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All-optical switching of magnetization has great potential for use in future ultrafast and energy efficient nanoscale magnetic storage devices. So far, research has been almost exclusively focused on rare-earth based materials, which limits device tunability and scalability. Here, we show that a perpendicularly magnetized synthetic ferrimagnet composed of two distinct transition metal ferromagnetic layers, Ni3Pt and Co, can exhibit helicity independent magnetization switching. Switching occurs between two equivalent remanent states with antiparallel alignment of the Ni3Pt and Co magnetic moments and is observable over a broad temperature range. Time-resolved measurements indicate that the switching is driven by a spin-polarized current passing through the subnanometer Ir interlayer. The magnetic properties of this model system may be tuned continuously via subnanoscale changes in the constituent layer thicknesses as well as growth conditions, allowing the underlying mechanisms to be elucidated and paving the way to a new class of data storage devices.

Optical properties of refractory intermetallic thin films of Au$_{3}$Zr were experimentally investigated for the first time, which show distinctive plasmonic properties in the visible and near infrared region. The films were fabricated through DC magnetron sputtering at various deposition temperature ranging from room temperature to 427$^{o}$C and annealed at different vacuum levels. Both the structural and optical properties are found to be critically dependent on deposition temperature and anneal conditions. Films deposited between 205-320$^{o}$C are shown to exhibit lower negative permittivity and better thermal stability, which could be linked to specific crystalline orientations. The films are stable when annealed at 10$^{-8}$ Torr, but are partially oxidized when annealed at 10$^{-6}$ Torr, suggesting oxidization could be a restricting issue for high-temperature applications in ambient environment., Comment: 12 pages, plus 3 pages in attached supplementary information. 7 figures in main text, plus 1 table and 1 figure in attached supplementary information

Mechanical exfoliation yields high‐quality 2D materials but is challenging to scale up due to the small lateral size and low yield of the exfoliated crystals. Gold‐mediated exfoliation of macroscale monolayer MoS2 and related crystals addresses this problem. However, it remains unclear whether this method can be extended to other metals. Herein, mechanical exfoliation of MoS2 on a range of metallic substrates is studied. It is found that Au outperforms all the other metals in their ability to exfoliate macroscale monolayer MoS2. This is rationalized by gold's ability to resist oxidation, which is compromised on other metals and leads to a weakened binding with MoS2. An anomalously high monolayer yield found for Ag suggests that the large interfacial strain in the metal–MoS2 heterostructures measured by Raman spectroscopy also is a critical factor facilitating the exfoliation, while the relative differences in the metal–MoS2 binding play only a minor role. These results provide a new incentive for investigations of 2D material‐substrate combinations applicable where high‐quality 2D crystals of macroscopic dimensions are of importance.

Being able to precisely control the reduction of two-dimensional graphene oxide films will open exciting opportunities for tailor-making the functionality of nanodevices with on-demand properties. Here we report the meticulously controlled reduction of individual graphene oxide flakes ranging from single to seven layers through controlled laser irradiation. It is found that the reduction can be customized in such a precise way that the film thickness can be accurately thinned with sub-nanometer resolution, facilitated by extraordinary temperature gradients >102 K nm−1 across the interlayers of graphene oxide films. Such precisely controlled reduction provides important pathways towards precision nanotechnology with custom-designed electrical, thermal, optical and chemical properties. We demonstrate that this can be exploited to fine tune the work function of graphene oxide films with unprecedented precision of only a few milli electronvolts.

Confining light in extremely small cavities is crucial in nanophotonics, central to many applications. Employing a unique nanoparticle-on-mirror plasmonic structure and using a graphene film as a spacer, we create nanoscale cavities with volumes of only a few tens of cubic nanometers. The ultracompact cavity produces extremely strong optical near-fields, which facilitate the formation of single carbon quantum dots in the cavity and simultaneously empower the strong coupling between the excitons of the formed carbon quantum dot and the localized surface plasmons. This is manifested in the optical scattering spectra, showing a magnificent Rabi splitting of up to 200 meV under ambient conditions. In addition, we demonstrate that the strong coupling is tuneable with light irradiation. This opens new paradigms for investigating the fundamental light emission properties of carbon quantum dots in the quantum regime and paves the way for many significant applications.

An in situ transmission-based system has been designed to optically monitor the ellipsometry constants of a hyperbolic plasmonic metamaterial during electrochemical growth. The metamaterial, made from an array of vertically aligned gold nanorods, has demonstrated an unprecedented ability to manipulate the polarization of light using subwavelength thickness slabs, making in situ ellipsometric data a powerful tool in the controlled design of such components. In this work, we show practical proof-of-principle of this design method and rationalize the ellipsometric output on the basis of the modal properties of the nanorod metamaterial. The real-time optical monitoring setup provides excellent control and repeatability of nanostructure growth for the design of future ultrathin optical components. The performance of the ellipsometric method was also tested as a refractive index sensor. Monitoring refractive index changes near the metamaterial’s epsilon near zero (ENZ) frequency showed a sensitivity on the order of 500°/RIU in the ellipsometric phase for a metamaterial that shows 250 nm/RIU sensitivity in its extinction.

Mechanical exfoliation is one of the most important methods of fabricating high-quality two-dimensional (2D) materials. Compared against other fabrication techniques such as chemical vapor deposition (CVD) and liquid phase exfoliation, films exfoliated by the traditional scotch-tape method retain the high quality of pristine crystals and are clean with little contamination. As such, they are instrumental to the research and technological development in the field of 2D materials.

Intermetallic alloys are increasingly attracting attention as important alternative plasmonic materials, due to their high melting temperatures and strong mechanical strength [1]. They are potential candidate materials in applications in harsh environments, such as heat-assisted magnetic recording (HAMR) and photothermal photovoltaics [2,3].

Photomechanics, i.e., the conversion of light into thermal and mechanical work is of significant importance for energy conversion/reconfigurable technologies. Advantages of such photo-thermal mechanisms for transducers include remote energy transfer, remote controllability, control of actuation using number of photons (intensity) and photon energies (wavelength), fast actuation (milliseconds), low signal to noise ratio, high stored elastic strain energy densities with hyperelastic elastomers and scalability at different length scales using batch fabrication and high-volume semiconductor manufacturing. However, only a few materials exist that can convert light into mechanical work. Azobenzene liquid crystal elastomers were one of the first materials to exhibit the photomechanical effect. However, their application required two different light sources for reversible thermal switching (420 nm and 365 nm) between an extended trans and a shorter cis configuration. In this talk, we will cover how light is used with new materials to create the mechanical effect. New nanomaterials, when mixed with polymeric materials, show the unusual photomechanical effect that can be practically harnessed for real-world application. Straining new 2D nanomaterials such as graphene, MoS2 and others creates a new effect called the coupled straintronic photo-thermic effect enables large light absorption and also increase in mechanical effect. The talk will go through an overview of this new and upcoming area of research based on light-matter interaction in 1D and 2D nanomaterial composites

Atomically-thin two-dimensional (2D) materials have attracted remarkable interest in a wide range of research and applications. However, one of the main challenges is how to visualise the extremely thin films and accurately identify its layer thickness. Due to the ultimately thin thickness and the low absorption of light, many 2D films, such as graphene, graphene oxide and hexagonal boron nitride (hBN) are nearly completely transparent on most surfaces. They are only visible when deposited on specific contrast-enhancing substrates. However, there is no universal substrates which can be used to visualise all 2D materials. A substrate often can only provide enhanced visibility for a specific category of 2D materials. For instance, the oxidised Si substrates can considerably enhance the optical contrast of graphene, but produce negligible enhancing effect on hBN. It is therefore desirable to develop a general theoretical guidance on how to design contrast-enhancing substrate for any given 2D materials. Here we report a universal theoretical model which can be employed to design high-contrast substrates for any 2D materials. For a given thin film of known optical properties, the optical contrast is completely defined by the complex reflectivity of the underlying substrate. By engineering the optical properties of the underlying substrate, we fabricated a range of structures, significantly enhancing the contrast of graphene, graphene oxides and hBN. Monolayers of these transparent 2D films are readily visible (>10% contrast) on a range of substrates with metallic or dielectric materials as top surface layers. The measured optical contrasts excellently match theoretical calculations.

The thickness of graphene films can be accurately determined by optical contrast spectroscopy. However, this becomes challenging and complicated when the flake size reduces to the micrometre scale, where the contrast spectrum is sensitively dependent on the polarization and incident angle of light. Here we report accurate measurement of the optical contrast spectra of micrometre-sized few-layer graphene flakes on Au substrate. Us-ing a high-resolution optical microscopy with a 100x magnification objective, we accurately determined the lay-er numbers of flakes as small as one micrometre in lateral size. We developed a rigorous theoretical model to accurately take into account the appropriate contribution of light incident at various angles and polarizations, which matched the experimental results extremely well. Furthermore, we demonstrate that the optical contrast spectroscopy is highly sensitive to detect the adsorption of a sub-monolayer airborne hydrocarbon molecules, which can reveal whether graphene is contaminated. Though the technique was demonstrated on graphene, it can be readily generalized to many other two-dimensional (2D) materials, which opens new avenues for devel-oping miniaturized and ultrasensitive molecular sensors.

Metals have been increasingly used as substrates in devices based on two-dimensional (2D) materials. However, the high reflectivity of bulk metals results in low optical contrast (2/Si substrate, the optical contrast of graphene and graphene oxide (GO) can be significantly enhanced in comparison to bulk Au, up to about 3 and 5 times, respectively. In particular, we achieved ∼17% optical contrast for monolayer GO, which is even 2 times higher than that on bare SiO2/Si substrate. The experimental results are in good agreement with theoretical simulations. This concept is demonstrated for Au, but the methodology is applicable to other metals and can be adopted to design a variety of high-contrast metallic substrates. This will facilitate research and applications of 2D materials in areas such as plasmonics, photonics, catalysis and sensors.

Extraordinarily high optical contrast is instrumental to research and applications of two-dimensional materials, such as, for rapid identification of thickness, characterisation of optical properties, and quality assessment. With optimal designs of substrate structures and light illumination conditions, unprecedented optical contrast of MoS2 on Au surfaces exceeding 430% for monolayer and over 2600% for bilayer is achieved. This is realised on custom-designed substrates of near-zero reflectance near the normal incidence. In particular, by using an aperture stop to restrict the angle of incidence, high-magnification objectives can be made to achieve extraordinarily high optical contrast in a similar way as the low-magnification objectives, but still retaining the high spatial resolution capability. The technique will allow small flakes of micrometre size to be located easily and identified with great accuracy, which will have significant implications in many applications.

We report the investigations of spin wave modes of arrays of Ni and Co nanorods using Brillouin light scattering. We have revealed the significant influence of spin wave modes along the nanorod axis in contrast to infinite magnetic nanowires. Unusual optical properties featuring an inverted Stokes/anti-Stokes asymmetry of the Brillouin scattering spectra have been observed. The spectrum of spin wave modes in the nanorod array has been calculated and compared with the experiment. Experimental observations are explained in terms of a combined numerical–analytical approach taking into account both the low aspect ratio of individual magnetic nanorods and dipolar magnetic coupling between the nanorods in the array. The optical studies of spin-wave modes in nanorod metamaterials with low aspect ratio nanorods have revealed new magnetic and magneto-optical properties compared to continuous magnetic films or infinite magnetic nanowires. Such magnetic artificial materials are important class of active metamaterials needed for prospective data storage and signal processing applications.

We show that aligned gold nanotube arrays capable of supporting plasmonic resonances can be used as high performance refractive index sensors in biomolecular binding reactions. A methodology to examine the sensing ability of the inside and outside walls of the nanotube structures is presented. The sensitivity of the plasmonic nanotubes is found to increase as the nanotube walls are exposed, and the sensing characteristic of the inside and outside walls is shown to be different. Finite element simulations showed good qualitative agreement with the observed behavior. Free standing gold nanotubes displayed bulk sensitivities in the region of 250 nm per refractive index unit and a signal-to-noise ratio better than 1000 upon protein binding which is highly competitive with state-of-the-art label-free sensors.

Summary The nonlinear optical properties of gold nanorod arrays have been studied with a two-colour continuosly working (CW) pump-probe spectroscopy. The hybridization of the nanorod arrays with a nonlinear polymer (poly-3BCMU) has been investigated for the purposes of active photonic component design. The sensitivity of the plasmonic resonances of the hybrid nanostructured system to pump-induced changes in the refractive index of the polymer surroundings has been used to control the optical extinction of the array. Both reversible and non-reversible behaviour has been observed reflecting the combined effects from the third-order nonlinear response of the hybrid metallo-dielectric system and post-photopolymerization triggered reactions in the polymer.

The fabrication and optical properties of a nanostructured system consisting of free-standing metallic nanorods surrounded by a dielectric nanoshell are reported. The adjustable core−shell geometry...

Arrays of nickel and gold nanorods have been grown on glass and silicon substrates using porous alumina templates of less than 500 nm thickness. A method is demonstrated for varying the diameter of the nanorods whilst keeping the spacing constant. Optical extinction spectra for the gold nanorods show two distinct maxima associated with the transverse and longitudinal axes of the rods. Adding small quantities of oxygen to the aluminium before anodization is found to improve the sharpness of the extinction peaks. The spectral position of the longitudinal peak is shown to be sensitive to the nanorod diameter for constant length and spacing. For the nickel nanorods it is shown that the magnetic properties are governed by both interactions between the wires and shape anisotropy.

The growth of magnetron sputtered Co/Au and Pd/Co/Au superlattices on Au and Pd buffer layers, deposited onto glass substrates, has been monitored optically and magneto-optically in real time, using rotating analyser ellipsometry and Kerr polarimetry, at a wavelength of 633 nm. The magneto-optical traces, combined with ex situ and in situ hysteresis loops, provide a detailed and informative fingerprint of the optical and magnetic properties of the films as they evolve during growth. For Co/Au, oscillations in the polar magneto-optical effect developed during the deposition of Au overlayers on Co and these may be attributed to quantum well states. However, the hysteresis measurements show that the magnetic field required to maintain saturation magnetization throughout the experiment was larger than available in situ, introducing a degree of confusion concerning the interpretation of the data. This problem was overcome by the incorporation of Pd layers into the Co/Au structure, thereby eliminating variation in magnetic orientation during growth of the Au layers as a contributory factor to the observations.

Existing quadrilayer and trilayer techniques for optimizing the magneto-optical effects from magnetic materials have been applied to new generation recording media to investigate the possibility of maximizing the signal-to-noise readout performance. Various methods are reviewed and the designs they produce are compared with each other and with the working media found in the literature. In order to address a number of inadequacies, a new numerical approach to the optimization of a quadrilayer structure is used to find further solutions that are considered more suitable for the practical recording media. The effects on design and performance of medium of incidence, type of storage layer and wavelength are all considered.

The effect of adjacent dielectric layers on sputter deposited GdFeCo, of thickness 10–30 nm, suitable as the readout layer for in-plane magnetic amplifying magneto-optic systems, was investigated by measuring the magnetic hysteresis using magneto-optical Kerr effect at room temperature and above. It was found that the magnetic properties were sensitive to the GdFeCo thickness and the presence of the dielectric layer material. Although alternative materials, ZnS and SiN, were also considered, the paper concentrates on the effects of reactively sputtered AlN, which was the only dielectric that produced the required properties for such thin GdFeCo layers of this type. The effect of reducing GdFeCo thickness was similar to that of reducing Gd content. The percentage of nitrogen used in the sputtering gas during AlN deposition was seen to be crucial to the magnetic properties and to the stability of the films. Films 10 nm thick were particularly affected, the best results requiring less nitrogen than was needed for the thicker films.

Thin, optically semi-infinite films of amorphous TbFeCo and GdFeCo, suitable for magneto-optical recording, have been deposited by DC magnetron sputtering onto glass. Ellipsometric techniques have been used to determine the complex refractive index and complex magneto-optical parameter of the films in the wavelength range 400–900 nm, thus characterizing the materials. A review of the literature is presented and shows that the results for the TbFeCo films compare favourably with published results obtained from measurements conducted in situ, with the films protected with ZnS barrier layers. It is found that GdFeCo and TbFeCo are optically very similar, but magneto-optically the materials are quite different.

In this work we present core–shell nanowire arrays of gold coated with a nanometric layer of cobalt. Despite the extremely small Co volume, these core–shell nanowires display large magneto-optical activity and plasmonic resonance determined by the geometry of the structure. Therefore, we are able to tune both the plasmonic and magneto-optical response in the visible range. Through optical and ellipsometric measurements in transmission, and applying a magnetic field to the sample, it is possible to modulate the value of the phase angle (Del {Δ}) between the S and P polarised components. It was found that the core–shell sample produced an order of magnitude larger variation in Del with changing magnetic field direction, compared with hollow cobalt tubes. The enhancement of magneto optical properties through the plasmonic nature of the gold core is complemented with the ability to induce magnetic influence over optical properties via an externally applied field. Moreover, we demonstrate for the first time the ability to use the remanent magnetisation of the Co, in conjunction with the optical properties defined by the Au, to observe remanent optical states in this uniquely designed structure. This new class of magnetoplasmonic metamaterial has great potential in a wide range of applications, from bio-sensing to data storage due to the tuneable nature of multiple resonance modes and dual functionality.

Despite being the most suitable candidates for solenoid pole pieces in state-of-the-art superconductor-based electromagnets, the intrinsic magnetic properties of heavy rare earth metals and their alloys have gained comparatively little attention. With the potential of integration in micro and nanoscale devices, thin films of Gd, Dy, Tb, DyGd and DyTb were plasma-sputtered and investigated for their in-plane magnetic properties, with an emphasis on magnetization versus temperature profiles. Based on crystal structure analysis of the polycrystalline rare earth films, which consist of a low magnetic moment fcc layer at the seed interface topped with a higher moment hcp layer, an experimental protocol is introduced which allows the direct magnetic analysis of the individual layers. In line with the general trend of heavy lanthanides, the saturation magnetization was found to drop with increasing unit cell size. In situ annealed rare earth films exceeded the saturation magnetization of a high-moment Fe65Co35 reference film in the cryogenic temperature regime, proving their potential for pole piece applications; however as-deposited rare earth films were found completely unsuitable. In agreement with theoretical predictions, sufficiently strained crystal phases of Tb and Dy did not exhibit an incommensurate magnetic order, unlike their single-crystal counterparts which have a helical phase. DyGd and DyTb alloys followed the trends of the elemental rare earth metals in terms of crystal structure and magnetic properties. Inter-rare-earth alloys hence present a desirable blend of saturation magnetization and operating temperature.

In situ ellipsometry and Kerr polarimetry have been used to follow the continuous evolution of the optical and magneto-optical properties of multiple layers of Co and Pd during their growth. Films were sputter deposited onto a Pd buffer layer on glass substrates up to a maximum of N = 10 bi-layer periods according to the scheme glass/Pd(10)N×(0.3Co/3Pd) (nm). Magnetic hysteresis measurements taken during the deposition consistently showed strong perpendicular anisotropy at all stages of film growth following the deposition of a single monolayer of Co. Magneto-optic signals associated with the normal-incidence polar Kerr effect indicated strong polarization of Pd atoms at both Co-Pd and Pd-Co interfaces and that the magnitude of the complex magneto-optic Voigt parameter and the magnetic moment of the Pd decrease exponentially with distance from the interface with a decay constant of 1.1 nm-1. Theoretical simulations have provided an understanding of the observations and allow the determination of the ultrathin-film values of the elements of the skew-symmetric permittivity tensor that describe the optical and magneto-optical properties for both Co and Pd. Detailed structure in the observed Kerr ellipticity shows distinct Pd-thickness-dependent oscillations with a spatial period of about 1.6 nm that are believed to be associated with quantum well levels in the growing Pd layer.

The requirements for metrology of magnetostriction in complex multilayers and on whole wafers present challenges. An elegant technique based on radius of curvature deformation of whole wafers in a commercial metrology tool is described. The method is based on the Villari effect through application of strain to a film by introducing a radius of curvature. Strain can be applied tensilely and compressively depending on the material. The design, while implemented on 3'' wafers, is scalable. The approach removes effects arising from any shape anisotropy that occurs with smaller samples, which can lead to a change in magnetic response. From the change in the magnetic anisotropy as a function of the radius, saturation magnetostriction λs can be determined. Dependence on film composition and film thickness was studied to validate the radius of curvature approach with other techniques. λs decreases from positive values to negative values through an increase in Ni concentration around the permalloy composition, and λs also increases with a decrease in film thickness, in full agreement with previous reports. We extend the technique by demonstrating the technique applied to a multi-layered structure. These results verify the validity of the method and are an important step to facilitate further work in understanding how manipulation of multilayered films can offer tailored magnetostriction.

There is renewed interest in rare-earth elements and gadolinium in particular for a range of studies in coupling physics and applications. However, it is still apparent that synthesis impacts understanding of the intrinsic magnetic properties of thin gadolinium films, particularly for thicknesses of topicality. We report studies on 50nm thick nanogranular polycrystalline gadolinium thin films on SiO2 wafers that demonstrate single-crystal like behavior. The maximum in-plane saturation magnetization at 4K was found to be 4{\pi}MS4K = (2.61{\pm}0.26)T with a coercivity of HC4K = (160{\pm}5)Oe. A maximum Curie point of TC = (293{\pm}2)K was measured via zero-field-cooled - field- cooled magnetization measurements in close agreement with values reported in bulk single crystals. Our measurements revealed magnetic transitions at T1 = (12{\pm}2)K (as deposited samples) and T2 = (22{\pm}2)K (depositions on heated substrates) possibly arising from the interaction of paramagnetic fcc grains with their ferromagnetic hcp counterparts., Comment: 14 pages, 3 figures, to be publ

We demonstrate excitation of additional electromagnetic waves in plasmonic nanorod metamaterials. These waves arising from a nonlocal optical response of metamaterial results in strongly enhanced ultrafast nonlinear response.

The optical and magneto-optical properties of Co/Au multilayers, grown by molecular beam epitaxy (MBE), have been examined in the wavelength range 300 to 900 nm using ellipsometry and normal incidence Kerr polarimetry. The dispersion of fundamental optical and magneto-optical constants and the complex Kerr rotation are discussed in terms of the interaction of electromagnetic radiation with a multilayered structure. This is done on the basis of a single equivalent layer approach for dealing with multilayered media using values for the optical constants of cobalt and gold measured on single films of these materials grown by MBE. It is suggested that a restriction of the mean free path of the conduction electrons in the gold layers, of the order of the individual sub-layer thickness, accounts for some aspects of the observed optical spectra.

Arrays of vertically aligned gold nanotubes are fabricated over several square centimetres which display a geometry tunable plasmonic extinction peak at visible wavelengths and at normal incidence. The fabrication method gives control over nanotube dimensions with inner core diameters of 15-30 nm, wall thicknesses of 5-15 nm and nanotube lengths of up to 300 nm. It is possible to tune the position of the extinction peak through the wavelength range 600-900 nm by varying the inner core diameter and wall thickness. The experimental data are in agreement with numerical modelling of the optical properties which further reveal highly localized and enhanced electric fields around the nanotubes. The tunable nature of the optical response exhibited by such structures could be important for various label-free sensing applications based on both refractive index sensing and surface-enhanced Raman scattering.

All-optical signal processing enables modulation and transmission speeds not achievable using electronics alone. However, its practical applications are limited by the inherently weak nonlinear effects that govern photon-photon interactions in conventional materials, particularly at high switching rates. Here, we show that the recently discovered nonlocal optical behaviour of plasmonic nanorod metamaterials enables an enhanced, ultrafast, nonlinear optical response. We observe a large (80%) change of transmission through a subwavelength thick slab of metamaterial subjected to a low control light fluence of 7 mJ cm(-2), with switching frequencies in the terahertz range. We show that both the response time and the nonlinearity can be engineered by appropriate design of the metamaterial nanostructure. The use of nonlocality to enhance the nonlinear optical response of metamaterials, demonstrated here in plasmonic nanorod composites, could lead to ultrafast, low-power all-optical information processing in subwavelength-scale devices.

We present an optical sensor based on plasmonic nanorod metamaterials. The sensor operates similar to well-established surface plasmon polariton sensors, but offers order-of-magnitude improvement over existing technology. Optical and biological applications are discussed.

Dynamic magnetic properties of arrays of Ni nanorods with a low aspect ratio have been investigated. It has been shown that the spectra of spin-wave resonances localized on nanorods with a low aspect ratio typically feature the presence of zones with high density of states resulting in a characteristic two-peak pattern of Stokes and anti-Stokes lines of magneto-optical (MO) Brillouin light scattering with pronounced Stokes--anti-Stokes (S-AS) asymmetry. A simple theoretical model based on the analysis of the elliptic character of the polarization of the optical wave interacting with a dipole magnetostatic wave has been proposed. It has been shown that the S-AS asymmetry is due entirely to the asymmetry of the MO interaction efficiency with respect to time reversal of the magnetic precession in a magnon.

In situ measurements of the magneto-optical polar Kerr effect have been made continuously during the deposition of a series of Co and Pt layers. The results indicate an exponentially decaying induced magnetic behaviour in the platinum. However, it is clear that there is asymmetry between the measurements at Co–Pt and Pt–Co interfaces. Data are simulated by electrodynamic theory using bulk optical constants and magneto-optical constants for Co and Pt extracted from experimental data for a single period.

We analyze the optical properties of plasmonic nanorod metamaterials in the epsilon-near-zero regime and show, both theoretically and experimentally, that the performance of these composites is strongly affected by nonlocal response of the effective permittivity tensor. We provide the evidence of interference between main and additional waves propagating in the room-temperature nanorod metamaterials and develop an analytical description of this phenomenon. Additional waves are present in the majority of low-loss epsilon-near-zero structures and should be explicitly considered when designing applications of epsilon-near-zero composites, as they represent a separate communication channel.

Label-free plasmonic biosensors rely either on surface plasmon polaritons or on localized surface plasmons on continuous or nanostructured noble-metal surfaces to detect molecular-binding events. Despite undisputed advantages, including spectral tunability, strong enhancement of the local electric field and much better adaptability to modern nanobiotechnology architectures, localized plasmons demonstrate orders of magnitude lower sensitivity compared with their guided counterparts. Here, we demonstrate an improvement in biosensing technology using a plasmonic metamaterial that is capable of supporting a guided mode in a porous nanorod layer. Benefiting from a substantial overlap between the probing field and the active biological substance incorporated between the nanorods and a strong plasmon-mediated energy confinement inside the layer, this metamaterial provides an enhanced sensitivity to refractive-index variations of the medium between the rods (more than 30,000 nm per refractive-index unit). We demonstrate the feasibility of our approach using a standard streptavidin-biotin affinity model and record considerable improvement in the detection limit of small analytes compared with conventional label-free plasmonic devices.

We demonstrate that the coupling between plasmonic modes of oriented metallic nanorods results in the formation of an extended (guided) plasmonic mode of the nanorod array. The electromagnetic field distribution associated to this mode is found to be concentrated between the nanorods within the assembly and propagates normally to the nanorod long axes, similar to a photonic mode waveguided by an anisotropic slab. This collective plasmonic mode determines the optical properties of nanorod assemblies and can be tuned in a wide spectral range by changing the nanorod array geometry. This geometry represents a unique opportunity for light guiding applications and manipulation at the nanoscale as well as sensing applications and development of molecular plasmonic devices.

Silver nanorods have been grown by electrodeposition into thin film porous alumina templates (AAO). Optical transmission measurements using p-polarized incident white light shows clear plasmon resonance extinction peaks. We successfully model the dependence on angle in incidence of extinction peak height and position using a multiple–multipoles (MMP) approach with the different spectral features being clearly associated with the effective electric field distribution and coupling between individual nanorods.

Controlling coherent electromagnetic interactions in molecular systems is a problem of both fundamental interest and important applicative potential in the development of photonic and opto-electronic devices. The strength of these interactions determines both the absorption and emission properties of molecules coupled to nanostructures, effectively governing the optical properties of such a composite metamaterial. Here we report on the observation of strong coupling between a plasmon supported by an assembly of oriented gold nanorods (ANR) and a molecular exciton. We show that the coupling is easily engineered and is deterministic as both spatial and spectral overlap between the plasmonic structure and molecular aggregates are controlled. We think that these results in conjunction with the flexible geometry of the ANR are of potential significance to the development of plasmonic molecular devices.

A series of thin films comprising gold nanorods embedded in an alumina matrix have been fabricated with lengths ranging from 75 to $330\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. Their optical properties, expressed in terms of extinction $\ensuremath{-}\mathrm{ln}(T)$, where $T$ is optical transmittance, have been measured as a function of wavelength, rod length, angle of incidence, and incident polarization state. The results are compared to a Maxwell-Garnett based theory modified to take into account the strongly anisotropic nature of the medium. Transverse and longitudinal plasmon resonances are observed. The interaction between the nanorods leads to the splitting of the longitudinal resonance with the longer-wavelength resonance being forbidden for direct optical observations. The shorter-wavelength resonance related to the symmetric coupling between longitudinal plasma excitations in the nanorods depends on rod length, polarization state, and angle of incidence of the probing light. The impact of electron confinement on the optical properties of the gold rods is also seen and may be incorporated into the Maxwell-Garnett theory by restricting the mean free path of the conduction electrons to produce excellent agreement between observations and the complete theory. Annealing experiments that modify the physical structure of the gold confirm this conclusion.

In an effort to achieve large high-field magnetization and increased Curie temperature, polycrystalline DyRh, (DyRh)95X5 and (DyRh)85X15 (X = Fe, Co, Ni, Gd) thin films have been prepared via ultra-high vacuum DC co-sputtering on SiO2 and Si wafers, using Ta as seed and cap material. A body-centred cubic CsCl-like crystal formation (B2 phase) was achieved for DyRh around the equiatomic equilibrium, known from single crystals. The maximum in-plane spontaneous magnetization at T = 4K in fields of μ0H = 5T of was found to be μ0MS,4K = (1.50 ± 0.09)T with a ferromagnetic transition at TC = (5 ± 1)K and a coercivity of μ0HC,4K[D] = (0.010 ± 0.001)T (at T = 4K) for layers deposited on substrates heated to 350°C. Samples prepared at room temperature exhibited poorer texture, smaller grains and less B2-phase content; this did impact on the Curie temperature which was higher compared to those layers with best crystallisation; however the maximal magnetization stayed unaffected. Ferromagnetic coupling was observed in ternary alloys of DyRhGd and DyRhNi with an increased Curie temperature, larger initial permeability, andhigh-field magnetization which was best for (DyRh)85Gd15 with μ0MS,4K[Gd15] = (2.10 ± 0.13)T. DyRhFe and DyRhCo showed antiparallel coupling of the spontaneous magnetic moments.

The search for materials or systems exhibiting a high magnetic saturation has been of longstanding importance. It has been suggested that increased saturation could be achieved by coupling a transition metal via a spacer to a rare earth. We report Gd/Cr/Fe70Co30 multilayer stacks and find reduced yet modulating magnetic moment as a function of Cr thickness. Through a micro structural analysis the lowered moment is indicated by the nucleation of the ultrathin Gd films into an fcc phase. We discuss the possible solution in terms of quasi-perfect lattice match seed material to promote growth of hcp Gd., Comment: 14 pages, 5 figures, submitted to Appl. Phys. Lett

For two-dimensional (2D) arrays of metallic nanorods arranged perpendicular to a substrate several methods have been proposed to determine the electromagnetic near-field distribution and the surface plasmon resonances, but an analytical approach to explain all optical features on the nanometer length scale has been missing to date. To fill this gap, we demonstrate here that the field distribution in such arrays can be understood on the basis of surface plasmon polaritons (SPPs) that propagate along the nanorods and form standing waves. Notably, SPPs couple laterally through their optical near fields, giving rise to collective surface plasmon (CSP) effects. Using the dispersion relation of such CSPs, we deduce the condition of standing-wave formation, which enables us to successfully predict several features, such as eigenmodes and resonances. As one such property and potential application, we show both theoretically and in an experiment that CSP propagation allows for polarization conversion and optical filtering in 2D nanorod arrays. Hence, these arrays are promising candidates for manipulating the light polarization on the nanometer length scale.

The magneto-optical properties of surface-plasmon polaritonic crystals on ferromagnetic substrates have been studied. The resonant optical transmission of such magneto-plasmonic nanostructures can be efficiently controlled with the applied static magnetic field. The effect is explained by the influence of magneto-optical effects on surface-plasmon polariton waves supported by the metal/magnetic-dielectric interface and, in particular, on the plasmonic bandgap formation.

Silver nanorods have been grown by electrodeposition into thin film porous alumina. Transmission measurements show two peaks related to the transverse and longitudinal resonance of the nanorods. The behaviour of the longitudinal resonance peak is found to vary with nanorod length and the spectral position to depend on nanorod diameter. As the distance between the nanorods is decreased a small blue-shift of the longitudinal peak is observed. Depositing a small gold cap on top of the silver nanorods causes a red-shift of the longitudinal peak whilst, conversely, the longitudinal peak of gold nanorod arrays is comparatively insensitive to the deposition of a silver cap. Gold-silver alloy nanorods were also deposited from a mixed salt bath and a linear dependence of the transverse peak position on alloy composition was observed.