We demonstrate large-area micro-transfer-printed thin-film lithium niobate (TFLN) on silicon nitride (SiN) racetrack resonators for integrated nonlinear photonics. A 300 nm thick TFLN coupon with a 670x680 mu m(2) area was deterministically placed on top of patterned SiN. In the near-infrared wavelength region, the fabricated racetrack resonators achieve a loaded quality factor Q of similar to 70,000 with no contribution from scattering losses of TFLN sidewalls. Second-harmonic generation (SHG) is realized via modal phase matching (MPM) between the TE00 pump and TE01 second-harmonic modes. A cavity-free single-pass waveguide exhibits a sinc2-shaped second-harmonic conversion efficiency with similar to 1 nm bandwidth, whereas integrating the same MPM section into a racetrack resonator generates bright green emission when the resonances overlap the SHG bandwidth. This mu TP TFLN-on-SiN approach is wafer-scalable, offering a versatile pathway to on-chip visible generation and chi(2) functionality co-located with ultra-low-loss SiN routing.

Miniaturized biomedical sensor development requires improvements in lithographic processes in terms of cost and scalability. Of particular promise is nanoimprint lithography (NIL), but this can suffer from a lack of high-fidelity pattern reproducibility between master and imprinted substrates. Herein, we present a multidisciplinary investigation into gold- and iron-coated NIL sensors including custom optics and spectroscopy, scanning probe microscopy, and data analysis insights. Polyurethane NIL-made nanodome arrays were interrogated with white light transmission spectroscopy, coupled with principal component analysis (PCA) to investigate potential offsets in the photon-substrate plane interaction angle, an imperfection in NIL substrates. Large-angle mismatches (2-10°) were found to be easily discernible by PCA with statistically significant differences (p = 0.05). Unexpected dips in some spectra are postulated to be due to interacting localized and propagating plasmon polaritons, which is supported with a coupled two-oscillator model. General insights are made regarding the interpretation of PCA loadings, which should be related to physical phenomena, and where maximum variance is not necessarily the most meaningful criterion. Smaller angles (<1°) show no significant differences with overlapping confidence intervals in PCA space. Surface-enhanced Raman spectroscopy (SERS) measurements on gold-coated nanodomes returned relative standard deviations of 6-10% via analysis of gelatin, which is of interest as a nasal lining approximation. Interestingly, nanodomes coated in iron produced small, but useful SERS enhancements, which was subsequently interrogated via scanning thermal probe microscopy showing temperature increases of up to 5 °C over the area of one nanostructure (∼1 μm2). Nanostructures remained intact despite the surprising large local temperature increase relative to a gold-coated comparison sample (∼2 °C). The current study provides a framework for the rapid and accurate quality control assessment of imperfections in NIL-produced nanostructures for sensing applications in SERS and surface plasmon resonance, which may need precisely fabricated nanostructures.

Nickel-platinum-based synthetic ferrimagnets (SFi's) are highly tunable and rare-earth-free materials that allow ultrafast all optical control of magnetism to be explored. This study considers a SFi composed of a ferromagnetic [Ni/Pt] multilayer and a ferromagnetic Co layer, separated by an Ir layer that mediates an antiferromagnetic coupling. Helicity-independent all optical switching (HI-AOS) between two antiparallel magnetization states is observed. AOS may be realized at increased temperature through reduction of the thickness of the Pt layers. Switching is unidirectional and has a strong dependence on the applied magnetic field history, which suggests the possible presence of a nanoscale magnetic texture that may be important in controlling AOS in SFi systems.

Cavity magnonics has become an intriguing field due to its potential to enable next-generation technologies centered around controlling information exchange in hybrid resonant systems. Investigating the tunability of magnon-photon coupling is key to advancing the field. Here, the observation of coupling between the first order magnon mode in a metallic thin film with a cavity photon mode is reported. An electromagnetic perturbation theory that takes account of perpendicular standing spin waves and their respective dissipation is utilized to estimate the coupling strength. The metallic thin film exhibits notably lower dissipation for the higher-order magnon mode, which is not observed in a thin film magnetic insulator. As such, and given that metallic Kittel magnons typically exhibit lower coherence times than their insulator counterparts, the excitation and coupling to specific higher order modes could lengthen these times compared to previous observations, which may be useful for future integration into quantum devices. This study investigates magnon-photon coupling with exchange magnon modes in metallic thin film Permalloy (Py) and insulating Yttrium Iron Garnet (YIG). It is noted that the exchange magnon mode in Py exhibits lower dissipation than the Kittel mode while maintaining similar coupling strength, which is not observed in YIG. This observation offers another potential route for tuning cavity magnonic systems. image

Titanium nitride (TiN) has emerged as a highly promising alternative to traditional plasmonic materials. This study focuses on the inclusion of a Cr90Ru10 buffer layer between the substrate and thin TiN film, which enables the use of cost-effective, amorphous technical substrates while preserving high film quality. We report best-in-class TiN thin films fabricated on fused silica wafers, achieving a maximum plasmonic figure of merit, -& varepsilon;'/& varepsilon;'', of approximately 2.8, even at a modest wafer temperature of around 300 degrees C. Furthermore, we delve into the characterization of TiN thin film quality and fabricated TiN triangular nanostructures, employing attenuated total reflectance and cathodoluminescence techniques to highlight their potential applications in surface plasmonics.

Nickel-platinum based synthetic ferrimagnets (SFi’s) offer a highly tunable system in which to study ultrafast all-optical control of magnetisation, without the requirement for rare earth materials. This study explores the behaviour of a transition metal SFi in which a [Ni/Pt] multilayer and a single Co layer, both of which possess perpendicular magnetic anisotropy (PMA), are antiferromagnetically coupled. Helicity-independent all-optical switching (AOS) between the two antiparallel magnetisation states (AP+ and AP-) is demonstrated. The tunability of the [Ni/Pt] layer allows the strength of the PMA to be increased and for AOS to be achieved at higher temperature than in SFis based on NiPt alloy layers.

The optical properties of thin films of intermetallic Au3Hf were experimentally investigated for the first time, which display significant negative epsilon' in the visible and near infrared regions, hence are clearly plasmonic materials. In contrast to similar alloys, such as films of Au3Zr, the films express more negative epsilon' values and lower epsilon '' values across most of the wavelengths (370-1570 nm) investigated. The Au3Hf films were fabricated by DC magnetron sputtering at a range of deposition temperatures, from room temperature to 415 degrees C, and annealed at different vacuum levels. The films mostly formed as a combination of Au3Hf, Au2Hf and Au4Hf phases when deposited below 400 degrees C, and exclusively Au3Hf phase at above 400 degrees C, indicating key conditions for isolating this phase. The films were stable when annealed at 10(-8) Torr, but when annealed again at 10(-6) Torr the films oxidised and changed into a mix of Au-Hf phases, suggesting resistance to oxidization may be an issue for unencapsulated applications at elevated temperatures. (C) 2022 Published by Elsevier B.V.

Optical properties of refractory intermetallic thin films of Au_3Zr 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^oC 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^oC 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.

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.

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.

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.

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 >10(2) 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.

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].

Metals have been increasingly used as substrates in devices based on two-dimensional ( 2D ) materials. However, the high re fl ectivity of bulk metals results in low optical contrast ( < 3% ) and therefore poor visibility of transparent mono- and few-layer 2D materials on these surfaces. Here we demonstrate that by engineering the complex re fl ectivity of a purpose-designed multilayer heterostructure composed of thin Au fi lms ( 2 – 8 nm ) on SiO 2 / Si substrate, the optical contrast of graphene and graphene oxide ( GO ) can be signi fi cantly 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 SiO 2 / 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. Supplementary material for this article is available online