Electron Quantum Research Articles

Exploring the vacuum ultraviolet photochemistry of astrochemically important triatomic molecules.

The recently constructed vacuum ultraviolet (VUV) free electron laser (FEL) at the Dalian Coherent Light Source (DCLS) is yielding a wealth of new and exquisitely detailed information about the photofragmentation dynamics of many small gas-phase molecules. This Review focuses particular attention on five triatomic molecules-H2O, H2S, CO2, OCS and CS2. Each shows excitation wavelength-dependent dissociation dynamics, yielding photofragments that populate a range of electronic and (in the case of diatomic fragments) vibrational and rotational quantum states, which can be characterized by different translational spectroscopy methods. The photodissociation of an isolated molecule from a well-defined initial quantum state provides a lens through which one can investigate how and why chemical reactions occur, and provides numerous opportunities for fruitful, synergistic collaborations with high-level ab initio quantum chemists. The chosen molecules, their photofragments and the subsequent chemical reaction networks to which they can contribute are all crucial in planetary atmospheres and in interstellar and circumstellar environments. The aims of this Review are 3-fold: to highlight new photochemical insights enabled by the VUV-FEL at the DCLS, notably the recently recognized central atom elimination process that is shown to contribute in all of these triatomic molecules; to highlight some of the potential implications of this rich photochemistry to our understanding of interstellar chemistry and molecular evolution within the universe; and to highlight other and future research directions in areas related to chemical reaction dynamics and astrochemistry that will be enabled by increased access to VUV-FEL sources.

The conformational behavior and structure of monosubstituted 1,3,5‐trisilacyclohexanes—Part III: 1‐Methyl‐1,3,5‐trisilacyclohexane

Abstract1‐Methyl‐1,3,5‐trisilacyclohexane was synthesized and its structure and conformational properties have been determined by gas‐phase electron diffraction (GED) and quantum chemical (QC) calculations. The molecule may exist in two forms differing from each other by the substituent's position. QC results show that the equatorial conformer is predicted to be slightly more stable than the axial conformer; note that one method (M06‐2X) with basis set 6‐311G** shows an equal amount of Ax and Eq conformers: ratio (Ax/Eq) = (30–50):(70–50)% (depending on the method and basis set). From the GED data, the molar fractions of the conformers were found to be Ax:Eq = 54(10):46(10) at 280(5) K. A temperature‐dependent Raman experiment resulted in an Ax:Eq ratio of 58(4):42(4). Conformational properties are compared in series of analogous 1‐X‐1‐(hetero)cyclohexanes.

Fine-tuning of plasmonics by Au@AuY/Au core–shell nanoparticle monolayer for enhancement of third-order nonlinearity

The manipulation of plasmonics on noble metal nanoparticles (NPs) is of great interest in developing nonlinear photonic devices, such as all-optical switches and frequency combs. An Au@AuY-core/Au-shell nanoparticle (Au@AuY/Au NP) monolayer is proposed for the fine-tuning of plasmonics and enhanced third-order nonlinearity. Based on the different thermodynamic mechanisms of Au and Y ions, the compact Au@AuY/Au core–shell architectures are designed and surface-modified in fused silica (SiO2) with enhanced free electron density, mobility, and quantum size effect. The flexible modulation of plasmonics is realized, resulting in significant absorption enhancement (165% for interband absorption and 38% for free electron absorption, respectively) and fine-tuning of the localized surface plasma resonance (LSPR) band. In addition, the physical mechanism is investigated by density functional theory (DFT) and Mie theory, which reveals a transition from size-independence to size-dependence of LSPR owing to the synergistic effect of multiple physical factors such as free electron density and mobility. With the above advantages, the third-order nonlinearity is enhanced by 4.4 times compared with traditional Au NPs. It indicates the significant potential of Au@AuY/Au core–shell NP monolayer in the performance improvement of nonlinear photonic devices.

Epitaxy of Group-IV Semiconductors for Quantum Electronics

We are growing at CEA (i) high purity 28Si layers and (ii) c-Ge/SiGe heterostructures for electron and hole spin quantum bits. We describe here strategies usable for the fabrication of 28SOI substrates, with a focus on 28SiH4 consumption minimization, as such a gas is very expensive and hard to come by. We also focus on the properties of Si0.26Ge0.74 and Si0.21Ge0.79 Virtual Substrates (VS) grown at 850°C, 20 Torr and a forward Ge ramping-up on Si(001) substrates. After some chemical polishing (to remove the surface cross-hatch), those VS are used as templates for the 500°C, 100 Torr growth of SiGe/c-Ge/SiGe 2D Hole Gas Gas (2DHG) stacks. Those c-Ge layers are, in X-Ray Diffraction, fully compressively strained on the relaxed SiGe VS underneath and of high crystalline quality. Some slight undulations are evidenced at c-Ge / SiGe cap interfaces, hinting at elastic strain relaxation, however. Magnetotransport measurements in Hall-bar devices were performed at 4.2 K to assess the electrical properties of the 2DHG in those SiGe/c-Ge heterostructures. At low magnetic field, a hole mobility of 1.2 x 105 cm2 V-1 s-1 was obtained for a hole density of n2DHG = 3.7x1011 cm-2 in a 16 nm thick c-Ge/55 nm thick Si0.21Ge0.79 cap sample.

MISCONCEPTION DIAGNOSTIC IN QUANTUM NUMBER MATERIALS AND ELECTRON CONFIGURATION

The purpose of this research is to design a four-tier diagnostic test instrument on electron configurations and quantum numbers that can be used to analyze misconceptions. The four-level diagnostic test instrument is an assessment instrument that functions to assess students' conceptual comprehension in understanding a subject matter. The four tier test has four levels, namely knowledge questions, confidence questions in completing questions, reasons for answering questions, and confidence in giving reasons. This study uses a descriptive qualitative method with the stages of analyzing the problem, collecting data, product design, validating the design, and conducting instrument trials. The results showed that the designed diagnostic instruments were feasible and reliable. Instrument test results indicate that indicator a) determines the magnitude of the four quantum numbers (n,ℓ,mℓ, ms) in an orbital; b) identify the characteristics and functions of the azimuth quantum number (ℓ); c) determine the spin magnetic quantum number (ms) of the electron in the orbital; and d) determine the spin magnetic quantum number (ms) of a single electron in an orbital, which is the most misunderstood.

An on-demand source of energy-entangled electrons using levitons

We propose a source of purely electronic energy-entangled states implemented in a solid-state system with potential applications in quantum information protocols based on electrons. The proposed device relies on the standard tools of electron quantum optics and exploits entanglement of the Cooper pairs of a BCS superconductor. The latter is coupled via an adjustable quantum point contact to two opposite spin-polarized electron wave-guides, which are driven by trains of Lorentzian pulses. This specific choice for the drive is crucial to inject purely electronic entangled states devoid of spurious electron–hole pairs. In the Andreev regime, a perturbative calculation in the tunnel coupling confirms that entangled electrons states are generated at the output of the normal side. For arbitrary tunnel coupling and for a periodic drive, direct current and noise (auto and cross correlations) are computed numerically using a Keldysh–Nambu–Floquet formalism. Importantly, for a periodic drive, the production of these states can be controlled in time, thus implementing an on-demand source of entangled states. We exploit realistic experimental parameters for our device to identify its optimal functioning point.

Structural design of triangular core–shell nanowires for sensing polarized mid-infrared light

Manipulating and detecting polarization states of light plays an important role in developing technology in various fields, such as remote sensing, medical phototherapy, and quantum information. However, polarization control in mid-infrared (mid-IR) wavelengths, especially longer than 10 µm, is obstructed by the limitation of material properties. Searching for materials and designing structures that respond to polarized light in this spectral range is still challenging. In this work, triangular core–shell AlGaAs/GaAs nanowires are numerically studied using the finite difference method. The effects of the core shift and rotating angle on the absorption coefficients are concentrated. Highly anisotropic absorption of polarized light in the mid-IR range is found when the core shifts upward and downward. Our results show that this anisotropic property is influenced by the symmetries of electron quantum states confined in the system. Broadband absorption wavelengths from 9.7 to 17.5 µm are unexpectedly found in the structure with appropriate system size. Our finding indicates that triangular core–shell nanowires are a potential platform for next-generation photonic devices capable of manipulating polarized light in a wide range of mid-IR wavelengths.

Emergence and Relaxation of an e–h Quantum Liquid Phase in Photoexcited MoS2 Nanoparticles at Room Temperature

AbstractLow‐dimensional transition metal dichalcogenide (TMDC) materials are heralding a new era in optoelectronics and valleytronics owing to their unique properties. Photo‐induced dynamics in these systems is mostly studied from the perspective of individual quasi‐particles—excitons, bi‐excitons, or, even, trions—their formation, evolution, and decay. The role of multi‐body and exciton dynamics, the associated collective behavior, condensation, and inter‐excitonic interactions remain intriguing and seek attention, especially in room‐temperature scenarios that are relevant for device applications. In this work, the formation and decay of an unexpected electron–hole quantum liquid phase at room‐temperature on ultrafast timescales in multi‐layer MoS2 nanoparticles is evidenced through femtosecond broadband transient absorption spectroscopy. The studies presented here reveal the complete dynamical picture: the initial electron–hole plasma (EHP) condenses into a quantum electron–hole liquid (EHL) phase that typically lasts as long as 10 ps, revealing its robustness, whereafter the system decays through phonons. The authors employ a successful physical model using a set of coupled nonlinear rate equations governing the individual populations of these constituent phases to extract their contributions to bandgap renormalization (BGR). Beyond the observation of the electron–hole liquid‐like state at room temperature, this work reveals the ultrafast dynamics of photo‐excited low‐dimensional systems arising out of collective many‐particle behavior and correlations.

On the electron spin and spectrum energy problems within the Fock many temporal and Feynman proper time paradigms

The quantum electron spin structure and the photon dressed electron energy spectrum problem are reanalyzed in the framework of the Fock many-temporal parameter approach. There is analyzed the spin structure and its dependence on the symmetry properties of the related representations of the basic Clifford algebra, generated by creation-annihilation operators. The self-interaction phenomenon is discussed within the quantum renormalized Lorenz constraint on a suitably reduced Fock space. The electron energy spectrum is analyzed within the many-temporal Fock and Feynman proper time paradigms.

Facile in-situ grown spinel MnCo2O4/MWCNT and MnCo2O4/Ti3C2 MXene composites for high-performance asymmetric supercapacitor with theoretical insight

The logical construction of electrode materials along with greater electrochemical features and solid architectural design is a strategic approach for boosting the electrochemical performance of supercapacitors. However, it is tough and complicated to develop diverse composite materials with better electronic conductivity and greater specific capacitance via rapid and cost-effective synthesis procedures. Herein, we propose a straightforward and simple approach by employing the hydrothermal technique for the synthesis of spinel MnCo2O4 composite nanostructures using 1D MWCNT and 2D MXene (Ti3C2Tx) materials with detailed analysis of the supercapacitor performance as compared to existing literature on similar studies. The MCO/TCX (MnCo2O4/Ti3C2Tx) composite shows an impressive capacitance of 860.22 F/g at a current density of 2 A/g after electrochemical optimization. Furthermore, an asymmetric supercapacitor device (ASCs) was constructed using MCO and its composites MCO/MWCNT and MCO/TCX as a positive, and AC was employed as a negative electrode to test its device capability. Comparatively, the MCO/TCX//AC SC device demonstrated exceptional energy storage properties with a better specific capacitance value of 126.58 F/g at 0.8 A/g of current density, an elevated energy density of 40 Wh/kg, with a power density of 4828 W/kg along a capacitance retention rate of 87 % over 5000 cycles, suggesting better cycle life. Whereas, the MCO/MWCNT//AC device shows a better cycling performance of 91 % after 5000 cycles with a superior energy and power density of 27.04 Wh/kg and 1448 W/kg respectively. Also the theoretical insight for further understanding of the charge-storage mechanism through DFT calculations provides an estimate of electronic properties and quantum capacitance calculated for the pristine MCO and its hybrids with CNT and Ti3C2Tx MXene and information on the interactions between orbitals, the bonding process, and the charge transfer capabilities of each electrode material. The theoretical studies also confirm that the electronic properties and therein charge storage performance have an increasing trend in the order of MCO < MCO/CNT < MCO/TCX consistent with the experimental findings. Additionally, these simulations conclude that the hybrid MCO/TCX has the largest quantum capacitance which is in accordance with the findings of the experiments. The improved performance of MCO/TCX is due to the enlarged surface area that allows higher charge transfer from TCX to MCO. The charge transferred from the C 2p orbital of TCX to the Mn 3d orbital of MCO is the leading cause for the capacitance improvement mechanism of hybrid MCO/TCX. This work offers a simple procedure for developing energy storage devices using spinel MnCo2O4-based composite electrode materials supported by 1D carbon nanotube and 2D MXene that offer superior electrochemical performance and the fabricated electrodes that could be employed further for energy storage-based applications.

Theoretical study on the electronic properties and quantum capacitance ofZr2CO2MXenewith atomic swap

AbstractMXenes have the excellent electrochemical properties as electrode of supercapacitors. Using density functional theory, we investigated the electronic properties and quantum capacitance of Zr2CO2with atomic swap. The atomic swap results in the appearance of Frenkel‐type defect and Schottky defect. The negative binding energy confirms the stability of the studied systems. The atomic swap makes ZrC1, ZrC2, ZrO1, ZrO2, CO2 systems maintain the indirect semiconductor character, and CO2 system has the direct semiconductor character. The thermionic emission performance of Zr2CO2MXene is greatly improved by atomic swap. ZrO1 and ZrO2 systems in aqueous system are appropriate anode materials. The wide voltage has little effect on the electrode type for perfect Zr2CO2, ZrO1, ZrO2, CO1, and CO2 systems, but changes ZrC1 and ZrC2 systems from cathode material in aqueous system to anode material in ionic/organic system. The work function and effective mass are also explored.

Ring Polymer Molecular Dynamics with Electronic Transitions.

Full quantum dynamics of molecules and materials is of fundamental importance, which requires a faithful description of simultaneous quantum motions of the electron and nuclei. A new scheme is developed for nonadiabatic simulations of coupled electron-nuclear quantum dynamics with electronic transitions based on the Ehrenfest theorem and ring polymer molecular dynamics. Built upon the isomorphic ring polymer Hamiltonian, time-dependent multistate electronic Schrödinger equations are solved self-consistently with approximate equation of motions for nuclei. Each bead bears a distinct electronic configuration and thus moves on a specific effective potential. This independent-bead approach provides an accurate description of the real-time electronic population and quantum nuclear trajectory, maintaining a good agreement with the exact quantum solution. Implementation of first-principles calculations enables us to simulate photoinduced proton transfer in H_{2}O-H_{2}O^{+} where we find a good agreement with experiment.

Impact of Local Composition on the Emission Spectra of InGaN Quantum-Dot LEDs.

A possible solution for the realization of high-efficiency visible light-emitting diodes (LEDs) exploits InGaN-quantum-dot-based active regions. However, the role of local composition fluctuations inside the quantum dots and their effect of the device characteristics have not yet been examined in sufficient detail. Here, we present numerical simulations of a quantum-dot structure restored from an experimental high-resolution transmission electron microscopy image. A single InGaN island with the size of ten nanometers and nonuniform indium content distribution is analyzed. A number of two- and three-dimensional models of the quantum dot are derived from the experimental image by a special numerical algorithm, which enables electromechanical, continuum k→·p→, and empirical tight-binding calculations, including emission spectra prediction. Effectiveness of continuous and atomistic approaches are compared, and the impact of InGaN composition fluctuations on the ground-state electron and hole wave functions and quantum dot emission spectrum is analyzed in detail. Finally, comparison of the predicted spectrum with the experimental one is performed to assess the applicability of various simulation approaches.

Spin-Liquid Insulators Can Be Landau's Fermi Liquids.

The long search for insulating materials that possess low-energy quasiparticles carrying electron's quantum numbers except charge-inspired by the neutral spin-1/2 excitations, the so-called spinons, exhibited by Anderson's resonating-valence-bond state-seems to have reached a turning point after the discovery of several Mott insulators displaying the same thermal and magnetic properties as metals, including quantum oscillations in a magnetic field. Here, we show that such anomalous behavior is not inconsistent with Landau's Fermi liquid theory of quasiparticles at a Luttinger surface. That is the manifold of zeros within the Brillouin zone of the single-particle Green's function at zero frequency, and which thus defines the spinon Fermi surface conjectured by Anderson.

Study on Electron Tunneling Lifetime by Projected Green’s Function Approach in Single Quantum Well Semiconductor

The tunnelling lifetime of an electron in a single quantum well subject to an externally applied electric field is calculated using the Projected Green’s Function (PGF) approach. The lifetime in the biased single well decreases as a function of the electric field in good agreement with the previous result. The tunnelling lifetime is revealed with the behavior of the ground-state shift and the wave amplitude in the first well. As the electric field increases, the ground state energy shifts, leading to lessened constructive interference between the initial and reflected electron waves. Consequently, the study is essential to characterize the performance of high-speed quantum devices.

Topological thermoelectrics: New opportunities and challenges

Due to the great application potential of the efficient interconversion between heat and electricity, thermoelectric materials have long been the research focal points in condensed matter physics and material science. Moreover, since the discovery of topological properties in solid materials, numerous research studies have recently expanded into the role of the topological state in thermoelectrics. Topological insulators and semimetals/metals are characterized by their exotic electronic band structures and quantum surface states, which can provide a new degree of freedom to manipulate thermoelectric properties. Herein, we present a summary on the advantageous combination of topological properties in thermoelectric materials for enhancing the thermoelectric energy conversion efficiency. We demonstrated this concept through some examples on the applications of novel topological materials as a practical strategy towards high thermoelectric performance. Furthermore, the role of different topological states and the corresponding working mechanism is explained, and the related challenges for further development are also discussed. This review article presents an advanced understanding of topological states in a thermoelectric transport mechanism, providing a new strategy to search for outstanding thermoelectric materials.

Molecular Bridge Engineering for Tuning Quantum Electronic Transport and Anisotropy in Nanoporous Graphene

Recent advances on surface-assisted synthesis have demonstrated that arrays of nanometer wide graphene nanoribbons can be laterally coupled with atomic precision to give rise to a highly anisotropic nanoporous graphene structure. Electronically, this graphene nanoarchitecture can be conceived as a set of weakly coupled semiconducting 1D nanochannels with electron propagation characterized by substantial interchannel quantum interferences. Here, we report the synthesis of a new nanoporous graphene structure where the interribbon electronic coupling can be controlled by the different degrees of freedom provided by phenylene bridges that couple the conducting channels. This versatility arises from the multiplicity of phenylene cross-coupling configurations, which provides a robust chemical knob, and from the interphenyl twist angle that acts as a fine-tunable knob. The twist angle is significantly altered by the interaction with the substrate, as confirmed by a combined bond-resolved scanning tunneling microscopy (STM) and ab initio analysis, and should accordingly be addressable by other external stimuli. Electron propagation simulations demonstrate the capability of either switching on/off or modulating the interribbon coupling by the corresponding use of the chemical or the conformational knob. Molecular bridges therefore emerge as efficient tools to engineer quantum transport and anisotropy in carbon-based 2D nanoarchitectures.

Quantum-quasiclassical analysis of center-of-mass nonseparability in hydrogen atom stimulated by strong laser fields *

We have developed a quantum-quasiclassical computational scheme for quantitative treating of the nonseparable quantum–classical dynamics of the 6D hydrogen atom in a strong laser pulse. In this approach, the electron is treated quantum mechanically and the center-of-mass (CM) motion classically. Thus, the Schrödinger equation for the electron and the classical Hamilton equations for the CM variables, nonseparable due to relativistic effects stimulated by strong laser fields, are integrated simultaneously. In this approach, it is natural to investigate the idea of using the CM- velocity spectroscopy as a classical ‘build-up’ set up for detecting the internal electron quantum dynamics. We have performed such an analysis using the hydrogen atom in linearly polarized laser fields as an example and found a strong correlation between the CM kinetic energy distribution after a laser pulse and the spectral density of electron kinetic energy. This shows that it is possible to detect the quantum dynamics of an electron by measuring the distribution of the CM kinetic energy.

Ultra-low-current driven InGaN blue micro light-emitting diodes for electrically efficient and self-heating relaxed microdisplay

InGaN-based micro-light-emitting diodes have a strong potential as a crucial building block for next-generation displays. However, small-size pixels suffer from efficiency degradations, which increase the power consumption of the display. We demonstrate strategies for epitaxial structure engineering carefully considering the quantum barrier layer and electron blocking layer to alleviate efficiency degradations in low current injection regime by reducing the lateral diffusion of injected carriers via reducing the tunneling rate of electrons through the barrier layer and balanced carrier injection. As a result, the fabricated micro-light-emitting diodes show a high external quantum efficiency of 3.00% at 0.1 A/cm2 for the pixel size of 10 × 10 μm2 and a negligible Jmax EQE shift during size reduction, which is challenging due to the non-radiative recombination at the sidewall. Furthermore, we verify that our epitaxy strategies can result in the relaxation of self-heating of the micro-light-emitting diodes, where the average pixel temperature was effectively reduced.

Electron-Beam Source with a Superconducting Niobium Tip

Electron-beam sources are foundational in high-resolution electron microscopy and spectroscopy, but applications have been limited due to their relatively large energy spread. The authors fabricate a monocrystalline niobium nanotip electron field emitter and characterize it in superconducting and normal-conducting regimes. This bright, stable, coherent electron beam source features an exceptionally narrow energy spread. The authors also study the role of xenon adsorption and two-electron correlations. This work may improve aberration-corrected microscopy and electron energy-loss spectroscopy and enable high-resolution vibrational spectroscopy or quantum electron microscopy.