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In this paper, we demonstrate a new, highly efficient method of crosslinking multilayer graphene, and create nanopores in it by its irradiation with low-energy argon cluster ions. Irradiation was performed by argon cluster ions with an acceleration energy E ≈ 30 keV, and total fluence of argon cluster ions ranging from 1 × 109 to 1 × 1014 ions/cm2. The results of the bombardment were observed by the direct examination of traces of argon-cluster penetration in multilayer graphene, using high-resolution transmission electron microscopy. Further image processing revealed an average pore diameter of approximately 3 nm, with the predominant size corresponding to 2 nm. We anticipate that a controlled cross-linking process in multilayer graphene can be achieved by appropriately varying irradiation energy, dose, and type of clusters. We believe that this method is very promising for modulating the properties of multilayer graphene, and opens new possibilities for creating three-dimensional nanomaterials.

The effectiveness of flash lamp processing and ion beam sputtering in surface cleaning of membrane foil from a Pd–Cu solid solution produced by rolling has been assessed using cyclic voltammetry and atomic force microscopy. It has been shown that it is reasonable to use cyclic voltammetry for assessing the degree of foil surface cleaning and that combined surface processing of membrane foil is effective in foil surface cleaning. Ion beam processing reproducing the surface elemental composition corresponding to the original composition of the solid solution and increasing surface roughness is a factor of 1.3 more effective than combined surface processing. [ABSTRACT FROM AUTHOR]

With high resistance against interdiffusion, electromigration, creep and fatigue, single-crystal films of refractory metals are highly desired for applications in opto- and micro-electronic devices. Their fabrication is nevertheless very challenging, primarily due to their high melting points. Requiring no external thermal input, ion-irradiation presents an alternative route for single-crystal films by converting from their polycrystalline counterparts through irradiation-induced selective grain growth. The incomplete poly- to single-crystal conversion is however a common problem which limits the application of this method. Here we use refractory W thin films, the element with the highest melting point, as a model system. We systematically investigate the influences of film microstructure (texture and grain size) and irradiation temperature (77 K and room temperature) on the evolution of selective grain growth under 4.5 MeV Au+ ion-irradiation. We find that the driving force for selective grain growth can be increased by narrowing the texture spread of the films, refining the grain size and decreasing the irradiation temperature. Following this guidance, a complete conversion of a polycrystalline W film into a single crystal is achieved. This study therefore provides insights into the mechanism of selective grain growth and proves that it is an effective technique for microstructure engineering in thin film materials. The concepts can be applied to all crystalline metal films. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Abstract Accelerator-based ion irradiation is commonly used to simulate neutron damage, in lieu of neutron irradiation due to limited availability of fast flux facilities and little to no activation of the samples. Neutron atypical effects, however, must be recognized and their impact minimized in order to achieve the most accurate microstructural evolution under ion bombardment. Mechanical property changes, which arise from the synergy of numerous radiation-induced changes, are especially susceptible to these neutron atypical effects. Of these effects, a recently studied neutron atypical effect, arising from Coulomb-drag of vacuum contaminants and subsequent compositional alteration, was shown to substantially suppress swelling. Through the use of an ion beam filtering system, the resulting void swelling was shown to closely match neutron irradiation data. In this study, the impact of compositional modification via Coulomb-drag on the mechanical property changes is examined through the use of nanoindentation on a ferritic/martensitic alloy, HT9, irradiated with and without the use of the ion beam filtering system. [ABSTRACT FROM AUTHOR]

Nanocrystalline metals generally exhibit exceptionally high strength. However, their susceptibility to grain growth restricts their applications in high temperature environments. The current study presents that nanocrystalline Cu thin films produced by ion beam assisted deposition (IBAD) are able to sustain their as-deposited microstructure and high hardness upon annealing at high temperatures. IBAD-Cu films exhibit a strong (1 1 1) fiber texture, which is caused by the ion beam induced effects of substrate cleaning, preferential damage and preferential sputtering. The microstructure of the IBAD-Cu films is stable at temperatures up to 800 °C (80% of the melting point of Cu). The hardness of the as-deposited IBAD-Cu films can reach a maximum value of 3.85 GPa. Even after annealing, their hardness is still much higher than that of the normally deposited (without ion beam) films as well as their bulk nanocrystalline counterparts before heat treatment. The excellent thermal stability of microstructure is attributed to the formation of nanometer-sized voids and their pinning effect on grain boundary migration. The kinetics of void formation, the contribution of twin boundaries and ion beam induced defects to the hardness are analyzed and discussed. The findings in this study demonstrate that IBAD is an effective method for the stabilization of microstructure and mechanical properties of nanocrystalline metal thin films. [ABSTRACT FROM AUTHOR]

The Oxide Dispersion Strengthened (ODS) materials are potential candidates as cladding tubes for Sodium-cooled Fast Reactors. The nano-oxides are finely dispersed within the grains and confer excellent mechanical properties to these alloys. Hence, assessing nano-particle stability under irradiation remains crucial to guarantee safe use of these materials. Although neutron irradiation remains a binding and challenging experimental study to conduct, difficulties can be overcome by ion beam processing. Ion beam processing of the ODS material allows to identify the radiation-induced Ostwald ripening as the mechanism governing the nano-particle response under irradiation. The result is the increase in size and a decrease in density of the finely dispersed Y2Ti2O7 nano-particles. Under neutron irradiation, radiation-induced Ostwald ripening appears to be less effective since a slight growth of nano-particles is observed. Further, our approach shows that nanoparticle growth kinetics should scale as φ1/3, φ being the radiation flux. This suggests that the low irradiation flux is at the origin of the slower growth kinetics of the neutron irradiated particles. Both neutron and ion irradiation induce a modification of the nanoparticles/matrix interfaces which are generally flat and sharp prior to irradiation and present steps after irradiation. This could alter the nano-particle coarsening during irradiation. [ABSTRACT FROM PUBLISHER]

For a better understanding of the local fracture behavior of semi-brittle materials, we carried out bending experiments on notched microcantilevers of varying sizes in the micrometer range using NiAl single crystals. Smaller and larger beams were milled with a focused ion beam in the so-called “soft” <110> and “hard” <100> orientation and were tested in situ in a scanning electron microscope and ex situ with a nanoindenter, respectively. The measurements were evaluated using both linear-elastic fracture mechanics and elastic–plastic fracture mechanics. The results show that (i) the fracture toughness is in the same range as the macroscopically determined one which is around 3.5 MPa$\sqrt {\rm{m}}$ for the soft orientation and around 8.5 MPa$\sqrt {\rm{m}}$ for the hard orientation, that (ii) there is a strong influence of the anisotropic behavior of NiAl on the fracture toughness values, and that (iii) the J-integral technique is the most accurate quantification method. [ABSTRACT FROM PUBLISHER]

Abstract: Vaporized water clusters were produced by an adiabatic expansion phenomenon, and various substrates such as Si(100), SiO2, polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), and polycarbonate (PC) were irradiated by water cluster ion beams. The sputtered depth increased with increasing acceleration voltage, and the sputtering rate was much larger than that obtained using Ar monomer ion irradiation. The sputtering yield for PMMA was approximately 200 molecules per ion, at an acceleration voltage of 9kV. X-ray photoelectron spectroscopy (XPS) measurements showed that high-rate sputtering for the PMMA surface can be ascribed to the surface erosion by the water cluster ion irradiation. Furthermore, the micropatterning was demonstrated on the PMMA substrate. Thus, the surface irradiation by water cluster ion beams exhibited a chemical reaction based on OH radicals, as well as excited hydrogen atoms, which resulted in a high sputtering rate and low irradiation damage of the substrate surfaces. [Copyright &y& Elsevier]

Thermal conductivity is a familiar property of materials: silver conducts heat well, and plastic does not. In recent years, an interdisciplinary group of materials scientists, engineers, physicists, and chemists have succeeded in pushing back long-established limits in the thermal conductivity of materials. Carbon nanotubes and graphene are at the high end of the thermal conductivity spectrum due to their high sound velocities and relative lack of processes that scatter phonons. Unfortunately, the superlative thermal properties of carbon nanotubes have not found immediate application in composites or interface materials because of difficulties in making good thermal contact with the nanotubes. At the low end of the thermal conductivity spectrum, solids that combine order and disorder in the random stacking of two-dimensional crystalline sheets, so-called “disordered layered crystals,” show a thermal conductivity that is only a factor of 2 larger than air. The cause of this low thermal conductivity may be explained by the large anisotropy in elastic constants that suppresses the density of phonon modes that propagate along the soft direction. Low-dimensional quantum magnets demonstrate that electrons and phonons are not the only significant carriers of heat. Near room temperature, the spin thermal conductivity of spin-ladders is comparable to the electronic thermal conductivities of metals. Our measurements of nanoscale thermal transport properties employ a variety of ultrafast optical pump-probe metrology tools that we have developed over the past several years. We are currently working to extend these techniques to high pressures (60 GPa), high magnetic fields (5 T), and high temperatures (1000 K). [ABSTRACT FROM AUTHOR]

We developed a polyatomic cluster ion beam system for materials processing, and polyatomic clusters of materials such as alcohol and water were produced by an adiabatic expansion phenomenon. In this article, cluster formation is discussed using thermodynamics and fluid dynamics. To investigate the interactions of polyatomic cluster ions with solid surfaces, various kinds of substrates such as Si(100), SiO2, mica, polymethyl methacrylate, and metals were irradiated by ethanol, methanol, and water cluster ion beams. To be specific, chemical reactions between radicals of polyatomic molecules and surface Si atoms were investigated, and low-irradiation damage as well as high-rate sputtering was carried out on the Si(100) surfaces. Furthermore, materials processing methods including high-rate sputtering, surface modification, and micropatterning were demonstrated with ethanol and water cluster ion beams. [ABSTRACT FROM PUBLISHER]

Abstract: Sputtering solid surfaces with low energy ions is well-known to induce a wide array of nanoscale pattern forming behavior (sputter ripples). A simple continuum model originally developed by Bradley and Harper (BH) provides a useful framework that can qualitatively explain multiple types of patterning behavior seen experimentally and their relationship to the ion beam and material parameters. The basis of the model is a dynamic competition between roughening by ion bombardment and smoothing by surface transport that leads to the growth of roughness with a preferred periodicity on the surface. However, there are many experimental results that cannot be accounted for within this framework and additional physical mechanisms are discussed that may close the gap in our understanding. [Copyright &y& Elsevier]

Abstract: Post-deposition ion bombardment can be employed to convert polycrystalline films into single crystals through a process of selective grain growth. Here we report a new technique that enables selective grain growth in self-ion bombarded gold films – a system in which the formation of large single crystal domains was prevented by the occurrence of ion-induced texture rotation. Our findings suggest that the extent of the texture rotation is a function of the ion fluence and the film initial microstructure. [Copyright &y& Elsevier]

Abstract: The deformation behavior of single- and polycrystalline gold pillars with diameters in the 150–1000nm range was investigated at room temperature by compression testing. The pillars were produced by nanoimprinting and focused ion-beam (FIB) milling, and characterized by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). No significant differences in the flow strength level or scaling behavior were observed when nanoimprinted pillars were compared with FIB-milled pillars with comparable diameters. These observations justify the use of FIB milling for the study of scaling behavior in this material system. Weibull statistics were used to analyze the distribution of strength levels, and a minimum in experimental scatter was identified at intermediate pillar size in comparison with their microstructural length scales. [Copyright &y& Elsevier]

Abstract: Common failure mechanisms in microelectronics, such as electromigration, creep and fatigue, can be positively influenced by microstructure optimization. In this paper a combination of post-deposition heat treatment and self-ion bombardment is proposed as a valid candidate to gain control over the microstructure of (111) fiber textured thin silver films. Irradiation can induce a strong in-plane texture and hence lead to biaxially textured films through a process of selective grain growth. Moreover, we report microstructural stability of the irradiated regions over a wide range of temperatures (up to 600°C), in contrast to non-irradiated portions of the film, which underwent abnormal growth of the (100) out-of-plane oriented grains, and a consequent texture change, at temperatures as low as 195°C. The thermal stress induced in the film upon heat treatment was quantified in situ and its role in texture change elucidated. [ABSTRACT FROM AUTHOR]

Abstract: A series of functionally graded hydroxyapatite (FGHA) coatings incorporated with various percentages of silver were deposited on titanium substrates using ion beam-assisted deposition. The analysis of the coating’s cross-section using transmission electron microscopy (TEM) and scanning transmission electron microscopy equipped with energy dispersive X-ray spectroscopy has shown a decreased crystallinity as well as a distribution of nanoscale (10–50nm) silver particles from the coating/substrate interface to top surface. Both X-ray diffraction and fast Fourier transforms on high-resolution TEM images revealed the presence of hydroxyapatite within the coatings. The amount of Ag (wt.%) on the outer surface of the FGHA, as determined from X-ray photoelectron spectroscopy, ranged from 1.09 to 6.59, which was about half of the average Ag wt.% incorporated in the entire coating. Average adhesion strengths evaluated by pull-off tests were in the range of 83±6 to 88±3MPa, which is comparable to 85MPa for FGHA without silver. Further optical observations of failed areas illustrated that the dominant failure mechanism was epoxy failure, and FGHA coating delamination was not observed. [Copyright &y& Elsevier]

ZrO2 dielectric layers were prepared by a two-step process, a deposition of pure Zr film with and without a negative substrate bias voltage and a subsequent oxidation of the Zr films. We focused on the effect of the negative substrate bias voltage on the Zr film deposition and the subsequent oxidation of the Zr films. As a result, the Zr film deposited at the substrate bias voltage of −50 V (Vs = −50 V) was found to have a high intensity peak of Zr (100) and a uniform and smooth surface. From the capacitance-voltage and current-voltage measurements of the ZrO2 films, a high dielectric constant of 21 and the equivalent oxide thickness (EOT) of 2.6 nm were obtained on the oxidation layer of the Zr film deposited at Vs = −50 V. On the other hand, a low dielectric constant of 15 and the EOT of 3.6 nm was obtained on that of the Zr film deposited at Vs = 0 V. The leakage current density of the ZrO2 film (Vs = −50 V) was 5.69×10−4 A/cm2, and this value was much lower than the 1.21×10−4 A/cm2 for the ZrO2 film (Vs = 0 V). It was found that the two-step process by subsequent oxidation after film deposition using a negative substrate bias voltage is useful for obtaining high-quality dielectric layers. [ABSTRACT FROM AUTHOR]

Abstract: The mechanical behavior of interfaces between silicon oxide and metallic thin films is investigated using an alternative approach which is based on the miniaturized cantilever deflection technique (Weihs et al., 1988 ). The critical energy release rates for three different silicon oxide/metal systems are determined and the results are discussed in this paper. The technique suggested may be applicable with high spatial resolution for a wide variety of structured thin film systems. [Copyright &y& Elsevier]

Abstract: We present quasi-static, room temperature compression data for Pd40Ni40P20 metallic glasses, with specimen sizes ranging from the submicron to several millimeters in diameter. We observe no change in deformation mode over this range. At all sizes, plastic flow is localized in shear bands, which are accompanied by sudden strain bursts. This metallic glass shows only a modest increase in strength in going from bulk to micrometer-sized specimens. We show that stress gradients in tapered specimens can complicate measurement of the yield strength of metallic glasses in microcompression. Estimates of yield strength based on the minimum cross-sectional area implicitly assume that yielding is controlled by a maximum effective shear stress criterion. An alternative is the shear plane yield criterion, in which the minimum shear stress on the shear band trajectory determines yield. Application of this criterion in tapered microspecimens reinforces the notion that metallic glasses possess relatively size-independent mechanical properties. [Copyright &y& Elsevier]

Abstract: Periodic arrays of ferromagnetic structures with micrometer and submicrometer lateral sizes have been prepared at the surface of a paramagnetic austenitic stainless steel by means of ion beam nitriding through different types of shadow masks (such as transmission electron microscopy grids or self-assembled porous alumina membranes). This method takes advantage of the formation of the ferromagnetic supersaturated nitrogen solid solution γ N phase (i.e., expanded austenite) upon nitriding at moderate temperatures. The local character of the induced ferromagnetism is confirmed by magneto-optical Kerr effect measurements together with magnetic force microscopy imaging. Furthermore, the influence of the nitriding temperature and time on the induced ferromagnetic and structural properties has been analyzed. [Copyright &y& Elsevier]

A focused ion beam technique that allows the characterization of spatial residual stresses in near-surface structures with a depth resolution on the nanoscale and a lateral resolution in the micron range is introduced. It is based on the fabrication of a micro-cantilever and the gradual removal of the residually stressed material, which leads to a change in the measured deflection. The method is presented by determining a spatial stress distribution around a scratch in an 840nm thin Ni film on Si. [Copyright &y& Elsevier]

We present quasi-static, room temperature compression data for Pd40Ni40P20 metallic glasses for both bulk and microscale specimens. At all sizes, plastic flow is localized in shear bands which are accompanied by sudden strain bursts in the microscale tests. We show a modest (∼9%) increase in the 0.2% offset yield strength in going from bulk specimens to the smallest measured (∼2μm), and attribute this increase to the effect of defects on shear band initiation, rather than to an intrinsic length scale dependence of plastic deformation. [Copyright &y& Elsevier]

Abstract: Co metastable structures are formed in Co–Ag alloy films with the aid of glancing incident ions during deposition. The structures of Co are characterized by X-ray absorption near-edge structure (XANES) spectroscopy at the Co K-edge. The results indicate that two kinds of Co phases coexist in every film. One is α-Co or β-Co and the other is named fcc-II with a =4.06Å. It is thought that the stress between Co and Ag clusters induces the formation of β-Co and the fcc-II phase. The role of glancing incident ions is to trigger a collision cascade on the surface and to facilitate both thermodynamics and kinetics aspects of cluster mixing. [Copyright &y& Elsevier]

Abstract: Sputtering by collimated low energy ion beams can lead to a wide range of spontaneous pattern formation on different surfaces under different conditions. We describe a kinetic phase diagram as a way to organize pattern formation behavior observed on Cu(001) surfaces as a function of flux and temperature. The characteristics of pattern formation in several kinetic regimes are described, and the transitions between the different regimes are discussed in terms of the competition between mechanisms for surface roughening and smoothing. [Copyright &y& Elsevier]

Abstract: The formation of ion-induced ripples on Cu(001) surfaces is the result of competing kinetic mechanisms for roughening and smoothing. A rate equation based on the Bradley–Harper instability and the effect of barriers to interlayer transport enables us to identify different regimes of pattern formation corresponding to different processing conditions. We use this approach to interpret measurements of ripple formation on Cu(001) surfaces. The temperature and flux dependence of the wavelength is used to determine the kinetic regime for production and transport of mobile surface defects. [Copyright &y& Elsevier]

Polymer substrates with tailored surface properties are increasingly desired in tissue engineering studies. In this work a procedure was developed to improve the use of a polycaprolactone (PCL) films for these applications. Ion beam treatments of PCL films activated the surface by different modification mechanisms. The PCL activation conditions were studied using several techniques to evaluate the modifications of the films surface. The results obtained from FTIR, X-ray photoelectron spectroscopy and atomic force microscopy indicated that a gradual modification of the composition and microstructure of the films was induced by the process. The modified surfaces induced shifts in Zeta potential vs pH curves and increased the polar component of the surface free energy. The protein adsorption characteristics of the PCL films were monitored by microgravimetric techniques confirming that the ion beam treatment was able to trigger bovine serum albumin adsorption onto the treated PCL surface. [ABSTRACT FROM AUTHOR]

Sputtering by collimated low energy ion beams can spontaneously create periodic structures on many surfaces. The pattern results from the balance between roughening by atom removal and smoothing, typically by surface diffusion. Experiments on a number of surfaces are considered in terms of linear and non-linear models of surface evolution. [Copyright &y& Elsevier]

Smoothing effect is one of the advantages of cluster ion beam. It is important to estimate an ion dose to achieve required surface smoothness. The smoothing rate with cluster ion beam depends on surface profiles. In this work, modeling of surface smoothing process with cluster ion beams was examined. Ar cluster ions with an energy of 20 keV was irradiated on rough Si Surface. Fast Fourier transform was applied to atomic force microscope data of 100 × 100 μm2, and power spectra were calculated. Smoothing rate depends on the wave number as well as the ion dose. Relationship between smoothing rate and wave number was derived. The surface smoothing process was modeled with the use of the wave number dependence of the smoothing rate. The calculated and the experimental surface profiles are in good agreements. [Copyright &y& Elsevier]

Ultraslow single- and multicharged ions (USMCI) have small kinetic energy compared with their potential energies. They can be used for surface preparation at room temperature, to engineer the top atomic layers of surfaces without modifying the substrate below, in processes such as ultrathin film growths, etching, deposition, or nanostructures fabrication. The energy for the reaction is brought to the surface through the USMCI potential energy, which can be controlled by varying the ion charge. The USMCI kinetic energy is so small that they do not penetrate below the surface. We have used various USMCI under low pressures of O2 (between 10−9 and 5×10−6 Torr) to grow ultrathin films of SiO2 on Si wafers, from 0.3 to 2.3 nm with a resolution of 0.1 nm and a uniformity of ±0.1 nm. To evaluate the layers and optimise this process, we have analysed the surfaces by Fourier transform infrared spectroscopy, Auger electron spectroscopy, spectroscopic ellipsometry, transmission electron microscopy, X-ray photoelectron spectroscopy and surface charge analysis. [Copyright &y& Elsevier]

In this paper, we demonstrate a new, highly efficient method of crosslinking multilayer graphene, and create nanopores in it by its irradiation with low-energy argon cluster ions. Irradiation was performed by argon cluster ions with an acceleration energy E ≈ 30 keV, and total fluence of argon cluster ions ranging from 1 × 10 9 to 1 × 10 14 ions/cm 2 . The results of the bombardment were observed by the direct examination of traces of argon-cluster penetration in multilayer graphene, using high-resolution transmission electron microscopy. Further image processing revealed an average pore diameter of approximately 3 nm, with the predominant size corresponding to 2 nm. We anticipate that a controlled cross-linking process in multilayer graphene can be achieved by appropriately varying irradiation energy, dose, and type of clusters. We believe that this method is very promising for modulating the properties of multilayer graphene, and opens new possibilities for creating three-dimensional nanomaterials.