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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.

It has been theoretically suggested by Yan et al. (Colloids Surf., A 2013, 429, 142–148) that the contact angle θc of a liquid droplet on any given surface can be controlled by immersing it in an a...

The rapid laser heating of materials beyond their boiling point has been associated with a variety of interesting phenomena, such as supersaturated vapor formation and explosive evaporation. Here, we study the nanosecond pulsed laser heating of Ag nanopyramids and thin films deposited on quartz substrates under various fluids. Rapid heating of Ag nanopyramids in vacuum demonstrated that a large fraction of the vaporized material was redeposited onto the substrate, confirming an explosive vaporization process. When the Ag nanostructures were heated under bulk fluids like water and glycerol, an increased localization of the vaporized material was observed. We hypothesize that the size of the bulk fluid’s vapor zone surrounding the metallic nanoparticles, which, in turn, is determined by the thermal diffusivity of the bounding fluid, confines the metal vaporization process. While a large amount of material is vaporized in this process, the redeposited material particles show a significant decrease in size and an increase in particle density, by nearly 250% in going from air to glycerol. This behavior of the metal vaporization under bounding fluids could be used to tailor the size and density of nanoparticles on a surface as well as investigate the highly non-equilibrium process of explosive vaporization.

Recently, amorphous/disordered oxide thin films made from Fe and lanthanides like Dy and Tb have been reported to have a rich set of magnetic, optical, and electronic properties, as well as room-temperature magneto-electric coupling with multiferroics [A. Malasi et al., Sci. Rep. 5, 18157 (2015); H. Taz et al., Sci. Rep. 6, 27869 (2016); and H. Taz et al., Sci. Rep. 10, 1–10 (2020)]. Here, we report the synthesis and detailed characterization of Fe 2.75Dy-oxide thin films prepared on various substrates using electron beam co-evaporation. The structure, chemistry, electric, magnetic, and optical properties were studied for the as-prepared and annealed (373 K, in air, 1 h) films of thickness 40 nm. High resolution transmission electron microscopy and electron diffraction study showed that the films were amorphous in both the as-prepared and annealed states. The electron energy-loss spectroscopy studies quantified that metal oxygen stoichiometry changed from Fe 2.75Dy-O 1.5 to Fe 2.75Dy-O 1.7 upon annealing. Synchrotron-based x-ray absorption spectroscopy investigation confirmed that the as-prepared films were highly disordered with predominantly metallic Fe and Dy states that became slightly oxidized with annealing in air. The as-prepared amorphous films demonstrated significantly high value of ordinary ( ∼ 10 cm 2/V s) and anomalous ( ∼ 10 2 cm 2/V s) Hall mobility and high electrical conductivity of ∼ 10 3 S/cm at room temperature. The cryogenic magnetic property measurement shows two-step magnetization below 200 K, suggesting exchange-spring magnetic interaction. The nature of the field cooled and zero-field cooled curves suggested a spin-glass like transition between 78 K and 80 K, with a characteristic broad peak. The Tauc plot analysis from optical transmission spectra confirms the existence of an optical bandgap of ∼ 2.42 eV that increased slightly to ∼ 2.48 eV upon annealing. This rich set of transport, optical, and magnetic properties in these thin films is very exciting and points to potential applicability in low-cost multifunctional devices requiring a combination of transparent, semiconducting, and magnetic responses, such as in spintronics.

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.

Discovery of new plasmonic behaviors from nanostructured materials can be greatly accelerated by the ability to prepare and characterize their near-field behaviors with high resolution in a rapid manner. Here, an efficient and cost-effective way is reported to make 2D periodic nanostructures on electron-transparent substrates for rapid characterization by transmission electron microscopy. By combining nanosphere lithography with a substrate float-off technique, large areas of electron-transparent periodic nanostructures can be achieved. For this study, the synthesis of plasmonic nanostructures of Ag, magnetic nanostructures of Co, and bimetallic nanostructures of Ag–Co are investigated. Characterization of the materials by a combination of transmission electron microscopy, far-field optical spectroscopy, and magnetization measurements reveals that this new approach can yield useful nanostructures on transparent, flexible, and transferable substrates with desirable plasmonic and/or magnetic properties.

This review summarizes the current state-of-the art electrode materials used for high-capacity lithium-ion-based batteries and their significant role towards revolutionizing the electrochemical energy storage landscape in the area of consumer electronics, transportation and grid storage application. We discuss the role of nanoscale effects on the electrochemical performance of high-capacity battery electrode materials. Decrease in the particle size of the primary electrode materials from micron to nanometre size improves the ionic and electronic diffusion rates significantly. Nanometre-thick solid electrolyte (such as lithium phosphorous oxynitride) and oxides (such as Al2O3, ZnO, TiO2 etc.) material coatings also improve the interfacial stability and rate capability of a number of battery chemistries. We elucidate these effects in terms of different high-capacity battery chemistries based on intercalation and conversion mechanism.

Techniques that can characterize the early stages of thin film deposition from liquid phase processes can aid greatly in our understanding of mechanistic aspects of chemical bath deposition (CBD). Here we have used localized surface plasmon resonance (LSPR) spectroscopy to monitor the in situ kinetics of early stage growth of cadmium sulfide (CdS) thin films on Ag nanoparticle on quartz substrates. Real-time shift during CdS deposition showed that the LSPR wavelength red-shifted rapidly due to random deposition of CdS on the substrate but saturated at longer times. LSPR modeling showed that these features could be interpreted as an initial deposition of CdS islands followed by preferential deposition onto itself. The CdS also showed significantly enhanced Raman signals up to 170 times due to surface-enhanced Raman scattering (SERS) from the CdS/Ag NP regions. The ex situ SERS effect supported the LSPR shift, suggesting that these techniques could be used to understand nucleation and growth phenomena from ...

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.

Currently, one of the challenges in high-resolution transmission electron microscopy (TEM) studies of nanomaterials is to make contamination-free materials in a simple and time-efficient way. Here, a method is demonstrated that combines nanosecond-pulsed laser dewetting of thin films with a film float-off technique to realize nanostructures (NSs) on electron-transparent substrates in a robust and rapid manner. NSs of metal (Ag) and bimetals (AgCo, AuCo) ranging from 20 to 150 nm are synthesized on thin carbon film deposited on mica substrates. The NS/carbon system is subsequently transferred onto TEM grids by a float-off process resulting from debonding of the carbon from mica due to their contrasting hydrophobic nature. This process enables the fabrication of different NSs on flexible and electron-transparent substrates.

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.

Ultrathin metal film dewetting continues to grow in interest as a simple means to make nano structures with well-defined properties. Here, we explored the quantitative thickness-dependent dewetting behavior of Au films under nanosecond (ns) pulsed laser melting on glass substrates. The trend in particle spacing and diameter in the thickness range of 3-16 nm was consistent with predictions of the classical spinodal dewetting theory. The early stage dewetting morphology of Au changed from bicontinuous-type to hole-like at a thickness between 8.5 and 10 nm, and computational modeling of nonlinear dewetting dynamics also captured the bicontinuous morphology and its evolution quite well. The thermal gradient forces were found to be significantly weaker than dispersive forces in Au due to its large effective Hamaker coefficient. This also resulted in Au dewetting length scales being significantly smaller than those of other metals such as Ag and Co.

Although Ag is considered a noble metal, its surface oxidizes relatively quickly on exposure to ambient air. On the nanos- cale, this degradation is especially deleterious to applications pertaining to its plasmonic behavior, such as surface plasmon resonance (SPR) sensing. In this Communication we show that oxidation of Ag nanoparticles under ambient conditions can be significantly suppressed by contacting Ag with immis- cible Co nanoparticles. As a consequence, while the plasmonic characteristic of pure Ag degrades by 25% within 500 h, Ag-Co nanoparticles take almost ten times longer to show a similar magnitude of decay in air, thus showing ultrastable plasmonics. We attribute this oxidation-resistance to a cathodic protection arising from galvanic coupling.

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 (

We report a class of amorphous thin film material comprising of transition (Fe) and Lanthanide metals (Dy and Tb) that show unique combination of functional properties. Films were deposited with different atomic weight ratio (R) of Fe to Lanthanide (Dy + Tb) using electron beam co-evaporation at room temperature. The films were found to be amorphous, with grazing incidence x-ray diffraction and x-ray photoelectron spectroscopy studies indicating that the films were largely oxidized with a majority of the metal being in higher oxidation states. Films with R = 0.6 were semiconducting with visible light transmission due to a direct optical band-gap (2.49 eV), had low resistivity and sheet resistance (7.15 × 10−4 Ω-cm and ~200 Ω/sq respectively) and showed room temperature ferromagnetism. A metal to semiconductor transition with composition (for R 0 oxidation state in the R = 0.6 case as well as a significantly higher fraction of oxidized Dy. The combination of amorphous microstructure and room temperature electronic and magnetic properties could lead to the use of the material in multiple applications, including as a transparent conductor, active material in thin film transistors for display devices and in spin-dependent electronics.

The impacts of the two-beam interference heating on the number of core-shell and embedded nanoparticles and on nanostructure coarsening are studied numerically based on the non-linear dynamical model for dewetting of the pulsed-laser irradiated, thin (< 20 nm) metallic bilayers. The model incorporates thermocapillary forces and disjoining pressures, and assumes dewetting from the optically transparent substrate atop of the reflective support layer, which results in the complicated dependence of light reflectivity and absorption on the thicknesses of the layers. Stabilizing thermocapillary effect is due to the local thickness-dependent, steady- state temperature profile in the liquid, which is derived based on the mean substrate temperature estimated from the elaborate thermal model of transient heating and melting/freezing. Linear stability analysis of the model equations set for Ag/Co bilayer predicts the dewetting length scales in the qualitative agreement with experiment.

The optical properties of multi-metal nanocomposites made from Cobalt (Co), and Silver (Ag) are analyzed theoretically within the mean field approximation, and experimentally verified using absorption spectroscopy. The experimental system was modeled as a thin layer composed of hemispherical nanoparticles formed by grains of Co and Ag in contact with air and the SiO $_{\text{2}}$ substrate. The main aspects of the absorption curve, such as the shape and spectral location of the localized surface plasmon resonance, are well captured by a simple self-consistent mixing model using a modified Maxwell-Garnett approach and the Milton lower bound.

Nanocrystalline indium oxide-doped tin oxide thin film sensors have been synthesized using sol–gel dip-coating technique. The sensors were spin-coated with three different types of polymer namely polymethyl methacrylate (PMMA), poly-perfluorobutenyl vinyl ether (Cytop), fluoropolymer (Fluoropel). The room temperature sensor characteristics (response time, electrical response and recovery time) of the three sensors with different polymer coating were compared at hydrogen concentrations of 600, 1500, 6000 and 15,000 ppm and at two different humidity levels of 14% and 65%. It was found that the polymer coating preserves the selective sensing property of indium oxide-doped tin oxide even at high humidity. The response kinetics of the sensors with different coatings has been compared.

Controlling the magnetic orientation of nanoparticles is important for many applications. Recently, it has been shown that single domain ferromagnetic hemispherical Co nanoparticles prepared by nanosecond laser-induced self-organization, show magnetic orientation that was related to the negative sign of the magnetostrictive coefficient λ S [J. Appl. Phys. v103, p073902, 2008]. Here we have extended this work to the Fe 50 Co 50 alloy, which has a positive λ S and Ni, which has a negative λ S . Patterned arrays of ferromagnetic nanoparticles of Fe 50 Co 50 , Ni, (and Co) were synthesized from their ultrathin metal films on SiO 2 substrate by nanosecond laser-induced self-organization. The morphology, nanostructure, and magnetic behavior of the nanoparticle arrays were investigated by a combination of electron microscopy, atomic force microscopy, and magnetic force microscopy techniques. Transmission electron microscopy investigations revealed a granular polycrystalline nanostructure, with the number of grains inside the nanoparticle increasing with their diameter. Magnetic force measurements showed that the magnetization direction of the hemispherical Co and Ni nanoparticles was predominantly out-of-plane while those for the Fe 50 Co 50 alloy was in the plane of the substrate. Finite element analysis was used to estimate the average residual strain in the nanoparticles, following laser processing. The difference in behavior is due to the dominating influence of magnetostrictive energy on the magnetization as a result of residual thermal strain following fast laser processing. Since λ S is negative for polycrystalline Co and Ni, and positive for Fe 50 Co 50 , the tensile residual strain forces the magnetization direction to out-of-plane and in-plane, respectively. This work demonstrates a cost-effective non-epitaxial technique for the synthesis of magnetic nanoparticles with tailored magnetization orientations.

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.

Techniques for processing nanoscale metallic structures with spatial order and tunable physical characteristics, such as size and microstructure, are paramount to realizing applications in the areas of magnetism, optics, and sensing. This paper discusses how pulsed laser melting of ultrathin films can be a powerful but simple and cost-effective technique to fabricate functional nanostructures. Ultrathin metal films (1 nm to 1,000 nm) on inert substrates like SiO2 are generally unstable, with their free energy resembling that of a spinodal system. Such films can spontaneously evolve into predictable nanomorphologies with well-defined length scales. This study reviews this laser-based experimental technique and provides examples of resulting robust nanostructures that can have applications in magnetism and optics.

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).

We have investigated the nanostructure and microstructure resulting from ns laser irradiation simultaneous with deposition of Co films on Si(001) substrates. The spatial order and length scales of the resulting nanopatterns and their crystalline microstructure were investigated as a function of film thickness h and laser energy density E using a combination of atomic force, scanning electron and transmission electron microscopies. The results could be classified into two distinct categories based on the laser energy density used. It was observed that the thickness-dependent E required to melt the Co film (E_{Co}) was lower than Si (E_{Si}) primarily because of the higher reflectivity of Si. Consequently, for energy densities E_{Co}, Comment: Submitted to J. Phys. D: Appl. Phys

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.

We have combined experiments and atomistic modeling in order to better understand the growth and structure of metal films deposited onto sidewalls of trenches and vias. Using x-ray reflectance, atomic force microscopy, and high-resolution transmission electron microscopy to characterize the microstructure and morphology of Ta films grown by magnetron sputtering onto inclined substrates, we find that films deposited at larger incidence angles tend towards columnar microstructure with high roughness and low density. We have used a three-dimensional Monte Carlo model (ADEPT) to simulate the growth process, under conditions close to those investigated experimentally. A binary collision model is included in the Monte Carlo deposition procedure to describe the interaction of energetic particles with the surface. Examination of the film microstructure and morphology resulting from the simulations indicates that the energetic impinging particles are necessary to produce film densities comparable to those found ex...

Ion implantation followed by thermal processing has been used to synthesize nanoparticles of cobalt–platinum (Co–Pt) alloys in single-crystal Al2O3. Several phases, including CoPt in the L10 structure, Co3Pt, and CoPt3 that has the L12 structure, are selectively formed by varying the atomic ratio of implanted Co and Pt. These alloys are crystallographically oriented with respect to the host Al2O3 matrix, exhibiting multiple distinct orientations. Rutherford backscattering and X-ray diffraction have been used to study the influence of the processing conditions, including temperature and dose, on the formation of the alloys. The degree of chemical ordering in the L10 and L12 phases is not high and it is not improved significantly with long annealing times. Magnetization studies have been conducted using a SQUID magnetometer. Coercivities as high as 14.2 kOe (9.7 kOe) at 5 K with the field normal (parallel) to the surface have been measured, and they remain significant at room temperature and above. The coercivity is a function of the Pt fraction in the alloy.

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.

In ion implantation related research in Si, the role of interstitial clusters in dopant diffusion is fairly well understood. But there is relatively poor understanding of vacancy clusters, mainly due to the inadequacy of present techniques to profile and especially to count vacancy defects. Recently, two important steps have been taken in the direction of understanding the vacancy-type defects. The first is the demonstration that high-energy ion implantation (HEI) can be used as a vacancy implanter to introduce vacancies (V) in Si that are separated from the interstitials (I) by relying on spatial separation of the Frenkel pairs due to the average forward momentum of the recoils. The second is the development of two techniques, Au labeling and cross-section X-ray microbeam diffuse scattering, which permit quantitative measurements of the vacancy-type defect clusters and their depth distribution. In this work we highlight the Au labeling technique and use the vacancy implanter in conjunction with Au labeling to study the evolution of excess vacancy defects (Vex) created by HEI of Si+ in Si(1 0 0) as a function of fluence and temperature. We show that a precise injection of Vex is possible by controlling implanted fluence . We also show that the Vex clusters formed by the HEI are extremely stable and their annihilation is governed by interstitial injection rather than vacancy emission in the temperature range of 800–900°C.

We have synthesized thin CNx films on Si (100) substrate at high temperatures (600 and 700°C) by nitrogen ion-assisted pulsed laser deposition (PLD). The bonding characteristics and microstructure determinations have been accomplished using X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM), respectively. The radial distribution function (RDF) analysis of the electron diffraction patterns was performed to determine the short range atomic order in these films. The results reveal the presence of carbon predominantly in the trigonally-coordinated state with small fractions of nitrogen (upto 20 at.%) bonded to carbon. The electron diffraction and the high resolution images in cross-section view reveal that there is a textured growth of nanotube or graphite-like ribbons. The plan-view specimens show high resolution images with bended layers similar to that of onion or nanotube like features. The kinetics of the ions assisting the growth is assumed to be important to grow the basal planes (00l) of graphite perpendicular to the substrate. The large anisotropic surface energies in two perpendicular directions in graphite suggest that ions can create nonequilibrium conditions to alter the growth mode of graphitic planes. The importance of ion-assisted PLD to grow novel nanotube or fullerenelike structure in the form of thin film composites for electron field emission devices is emphasized.

Grain boundaries in laser-deposited YBa2Cu3O7−δ(YBCO)/MgO thin films have been investigated by high-resolution transmission electron microscopy. The films exhibit perfect texturing with YBCO(001)/MgO(001) giving rise to low-angle [001] tilt grain boundaries resulting from the grains with thecaxis normal to the substrate surface and with misorientation in thea-bplane. The atomic structure of the grain boundaries was analyzed by using a dislocation model. Low-angle grain boundaries have been found to be aligned along (100) and (110) interface planes. For the (110) boundary plane, the low-energy dislocation configuration was found to consist of an array of alternating [100] and [010] dislocations. We have calculated the energy of various configurations and shown that the energy of the (110) boundary with dissociated dislocations is comparable to that of the (100) boundary, which explains the coexistence of (100) and (110) interface facets along the boundary. We have also modeled critical current transport through grain boundaries with various structures and found that the low-energy (110) grain boundary with dissociated dislocation array is expected to transport a lower superconducting current (by 25% for 6° misorientation) than (100) boundaries.

We have studied systematically the role of silver in improving microstructure and properties of Y1Ba2Cu3O7−δ (YBCO) thin films. We have more than doubled the grain size to nearly 1.8 μm and reduced processing temperatures by incorporating Ag in the YBCO films, which is accomplished by using a composite target containing 15% by weight of Ag. These films show approximately four times higher Jc than the best films obtained on MgO(001) substrates deposited from stoichiometric Y1Ba2Cu3O7−δ targets. Study of the silver content in the film as a function of the deposition temperature shows clearly a decreasing concentration with increasing temperature and a segregation of the Ag to the surface. The increased oxygen content in the films is also observed at lower processing temperatures, providing strong support for the efficient oxygenation of YBCO via the presence of silver. A qualitative model suggests that the formation of silver oxide, rapid surface diffusion of Ag on MgO surfaces, and the nonreactivity of Ag ...

Most metals on SiO2 have a finite contact angle and are therefore subject to dewetting during thermal processing. The resulting dewetting morphology is determined primarily by nucleation and growth or instabilities. The dewetting mechanism implies a disordered spatial arrangement for homogeneous nucleation, but an ordered one for instabilities such as spinodal decomposition. Here, we show that the morphology of laser-melted ultrathin Co film (4-nm thick) can be attributed to dewetting via an instability. Dewetting leads to breakup of the continuous Co film into nanoparticles with a monomodal size distribution with an average particle diameter of 75 nm±23 nm. These nanoparticles have short-range order (SRO) of 130 nm in their separation. This result has important implications for nanomanufacturing with a robust spacing or size selection of nanoparticles in addition to spatial ordering.

A distinctive characteristic of silver in oxygen incorporation of oxide thin films during pulsed laser ablation has been discovered. Optical emission spectroscopy studies of laser-induced plume of Ag-target indicates the presence of AgO species whose concentration increases with an increase in oxygen partial pressure. The formation of AgO in laser-plume has been found to be very useful for the realization of high temperature superconducting YBa2Cu3O7-delta (YBCO) and giant magnetoresistive La0.7MnO3-delta (LMO) thin films with dramatically superior quality if the target materials contained a small amount of silver. The improvement in the quality of these films is brought about by the supply of atomic oxygen to oxide lattices during their formation. This becomes possible due to the fact that Ag, after it is ablated with other constituent materials in the target, gets moderately oxidized in an oxygen atmosphere and the oxidized species dissociate back into Ag and nascent O at the substrate surface. The nascent oxygen is very highly reactive and is easily assimilated into the lattice of these compounds. (C) 1997 Elsevier Science S.A.

Transport, magnetoresistance and structural properties of La 0.6 Y 0.07 Ca 0.03 MnO x (LYCMO) thin films grown in situ by pulsed laser ablation have been studied. Transmission electron microscopy and X-ray diffraction measurements have shown that the LYCMO films grow epitaxially on (100) LaAlO 3 substrates and are cubic with a lattice parameter of 0.3849 run. The as-deposited films exhibited a metal-insulator transition at 130 K and a giant magnetoresistance at 125 K with a MR ratio (Δ R/R H ) of 1500% in 6 Tesla magnetic field. By subsequent annealing of LYCMO films at 900 °C for half an hour in an oxygen ambient, this MR ratio was improved to 3200% at 192 K in the presence of the same magnetic field. This value of the MR ratio is the highest so far reported in this temperature regime. We ascribe this colossal magnetoresistance to the improved magnetic exchange between Mn 3+ and Mn 4+ ions resulting from the suppressed separation between Mn-O layers caused by a smaller sized Y-cation. We also report a non-ohmic response in the LYCMO films which is observed only in the region of the resistance peak and lends support to a conduction mechanism in these materials based on spin-dependent scattering of electrons.

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.

Plasmon-mediated extraordinary optical transmission (EOT) is finding increased interest for biosensing applications. While Ag nanostructures are capable of the highest plasmonic quality factor of all metals, the performance reliability of pure Ag EOT devices is limited by degradation through environmental interactions. Here we show that EOT devices consisting of nanostructured hole arrays in Ag/Co bilayers show comparable transmission with that of identical hole arrays in Agthin films as well as enhanced reliability measured by the rate of resonance peak redshift and broadening with time. The Ag/Co EOT devices showed 2.6× and 1.9× smaller red shift in short timescales (20 days) and after 100 days, respectively, while they showed a 1.7× steady-state decrease in rate of bandwidth broadening. This improvement is likely due to the Co metal stabilizing the Agfilm from morphological changes by reducing its propensity to diffuse or dewet on the underlying substrate. The improved reliability of Ag/Co bilayer EOT devices could enable the use of their superior plasmonic properties for optical detection of trace chemicals.

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.

The electrical activation of B in n-type epitaxial-Si(100) has been enhanced in the temperature range of 400–800 °C. This enhanced activation was measured for 40 keV, 2×1014 cm−2 dose of B implanted into a vacancy-rich Si region. The vacancy-rich region consists of excess vacancies (Vex) generated by a 2 MeV Si implant in the dose range of 3×1015–10×1015 cm−2. The B activation in vacancy-rich Si is found to be a factor of ∼2.4 larger with up to ∼80% of the B activated as compared to similar B implant and activation anneals carried out in the bulk Si. The dependence of B activation on Vex concentration shows that the active B concentration increases with the Vex concentration. From this dependence it was estimated that at least three vacancies are required to activate an additional B atom. This process is distinctly different from the low temperature activation that occurs during solid-phase epitaxial recrystallization of B-doped amorphous Si as no amorphous Si is produced during any step. This low tempera...

Undoped nanostructured tin oxide (SnO(2)) arrays were prepared on oxidized Si substrates by nanosecond pulsed laser interference irradiation for hydrogen gas sensing applications. Scanning electron microscopy (SEM), in combination with Atomic Force Microscopy (AFM), showed that the SnO(2) surface consisted of periodic features of ∼130 nm width, ∼228 nm spacing, an average height of ∼8 nm along the periodicity and tens of microns length. The SnO(2) nanostructured arrays and precursor thin films were tested by cyclic exposure under dynamic conditions of hydrogen in the concentration range of 300-9000 ppm. The observed electrical response of SnO(2) towards hydrogen at low concentrations and room temperature drastically improved in the nanostructured array as compared to the thin film. The results suggest that this method to fabricate SnO(2) nanostructured arrays has the potential to produce nanodevices that have ultra-low detection limits, and fast response and recovery times, which are suited for practical hydrogen sensing applications.

In spontaneous pattern formation by spinodal dewetting, attractive intermolecular forces overcome surface tension and cause an ultrathin liquid film on a low energy substrate to produce ordered structures. Spinodal dewetting in single-layer film on a substrate is usually manifested by an early stage surface deformation and a highly nonlinear ripening stage that results in characteristic morphologies, typically bicontinuous- or holelike states. Here we have experimentally constructed the dewetting morphology phase diagrams for a bilayer (Ag, Co) liquid film system on SiO${}_{2}$. Nanosecond pulsed laser melting was used to initiate and foster the dewetting as a function of film thickness and arrangement. The early stage ripening morphology was observed by scanning electron microscopy from which the phase diagrams were constructed. Unlike single-layer films, which only show one morphology transition between the bicontinuous to hole states as the film thickness is increased, the bilayer system can have multiple transitions. We have utilized the thickness-dependent free energy curvature approach [Sharma and Khanna, Phys. Rev. Lett. 81, 3463 (1998)] to analyze the phase diagram. The location of the multiple transitions cannot be predicted from the curvature minima, as was the case for single-layer films. Nevertheless, despite the complexity from multiple interacting forces and different surface deformation mode in bilayer systems, the phase diagram can be completely generated by knowledge of the free energy curvature of the respective single-layer films. These results can permit improved modeling of the nonlinear dynamics in naturally driven self-organized phenomenon and help design nanomaterials for advanced applications.

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.

Magnetic systems are an exciting realm of study that is being explored on smaller and smaller scales. One extremely interesting magnetic state that has gained momentum in recent years is the skyrmionic state. It is characterized by a vortex where the edge magnetic moments point opposite to the core. Although skyrmions have many possible realizations, in practice, creating them in a laboratory is a difficult task to accomplish. In this work, different methods for skyrmion generation and customization are suggested. Skyrmionic behavior was numerically observed in minimally customized simulations of spheres, hemisphere, ellipsoids, and hemiellipsoids, for typical Cobalt parameters, in a range approximately $40--120\phantom{\rule{0.222222em}{0ex}}\text{nm}$ in diameter simply by applying a field.

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.

A deep band of {311} defects was created 520 nm below the silicon surface with a 350 keV Si implant followed by a cluster-forming rapid thermal anneal (800 °C, 1000 s). Chemical etching was used to vary the depth to the surface of the {311}-defect band. Afterwards, the defect dissolution was investigated at 750 °C for different times. Varying the depth in this fashion assures that only the depth and no other feature of the cluster distribution is changed. The {311} defects were analyzed by plan-view, transmission electron microscopy. We show that the dissolution time of the {311}-defect band varies linearly with depth, confirming that surface recombination controls the dissolution and is consistent with analogous observations of transient enhanced diffusion.