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Materials synthesized by deposition techniques are often plagued by high levels of residual stress. While the origin and control of this stress in thin (sub-micron) films has been an active area of research, it is not clear how the results extrapolate with thickness. In the present work, in situ residual stress measurements are performed during the sputter deposition of beryllium, spanning the transition from thin to thick. Variables including sputtering gas pressure and substrate biasing are shown to strongly affect both the average and instantaneous stress levels measured during film growth. Detailed microstructural characterization is performed to assess the grain structure, surface morphology, and crystallographic growth texture of representative specimens. The microstructure is correlated with theoretical models of stress generation to interpret experimental measurements. A stress map is also constructed, generalizing the effects of processing and material parameters on stress state.

To study both the effect of Ag and the relative density on the elastic properties of nanoporous Au (np-Au) foams, partially as well as fully dealloyed np-Au samples with various ligament sizes were prepared. Additionally, Ag-coated np-Au samples were synthesized by immersing np-Au in a 1 M Ag nitrate solution, followed by drying and thermal decomposition of the deposited Ag nitrate salt to Ag, NO2, and O2. Cross-sectional analysis revealed that this method yields a homogeneous Ag distribution and that the Ag concentration can be adjusted within the range of 0 to 20 at.%. Mechanical testing was performed by depth-sensing nanoindentation. It was observed that the effect of the relative density on the elastic properties of np-Au seems to be much stronger than predicted by the Gibson and Ashby relationship: Even Ag contents as low as 1 at.% can significantly change the modulus values. On the other hand, the elastic modulus of np-Au seems to be independent of the ligament size.

Targets were fabricated at Lawrence Livermore National Laboratory and were shot on the Omega laser to study the equation of state of nanoporous copper. The targets had a planar configuration and co...

The unique properties of gold especially in low temperature CO oxidation have been ascribed to a combination of various effects. In particular, particle sizes below a few nanometers and specific particle-support interactions have been shown to play important roles. In contrast, recent reports revealed that monolithic nanoporous gold (npAu) prepared by leaching a less noble metal, such as Ag, out of the corresponding alloy can also exhibit a remarkably high catalytic activity for CO oxidation, even though no support is present. Therefore, it was claimed to be a pure and unsupported gold catalyst. We investigated npAu with respect to its morphology, surface composition, and catalytic properties. In particular, we studied the reaction kinetics for low temperature CO oxidation in detail, taking the mass transport limitation due to the porous structure of the material into account. Our results reveal that Ag, even if removed almost completely from the bulk, segregates to the surface, resulting in surface concentrations of up to 10 atom %. Our data suggest that this Ag plays a significant role in activating of molecular oxygen. Therefore, npAu should be considered a bimetallic catalyst rather than a pure Au catalyst.

Although actuation in biological systems is exclusively powered by chemical energy, this concept has not been realized in man-made actuator technologies, as these rely on generating heat or electricity first. Here, we demonstrate that surface-chemistry-driven actuation can be realized in high-surface-area materials such as nanoporous gold. For example, we achieve reversible strain amplitudes of the order of a few tenths of a per cent by alternating exposure of nanoporous Au to ozone and carbon monoxide. The effect can be explained by adsorbate-induced changes of the surface stress, and can be used to convert chemical energy directly into a mechanical response, thus opening the door to surface-chemistry-driven actuator and sensor technologies.

We review different routes for the generation of nanoporous metallic foams and films exhibiting well-defined pore size and short-range order. Dealloying and templating allows the generation of both 2D and 3D structures that promise a plasmonic response determined by material constituents and porosity. Viewed in the context of metamaterials, the ease of fabrication of samples covering macroscopic dimensions is highly promising, and suggests more in-depth investigations of the plasmonic and photonic properties of this material system for photonic applications.

A method has been developed to bond low-density nanoporous copper foam components to an aluminum substrate using solder that is sputtered onto the surfaces. After assembling the components together and heating them to melt the solder, they were joined together by a layer of solder with a thickness of less than 2 μm.

Atomic layer deposition (ALD) appears to be uniquely suited for coating substrates with ultrahigh aspect ratios (or similar 10(3)), including nanoporous solids. Here, we study the ALD of Cu and Cu3N on the inner surfaces of low-density nanoporous silica aerogel monoliths. Results show that Cu depth profiles in nanoporous monoliths are limited not only by Knudsen diffusion of heavier precursor molecules into the pores, as currently believed, but also by other processes such as the interaction of precursor and reaction product molecules with pore walls. Similar behavior has also been observed for Fe, Ru, and Pt ALD on aerogels. On the basis of these results, we discuss design rules for ALD precursors specifically geared for coating nanoporous solids.

This Feature Article reviews recent work on an optical technique for fabricating, in a single exposure step, three-dimensional (3D) nanostructures with diverse structural layouts. The approach, which we refer to as proximity field nanopatterning, uses conformable, elastomeric phase masks to pattern thick layers of transparent, photosensitive materials in a conformal contact mode geometry. Aspects of the optics, the materials, and the physical chemistry associated with this method are outlined. A range of 3D structures illustrate its capabilities, and several application examples demonstrate possible areas of use in technologies ranging from microfluidics to photonic materials to density gradient structures for chemical release and high-energy density science.

Laser experiments, such as those planned at the National Ignition Facility (NIF) and the Omega facility, use small targets with the goal of studying high-energy density physics and inertial confinement fusion. One particular application is a target with layers whose density changes in a carefully designed gradient (from 0.2 to 1.2 g/cm 3 ) for use in isentropic compression experiments (ICE). We are nondestructively determining the density of these layers using two X-ray microscopes. Because of the many interfaces that comprise the layers, a plethora of X-ray phase contrast fringes appear in the images, leading to many radiographic and tomographic artifacts which compromise the ability to infer the density of the layer. In this paper, we describe how we are attacking this problem with a variety of radiographic standards and through radiographic simulation using the HADES radiographic simulation code.

The marine atmospheric boundary layer (MABL) plays a vital role in the transport of momentum and heat from the surface of the ocean into the atmosphere. A detailed study on the MABL characteristics was carried out using high-resolution surface-wind data as measured by the QuikSCAT (Quick scatterometer) satellite. Spatial variations in the surface wind, frictional velocity, roughness parameter and drag coefficient for the different seasons were studied. The surface wind was strong during the southwest monsoon season due to the modulation induced by the Low Level Jetstream. The drag coefficient was larger during this season, due to the strong winds and was lower during the winter months. The spatial variations in the frictional velocity over the seas was small during the post-monsoon season (∼0.2 m s−1). The maximum spatial variation in the frictional velocity was found over the south Arabian Sea (0.3 to 0.5 m s−1) during the southwest monsoon period, followed by the pre-monsoon over the Bay of Bengal (0.1 to 0.25 m s−1). The mean wind-stress curl during the winter was positive over the equatorial region, with a maximum value of 1.5×10−7 N m−3, but on either side of the equatorial belt, a negative wind-stress curl dominated. The area average of the frictional velocity and drag coefficient over the Arabian Sea and Bay of Bengal were also studied. The values of frictional velocity shows a variability that is similar to the intraseasonal oscillation (ISO) and this was confirmed via wavelet analysis. In the case of the drag coefficient, the prominent oscillations were ISO and quasi-biweekly mode (QBM). The interrelationship between the drag coefficient and the frictional velocity with wind speed in both the Arabian Sea and the Bay of Bengal was also studied.

Indirectly driven double shell implosions are being investigated as a possible noncryogenic path to ignition on the National Ignition Facility. Lawrence Livermore National Laboratory has made several technological advances that have produced double shell targets that represent a significant improvement to previously fielded targets. The inner capsule is supported inside the ablator shell by SiO2 aerogel with a nominal density of 50 mg/cm3. The aerogel is cast around the inner capsule and then machined concentric to it. The seamless sphere of aerogel containing the embedded capsule is then assembled between the two halves of the ablator shell. The concentricity between the two shells has been improved to less than 1.5 μm. The ablator shell consists of two hemispherical shells that mate at a step joint that incorporates a gap with a nominal thickness of 0.1 μm. Using a new flexure-based tool holder that precisely positions the diamond cutting tool on the diamond turning machine, step discontinuities...

A comprehensive study on the relationship between yield strength, relative density and ligament sizes is presented for nanoporous Au foams. Depth-sensing nanoindentation tests were performed on nanoporous foams ranging from 20% to 42% relative density with ligament sizes ranging from 10 to 900 nm. The Gibson and Ashby yield strength equation for open-cell macrocellular foams is modified in order to incorporate ligament size effects. This study demonstrates that, at the nanoscale, foam strength is governed by ligament size, in addition to relative density. Furthermore, we present the ligament length scale as a new parameter to tailor foam properties and achieve high strength at low densities.

Recent experiments on the National Ignition Facility [M. J. Edwards et al., Phys. Plasmas 20, 070501 (2013)] demonstrate that utilizing a near-vacuum hohlraum (low pressure gas-filled) is a viable option for high convergence cryogenic deuterium-tritium (DT) layered capsule implosions. This is made possible by using a dense ablator (high-density carbon), which shortens the drive duration needed to achieve high convergence: a measured 40% higher hohlraum efficiency than typical gas-filled hohlraums, which requires less laser energy going into the hohlraum, and an observed better symmetry control than anticipated by standard hydrodynamics simulations. The first series of near-vacuum hohlraum experiments culminated in a 6.8 ns, 1.2 MJ laser pulse driving a 2-shock, high adiabat (α ~ 3.5) cryogenic DT layered high density carbon capsule. This resulted in one of the best performances so far on the NIF relative to laser energy, with a measured primary neutron yield of 1.8 X 10¹⁵ neutrons, with 20% calculated alpha heating at convergence ~27X.

Indirect-drive implosions with a high-density carbon (HDC) capsule were conducted on the National Ignition Facility (NIF) to test HDC properties as an ablator material for inertial confinement fusion. A series of five experiments were completed with $76\text{\ensuremath{-}}\ensuremath{\mu}\mathrm{m}$-thick HDC capsules using a four-shock laser pulse optimized for HDC. The pulse delivered a total energy of $1.3$ MJ with a peak power of 360 TW. The experiment demonstrated good laser to target coupling $(\ensuremath{\sim}90%)$ and excellent nuclear performance. A deuterium and tritium gas-filled HDC capsule implosion produced a neutron yield of $1.6\ifmmode\times\else\texttimes\fi{}{10}^{15}\ifmmode\pm\else\textpm\fi{}3\ifmmode\times\else\texttimes\fi{}{10}^{13}$, a yield over simulated in one dimension of $70%$.

The first hydrodynamic instability growth measurements with three-dimensional (3D) surface-roughness modulations were performed on CH shell spherical implosions at the National Ignition Facility (NIF) [G. H. Miller, E. I. Moses, and C. R. Wuest, Opt. Eng. 43, 2841 (2004)]. The initial capsule outer-surface amplitudes were increased approximately four times, compared with the standard specifications, to increase the signal-to-noise ratio, helping to qualify a technique for measuring small 3D modulations. The instability growth measurements were performed using x-ray through-foil radiography based on time-resolved pinhole imaging. Averaging over 15 similar images significantly increased the signal-to-noise ratio, making possible a comparison with 3D simulations. At a convergence ratio of ${\sim}2.4$ , the measured modulation levels were ${\sim}3$ times larger than those simulated based on the growth of the known imposed initial surface modulations. Several hypotheses are discussed, including increased instability growth due to modulations of the oxygen content in the bulk of the capsule. Future experiments will be focused on measurements with standard 3D ‘native-roughness’ capsules as well as with deliberately imposed oxygen modulations.

In this talk, we will discuss the progress towards ignition on the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL) in Northern California. We will cover the some of the setbacks encountered during the progress of the research at NIF, but also cover the great advances that have been made including the achievements of greater than unity fusion ‘fuel gain’ and alpha-heating dominated fusion plasmas. The research strategy for the future will also be discussed.

Commercial purity nanostructured titanium prepared by equal channel angular pressing plus cold rolling (grain size ∼260 nm) exhibits a nonnegligible strain hardening behavior at large compressive strains (>15%) and quasistatic loading conditions. The degree of the strain hardening increases with increasing strain rates and becomes more pronounced at dynamic loading rates. This behavior is in contrast with what we have seen so far in other nanostructured materials, where flat stress-strain curves are often seen. It was concluded from transmission electron microscopy investigations that in addition to dislocation slips, deformation twinning may have played a significant role in plastic deformation of nanostructured Ti. The structural failure behavior is in-situ recorded by a CCD camera and reasoned according to the microscopic observations.

In recently developed laser-driven shockless compression experiments an ablatively driven shock in a primary target is transformed into a ramp compression wave in a secondary target via unloading followed by stagnation across an intermediate vacuum gap. Current limitations on the achievable peak longitudinal stresses are limited by the ability of shaping the temporal profile of the ramp compression pulse. We report on new techniques using graded density reservoirs for shaping the loading profile and extending these techniques to high peak pressures.

Monolithic nanoporous copper was synthesized by dealloying Mn0.7Cu0.3 by two distinct methods: potentiostatically driven dealloying and free corrosion. Both the ligament size and morphology were found to be highly dependent on the dealloying methods and conditions. For example, ligaments from 16 nm–125 nm were obtained by dealloying either electrochemically or by free corrosion, respectively. Optimization of the starting Mn–Cu alloy microstructure allowed us to synthesize uniform porous structures; but we found cracking to be unavoidable. Despite the presence of unavoidable defects, the nanoporous material still exhibits higher than expected yield strength.

Recent nanomechanical tests on submicron metal columns and wires have revealed a dramatic increase in yield strength with decreasing sample size. Here, we demonstrate that nanoporous metal foams can be envisioned as a three-dimensional network of ultrahigh-strength nanowires, thus bringing together two seemingly conflicting properties: high strength and high porosity. Specifically, we characterized the size-dependent mechanical properties of nanoporous gold using a combination of nanoindentation, column microcompression, and molecular dynamics simulations. We find that nanoporous gold can be as strong as bulk Au, despite being a highly porous material, and that the ligaments in nanoporous gold approach the theoretical yield strength of Au.

Here the authors present current issues in understanding the mechanical behavior of nanoporous foams as a new class of high yield strength/low density materials. Gold nanoporous foams are used for a systematic study of mechanical properties since they can be synthesized with a wide range of ligaments sizes and densities. Preliminary tests demonstrate that a) Au foams have a fracture behavior dictated by the ligament size, and b) nanoporous Au is a high yield strength material.

Repeated stress relaxation tests and strain rate jump tests have been carried out over a range of deformation temperatures (77–373 K) on electrodeposited nanocrystalline Ni with an average grain size of ∼30 nm. The strain rate sensitivity, the apparent and physical activation volume, and the activation energy have been determined. The magnitude observed for these characteristic deformation parameters, as well as their temperature-dependent behavior, is very different from those of coarse-grained Ni. This suggests that the thermally activated process in nanocrystalline Ni is different from the conventional forest dislocation cutting mechanism. It is concluded that grain boundary diffusion-controlled processes such as Coble creep and grain boundary sliding can be ruled out as dominant mechanisms for the grain sizes and temperature range studied. Instead, our experimental findings and analysis suggest that the deformation kinetics are controlled by the activities of dislocations. The dominant thermally activated mechanism is suggested to originate from three possible processes, all involving interactions of mobile dislocations with grain boundaries.

Depleted uranium samples were ablated using five nanosecond pulses from a Nd:YAG laser and produced films of ∼1600 A thickness that were deposited with an angular distribution typical of a completely thermal ablation (cos1 θ). The films remained contiguous for many months in vacuum but blistered due to tensile stress induced in the films several days after being brought into air. While under vacuum (2 × 10−10 Torr base pressure) the films were allowed to oxidize from the residual gases, of which water vapor was found to be the primary oxidizer. During the oxidation, the samples were monitored with both X-ray and ultraviolet photoemission spectroscopy (XPS and UPS) and were found to oxidize following Langmuir kinetics. That a 2D-surface growth model described the oxidation indicates that, even at these low pressures, oxygen accumulation on the surface is a much faster process than diffusion into the bulk. While bulk diffusion did occur, the oxygen present at the surface saturated the measurements taken using photoemission and diffusion was difficult to observe. A method for determining oxide concentration via photoemission from the valence level, as opposed to the more conventional core levels, is also presented.

Diamond has a unique combination of physical properties for the inertial confinement fusion ablator application, such as appropriate optical properties, high atomic density, high yield strength, an...

The current point design for ignition targets for the National Ignition Facility has a beryllium ablator. As Be is essentially impermeable to hydrogen, conceptually the shell will be filled by bori...

The total electron emission yields following the interaction of “Slow (⩽2 keV/a.u.) Highly Charged Ions” (SHCI) (O 3+⋯7+ , Xe 12+⋯52+ , Au 54+⋯69+ ) with different target surfaces (highly-oriented pyrolytic graphite (HOPG), Au and SiO2) have been measured. The emission yields increase with charge state, and is found to be highest for carbon, the HOPG target, and lowest for the SiO 2 target. An empirical formula for the electron emission is including recent results from investigations of plasmon excitation following SHCI impact are used to interpret the results.

We describe a two-step dealloying/compaction process to produce nanocrystalline Au. First, nanocrystalline/nanoporous Au foam was synthesized by electrochemically driven dealloying. The resulting Au foams exhibited porosities of ∼60% with pore sizes of 40 and 100 nm and a typical grain size of

An instrument for the synthesis and analysis of nanoparticles and ultrathin films of Pu and other actinides has been constructed. To facilitate the production of nanoscale specimens of these materials, pulsed laser ablation was chosen for the deposition process. The highly toxic and radioactive nature of these materials created a challenging safety environment that needed to be addressed before any work could begin. Particular attention has been paid in this respect towards our future work with plutonium, though the design structure presented here would work equally well with other nonradioactive toxic or reactive materials. The analytical capabilities of the instrument include in situ photoelectron spectroscopy, low energy electron diffraction, scanning tunneling microscopy, and scanning tunneling spectroscopy. The instrument design and first results will be discussed.

The intense, ultra-fast electronic excitation of clean silicon (100)–(2×1) surfaces leads to the formation of silicon nanostructures embedded in silicon, which photoluminesce in the yellow-green (∼2-eV band gap). The silicon surfaces were irradiated with slow, highly charged ions (e.g. Xe44+ and Au53+) to produce the ultra-fast electronic excitation. The observation of excitonic features in the luminescence from these nanostructures has recently been reported. In this paper we report the dispersion of the excitonic features with laser excitation energy. A phonon-scattering process is proposed to explain the observed dispersion.

New emission-based MeV nuclear microscopies have been in the process of development for the past four years. These techniques all fall under the heading of ion-induced emission microscopy (I-IEM), and the first to be developed was ion-electron emission microscopy (IEEM). With I-IEM the ion beam is not focused, but instead, secondary particles emitted when a single-ion strikes the sample are projected at great magnification onto a high efficiency single particle detector generating position signals. These X and Y signals are then put into coincidence with other signals made by this same ion in a fashion completely analogous to traditional nuclear microprobe analysis. In this paper, we update the current state of I-IEMs, which currently includes IEEM and highly charged ion-secondary ion mass spectroscopy (HCI-SIMS or IIEM) and ion-photon emission microscopy. At the present time none of these microscopies have atomic resolution, but the potential exists for resolution adequate for many scientific and nanotechnology applications.

We compare deformation behavior of conventional carbon and carbon-nanotube (CNT) based aerogels with monolith densities of 30–300 mg cm −3 . Results show that CNT-based aerogels have superior elastic moduli, comparable failure stresses, and, hence, lower failure strains. The density scaling law exponents are statistically indistinguishable for both types of aerogels, suggesting the same ligaments connectivity. The superior elastic properties and lower failure strains of CNT-based aerogels are attributed to a higher stiffness of CNT-based ligaments, while comparable failure stresses are attributed to the common junction geometry. Practical implications of these findings are discussed.

We describe results from highly charged ion extraction experiments at the Electron Beam Ion Trap (EBIT) facility which is now operated at Lawrence Berkeley National Laboratory after transfer from Lawrence Livermore National Laboratory. Requirements on ion source performance for the application of highly charged ions (e.g., Xe44+) in surface analysis and materials science are discussed.

Hydrodynamic instability growth of the capsule support membranes (or “tents”) and fill tubes has been studied in spherical, glow discharge polymer plastic capsule implosions at the National Ignition Facility (NIF) [Campbell et al., AIP Conf. Proc. 429, 3 (1998)]. In NIF implosions, the capsules are supported by tents because the nominal 10-μm thick fill tubes are not strong enough to support capsules by themselves. After it was recognized that the tents had a significant impact of implosion stability, new support methods were investigated, including thicker, 30-μm diameter fill tubes and cantilevered fill tubes, as described in this article. A new “sub-scale” version of the existing x-ray radiography platform was developed for measuring growing capsule perturbations in the acceleration phase of implosions. It was calibrated using hydrodynamic growth measurements of pre-imposed capsule modulations with Legendre modes of 60, 90, 110, and 140 at convergence ratios up to ∼2.4. Subsequent experiments with 3-D ...

Several new platforms have been developed to experimentally measure hydrodynamic instabilities in all phases of indirect-drive, inertial confinement fusion implosions on National Ignition Facility. At the ablation front, instability growth of pre-imposed modulations was measured with a face-on, x-ray radiography platform in the linear regime using the Hydrodynamic Growth Radiography (HGR) platform. Modulation growth of "native roughness" modulations and engineering features (fill tubes and capsule support membranes) were measured in conditions relevant to layered DT implosions. A new experimental platform was developed to measure instability growth at the ablator-ice interface. In the deceleration phase of implosions, several experimental platforms were developed to measure both low-mode asymmetries and high-mode perturbations near peak compression with x-ray and nuclear techniques. In one innovative technique, the self-emission from the hot spot was enhanced with argon dopant to "self-backlight" the shell in-flight. To stabilize instability growth, new "adiabat-shaping" techniques were developed using the HGR platform and applied in layered DT implosions.

Hydrodynamic instability growth has been studied using three-dimensional (3-D) broadband modulations by comparing “high-foot” and “low-foot” spherical plastic (CH) capsule implosions at the National Ignition Facility (NIF) [E. M. Campbell et al., AIP Conf. Proc. 429, 3 (1998)]. The initial perturbations included capsule outer-surface roughness and capsule-mounting membranes (“tents”) that were similar to those used in a majority of implosions on NIF. The tents with thicknesses of 31-nm, 46-nm, and 109-nm were used in the experiments. The outer-surface roughness in the “low-foot” experiment was similar to the standard specification, while it was increased by ∼4 times in the “high-foot” experiment to compensate for the reduced growth. The ablation-front instability growth was measured using a Hydrodynamic Growth Radiography platform at a convergence ratio of ∼3. The dominant capsule perturbations, generated by the tent mountings, had measured perturbation amplitudes comparable to the capsule thickness with ...

Ultralow-density, ultra-high suface area Al2O3 and TiO2 bulk materials with interconnected nanotubular morphology are synthesized.

Ignition experiments have shown an anomalous susceptibility to hydrodynamic instability growth. To help understand these results, the first hydrodynamic instability growth measurements in indirectly driven implosions on the National Ignition Facility were performed at ignition conditions with peak radiation temperatures up to ∼300 eV. Plastic capsules with two-dimensional preimposed, sinusoidal outer surface modulations of initial wavelengths of 240 (corresponding to a Legendre mode number of 30), 120 (mode 60), and 80 μm (mode 90) were imploded by using actual low-adiabat ignition laser pulses. The measured growth was in excellent agreement, validating 2D hydra simulations for the most dangerous modes in the acceleration phase. These results reinforce confidence in the predictive capability of calculations that are paramount to illuminating the path toward ignition.

Alternatives to traditional nuclear microprobe analysis (NMA) emerged two years ago with the invention of ion electron emission microscopy (IEEM). With nuclear emission microscopy (NEM) the ion beam is only partially focused so as to fill the field of view of a special emission particle microscope system fitted with a single particle position sensitive detector (PSD). When a single ion strikes the sample, the emitted secondaries (e.g. electrons, photons, ions, etc.) are projected at great magnification onto this PSD where position signals are generated. These X and Y signals are then put into coincidence with other signals made by this same ion in a fashion completely analogous to traditional nuclear microprobe analysis. In this paper, an update will be given on the state of NEMs, which currently includes IEEM and highly charged ion–secondary ion mass spectroscopy (HCI–SIMS). In addition, a new type of full-field nuclear imaging is proposed: ion photon emission microscopy or IPEM.

Highly Charged Ion (HCI) Time-of-Flight (TOF) Secondary Ion Mass Spectrometry (SIMS) has been employed to analyze the changes in the surface composition of TATB caused by low energy electron, ultraviolet, and Gamma ray irradiation. Comparisons are made between canary yellow (not irradiated) TATB and TATB that has been “greened” by exposure to radiation. We ascribe the color change from yellow to green to a loss of oxygen. Another striking aspect of this study is the presence of a feature at m/z = 30 (NO+) for highly charged ion SIMS, which does not occur in singly charged ion TOF SIMS.

The emission of small (hydrogenated) carbon cluster ions CnHm + (n =2-22) upon highly charged Xeq+ (q =20-44) impact on C84 surfaces is studied by means of time-of-flight secondary ion mass spectrometry. The respective stage of hydrogenation/protonation of a certain carbon cluster ion Cn + is a strong indication for its geometrical structure. From the cluster ion yield as a function of cluster size it can be concluded, that the hydrogenation takes place after the initial carbon cluster formation. The carbon clusters seem to be emitted as an entity in agreement with “equilibrium” and “shock wave” models.

A highly charged ion based time-of-flight emission microscope has been designed, which improves the surface sensitivity of static SIMS measurements because of the higher ionization probability of highly charged ions. Slow, highly charged ions are produced in an electron beam ion trap and are directed to the sample surface. The sputtered secondary ions and electrons pass through a specially designed objective lens to a microchannel plate detector. This new instrument permits high surface sensitivity (10 10 atoms/cm 2 ), high spatial resolution (100 nm), and chemical structural information due to the high molecular ion yields. The high secondary ion yield permits coincidence counting, which can be used to enhance determination of chemical and topological structure and to correlate specific molecular species.

Electronic sputtering in the interaction of slow (v < vBohr), highly charged ions (SHCI) with solid surfaces has been subject of controversial discussions for almost 20 years. We review results from recent studies of total sputtering yields and discuss distinct microscopic mechanisms (such as defect mediated desorption, Coulomb explosions and eAects of intense electronic excitation) in the response of insulators and semiconductors to the impact of SHCI. We then describe an application of ions like Xe 44a and Au 69a as projectiles in time-of-flight secondary ion mass spectrometry for surface characterization of semiconductors. ” 2000 Elsevier Science B.V. All rights reserved.

We have measured the deposition of potential energy of slow $(\ensuremath{\sim}6\ifmmode\times\else\texttimes\fi{}{10}^{5}\mathrm{m}/\mathrm{s})$, highly charged ions in solids with an ion implanted silicon detector. A large fraction (about $35%$ or 60 keV) of the potential energy dissipated by ${\mathrm{Au}}^{69+}$ ions can be traced in electronic excitations deep $(g50\mathrm{nm})$ inside the solid. In contrast, only about $10%$ of the potential energy has been accounted for in measurements of emitted secondary particles.

We report observations of nonequilibrium charge state distributions of slow, highly charged (33+{le} q{le}75+) ions after transmission of thin carbon foils. Charge equilibration times are determined directly from the dependencies of exit charge states on projectile velocity (0.5{times}10{sup 6}{lt}v{lt}10{sup 6} m/s) and foil thickness (5{endash}10thinspthinspnm). Ions like Xe{sup 44+} and Au{sup 68+} are found to equilibrate inside of solid matter in a time of only 7thinspthinspfs. {copyright} {ital 1999} {ital The American Physical Society}

The present article reviews recent advances in the studies of the interaction of slow (v < vBohr), very highly charged ions (such as Xe 52+ and Au 69+ ) with surfaces of metals, semiconductors, and insulators (including biological materials). After a brief summary of past developments, we describe key experimental techniques for studies of secondary particle emission and the de-excitation dynamics of the highly charged ions. Recent progress in measurement and determination of the mechanisms leading to secondary electron yields, secondary ion yields and total sputtering yields will be discussed. The deexcitation dynamics are addressed in experiments on projectile neutralization and energy loss in thin films of material. We review the theoretical concepts briefly and introduce theoretical models in the discussion of experimental results. Following the presentation of fundamental studies we will address emerging applications of slow, very highly charged ions in surface analysis and surface modification. # 1999 Published by Elsevier Science Ltd. All rights reserved.

The cluster ion yields and cluster ion distribution for highly charged ion sputtering have been measured for a uranium oxide target for Xe 44+ , Au 63;66;69+ and Th 75+ incident ions. The cluster yields exhibit a power law dependence on the cluster size with exponents increasing from 4 to 2:4 with increasing primary ion charge from 44+ to 75+. The power law exponent is also correlated with the total sputter yield.

A method to prepare hierarchical porous gold monoliths was developed. Cast hollow Au/Ag spheres, templated by polystyrene beads, were dealloyed to prepare hollow nanoporous shells, and robust gold monoliths with 2% relative density were readily achieved.