Applied Physics Research Articles

Tuning Quantum Phase Transitions at Half Filling in 3L−MoTe2/WSe2 Moiré Superlattices

Many sought-after exotic states of matter are known to emerge close to quantum phase transitions, such as quantum spin liquids and unconventional superconductivity. It is, thus, desirable to experimentally explore systems that can be continuously tuned across these transitions. Here, we demonstrate such tunability and the electronic correlation effects in triangular moiré superlattices formed between trilayer MoTe2 and monolayer WSe2 (3L−MoTe2/WSe2). Through transport measurements, we observe an electronic analog of the Pomeranchuk effect at half filling of the first moiré subband, where increasing temperature paradoxically enhances charge localization. At low temperatures the system exhibits the characteristic of a Fermi liquid with strongly renormalized effective mass, suggesting a correlated metal state. The state is highly susceptible to out-of-plane electric and magnetic fields, which induce a Lifshitz transition and a metal-insulator transition (MIT), respectively. It enables identification of a tricritical point in the quantum phase diagram at the base temperature. We explain the Lifshitz transition in terms of interlayer charge transfer under the vertical electric field, which leads to the emergence of a new Fermi surface and immediate suppression of the Pomeranchuk effect. The existence of quantum criticality in the magnetic-field-induced MIT is supported by scaling behaviors of the resistance. Our work shows the 3L−MoTe2/WSe2 lies in the vicinity to the MIT point of the triangular lattice Hubbard model, rendering it a unique system to manifest the rich correlation effects at an intermediate interaction strength.Received 27 February 2022Revised 10 August 2022Accepted 14 September 2022DOI:https://doi.org/10.1103/PhysRevX.12.041015Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCritical phenomenaDensity of statesElectrical conductivityFermi surfaceHall effectLandau levelsMagnetotransportPhase diagramsQuantum phase transitionsQuantum transportTransport phenomenaCondensed Matter, Materials & Applied Physics

Competing spin-orbital singlet states in the 4d4 honeycomb ruthenate Ag3LiRu2O6

When spin-orbit-entangled $d$-electrons reside on a honeycomb lattice, rich quantum states are anticipated to emerge, as exemplified by the $d^5$ Kitaev materials. Distinct yet equally intriguing physics may be realized with a $d$-electron count other than $d^5$. We found that the layered ruthenate Ag$_3$LiRu$_2$O$_6$ with $d^4$ Ru$^{4+}$ ions at ambient pressure forms a honeycomb lattice of spin-orbit-entangled singlets, which is a playground for frustrated excitonic magnetism. Under pressure, the singlet state does not develop the expected excitonic magnetism but experiences two successive transitions to other nonmagnetic phases, first to an intermediate phase with moderate distortion of honeycomb lattice, and eventually to a high-pressure phase with very short Ru-Ru dimer bonds. While the strong dimerization in the high-pressure phase originates from a molecular orbital formation as in the sister compound Li$_2$RuO$_3$, the intermediate phase represents a spin-orbit-coupled $J$-dimer state which is stabilized by the admixture of upper-lying $J_{\rm eff} = 1$-derived states. We argue that the $J$-dimer state is induced by a pseudo-Jahn-Teller effect associated with the low-lying spin-orbital excited states and is unique to spin-orbit-entangled $d^4$ systems. The discovery of competing singlet phases demonstrates rich spin-orbital physics of $d^4$ honeycomb compounds and paves the way for realization of unconventional magnetism.

Puviani etal. Reply.

Received 26 July 2022Accepted 5 October 2022DOI:https://doi.org/10.1103/PhysRevLett.129.199702Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasSuperconducting fluctuationsSuperconducting gapSuperconducting order parameterPhysical SystemsCupratesHigh-temperature superconductorsTechniquesBCS theoryBethe-Salpeter equationCollective modelsDiagrammatic methodsMethods in superconductivityRaman spectroscopyRandom phase approximationCondensed Matter, Materials & Applied Physics

Comment on "Calculation of an Enhanced A_{1g} Symmetry Mode Induced by Higgs Oscillations in the Raman Spectrum of High-Temperature Cuprate Superconductors".

In a recent manuscript Phys. Rev. Lett. 127, 197001 (2021) Puviani et al. claim that the Higgs mode gives an enhancement of the Raman response in the symmetric $A_{1g}$ Raman channel of cuprates. Here we report a series of technical mistakes in their derivation that completely invalidate this conclusion. In particular, the Raman response function contains two renormalized vertices, with a clearly overcounting of diagrams and uncontrolled results for the Higgs-mode contribution.

Implementation of Augmented Reality (AR) using Assembler in High School Applied Physics Education with the ADDIE Model Approach

Since early March 2020, Indonesia has been shocked by the emergence of the SARS-COV-2 or Covid-19 virus from Wuhan, China. The Pandemic crisis has stopped the education system through face-to-face school learning. One adaptive learning model with the current situation through the network. The technology can be applied in the form of the use of Augmented Reality (AR). In addition, using the ADDIE model approach consists of Analysis, Design, Development, Implementation, and Evaluation. This model can be used in developing learning models, learning strategies, learning methods, learning media, and teaching materials. In general, some previous studies/writing only focused on one object of discussion. Where this study offers several objects that will be displayed, some of these objects are in the form of quantities and units, fluids, elasticity, vectors, energy and efforts, momentum and impulses, dynamics, and thermodynamics.

Erratum: Anharmonic phonon damping enhances the Tc of BCS-type superconductors [Phys. Rev. B 102 , 174506 (2020)

Received 9 August 2022DOI:https://doi.org/10.1103/PhysRevB.106.139901©2022 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAcoustic phononsAnharmonic lattice dynamicsElectron-phonon couplingImpurities in superconductorsPressure effectsSuperconducting phase transitionPhysical SystemsLow-temperature superconductorsTechniquesBCS theoryMethods in superconductivityCondensed Matter, Materials & Applied Physics

Correlated Chern insulators in two-dimensional Raman lattices: A cold-atom regularization of strongly coupled four-Fermi field theories

We show that synthetic spin-orbit coupling for ultracold atoms in optical Raman potentials can be exploited to build versatile quantum simulators of correlated Chern insulators connected to strongly coupled four-Fermi field theories similar to the Gross-Neveu model in (2+1) dimensions. Exploiting this multidisciplinary perspective, we identify a large-N quantum anomalous Hall (QAH) effect in absence of any external magnetic field, and use it to delimit regions in parameter space where these correlated topological phases appear, the boundaries of which are controlled by strongly coupled fixed points of these four-Fermi relativistic field theories. We further show how, for strong interactions, the QAH effect gives way to magnetic phases described by a two-dimensional quantum compass model in a transverse field. We present a detailed description of the phase diagram using the large-N effective potential, and variational techniques such as projected entangled pairs.Received 22 December 2020Revised 8 July 2022Accepted 25 July 2022DOI:https://doi.org/10.1103/PhysRevResearch.4.L042012Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasChern insulatorsLattice field theoryOptical lattices & trapsQuantum simulationAtomic, Molecular & OpticalQuantum InformationCondensed Matter, Materials & Applied Physics

Ultrafast perturbation of magnetic domains by optical pumping in a ferromagnetic multilayer

Ultrafast optical pumping of spatially nonuniform magnetic textures is known to induce far-from-equilibrium spin transport effects. Here, we use ultrafast x-ray diffraction with unprecedented dynamic range to study the laser-induced dynamics of labyrinth domain networks in ferromagnetic CoFe/Ni multilayers. We detected azimuthally isotropic, odd order, magnetic diffraction rings up to fifth order. The amplitudes of all three diffraction rings quench to different degrees within 1.6 ps. In addition, all three of the detected diffraction rings both broaden by 15% and radially contract by 6% during the quench process. We are able to rigorously quantify a 31% ultrafast broadening of the domain walls via Fourier analysis of the order-dependent quenching of the three detected diffraction rings. The broadening of the diffraction rings is interpreted as a reduction in the domain coherence length, but the shift in the ring radius, while unambiguous in its occurrence, remains unexplained. In particular, we demonstrate that a radial shift explained by domain-wall broadening can be ruled out. With the unprecedented dynamic range of our data, our results provide convincing evidence that labyrinth domain structures are spatially perturbed at ultrafast speeds under far-from-equilibrium conditions, albeit the mechanism inducing the perturbations remains yet to be clarified.7 MoreReceived 15 June 2022Revised 15 September 2022Accepted 26 September 2022DOI:https://doi.org/10.1103/PhysRevB.106.144422©2022 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasDomain wallsMagnetic domainsMagnetic textureMagnetismMagnetization dynamicsUltrafast demagnetizationUltrafast magnetic effectsUltrafast magnetization dynamicsCondensed Matter, Materials & Applied Physics

New Spin-Polarized Electron Source Based on Alkali Antimonide Photocathode.

New spin-dependent photoemission properties of alkali antimonide semiconductor cathodes are predicted based on the detected optical spin orientation effect and DFT band structure calculations. Using these results, the Na_{2}KSb/Cs_{3}Sb heterostructure is designed as a spin-polarized electron source in combination with the Al_{0.11}Ga_{0.89}As target as a spin detector with spatial resolution. In the Na_{2}KSb/Cs_{3}Sb photocathode, spin-dependent photoemission properties were established through detection of a high degree of photoluminescence polarization and high polarization of the photoemitted electrons. It was found that the multi-alkali photocathode can provide electron beams with emittance very close to the limits imposed by the electron thermal energy. The vacuum tablet-type sources of spin-polarized electrons have been proposed for accelerators, which can exclude the construction of the photocathode growth chambers for photoinjectors.

Spontaneous Ferromagnetism Induced Topological Transition in EuB_{6}.

The interplay between various symmetries and electronic bands topology is one of the core issues for topological quantum materials. Spontaneous magnetism, which leads to the breaking of time-reversal symmetry, has been proven to be a powerful approach to trigger various exotic topological phases. In this Letter, utilizing the combination of angle-resolved photoemission spectroscopy, magneto-optical Kerr effect microscopy, and first-principles calculations, we present the direct evidence on the realization of the long-sought spontaneous ferromagnetism induced topological transition in soft ferromagnetic EuB_{6}. Explicitly, we reveal the topological transition is from Z_{2}=1 topological insulator in paramagnetic state to χ=1 magnetic topological semimetal in low temperature ferromagnetic state. Our results demonstrate that the simple band structure near the Fermi level and rich topological phases make EuB_{6} an ideal platform to study the topological phase physics.

Pseudogap suppression by competition with superconductivity in La-based cuprates

We carried out a comprehensive high-resolution angle-resolved photoemission spectroscopy (ARPES) study of the pseudogap interplay with superconductivity in La-based cuprates. The three systems La2−xSrxCuO4, La1.6−xNd0.4SrxCuO4, and La1.8−xEu0.2SrxCuO4 display slightly different pseudogap critical points in the temperature versus doping phase diagram. We studied the pseudogap evolution into the superconducting state for doping concentrations just below the critical point. In this setting, near optimal doping for superconductivity and in the presence of the weakest possible pseudogap, we uncover how the pseudogap is partially suppressed inside the superconducting state. This conclusion is based on the direct observation of a reduced pseudogap energy scale and re-emergence of spectral weight suppressed by the pseudogap. Altogether these observations suggest that the pseudogap phenomenon in La-based cuprates is in competition with superconductivity for antinodal spectral weight.Received 27 April 2022Accepted 30 August 2022DOI:https://doi.org/10.1103/PhysRevResearch.4.043015Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasElectronic structurePhysical SystemsCupratesTechniquesAngle-resolved photoemission spectroscopyCondensed Matter, Materials & Applied Physics

(Invited, Digital Presentation) Optimization of Mass Transport in a Plasma-Liquid Reactor

A considerable amount of research over the past decade has been directed toward the development of plasma based Advanced Oxidation Processes (AOPs) for the degradation of pollutants in wastewater. Despite these efforts and the exceptional efficiencies reported in laboratory-based tests, the direct contact between a non-thermal plasma (NTP) and liquid introduces a number of challenges. Critically, the characteristics of the NTP, and therefore its chemical composition, are directly linked to the electrical properties of the contaminated water, which inevitably varies. Furthermore, the use of short-duration high voltage pulses to generate NTP is considered the most effective approach, yet the generation of such pulses to create uniform large volume NTP is particularly challenging.Given the drawbacks and challenges associated with direct-contact NTP reactors, several recent studies have examined the use of indirect-contact NTP systems for water treatment [1,2]. In particular, the surface barrier discharge (SBD) configuration enables large volume NTP generation in humid air with modest power supply requirements. Unfortunately, a key drawback associated with the use of indirect-contact plasma liquid reactors is the reduced transport of chemical species from the discharge to the liquid. Highly reactive species produced by NTP generated in humid air, such as atomic oxygen and hydroxyl radicals, rapidly react beyond the plasma to form longer-lived and less reactive intermediaries, such as ozone and hydrogen peroxide. To enhance the efficiency of an indirect-contact NTP reactor the transport of longer-lived intermediary species to the liquid must be maximized. One particularly convenient method to achieve this is through the use of a falling film reactor [3], whereby a thin liquid film flows in close proximity to an NTP source. Such reactors have been used extensively in direct-contact NTP studies [4,5], but have not yet been used for the in-direct NTP treatment of contaminated water.This contribution considers the hypothesis that the efficiency of an indirect-contact NTP wastewater treatment processes can rival that of direct-contact treatment process by combining a falling film reactor with a SBD, figure 1. To test the hypothesis the decolorization of indigo carmine dye was examined as a function of plasma operating parameters whilst the generation of chemical species was assessed in both the liquid and gas phase. Analysis of dye decolorization as a function of energy input revealed that complete decolorization of Indigo Carmine could be achieved, figure 2. However, more energy was used at higher discharge powers to obtain total decolorization. To explain the faster and more efficient decolorization of dye at lower power, FTIR was used to quantify gas phase chemical species. Under high power operation it was observed that the gas phase chemistry rapidly transitioned from being ozone dominated to NOx dominated, attributed to process known as Ozone poisoning. It was shown that the shift in gas-phase chemistry is primarily responsible for the reduction in decolorization efficiency under high power operation.Using optimized NTP parameters the decolorization results were compared against several other plasma-based AOP approaches and alternative AOP technologies, Figure 3. The comparison illustrates the G50 (g/kWh) value (i.e., the energy consumed to decompose one gram of pollutant) against the time needed to reach 50 % decomposition (t50). It is clear that the indirect-contact plasma system investigated in this contribution compares favorably with other plasma-based studies, including those using direct-contact systems. It is also clear that the approach offers a higher efficiency compared to alternative AOP technologies, such as UV, UV/ H2O2 [6], H2O2/photo Fenton, UV/TiO2 and Fenton/photo Fenton [7].In summary, the combination of a large-area SBD and falling film reactor provides a convenient means for wastewater remediation without many of the challenges associated with direct-contact plasma-liquid systems. Despite the limited mass-transport of highly reactive species to the liquid layer, the large flux of longer-lived species was found to be highly effective for the efficient degradation of Indigo Carmine.[1] Kumar et al., Frontiers in Physics, vol. 10, 2022.[2] Pavlovich et al., Journal of Physics D: Applied Physics, vol. 46, no. 14, p. 145202, 2013.[3] Krupež et al., Journal of Physics D: Applied Physics, vol. 51, no. 17, p. 174003, 2018.[4] Hama Aziz et al., Journal of Hazardous Materials, vol. 343, pp. 107-115, 2018.[5] Kozakova et al., Plasma Processes and Polymers, vol. 15, no. 6, p. 1700178, 2018.[6] Rodríguez et al., Environmental Engineering Science, vol. 24, no. 3, pp. 363-371, 2007.[7] Palma-Goyes et al., Electrochimica Acta, vol. 140, pp. 427-433, 2014. Figure 1

Effective Penetration Depths Investigation on Synchrotron X-Ray Topographic Images of Basal Plane Dislocations in 4H-SiC Crystals through Ray-Tracing Simulation

The demand for power electronic devices fabricated from silicon carbide (SiC) has increased rapidly in recent years for a diverse range of existing and emerging applications. The development of device technology highly depends on the quality of substrate and epitaxial material and the number of deleterious defects within, as those are critical factors that impact the device performance and long-term reliability [1, 2]. Therefore, understanding the nature of defects is of great importance for preventing the degradation or premature breakdown of devices. Synchrotron X-ray topography (XRT) is a dominant analytical method for the imaging and characterization of crystallographic defects. For 4° off-axis (0001) 4H-SiC wafers, the grazing-incidence geometry topographic technique is commonly employed to focus on the defect investigation near surface region. In this geometry, a small incidence angles (~1-2°) is used for allowing X-ray to only penetrate the sample with a shallow depth below the surface, therefore, it is essential to establish a procedure to define the effective penetration depth for detailed analysis of dislocation structures and density calculations. In earlier studies, Dudley in 1989 concluded that the observed penetration depths are limited by photoelectric absorption rather than extinction [3]. Ishiji in 2017 estimated the penetration depth based on the photoelectric absorption experienced by the diffracted X-rays [4]. However, only basal plane dislocations (BPDs) with screw segments parallel to the off-cut [11-20]-direction were evaluated in that study, which is insufficient for evaluating other types of BPDs. Therefore, a universal method to determine the effective penetration depth for all dislocation types would be of more practical importance.In this study, a procedure to define this effective penetration depth is demonstrated by investigating physical vapor transport (PVT) grown 4° off-axis 4H-SiC crystals through preforming systematic analysis of topographic and ray-tracing simulated contrast of BPDs with different Burgers vector and line direction combinations. The topographic images are recorded through synchrotron monochromatic beam in grazing incidence geometry. The simulation model is based on the principle of orientation contrast mechanism [5, 6] and developed by considering both the effects of surface relaxation [7] and X-ray absorption [8, 9] for evaluating the contributed factors of dislocation contrast formation. Analysis of the results indicates the observable dislocation contrast depends on the effective misorientation associated with the dislocation modulated by the photoelectric absorption effect. The dislocations with larger effective misorientation are associated with longer projected lengths and corresponding deeper effective penetration depths. A more simplified factor based on an approximate expression for the misorientation is also introduced in this study as an alternative to the full ray-tracing simulation approach. The effective penetration depth determination method presented in this study enables three-dimensional dislocation configuration analysis and accurate density calculations.Reference: Das, H., et al., Materials Science Forum, 2019. 963: p. 284-287.Kimoto, T., et al. 2017 IEEE International Reliability Physics Symposium (IRPS). 2017.Dudley, M., J. Wu, and G.D. Yao, Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1989. 40-41: p. 388-392.Ishiji, K., et al., Japanese Journal of Applied Physics, 2017. 56(10): p. 106601.Dudley, M., X.R. Huang, and W. Huang, Journal of Physics D: Applied Physics, 1999. 32(10A): p. A139-A144.Huang, X.R., et al., Journal of Applied Crystallography, 1999. 32(3): p. 516-524.Peng, H., et al., Journal of Applied Crystallography, 2021. 54(2): p. 439-443.Fujie, F., et al., Acta Materialia, 2021. 208: p. 116746.Ailihumaer, T., et al., Materials Science and Engineering: B, 2021. 271: p. 115281. Figure 1

(Invited) Comparison of Compositional, Optical and Mechanical Properties of Sicn Thin Films Prepared By Ecr-PECVD with Different Hydrocarbon Precursors

Silicon carbon nitride (SiCN) ternary compounds present remarkable mechanical strength, bandgap tunability, optical responsivity in the UV region, and dielectric performance in microelectronics due to the combined features of silicon nitride (SiN), silicon carbide (SiC), and carbonitride (CN) [1]. The SiCN compounds can be formed using fabrication methods such as physical vapor deposition (PVD), chemical vapor deposition (CVD), and chemical synthesis. Successful SiCN thin films fabricated with different techniques and their characteristics have been reported extensively in the literature; however, the influence of hydrocarbon gas precursors has not drawn the same amount of attention for SiCN. Chemical, physical, and mechanical properties of thin films are determined by the growth parameters and the choice of sources used, like the organic single-molecule (methylsilazanes) or highly pure individual gas precursors [2,3]. The chemical vapor deposition systems mainly affect the energy of bombarding ions. Plasma-enhanced CVD has been commonly used for thin-film depositions since it provides low deposition temperature, high purity, good step coverage, and easy control of reaction parameters.Our work focuses on the electron-cyclotron resonance plasma-enhanced chemical vapor deposition (ECR PECVD) method to fabricate SiCN thin films. This method differs from other PECVD methods because it can generate a dense, highly ionized plasma (1011 ions/cm3) and ion impingement energies on the substrate as low as 20 eV [4]. A combination of argon diluted silane (SiH4) and molecular nitrogen (N2) are utilized. For carbon incorporation, we explored the influence of methane (CH4), acetylene (C2H2), and ethane (C2H6) hydrocarbon gas precursors on SiCN thin film properties. The stoichiometry, density of the thin film, optical constants, and the bonding structure of SiCN thin films as a function of hydrocarbon carbon flow rates are presented. Due to the hydrogen-containing precursors used, the silicon carbonitride films deposited by CVD methods contain a significant amount of hydrogen (H), lowest for C2H2 and highest for C2H6. Nearly stoichiometric silicon nitride and silicon carbide thin films were also prepared to interpret the measurements further. From Rutherford backscattering spectrometry (RBS) and elastic recoil detection (ERD) analysis, quantitative elemental composition distributions including H were found for films deposited with both carbon sources. For further investigation of the bonding structure of SiCN, Fourier Transform Infrared (FTIR) Spectroscopy was performed. Furthermore, we studied the hardness and Young’s modulus by nanoindentation, and optical constants were measured by variable angle spectroscopic ellipsometry (VASE).[1] C.W. Chen, C.C. Huang, Y.Y. Lin, L.C. Chen, K.H. Chen, W.F. Su, Optical prop- erties and photoconductivity of amorphous silicon carbon nitride thin film and its application for UV detection, Diamond Relat. Mater. 14 (3-7) (2005) 1010–1013.[2] Schwarz-Selinger, T., Von Keudell, A., & Jacob, W. (1999). Plasma chemical vapor deposition of hydrocarbon films: The influence of hydrocarbon source gas on the film properties. Journal of Applied Physics, 86(7), 3988-3996.[3] V.I. Ivashchenko, A.O. Kozak, O.K. Porada, L.A. Ivashchenko, O.K. Sinelnichenko, O.S. Lytvyn, T.V. Tomila, V.J. Malakhov, Characterization of SiCN thin films: experimental and theoretical investigations, Thin Solid Films 569 (2014) 57–63.[4] M. G. Boudreau, "SiOxNy Waveguides Deposited by ECR-PECVD", M.Eng. thesis, McMaster University, 1993.

Operando Raman Spectroscopy of Phase Changes in Nanocrystalline Metal Oxide Lithium-Ion Battery Electrodes

As the demands for clean electricity, transport and highly functional portable electronics grow faster than ever, energy storage remains the main roadblock to progression. Electrochemical devices such as lithium-ion batteries (LIBs), have been the source of most success in overcoming this roadblock. The primary issue with these devices is lifetime decay due primarily to the degradation of the electrodes within the battery. Nanocrystalline materials are often chosen,1 which enhance battery performance by reducing ion diffusion lengths and thus improving rate capabilities. However, structural changes prove difficult to monitor due to their dimensions. The electrochemical processes which cause these changes are also difficult to probe because of their metastability and lifetimes, which can be of nanosecond to sub nanosecond time domains.2 Consequently, the development of methods to capture these processes proves challenging, requiring state-of-the-art techniques. Our work demonstrates that the processes which lead to electrode degradation can in fact be captured by using novel cell designs that provide the ability to adapt analytical techniques to probe battery systems in real time.Raman spectroscopy is particularly useful for multi-layered materials such as the porous metal oxides often used in battery electrodes.3 Information can be revealed on crystal structure, electronic structure, lattice vibrations and flake thickness of layered materials, and can be used to probe the strain, stability, charge transfer, stoichiometry, and stacking order.4 The correlation between the capacity of intercalation in an electrode to the degree of disorder in the material can also be determined.5 Such analysis can be performed during cycling, once the cell is modified to enable light penetration. A pathway is usually provided in the form of an optical window, allowing measurements to be obtained non-destructively in real-time.6 The window material must be transparent to the frequency of incident light chosen for measurements.7 These constitute spectroelectrochemical cells, providing the ability to perform electrochemical and optical measurements simultaneously.Here, we demonstrate a non-destructive approach to monitoring battery degradation in operando. Access for Raman spectroscopy during cycling is provided by a novel cell design. Sapphire is employed as window material, transparent to the 532 nm laser beam used for our Raman measurements. We describe the process applied to a lithium-ion battery based on a metal oxide inverse opals8,9 where the interconnected order porous structure is known to facilitate stable and long term cycling in the absence of binders and conductive additives11-17. However, the same methodology can be extended to any electrode materials with Raman active phase changes at the electrode-electrolyte interface.10 This work provides information on structural and phase changes to the electrode which are compared to microscopy and electrochemical data. References 1 C. Zhu, R. E. Usiskin, Y. Yu, and J. Maier, Science 358, eaao2808 (2017). 2 O. Pecher, J. Carretero-González, K. J. Griffith, and C. P. Grey, Chemistry of Materials 29, 213 (2017). 3 S. Fang, D. Bresser, and S. Passerini, Advanced Energy Materials 10, 1902485 (2020). 4 J.-B. Wu, M.-L. Lin, X. Cong, H.-N. Liu, and P.-H. Tan, Chemical Society Reviews 47, 1822 (2018). 5 K. Kirshenbaum, D. Bock, C.-Y. Lee, Z. Zhong, K. Takeuchi, A. Marschilok, and E. Takeuchi, Science 347, 149 (2015). 6 E. Armstrong, D. McNulty, H. Geaney, and C. O’Dwyer, ACS Applied Materials & Interfaces 7, 27006 (2015). 7 L. Mai, Y. Dong, L. Xu, and C. Han, Nano Letters 10, 4273 (2010). 8 A. Lonergan, D. McNulty, and C. O'Dwyer, Journal of Applied Physics 124, 095106 (2018). 9 J. Yu, J. Lei, L. Wang, J. Zhang, and Y. Liu, Journal of Alloys and Compounds 769, 740 (2018). 10 C. Julien and A. Mauger, AIMS Materials Science 5, 650 (2018). 11 S. O'Hanon, D. McNulty, R. Tian, J. Coleman, and C. O'Dwyer, J. Electrochem. Soc. 167, 140532 (2020). 12 D. McNulty, H. Geaney, Q. Ramasse, and C. O'Dwyer, 2005073 (2020). 13 D. McNulty, H. Geaney, D. Buckley, and C. O'Dwyer, Nano Energy 43, 11 (2018). 14 D. McNulty, E. Carroll, and C. O'Dwyer, Adv. Energy Mater. 7, 1602291 (2017). 15 D. McNulty, A. Lonergan, S. O'Hanlon, and C. O'Dwyer, Solid State Ionics 314, 195 (2018). 16 S. O'Hanlon, D. McNulty, and C. O'Dwyer, J. Electrochem. Soc. 164, D111 (2017). 17 C. O'Dwyer, Adv. Mater. 28, 5681 (2016).

Substitutional Carbon Incorporation in SiGeC/Si Heterostructures: Influence of Silicon Precursors

The incorporation of germanium and carbon by RP-CVD epitaxy in silicon brings lots of interest in silicon devices thanks to the variety of properties that can be addressed: band gap or lattice parameter engineering, dopant diffusion reduction, chemical properties, optical properties...For all the applications requiring SiGeC materials, carbon atoms must be incorporated in fully substitutional site (Cs) despite its low bulk solubility into the Si and SiGe lattice (3x1017 at.cm-3 at the Si melting point). Beyond a total carbon concentration (depending on process parameter), carbon atoms are also incorporated into interstitial sites (Ci). These Ci atoms usually form extended defects such as clusters or SiC precipitates which are harmful for devices performances.Solubility limits of carbon can be extended into the metastable domain by optimizing the epitaxy process. Indeed, it is well established that low temperature and high growth rate are favorable to obtain high Cs atoms incorporation [1].This work compares silane (SiH4) and disilane (Si2H6) precursors coupled with germane (GeH4) and methylsilane (SiH3CH3 or MS) to process low temperature thin film of SiGeC with the highest amount of Cs without Ci.First, the SiGe growth kinetics using silane and disilane have been studied. The temperature range investigated varied from 500 °C to 600 °C at low pressure. Using similar atomic fluxes of Si, and with all the other parameters constant, a higher growth rate and lower germanium content has been observed with disilane compared to silane. For instance, there is a factor of 1.85 at 550°C. The germanium concentration was varying from 30.4 to 22.3 % and from 19.4 to 15.7 % for silane and disilane, respectively. To have a better understanding about this kinetics difference, an impoverishment rate or theoretical yield, of the gas phase, in reactive species has been calculated. The hypothesis is that the impoverishment rate is linked to the reactivity of a molecule, and thus related to the sticking probability of a molecule onto a same surface [2].The impoverishment rate is defined as the ratio between the number of moles of Si (or Ge) deposited per minute (nDeposited) and the number of moles of silicon precursor (or germanium) injected per minute(nInjected) in the epitaxy reactor: αPrecursor = nDeposited/nInjected. The impoverishment rate of the disilane molecule increases much more rapidly than the silane molecule as the temperature increases (Fig.1a). Disilane is more consumed than silane which is relevant of the higher reactivity of disilane compared to silane.Moreover, the impoverishment of germane increases more rapidly with disilane than with silane (Fig.1b). The GeH4 contribution to epitaxy is more significant using disilane than silane. The impoverishment rate of precursors according to the germane flow will be presented later.Then, silane and disilane precursors have been compared with respect to the C incorporation at 550 °C. Ge concentration was fixed to 20 % with both silicon precursors. This leads to a growth rate of SiGe equal to 2.9 and 14.1 nm.min-1 using silane and disilane, respectively. XRD has been used to gain access to the “apparent” Ge concentration in Si1-x-yGexCy layers (Fig.2(a), (b)). Carbon atoms, much smaller than silicon and germanium, compensate the compressive strain induced by germanium in the SiGe layers. It then yields smaller Ge concentration in XRD than the real Ge concentration. The carbon in substitutional position can therefore be extracted using this coefficient: 1 % of carbon compensate 12 % of Ge [3].Using disilane, the substitutional carbon concentration linearly increases with the MS flow over the whole studied range (Fig.3). However, using silane, a deviation from the linearity is observed (above 0.7 %). In the linearity part of the curves, all the carbon incorporated are in substitutional site (as the total amount of carbon atoms increasing linearly with the MS flow [4]). When a non-linearity occurs, C atoms started to be incorporated in interstitial position also. SIMS measurement will be performed to confirm that. At 550 °C, the growth rate of SiGe is more important with disilane precursor due its higher reactivity than silane. Its leads to a better substitutional carbon incorporation. Indeed, using disilane, up to 1.15 % of fully substitutional carbon can be reached while using silane, only 0.7 % is reached.[1] V. Loup et al., J. Vac. Sci. Technol. B 21(1), Jan/Feb 2003.[2] D.J. Robbins et al., Journal of Applied Physics 69, 3729 (1991).[3] D. De Salvador et al., Phys. Rev. B, vol. 61, pp. 13005, 2000.[4] V. Loup et al., J. Vac. Sci. Technol. B 20(3), May/Jun 2002. Figure 1

Growth and Properties of Graphene and Graphene Nanoribbons on Ge

The synthesis of graphene directly on Ge and on Ge deposited on Si provides a scalable route toward integrating graphene onto conventional semiconductors. This presentation will first survey the growth modes of graphene on Ge(001), Ge(011), Ge(111), Ge(112), Ge(001)-6°, and Ge(001)-9° via chemical vapor deposition (CVD), reporting on the effect of Ge surface orientation on graphene island formation and shape, strain in large-area graphene films, and the nanofaceting of the Ge below graphene.[1] We will then focus on the anisotropic growth of semiconducting graphene nanoribbons on Ge(001) and Ge(001)-9° and of nominally single crystal graphene on Ge(110).On Ge(001), we have discovered how to drive graphene crystal growth with a large shape anisotropy through control of kinetics.[2-6] This discovery enables the direct synthesis of narrow, armchair, semiconducting nanoribbons. The ribbons are self-orienting, self-defining, and have smooth edges. The ribbons exhibit excellent transport properties (e.g., high on-state conductance and on/off ratio at room temperature) and provide a promising pathway towards the direct integration of high-performance nanocarbon electronics onto conventional semiconductor wafer platforms.On Ge(001), nominally single crystal graphene has been reported in limited cases; however, conflicting studies have evidenced polycrystallinity. Here, the factors affecting the mosaicity of graphene on Ge(110) will be elucidated using low energy electron diffraction and microscopy data.[7][1] R. M. Jacobberger, D. E. Savage, X. Zheng, P. Sookchoo, R. R. Delgado, M. G. Lagally, M. S. Arnold, SUBMITTED (2022).[2] R. M. Jacobberger, M. S. Arnold, et al., Direct Oriented Growth of Armchair Graphene Nanoribbons on Germanium, NATURE COMMUNICATIONS, 6, 8006 (2015).[3] B. Kiraly, M. S. Arnold, M. C. Hersam, N. P. Guisinger et al., Sub-5 nm, Globally Aligned Graphene Nanoribbons on Ge (001), APPLIED PHYSICS LETTERS, 108, 213101 (2016).[4] A. J. Way, R. M. Jacobberger, M. S. Arnold, Seed-Initiated Anisotropic Growth of Unidirectional Armchair Graphene Nanoribbon Arrays on Germanium, NANO LETTERS, 18, 898 (2018).[5] V. Saraswat, Y. Yamamoto, H.J. Kim, R.M. Jacobberger, K.R. Jinkins, A.J. Way, N.P. Guisinger, M.S. Arnold Synthesis of armchair graphene nanoribbons on germanium-on-silicon, THE JOURNAL OF PHYSICAL CHEMISTRY C 123 (30), 18445-18454 (2019).[6] A. J. Way, R. M. Jacobberger, N. P. Guisinger, V. Saraswat, X. Zheng, A. Suresh, J. H. Dwyer, P. Gopalan, Michael S. Arnold, SUBMITTED (2022).[7] R. M. Jacobberger, Z. Miao, T. Yu, V. Saraswat, M. G. Lagally, M. S. Altman, M. S. Arnold, SUBMITTED (2022).

Electrodeposition of Rhenium Sandwich Structures and the Superconducting Transition Behavior

Superconductors with enhanced superconducting critical temperatures (Tc) above the boiling point of liquid helium (4.2 K) are of interest for interconnections in superconducting quantum computing systems to avoid ohmic heating[1]. Crystalline Re in bulk is a type-I superconductor with a Tc of about 1.7K[2]. An elevated Tc up to about 6K in electrodeposited amorphous Re has been reported[3]. In addition, various elevation in Tc has also been reported for Re film under shear strain[4] or doped with foreign elements such as Tungsten (W), Osmium (Os), and Carbon (C)[5, 6].This work aims to test a hypothesis that the Tc of electrodeposited Re films can be tuned using compressive and tensile strains on the Re films generated with thermal expansions difference. Figure 1 shows a diagram of the strains on Re film sandwiched between metals with different coefficients of thermal expansions (CTEs) when the temperature is lowered. For example, Cu has a higher CTE than Re and Cr has a slightly lower CTE than Re. Such sandwich structures are prepared at room temperature using electrochemical deposition. The DC resistance measurements at cryogenic temperatures confirmed that the superconducting transition for the Re films sandwiched between Cu occurs at a lower temperature than the Re film alone. On the other hand, when Cr is used, the sandwiched Re structure shows a slightly enhanced superconducting critical temperature. The effect of thermal annealing i.e., the recrystallization of electrodeposited Re films at an elevated temperature, and electrochemical behavior of Re, Cr, and Cu electrodeposition will be discussed in the talk. References Radenbaugh, R., Refrigeration for superconductors. Proceedings of the IEEE, 2004. 92(10): p. 1719-1734.Hulm, J.K., Superconductivity of Pure Metallic Rhenium. Physical Review, 1954. 94(5): p. 1390-1391.Pappas, D.P., et al., Enhanced superconducting transition temperature in electroplated rhenium. Applied Physics Letters, 2018. 112(18): p. 182601.Mito, M., et al., Large enhancement of superconducting transition temperature in single-element superconducting rhenium by shear strain. Scientific Reports, 2016. 6(1): p. 36337.Chu, C.W., W.L. McMillan, and H.L. Luo, Superconductivity of Re-Os, Re-Ru, Ru-Os, and Re-W hcp Alloy Systems and Slightly Doped Re. Physical Review B, 1971. 3(11): p. 3757-3762.Zhu, Q., et al., Anisotropic lattice expansion and enhancement of superconductivity induced by interstitial carbon doping in Rhenium. Journal of Alloys and Compounds, 2021. 878: p. 160290. Figure 1

Microstructure and Mechanical Properties of Rexnbmotaw Thin Films Prepared By RF Magnetron Sputtering

High Entropy Alloys (HEAs) and Refractory High-Entropy Alloys (RHEAs) are novel potential materials for high-temperature applications [1]. NbMoTaW, a RHEAs, such as the one in Fig. 1, possess superior mechanical properties, combining high strength, outstanding thermal stability, and resistance to softening at high temperatures [2]. The influence of adding Vanadium [3], Tantalum [4], and Rhenium [5] to NbMoTaW alloys on the bulk mechanical behavior was investigated by the previous studies. In this research, the effect of adding Rhenium with different (Re0, Re0.5, Re1) on the microstructure and the mechanical properties of NbMoTaW thin films will be nvestigated. The larger the enthalpy of mixing in negative values, the higher the binding force between the elements, which has been enhanced with Rhenium addition. As for the entropy of mixing, it increased from 11.53 to 13.38 for Re0 and Re1, respectively. The higher the mixture entropy suggests a more stable solid solution. This is confirmed by calculating the thermodynamic parameters proposed by Yang et. Al [6] where they suggested that a mixture with δ < 6.6 and Ω > 1.1 correspond to solid solution formation. The anticipated crystal structure for the three samples is BCC structure according to the valence electron concentration (VEC) theory, where the VEC values were less than 6.87 as suggested by Gou et. Al [7]. The RexNbMoTaW HEAs thin films are fabricated using RF magnetron sputtering. The film thickness, deposition power, and temperature impact on the films’ characteristics are studied. Field emission (FE-SEM), X-ray diffraction (XRD), and nanoindentation are used to investigate the RexNbMoTaW thin films’ crystal structure, surface morphology, and mechanical properties. The mechanical properties of the thin films will be compared with their counterpart bulk materials.References Kim, H., et al., International Journal of Refractory Metals and Hard Materials, 2019. 80: p. 286-291.Feng, X., et al., Materials Letters, 2018. 210: p. 84-87.Senkov, O.N., et al., Intermetallics, 2011. 19(5): p. 698-706.Han, Z.D., et al., Materials Science and Engineering: A, 2018. 712: p. 380-385.Zhang, J., et al., Journal of Alloys and Compounds, 2020. 827.Yang, X. and Y. Zhang, Materials Chemistry and Physics, 2012. 132(2-3): p. 233-238.Guo, S., et al., Journal of Applied Physics, 2011. 109(10): p. 103505. Figure 1

Reflections on Lisa Zurk as an Educator

Lisa Zurk was my advisor and mentor through both my masters and doctoral degree programs. I had the pleasure of working with her beginning in 2008; first as her graduate student, then in my subsequent professional career while she was a program manager in the Strategic Technology Office at DARPA. I consider myself extremely fortunate to have been part of the Northwest Electromagnetics and Acoustics Research Laboratory (NEAR-Lab), which she founded at Portland State University in 2005. Under her guidance and leadership, the group became a diverse community of tight-knit students, faculty, and other researchers; united in our passion for research in terahertz imaging and spectroscopy, underwater acoustics, and physics-based signal processing. My experience there, and that of my fellow students, paved the way for our future careers in science and engineering in industry, academia, and everywhere in between. Today, NEAR-Lab alumni can be found at top tech companies such as Apple, Boeing, Intel, Tektronix, and Metron; nationally-renowned research organizations like The Johns Hopkins University Applied Physics Laboratory, MIT Lincoln Laboratory, and the Pacific Northwest National Laboratory; and even internationally at the University of Victoria, British Columbia, and JASCO Applied Sciences. The success of her students speaks volumes about her impact on the generation of innovators that followed her. This talk will reflect on Dr. Zurk as an educator and will present some of the work she coauthored and published with her students.