.

Long-term time dependence of internal stress in lanthanum titanium oxide (H4) optical thin films.

The time variation in the internal stress of optical thin films composed of lanthanum titanium oxide (H4) deposited by ion-beam assisted deposition (IAD) and electron beam deposition was observed over a period of 10 years after deposition, and it was found that the internal stresses in the optical thin films can be controlled by optimizing the IAD conditions. Both tensile stress and compressive stress could be created by IAD, and the chemical bonding state of Ti may affect the stress behavior. The network size of the chemical bonds may affect the stress direction.

Biased Target Ion Beam Deposition and Nanoskiving for Fabricating NiTi Alloy Nanowires

Nanoskiving is a novel nanofabrication technique to produce shape memory alloy nanowires. Our previous work was the first to successfully fabricate NiTi alloy nanowires using the top-down approach, which leverages thin film technology and ultramicrotomy for ultra-thin sectioning. For this work, we utilized biased target ion beam deposition technology to fabricate nanoscale (i.e., sub-micrometer) NiTi alloy thin films. In contrast to our previous work, rapid thermal annealing was employed for heat treatment, and the B2 austenite to R-phase martensitic transformation was confirmed using stress-temperature and diffraction measurements. The ultramicrotome was programmable and facilitated sectioning the films to produce nanowires with thickness-to-width ratios ranging from 4:1 to 16:1. Energy dispersive X-ray spectroscopy analysis confirmed the elemental Ni and Ti make-up of the wires. The findings exposed the nanowires exhibited a natural ribbon-like curvature, which depended on the thickness-to-width ratio. The results demonstrate nanoskiving is a potential nanofabrication technique for producing NiTi alloy nanowires that are continuous with an unprecedented length on the order of hundreds of micrometers.

Magnetic Properties of Fe/Ni and Fe/Co Multilayer Thin Films

In this work, the magnetic and transport properties of Fe/SiO2/Ni and Fe/SiO2/Co multilayers grown on Si/SiO2 substrates have been studied. The samples have been prepared by two-stage deposition process. In the first stage, Fe layer and SiO2 interlayer of both samples are grown by ion beam deposition technique at room temperature. Then the samples are taken out to ambient atmosphere and loaded into a pulse laser deposition (PLD) chamber. Prior to the deposition of top layer, the samples are cleaned by annealing at 150 °C. In the second stage, Ni (or Co) layer is prepared by PLD technique at room temperature. The thickness of deposited layers has been measured by Rutherford back scattering (RBS). Magnetic properties of ferromagnetic bilayers have been investigated by room-temperature ferromagnetic resonance (FMR) and vibrating sample magnetometer (VSM) techniques. Standard four-point magneto-transport measurements at various temperatures have been performed. Two-step switching in the in-plane hysteresis loops of Fe/SiO2/Ni and Fe/SiO2/Co samples is observed. A crossing in the middle of hysteresis loops of both samples points to a weak antiferromagnetic interaction between the magnetic layers of the stacks. Saturation magnetization values have been obtained from the VSM measurements of samples with DC magnetic field perpendicular to the films surface. Magneto-transport measurements have shown the predominant contribution of anisotropic magnetic resistance both at room and low temperatures. FMR studies of Fe/SiO2/Ni and Fe/SiO2/Co samples have revealed additional non-uniform (surface and bulk SWR) modes, which behavior has been explained in the framework of the surface inhomogeneity model. An origin of the antiferromagnetic interaction has been discussed.