Publications
124 results found
Kaur A, Darvill D, Xiang S, et al., 2023, Development of nanopackaging for storage and transport of loaded lipid nanoparticles, Nano Letters, Vol: 23, Pages: 6760-6767, ISSN: 1530-6984
Easily deploying new vaccines globally to combat disease outbreaks has been highlighted as a major necessity by the World Health Organization. RNA-based vaccines using lipid nanoparticles (LNPs) as a drug delivery system were employed to great effect during the recent COVID-19 pandemic. However, LNPs are still unstable at room temperature and agglomerate over time during storage, rendering them ineffective for intracellular delivery. We demonstrate the suitability of nanohole arrays (nanopackaging) as patterned surfaces to separate and store functionalized LNPs (fLNPs) in individual recesses, which can be expanded to other therapeutics. Encapsulating calcein as a model drug, we show through confocal microscopy the effective loading of fLNPs into our nanopackaging for both wet and dry systems. We prove quantifiably pH-mediated capture and subsequent unloading of over 30% of the fLNPs using QCM-D on alumina surfaces altering the pH from 5.5 to 7, displaying controllable storage at the nanoscale.
Yao Q, Berenov AV, Bower R, et al., 2023, Crystalline AuNP-Decorated Strontium Niobate Thin Films: Strain-Controlled AuNP Morphologies and Optical Properties for Plasmonic Applications., ACS Appl Nano Mater, Vol: 6, Pages: 11115-11123
Gold nanoparticle (AuNP) decoration is a commonly used method to enhance the optical responses in many applications such as photocatalysis, biosensing, solar cells, etc. The morphology and structure of AuNPs are essential factors determining the functionality of the sample. However, tailoring the growth mechanism of AuNPs on an identical surface is not straightforward. In this study, AuNPs were deposited on the surface of a perovskite thin film, strontium niobate (SNO), using pulsed laser deposition (PLD). AuNPs exhibited a dramatic variation in their growth mechanisms, depending on whether they were deposited on SNO thin films grown on magnesium oxide (SNO/MgO) or strontium titanate (SNO/STO) substrates. On SNO/MgO, the Au aggregates form large NPs with an average size of up to 3500 nm2. These AuNPs are triangular with sharp edges and corners. The out-of-plane direction of growth is favored, and the surface coverage ratio by AuNPs is low. When deposited on SNO/STO, the average size of AuNPs is much smaller, i.e., ∼250 nm2. This reduction in the average size is accompanied by an increase in the number density of NPs. AuNPs on SNO/STO have a round shape and high coverage ratio. Such an impact from the substrate selection on the AuNP structure is significant when the sandwiched SNO film is below 80 nm thickness and is weakened for 200 nm of SNO films. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize all samples. Strain analysis was used to explain the growth mechanism of AuNPs. The average height of AuNPs was measured by using atomic force microscopy (AFM). Ellipsometry in the visible-near-infrared (vis-NIR) region was used to characterize the optical response of all samples. AuNP-decorated SNO/MgO and SNO/STO thin films exhibit different optical properties, with only gold-decorated SNO/MgO samples showing a size-dependent epsilon-near-zero behavior of nanoparticles. These results provide an additional route to control the s
Wang Y, Guerenneur A, Ramadan S, et al., 2023, Toward fabrication of devices based on graphene/oxide multilayers, ACS Applied Electronic Materials, Vol: 5, Pages: 3261-3267, ISSN: 2637-6113
Owing to its high electrical conductivity, low density, and flexibility, graphene has great potential for use as a building block in a wide range of applications from nanoelectronics to biosensing and high-frequency devices. For many device applications, it is required to deposit dielectric materials on graphene at high temperatures and in ambient oxygen. This has been proven to be highly challenging because these conditions cause significant degradation in graphene. In this work, we investigate the degradation of graphene at elevated temperatures in an oxygen atmosphere and possible protection mechanisms to enable the growth of oxide thin films on graphene at higher temperatures. We show that coating graphene with self-assembled monolayers of hexamethyldisilazane (HMDS) prior to a high-temperature deposition can significantly reduce the damage induced. Furthermore, a graphene sample treated with HMDS displayed a weaker doping effect due to weak interaction with oxygen species than bare graphene, and a much slower rate of electrical resistance degradation was exhibited during annealing. Thus, it is a promising approach that could enable the deposition of metal oxide materials on graphene at high temperatures without significant degradation in graphene quality, which is critical for a wide range of applications.
Doiron B, Li Y, Bower R, et al., 2023, Optimizing hot electron harvesting at planar metal–semiconductor interfaces with titanium oxynitride thin films, ACS Applied Materials and Interfaces, Vol: 25, Pages: 30417-30426, ISSN: 1944-8244
Understanding metal-semiconductor interfaces is critical to the advancement of photocatalysis and sub-bandgap solar energy harvesting where electrons in the metal can be excited by sub-bandgap photons and extracted into the semiconductor. In this work, we compare the electron extraction efficiency across Au/TiO2 and titanium oxynitride (TiON)/TiO2-x interfaces, where in the latter case the spontaneously forming oxide layer (TiO2-x) creates a metal-semiconductor contact. Time-resolved pump-probe spectroscopy is used to study the electron recombination rates in both cases. Unlike the nanosecond recombination lifetimes in Au/TiO2, we find a bottleneck in the electron relaxation in the TiON system, which we explain using a trap-mediated recombination model. Using this model, we investigate the tunability of the relaxation dynamics with oxygen content in the parent film. The optimized film (TiO0.5N0.5) exhibits the highest carrier extraction efficiency (NFC ≈ 2.8 × 1019 m-3), slowest trapping, and an appreciable hot electron population reaching the surface oxide (NHE ≈ 1.6 × 1018 m-3). Our results demonstrate the productive role oxygen can play in enhancing electron harvesting and prolonging electron lifetimes, providing an optimized metal-semiconductor interface using only the native oxide of titanium oxynitride.
Wang Y, Zou B, Rente B, et al., 2023, Deposition of nanocrystalline multilayer graphene using pulsed laser deposition, Crystals, Vol: 13, Pages: 1-8, ISSN: 2073-4352
The wide application of graphene in the industry requires the direct growth of graphene films on silicon substrates. In this study, we found a possible technique to meet the requirement above. Multilayer graphene thin films (MLG) were grown without a catalyst on Si/SiO2 using pulsed laser deposition (PLD). It was found that the minimum number of laser pulses required to produce fully covered (uninterrupted) samples is 500. This number of laser pulses resulted in samples that contain ~5 layers of graphene. The number of layers was not affected by the laser fluence and the sample cooling rate after the deposition. However, the increase in the laser fluence from 0.9 J/cm2 to 1.5 J/cm2 resulted in a 2.5-fold reduction in the MLG resistance. The present study reveals that the PLD method is suitable to produce nanocrystalline multilayer graphene with electrical conductivity of the same magnitude as commercial CVD graphene samples.
Bower R, McPolin C, Krasavin A, et al., 2022, Temperature stability of individual plasmonic Au and TiN nanodiscs, Optical Materials Express, Vol: 12, Pages: 3471-3479, ISSN: 2159-3930
Refractory plasmonic materials are of interest for high-temperature plasmonic applications due to their increased thermal stability when compared to gold and silver. Titanium nitride (TiN) has been highlighted as a promising refractory material, offering both strong plasmonic and thermal performance. In this work, we analyze the stability of both the structural and optical response of individual plasmonic nanodiscs of various diameters subjected to elevated temperature conditions in air. Using cathodoluminescence spectroscopy, we trace the resonance spectra and shape modifications of the same single TiN and Au discs annealed at increasing temperatures up to 325 ℃. TiN discs display greater morphological stability, but the optical properties of both materials deteriorate from 200 °C, although the mechanisms of degradation are different. The results are essential for optimizing nanostructured materials for high temperature nanophotonic applications.
Xu L, Ramadan S, Rosa BG, et al., 2022, On-chip integrated graphene aptasensor with portable readout for fast and label-free COVID-19 detection in virus transport medium., Sens Diagn, Vol: 1, Pages: 719-730
Graphene field-effect transistor (GFET) biosensors exhibit high sensitivity due to a large surface-to-volume ratio and the high sensitivity of the Fermi level to the presence of charged biomolecules near the surface. For most reported GFET biosensors, bulky external reference electrodes are used which prevent their full-scale chip integration and contribute to higher costs per test. In this study, GFET arrays with on-chip integrated liquid electrodes were employed for COVID-19 detection and functionalized with either antibody or aptamer to selectively bind the spike proteins of SARS-CoV-2. In the case of the aptamer-functionalized GFET (aptasensor, Apt-GFET), the limit-of-detection (LOD) achieved was about 103 particles per mL for virus-like particles (VLPs) in clinical transport medium, outperforming the Ab-GFET biosensor counterpart. In addition, the aptasensor achieved a LOD of 160 aM for COVID-19 neutralizing antibodies in serum. The sensors were found to be highly selective, fast (sample-to-result within minutes), and stable (low device-to-device signal variation; relative standard deviations below 0.5%). A home-built portable readout electronic unit was employed for simultaneous real-time measurements of 12 GFETs per chip. Our successful demonstration of a portable GFET biosensing platform has high potential for infectious disease detection and other health-care applications.
Bower R, Wells MP, Johnson F, et al., 2021, Tunable double epsilon-near-zero behavior in niobium oxynitride thin films, Applied Surface Science, Vol: 569, Pages: 150912-150912, ISSN: 0169-4332
Petrov P, Altynnikov A, Platonov R, et al., 2021, Formation of millimeter waves with electrically tunable orbital angular momentum, Coatings, Vol: 11, Pages: 1-9, ISSN: 2079-6412
A method for forming electromagnetic waves with a tunable nonzero orbital angular momentum (OAM) is proposed. The approach is based on transforming an incident plane wave into a helical one using an electrically tunable ferroelectric lens. It uses high-resistive thin/thick film electrodes with a special discrete topology. The correlation between film electrodes topology and the highest order of OAM modes that the lens can form is described. A lens prototype based on Ba0.55Sr0.45TiO3 ferroelectric material and operating at a frequency of 60 GHz was designed, manufactured, and tested. The amplitude and phase distribution of the OAM wave with l = +1 formed by prototype were measured to confirm the effectiveness of the proposed method. The proposed lens has a combination of advantages such as low dimensions, electrical control over the OAM modes, and the possibility to operate in the millimeter wavelength range.
Berenov A, Petrov P, Moffat B, et al., 2021, Pyroelectric and photovoltaic properties of Nb doped PZT thin films, APL Materials, Vol: 9, ISSN: 2166-532X
Nb-doped lead zirconate titanate (PZT) films with up to 12 at. % of Nb were co-sputtered from oxide PZT and metallic Nb targets at a substrate temperature of 600 °C. Up to 4 at. % of Nb was doped into the perovskite structure with the formation of B-site cation vacancies for charge compensation. The preferential (111) PZT orientation decreased with Nb-doping within the solid solution region. The ferroelectric response of the films was affected by the large values of the internal field present in the samples (e.g., −84.3 kV cm−1 in 12 at. % Nd doped films). As-deposited unpoled films showed large values of the pyroelectric coefficient due to self-poling. The pyroelectric coefficient increased with Nb-doping and showed a complex dependence on the applied bias. The photovoltaic effect was observed in the films. The value of the photocurrent increased with the A/B ratio. The combined photovoltaic–pyroelectric effect increased the values of the measured current by up to 47% upon light illumination.
Ramadan S, Lobo R, Zhang Y, et al., 2021, Carbon-dot-enhanced graphene field-effect transistors for uitrasensitive detection of exosomes, ACS Applied Materials and Interfaces, Vol: 13, Pages: 7854-7864, ISSN: 1944-8244
Graphene field-effect transistors (GFETs) are suitable building blocks for high-performance electrical biosensors, because graphene inherently exhibits a strong response to charged biomolecules on its surface. However, achieving ultralow limit-of-detection (LoD) is limited by sensor response time and screening effect. Herein, we demonstrate that the detection limit of GFET biosensors can be improved significantly by decorating the uncovered graphene sensor area with carbon dots (CDs). The developed CDs-GFET biosensors used for exosome detection exhibited higher sensitivity, faster response, and three orders of magnitude improvements in the LoD compared with nondecorated GFET biosensors. A LoD down to 100 particles/μL was achieved with CDs-GFET sensor for exosome detection with the capability for further improvements. The results were further supported by atomic force microscopy (AFM) and fluorescent microscopy measurements. The high-performance CDs-GFET biosensors will aid the development of an ultrahigh sensitivity biosensing platform based on graphene for rapid and early diagnosis of diseases.
Ramadan S, Zhang Y, Tsang DKH, et al., 2021, Enhancing structural properties and performance of graphene-based devices using self-assembled HMDS monolayers, ACS Omega, Vol: 6, Pages: 4767-4775, ISSN: 2470-1343
The performance of graphene devices is often limited by defects and impurities induced during device fabrication. Polymer residue left on the surface of graphene after photoresist processing can increase electron scattering and hinder electron transport. Furthermore, exposing graphene to plasma-based processing such as sputtering of metallization layers can increase the defect density in graphene and alter the device performance. Therefore, the preservation of the high-quality surface of graphene during thin-film deposition and device manufacturing is essential for many electronic applications. Here, we show that the use of self-assembled monolayers (SAMs) of hexamethyldisilazane (HMDS) as a buffer layer during the device fabrication of graphene can significantly reduce damage, improve the quality of graphene, and enhance device performance. The role of HMDS has been systematically investigated using surface analysis techniques and electrical measurements. The benefits of HMDS treatment include a significant reduction in defect density compared with as-treated graphene and more than a 2-fold reduction of contact resistance. This surface treatment is simple and offers a practical route for improving graphene device interfaces, which is important for the integration of graphene into functional devices such as electronics and sensor devices.
Bower R, Loch DAL, Ware E, et al., 2020, Complementary Metal-Oxide-Semiconductor Compatible Deposition of Nanoscale Transition-Metal Nitride Thin Films for Plasmonic Applications, ACS APPLIED MATERIALS & INTERFACES, Vol: 12, Pages: 45444-45452, ISSN: 1944-8244
Petrova NL, Cai Q, Petrov PK, et al., 2020, Can novel bone substitutes withstand the enhanced resorbing activity of Charcot osteoclasts?, Publisher: WILEY, Pages: 48-48, ISSN: 0742-3071
Petrova NL, Petrov PK, Shanahan CM, et al., 2020, Clinical care: Technology, Publisher: WILEY, Pages: 6-6, ISSN: 0742-3071
Doiron B, Gusken NA, Lauri A, et al., 2020, Hot Carrier Optoelectronics with Titanium Nitride, Lasers and Electro-Optics Society Annual Meeting-LEOS, ISSN: 1092-8081
© 2020 OSA. Titanium oxynitride enables a range of plasmonic and optoelectronic functionality using long-lived photo-generated hot carriers. We explore the time scale of hot carriers in TiN and their use in photochemical reduction and Schottky detectors.
Gusken NA, Lauri A, Li Y, et al., 2020, IR hot carrier based photodetection in titanium nitride oxide thin film-Si junctions, MRS Advances, Vol: 5, Pages: 1843-1850, ISSN: 2059-8521
Hot carrier based methods constitute a valuable approach for efficient and silicon compatible sub-bandgap photodetection. Although, hot electron excitation and transfer have been studied extensively on traditional materials such as Au and Ti, reports on alternative materials such as titanium nitride (TiN) are rare. Here, we perform hot hole photodetection measurements on a p-Si/metal thin film junction using Ti, Au and TiN. This material is of interest as it constitutes a refractory alternative to Au which is an important property for plasmonic applications where high field intensities can occur. In contrast to Au, a TiN/Si junction does not suffer from metal diffusion into the Si, which eases the integration with current Si-fabrication techniques. This work shows that a backside illuminated p-Si/TiN system can be used for efficient hot hole extraction in the IR, allowing for a responsivity of 1 mA/W at an excitation wavelength of 1250 nm and at zero bias. Via a comparison between TiN and other commonly used materials such as Au, the origin of this comparably high photoresponse can be traced back to be directly linked to a thin TiO2-x interfacial layer allowing for a distinct hot-hole transfer mechanism. Moreover, the fabrication of TiN nanodisk arrays is demonstrated which bears great promise to further boost the device efficiency.
Doiron B, Güsken NA, Lauri A, et al., 2020, Hot carrier optoelectronics with titanium nitride
Titanium oxynitride enables a range of plasmonic and optoelectronic functionality using long-lived photo-generated hot carriers. We explore the time scale of hot carriers in TiN and their use in photochemical reduction and Schottky detectors.
Cohen L, Boldrin D, Johnson F, et al., 2019, The biaxial strain dependence of magnetic order in spin frustrated mn3nin thin films, Advanced Functional Materials, Vol: 29, ISSN: 1616-301X
Multi-component magnetic phase diagrams are a key property of functional materials for a variety of uses, such as manipulation of magnetisation for energy efficient memory, data storage and cooling applications. Strong spin-lattice coupling extends this functionality further by allowing electric-field-control of magnetisation via strain coupling with a piezoelectric . Here we explore the magnetic phase diagram of piezomagnetic Mn3NiN thin films, with a frustrated non-collinear antiferromagnetic (AFM) structure, as a function of the growth induced biaxial strain. Under compressive strain the films support a canted AFM state with large coercivity of the transverse anomalous Hall resistivity, ρxy, at low temperature, that transforms at a well-defined Néel transition temperature (TN) into a soft ferrimagnetic-like (FIM) state at high temperatures. In stark contrast, under tensile strain the low temperature canted AFM phase transitions to a state where ρxy is an order of magnitude smaller and therefore consistent with a low magnetisation phase. Neutron scattering confirms that the high temperature FIM-like phase of compressively strained films is magnetically ordered and the transition at TN is 1st-order. Our results open the field towards future exploration of electric-field driven piezospintronic and thin film caloric cooling applications in both Mn3NiN itself and the broader Mn3AN family.
Cohen L, Boldrin D, 2019, Anomalous Hall effect in noncollinear antiferromagnetic Mn 3NiN thin films, Physical Review Materials, Vol: 3, ISSN: 2475-9953
We have studied the anomalous Hall effect (AHE) in strained thin lms of the frustrated anti-ferromagnet Mn3NiN. The AHE does not follow the conventional relationships with magnetizationor longitudinal conductivity and is enhanced relative to that expected from the magnetization inthe antiferromagnetic state belowTN= 260 K. This enhancement is consistent with origins fromthe non-collinear antiferromagnetic structure, as the latter is closely related to that found in Mn3Irand Mn3Pt where a large AHE is induced by the Berry curvature. As the Berry phase inducedAHE should scale with spin-orbit coupling, yet larger AHE may be found in other members of thechemically exible Mn3AN structure.
Doiron B, Li Y, Mihai A, et al., 2019, Plasmon-enhanced electron harvesting in robust titanium nitride nanostructures, The Journal of Physical Chemistry Part C: Nanomaterials and Interfaces, Vol: 123, Pages: 18521-18527, ISSN: 1932-7447
Titanium nitride (TiN) continues to prove itself as an inexpensive, robust, and efficient alternative to gold in plasmonic applications. Notably, TiN has improved hot electron-harvesting and photocatalytic abilities compared to gold systems, which we recently attributed to the role of oxygen in TiN and its native semiconducting TiO2–x surface layer. Here, we explore the role of localized surface plasmon resonances (LSPRs) on electron harvesting across the TiN/TiO2–x interface and probe the resilience of TiN nanostructures under high-power laser illumination. To investigate this, we fabricate TiN strips, in which the lateral confinement allows for the polarization-selective excitation of the LSPR. Using ultrafast pump–probe spectroscopy, optical characterization, and Raman vibrational spectroscopy, we relate the differences and changes observed in the electron behavior to specific material properties. We observe plasmon-enhanced electron harvesting beyond what is expected resulting from the enhanced absorption of the plasmonic mode. We accredit this to the surface oxide damping the plasmon resonance, providing additional nonradiative loss channels. Subsequently, we show that low-power annealing of the surface oxide layer reduces the trap density at the interface and increases the initial harvested electron concentration. The unique properties of TiN make it important in the future development of plasmonic electron-harvesting applications.
Pang JS, Theodorou IG, Centeno A, et al., 2019, Tunable three-dimensional plasmonic arrays for large near-infrared fluorescence enhancement, ACS Applied Materials and Interfaces, Vol: 11, Pages: 23083-23092, ISSN: 1944-8244
Metal-enhanced fluorescence (MEF), resulting from the near-field interaction of fluorophores with metallic nanostructures, has emerged as a powerful tool for dramatically improving the performance of fluorescence-based biomedical applications. Allowing for lower autofluorescence and minimal photoinduced damage, the development of multifunctional and multiplexed MEF platforms in the near-infrared (NIR) windows is particularly desirable. Here, a low-cost fabrication method based on nanosphere lithography is applied to produce tunable three-dimensional (3D) gold (Au) nanohole–disc arrays (Au-NHDAs). The arrays consist of nanoscale glass pillars atop nanoholes in a Au thin film: the top surfaces of the pillars are Au-covered (effectively nanodiscs), and small Au nanoparticles (nanodots) are located on the sidewalls of the pillars. This 3D hole–disc (and possibly nanodot) construct is critical to the properties of the device. The versatility of our approach is illustrated through the production of uniform and highly reproducible Au-NHDAs with controlled structural properties and tunable optical features in the NIR windows. Au-NHDAs allow for a very large NIR fluorescence enhancement (more than 400 times), which is attributed to the 3D plasmonic structure of the arrays that allows strong surface plasmon polariton and localized surface plasmon resonance coupling through glass nanogaps. By considering arrays with the same resonance peak and the same nanodisc separation distance, we show that the enhancement factor varies with nanodisc diameter. Using computational electromagnetic modeling, the electric field enhancement at 790 nm was calculated to provide insights into excitation enhancement, which occurs due to an increase in the intensity of the electric field. Fluorescence lifetime measurements indicate that the total fluorescence enhancement may depend on controlling excitation enhancement and therefore the array morphology. Our findings provide important in
Gusken NA, Lauri A, Li Y, et al., 2019, TiO2-x-enhanced IR hot carrier based photodetection in metal thin film-si junctions, ACS Photonics, Vol: 6, Pages: 953-960, ISSN: 2330-4022
We investigate titanium nitride (TiN) thin film coatings on silicon for CMOS-compatible sub-bandgap charge separation upon incident illumination, which is a key feature in the vast field of on-chip photodetection and related integrated photonic devices. Titanium nitride of tunable oxidation distributions serves as an adjustable broadband light absorber with high mechanical robustness and strong chemical resistivity. Backside-illuminated TiN on p-type Si (pSi) constitutes a self-powered and refractory alternative for photodetection, providing a photoresponsivity of about ∼1 mA/W at 1250 nm and zero bias while outperforming conventional metal coatings such as gold (Au). Our study discloses that the enhanced photoresponse of TiN/pSi in the near-infrared spectral range is directly linked to trap states in an ultrathin TiO2–x interfacial interlayer that forms between TiN and Si. We show that a pSi substrate in conjunction with a few nanometer thick amorphous TiO2–x film can serve as a platform for photocurrent enhancement of various other metals such as Au and Ti. Moreover, the photoresponse of Au on a TiO2–x/pSi platform can be increased to about 4 mA/W under 0.45 V reverse bias at 1250 nm, allowing for controlled photoswitching. A clear deviation from the typically assumed Fowler-like response is observed, and an alternative mechanism is proposed to account for the metal/semiconductor TiO2–x interlayer, capable of facilitating hole transport.
Doiron B, Mota M, Wells MP, et al., 2019, Quantifying figures of merit for localized surface plasmon resonance applications: a materials survey, ACS Photonics, Vol: 6, Pages: 240-259, ISSN: 2330-4022
Using localized surface plasmon resonances (LSPR) to focus electromagnetic radiation to the nanoscale shows the promise of unprecedented capabilities in optoelectronic devices, medical treatments and nanoscale chemistry, due to a strong enhancement of light-matter interactions. As we continue to explore novel applications, we require a systematic quantitative method to compare suitability across different geometries and a growing library of materials. In this work, we propose application-specific figures of merit constructed from fundamental electronic and optical properties of each material. We compare 17 materials from four material classes (noble metals, refractory metals, transition metal nitrides, and conductive oxides) considering eight topical LSPR applications. Our figures of merit go beyond purely electromagnetic effects and account for the materials’ thermal properties, interactions with adjacent materials, and realistic illumination conditions. For each application we compare, for simplicity, an optimized spherical antenna geometry and benchmark our proposed choice against the state-of-the-art from the literature. Our propositions suggest the most suitable plasmonic materials for key technology applications and can act as a starting point for those working directly on the design, fabrication, and testing of such devices.
Maslakov K, Teterin YA, Popel AJ, et al., 2018, XPS study of ion irradiated and unirradiated CeO2 bulk and thin film samples, APPLIED SURFACE SCIENCE, Vol: 448, Pages: 154-162, ISSN: 0169-4332
Maslakov KI, Teterin YA, Ryzhkov MV, et al., 2018, The electronic structure and the nature of the chemical bond in CeO2, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 20, Pages: 16167-16175, ISSN: 1463-9076
Wells M, Bower R, Kilmurray B, et al., 2018, Temperature stability of thin film refractory plasmonic materials, Optics Express, Vol: 12, Pages: 15726-15744, ISSN: 1094-4087
Materials such as W, TiN, and SrRuO3 (SRO) have been suggested as promising alternatives to Au and Ag in plasmonic applications owing to their stability at high operational temperatures. However, investigation of the reproducibility of the optical properties after thermal cycling between room and elevated temperatures is so far lacking. Here, thin films of W, Mo, Ti, TiN, TiON, Ag, Au, SrRuO3 and SrNbO3 are investigated to assess their viability for robust refractory plasmonic applications. These results are further compared to the performance of SrMoO3 reported in literature. Films ranging in thickness from 50 to 105 nm are deposited on MgO, SrTiO3 and Si substrates by e-beam evaporation, RF magnetron sputtering and pulsed laser deposition, prior to characterisation by means of AFM, XRD, spectroscopic ellipsometry, and DC resistivity. Measurements are conducted before and after annealing in air at temperatures ranging from 300 to 1000° C for one hour, to establish the maximum cycling temperature and potential longevity at elevated temperatures for each material. It is found that SrRuO3 retains metallic behaviour after annealing at 800° C, while SrNbO3 undergoes a phase transition resulting in a loss of metallic behaviour after annealing at 400° C. Importantly, the optical properties of TiN and TiON are degraded as a result of oxidation and show a loss of metallic behaviour after annealing at 500° C, while the same is not observed in Au until annealing at 600° C. Nevertheless, both TiN and TiON may be better suited than Au or SRO for high temperature applications operating under vacuum conditions.
Petrov PK, Wells M, Zou B, et al., 2018, Multiphase strontium molybdate thin films for plasmonic local heating applications, Optical Materials Express, Vol: 8, Pages: 1806-1817, ISSN: 2159-3930
In the search for alternative plasmonic materials SrMoO3 has recently been identified as possessing a number of desirable optical properties. Owing to the requirement for many plasmonic devices to operate at elevated temperatures however, it is essential to characterize the degradation of these properties upon heating. Here, SrMoO3 thin films are annealed in air at temperatures ranging from 75 - 500{\deg} C. Characterizations by AFM, XRD, and spectroscopic ellipsometry after each anneal identify a loss of metallic behaviour after annealing at 500{\deg} C, together with the underlying mechanism. Moreover, it is shown that by annealing the films in nitrogen following deposition, an additional crystalline phase of SrMoO4 is induced at the film surface, which suppresses oxidation at elevated temperatures.
Boldrin D, Mihai A, Zou B, et al., 2018, Giant Piezomagnetism in Mn3NiN., ACS Appl Mater Interfaces, Vol: 10, Pages: 18863-18868
Controlling magnetism with electric field directly or through strain-driven piezoelectric coupling remains a key goal of spintronics. Here we demonstrate that giant piezomagnetism, a linear magneto-mechanic coupling effect, is manifest in antiperovskite Mn3NiN, facilitated by its geometrically frustrated antiferromagnetism opening the possibility of new memory device concepts. Films of Mn3NiN with intrinsic biaxial strains of ±0.25% result in Néel transition shifts up to 60K and magnetisation changes consistent with theory. Films grown on BaTiO3 display a striking magnetisation jump in response to uniaxial strain from the intrinsic BaTiO3 structural transition, with an inferred 44% strain coupling efficiency and a magnetoelectric coefficient α (where α=dB/dE) of 0.018 G cm/V. The latter agrees with the 1000-fold increase over Cr2O3 predicted by theory. Overall our observations pave the way for further research into the broader family of Mn-based antiperovskites where yet larger piezomagnetic effects are predicted to occur at room temperature.
Mignuzzi S, Mota M, Coenen T, et al., 2018, Energy-momentum cathodoluminescence spectroscopy of dielectric nanostructures, ACS Photonics, Vol: 5, Pages: 1381-1387, ISSN: 2330-4022
Precise knowledge of the local density of optical states (LDOS) is fundamental to understanding nanophotonic systems and devices. Complete LDOS mapping requires resolution in energy, momentum, and space, and hence a versatile measurement approach capable of providing simultaneous access to the LDOS components is highly desirable. Here, we explore a modality of cathodoluminescence spectroscopy able to resolve, in single acquisitions, the dispersion in energy and momentum of the radiative LDOS. We perform measurements on a titanium nitride diffraction grating, bulk molybdenum disulfide, and silicon to demonstrate that the technique can probe and disentangle the dispersion of coherent and incoherent cathodoluminescence signals. The approach presented raises cathodoluminescence spectroscopy to a versatile tool for subwavelength design and optimization of nanophotonic devices in the reciprocal space.
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