Publications
448 results found
Cohen LF, 2020, Applied Physics Letters welcomes papers in quantum technologies, Applied Physics Letters, Vol: 116, ISSN: 0003-6951
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.
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.
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.
Dion T, Arroo DM, Yamanoi K, et al., 2019, Tunable magnetization dynamics in artificial spin ice via shape anisotropy modification, Physical Review B, Vol: 100, ISSN: 2469-9950
Ferromagnetic resonance (FMR) is performed on kagome artificial spin ice (ASI) formed of disconnected Ni80 Fe20 nanowires. Here we break the threefold angular symmetry of the kagome lattice by altering the coercive field of each sublattice via shape anisotropy modification. This allows for distinct high-frequency responses when a magnetic field is aligned along each sublattice and additionally enables simultaneous spin-wave resonances to be excited in all nanowire sublattices, unachievable in conventional kagome ASI. The different coercive field of each sublattice allows selective magnetic switching via global field, unlocking novel microstates inaccessible in homogeneous-nanowire ASI. The distinct spin-wave spectra of these states are detected experimentally via FMR and linked to underlying microstates using micromagnetic simulation.
Ouyang M, Boldrin P, Maher R, et al., 2019, A mechanistic study of the interactions between methane and nickel supported on doped ceria, Applied Catalysis B: Environmental, Vol: 248, Pages: 332-340, ISSN: 0926-3373
A novel combined method using modified methane pulses and in-situ Raman spectroscopy together with mass spectrometry is applied to impregnated Ni/gadolinium-doped ceria (CGO). The partial oxidation of methane is deduced to proceed via a Mars-van-Krevelen type mechanism composed of initial methane decomposition together with carbon oxidation by oxygen from CGO. The critical role of the ceria surface and the bulk oxygen in the reaction is defined in detail. Oxygen is a necessary reactant in the reaction, as well as inhibiting carbon deposition. Oxygen spill-over is the driving force for the carbon oxidation and the ceria surface oxygen is resupplied by bulk oxygen after depletion. Bulk migration of oxygen to the surface is the rate-determining step. We also demonstrate that the ceria oxygen stoichiometry significantly affects the type of reaction and the rate of reaction between methane and Ni/CGO: The total oxidation of methane happens only when the oxygen stoichiometry is high while the oxygen spill-over rate decreases with decreasing oxygen stoichiometry, which reduces the rate of carbon elimination and results in reduction in the rate of methane oxidation. This work lays out a comprehensive evaluation methodology and provides important insights for future design of methane oxidation catalysts for solid oxide fuel cells, and more widely for methane reforming with different oxidants (steam, CO2, NO2 etc).
Cohen LF, 2019, View from the Bridge, Applied Physics Letters, Vol: 115, Pages: 1-1, ISSN: 1077-3118
Shautsova V, Gusken NA, Sidiropoulos T, et al., 2019, Plasmonic photo-thermo-electric effect in graphene, Conference on Lasers and Electro-Optics (CLEO), Publisher: IEEE, ISSN: 2160-8989
We present a novel photo-thermo-electric effect in graphene photo-detectors established by hot electrons concentration gradients at plasmonic contacts. Our description is crucial for an in depth understanding of graphene-based photo detection devices.
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.
Jeon K-R, Ciccarelli C, Kurebayashi H, et al., 2019, Abrikosov vortex nucleation and its detrimental effect on superconducting spin pumping in Pt/Nb/Ni80Fe20/Nb/Pt proximity structures, Physical Review B (Condensed Matter), Vol: 99, ISSN: 0163-1829
We report Abrikosov vortex nucleation in Pt/Nb/Ni80Fe20/Nb/Pt proximity-coupled structures under oblique ferromagnetic resonance that turns out to be detrimental to superconducting spin pumping. By measuring an out-of-plane field-angle θH dependence and comparing with Pt-absent control samples, we show that as θH increases, the degree of enhancement (suppression) of spin pumping efficiency in the superconducting state for the Pt-present (Pt-absent) sample diminishes and it reverts to the normal state value at θH=90∘. This can be explained in terms of a substantial out-of-plane component of the resonance field for the Ni80Fe20 layer (with in-plane magnetization anisotropy and high aspect ratio) that approaches the upper critical field of the Nb, turning a large fraction of the singlet superconductor volume into the normal state.
Sundar S, Salem-Sugui S, Chattopadhyay MK, et al., 2019, Study of Nb0:18Re0:82 non-centrosymmetric superconductor in the normal and superconducting states, Superconductor Science and Technology, Vol: 32, Pages: 1-11, ISSN: 0953-2048
We examine the evidence for multiband superconductivity and non s-wave pairing in the non-centrosymmetric superconductor Nb0.18Re0.82, using electrical transport, magnetization and spe-cific heat measurements. In the normal state, the evolution of electrical resistivity with temperatureand magnetic field support the phonon assisted interband scattering and multiband picture. Inthe superconducting state, the temperature dependence of the upper critical field,Hc2(T), is foundlinear and can not be described within the Werthamer, Helfand and Hohenberg (WHH) model overthe whole temperature range measured. In addition, the observedHc2(0) exceeds the Pauli limit,suggesting non-s-wave pairing. Interestingly, the Kadowaki-Woods ratio and Uemura plot reveala behavior in Nb0.18Re0.82which is similar to that found in unconventional superconductors. Thenormalized superfluid density (ρs), estimated using the temperature dependence of the lower criticalfield,Hc1(T), is well explained with the help of the multiband description. Phase-fluctuation analysisconducted on the reversible magnetization data, reveals a significant deviation from the mean-fieldconventional s-wave behavior. This trend is interpreted in terms of a non s-wave spin-triplet com-ponent in the pairing symmetry as might be anticipated in a non-centrosymmetric superconductorwhere anti-symmetric spin-orbit coupling plays a dominant role. Recently, time reversal symmetrybreaking (TRSB) observed in Nb0.18Re0.82supports this picture.
Guo L, Lovell E, Wilson N, et al., 2019, The electrochemical behaviour of magnetocaloric alloys La(Fe,Mn,Si)13Hx under magnetic field conditions, Chemical Communications, Vol: 55, Pages: 3642-3645, ISSN: 1359-7345
The degradation mechanism of La(Fe,Mn,Si)13Hx has been examined under conditions representative of the complex operating parameters of a refrigeration cycle. The magnetic field effects are found to be dominated by magneto-transport and are most significant when the material is in its paramagnetic state - resulting in significantly accelerated corrosion rates.
Sundar S, Salem Sugui Jr S, Lovell E, et al., 2019, Doping dependence of the second magnetization peak, critical current density and pinning mechanism in BaFe2−xNixAs2 Pnictide superconductors, ACS Applied Electronic Materials, Vol: 1, Pages: 179-188, ISSN: 2637-6113
A series of high quality BaFe$_{2-x}$Ni$_x$As$_2$ pnictide superconductors were studied using magnetic relaxation and isothermal magnetic measurements in order to study the second magnetization peak (SMP) and critical current behaviour in Ni-doped 122 family. The temperature dependence of the magnetic relaxation rate suggests a pinning crossover, whereas, it's magnetic field dependence hints a vortex-lattice structural phase-transition. The activation energy ($U$) estimated using the magnetic relaxation data was analyzed in detail for slightly-underdoped, slightly-overdoped and an overdoped samples, using Maley's method and collective creep theory. Our results confirm that the SMP in these samples is due to the collective (elastic) to plastic creep crossover as has been observed for the other members of 122-family. In addition, we also investigated the doping dependence of the critical current density ($J_c$) and the vortex-pinning behaviour in these compounds. The observed $J_c$ is higher than the threshold limit (10$^5$ A/cm$^2$) considered for the technological potential and even greater than 1 MA/cm$^2$ for slightly underdoped Ni-content, x = 0.092 sample. The pinning characteristics were analyzed in terms of the models developed by Dew-Hughes and Griessen $et$ $al$, which suggest the dominant role of $\delta l$-type pinning.
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.
Jeon K-R, Ciccarelli C, Kurebayashi H, et al., 2019, Effect of Meissner screening and trapped magnetic flux on magnetization dynamics in thick Nb/Ni80Fe20/Nb trilayers, Physical Review Applied, Vol: 11, ISSN: 2331-7019
We investigate the influence of Meissner screening and trapped magnetic flux on magnetization dynamics for a Ni80Fe20 film sandwiched between two thick Nb layers (100 nm) using broadband (5–20 GHz) ferromagnetic resonance (FMR) spectroscopy. Below the superconducting transition Tc of Nb, significant zero-frequency line broadening (5–6 mT) and dc-resonance field shift (50 mT) to a low field are both observed if the Nb thickness is comparable to the London penetration depth of Nb films (≥100 nm). We attribute the observed peculiar behaviors to the increased incoherent precession near the Ni80Fe20/Nb interfaces and the effectively focused magnetic flux in the middle Ni80Fe20 caused by strong Meissner screening and (defect-)trapped flux of the thick adjacent Nb layers. This explanation is supported by static magnetic properties of the samples and comparison with FMR data on thick Nb/Ni80Fe20 bilayers. Great care should, therefore, be taken in the analysis of FMR response in ferromagnetic Josephson structures with thick superconductors, a fundamental property for high-frequency device applications of spin-polarized supercurrents.
Rogdakis K, Sud A, Amado M, et al., 2019, Spin transport parameters of NbN thin films characterised by spin pumping experiments, Physical Review Materials, Vol: 3, ISSN: 2475-9953
We present measurements of ferromagnetic resonance driven spin pumping and inverse spin Hall effect in NbN/Y3Fe5O12 (YIG) bilayers. A clear enhancement of the (effective) Gilbert damping constant of the thin-film YIG was observed due to the presence of the NbN spin sink. By varying the NbN thickness and employing spin-diffusion theory, we have estimated the room-temperature values of the spin-diffusion length and the spin Hall angle in NbN to be 14 nm and −1.1×10−2, respectively. Furthermore, we have determined the spin mixing conductance of the NbN/YIG interface to be 10nm−2. The experimental quantification of these spin transport parameters is an important step towards the development of superconducting spintronic devices involving NbN thin films.
Jeon K-R, Ciccarelli C, Kurebayashi H, et al., 2019, Exchange-field enhancement of superconducting spin pumping, Physical Review B, Vol: 99, ISSN: 2469-9950
A recent ferromagnetic resonance study [Jeon et al., Nat. Mater. 17, 499 (2018)] has reported that spin pumping into a singlet superconductor (Nb) can be greatly enhanced over the normal state when the Nb is coupled to a large spin-orbit-coupling (SOC) spin sink such as Pt. This behavior has been explained in terms of the generation of spin-polarized triplet supercurrents via SOC at the Nb/Pt interface, acting in conjunction with a nonlocally induced magnetic exchange field. Here we report the effect of adding a ferromagnet (Fe) to act as an internal source of an additional exchange field to the adjacent Pt spin sink. This dramatically enhances the spin pumping efficiency in the superconducting state compared with either Pt and Fe separately, demonstrating the critical role of the exchange field in generating superconducting spin currents in the Nb.
Shautsova V, Sidiropoulos T, Xiao X, et al., 2018, Plasmon induced thermoelectric effect in graphene, Nature Communications, Vol: 9, ISSN: 2041-1723
Graphene has emerged as a promising material for optoelectronics due to its potential for ultrafast and broad-band photodetection. The photoresponse of graphene junctions is characterized by two competing photocurrent generation mechanisms: a conventional photovoltaic effect and a more dominant hot-carrier-assisted photothermoelectric (PTE) effect. The PTE effect is understood to rely on variations in the Seebeck coefficient through the graphene doping profile. A second PTE effect can occur across a homogeneous graphene channel in the presence of an electronic temperature gradient. Here, we study the latter effect facilitated by strongly localised plasmonic heating of graphene carriers in the presence of nanostructured electrical contacts resulting in electronic temperatures of the order of 2000 K. At certain conditions, the plasmon-induced PTE photocurrent contribution can be isolated. In this regime, the device effectively operates as a sensitive electronic thermometer and as such represents an enabling technology for development of hot carrier based plasmonic devices.
Boldrin D, Mendive-Tapia E, Zemen J, et al., 2018, Multi-site exchange enhanced barocaloric response in Mn3NiN, Physical Review X, Vol: 8, ISSN: 2160-3308
We study the barocaloric effect (BCE) in the geometrically frustrated antiferromagnet Mn3NiN across the Néel transition temperature. Experimentally, we find a larger barocaloric entropy change by a factor of 1.6 than that recently discovered in the isostructural antiperovskite Mn3GaN despite significantly greater magnetovolume coupling in Mn3GaN. By fitting experimental data to theory, we show that the larger BCE of Mn3NiN originates from multisite exchange interactions amongst the local Mn magnetic moments and their coupling with itinerant electron spins. Using this framework, we discuss the route to maximize the BCE in the wider Mn3AN family.
Li B, Famili M, Pensa E, et al., 2018, Cross-plane conductance through a graphene/molecular monolayer/Au sandwich, Nanoscale, Vol: 10, Pages: 19791-19798, ISSN: 2040-3364
The functionalities offered by single-molecule electrical junctions are yet to be translated into monolayer or few-layer molecular films, where making effective and reproducible electrical contact is one of the challenging bottlenecks. Here we take a significant step in this direction by demonstrating that excellent electrical contact can be made with a monolayer biphenyl-4,4′-dithiol (BPDT) molecular film, sandwiched between gold and graphene electrodes. This sandwich device structure is advantageous, because the current flows through the molecules to the gold substrate in a ‘cross-plane’ manner, perpendicular to the plane of graphene, yielding high-conductance devices. We elucidate the nature of the cross-plane graphene/molecule/Au transport using quantum transport calculations and introduce a simple analytical model, which captures generic features of the current–voltage characteristic. Asymmetry in junction properties results from the disparity in electrode electrical properties, the alignment of the BPDT HOMO–LUMO energy levels and the specific characteristics of the graphene electrode. The experimental observation of scalability of junction properties within the junction area, in combination with a theoretical description of the transmission probability of the thiol–graphene contact, demonstrates that between 10% and 100% of the molecules make contact with the electrodes, which is several orders of magnitude greater than that achieved to date in the literature.
Maher RC, Kerherve G, Payne DJ, et al., 2018, The reduction properties of M‐Doped (M=Zr, Gd) CeO2/YSZ scaffolds co‐infiltrated with nickel, Energy Technology, Vol: 6, Pages: 2045-2052, ISSN: 2194-4296
In recent years infiltration of materials into porous ceramic scaffolds has been shown to be an effective way of creating catalytically active components for solid oxide fuel cells (SOFCs). However, the redox properties of these novel structures are not well understood. Here, we use X‐ray photoelectron spectroscopy (XPS) and in‐situ Raman spectroscopy to investigate the oxidation properties of yttria‐stabilised zirconia (YSZ) scaffolds infiltrated with ceria (CeO2), gadolinium‐doped ceria (GDC) and zirconia‐doped ceria (ZDC), with and without Ni. XPS shows that doping ceria with zirconia increases the ratio of Ce3+ to Ce4+, while gadolinium doping results in a decrease of Ce3+. The presence of Ni increases the Ce3+/Ce4+ ratio for CeO2 and GDC, but had little effect on ZDC. We used the shift of the F2g Raman peak to monitor in‐situ, the oxidation state of ceria. In the as‐made compounds, we show that while the gadolinium and zirconium dopants significantly change the oxidation characteristics of ceria, the resulting materials are only significantly reduced above 500 °C when co‐infiltrated with Ni. In‐situ Raman monitoring during reduction as a function of temperature showed that while ZDC reduces much more readily than undoped ceria or GDC, the presence of Ni dominated the reduction dynamics.
Connor PA, Yue X, Savaniu, et al., 2018, Tailoring SOFC electrode microstructures for improved performance, Advanced Energy Materials, Vol: 8, Pages: 1-20, ISSN: 1614-6832
The key technical challenges that fuel cell developers need to address are performance, durability, and cost. All three need to be achieved in parallel; however, there are often competitive tensions, e.g., performance is achieved at the expense of durability. Stability and resistance to degradation under prolonged operation are key parameters. There is considerable interest in developing new cathodes that are better able to function at lower temperature to facilitate low cost manufacture. For anodes, the ability of the solid oxide fuel cell (SOFC) to better utilize commonly available fuels at high efficiency, avoid coking and sulfur poisoning or resistance to oxidation at high utilization are all key. Optimizing a new electrode material requires considerable process development. The use of solution techniques to impregnate an already optimized electrode skeleton, offers a fast and efficient way to evaluate new electrode materials. It can also offer low cost routes to manufacture novel structures and to fine tune already known structures. Here impregnation methodologies are discussed, spectral and surface characterization are considered, and the recent efforts to optimize both cathode and anode functionalities are reviewed. Finally recent exemplifications are reviewed and future challenges and opportunities for the impregnation approach in SOFCs are explored.
Yates K, Cohen L, 2018, Andreev reflection spectroscopy in transition metal oxides, Philosophical Transactions of the Royal Society A. Mathematical, Physical and Engineering Sciences, Vol: 376, Pages: 1-12, ISSN: 1364-503X
Here we review the literature concerning measurement of the Andreev reflection between a superconductor (S) and ferromagnet (F), with particular attention to the case where the ferromagnet is a transition metal oxide. We discuss the practicality of utilisation of the current models for determination of the transport current spin polarisation and examine the evidence for Andreev bound states.
Black NCG, Rungger I, Li B, et al., 2018, Adsorption dynamics of CVD graphene investigated by a contactless microwave method, 2D Materials, Vol: 5, ISSN: 2053-1583
We use a contactless microwave dielectric resonator gas sensing platform to study the adsorption dynamics of NO2 gas present in air onto a graphene surface. The use of microwaves removes the need for metal contacts that would otherwise be necessary for traditional conductivity measurements, and therefore allows non-invasive determination of NO2 concentrations to sub parts per million. As a result, gas−metal interactions and localised graphene doping in the vicinity of metal contacts are eliminated, with the advantage that only graphene−gas adsorbate interactions are responsible for the measured signal. We show that the sensor response for all considered concentrations can be described using a surface coverage dependent Langmuir model. We demonstrate that the possible variation of the NO2 binding energy, which is frequently considered as the main parameter, plays only a secondary role compared to the rising adsorption energy barrier with increasing NO2 coverage. The continuous distribution of the properties of the graphene adsorption sites used in the theoretical model is supported by our Kelvin probe and Raman surface analysis. Our results demonstrate that the non-invasive microwave method is a promising alternative platform for gas sensing. Moreover it provides valuable insights towards the understanding of the microscopic processes occurring in graphene based gas sensors, which is a key factor in the realization of reproducible and optimized device properties.
Jeon K-R, Ciccarelli C, Kurebayashi H, et al., 2018, Spin-pumping-induced inverse spin hall effect in Nb/Ni80Fe20 bilayers and its strong decay across the superconducting transition temperature, Physical Review Applied, Vol: 10, ISSN: 2331-7019
We quantify the spin Hall angle θSH and spin-diffusion length lsd of Nb from inverse spin Hall effect (ISHE) measurements in Nb/Ni80Fe20 bilayers under ferromagnetic resonance. By varying the Nb thickness tNb and comparing to a Ni80Fe20/Pt reference sample, room temperature values of θSH and lsd for Nb are estimated to be approximately −0.001 and 30 nm, respectively. We also investigate the ISHE as a function of temperature T for different tNb. Above the superconducting transition temperature Tc of Nb , a clear tNb-dependent T evolution of the ISHE is observed whereas below Tc, the ISHE voltage drops rapidly and is below the sensitivity of our measurement setup at a lower T. This suggests the strong decay of the quasiparticle (QP) charge-imbalance relaxation length across Tc, as supported by an additional investigation of the ISHE in a different sample geometry along with model calculation. Our finding suggests careful consideration should be made when developing superconductor spin Hall devices that intend to utilize QP-mediated spin-to-charge interconversion.
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.
Perkins GK, Kustov M, Lovell E, et al., 2018, Hexapod Hall scanner for high-resolution large area magnetic imaging, Review of Scientific Instruments, Vol: 89, ISSN: 0034-6748
We demonstrate a six-axis scanning imaging apparatus using piezo bending actuators with a large scan range. The six axes of motion of the bending actuators together with the coupling mechanism to the translation stage allow complete control of the sensor position and orientation over the scanning surface, which is ideal for the use of planar sensors such as Hall devices. In particular, the design allows for in situ correction of the probe tilt angle so that the sensor distance to sample surface can be minimized. We investigate the impact of this alignment on the quality of the measured data using an InSb Hall sensor and a magnetic sample. We also demonstrate a synchronous commutation setup that can greatly enhance the magnetic image by reducing the Hall signal offset.
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.
Matsui T, Li Y, Hsu M-HM, et al., 2018, Highly Stable Plasmon Induced Hot Hole Transfer into Silicon via a SrTiO3 Passivation Interface, ADVANCED FUNCTIONAL MATERIALS, Vol: 28, ISSN: 1616-301X
Extracting plasmon‐induced hot carriers over a metal–semiconductor Schottky barrier enables photodetection below the semiconductor bandgap energy. However, interfacial carrier recombination hinders the efficiency and stability of this process, severely limiting its implementation in telecommunication. This study proposes and demonstrates the use of epitaxially grown lattice‐matched SrTiO3 for interfacial passivation of silicon‐based plasmonic Schottky devices. The devices are activated by an electrical soft‐breakdown of the interfacial SrTiO3 layer, resulting in reproducible rectified Schottky characteristics. The transition to a low resistance state of the SrTiO3 layer boosts the extraction efficiency of hot holes upon resonant plasmonic excitation, giving rise to a two orders of magnitude higher photocurrent compared to devices with a native oxide layer. Photoresponse, tunability, and barrier height studies under reverse biases as high as 100 V present superior stability with the incorporation of the SrTiO3 layer. The investigation paves the way toward plasmon‐induced photodetection for practical applications including those under challenging operating conditions.
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