Tunable Electron Research Articles

Observation of the Smallest Three‐Dimensional Neutral Boron Cluster

Despite major progress in the investigation of boron cluster anions, direct experimental study of neutral boron clusters remains a significant challenge because of the difficulty in size selection. Here we report a size‐specific study of the neutral B9 cluster using threshold photoionization with a tunable vacuum ultraviolet free electron laser. The ionization potential of B9 is measured to be 8.45 ± 0.02 eV and it is found to have a heptagonal bipyramid D7h structure, quite different from the planar molecular wheel of the B9‐ anionic cluster. Chemical bonding analyses reveal superior stability of the bipyramidal structure arising from delocalized s and p bonding interactions within the B7 ring and between the B7 ring and the capping atoms. Photoionization of B9 breaks the single‐electron B‐B bond of the capping atoms, which undergo off‐axis distortion to enhance interactions with the B7 ring in the singlet ground state of B9+. The single‐electron B‐B bond of the capping atoms appears to be crucial in stabilizing the D7h structure of B9. This work opens avenues for direct size‐dependent experimental studies of a large variety of neutral boron clusters to explore the stepwise development of network structures.

Observation of the Smallest Three-Dimensional Neutral Boron Cluster.

Despite major progress in the investigation of boron cluster anions, direct experimental study of neutral boron clusters remains a significant challenge because of the difficulty in size selection. Here we report a size-specific study of the neutral B9 cluster using threshold photoionization with a tunable vacuum ultraviolet free electron laser. The ionization potential of B9 is measured to be 8.45 ± 0.02 eV and it is found to have a heptagonal bipyramid D7h structure, quite different from the planar molecular wheel of the B9- anionic cluster. Chemical bonding analyses reveal superior stability of the bipyramidal structure arising from delocalized s and p bonding interactions within the B7 ring and between the B7 ring and the capping atoms. Photoionization of B9 breaks the single-electron B-B bond of the capping atoms, which undergo off-axis distortion to enhance interactions with the B7 ring in the singlet ground state of B9+. The single-electron B-B bond of the capping atoms appears to be crucial in stabilizing the D7h structure of B9. This work opens avenues for direct size-dependent experimental studies of a large variety of neutral boron clusters to explore the stepwise development of network structures.

Engineering the electron localization of metal sites on nanosheets assembled periodic macropores for CO2 photoreduction

Photocatalytic conversion of CO2 into syngas is highly appealing, yet still suffers from the undesirable product yield due to the sluggish carrier transfer and the uncontrollable affinity between catalytic sites and intermediates. Here we report the fabrication of Co sites with tunable electron localization capability on two dimensional (2D) nanosheets assembled three dimensional (3D) ordered macroporous framework (3DOM-NS). The as-prepared Co-based 3DOM-NS catalysts exhibit attractive photocatalytic performances toward CO2 reduction, among which the cobalt sulfide one (3DOM Co-SNS) shows the highest syngas generation rate up to 347.3 μmol h−1 under the irradiation of visible light and delivers a remarkable catalytic activity (1150.7 μmol h−1) in a flow reaction system under natural sunlight. Mechanism studies reveal that the high electron localization of metal sites in 3DOM Co-SNS strengthens the interaction between Co and HCOO* via the orbital interactions of dyz/dxz-p and s-s, thus facilitating the cleaving process of C-O bond. Additionally, the ordered macroporous framework with nanosheet subunits elevates the transfer efficiency of photoexcited electrons, which contributes to its high activity.

Graphene-based Nanomaterials As Catalysts for the Synthesis of Medicinally Privileged Heterocycles: Importance and Outlook

: Catalysis is an integral part of sustainable and green chemical processes. During the last two decades, the wonder 2D carbon material with honeycomb structure, graphene, and other functionalized graphenes have emerged as extremely versatile and robust nanomaterials in heterogeneous catalysis. The incredible catalytic efficacy of such carbon nanomaterials relies on their unique physicochemical properties, including large surface area, diverse catalytic active sites, multiple chemical functionalities, tunable electron density, synergistic effect, etc., making them noteworthy as metal-free catalysts and catalytic supports. : The article presents an overview of the catalytic applications of various graphene-based nanomaterials (GBNs), either metal-free or embedded with metal/metal oxide NPs, in synthesizing medicinally privileged heterocyclic compounds. It also summarizes the general methodologies for preparing graphene and various GBNs, their chemical structures, characterization techniques, and discussions on the potential active sites that are responsible for wider catalytic activity. Overall discussions unequivocally establish a promising paradigm for uncovering more innovative graphene-based materials and their subsequent applications in diverse fields, including heterogeneous catalysis.

The effect of dilution on the energy dissipation in water interstellar ice analogues

Context. Interstellar ices and their energetic processing play an important role in advancing the chemical complexity in space. Interstellar ices covering dust grains are intrinsically mixed, and it is assumed that physicochemical changes induced by energetic processing – triggered by photons, electrons, and ions – strongly depend on the content of the ice. Yet, the modelling of these complex mixed systems in experiments and theory is complicated. Aims. In this paper, we investigate the effect of infrared irradiation on a series of different molecules mixed with porous amorphous solid water (pASW) to study the release of vibrational energy in the hydrogen-bonding network of water as a function of mixing ratio and ice content. Particularly, we select mixtures of 20:1 H2O:X and 5:1 H2O:X with X=CO2, NH3, or CH4. Methods. Infrared radiation was supplied by the intense and tunable free electron laser (FEL) 2 at the HFML-FELIX facility. We monitored the structural changes in the interstellar ice analogue after resonant infrared excitation using Fourier-transform reflection absorption infrared (FT-RAIR) spectroscopy. Results. We observed that on-resonance irradiation at the OH-stretching vibration of pASW results in quantitatively identical changes compared to pure pASW for all investigated mixtures. The structural changes we observed closely resemble the previously reported local reordering. The 5:1 mixtures show weaker changes compared to pure pASW, with a decrease in strength from NH3 to CO2. Conclusions. Since the hydrogen-bonding network of pASW restructures similarly upon FEL irradiation, regardless of the mixing component, treating ice layers in models that simulate energy dissipation in the hydrogen-bonding network as pure H2O ice layers can be a justified approximation. Hence, complex systems might not always be necessary to describe the infrared energetic processing of ices.

Functionalized Quasi-Solid-State Electrolytes in Aqueous Zn-Ion Batteries for Flexible Devices: Challenges and Strategies.

The rapid development of wearable and intelligent flexible devices has posed strict requirements for power sources, including excellent mechanical strength, inherent safety, high energy density, and eco-friendliness. Zn-ion batteries with aqueous quasi-solid-state electrolytes (AQSSEs) with various functional groups that contain electronegative atoms (O/N/F) with tunable electron accumulation states are considered as a promising candidate to power the flexible devices and tremendous progress has been achieved in this prospering area. Herein, this review proposes a comprehensive summary of the recent achievements using the AQSSE in flexible devices by focusing on the significance of different functional groups. The fundamentals and challenges of the ZIBs are introduced from a chemical view in the first place. Then, the mechanism behind the stabilization of the flexible ZIBs with the functionalized AQSSE is summarized and explained in detail. Then the recent progress regarding the enhanced electrochemical stability of the ZIBs with the AQSSE is summarized and classified based on the functional groups on the polymer chain. The advanced characterization methods for the AQSSE are briefly introduced in the following sections. Last but not least, current challenges and future perspectives for this promising area are provided from the authors' point of view.

Scalable on-chip multiplexing of silicon single and double quantum dots

Owing to the maturity of complementary metal oxide semiconductor (CMOS) microelectronics, qubits realized with spins in silicon quantum dots (QDs) are considered among the most promising technologies for building scalable quantum computers. For this goal, ultra-low-power on-chip cryogenic CMOS (cryo-CMOS) electronics for control, read-out, and interfacing of the qubits is an important milestone. We report on-chip interfacing of tunable electron and hole QDs by a 64-channel cryo-CMOS multiplexer with less-than-detectable static power dissipation. We analyze charge noise and measure state-of-the-art addition energies and gate lever arm parameters in the QDs. We correlate low noise in QDs and sharp turn-on characteristics in cryogenic transistors, both fabricated with the same gate stack. Finally, we demonstrate that our hybrid quantum-CMOS technology provides a route to scalable interfacing of a large number of QD devices, enabling, for example, variability analysis and QD qubit geometry optimization, which are prerequisites for building large-scale silicon-based quantum computers.

Enhancement of high-efficiency potassium ion hybrid supercapacitors utilizing oxygen-deficient Co2NiO4@nitrogen-doped carbon nanoflower

Transition metal oxides represent a promising category of pseudocapacitive materials for potassium-ion hybrid supercapacitors (PIHCs) characterized by high energy density. Nevertheless, their utility is hindered by intrinsic low conductivity, restricted electrochemical sites, and notable volume expansion, all of which directly contribute to the degradation of their electrochemical performance, thereby limiting their practical applicability in supercapacitor systems. In this study, we present a facile synthesis approach to fabricate nitrogen-doped carbon-supported oxygen vacancy-rich Co2NiO4 nanoflowers (Ov-Co2NiO4/NC NFs) featuring tunable surface layering and electron distribution. The nanoflower structure augments the contact area between the material and the electrolyte. Density functional theory (DFT) calculations reveal oxygen vacancies could bring an enhanced charge density across the entire Fermi level in Co2NiO4 and expand the interatomic distances between adjacent cobalt and nickel atoms to 3.370 Å. N-doped carbon carriers further accelerate charge transfer, increase the electrostatic energy storage and inhibit the structural collapse of Co2NiO4. These structural modifications serve to improve electrochemical reaction kinetics, augment the binding energy of K+ (−2.87 eV), and mitigate structural variations during K+ storage. In a 6 M KOH electrolyte, Ov-Co2NiO4/NC NF exhibits a specific capacitance of 1104 F g−1 at a current density of 0.5 A g−1, with a remarkable capacitance retention rate of 91.48 % after 6500 cycles. Furthermore, the assembled PIHCs demonstrate an energy density of 47.8 Wh kg−1 and an ultra-high power density of 376 W kg−1, alongside notable cycle stability, retaining 90.13 % of its capacitance after 8000 cycles in a 6 M KOH electrolyte.

High Electron Mobility in Si-Doped Two-Dimensional β-Ga2O3 Tuned Using Biaxial Strain.

Two-dimensional (2D) semiconductors have attracted much attention regarding their use in flexible electronic and optoelectronic devices, but the inherent poor electron mobility in conventional 2D materials severely restricts their applications. Using first-principles calculations in conjunction with Boltzmann transport theory, we systematically investigated the Si-doped 2D β-Ga2O3 structure mediated by biaxial strain, where the structural stabilities were determined by formation energy, phonon spectrum, and ab initio molecular dynamic simulation. Initially, the band gap values of Si-doped 2D β-Ga2O3 increased slightly, followed by a rapid decrease from 2.46 eV to 1.38 eV accompanied by strain modulations from -8% compressive to +8% tensile, which can be ascribed to the bigger energy elevation of the σ* anti-bonding in the conduction band minimum than that of the π bonding in the valence band maximum. Additionally, band structure calculations resolved a direct-to-indirect transition under the tensile strains. Furthermore, a significantly high electron mobility up to 4911.18 cm2 V-1 s-1 was discovered in Si-doped 2D β-Ga2O3 as the biaxial tensile strain approached 8%, which originated mainly from the decreased quantum confinement effect on the surface. The electrical conductivity was elevated with the increase in tensile strain and the enhancement of temperature from 300 K to 800 K. Our studies demonstrate the tunable electron mobilities and band structures of Si-doped 2D β-Ga2O3 using biaxial strain and shed light on its great potential in nanoscale electronics.

Building a highly concentration responsive optical thermometer via tunable electron transfer pathways supported by intervalence charge transfer states

The thermal-coupled levels (TCLs) of lanthanides have attracted great attention in the field of optical thermometer, offering an efficient method to achieve non-contect temperatuer feedback in complex environment. However, the iner 4f electrons are shielded, which becomes the core obstacle in improving the sensing performance. This issue is now circumvented by constructing an electron transfer pathway between Tm3+(1D2) and Eu3+(5D0) configurations. As a result, the electron transfer barrier is related to the relative temperature sensitivity, giving an insight into the modulation mechanism. Compared to the conventional TCLs systems, the relative temperature sensitivity of this strategy is highly concentration-responsive, increasing from 5.56 to 10.1 % K−1 as the Eu3+ molar concentration rises from 0.3 to 0.5 mol%. This work reveals the inner emission mechanism based on IVCT-supported emission mode, and presents the highly adjustability of sensing performance.

Hollow CoP-FeP cubes decorating carbon nanotubes heterostructural electrocatalyst for enhancing the bidirectional conversion of polysulfides in advanced lithium-sulfur batteries

The sluggish redox reaction kinetics and “shuttle effect” of lithium polysulfides (LPSs) impede the advancement of high-performance lithium-sulfur batteries (LSBs). Transition metal phosphides exhibit distinctive polarity, metallic properties, and tunable electron configuration, thereby demonstrating enhanced adsorption and electrocatalytic capabilities towards LPSs. Consequently, they are regarded as exceptional sulfur hosts for LSBs. Moreover, the introduction of a heterogeneous structure can enhance reaction kinetics and expedite the transport of electrons/ions. In this study, a composite of hollow CoP-FeP cubes with heterostructure modified carbon nanotube (CoFeP-CNTs) was fabricated and utilized as sulfur host in advanced LSBs. The presence of carbon nanotubes (CNTs) facilitates enhanced electron and Li+ transport. Meanwhile, the active sites within the heterogeneous interface of CoP-FeP suppress the “shuttle effect” and enhance the conversion kinetics of LPSs. Therefore, the CoFeP-CNTs/S electrode exhibited exceptional cycling stability and demonstrated a capacity attenuation of merely 0.051 % per cycle over 600 cycles at 1C. This study presents a highly effective tactic for synthesizing dual-acting transition metal phosphides with heterostructure, which will play a pivotal role in advancing the development of efficient LSBs.

Electron Divergence of Cuδ- and Pdδ+ in Cu3Pd Alloy-Based Heterojunctions Boosts Concerted C≡C Bond Binding and the Volmer Step for Alkynol Semihydrogenation.

Electrocatalytic semihydrogenation of alkynols presents a sustainable alternative to conventional thermal methodologies for the high-value production of alkenols. The design of efficient catalysts with superior catalytic and energy efficiency for semihydrogenation poses a significant challenge. Here, we present the application of an electron-divergent Cu3Pd alloy-based heterojunction in promoting the electrocatalytic semihydrogenation of alkynols to alkenols using water as the proton source. The tunable electron divergence of Cuδ- and Pdδ+, modulated by rectifying contact with nitrogen-rich carbons, enables the concerted binding of active H species from the Volmer step of water dissociation and the C≡C bond of alkynols on Pdδ+ sites. Simultaneously, the pronounced electron divergence of Cu3Pd facilitates the universal adsorption of OH species from the Volmer step and alkynols on the Cuδ- sites. The electron-divergent dual-center substantially boosts water dissociation and inhibition of completing hydrogen evolution to give a turnover frequency of 2412 h-1, outperforming the reported electrocatalysts' value of 7.3. Moreover, the continuous production of alkenols at industrial-related current density (-200 mA cm-2) over the efficient and durable Cu3Pd-based electrolyzer could achieve a cathodic energy efficiency of 45 mol kW·h-1, 1.7 times the bench-marked reactors, promising great potential for sustainable industrial synthesis.

Enhanced Femtosecond Nonlinear Optical Susceptibility and Terahertz Conductivity in MoSe2‐Noble Metal Nanocomposites

AbstractCreating heterojunctions or composites by incorporating noble metals offers a remarkable means to modulate the electronic charge transfer and the nonlinear optical (NLO) properties in 2D transition metal dichalcogenides (TMDCs). The response of such 2D‐TMDC‐noble metal composites to femtosecond (fs) infrared (IR) and terahertz (THz) radiation, however, remains vastly unexplored. While the linear optical characteristics of a prototypical 2D‐TMDC, namely, MoSe2 nanosheets incorporated with noble metal (such as Au, Pt, and Ag) nanoparticles in the UV–Vis and the THz spectral range, the NLO characteristics are measured using a 70‐fs pulse at 800 nm excitation is investigated. The results demonstrate a clear reduction of band gap with the incorporation of noble metals in MoSe2, indicating an effective charge transfer mechanism at play. Notably, the MoSe2‐noble metal nanocomposites depicted a significant enhancement in the THz conductivities. In addition, a dramatic 4‐fold enhancement in the third‐order nonlinear coefficient and ≈2‐fold enhancement in the third‐order NLO susceptibility is achieved in MoSe2‐Ag nanocomposite. These results univocally suggest that the noble metal‐based composites with suitable charge transfer channels promote enhanced carrier mobilities and tunable electron transfer dynamics, making these hybrid materials promising candidates for optoelectronic applications both at IR and THz frequencies.

Constructing electron transfer bridge of Pr doping MIL-125(Ti) for high-efficient photoreduction CO2

MIL-125(Ti) is well known for having stable structure, tunable electron structure, and multiple active sites, which is commonly studied in the field of photocatalysis. In this work, a series of rare earth (RE) doped MIL-125(Ti) (RE=Ce, Pr, Tm, Dy, Eu, and Sm) are prepared via the one-step hydrothermal method. Notably, Pr-MIL-125 displays a significantly enhanced catalytic performance than other RE-doped MIL-125, resulting in a maximal CO and CH4 yield of 13.30 and 0.87 µmol·g−1·h−1, respectively, which are 2.53-fold and 4.14-fold of the pristine MIL-125. The layered morphology endows Pr-MIL-125 with more active sites and facilitates the reaction of photoreduction CO2. Furthermore, the promoted photoactivities attributed to Pr ion dopant can act as electron transfer bridge and suppress charge recombination. This work would provide insight and guidance for designing RE-MOF based photocatalysts and enhancing the performance of photoreduction CO2.

Size-Specific Infrared Spectroscopy of Neutral Hydrated Clusters Based on a Vacuum Ultraviolet Free Electron Laser.

Spectroscopic study of neutral hydrated clusters provides microscopic insights into the local structures and dynamics of complex systems but is very challenging because of the difficulty in size discrimination. Recently, we developed infrared (IR) spectroscopy based on threshold ionization using a tunable vacuum ultraviolet free electron laser (VUV-FEL). This experimental method allows for size-specific IR spectroscopic measurement of numerous neutral clusters without confinement, such as messenger tags, ultraviolet chromophores, and host matrix. This Perspective aims to highlight the latest advances in VUV-FEL-based IR spectroscopic studies on the confinement-free neutral amine-water, sulfur dioxide-water, and metal-water clusters. Fruitful collaborations with high-level quantum chemical calculations are reviewed. Future research directions with relevance to the atmosphere, biology, and catalysis are proposed.

Extremely Stable Ag-Based Photonics, Plasmonic, Optical, and Electronic Materials and Devices Designed with Surface Chemistry Engineering for Anti-Tarnish.

Silver (Ag) metal-based structures are promising building blocks for next-generation photonics and electronics owing to their unique characteristics, such as high reflectivity, surface plasmonic resonance effects, high electrical conductivity, and tunable electron transport mechanisms. However, Ag structures exhibit poor sustainability in terms of device performance because harsh chemicals, particularly S2- ions present in the air, can damage their structures, lowering their optical and electrical properties. Here, the surface chemistry of Ag structures with (3-mercaptopropyl)trimethoxysilane (MPTS) ligands at room temperature and under ambient conditions is engineered to prevent deterioration of their optical and electrical properties owing to S2- exposure. Regardless of the dimensions of the Ag structures, the MPTS ligands can be applied to each dimension (0D, 1D, and 3D). Consequently, highly sustainable plasmonic effects (Δλ < 2nm), Fabry-Perot cavity resonance structures (Δλ < 2nm), reflectors (ΔRReflectance < 0.5%), flexible electrodes (ΔRelectrical < 0.1 Ω), and strain gauge sensors (ΔGF < 1), even in S2- exposing conditions is achieved. This strategy is believed to significantly contribute to environmental pollution reduction by decreasing the volume of electronic waste.

Physics-agnostic inverse design using transfer matrices

Inverse design is an application of machine learning to device design, giving the computer maximal latitude in generating novel structures, learning from their performance, and optimizing them to suit the designer’s needs. Gradient-based optimizers, augmented by the adjoint method to efficiently compute the gradient, are particularly attractive for this approach and have proven highly successful with finite-element and finite-difference physics simulators. Here, we extend adjoint optimization to the transfer matrix method, an accurate and efficient simulator for a wide variety of quasi-1D physical phenomena. We leverage this versatility to develop a physics-agnostic inverse design framework and apply it to three distinct problems, each presenting a substantial challenge for conventional design methods: optics, designing a multivariate optical element for compressive sensing; acoustics, designing a high-performance anti-sonar submarine coating; and quantum mechanics, designing a tunable double-bandpass electron energy filter.

Ultrahigh-brightness 50 MeV electron beam generation from laser wakefield acceleration in a weakly nonlinear regime

We propose an efficient scheme to produce ultrahigh-brightness tens of MeV electron beams by designing a density-tailored plasma to induce a wakefield in the weakly nonlinear regime with a moderate laser energy of 120 mJ. In this scheme, the second bucket of the wakefield can have a much lower phase velocity at the steep plasma density down-ramp than the first bucket and can be exploited to implement longitudinal electron injection at a lower laser intensity, leading to the generation of bright electron beams with ultralow emittance together with low energy spread. Three-dimensional particle-in-cell simulations are carried out and demonstrate that high-quality electron beams with a peak energy of 50 MeV, ultralow emittance of ∼28 nm rad, energy spread of 1%, charge of 4.4 pC, and short duration less than 5 fs can be obtained within a 1-mm-long tailored plasma density, resulting in an ultrahigh six-dimensional brightness B6D,n of ∼2 × 1017 A/m2/0.1%. By changing the density parameters, tunable bright electron beams with peak energies ranging from 5 to 70 MeV, a small emittance of ≤0.1 mm mrad, and a low energy spread at a few-percent level can be obtained. These bright MeV-class electron beams have a variety of potential applications, for example, as ultrafast electron probes for diffraction and imaging, in laboratory astrophysics, in coherent radiation source generation, and as injectors for GeV particle accelerators.

Tunable 2D Electron- and 2D Hole States Observed at Fe/SrTiO3 Interfaces.

Oxide electronics provide the key concepts and materials for enhancing silicon-based semiconductor technologies with novel functionalities. However, a basic but key property of semiconductor devices still needs to be unveiled in its oxidic counterparts: the ability to set or even switch between two types of carriers-either negatively (n) charged electrons or positively (p) charged holes. Here, direct evidence for individually emerging n- or p-type 2D band dispersions in STO-based heterostructures is provided using resonant photoelectron spectroscopy. The key to tuning the carrier character is the oxidation state of an adjacent Fe-based interface layer: For Fe and FeO, hole bands emerge in the empty bandgap region of STO due to hybridization of Ti- and Fe- derived states across the interface, while for Fe3O4 overlayers, an 2D electron system is formed. Unexpected oxygen vacancy characteristics arise for the hole-type interfaces, which as of yet hadbeen exclusively assigned to the emergence of 2DESs. In general, this finding opens up the possibility to straightforwardly switch the type of conductivity at STO interfaces by the oxidation state of a redox overlayer. This will extend the spectrum of phenomena in oxide electronics, including the realization of combined n/p-type all-oxide transistors or logicgates.

Formation of oxygen protective layer on monolayer MoS2 via low energy electron irradiation.

Monolayer molybdenum disulfide (MoS2) semiconductors are the new generation of two-dimensional materials that possess several advantages compared to graphene due to their tunable bandgap and high electron mobility. Several approaches have been used to modify their physical properties for optical device applications. Here, we report a facile and non-destructive surface modification method for monolayer MoS2 via electron irradiation at a low, 5 kV accelerating voltage. After electron irradiation, the results of Raman and photoluminescence spectroscopy confirmed that the structure remains unchanged. However, when the modified surface was illuminated with a 532 nm laser for a prolonged period, the PL intensity was quenched as a result of oxygen desorption. Interestingly, the PL intensity can be recovered when left in ambient conditions for 10 h. The analysis of the PL spectrum revealed a decrease of trion, which is consistent with the readsorbed O2 molecules on the surface that deplete electrons and lead to PL recovery. We attribute this effect to the enhancement of the n-type character of monolayer MoS2 after electron irradiation. The sensitive nature of the modified surface to oxygen suggests that this approach may be used as a tool for the fabrication of MoS2 oxygen sensors.