Controlled Bipolar Doping of One-Dimensional van der Waals Nb2Pd3Se8.

Tailoring the electrical properties of one-dimensional (1D) van der Waals (vdW) materials is desirable for their applications toward electronic devices by exploiting their unique characteristics. However, 1D vdW materials have not been extensively investigated for modulation of their electrical properties. Here we control doping levels and types of 1D vdW Nb2Pd3Se8 over a wide energy range by immersion in AuCl3 or ß-nicotinamide adenine dinucleotide (NADH) solutions, respectively. Through spectroscopic analyses and electrical characterizations, we confirm that the charges were effectively transferred to Nb2Pd3Se8, and the dopant concentration was adjusted to the immersion time. Furthermore, we make the axial p-n junction of 1D Nb2Pd3Se8 by a selective area p-doping using the AuCl3 solution, which exhibits rectifying behavior with an Iforward/Ireverse of 81 and an ideality factor of 1.2. Our findings could pave the way to more practical and functional electronic devices based on 1D vdW materials.

Connection between the time distribution and length scale of dynamic heterogeneity explored by probe reorientations of different sizes.

The rotational dynamics of fluorescent probes of different sizes in glass-forming materials were examined to correlate the time distribution and length scale of the dynamic heterogeneity (ξhet). As the size of the probe increased, the temperature dependence of the rotation correlation time (τc) shifted to longer times, and from this shift, the length scale associated with the glass transition (ξα) was estimated through the Debye-Stokes-Einstein (DSE) relationship and the length scale of the probe (ξsDFT) estimated from quantum mechanical calculations. The estimated ξα values roughly matched with ξhet obtained from calorimetric analysis but were considerably smaller than those deduced from 4D NMR, boson peak, and four-point dynamic susceptibility measurements but with a similar trend of decrease in the length scale upon the increase in the stretching exponent (ß) of the system. Because ß of the glass formers represents the time distribution of the system, and τc is related to the weighted average of the distribution, the length-scale distribution of the glass transition can be deduced by adopting the DSE relationship and assuming ξα is the weighted average of this distribution at the glass transition temperature. In such a case, the upper bound of the length scale and trend matches the experimentally obtained ξhet from 4D NMR, boson peak, and four-point dynamic susceptibility measurements. Furthermore, at a given temperature, as the probe size increased, the ß value reported by the probe increased, whereas the temperature dependence of ß, which strongly correlates with the fragility of the system, was independent of the probe size.

Unveiling two-dimensional magnesium hydride as a hydrogen storage material via a generative adversarial network.

This study used an artificial intelligence (AI)-based crystal inverse-design approach to investigate the new phase of two-dimensional (2D) pristine magnesium hydride (Mg x H y ) sheets and verify their availability as a hydrogen storage medium. A 2D binary phase diagram for the generated crystal images was constructed, which was used to identify significant 2D crystal structures. Then, the electronic and dynamic properties of the Mg x H y sheets in low-energy periodic phases were identified via density functional theory (DFT) calculations; this revealed a previously unknown phase of 2D MgH2 with a P4̄m2 space group. In the proposed structure, the adsorption behaviors of the Li-decorated system were investigated for multiple hydrogen molecules. It was confirmed that Li-decorated MgH2 has an expected theoretical gravimetric density of 6 wt%, with an average H2 adsorption energy of -0.105 eV. Therefore, it is anticipated that P4̄m2 MgH2 sheets can be employed effectively as a medium for hydrogen storage. Additionally, this finding indicates that a deep learning-based approach is beneficial for exploring unrevealed 2D materials.

Midwavelength Infrared Colloidal Nanowire Laser.

Realizing bright colloidal infrared emitters in the midwavelength infrared (or mid-IR), which can be used for low-power IR light-emitting diodes (LEDs), sensors, and deep-tissue imaging, has been a challenge for the last few decades. Here, we present colloidal tellurium nanowires with strong emission intensity at room temperature and even lasing at 3.6 µm (ω) under cryotemperature. Furthermore, the second-harmonic field at 1.8 µm (2ω) and the third-harmonic field at 1.2 µm (3ω) are successfully generated thanks to the intrinsic property of the tellurium nanowire. These unique optical features have never been reported for colloidal tellurium nanocrystals. With the colloidal midwavelength infrared (MWIR) Te nanowire laser, we demonstrate its potential in biomedical applications. MWIR lasing has been clearly observed from nanowires embedded in a human neuroblastoma cell, which could further realize deep-tissue imaging and thermotherapy in the near future.

BoostSweet: Learning molecular perceptual representations of sweeteners.

The development of safe artificial sweeteners has attracted considerable interest in the food industry. Previous machine learning (ML) studies based on quantitative structure-activity relationships have provided some molecular principles for predicting sweetness, but these models can be improved via the chemical recognition of sweetness active factors. Our ML model, a soft-vote ensemble model that has a light gradient boosting machine and uses both layered fingerprints and alvaDesc molecular descriptor features, demonstrates state-of-the-art performance, with an AUROC score of 0.961. Based on an analysis of feature importance and dataset, we identified that the number of nitrogen atoms that serve as hydrogen bond donors in molecules can play an essential role in determining sweetness. These results potentially provide an advanced understanding of the relationship between molecular structure and sweetness, which can be used to design new sweeteners based on molecular structural dependence.

Carrier mobility of one-dimensional vanadium selenide (V2Se9) monolayer and nanoribbon systems: DFT study.

Vanadium selenide (V2Se9) is a true one-dimensional (1D) crystal composed of atomic nanochains bonded by van der Waals (vdW) interactions. Recent experiments revealed the mechanical exfoliation of newly synthesized V2Se9. In this study, we predicted the electronic and transport properties of V2Se9through computational analyses. We calculated the intrinsic carrier mobility of V2Se9monolayers (MLs) and nanoribbons (NRs) using density functional theory and deformation potential theory. We found that the electron mobility of the two-dimensional (2D) (010)-plane ML of V2Se9is highly anisotropic, reachingµ2D,ze=1327cm2V-1s-1across the chain direction. The electron mobility of 1D NR systems in a (010)-plane ML of V2Se9along the chain direction continuously increased as the thickness increased from 1-chain to 4-chain NR (width below 3 nm). Interestingly, the electron mobility of 1D 4-chain NR along the chain direction (µ1D,xe=775cm2V-1s-1) was higher than that of a 2D (010)-plane ML (µ2D,xe=567cm2V-1s-1). These results demonstrate the potential of vdW-1D crystal V2Se9as a new nanomaterial for ultranarrow (sub-3 nm width) optoelectronic devices with high electron mobility.

Theoretical Study of Anisotropic Carrier Mobility for Two-Dimensional Nb2Se9 Material.

Finding new materials with satisfying all the desired criteria for nanodevices is an extremely difficult work. Here, we introduce a novel Nb2Se9 material as a promising candidate, capable of overcoming some physical limitations, such as a suitable band gap, high carrier mobility, and chemical stability. Unlike graphene, it has a noticeable band gap and no dangling bonds at surfaces that deteriorate transport properties, owing to its molecular chain structure. Using density functional theory (DFT) calculations with deformation potential (DP) theory, we find that the electron mobility of 2D Nb2Se9 across the axis direction reaches up to 2.56 × 103 cm2 V-1 s-1 and is approximately 2.5-6 times higher than the mobility of other 2D materials, such as MoS2, black phosphorous, and InSe, at room temperature. Moreover, the mobility of 2D Nb2Se9 is highly anisotropic (µ a /µ c ≈ 6.5). We demonstrate the potential of 2D Nb2Se9 for applications in nanoscale electronic devices and, possibly, mid-infrared photodetectors.

One-dimensional van der Waals stacked p-type crystal Ta2Pt3Se8 for nanoscale electronics.

Recently, ternary transition metal chalcogenides Ta2X3Se8 (X = Pd or Pt) have attracted great interest as a class of emerging one-dimensional (1D) van der Waals (vdW) materials. In particular, Ta2Pd3Se8 has been actively studied owing to its excellent charge transport properties as an n-type semiconductor and ultralong ballistic phonon transport properties. Compared to subsequent studies on the Pd-containing material, Ta2Pt3Se8, another member of this class of materials has been considerably less explored despite its promising electrical properties as a p-type semiconductor. Herein, we demonstrate the electrical properties of Ta2Pt3Se8 as a promising channel material for nanoelectronic applications. High-quality bulk Ta2Pt3Se8 single crystals were successfully synthesized by a one-step vapor transport reaction. Scanning Kelvin probe microscopy measurements were used to investigate the surface potential difference and work function of the Ta2Pt3Se8 nanoribbons of various thicknesses. Field-effect transistors fabricated on exfoliated Ta2Pt3Se8 nanoribbons exhibited moderate p-type transport properties with a maximum hole mobility of 5 cm2 V-1 s-1 and an Ion/Ioff ratio of >104. Furthermore, the charge transport mechanism of Ta2Pt3Se8 was analyzed by temperature-dependent transport measurements in the temperature range from 90 to 320 K. To include Ta2Pt3Se8 in a building block for modern 1D electronics, we demonstrate p-n junction characteristics using the electron beam doping method.

Unveiling the role of micropores in porous carbon for Li-S batteries using operando SAXS.

The movement of the sulfur species of a lithium-sulfur battery cathode was directly observed through pioneering operando SAXS analysis. Micropore is a prior repository for sulfur before and after the electrochemical reaction. Mesopore is actual reaction site for sulfur species. The separate properties of the pores were established, adding critical insight to advanced carbon cathode material design.

Ta2 Ni3 Se8 : 1D van der Waals Material with Ambipolar Behavior.

In this study, high-purity and centimeter-scale bulk Ta2 Ni3 Se8 crystals are obtained by controlling the growth temperature and stoichiometric ratio between tantalum, nickel, and selenium. It is demonstrated that the bulk Ta2 Ni3 Se8 crystals could be effectively exfoliated into a few chain-scale nanowires through simple mechanical exfoliation and liquid-phase exfoliation. Also, the calculation of electronic band structures confirms that Ta2 Ni3 Se8 is a semiconducting material with a small bandgap. A field-effect transistor is successfully fabricated on the mechanically exfoliated Ta2 Ni3 Se8 nanowires. Transport measurements at room temperature reveal that Ta2 Ni3 Se8 nanowires exhibit ambipolar semiconducting behavior with maximum mobilities of 20.3 and 3.52 cm2 V-1 s-1 for electrons and holes, respectively. The temperature-dependent transport measurement (from 90 to 295 K) confirms the carrier transport mechanism of Ta2 Ni3 Se8 nanowires. Based on these characteristics, the obtained 1D vdW material is expected to be a potential candidate for additional 1D materials as channel materials.

Additive-free photo-mediated oxidative cyclization of pyridinium acylhydrazones to 1,3,4-oxadiazoles: solid-state conversion in a microporous organic polymer and supramolecular energy-level engineering.

We discovered the efficient catalyst-free, photo-mediated oxidative cyclization reaction of bis-p-pyridinium benzoyl hydrazone (BH1) to 2-pyridinium-5-phenyl-1,3,4-oxadiazoles. This photoreaction is remarkable because it does not require additives (e.g., bases, strong oxidants, or photocatalysts), which are essential in previous reports, and proceeds very effectively even with solid-state microporous organic polymers. Interestingly, we found that the inclusion complexation of BH1 with cucurbit[7]uril (CB7) interferes with the photo-induced electron transfer from BH1 to molecular oxygen through modification of the LUMO energy level, thus inhibiting the photo-medicated oxidative cyclization.

Entangling bosons through particle indistinguishability and spatial overlap.

Particle identity and entanglement are two fundamental quantum properties that work as major resources for various quantum information tasks. However, it is still a challenging problem to understand the correlation of the two properties in the same system. While recent theoretical studies have shown that the spatial overlap between identical particles is necessary for nontrivial entanglement, the exact role of particle indistinguishability in the entanglement of identical particles has never been analyzed quantitatively before. Here, we theoretically and experimentally investigate the behavior of entanglement between two bosons as spatial overlap and indistinguishability simultaneously vary. The theoretical computation of entanglement for generic two bosons with pseudospins is verified experimentally in a photonic system. Our results show that the amount of entanglement is a monotonically increasing function of both quantities. We expect that our work provides an insight into deciphering the role of the entanglement in quantum networks that consist of identical particles.

Tuning the electronic properties of highly anisotropic 2D dangling-bond-free sheets from 1D V2Se9 chain structures.

True one-dimensional (1D) van der Waals materials can form two-dimensional (2D) dangling-bond-free anisotropic surfaces. Dangling bonds on surfaces act as defects for transporting charge carriers. In this study, we consider true 1D materials to be V2Se9 chains, and then the electronic structures of 2D sheets composed of true 1D V2Se9 chains are calculated. The (010) plane has indirect bandgap with 0.757 eV (1.768 eV), while the (111̅) plane shows a nearly direct bandgap of 1.047 eV (2.118 eV) for DFT-D3 (HSE06) correction, respectively. The (111̅) plane of V2Se9 is expected to be used in optoelectronic devices because it contains a nearly direct bandgap. Partial charge analysis indicates that the (010) plane exhibits interchain interaction is stronger than the (111̅) plane. To investigate the strain effect, we increased the interchain distance of planes until an indirect-to-direct bandgap transition occurred. The (010) plane then demonstrated a direct bandgap when interchain distance increased by 30%, while the (111̅) plane demonstrated a direct bandgap when the interchain distance increased by 10%. In mechanical sensors, this change in the bandgap was induced by the interchain distance.

Edge Defect-Free Anisotropic Two-Dimensional Sheets with Nearly Direct Band Gaps from a True One-Dimensional Van der Waals Nb2Se9 Material.

Dangling-bond-free two-dimensional (2D) materials can be isolated from the bulk structures of one-dimensional (1D) van der Waals materials to produce edge-defect-free 2D materials. Conventional 2D materials have dangling bonds on their edges, which act as scattering centers that deteriorate the transport properties of carriers. Highly anisotropic 2D sheets, made of 1D van der Waals Nb2Se9 material, have three planar structures depending on the cutting direction of the bulk Nb2Se9 crystal. To investigate the applications of these 2D Nb2Se9 sheets, we calculated the band structures of the three planar sheets and observed that two sheets had nearly direct band gaps, which were only slightly greater (0.01 eV) than the indirect band gaps. These energy differences were smaller than the thermal energy at room temperature. The 2D Nb2Se9 plane with an indirect band gap had the shortest interchain distance for selenium ions among the three planes and exhibited significant interchain interactions on the conduction band. The interchain strain induced an indirect-to-direct band gap transition in the 2D Nb2Se9 sheets. These 2D sheets of Nb2Se9 with direct band gaps also had different band structures because of different interactions between chains, implying that they can have different charge mobilities. We expect these dangling-bond-free 2D Nb2Se9 sheets to be applied in optoelectronic devices because they allow for nearly direct band gaps. They can also be used in mechanical sensors because the band gaps can be controlled by varying the interchain strain.

Connection between BosonSampling with quantum and classical input states.

BosonSampling is a problem of sampling events according to the transition probabilities of indistinguishable photons in a linear optical network. Computational hardness of BosonSampling depends on photon-number statistics of the input light. BosonSampling with multi-photon Fock states at the input is believed to be classically intractable but there exists an efficient classical algorithm for classical input states. In this paper, we present a mathematical connection between BosonSampling with quantum and classical light inputs. Specifically, we show that the generating function of a transition probability for Fock-state BosonSampling (FBS) can be expressed as a transition probability of thermal-light inputs. The closed-form expression of a thermal-light transition probability allows all possible transition probabilities of FBS to be obtained by calculating a single matrix permanent. Moreover, the transition probability of FBS is shown to be expressed as an integral involving a Gaussian function multiplied by a Laguerre polynomial, resulting in a fast oscillating integrand. Our work sheds new light on computational hardness of FBS by identifying the mathematical connection between BosonSampling with quantum and classical light.

Indirect-To-Direct Band Gap Transition of One-Dimensional V2Se9: Theoretical Study with Dispersion Energy Correction.

Recently, we synthesized a one-dimensional (1D) structure of V2Se9. The 1D V2Se9 resembles another 1D material, Nb2Se9, which is expected to have a direct band gap. To determine the potential applications of this material, we calculated the band structures of 1D and bulk V2Se9 using density functional theory by varying the number of chains and comparing their band structures and electronic properties with those of Nb2Se9. The results showed that a small number of V2Se9 chains have a direct band gap, whereas bulk V2Se9 possesses an indirect band gap, like Nb2Se9. We expect that V2Se9 nanowires with diameters less than ∼20 Šwould have direct band gaps. This indirect-to-direct band gap transition could lead to potential optoelectronic applications for this 1D material because materials with direct band gaps can absorb photons without being disturbed by phonons.

Quantum Algorithm for Calculating Molecular Vibronic Spectra.

We present a quantum algorithm for calculating the vibronic spectrum of a molecule, a useful but classically hard problem in chemistry. We show several advantages over previous quantum approaches: vibrational anharmonicity is naturally included; after measurement, some state information is preserved for further analysis; and there are potential error-related benefits. Considering four triatomic molecules, we numerically study truncation errors in the harmonic approximation. Further, in order to highlight the fact that our quantum algorithm's primary advantage over classical algorithms is in simulating anharmonic spectra, we consider the anharmonic vibronic spectrum of sulfur dioxide. In the future, our approach could aid in the design of materials with specific light-harvesting and energy transfer properties, and the general strategy is applicable to other spectral calculations in chemistry and condensed matter physics.

Structural and electronic properties of Mo6S3I6 nanowires by newly proposed theoretical compositional ordering.

The structural, electronic, and magnetic properties of molybdenum-based nanowires have been actively investigated for their potential applications in nanodevices; however, further advancement is hindered by incomplete knowledge of the electronic and atomic structures of Mo6S3I6. To facilitate further development of Mo6S3I6 nanowire devices, we propose possible atomic structures and corresponding electronic properties of Mo6S3I6 nanowires based on density functional theory. We explored various combinations of atomic structures by changing the positions of sulfur and iodine atoms linked to the two Mo6 octahedra in the Mo6S3I6 unit cell. We found two stable local energy minima structures characterized by elongation of the wire length, and therefore propose 28 possible atomic configurations. We calculated band structures of the newly proposed atomic models and found three structures that behaved as conductors. According to our compositional ordering structural analysis, we concluded that (i) periodic distortion of the bond lengths influences the behavior of the electrons in the system, (ii) the role of sulfur atoms in the bridging plane is important for intramolecular charge transport due to delocalized charge differences, and (iii) the electronic band gap energy is proportional to the integrated Mo-S bonding orbital energy.

Universal bound on sampling bosons in linear optics and its computational implications.

In linear optics, photons are scattered in a network through passive optical elements including beam splitters and phase shifters, leading to many intriguing applications in physics, such as Mach-Zehnder interferometry, the Hong-Ou-Mandel effect, and tests of fundamental quantum mechanics. Here we present the fundamental limit in the transition amplitudes of bosons, applicable to all physical linear optical networks. Apart from boson sampling, this transition bound results in many other interesting applications, including behaviors of Bose-Einstein condensates (BEC) in optical networks, counterparts of Hong-Ou-Mandel effects for multiple photons, and approximating permanents of matrices. In addition, this general bound implies the existence of a polynomial-time randomized algorithm for estimating the transition amplitudes of bosons, which represents a solution to an open problem raised by Aaronson and Hance (Quantum Inf Comput 2012; 14: 541-59). Consequently, this bound implies that computational decision problems encoded in linear optics, prepared and detected in the Fock basis, can be solved efficiently by classical computers within additive errors. Furthermore, our result also leads to a classical sampling algorithm that can be applied to calculate the many-body wave functions and the S-matrix of bosonic particles.

Highly concentrated single-chain atomic crystal LiMo3Se3 solution using ion-exchange chromatography.

Ion-exchange chromatography can be used to effectively replace the lithium ion of LiMo3Se3 with a proton. The enlargement of the Stern layer distance caused by this ion exchange improves the dispersibility of (Mo3Se3-)∞ chains and also prevents the re-bundling and aggregation of nanowires in aqueous solutions, even at high concentrations (1 mg mL-1).