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There is a pressing need to discover magneto-optical materials and devices with better performance and lower cost that operate at telecommunication wavelengths. Here we report the discovery of giant negative nonlinear refraction and nonlinear Faraday rotation at 1550 nm using an array of bimetallic Fe-Ag nanopyramids. This system exhibited a very large third order nonlinear refractive index (n2 = -2.32 cm2/GW) and nonlinear figure of merit (F = 2.3). The same system also exhibited an extraordinarily large magneto-optical susceptibility (χi4 = 6.5 × 10-12 esu) and photoinduced nonlinear Faraday rotation up to 2.5 radian/μm at a magnetic field of 0.5 T. The nonlinear response was dependent on the degree of overlap of the Fe nanopyramid on the Ag nanopyramid which influences the strength of plasmon induced dipoles on the Ag nanopyramid. This nanoscale system opens up a rich new set of possibilities in utilizing magneto-plasmonic materials to miniaturize future multifunctional devices at telecommunication wavelengths.

A room temperature amorphous ferromagnetic oxide semiconductor can substantially reduce the cost and complexity associated with utilizing crystalline materials for spintronic devices. We report a new material (Fe0.66Dy0.24Tb0.1)3O7-x (FDTO), which shows semiconducting behavior with reasonable electrical conductivity (~500 mOhm-cm), an optical band-gap (2.4 eV), and a large enough magnetic moment (~200 emu/cc), all of which can be tuned by varying the oxygen content during deposition. Magnetoelectric devices were made by integrating ultrathin FDTO with multiferroic BiFeO3. A strong enhancement in the magnetic coercive field of FDTO grown on BiFeO3 validated a large exchange coupling between them. Additionally, FDTO served as an excellent top electrode for ferroelectric switching in BiFeO3 with no sign of degradation after ~1010 switching cycles. RT magneto-electric coupling was demonstrated by modulating the resistance states of spin-valve structures using electric fields.

In this work, we demonstrate how to suppress the shape instability of silver (Ag) nanotriangular pyramids following high-temperature annealing without a coating or encapsulation, thus producing a more stable optical plasmonic system. Nanosphere lithography (NSL) was used to fabricate large-area arrays of nanotriangular pyramids of Ag on glass substrates. By using a combination of morphology and spectroscopic studies it was found that exposure of this system to high temperatures of 473 K and beyond in air led to a rapid change in nanostructure shape, and thus, the surface area, with a substantial change to the original plasmonic character. On the other hand, NSL nanotriangular pyramids made from bilayers of Ag on Co or Co on Ag showed much smaller changes in shape and area following annealing up to 573 K in air. In the case of pure Ag, the NSL nanotriangular pyramid changed into a more spherical shape with an overall decrease of ∼24% in its surface area following annealing at 573 K. This lead to a large blue shift of over ∼287 nm or ∼39% in the location of the dipolar plasmonic resonance. On the other hand, the triangular shape of Ag was retained in both the metal bilayer cases, with much smaller area changes of ∼10 and ∼9%, for the Ag deposit when on Co and when under Co, respectively. Consequently, the plasmonic shifts were substantially smaller, of ∼65 nm or about 9%, in these bilayer systems. The mechanism for this stabilization was attributed to the higher surface energy of Co and much lower diffusivity of Co as well as Ag on Co that resulted in an anchoring of the Ag shape to its original state. The plasmonic quality factor for the bimetal NSL nanotriangular pyramids also showed substantially improved stability over pure Ag, further indicating that this anchoring approach is a viable pathway to produce pristine Ag surfaces for high-temperature plasmonic applications.

Plasmonic metal nanostructures have been known to tune optoelectronic properties of fluorophores. Here, we report the first-ever experimental observation of plasmon-induced photocurrent enhancements from Photosystem I (PSI) immobilized on Fischer patterns of silver nanopyramids (Ag-NP). To this end, the plasmonic peaks of Ag-NP were tuned to match the PSI absorption peaks at ∼450 and ∼680 nm wavelengths. Specifically, the plasmon-enhanced photocurrents indicate enhancement factors of ∼6.5 and ∼5.8 as compared to PSI assembly on planar Ag substrates for nominal excitation wavelengths of 660 and 470 nm, respectively. The comparable enhancement factors from both 470 and 660 nm excitations, in spite of a significantly weaker plasmon absorption peak at ∼450 nm for the Ag-NP structures, can be rationalized by previously reported excessive plasmon-induced fluorescence emission losses from PSI in the red region as compared to the blue region of the excitation wavelengths.

One dimensional (1D) magnetic nanowires show unique magnetic behaviors, such as large coercivity and high remanence, in comparison to the bulk and thin film materials. Here, planar arrays of Co nanowires, nanorods and nanoparticles were fabricated from thin Co films by a nanosecond pulsed laser interference irradiation technique. Magnetic force microscopy (MFM) and surface magneto-optic Kerr effect (SMOKE) techniques were used to study the individual and average magnetic properties of the nanostructures. Magnetic domain orientation was found to depend on the in-plane aspect ratio of the nanostructure. The magnetic orientation was out-of-plane for in-plane aspect ratio ranging from 1 to 1.4 and transitioned to an in-plane orientation for aspect ratios greater than 1.4 (such as in nanorods and nanowires). Our results also showed that polycrystalline Co nanowires showed much higher coercivity and remanence as compared to bulk and thin film materials, as well as shapes with smaller aspect ratio. This result was attributed mainly to the shape anisotropy. This study demonstrated that nanosecond pulsed laser synthesis is capable of fabricating various nanostructures in a simple, robust and rapid manner and SMOKE is a reliable technique to rapidly characterize such magnetic nanostructures.

In this article, we show nanosecond switchable localized surface plasmon resonance (LSPR) dipole and quadrupole modes from silver (Ag) nanoparticles on fused quartz substrates. Nearly spherical Ag nanoparticles (contact angle of ~166/+-9) were synthesized by Ultra Violet (UV) laser dewetting of Ag thin films under a glycerol fluid environment. Under a single 9 nanosecond laser pulse irradiation of the particles in air, the particles were changed into a near-hemispherical shape (with contact angle of ~103 /+-7). The resulting changes in the particle contact area and volume fraction in the dielectric media resulted in substantial shift in the wavelength and intensity of the dipolar and quadrupolar LSPR modes to the violet side of visible spectrum. This switching of the plasmon resonance wavelength position could be repeated over multiple cycles by resetting the contact angle by laser re-irradiation under glycerol. This reusable nanoparticle system with reversible plasmonic properties within nanosecond time scales could prove a cost-effective way of designing high-speed plasmonic devices in desired wavelength regions.

Nanosecond pulsed laser melting of ultrathin gold films immersed inside glycerol-water mixtures assemble into monomodal sized nanoparticles with small spacing. This is a result of the large vapor pressure gradient created at the metal-fluid interface.

Interaction of photons with matter at length scales far below their wavelengths has given rise to many novel phenomena, including localized surface plasmon resonance (LSPR). However, LSPR with narrow bandwidth (BW) is observed only in a select few noble metals, and ferromagnets are not among them. Here, we report the discovery of LSPR in ferromagnetic Co and CoFe alloy (8% Fe) in contact with Ag in the form of bimetallic nanoparticles prepared by pulsed laser dewetting. These plasmons in metal-ferromagnetic nanostructures, or ferroplasmons (FP) for short, are in the visible spectrum with comparable intensity and BW to those of the LSPRs from the Ag regions. This finding was enabled by electron energy-loss mapping across individual nanoparticles in a monochromated scanning transmission electron microscope. The appearance of the FP is likely due to plasmonic interaction between the contacting Ag and Co nanoparticles. Since there is no previous evidence for materials that simultaneously show ferromagnetism and such intense LSPRs, this discovery may lead to the design of improved plasmonic materials and applications. It also demonstrates that materials with interesting plasmonic properties can be synthesized using bimetallic nanostructures in contact with each other.

Various forms of Si including amorphous Si (a-Si) are important photovoltaic (PV) materials. However, in order to improve the cost-to-performance aspects of Si solar cells, such as by enabling ultrathin (

Reliable and cost-effective techniques to process surface nanoscale metallic structures with controllable and complex nanomorphologies is important toward progress in technologies related to sensing, energy harvesting, information storage, and computing. Here we discuss how pulsed laser melting and the ensuing self-organization by dewetting of ultrathin films can be utilized to fabricate various nanomorphologies in a predictable manner. Ultrathin metal films (1–100 nm) on inert substrates like SiO2 are generally unstable, with their free energy resembling that of a spinodal system. The energy rate theory of self-organization, which is based on balancing the rate of thermodynamic free energy change to the rate of energy dissipation, predicts the appearance of characteristic length scales. This is borne out in experiments of nanosecond pulsed laser melting of a variety of metal films. We review this laser-based self-organization technique with various examples from the behavior of Ag and Co metals on SiO2 substrates. Specifically, film thickness and film roughness can be used to control dewetting length scales, whereas knowledge of the intermolecular forces responsible for the free energy of the system control the type of morphology. Furthermore, novel dewetting is observed that is attributable to nanoscale heating effects resulting from the thickness-dependent pulsed laser heating. These results help elucidate the basic mechanisms of pulsed laser induced dewetting of metal films, but they also provide potential routes for cost-effective nanomanufacturing of metallic surfaces for applications in sensing, energy harvesting, and information processing.

Fast, sensitive and discriminating detection of hydrogen at room temperature is crucial for storage, transportation, and distribution of hydrogen as an energy source. One dimensional nanowires of SnO2 are potential candidates for improved H2 sensor performance. The single directional conducting continuous nanowires can decrease electrical noise, and their large active surface area could improve the response and recovery time of the sensor. In this work we discuss synthesis and characterization of nanowire arrays made using nanosecond ultraviolet wavelength (266 nm) laser interference processing of ultrathin SnO2 films on SiO2 substrates. The laser energy was chosen to be above the melting point of the films. The results show that the final nanowire formation is dominated by preferential evaporation as compared to thermocapillary flow. The nanowire height (and hence wire aspect ratio) increased with increasing initial film thickness h0 and with increasing laser energy density Eo. Furthermore, a self-limiting effect was observed where-in the wire formation ceased at a specific final remaining thickness of SnO2 that was almost independent of h0 for a given Eo. To understand these effects, finite element modeling of the nanoscale laser heating was performed. This showed that the temperature rise under laser heating was a strong non-monotonic function of film thickness. As a result, the preferential evaporation rate varies as wire formation occurs, eventually leading to a shut-off of evaporation at a characteristic thickness. This results in the stoppage of wire formation. This combination of nanosecond pulsed laser experiments and thermal modeling shows that several unique synthesis approaches can be utilized to control the nanowire characteristics.

Ultrathin discontinuous films from a stoichiometric target of TiB2 have been deposited on Si(001) at room temperature via pulsed laser ablation. The resulting film morphology and nanostructure was studied using transmission electron microscopy. The typical results were that the films consisted of two distinct morphologies: areas of polycrystalline nanoparticles with the hexagonal TiB2 structure and smaller areas with epitaxial grains. The resulting epitaxial phase was verified to be cubic with a lattice parameter of 3.83 A and aligned with TiBx(001) // Si(001), with x ∼ 2. We suggest that the cubic phase forms because of minimization of energy as a consequence of the excellent epitaxial matching of the film phase to Si(001).

An approach to pattern directly thin films of various materials deposited by different physical vapor deposition methods is presented. Co and Ag films deposited by pulsed laser deposition and e-beam evaporation, respectively, were fabricated into 650- and 1000-nm-spaced parallel stripes on Si(100) surfaces by simultaneous two-beam ultraviolet laser interference irradiation of the substrate surface during deposition. The resulting morphology consists of 1- to 2-nm-height stripes, which have the same direction and spacing as the interference fringes. This approach has the potential to allow long-range ordering of well-defined patterns over large areas because the spacing and geometrical patterns are defined by the laser interference. Furthermore, the fact that this method works for different materials and does not require any lithography masks, etching steps, or substrate prepatterning, makes it promising as a simple and economical lateral patterning approach.

In this work we report the discovery of phase array self-assembly, a new way to spontaneously make periodic arrangements of metal nanoparticles. An initially random arrangement of gold (Au) or silver (Ag) nanoparticles on SiO2/Si substrates was irradiated with linearly polarized (P) laser light in the presence of a dc electric (E) field applied to the insulating substrate. For E fields parallel to the laser polarization (E||P), the resulting periodic ordering was single-crystal like with extremely low defect density and covered large macroscopic areas. The E field appears to be modifying the phase between radiation scattered by the individual nanoparticles thus leading to enhanced interference effects. While phase array behavior is widely known in antenna technology, this is the first evidence that it can also aid in nanoscale self-assembly. These results provide a simple way to produce periodic metal nanoparticles over large areas.

Plasmonic nanoparticles are amongst the most effective ways to resonantly couple optical energy into and out of nanometer sized volumes. However, controlling and/or tuning the transfer of this incident energy to the surrounding near and far field is one of the most interesting challenges in this area. Due to the dielectric properties of metallic silver (Ag), its nanoparticles have amongst the highest radiative quantum efficiencies (η), i.e., the ability to radiatively transfer the incident energy to the surrounding. Here we report the discovery that bimetallic nanoparticles of Ag made with immiscible and plasmonically weak Co metal can show comparable and/or even higher η values. The enhancement is a result of the narrowing of the plasmon bandwidth from these bimetal systems. The phenomenological explanation of this effect based on the dipolar approximation points to the reduction in radiative losses within the Ag nanoparticles when in contact with cobalt. This is also supported by a model of coupling between poor and good conductors based on the surface to volume ratio. This study presents a new type of bandwidth engineering, one based on using bimetal nanostructures, to tune and/or enhance the quality factor and quantum efficiency for near and far-field plasmonic applications.

An approach to directly make controlled nanostructured films in situ with physical vapor thin film deposition is presented. Co films were formed into lines with 3.2±0.8 nm thickness and were regularly spaced 550±20 nm apart on a Si(100) surface. The line pattern results during pulsed laser deposition of Co simultaneous with two-beam laser interference irradiation of the Si surface. Preliminary results indicate that preferential evaporation is not the primary mechanism. This patterning is likely due to anisotropic diffusion modified growth of Co under thermal gradients. This one step patterning process, without need of any pre- or post-patterning of the substrate or film, is promising as an economical and simple nanostructured film fabrication approach.

We demonstrate a promising synthesis route based on pulsed laser dewetting of bilayer films (Ag and Co) to make bimetallic nanoparticle arrays. By combining experiment and theory we establish a parameter space for the independent control of composition and diameter for the bimetallic nanoparticles. As a result, physical properties, such as the localized surface plasmon resonance (LSPR), that depend on particle size and composition can be readily tuned over a wavelength range one order of magnitude greater than for pure Ag nanoparticles. The LSPR detection sensitivity of the bimetallic nanoparticles with narrow size distribution was found to be high—comparable with pure Ag (∼60 nm/RIU). Moreover, they showed significantly higher long-term environmental stability over pure Ag.

Measurements of the binding energy (Eb) of vacancies to vacancy clusters formed in silicon following high-energy ion implantation are reported. Vacancy clusters were created by 2 MeV, 2×1015 cm−2 dose Si implant and annealing. To prevent recombination of the excess vacancies (Vex) with interstitials from the implant damage near the projected range (Rp), a Si-on-insulator substrate was used such that the Rp damage was separated from the Vex by the buried oxide (BOX). Two Vex regions were observed: one in the middle of the top Si layer (V1ex) and the other at the front Si/BOX interface (V2ex). The rates of vacancy evaporation were directly measured by Au labeling following thermal treatments at temperatures between 800 and 900 °C for times ranging from 600 to 1800 s. The rate of vacancy evaporation from V2ex was observed to be greater than from V1ex. The binding energy of vacancies to clusters in the middle of the silicon top layer was 3.2±0.2 eV as determined from the kinetics for vacancy evaporation.

Efficient and dependable characterization methods of magnetic-plasmonic nanostructures are essential towards the implementation of new nanoscale materials in magneto-optical applications. Surface magneto-optic Kerr effect (SMOKE) is a powerful characterization technique, because of its simplicity and high sensitive to even monolayer thick magnetic materials. It relies on the measurement of polarization and absorption changes of reflected light in the presence of a magnetic field. While SMOKE has been applied in the past to investigate the magnetic information of continuous films, there is little work on applying it to characterize arrays of nanoparticles with variable magnetic and optical properties. Here, we have used it to investigate the magnetic behavior of nanoparticle arrays made by nanosecond pulsed laser self-organization. This technique produces an array of single-domain magnetic nanoparticles with size-dependent magnetic orientation. Nanoparticle arrays of Co and Ni were prepared on SiO2 substrates. SMOKE measurements were performed for a variety of different particle sizes and material. Systematic differences in saturation and coercivity were observed for the different samples. These results demonstrated that SMOKE is a reliable technique to rapidly characterize the magnetic behavior of nanoparticle arrays.

Metallic nanoparticles embedded in dielectrics permit enhanced capture of light at specific wavelengths through excitation of plasmons, i.e. the quanta of coherent and collective oscillations of large concentrations of nearly free electrons. In order to maximize the potential of such enhanced absorption in useful tasks, such as the generation of carriers in photocatalysts and semiconductors, it is important to be able to predict and design plasmonic nanocomposites with desired wavelength-dependent optical absorption. Recently, a mixing approach formulated by Garcia and co-workers [Phys. Rev. B, 75, 045439 (2007)] has been successfully applied to model the experimentally measured broadband optical absorption for ternary nanocomposites containing alloys or mixtures of two metals (from Ag, Au or Cu) in SiO dielectric. In this work we present the broadband optical behavior of important optical coating dielectrics (SiN and SiO) and photocatalyst (TiO) containing various configuration of nanoparticles of Al, Au, Ag, or Cu. The spectral behavior of various combinations of the metallic species in the dielectrics was optimized to show either broadband solar absorption or strong multiple plasmonic absorption peaks. The applications of such nanocomposite materials in solar energy harvesting and spectral sensing are also presented and discussed., 14 pages, 3 figures

It has been shown recently that Au labeling [V. C. Venezia, D. J. Eaglesham, T. E. Haynes, A. Agarwal, D. C. Jacobson, H.-J. Gossmann, and F. H. Baumann, Appl. Phys. Lett. 73, 2980 (1998)] can be used to profile vacancy-type defects located near half the projected range (12 Rp) in MeV-implanted Si. In this letter, we have determined the ratio of vacancies annihilated to Au atoms trapped (calibration factor “k”) for the Au-labeling technique. The calibration experiment consisted of three steps: (1) a 2 MeV Si+ implant into Si(100) followed by annealing at 815 °C to form stable excess vacancy defects; (2) controlled injection of interstitials in the 12 Rp region of the above implant via 600 keV Si+ ions followed by annealing to dissolve the {311} defects; and (3) Au labeling. The reduction in Au concentration in the near-surface region (0.1–1.6 μm) with increasing interstitial injection provides the most direct evidence so far that Au labeling detects the vacancy-type defects. By correlating this reduction ...

Previous studies on dewetting of ultrathin Co films by nanosecond pulsed laser melting have shown that the films dewet due to a thin film hydrodynamic instability and form a system of ordered nanoparticles with uniform average size and nearest neighbor particle spacing. For Co films less than 8 nm thick, the nanoparticle spacing, λ NN was dependent on the initial film thickness, h, and varied as h 2 . For Co films thicker than 8nm, the nanoparticle spacing decreased with increasing film thickness, due to a thermocapillary effect generated by the ns laser heating. Here we show the results from investigations on dewetting of Co films that had initially much rougher surfaces with root mean square roughness values, 0.9 < R rms < 2.8 nm as compared to smoother films examined in prior investigations, for which R rms ≤ 0.2 nm. Laser induced dewetting of Co films with much large R ms values generated nanoparticles that were qualitatively similar to those created from smoother Co films. The size distribution of the nanoparticles was monodispersed and there was short range spatial order present in the system from the average nearest neighbor nanoparticle spacing; however, a drastic reduction in the characteristic length scales was observed in the nanoparticulate arrays created from the rougher Co films. This result suggests that knowledge of film thickness and roughness are important towards predicting characteristic length scales from metal film dewetting.

When an ultrathin metal film of thickness $h$ $(l20\text{ }\text{ }\mathrm{nm})$ is melted by a nanosecond pulsed laser, the film temperature is a nonmonotonic function of $h$ and achieves its maximum at a certain thickness ${h}^{*}$. This is a consequence of the $h$ and time dependence of energy absorption and heat flow. Linear stability analysis and nonlinear dynamical simulations that incorporate such intrinsic interfacial thermal gradients predict a characteristic pattern length scale $\ensuremath{\Lambda}$ that decreases for $hg{h}^{*}$, in contrast to the classical spinodal dewetting behavior where $\ensuremath{\Lambda}$ increases monotonically as ${h}^{2}$. These predictions agree well with experimental observations for Co and Fe films on ${\mathrm{SiO}}_{2}$.

Functional nanostructured surfaces comprised of spatially ordered features, like clusters, wires or thin films, are important in various applications, including nonlinear photonics, magnetic data storage and gas sensing. The primary challenge to realizing the potential of this area is to develop cost-effective fabrication techniques and reliable characterization of such nanostructures. In this chapter we discuss the potential towards controlling the spatial arrangement of surface structures by modification to thin film nucleation and growth processes during physical vapor deposition. We also review structures resulting from surface instabilities generated by energetic ion beam irradiation—another active research area that promises simple and reliable self-assembly of nanostructures. Careful characterization of spatial order and thin film morphological properties like size, shape and connectedness are very important towards understanding the role of processing parameters, as well as in structure-property correlations. In this regard, image analysis can be a simple but vital step. We review the techniques of Fourier analysis and Minkowski functional analysis to understand the length scales and morphologies of surface nanostructures. Finally, examples of applications from the areas of nonlinear optics, magnetism and gas sensing are provided which highlight the need for control of size and spatial order in nanostructures.

Recently, a homogenization procedure has been proposed, based on the tight lower bounds of the Bergman-Milton formulation, and successfully applied to dilute ternary nanocomposites to predict optical data without using any fitting parameters [Garcia et al. Phys. Rev. B, 75, 045439 (2007)]. The procedure has been extended and applied to predict the absorption coefficient of a quaternary nanocomposite consisting of Cu, Ag, and Au nanospheres embedded in a SiO2 host matrix. Significant enhancement of the absorption coefficient is observed over the spectral range 350-800 nm. The magnitude of this enhancement can be controlled by varying the nanosphere diameter and the individual metal volume fraction with respect to the host matrix. We have determined the optimal composition resulting in enhanced broadband (350nm-800nm) absorption of the solar spectrum using a simulated annealing algorithm. Fabricating such composite materials with a desired optical absorption has potential applications in solar energy harvesting., Comment: submitted to SPIE Optics+Photonics, 2007

We have expressed the nonlinear optical absorption of a semiconductor in terms of its linear spectrum. We determined that the two-photon absorption coefficient in a strong DC-electric field of a direct gap semiconductor can be expressed as the product of a differential operator times the convolution integral of the linear absorption without a DC-electric field and an Airy function. We have applied this formalism to calculate the two-photon absorption coefficient and nonlinear refraction for GaAs and ZnSe using their linear absorption and have found excellent agreement with available experimental data., 8 pages, 2 figures (6 sub fugures)

We have developed a self consistent technique to predict the behavior of plasmon resonances in multi-component systems as a function of wavelength. This approach, based on the tight lower bounds of the Bergman-Milton formulation, is able to predict experimental optical data, including the positions, shifts and shapes of plasmonic peaks in ternary nanocomposites without using any ftting parameters. Our approach is based on viewing the mixing of 3 components as the mixing of 2 binary mixtures, each in the same host. We obtained excellent predictions of the experimental optical behavior for mixtures of Ag:Cu:SiO2 and alloys of Au-Cu:SiO2 and Ag-Au:H2 O, suggesting that the essential physics of plasmonic behavior is captured by this approach., Comment: 7 pages and 4 figures

The two-photon absorption coefficient of an indirect gap semiconductor (phonon-assisted two-photon absorption) in the presence of a strong dc-electric field applied perpendicular to the direction of propagation of the optical field is calculated using the formalism developed elsewhere (Aspnes 1996 Phys. Rev. B. 147 554). We show that depending on the type of transition (i.e., allowed–allowed, allowed–forbidden or forbidden–forbidden), the absorption coefficient followed different dispersion relations. In the limit of a weak electric field, we recovered results previously calculated using perturbation theory. In the strong dc-field regime, we found that below the rescaled energy gap given by Eg/N, where N is the number of photons, the tunnelling effect is present, but to our surprise, above the rescaled gap, the Franz–Keldysh oscillations are present only for the allowed–allowed transition. This absence of the oscillations in the allowed–forbidden and forbidden–forbidden transitions is possible due to the weak coupling of the tails of the electron and hole wavefunctions.

Increasing the efficiency and the relative ease of creating ordered nanostructures is essential to the advancement of nanotechnology. The practical benefits from ambient processing of nanostructures, like reduced complexity and increased efficiency, makes it an important avenue for investigation as nanomanufacturing processes. We have recently shown that pulsed laser melting of ultrathin metal films in vacuum leads to nanostructure ordering presumably due to metal dewetting. Here we show that UV pulsed laser irradiation (10 ns pulse width) of ultrathin Co films on SiO2 substrates under ambient conditions with a two-beam laser interference pattern generates Co nanoparticles with both long- and short-range order (LRO and SRO) and are qualitatively comparable to those created in vacuum. Furthermore, preferential etching of the metal shows that there is minimal interaction of the Co with the substrate. These results show that the presence of oxygen in the ambient does not substantially influence the resulting nanostructure formation. Therefore, ns pulsed laser processing under ambient conditions may be a practical way to realize ordered metal nanostructures.

We present novel results showing that the application of a rapid spatio-temporal surface modulation in-situ with film deposition directs the assembly of ordered nanostructures. Co nanoclusters of approximately 50 nm in size were assembled into one-dimensionally ordered arrays spaced 400 nm apart on Si (100) substrates during film growth of a 0.5 nm thick film. This ordered arrangement was achieved under e-beam evaporation of Co with simultaneous two-beam pulsed laser interference irradiation. The ordering length scale was consistent with the theoretical two-beam fringe spacing. For a thicker Co film, the particles were irregularly shaped, like that of a rapidly solidified liquid-like structure. From this evidence, the mechanism for ordering is partly attributed to thermal effects due to the spatially periodic laser interference heating of the cobalt nanoparticles. This dynamic in-situ process, without the need of any pre-or post-patterning of the substrate or film, is promising as an economical and simple approach to assemble ordered nanostructured films. The author can be reached via e-mail at ramkik@wuphys.wustl.edu

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

The Mie theory gives the exact solution to scattering from spherical particles while the Fresnel theory provides the solution to optical behavior of multilayer thin film structures. Often, the bridge between the two theories to explain the behavior of materials such as nanoparticles in a host dielectric matrix, is done by effective medium approximation (EMA) models which exclusively rely on the dipolar response of the scattering objects. Here, we present a way to capture multipole effects using EMA. The effective complex dielectric function of the composite is derived using the Clausius–Mossotti relation and the multipole coefficients of the approximate Mie theory. The optical density (OD) of the dielectric slab is then calculated using the Fresnel approach. We have applied the resulting equation to predict the particle size dependent dipole and quadrupole behavior for spherical Ag nanoparticles embedded in glass matrix. This dielectric function contains the relevant properties of EMA and at the same time predicts the multipole contributions present in the single particle Mie model.

We discuss the development of X-ray multilayer coatings for use as broad-band reflectors operating at energiesabove 100 keV. Such coatings can be used to produce hard X-ray telescopes that will make possible a variety of entirely newastronomical observations. We summarize our recent investigation into the growth, structure and hard X-ray performance ofdepth-graded W/Si multilayers, present follow-up information on Cu/Si multilayers, and discuss preliminary results obtainedwith Ni/Si, Ni8Cr2/Si, and Ni93V07/Si multilayers.Keywords: multilayer coatings, hard X-ray optics 1. INTRODUCTION Depth-graded multilayers are the enabling technology for a new generation of hard X-ray astronomical telescopes,including those being developed for the HEFT [1] and In-Focus [2] balloon instruments, and the Astro-G and Constellation-Xsatellite instruments [3]. These new telescopes, operating at photon energies in the range 20 — 100 keV, will provide animprovement in sensitivity by a factor of -4000 or more over previous (non-focusing) instruments, and will undoubtedly leadto a number of important astronomical discoveries.We describe here the development of depth-graded multilayer structures for use as hard X-ray reflectors operating atenergies greater than 100 keV. With a high-resolution, high-energy focusing mission based on such technology a variety ofnew observations will become possible, including: measuring the time-history of the emission from 5'Ni (158 keV) in Typela SNe; investigating the sites of particle acceleration in young SNR; measuring the nuclear continuum and cutoff in SeyfertI galaxies; and detection of Compton backscatter radiation (170 keV) in Galactic black hole candidates.Unlike periodic multilayers, which provide high reflectance only over a limited range of angles and X-ray energies,depth-graded multilayers are used for broadband reflectance: in a depth-graded multilayer structure the layer thicknessesvary with depth into the film stack, such that each bilayer is effectively tuned to a different X-ray wavelength. Depth-gradedmultilayer structures are particularly effective in the hard X-ray region (E > 20 keV) where hundreds or even thousands ofbilayers can be used, in principle, as a result of the low absorption and consequently high penetration depth in the film atthese energies. However, the performance of such structures depends critically on the achievable level of interfaceperfection: deviations from atomically smooth and chemically abrupt interfaces —

We describe the development of depth-graded W/Si multilayer films prepared by magnetron sputtering for use as broad-band reflective coatings for hard x-ray optics. We have used specular and nonspecular x-ray reflectance analysis to characterize the interface imperfections in both periodic and depth-graded W/Si multilayer structures, and high-resolution transmission electron microscopy (TEM) and selected area electron diffraction (SAED) to characterize the interface structure and layer morphology as a function of depth in an optimized depth-graded multilayer. From x-ray analysis we find interface widths in the range sigma=0.275-0.35 nm for films deposited at low argon pressure (with a slight increase in interface width for multilayers having periods greater than similar to 20 nm, possibly due to the transition from amorphous to polycrystalline metal layers identified by TEM and SAED), and somewhat larger interface widths (i.e., sigma=0.35-0.4 nm) for structures grown at higher Ar pressures, higher background pressures, or with larger target-to-substrate distances. We find no variation in interface widths with magnetron power. Nonspecular x-ray reflectance analysis and TEM suggest that the dominant interface imperfection in these films is interfacial diffuseness; interfacial roughness is minimal (sigma(r)similar to 0.175 nm) in structures prepared under optimal conditions, but can increase under conditions in which the beneficial effects of energetic bombardment during growth are compromised. X-ray reflectance analysis was also used to measure the variation in the W and Si deposition rates with bilayer thickness: we find that the W and Si layer thicknesses are nonlinear with the deposition times, and we discuss possible mechanisms responsible for this nonlinearity. Finally, hard x-ray reflectance measurements made with synchrotron radiation were used to quantify the performance of optimized depth-graded W/Si structures over the photon energy range from 18 to 212 keV. We find good agreement between the synchrotron measurements and calculations made using either 0.3 nm interface widths, or with a depth-graded distribution of interface widths in the range sigma=0.275-0.35 nm (as suggested by 8 keV x-ray and TEM analyses) for a structure containing 150 bilayers, and designed for high reflectance over the range 20 keV

We present experimental results directed at understanding the growth and structure of metallic barrier layer and interconnect films. Numerical simulation results associated with this experimental work are presented in an accompanying paper in these proceedings. Here, thin films of Al, Ti, Cu and Ta have been grown by magnetron sputtering onto oxidized Si substrates. Using a specially-constructed substrate holder, the orientation of the substrate with respect to the growth direction was varied from horizontal to vertical. Films were grown at both low and high argon pressure; in the case of Ta, the cathode power was varied as well. The film structure and in particular the surface roughness was measured by X-ray reflectance and also by atomic force microscopy. We find that the surface roughness increases markedly with orientation angle in the case of Ta and Cu films, and in Ti films grown at high argon pressure. At low pressure, however, the Ti film surface roughness remains constant for all substrate orientations. No variation in roughness with either orientation angle or argon pressure was observed in the Al films. These results suggest that, under certain circumstances, shadowing effects and/or grain orientation (i.e., texture) competition during growth can give rise to lower density, more porous (and thus more rough) films, particularly at large orientation angles, as on sidewalls in sub-micron trenches.

In this paper we report our investigations related to the growth and characterization of superconducting stacked structures of YBaCuO(undoped)/YBaCuO(Ag-doped)/YSZ layers processed on Si(100) substrates. These films were deposited using pulsed laser deposition (PLD), and have been characterized using X-ray diffraction, scanning electron microscopy (SEM), and four probe electrical measurements. SIMS analysis has also been used to study the incorporation and diffusion of carbon in the superconducting layer. The focus of this work is on the issues of the role of silver in the superconductor, and its effects on the transport properties and microstructure of the structure. We also discuss the use of these films for bolometer device applications.

The lower and upper bounds for the nonlinear susceptibility of a multi-component nanocomposite composed of a glass host and nanoparticles of multiple metals are calculated within the context of the Hashin–Shtrikman formulation. We have applied this effective medium theory to the following ternary composites: AgCu:SiO2 and AgAu:SiO2 in the form of mixtures. These bounds were used to estimate the limits of the nonlinear effective third-order susceptibility of the composite as a function of wavelength, volume fraction and particle size. It is shown that the modulation of the third-order susceptibility of the metal by local-field enhancement due to plasmon resonance results in unexpected nonlinear responses which could be of interest to surface-enhanced Raman scattering, plasmonics and nanophotonics.

Selecting nanocomposites for photonic switching applications requires optimizing their thermal, nonlinear and two-photon absorption characteristics. We simplify this step by defining a compound figure of merit (FOM_{C}) for nanocomposites of noble metals in dielectric based on criteria that limit these structures in photonic applications, i.e. thermal heating and two-photon absorption. The device independent results predict extremely large values of FOM_{C} for a specific combination of the metal and insulator dielectric constant given by \epsilon_{h}=\frac{\epsilon_{1}-\epsilon_{2}}{2}, where \epsilon_{h} is the dielectric constant of the host and \epsilon_{1} and \epsilon_{2} are the real and imaginary parts for the metal., Comment: Appearing in Appl. Phys. Lett. (2006)

Laser irradiation of ultrathin Co films leads to pattern formation by dewetting with short-range order (SRO) as well as long-range order (LRO). When a 1.5nm thick Co film is irradiated by a single laser beam, a monomodal size distribution of particles with average diameter of 31±10nm and nearest-neighbor spacing of 75nm is observed. Moreover, melting by two-beam interference irradiation produces LRO as well as SRO giving a quasi-two-dimensional arrangement of nanoparticles. The SRO is attributed to spinodal dewetting while the LRO is conjectured to be induced by in-plane interfacial tension gradients. Laser-induced dewetting of metals could be a simple technique to fabricate ordered metal nanoarrays.

Experimental evidence for dynamic modification of a growing thin film into ordered nanoclusters is presented. Co nanoclusters of approximately 50nm diameter were assembled into one-dimensionally ordered arrays spaced 400nm apart on Si(100) substrates during film growth. This ordered arrangement was achieved under e-beam evaporation of Co with simultaneous two-beam laser interference irradiation of the substrate. The ordering length scale was consistent with the two-beam fringe spacing of 400nm. In comparison, the unirradiated film shows a random distribution of Co clusters with average diameter of 17nm. The mechanism for assembly is tentatively attributed to thermal effects arising from the spatially periodic laser interference heating of the substrate and∕or film. This one step process, without the need of any pre- or postpatterning of the substrate or film, is promising as an economical and simple approach to assemble ordered nanostructured films.

We experimentally demonstrate an amorphous ternary metal oxide of Fe, Tb, and Dy exhibiting high electronic conductivity, Hall mobility, and optical transparency driven by partly filled d- and f-subshells.