Showing papers in "Journal of Materials Research in 2011"

Nanoindentation strain-rate jump tests for determining the local strain-rate sensitivity in nanocrystalline Ni and ultrafine-grained Al

Abstract: A nanoindentation strain-rate jump technique has been developed for determining the local strain-rate sensitivity (SRS) of nanocrystalline and ultrafine-grained (UFG) materials. The results of the new method are compared to conventional constant strain-rate nanoindentation experiments, macroscopic compression tests, and finite element modeling (FEM) simulations. The FEM simulations showed that nanoindentation tests should yield a similar SRS as uniaxial testing and generally a good agreement is found between nanoindentation strain-rate jump experiments and compression tests. However, a higher SRS is found in constant indentation strain-rate tests, which could be caused by the long indentation times required for tests at low indentation strain rates. The nanoindentation strain-rate jump technique thus offers the possibility to use single indentations for determining the SRS at low strain rates with strongly reduced testing times. For UFG-Al, extremely fine-grained regions around a bond layer exhibit a substantial higher SRS than bulk material.

Oxide thermoelectrics: The challenges, progress, and outlook

Abstract: Most state-of-the-art thermoelectric (TE) materials contain heavy elements Bi, Pb, Sb, or Te and exhibit maximum figure of merit, ZT∼1–2. On the other hand, oxides were believed to make poor TEs because of the low carrier mobility and high lattice thermal conductivity. That is why the discoveries of good p-type TE properties in layered cobaltites NaxCoO2, Ca4Co3O9, and Bi2Sr2Co2O9, and promising n-type TE properties in CaMnO3- and SrTiO3-based perovskites and doped ZnO, broke new ground in thermoelectrics study. The past two decades have witnessed more than an order of magnitude enhancement in ZT of oxides. In this article, we briefly review the challenges, progress, and outlook of oxide TE materials in their different forms (bulk, epitaxial film, superlattice, and nanocomposites), with a greater focus on the nanostructuring approach and the late development of the oxide-based TE module.

Directed block copolymer self-assembly for nanoelectronics fabrication

Abstract: This paper provides an overview of directed self-assembly (DSA) options that exhibit potential for enabling extensible high-volume patterning of nanoelectronics devices. It describes the current set of research requirements, which a DSA technology must satisfy to warrant insertion consideration, and summarizes the state-of-the art. The primary focus is on chemical patterning and graphoepitaxial approaches to directing block copolymer (BCP) based assembly. These options exhibit the nearest-term potential, among the emerging DSA technologies, for satisfying projected International Technology Roadmap for Semiconductors (ITRS) patterning requirements. The paper concludes with a selected set of additional challenges, which represent potential barriers to the integration of directed BCP patterning into a nanoelectronics manufacturing line, as well as a few emerging application opportunities for related functional materials. A glossary of acronyms and terms may be found at the end of this manuscript.

Measuring substrate-independent modulus of thin films

Abstract: Substrate influence is a common problem when using instrumented indentation (also known as nano-indentation) to evaluate the elastic modulus of thin films. Many have proposed models to be able to extract the film modulus (Ef) from the measured substrate-affected modulus, assuming that the film thickness (t) and substrate modulus (Es) are known. Existing analytic models work well if the film is more compliant than the substrate. However, no analytic model accurately predicts response when the modulus of the film is more than double the modulus of the substrate. In this work, a new analytic model is proposed. This new model is shown by finite-element analysis to be able to accurately predict composite response over the domain 0.1 < Ef/Es < 10. Finally, the new model is used to analyze experimental data for compliant films on stiff substrates and stiff films on compliant substrates.

Doping of semiconductor nanowires

Abstract: A cornerstone in the successful application of semiconductor nanowire devices is controlled impurity doping. In this review article, we discuss the key results in the field of semiconductor nanowire doping. Considerable development has recently taken place in this field, and half of the references in this review are less than 3 years old. We present a simple model for dopant incorporation during in situ doping of particle-assisted growth of nanowires. The effects of doping on nanowire growth are thoroughly discussed since many investigators have seen much stronger and more complex effects than those observed in thin-film growth. We also give an overview of methods of characterizing doping in nanowires since these in many ways define the boundaries of our current understanding.

Co-based ternary bulk metallic glasses with ultrahigh strength and plasticity

Abstract: A family of ultrahigh strength Co-based bulk metallic glasses (BMGs) with critical diameters up to 2 mm is synthesized in Co65–xTaxB35 (at.%, x = 5–10) alloys by copper mold casting. The improved glass-forming ability associated with near eutectic compositions is attributed to the appropriate addition of Ta. The glassy alloys exhibit high glass transition temperature of 930–975 K, ultrahigh compressive strength of 5.6–6.0 GPa, high specific strength of 639–654 N·m/g, Vickers hardness of 15–16 GPa, and distinct plastic strain of 0.5–1.5%. The strength and the specific strength are the highest values reported for bulk metallic materials known so far. Several universal criteria correlated with the thermal properties, elastic constants, and mechanical properties were validated in the Co-based BMG system. These Co–Ta–B BMGs combining with superior mechanical properties, high thermal stability, and simple elemental composition are significant for scientific research as modeling materials and industrial application as advanced structural materials.

Half-Heusler phases and nanocomposites as emerging high-ZT thermoelectric materials

Abstract: Half-Heusler (HH) phases, a versatile class of alloys with promising functional properties, have recently gained attention as emerging thermoelectric materials. These materials are investigated from the perspective of thermal and electronic transport properties for enhancing the dimensionless figure of merit (ZT) at 800–1000 K. The electronic origin of thermopower enhancement is reviewed. Grain refinement and embedment of nanoparticles in HH alloy hosts were used to produce fine-grained as well as nanocomposites and monolithic nanostructured materials. Present experiments indicated that n-type Hf0.6Zr0.4NiSn0.995Sb0.005 HH alloys and p-type Hf0.3Zr0.7CoSn0.3Sb0.7/nano-ZrO2 composites can attain ZT = 1.05 and 0.8 near 900–1000 K, respectively. The observed ZT enhancements could be attributed to multiple origins; in particular, the electronic origin was identified. The prospect for higher ZT was investigated in light of a recently developed nanostructure model of lattice thermal conductivity. Tests performed on p–n couple devices from the newly developed HH materials showed good power generation efficiencies—achieving 8.7% efficiency for hot-side temperatures of about 700 °C.

Threading defect elimination in GaN nanowires

Abstract: This study describes the elimination of threading dislocations (TDs) in GaN nanostructures. Cross-sectional transmission electron microscopy (XTEM) analysis reveals that the nominal [0001] line direction of a TD changes when it enters a GaN nanostructure and the dislocation then terminates at a sidewall facet. It is suggested that the driving force for this process is the reduction of dislocation line energy, and for a pure-edge dislocation, this TD elimination process can be accomplished simply by dislocation climb. This mechanism is active whenever a threading defect is in close proximity to a surface. Preliminary XTEM analysis of defects in AlGaN and InGaN core–shell growth onto GaN nanostructures is also shown. Although more work is required to improve the quality of core–shell InGaN epitaxial growth, nanostructures appear to offer a route to defect-free, nonpolar GaN-based devices.

Selective-area growth of III-V nanowires and their applications

Abstract: We review the position-controlled growth of III-V nanowires (NWs) by selective-area metal-organic vapor-phase epitaxy (SA-MOVPE) This epitaxial technique enables the positioning of the vertical NWs on (111) oriented surfaces with lithographic techniques Core-shell structures have also been achieved by controlling the growth mode during SA-MOVPE The core-shell III-V NW-based devices such as light-emitting diodes, photovoltaic cells, and vertical surrounding-gate transistors are discussed in this article Nanometer-scale growth also enabled the integration of III-V NWs on Si regardless of lattice mismatches These demonstrated achievements should have broad applications in laser diodes, photodiodes, and high-electron mobility transistors with functionality on Si not made possible with conventional Si-CMOS techniques

Surface-induced effects in GaN nanowires

Abstract: Semiconductor nanowires (NWs) are characterized by an extraordinarily large surface-to-volume ratio. Consequently, surface effects are expected to play a much larger role than in thin films. Here, we review a research focused on the impact of the surface on the electrical and optical properties of catalyst-free GaN NWs with growth direction . Using a combination of complementary experimental techniques, it has been shown that the Fermi level is pinned at the NW sidewall surfaces, resulting in internal electric fields and in full depletion for NWs below a critical diameter. Deoxidation of the surfaces unpins the Fermi level, leading to enhanced radiative recombination of excitons. Prominent absorption below the bandgap is caused by the Franz-Keldysh effect. Close to the surface, the ionization energy of donors is reduced. The consideration of surface-induced effects is mandatory for an understanding of the physical properties of NWs as well as their application in devices.

Stick-slip dynamics and recent insights into shear banding in metallic glasses

Abstract: Despite extensive research, the understanding of the fundamental processes governing yielding and plastic flow in metallic glasses remains poor. This is due to experimental difficulties in capturing plastic flow as a result of a strong localization in space and time by the formation of shear bands at low homologous temperatures. Unveiling the mechanism of shear banding is hence key to developing a deeper understanding of plastic deformation in metallic glasses. We will compile recent progress in studying the dynamics of shear-band propagation from serrated flow curves. We will also take a perspective gleaned from stick-slip theory and show how the insights gained can be deployed to explain fundamental questions concerning the origin, mechanism, and characteristics of flow localization in metallic glasses.

Realization of high thermoelectric performance in n-type partially filled skutterudites

Abstract: Skutterudites are among the most exciting thermoelectric (TE) materials that could be used for various intermediate temperature applications. This study summarized our recent work on n-type partially filled skutterudites. By combining theoretical and experimental approaches, we revealed the underlying mechanism of void filling in the intrinsic lattice voids in CoSb3. With that, the electronegativity selection rule is established for the current stable filled skutterudites and further used for the discovery of a few novel filled CoSb3 compounds. The correlation between the thermal/electrical transport properties and impurity fillers in n-type partially filled skutterudites was also carefully investigated. Our results provide fundamental understanding to how those filler impurities affect electronic structures and lattice dynamics. Based on these basic understanding on transport mechanisms and sophisticated strategy in materials synthesis, TE figure of merit for n-type materials were continually increased from 1.1 to 1.4 and then to 1.7 for single-, double-, and triple-filled skutterudites.

The influence of ∑3 twin boundaries on the formation of radiation-induced defect clusters in nanotwinned Cu

Abstract: We investigate the collective effect of a high volume fraction of ∑3 twin boundaries on the response of nanotwinned Cu to high dose He implantation near room temperature and find that they do not curtail the formation of vacancy and interstitial clusters. This result is rationalized through atomistic modeling, which shows that point defects at these boundaries have nearly identical properties to those in pure fcc Cu.

Continuum modeling of dislocation plasticity: Theory, numerical implementation, and validation by discrete dislocation simulations

Abstract: Miniaturization of components and devices calls for an increased effort on physically motivated continuum theories, which can predict size-dependent plasticity by accounting for length scales associated with the dislocation microstructure. An important recent development has been the formulation of a Continuum Dislocation Dynamics theory (CDD) that provides a kinematically consistent continuum description of the dynamics of curved dislocation systems [T. Hochrainer, et al., Philos. Mag. 87, 1261 (2007)]. In this work, we present a brief overview of dislocation-based continuum plasticity models. We illustrate the implementation of CDD by a numerical example, bending of a thin film, and compare with results obtained by three-dimensional discrete dislocation dynamics (DDD) simulation.

A novel biomimetic material duplicating the structure and mechanics of natural nacre

Abstract: Nacre from mollusk shell is a high-performance natural composite composed of microscopic mineral tablets bonded by a tough biopolymer. Under tensile stress, the tablets slide on one another in a highly controlled fashion, which makes nacre 3000 times tougher than the mineral it is made of. Significant efforts have led to nacre-like materials, but none can yet match this amount of toughness amplification. This article presents the first synthetic material that successfully duplicates the mechanism of tablet sliding observed in nacre. Made of millimeter-size wavy poly-methyl-methacrylate tablets held by fasteners, this “model material” undergoes massive tablet sliding under tensile loading, accompanied by strain hardening. Analytical and finite element models successfully captured the salient deformation mechanisms in this material, enabling further design refinements and optimization. In addition, two new mechanisms were identified: the effect of free surfaces and “unzipping.” Both mechanisms may be relevant to natural materials such as nacre or bone.

Influence of Co content on stacking fault energy in Ni–Co base disk superalloys

Abstract: The influence of Co content on stacking fault energy (SFE) of the γ matrix in four Ni–Co base superalloys, including newly developed alloys, has been studied by utilizing high-resolution transmission electron microscopy. The results indicated the SFE was not linear with Co content of the γ matrix. The lowest SFE could be attained at around 34.0 at.% Co. This effect was attributed to variation of electron holes, saturated Co content in the matrix, and the effect of Co on the partition coefficient of other alloying elements. A high density of twins was related to low SFE and could improve the mechanical properties.

On the root cause of Kirkendall voiding in Cu3Sn

Abstract: Soldering to Cu interconnect pads with Sn-containing alloys usually leads to the formation of a layered Cu3Sn/Cu6Sn5 structure on the pad/solder interface. Frequently, microscopic voids within Cu3Sn have been observed to develop during extended thermal aging. This phenomenon, commonly referred to as Kirkendall voiding, has been the subject of a number of studies and speculations but so far the root cause has remained unidentified. In the present work, 103 different Cu samples, consisting of 101 commercially electroplated Cu and two high-purity wrought Cu samples, were surveyed for voiding propensity. A high temperature anneal of the Cu samples before soldering was seen to significantly reduce the voiding level in subsequent thermal aging. For several void-prone Cu foils, the anneal led to significant pore formation inside the Cu. In the mean time, Cu grain growth in the void-prone foils showed impeded grain boundary mobility. Such behaviors suggested that the root cause for voiding is organic impurities incorporated in the Cu during electroplating, rather than the Kirkendall effect.

Towards an integrated materials characterization toolbox

Abstract: The material characterization toolbox has recently experienced a number of parallel revolutionary advances, foreshadowing a time in the near future when material scientists can quantify material structure evolution across spatial and temporal space simultaneously. This will provide insight to reaction dynamics in four-dimensions, spanning multiple orders of magnitude in both temporal and spatial space. This study presents the authors’ viewpoint on the material characterization field, reviewing its recent past, evaluating its present capabilities, and proposing directions for its future development. Electron microscopy; atom probe tomography; x-ray, neutron and electron tomography; serial sectioning tomography; and diffraction-based analysis methods are reviewed, and opportunities for their future development are highlighted. Advances in surface probe microscopy have been reviewed recently and, therefore, are not included [D.A. Bonnell et al.: Rev. Modern Phys. in Review]. In this study particular attention is paid to studies that have pioneered the synergetic use of multiple techniques to provide complementary views of a single structure or process; several of these studies represent the state-of-the-art in characterization and suggest a trajectory for the continued development of the field. Based on this review, a set of grand challenges for characterization science is identified, including suggestions for instrumentation advances, scientific problems in microstructure analysis, and complex structure evolution problems involving material damage. The future of microstructural characterization is proposed to be one not only where individual techniques are pushed to their limits, but where the community devises strategies of technique synergy to address complex multiscale problems in materials science and engineering.

Indentation of polydimethylsiloxane submerged in organic solvents

Abstract: This work uses a method based on indentation to characterize a polydimethylsiloxane (PDMS) elastomer submerged in an organic solvent (decane, heptane, pentane, or cyclohexane). An indenter is pressed into a disk of a swollen elastomer to a fixed depth, and the force on the indenter is recorded as a function of time. By examining how the relaxation time scales with the radius of contact, one can differentiate the poroelastic behavior from the viscoelastic behavior. By matching the relaxation curve measured experimentally to that derived from the theory of poroelasticity, one can identify elastic constants and permeability. The measured elastic constants are interpreted within the Flory–Huggins theory. The measured permeability indicates that the solvent migrates in PDMS by diffusion, rather than by convection. This work confirms that indentation is a reliable and convenient method to characterize swollen elastomers.

Improved electrical and dielectric properties of La-doped Co ferrite

Abstract: We report on the enhanced dielectric constant and electrical resistivity of the Co-ferrite (CoO.Fe2O3) by partially substituting Fe with La. Structural characteristics of La-doped Co ferrite namely CoO.Fe1.925La0.075O3 indicate the cubic inverse spinel phase with a small amount of LaFeO3 additional phase. The lattice parameter obtained is 8.401 A (±0.001 A), which is higher than that reported for Co ferrite (8.387 A, ±0.001 A). The dielectric constant and electrical resistivity of CoO.Fe1.925La0.075O3 are higher compared with pure Co ferrite. The dielectric constant dispersion of CoO.Fe1.925La0.075O3 in the frequency range of 100 Hz to 1 MHz fits to the modified Debye’s function with more than one ion contributing to the relaxation. Temperature-dependent electrical resistivity curves exhibit two distinct regions indicative of two different types of conduction mechanisms. Analysis of the data indicates that the small polaron and variable-range hopping mechanisms are operative in the 220 to 300 K and 160 to 220 K temperature regions, respectively.

Spinning yarn from long carbon nanotube arrays

Abstract: Spinning carbon nanotube (CNT) thread directly from 4–6 mm long aligned carbon nanotube arrays is reported here. The strength of carbon nanotube thread was improved by optimizing the chemical vapor deposition parameters for growing long aligned carbon nanotube arrays. The morphological and structural characterization of CNT arrays and threads were studied by Raman spectroscopy, transmission electron microscopy, and scanning electron microscopy. After optimization of growth parameters threads were spun with diameters between 10 and 70 μm. We have achieved thread strength of about 280 MPa.

The mechanical properties of bamboo and vascular bundles

Abstract: Bamboo is a typical natural fiber-reinforced composite material with superior mechanical properties. As the reinforce phase in bamboo composite, the vascular bundles were extracted from different height locations of a Moso bamboo with an alkali treatment method, and the mechanical properties were investigated via the tensile test. It is found that both the longitudinal Young’s modulus and strength of the vascular bundles are linearly increased from the inner to outer side. To study the variation of mechanical properties of bamboo culm along the radial direction, thin bamboo slices were also tested. Using a modified rule of mixtures, the longitudinal Young’s modulus of bamboo slices are analyzed and excellent agreement can be found between experimental and theoretical results, which indicates that the longitudinal Young’s modulus of bamboo culm is cubically increased in the radial direction.

Predicting the dislocation nucleation rate as a function of temperature and stress

Abstract: Predicting the dislocation nucleation rate as a function of temperature and stress is crucial for understanding the plastic deformation of nanoscale crystalline materials. However, the limited time scale of molecular dynamics simulations makes it very difficult to predict the dislocation nucleation rate at experimentally relevant conditions. We recently develop an approach to predict the dislocation nucleation rate based on the Becker–Doring theory of nucleation and umbrella sampling simulations. The results reveal very large activation entropies, which originated from the anharmonic effects, that can alter the nucleation rate by many orders of magnitude. Here we discuss the thermodynamics and algorithms underlying these calculations in greater detail. In particular, we prove that the activation Helmholtz free energy equals the activation Gibbs free energy in the thermodynamic limit and explain the large difference in the activation entropies in the constant stress and constant strain ensembles. We also discuss the origin of the large activation entropies for dislocation nucleation, along with previous theoretical estimates of the activation entropy.

Thermoelectric properties of spark plasma sintered composites based on TiNiSn half-Heusler alloys

Abstract: Half-Heusler (HH) and especially TiNiSn-based alloys have shown high potential as thermoelectric (TE) materials for power generation applications. The reported transport properties show, however, a significant spread of results, due mainly to the difficulty in fabricating single-phase HH samples in these multicomponent and multiphased systems. In particular, little attention has been paid to the influence of the various minority phases on the TE performance of these compounds. A clear understanding of these issues is mandatory for the design of improved and stable TE HH-based composites. This study examines the structural and compositional influence of the residual metallic (Sn) and intermetallic phases (mainly Ti6Sn5 and the Heusler compound TiNi2Sn) on the TE properties of the TiNiSn HH compounds processed by spark plasma sintering.

Ni- and Cu-free Zr–Al–Co–Ag bulk metallic glasses with superior glass-forming ability

Abstract: Ni- and Cu-free Zr–Al–Co–Ag bulk metallic glasses (BMGs) with diameters up to 20 mm were synthesized by copper mold casting. The effects of Ag alloying on the superior glass-forming ability (GFA) of Zr–Al–Co–Ag alloys were studied based on the localized atomic structure and crystallization behavior. High-energy synchrotron radiation x-ray diffraction result reveals that Ag addition in Zr–Al–Co system results in a more homogeneous local atomic structure, which could be an origin for the improved GFA of the Zr–Al–Co–Ag alloy. Crystallization products of the Zr–Al–Co–Ag glassy alloy are more complex than those of the Zr–Al–Co glassy alloy. The Zr–Al–Co–Ag BMGs free from highly toxic elements Ni and Cu exhibited a combination of superior GFA, high compressive fracture strength over 2000 MPa, low Young’s modulus of 93 to 94 GPa, and good corrosion resistance in phosphate-buffered solution (PBS), inspiring their potential biomedical applications.

Vanadium oxide nanowires for Li-ion batteries

Abstract: Vanadium oxide nanowires have gained increasing interest as the electrode materials for Li-ion batteries. This article presents the recent developments of vanadium oxide nanowire materials and devices in Li-ion batteries. First, we will describe synthesis and construction of vanadium oxide nanowires. Then, we mainly focus on the electrochemical performances of vanadium oxide nanowires, such as VO2, V2O5, hydrated vanadium oxides, LiV3O8, silver vanadium oxides, etc. Moreover, design and in situ characterization of the single nanowire electrochemical device are also discussed. The challenges and opportunities of vanadium oxide nanowire electrode materials will be discussed as a conclusion to push the fundamental and practical limitations of this kind of nanowire materials for Li-ion batteries.

Investigation of the sintering pressure and thermal conductivity anisotropy of melt-spun spark-plasma-sintered (Bi,Sb)2Te3 thermoelectric materials

Abstract: A combined melt-spinning and spark-plasma-sintering (SPS) procedure has proven to be effective in preparing high-performance (Bi,Sb)2Te3 thermoelectric (TE) nanocomposites via creating and optimizing their resulting multiscale microstructures. (Bi,Sb)2Te3 possesses a highly anisotropic crystal structure; therefore, it is important to investigate any potential correlation between the SPS conditions, the as-formed microstructures, and the resulting TE properties. In this work, we investigate the correlation between the SPS pressure, the microstructure texture, and the anisotropy of the total thermal conductivity in these melt-spun spark-plasma-sintered (Bi,Sb)2Te3 compounds. The thermal conductivity has been measured in directions that are both perpendicular and parallel to the pressing (or force) direction by rearranging the sample geometry as described in the text. The results show that the anisotropy of thermal conductivity is ∼0, 2–3, 6–7, and 13–15% for the samples sintered at pressures of 20, 30, 45, and 60 MPa, respectively. These results are consistent with an increasing degree of orientation observed by x-ray diffraction and electron microscopy.

Thermal expansion of Cu6Sn5 and (Cu,Ni)6Sn5

Abstract: Cu6Sn5 is a common intermetallic compound formed during electrical packaging. It has an allotropic transformation from the low-temperature monoclinic η′-Cu6Sn5 to high-temperature hexagonal η-Cu6Sn5 at equilibrium temperature 186 °C. In this research, the effects of this allotropie transformation and Ni addition on the thermal expansion of η′- and/or r)-Cu6Sn5 were characterized using synchrotron x-ray diffraction and dilatometry. A volume expansion during the monoclinic to hexagonal transformation was found. The addition of Ni was found to decrease the undesirable thermal expansion by stabilizing the hexagonal Cu6Sn5 at temperatures below 186 °C and reducing the overall thermal expansion of Cu6Sn5.

Origin and magnitude of the large piezoelectric response in the lead-free (1–x)BiFeO3–xBaTiO3 solid solution

Abstract: Mechanisms and magnitudes of the large piezoelectric response observed in lead-free (1-x) BiFeO3-xBaTiO3 (BFBT) ceramics are investigated. Preceding studies reported significant strain hysteresis and hard ferroelectric behavior in BFBT leading to a small low-field piezoelectric coefficient, instability of the poled domain state, and rapid degradation of piezoelectric properties. The current investigation shows that under application of a suitable direct current (dc) bias to stabilize the ferroelectric phase low- and high-field piezoelectric coefficients (d33) of 150 pC/N and 250 pC/N are observed for the composition 0.67BiFeO3-0.33BaTiO3 + 0.1 wt% MnO with a Curie temperature of 605 °C. Such enhancement of electromechanical properties under dc bias is in contrast to the expected behavior in traditional piezoelectric materials such as soft lead zirconate titanate (PZT). The large piezoelectric coefficients confirm strong intrinsic and extrinsic contributions to the piezoelectric response in BFBT, which coupled with high ferroelectric Curie temperature TC > 500 °C, suggests BFBT-based materials as promising lead-free alternatives to PZT piezoceramics.

The optical properties of Cu-Ni nanoparticles produced via pulsed laser dewetting of ultrathin films: The effect of nanoparticle size and composition on the plasmon response

Abstract: Thin film Cu-Ni alloys ranging from 2–8 nm were synthesized and their optical properties were measured as-deposited and after a laser treatment which dewet the films into arrays of spatially correlated nanoparticles. The resultant nanoparticle size and spacing are attributed to a laser induced spinodal dewetting process. The evolution of the spinodal dewetting process is investigated as a function of the thin film composition which ultimately dictates the size distribution and spacing of the nanoparticles. The optical measurements of the copper rich alloy nanoparticles reveal a signature absorption peak suggestive of a plasmon peak that red-shifts with increasing nanoparticle size and blue-shifts and dampens with increasing nickel concentration.