arXiv subjects

Andrivo Rusydi

Publications and source records attributed to Andrivo Rusydi.

At least 19 recordsLinked to original sources

arXiv2023

Unravelling metallic contaminants in complex polyimide heterostructures using deep ultraviolet spectroscopic ellipsometry

Metallic contaminants in complex heterostructures are important topics due to their significant roles in determining physical properties as well as device performance. Heterostructures of polyimide via on Al pad and Cu redistribution layer (RDL) on polyimide have shown exotic properties and are important for advanced semiconductor packaging systems. One main problem is significant leakage current variations, which affect the performance of the devices, yet the origin is far from understood. Furthermore, metal contaminations would occur at the buried interfaces and it is particularly challenging to probe them. Until now, the electronic and optical properties of complex polyimide heterostructures and the roles of metallic contaminants, especially in the deep ultraviolet (DUV) have not been studied extensively. Herewith, using spectroscopic ellipsometry (SE) in a broad DUV range supported with finite-difference time-domain (FDTD) calculations, we determine optical properties of contaminants with various concentrations and reveal their influence on device performance of under-bump vias and redistribution layer (RDL) architectures. The complex dielectric function shows varying contamination levels and different metals responsible for chip performance. Metallic contaminants are found embedded within 50 nm in the polyimide and different metals are distinguishable with varying concentrations, in agreement with contact measurements in highly complex structures. Our result shows the potency of spectroscopic ellipsometry in the DUV and paves the way for non-destructive, advanced quality control and metrology applications in integrated advanced electronics packaging systems.

physics.app-ph↗

arXiv2023

Overcoming voltage fluctuation in electric vehicles by considering Al electrolytic capacitor-based voltage stabilizer

Battery pack used in electrical vehicles (EVs) have developed fastly nowadays and are important due to its capability to stores electric charge. However, it is still found that there is an electrical voltage fluctuations due to sudden load changes or faults in the power system. To overcome this problem, the conventional strategy focuses on using voltage stabilizer with inductor-capacitor resonant circuits, leaving the problem of using capacitors at cryogenic temperatures. Herewith, we design a vehicle automatic voltage stabilizer (VAVS) operating at room temperature. The VAVS consists of nine main components, including resistors, capacitors, transistors, and diodes arranged with a specific composition to stabilize the voltage. By considering Al electrolytic capacitor, type of diode, resistor, and transistor, the VAVS device stabilizes the input voltage from 10-15V to obtain an output voltage of 12V. Then, by varying the engine rotation speed of vehicle, VAVS applied in vehicle battery supplies a constant voltage of about 12.1 V. The lowest line regulation analysis reveals a regulated voltage fluctuation of 0.17%/V. Our result shows that VAVS design works at room temperature, overcomes the voltage fluctuation and complies with the standard regulation of voltage stabilizers.

eess.SY↗

arXiv2023

Light absorption enhancement of perovskite solar cells by a modified anti-reflection layer with corrugated void-like nanostructure using finite difference time domain methods

Perovskite solar cells (PSC) have become a growing research interest due to their flexibility, attractive properties, and low production cost. However, the thin-film structure of PSC often results in a not fully absorbed incident light by the active layer, which is crucial to determine PSC efficiency. Thus, the fabrication of an active layer with unique nanostructures is often used to enhance light absorption and general PSC efficiency. Using the theoretical simulation based-on Finite-Difference Time-Domain (FDTD) technique, this work demonstrates the successful improvement of light absorption by embedding corrugated void-like structure and perovskite thickness modification. The investigation of a corrugated void-type anti-reflection layer effect on light absorption is done by modifying the radius (r) and lattice constant (a) to obtain the optimum geometry. In addition, the MAPbI3 perovskite layer thickness is also adjusted to examine the optimum light absorption within the visible length to nearinfrared. The theoretical calculations show that the optimum r=692 nmand a=776 nm. Meanwhile, the optimum absorber layer thickness is 750 nm. Compared to flat PSC, our proposed PSC absorbed more light, especially in the near-infrared region. Our result shows demonstrates the successful enhancement of light absorption by embedding corrugated void-like structure and modifying the perovskite thickness using a theoretical simulation based on theFDTD technique.

physics.optics↗

arXiv2023

High-performance Kerr quantum battery

We propose and investigate the performance of a hybrid quantum battery, the so-called Kerr quantum battery, which consists of two interacting quantum oscillators, i.e., the charger is a harmonic oscillator and the battery is an anharmonic oscillator involving the Kerr nonlinearity. Such a setup creates nonuniform spacing between energy levels of the quantum oscillator that increases with the energy level. We find that the Kerr quantum battery can store more energy than the qubit battery and reaches maximum stored energy faster than the harmonic oscillator battery. In particular, the average charging power of the Kerr quantum battery is larger than the qubit battery. Furthermore, most of the stored energy in the Kerr quantum battery can be extracted for work. All of the properties of the Kerr quantum battery are controlled by the strength of nonlinearity, in which the enhancement of the nonlinearity transforms the battery from a harmonic oscillator to a qubit.

quant-ph↗

arXiv2023

Coexistence of surface oxygen vacancy and interface conducting states in LaAlO3/SrTiO3 revealed by low-angle resonant soft X-ray scattering

Oxide heterostructures have shown rich physics phenomena, particularly in the conjunction of exotic insulator-metal transition (IMT) at the interface between polar insulator LaAlO3 and non-polar insulator SrTiO3 (LaAlO3/SrTiO3). Polarization catastrophe model has suggested an electronic reconstruction yielding to metallicity at both the interface and surface. Another scenario is the occurrence of surface oxygen vacancy at LaAlO3 (surface-Ov), which has predicted surface-to-interface charge transfer yielding metallic interface but insulating surface. To clarify the origin of IMT, one should probe surface-Ov and the associated electronic structures at both the surface and the buried interface simultaneously. Here, using low-angle resonant soft X-ray scattering (LA-RSXS) supported with first-principles calculations, we reveal the co-existence of the surface-Ov state and the interface conducting state only in conducting LaAlO3/SrTiO3 (001) films. Interestingly, both the surface-Ov state and the interface conducting state are absent for the insulating film. As a function of Ov density, while the surface-Ov state is responsible for the IMT, the spatial charge distribution is found responsible for a transition from two-dimensional-like to three-dimensional-like conducting accompanied by spectral weight transfer, revealing the importance of electronic correlation. Our results show the importance of surface-Ov in determining interface properties and provides a new strategy in utilizing LA-RSXS to directly probe the surface and buried interface electronic properties in complex oxide heterostructures.

cond-mat.mtrl-sci↗

arXiv2020

Tunable spin and orbital polarization in SrTiO3-based heterostructures

We formulate the effective Hamiltonian of Rashba spin-orbit coupling (RSOC) in $\mathrm{LaAlO_3/SrTiO_3}$ (LAO/STO) heterostructures. We derive analytical expressions of properties, e.g., Rashba parameter, effective mass, band edge energy and orbital occupancy, as functions of material and tunable heterostructure parameters. While linear RSOC is dominant around the $Γ$-point, cubic RSOC becomes significant at the higher-energy anti-crossing region. We find that linear RSOC stems from the structural inversion asymmetry (SIA), while the cubic term is induced by both SIA and bulk asymmetry. Furthermore, the SOC strength shows a striking dependence on the tunable heterostructure parameters such as STO thickness and the interfacial electric field which is ascribed to the quantum confinement effect near the LAO/STO interface. The calculated values of the linear and cubic RSOC are in agreement with previous experimental results.

cond-mat.mes-hall↗

arXiv2020

Topological Hall Effect and Skyrmion-like Bubbles at a Charge-transfer Interface

Exploring exotic interface magnetism due to charge transfer and strong spin-orbit coupling has profound application in future development of spintronic memory. Here, the emergence, tuning and interpretation of hump-shape Hall Effect from a CaMnO3/CaIrO3/CaMnO3 trilayer structure are studied in detail. The hump signal can be recognized as Topological Hall Effect suggesting the presence of Skyrmion-like magnetic bubbles; but the debated alternative interpretation where the signal being an artefact between two cancelling Anomalous Hall Effect loops is also discussed. Firstly, by tilting the magnetic field direction, the evolution of Hall signal suggests transformation of the bubbles topology into a more trivial kind. Secondly, by varying the thickness of CaMnO3, the optimal thicknesses for the hump signal emergence are found, suggesting a tuning of charge transfer fraction. Using high-resolution transmission electron microscopy, a stacking fault is also identified, which distinguishes the top and bottom CaMnO3/CaIrO3 interfaces in terms of charge transfer fraction and possible interfacial Dzyaloshinskii-Moriya Interaction. Finally, a spin-transfer torque experiment revealed a low threshold current density of ~10^9 A/m^2 for initiating the motion of bubbles. This discovery opens a possible route for integrating Skyrmions with antiferromagnetic spintronics.

cond-mat.mes-hall↗

arXiv2020

Tunable and Enhanced Rashba Spin-Orbit Coupling in Iridate-Manganite Heterostructures

Tailoring spin-orbit interactions and Coulomb repulsion are the key features to observe exotic physical phenomena such as magnetic anisotropy and topological spin texture at oxide interfaces. Our study proposes a novel platform for engineering the magnetism and spin-orbit coupling at LaMnO3/SrIrO3 (3d-5d oxide) interfaces by tuning the LaMnO3 growth conditions which controls the lattice displacement and spin-correlated interfacial coupling through charge transfer. We report on a tunable and enhanced interface-induced Rashba spin-orbit coupling and Elliot-Yafet spin relaxation mechanism in LaMnO3/SrIrO3 bilayer with change in the underlying magnetic order of LaMnO3. We also observed enhanced spin-orbit coupling strength in LaMnO3/SrIrO3 compared to previously reported SrIrO3 layers. The X-Ray spectroscopy measurement reveals the quantitative valence of Mn and their impact on charge transfer. Further, we performed angle-dependent magnetoresistance measurements, which show signatures of magnetic proximity effect in SrIrO3 while reflecting the magnetic order of LaMnO3. Our work thus demonstrates a new route to engineer the interface induced Rashba spin-orbit coupling and magnetic proximity effect in 3d-5d oxide interfaces which makes SrIrO3 an ideal candidate for spintronics applications.

cond-mat.str-el↗

arXiv2020

Characteristic Lengths of Interlayer Charge-Transfer in Correlated Oxide Heterostructures

Using interlayer interaction to control functional heterostructures with atomic-scale designs has become one of the most effective interface-engineering strategies nowadays. Here, we demonstrate the effect of a crystalline LaFeO3 buffer layer on amorphous and crystalline LaAlO3/SrTiO3 heterostructures. The LaFeO3 buffer layer acts as an energetically favored electron acceptor in both LaAlO3/SrTiO3 systems, resulting in modulation of interfacial carrier density and hence metal-to-insulator transition. For amorphous and crystalline LaAlO3/SrTiO3 heterostructures, the metal-to-insulator transition is found when the LaFeO3 layer thickness crosses 3 and 6 unit cells, respectively. Such different critical LaFeO3 thicknesses are explained in terms of distinct characteristic lengths of the redox-reaction-mediated and polar-catastrophe-dominated charge transfer, controlled by the interfacial atomic contact and Thomas-Fermi screening effect, respectively. Our results not only shed light on the complex interlayer charge transfer across oxide heterostructures but also provides a new route to precisely tailor the charge-transfer process at a functional interface.

cond-mat.mtrl-sci↗

arXiv2020

The Emergence of Unconventional Plasmons Driven by Correlated Electron Interaction in B-site of 2D Hybrid Organic-Inorganic Perovskites

Hybrid organic-inorganic perovskites (HOIPs) have emerged to the forefront of optoelectronic materials advancement in the past few years. Due to the nature of organic compounds within the perovskite structure, its optoelectronic properties are affected by complex interaction and correlation effects between the organic and inorganic ions. Using spectroscopic ellipsometry, we observe two broad plasmonic excitation from the calculated loss function (LF) -Im[\varepislon^{-1} (ω)], peak A' and B' at 3.28 eV and 4.26 eV, respectively.The presence of these two asymmetric peaks in the spectroscopic ellipsometry (SE) spectra indicates the existence of unconventional plasmons at room temperature. This is inferred due to the absence of the zero-crossing in the real part of dielectric function \varepsilon_1 (ω). Through combined Near-Edge X-ray Absorption Fine Structure (NEXAFS) and Resonant Photoemission Spectroscopies (ResPES), we observe resonance enhancement peak close to 15 eV in the C K-edge region that unravels a charge transfer event due to the opening of an extra autoionization channel. Additionally, photoluminescence (PL) spectrum confirms the presence of broadband emission originating from the self-trapped emission excitons at 2.38 eV due to the soft 2D-HOIPs crystal structure. We believe that these phenomena directly impact the correlation strength in 2D-HOIPs. Our results have confirmed the existence of unconventional plasmons of 2D-HOIPs at room temperature. Such studies in the emission and plasmonic behavior of perovskites will pave the way for the efficient light emitting devices or lasers with minimal integrations of the materials.

cond-mat.mtrl-sci↗

arXiv2018

Generation of multiple plasmons in strontium niobates mediated by local field effects

Recently, an anomalous generation of multiple plasmons with large spectral weight transfer in the visible to ultraviolet range (energies below the band gap) has been experimentally observed in the insulating-like phase of oxygen-rich strontium niobium oxides (SrNbO$_{3+δ}$). Here, we investigate the ground state and dielectric properties of SrNbO$_{3+δ}$ as a function of $δ$ by means of extensive first principle calculations. We find that in the random phase approximation by taking into account the local field effects (LFEs), our calculations are able to reproduce both the unconventional multiple generations of plasmons and spectral weight transfers, consistent with experimental data. Interestingly, these unconventional plasmons can be tuned by oxygen stoichiometry as well as microscopic superstructure. This unusual predominance of LFEs in this class of materials is ascribed to the strong electronic inhomogeneity and high polarizability and paves a new path to induce multiple plasmons in the untapped visible to ultraviolet ranges of insulating-like oxides.

cond-mat.str-el↗

arXiv2017

La interstitial defect-induced insulator-metal transition in oxide heterostructures LaAlO3/SrTiO3

Perovskite oxide interfaces have attracted tremendous research interest for their fundamental physics and promising all-oxide electronics applications. Here, based on first-principles calculations, we propose a novel surface La interstitial promoted interface insulator-metal transition in LaAlO3/SrTiO3 (110). Compared with surface oxygen vacancies, which play a determining role on the insulator-metal transition of LaAlO3/SrTiO3 (001) interfaces, we find that surface La interstitials can be more experimentally realistic and accessible for manipulation and more stable in ambient atmospheric environment. Interestingly, these surface La interstitials also induce significant spin-splitting states with Ti dyz/dxz character at conducting LaAlO3/SrTiO3 (110) interface. On the other hand, for insulating LaAlO3/SrTiO3 (110) (<4 unit cells LaAlO3 thickness), a distortion between La (Al) and O atoms is found at the LaAlO3 side, partially compensating the polarization divergence. Our results reveal the origin of metal-insulator transition in LaAlO3/SrTiO3 (110) heterostructures, and also shed light on the manipulation of the superior properties of LaAlO3/SrTiO3 (110) for new possibilities of electronic and magnetic applications.

cond-mat.mtrl-sci↗

arXiv2017

The Mechanism of Electrolyte Gating on High-Tc Cuprates: The Role of Oxygen Migration and Electrostatics

Electrolyte gating is widely used to induce large carrier density modulation on solid surfaces to explore various properties. Most of past works have attributed the charge modulation to electrostatic field effect. However, some recent reports have argued that the electrolyte gating effect in VO2, TiO2 and SrTiO3 originated from field-induced oxygen vacancy formation. This gives rise to a controversy about the gating mechanism, and it is therefore vital to reveal the relationship between the role of electrolyte gating and the intrinsic properties of materials. Here, we report entirely different mechanisms of electrolyte gating on two high-Tc cuprates, NdBa2Cu3O7-δ (NBCO) and Pr2-xCexCuO4 (PCCO), with different crystal structures. We show that field-induced oxygen vacancy formation in CuO chains of NBCO plays the dominant role while it is mainly an electrostatic field effect in the case of PCCO. The possible reason is that NBCO has mobile oxygen in CuO chains while PCCO does not. Our study helps clarify the controversy relating to the mechanism of electrolyte gating, leading to a better understanding of the role of oxygen electro migration which is very material specific.

cond-mat.str-el↗

arXiv2017

Oxygen passivation mediated tunability of trion and excitons in MoS$_2$

Using wide spectral range in situ spectroscopic ellipsometry with systematic ultra high vacuum annealing and in situ exposure to oxygen, we report the complex dielectric function of MoS$_2$ isolating the environmental effects and revealing the crucial role of unpassivated and passivated sulphur vacancies. The spectral weights of the A ($1.92$ eV) and B ($2.02$ eV) exciton peaks in the dielectric function reduce significantly upon annealing, accompanied by spectral weight transfer in a broad energy range. Interestingly, the original spectral weights are recovered upon controlled oxygen exposure. This tunability of the excitonic effects is likely due to passivation and reemergence of the gap states in the bandstructure during oxygen adsorption and desorption, respectively, as indicated by ab initio density functional theory calculation results. This work unravels and emphasizes the important role of adsorbed oxygen in the optical spectra and many-body interactions of MoS$_2$.

cond-mat.mes-hall↗

arXiv2017

Unravelling local spin polarization of Zhang-Rice singlet in lightly hole-doped cuprates using high-energy optical conductivity

Unrevealing local magnetic and electronic correlations in the vicinity of charge carriers is crucial in order to understand rich physical properties in correlated electron systems. Here, using high-energy optical conductivity (up to 35 eV) as a function of temperature and polarization, we observe a surprisingly strong spin polarization of the local spin singlet with enhanced ferromagnetic correlations between Cu spins near the doped holes in lightly hole-doped La$_{1.95}$Sr$_{0.05}$Cu$_{0.95}$Zn$_{0.05}$O$_{4}$. The changes of the local spin polarization manifest strongly in the temperature-dependent optical conductivity at ~7.2 eV, with an anomaly at the magnetic stripe phase (~25 K), accompanied by anomalous spectral-weight transfer in a broad energy range. Supported by theoretical calculations, we also assign high-energy optical transitions and their corresponding temperature dependence, particularly at ~2.5 ~8.7, ~9.7, ~11.3 and ~21.8 eV. Our result shows the importance of a strong mixture of spin singlet and triplet states in hole-doped cuprates and demonstrates a new strategy to probe local magnetic correlations using high- energy optical conductivity in correlated electron systems.

cond-mat.str-el↗

arXiv2016

The Nature of Electron Transport and visible light absorption in Strontium Niobate -- A Plasmonic Water Splitter

Semiconductor compounds are widely used for water splitting applications, where photo-generated electron-hole pairs are exploited to induce catalysis. Recently, powders of a metallic oxide (Sr$_{1-x}$NbO$_3$, 0.03 < x < 0.20) have shown competitive photocatalytic efficiency, opening up the material space available for finding optimizing performance in water-splitting applications. The origin of the visible light absorption in these powders was reported to be due to an interband transition and the charge carrier separation was proposed to be due to the high carrier mobility of this material. In the current work we have prepared epitaxial thin films of Sr$_{0.94}$NbO$_{3+δ}$ and found that the bandgap of this material is ~4.1 eV, which is very large. Surprisingly the carrier density of the conducting phase reaches 10$^{22}$ cm$^{-3}$, which is only one order smaller than that of elemental metals and the carrier mobility is only 2.47 cm$^2$/(V$\cdot$s). Contrary to earlier reports, the visible light absorption at 1.8 eV (~688 nm) is due to the bulk plasmon resonance, arising from the large carrier density, instead of an interband transition. Excitation of the plasmonic resonance results in a multifold enhancement of the lifetime of charge carriers. Thus we propose that the hot charge carriers generated from decay of plasmons produced by optical absorption is responsible for the water splitting efficiency of this material under visible light irradiation.

cond-mat.mtrl-sci↗

arXiv2015

Anisotropic optical properties of rhombohedral and tetragonal thin film BiFeO$_3$ phases

The anisotropic optical properties of multiferroic BiFeO$_3$ thin films have been determined with Mueller matrix ellipsometry at room-temperature. The full dielectric tensors of tetragonal-like and rhombohedral-like BiFeO$_3$ phases epitaxially grown on LaAlO$_3$ and SrTiO$_3$ single crystal substrates, respectively, within the spectral range of 0.6 and 6.5 eV are reported. Strain-driven anisotropy changes and transition shifts are observed as well as evidence of sub-band gap many-particle excitations are found. The transition shifts, mostly to higher energies for the highly strained tetragonal-like BiFeO$_3$ phase on LaAlO$_3$, are indicative of band structure differences. Additionally, optical modelling, confirmed by piezoelectric force microscopy studies, revealed that the average polarization direction of bivariant BiFeO$_3$ on LaAlO$_3$ is not parallel to the crystallographic [001] direction but tilted by about $7^{\circ}$. Spectral weight analyses reveal phase-dependent differences underlining that theoretical calculations of optical spectra need further improvement to appropriately account for electronic and excitonic correlations to fully understand multiferroic BiFeO$_3$.

cond-mat.mtrl-sci↗

arXiv2015

The interplay of electronic reconstructions, lattice distortions, and surface oxygen vacancies in insulator-metal transition of LaAlO$_{3}$/SrTiO$_{3}$

The mechanism responsible for the extraordinary interface conductivity of LaAlO$_{3}$ on SrTiO$_{3}$ and its insulator-metal transition remains controversial. Here, using density functional theory calculations, we establish a comprehensive and coherent picture that the interplay of electronic reconstructions, lattice distortions, and surface oxygen vacancies fully compensates the polarization potential divergence in LaAlO$_{3}$/SrTiO$_{3}$, explaining naturally the experimental observations under different conditions. While lattice distortions and a charge redistribution between LaO and AlO$_2$ sub-layers play a dominant role in insulating state, a spontaneous appearance of 1/4 oxygen vacancies per AlO$_{2}$ sub-layer at the LaAlO$_{3}$ surface accompanied by 0.5$e^{-}$ charge-transfer into the interface is responsible for interface conductivity and the discontinuous transition in LaAlO$_{3}$/SrTiO$_{3}$. Our model also explain properties of LaAlO$_{3}$/SrTiO$_{3}$ prepared with different growth conditions.

cond-mat.str-el↗