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Hot spots can generate intense local electromagnetic (EM) fields, thereby boosting diverse innovative applications. However, these applications may face challenges due to their subtle structural changes that can significantly impact their EM field strength. Herein, we report a large-scale synthesis of monodisperse, highly spherical, single crystalline (SC) Au nanospheres (Au NSs) with tunable sizes ranging from 38 to 92 nm for constructing uniform and reproducible hot spots with a nanosphere-on-mirror (NSoM) configuration. Surface-enhanced Raman scattering tests reveal that single NSoM hot spots generate homogeneous EM fields with intensity variation of <4.0% due to their identical "point-to-mirror" configuration. Moreover, the SC nature of the Au NSs can further increase the EM field by 9% because of their higher quality factor, resulting in less energy dissipation in the plasmon. Therefore, these Au NSs may serve as ideal building blocks for the construction of hot spots with homogeneous EM fields.

Two-dimensional (2D) Fe 3 Sn 2 , which is a room-temperature ferromagnetic kagome metal, has potential applications in spintronic devices. However, the systematic synthesis and magnetic study of 2D Fe 3 Sn 2 single crystals have rarely been reported. Here we have synthesized 2D hexagonal and triangular Fe 3 Sn 2 nanosheets by controlling the amount of FeCl 2 precursors in the chemical vapor deposition (CVD) method. It is found that the hexagonal Fe 3 Sn 2 nanosheets exist with Fe vacancy defects and show no obvious coercivity. While the triangular Fe 3 Sn 2 nanosheet has obvious hysteresis loops at room temperature, its coercivity first increases and then remains stable with an increase in temperature, which should result from the competition of the thermal activation mechanism and spin direction rotation mechanism. A first-principles calculation study shows that the Fe vacancy defects in Fe 3 Sn 2 can increase the distances between Fe atoms and weaken the ferromagnetism of Fe 3 Sn 2 . The resulting 2D Fe 3 Sn 2 nanosheets provide a new choice for spintronic devices.

The reduced dimensionality and interfacial effects in magnetic nanostructures open the feasibility to tailor magnetic ordering. Here, we report the synthesis of ultrathin metallic Co 2 Si nanoplates with a total thickness that is tunable to 2.2 nm. The interfacial magnetism coupled with the highly anisotropic nanoplate geometry leads to strong perpendicular magnetic anisotropy and robust hard ferromagnetism at room temperature, with a Curie temperature ( T C ) exceeding 950 K and a coercive field ( H C ) > 4.0 T at 3 K and 8750 Oe at 300 K. Theoretical calculations suggest that ferromagnetism originates from symmetry breaking and undercoordinated Co atoms at the Co 2 Si and SiO 2 interface. With protection by the self-limiting intrinsic oxide, the interfacial ferromagnetism of the Co 2 Si nanoplates exhibits excellent environmental stability. The controllable growth of ambient stable Co 2 Si nanoplates as 2D hard ferromagnets could open exciting opportunities for fundamental studies and applications in Si-based spintronic devices.

van der Waals heterostructures (vdWHs) based on two-dimensional (2D) semiconductors have attracted considerable attention. However, the reported vdWHs are largely based on vertical device structure with large overlapping area, while the realization of lateral heterostructures contacted through 2D edges remains challenging and is majorly limited by the difficulties of manipulating the lateral distance of 2D materials at nanometer scale (during transfer process). Here, we demonstrate a simple interfacial sliding approach for realizing an edge-by-edge lateral contact. By stretching a vertical vdWH, two 2D flakes could gradually slide apart or toward each other. Therefore, by applying proper strain, the initial vertical vdWH could be converted into a lateral heterojunction with intimately contacted 2D edges. The lateral contact structure is supported by both microscope characterization and in situ electrical measurements, exhibiting carrier tunneling behavior. Finally, this approach can be extended to 3D thin films, as demonstrated by the lateral 2D/3D and 3D/3D Schottky junction.

WSe 2 has a high mobility of electrons and holes, which is an ideal choice as active channels of electronics in extensive fields. However, carrier-type tunability of WSe 2 still has enormous challenges, which are essential to overcome for practical applications. In this work, the direct growth of n-doped few-layer WSe 2 is realized via in situ defect engineering. The n-doping of WSe 2 is attributed to Se vacancies induced by the H 2 flow purged in the cooling process. The electrical measurements based on field effect transistors demonstrate that the carrier type of WSe 2 synthesized is successfully transferred from the conventional p-type to the rarely reported n-type. The electron carrier concentration is efficiently modulated by the concentration of H 2 during the cooling process. Furthermore, homomaterial inverters and self-powered photodetectors are fabricated based on the doping-type-tunable WSe 2 . This work reveals a significant way to realize the controllable carrier type of two-dimensional (2D) materials, exhibiting great potential in future 2D electronics engineering.

Lithium (Li) metal has attracted great attention as a promising high-capacity anode material for next-generation high-energy-density rechargeable batteries. Nonuniform Li + transport and uneven Li plating/stripping behavior are two key factors that deteriorate the electrochemical performance. In this work, we propose an interphase acid-base interaction effect that could regulate Li plating/stripping behavior and stabilize the Li metal anode. ZSM-5, a class of zeolites with ordered nanochannels and abundant acid sites, was employed as a functional interface layer to facilitate Li + transport and mitigate the cell concentration polarization. As a demonstration, a pouch cell with a high-areal-capacity LiNi 0.95 Co 0.02 Mn 0.03 O 2 cathode (3.7 mAh cm -2 ) and a ZSM-5 modified thin lithium anode (50 μm) delivered impressive electrochemical performance, showing 92% capacity retention in 100 cycles (375.7 mAh). This work reveals the effect of acid-base interaction on regulating lithium plating/stripping behaviors, which could be extended to developing other high-performance alkali metal anodes.

Periodic assembly of heterogeneous nanoparticles provides a strategy for integrating distinct nanocatalyst blocks where their synergic effects can be explored for diverse applications. To achieve the synergistic enhancement, an intimate clean interface is preferred which however is usually plagued by the bulky surfactant molecules used in the synthesis and assembly process. Herein, we showed the creation of one-dimensional Pt-Au nanowires (NWs) with periodic alternating Pt and Au nanoblocks, by assembling Pt-Au Janus nanoparticles with the assistance of peptide T7 (Ac-TLTTLTN-CONH 2 ). It is demonstrated that the Pt-Au NWs showed much-improved performance in the methanol oxidation reaction (MOR), exhibiting 5.3 times higher specific activity and 2.5 times higher mass activity than the current state-of-the-art commercial Pt/C catalyst. In addition, the periodic heterostructure also improves the stability of Pt-Au NWs in the MOR, where the Pt-Au NWs retained 93.9% of their initial mass activity much higher than commercial Pt/C (30.6%).

Two-dimensional (2D) materials with large linear magnetoresistance (LMR) are very interesting owing to their potential application in magnetic storage or sensor devices. Here, we report the synthesis of 2D MoO 2 nanoplates grown by a chemical vapor deposition (CVD) method and observe large LMR and nonlinear Hall behavior in MoO 2 nanoplates. As-obtained MoO 2 nanoplates exhibit rhombic shapes and high crystallinity. Electrical studies indicate that MoO 2 nanoplates feature a metallic nature with an excellent conductivity of up to 3.7 × 10 7 S m -1 at 2.5 K. MoO 2 nanoplates display a large LMR of up to 455% at 3 K and -9 T. A thickness-dependent LMR analysis suggests that LMR values increase upon increasing the thickness of nanoplates. Besides, nonlinearity has been found in the magnetic-field-dependent Hall resistance, which decreases with increasing temperatures. Our studies highlight that MoO 2 nanoplates are promising materials for fundamental studies and potential applications in magnetic storage devices.

Large-scale screening of molecules in organisms requires high-throughput and cost-effective evaluating tools during preclinical development. Here, a novel in vivo screening strategy combining hierarchically structured biohybrid triboelectric nanogenerators (HB-TENGs) arrays with computational bioinformatics analysis for high-throughput pharmacological evaluation using Caenorhabditis elegans is described. Unlike the traditional methods for behavioral monitoring of the animals, which are laborious and costly, HB-TENGs with micropillars are designed to efficiently convert animals' behaviors into friction deformation and result in a contact-separation motion between two triboelectric layers to generate electrical outputs. The triboelectric signals are recorded and extracted to various bioinformation for each screened compound. Moreover, the information-rich electrical readouts are successfully demonstrated to be sufficient to predict a drug's identity by multiple-Gaussian-kernels-based machine learning methods. This proposed strategy can be readily applied to various fields and is especially useful in in vivo explorations to accelerate the identification of novel therapeutics.

Schottky diode is the fundamental building blocks for modern electronics and optoelectronics. Reducing the semiconductor layer thickness could shrink the vertical size of a Schottky diode, improving its speed and integration density. Here, we demonstrate a new approach to fabricate a Schottky diode with ultrashort physical length approaching atomic limit. By mechanically laminating prefabricated metal electrodes on both-sides of two-dimensional MoS 2 , the intrinsic metal-semiconductor interfaces can be well retained. As a result, we demonstrate the thinnest Schottky diode with a length of 2.6 nm and decent rectification behavior. Furthermore, with a diode length smaller than the semiconductor depletion length, the carrier transport mechanisms are investigated and explained by thickness-dependent and temperature-dependent electrical measurements. Our study not only pushes the scaling limit of a Schottky diode but also provides a general double-sided electrodes integration approach for other ultrathin vertical devices.

The wettability of graphene is critical for numerous applications but is very sensitive to its surface cleanness. Herein, by clarifying the impact of intrinsic contamination, i.e., amorphous carbon, which is formed on the graphene surface during the high-temperature chemical vapor deposition (CVD) process, the hydrophilic nature of clean graphene grown on single-crystal Cu(111) substrate was confirmed by both experimental and theoretical studies, with an average water contact angle of ∼23°. Furthermore, the wettability of as-transferred graphene was proven to be highly dependent on its intrinsic cleanness, because of which the hydrophilic, clean graphene exhibited improved performance when utilized for cell culture and cryoelectron microscopy imaging. This work not only validates the intrinsic hydrophilic nature of graphene but also provides a new insight in developing advanced bioapplications using CVD-grown clean graphene films.

Lithium-sulfur (Li-S) batteries suffer from sluggish sulfur redox reactions under high-sulfur-loading and lean-electrolyte conditions. Herein, a typical Co@NC heterostructure composed of Co nanoparticles and a semiconductive N-doped carbon matrix is designed as a model Mott-Schottky catalyst to exert the electrocatalytic effect on sulfur electrochemistry. Theoretical and experimental results reveal the redistribution of charge and a built-in electric field at the Co@NC heterointerface, which are critical to lowering the energy barrier of polysulfide reduction and Li 2 S oxidation in the discharge and charge process, respectively. With Co@NC Mott-Schottky catalysts, the Li-S batteries display an ultrahigh capacity retention of 92.1% and a system-level gravimetric energy density of 307.8 Wh kg -1 under high S loading (10.73 mg cm -2 ) and lean electrolyte (E/S = 5.9 μL mg sulfur -1 ) conditions. The proposed Mott-Schottky heterostructure not only deepens the understanding of the electrocatalytic effect in Li-S chemistry but also inspires a rational catalyst design for advanced high-energy-density batteries.

All-inorganic lead halide perovskites have attracted tremendous interest for their excellent stability when compared with hybrid perovskites. Here we report a large-area growth of monocrystalline all-inorganic perovskite thin films and further patterning them into heterostructure arrays. We show that highly oriented CsPbBr 3 microcrystal domains can be readily grown on muscovite mica substrates with a well-defined epitaxial relationship, which can further expand and eventually merge into large-area monocrystalline CsPbBr 3 thin films with an excellent optical quality. Taking a step further, we show the large-area CsPbBr 3 thin film can be further patterned and selectively transformed into CsPbI 3 using a selective anion-exchange process to produce CsPbBr 3 -CsPbI 3 lateral heterostructure arrays with spatially modulated photoluminescence emission and an apparent current rectification behavior. The capability to grow large-area CsPbBr 3 monocrystalline thin films and heterostructure arrays defines a robust material platform for both the fundamental investigations and potential applications in optoelectronics.

Developing low-cost and efficient electrocatalysts to accelerate oxygen evolution reaction (OER) kinetics is vital for water and carbon-dioxide electrolyzers. The fastest-known water oxidation catalyst, Ni(Fe)O x H y , usually produced through an electrochemical reconstruction of precatalysts under alkaline condition, has received substantial attention. However, the reconstruction in the reported catalysts usually leads to a limited active layer and poorly controlled Fe-activated sites. Here, we demonstrate a new electrochemistry-driven F-enabled surface-reconstruction strategy for converting the ultrathin NiFeO x F y nanosheets into an Fe-enriched Ni(Fe)O x H y phase. The activated electrocatalyst shows a low OER overpotential of 218 ± 5 mV at 10 mA cm -2 and a low Tafel slope of 31 ± 4 mV dec -1 , which is among the best for NiFe-based OER electrocatalysts. Such superior performance is caused by the effective formation of the Fe-enriched Ni(Fe)O x H y active-phase that is identified by operando Raman spectroscopy and the substantially improved surface wettability and gas-bubble-releasing behavior.

Transplantation of neural stem cells (NSCs) is a promising treatment paradigm to replace lost neurons and reconstruct the damaged neural circuit after ischemic stroke. However, most transplanted NSCs often differentiate into astrocytes rather than functional neurons, and the poor neuronal differentiation adversely affects the therapeutic outcome of NSCs and limits their clinical translation for stroke therapy. Herein, a theranostic nanomedicine is developed to codeliver superparamagnetic iron oxide nanoparticles (SPIO) and small interfering RNA/antisense oligonucleotides (siRNA/ASO) against Pnky long noncoding RNA (lncRNA) into NSCs. This nanomedicine not only directs neuronal differentiation of NSCs through silencing the Pnky lncRNA but also allows an in vivo tracking of NSCs with magnetic resonance imaging. The enhanced neuronal differentiation of NSCs significantly improved the structural and functional recovery of the damaged brain after a stroke. The results demonstrate the great potential of the multifunctional nanomedicine targeting lncRNA to enhance stem cell-based therapies for a stroke.

Lithium metal represents an ultimate anode material of lithium batteries for its high energy density. However, its large negative redox potential and reactive nature can trigger electrolyte decomposition and dendrite formation, causing unstable cycling and short circuit of batteries. Herein, we engineer a resilient solid electrolyte interphase on the Li anode by compositing the battery separator with organosulfur compounds and inorganic salts from garlic. These compounds take part in battery reactions to suppress dendrite growth through reversible electrochemistry and attenuate ionic concentration gradient. When the Li anode and the separator are paired with the LiFePO 4 cathode, one obtains a battery delivering long-term cycling stability of 3000 cycles, a rate capacity of 100 mAh g -1 at 10 C (2.5 mA cm -2 ), a Coulombic efficiency of 99.9%, and a low battery polarization. Additionally, with high-loading 20 mg cm -2 LiFePO 4 cathodes, an areal capacity of 3.4 mAh cm -2 is achieved at 0.3 C (1 mA cm -2 ).

van der Waals (vdW) integration offers a flexible strategy to nearly arbitrarily combine materials of radically different chemical compositions, crystal structures, or lattice orientations, enabling versatile heterostructures with unique electronic and photonic characteristics or other exotic properties that are difficult to access in traditional epitaxial heterostructures, as highlighted by a recent blossom in two-dimensional (2D) vdW heterostructures. However, the studies on vdW heterostructures currently have been largely limited to 2D materials, with few reports of vdW integration of traditional three-dimensional (3D) materials. Here, we show that the vdW integration approach could be extended to 3D materials for flexible integration of highly disparate materials. In particular, by assembling nanomembranes fabricated from bulk β-gallium oxide, silicon, and platinum, we demosntrate a variety of functional devices including Schottky diodes, p-n diodes, metal-semiconductor field-effect transistors, and junction field-effect transistors. These devices exhibit excellent electronic performance, in terms of ideality factor, current on/off ratio, and subthreshold swing, laying the foundations for constructing high-performance heterostructure devices.

Nanomedicines have been demonstrated as promising strategies for cancer therapy due to the advantages in pharmacokinetics and drug targeting delivery to tumor tissues. However, creation of delivery platforms able to intrinsically and spatially optimize drug cellular uptake during the entire delivering process remain challenging. To address this challenge, here we report on tumor microenvironment-adaptable self-assembly (TMAS) of pentapeptides regulated by the pH-sensitive cis/trans isomerization of 4-amino-proline (Amp) amide bonds for enhanced drug delivery and photodynamic therapeutic (PDT) efficacy. We found that decreasing solution pH led to the cis → trans isomerization of Amp amide bonds, thus promoting reversible self-assembly of pentapeptide FF-Amp-FF (AmpF) into superhelices and nanoparticles upon alternating exposure to neutral and mild acidic conditions. Co-assembly of peptide AmpF with its derivative containing a photosensitizer Chlorin e6 (AmpF-C) allows for creation of TMAS systems undergoing a morphological transition adaptable to the pH gradient present in cellular uptake pathway. Ex vivo studies revealed that TMAS nanomedicines prolonged circulation in the animal body and improved accumulation at tumor sites compared to morphology-persistent nanomedicines. In addition to the optimized cellular uptake, the morphological transition of TMAS into nanofibers in cytoplasm caused an enhanced intracellular ROS level compared to nanoparticle counterparts, thus leading to a lowered half lethal dose value for cancer cells. The combined advantages of TMAS eventually allowed in vivo PDT therapy for significant inhibition of tumor growth, thus demonstrating the improved drug delivery efficiency and therapeutic efficacy of TMAS systems toward new-generation nanomedicines.

The electrochemical molecular intercalation of two-dimensional layered materials (2DLMs) produces stable and highly tunable superlattices between monolayer 2DLMs and self-assembled molecular layers. This process allows unprecedented flexibility in integrating highly distinct materials with atomic/molecular precision to produce a new generation of organic/inorganic superlattices with tunable chemical, electronic, and optical properties. To better understand the intercalation process, we developed an on-chip platform based on MoS 2 model devices and used optical, electrochemical, and in situ electronic characterizations to resolve the intermediate stages during the intercalation process and monitor the evolution of the molecular superlattices. With sufficient charge injection, the organic cetyltrimethylammonium bromide (CTAB) intercalation induces the phase transition of MoS 2 from semiconducting 2H phase to semimetallic 1T phase, resulting in a dramatic increase of electrical conductivity. Therefore, in situ monitoring the evolution of the device conductance reveals the electrochemical intercalation dynamics with an abrupt conductivity change, signifying the onset of the molecule intercalation. In contrast, the intercalation of tetraheptylammonium bromide (THAB), a branched molecule in a larger size, resulting in a much smaller number of charges injected to avoid the 2H to 1T phase transition. Our study demonstrates a powerful platform for in situ monitoring the molecular intercalation of many 2DLMs (MoS 2 , WSe 2 , ReS 2 , PdSe 2 , TiS 2 , and graphene) and systematically probing electronic, optical, and optoelectronic properties at the single-nanosheet level.

Direct methanol/ethanol alkaline fuel cells (DMAFCs/DEAFCs) represent an attractive mobile power generation technology. The methanol/ethanol oxidation reaction (MOR/EOR) often requires high-performance yet expensive Pt-based catalysts that may be easily poisoned. Herein, we report the development of PtCuNi tetrahedra electrocatalysts with optimized specific activity and mass activity for MOR and EOR. Our synthetic and structural characterizations show that these PtCuNi tetrahedra have Cu-rich core and PtNi-rich shell with tunable surface composition. Electrocatalytic studies demonstrate that Pt 56 Cu 28 Ni 16 exhibits exceptional MOR and EOR specific activities of 14.0 ± 1.0 mA/cm 2 and 11.2 ± 1.0 mA/cm 2 , respectively and record high mass activity of 7.0 ± 0.5 A/mg Pt and 5.6 ± 0.6 A/mg Pt , comparing favorably with the best MOR or EOR Pt alloy-based catalysts reported to date. Furthermore, we show that the unique core-shell tetrahedra configuration can also lead to considerably improved durability.

Lithium sulfur (Li-S) batteries are attracting increasing interest for high-density energy storage. However, the practical application is limited by the rapid capacity fading over repeated charge/discharge cycles which is largely attributed to the formation and shuttling of soluble polysulfide species. To address these issues, we develop a hierarchical structure composite with triple protection strategy via graphene, organic conductor PEDOT, and nitrogen and phosphorus codoped biological carbon to encapsulate sulfur species (GOC@NPBCS). This unique hierarchical structure can effectively immobilize the sulfur species while at the same time improve the electrical conductivity and ensure efficient lithium ion transport to enable excellent Li-S battery performance. In particular, the biological carbon derived from natural bacteria features inherent nitrogen and phosphorus codoping with a strong absorption to lithium polysulfides, which can greatly suppress the dissolution and shuttling of polysulfides that are responsible for rapid capacity fading. With these synergistic effects, the GOC@NPBCS cathode exhibits exceptionally stable cycling stability (an ultralow capacity fading rate of 0.045% per cycle during 1000 cycles at the current rate of 5 C), high specific capacity (1193.8 mAh g -1 at 0.5 C based on sulfur weight), and excellent rate capability.

Soft and magnetic resonance imaging (MRI) compatible neural electrodes enable stable chronic electrophysiological measurements and anatomical or functional MRI studies of the entire brain without electrode interference with MRI images. These properties are important for many studies, ranging from a fundamental neurophysiological study of functional MRI signals to a chronic neuromodulatory effect investigation of therapeutic deep brain stimulation. Here we develop soft and MRI compatible neural electrodes using carbon nanotube (CNT) fibers with a diameter from 20 μm down to 5 μm. The CNT fiber electrodes demonstrate excellent interfacial electrochemical properties and greatly reduced MRI artifacts than PtIr electrodes under a 7.0 T MRI scanner. With a shuttle-assisted implantation strategy, we show that the soft CNT fiber electrodes can precisely target specific brain regions and record high-quality single-unit neural signals. Significantly, they are capable of continuously detecting and isolating single neuronal units from rats for up to 4-5 months without electrode repositioning, with greatly reduced brain inflammatory responses as compared to their stiff metal counterparts. In addition, we show that due to their high tensile strength, the CNT fiber electrodes can be retracted controllably postinsertion, which provides an effective and convenient way to do multidepth recording or potentially selecting cells with particular response properties. The chronic recording stability and MRI compatibility, together with their small size, provide the CNT fiber electrodes unique research capabilities for both basic and applied neuroscience studies.

Afterglow imaging through the collection of persistent luminescence after the stopping of light excitation holds enormous promise for advanced biomedical uses. However, efficient near-infrared (NIR)-emitting afterglow luminescent materials and probes (particularly the organic and polymeric ones) are still very limited, and their in-depth biomedical applications such as precise image-guided cancer surgery are rarely reported. Here, we design and synthesize a NIR afterglow luminescent nanoparticle with aggregation-induced emission (AIE) characteristics (named AGL AIE dots). It is demonstrated that the AGL AIE dots emit rather-high NIR afterglow luminescence persisting over 10 days after the stopping of a single excitation through a series of processes occurring in the AIE dots, including singlet oxygen production by AIE luminogens (AIEgens), Schaap's dioxetane formation, chemiexcitation by dioxetane decomposition, and energy transfer to NIR-emitting AIEgens. The animal studies reveal that the AGL AIE dots have the innate property of fast afterglow signal quenching in normal tissues, including the liver, spleen, and kidney. After the intravenous injection of AGL AIE dots into peritoneal carcinomatosis bearing mice, the tumor-to-liver ratio of afterglow imaging is nearly 100-fold larger than that for fluorescence imaging. The ultrahigh tumor-to-liver signal ratio, together with low afterglow background noise, enables AGL AIE dots to give excellent performance in precise image-guided cancer surgery.

Two-dimensional layered materials (2DLMs) are of considerable interest for high-performance electronic devices for their unique electronic properties and atomically thin geometry. However, the atomically thin geometry makes their electronic properties highly susceptible to the environment changes. In particular, some 2DLMs (e.g., black phosphorus (BP) and SnSe 2 ) are unstable and could rapidly degrade over time when exposed to ambient conditions. Therefore, the development of proper passivation schemes that can preserve the intrinsic properties and enhance their lifetime represents a key challenge for these atomically thin electronic materials. Herein we introduce a simple, nondisruptive, and scalable van der Waals passivation approach by using organic thin films to simultaneously improve the performance and air stability of BP field-effect transistors (FETs). We show that dioctylbenzothienobenzothiophene (C8-BTBT) thin films can be readily deposited on BP via van der Waals epitaxy approach to protect BP against oxidation in ambient conditions over 20 d. Importantly, the noncovalent van der Waals interface between C8-BTBT and BP effectively preserves the intrinsic properties of BP, allowing us to demonstrate high-performance BP FETs with a record-high current density of 920 μA/um, hole drift velocity over 1 × 10 7 cm/s, and on/off ratio of 1 × 10 4 to ∼1 × 10 7 at room temperature. This approach is generally applicable to other unstable two-dimensional materials, defining a unique pathway to modulate their electronic properties and realize high-performance devices through hybrid heterojunctions.

The DNA origami technique has empowered a new paradigm in plasmonics for manipulating light and matter at the nanoscale. This interdisciplinary field has witnessed vigorous growth, outlining a viable route to construct advanced plasmonic architectures with tailored optical properties. However, so far plasmonic systems templated by DNA origami have been restricted to respond to only single stimuli. Despite broad interest and scientific importance, thermal and aptamer-target regulations have not yet been widely utilized to reconfigure three-dimensional plasmonic architectures. In this Letter, we demonstrate a chiral plasmonic nanosystem integrated with split aptamers, which can respond to both thermal and aptamer-target regulations. We show that our dual-responsive system can be noninvasively tuned in a wide range of temperatures, readily correlating thermal control with optical signal changes. Meanwhile, our system can detect specific targets including adenosine triphosphate and cocaine molecules, which further enhance the optical response modulations and in turn influence the thermal tunability.

The recent discovery of topological semimetals has stimulated extensive research interest due to their unique electronic properties and novel transport properties related to a chiral anomaly. However, the studies to date are largely limited to bulk crystals and exfoliated flakes. Here, we report the controllable synthesis of ultrathin two-dimensional (2D) platinum telluride (PtTe 2 ) nanosheets with tunable thickness and investigate the thickness-dependent electronic properties. We show that PtTe 2 nanosheets can be readily grown, using a chemical vapor deposition approach, with a hexagonal or triangular geometry and a lateral dimension of up to 80 μm, and the thickness of the nanosheets can be systematically tailored from over 20 to 1.8 nm by reducing the growth temperature or increasing the flow rate of the carrier gas. X-ray-diffraction, transmission-electron microscopy, and electron-diffraction studies confirm that the resulting 2D nanosheets are high-quality single crystals. Raman spectroscopic studies show characteristics E g and A 1g vibration modes at ∼109 and ∼155 cm -1 , with a systematic red shift with increasing nanosheet thickness. Electrical transport studies show the 2D PtTe 2 nanosheets display an excellent conductivity up to 2.5 × 10 6 S m -1 and show strong thickness-tunable electrical properties, with both the conductivity and its temperature dependence varying considerably with the thickness. Moreover, 2D PtTe 2 nanosheets show an extraordinary breakdown current density up to 5.7 × 10 7 A/cm 2 , the highest breakdown current density achieved in 2D metallic transition-metal dichalcogenides to date.

Recent developments of transparent electrode arrays provide a unique capability for simultaneous optical and electrical interrogation of neural circuits in the brain. However, none of these electrode arrays possess the stretchability highly desired for interfacing with mechanically active neural systems, such as the brain under injury, the spinal cord, and the peripheral nervous system (PNS). Here, we report a stretchable transparent electrode array from carbon nanotube (CNT) web-like thin films that retains excellent electrochemical performance and broad-band optical transparency under stretching and is highly durable under cyclic stretching deformation. We show that the CNT electrodes record well-defined neuronal response signals with negligible light-induced artifacts from cortical surfaces under optogenetic stimulation. Simultaneous two-photon calcium imaging through the transparent CNT electrodes from cortical surfaces of GCaMP-expressing mice with epilepsy shows individual activated neurons in brain regions from which the concurrent electrical recording is taken, thus providing complementary cellular information in addition to the high-temporal-resolution electrical recording. Notably, the studies on rats show that the CNT electrodes remain operational during and after brain contusion that involves the rapid deformation of both the electrode array and brain tissue. This enables real-time, continuous electrophysiological monitoring of cortical activity under traumatic brain injury. These results highlight the potential application of the stretchable transparent CNT electrode arrays in combining electrical and optical modalities to study neural circuits, especially under mechanically active conditions, which could potentially provide important new insights into the local circuit dynamics of the spinal cord and PNS as well as the mechanism underlying traumatic injuries of the nervous system.

Doping with a transition metal was recently shown to greatly boost the activity and durability of PtNi/C octahedral nanoparticles (NPs) for the oxygen reduction reaction (ORR), but its specific roles remain unclear. By combining electrochemistry, ex situ and in situ spectroscopic techniques, density functional theory calculations, and a newly developed kinetic Monte Carlo model, we showed that Mo atoms are preferentially located on the vertex and edge sites of Mo-PtNi/C in the form of oxides, which are stable within the wide potential window of the electrochemical cycle. These surface Mo oxides stabilize adjacent Pt sites, hereby stabilizing the octahedral shape enriched with (111) facets, and lead to increased concentration of Ni in subsurface layers where they are protected against acid dissolution. Consequently, the favorable Pt 3 Ni(111) structure for the ORR is stabilized on the surface of PtNi/C NPs in acid against voltage cycling. Significantly, the unusual potential-dependent oxygen coverage trend on Mo-doped PtNi/C NPs as revealed by the surface-sensitive Δμ analysis suggests that the Mo dopants may also improve the ORR kinetics by modifying the coordination environments of Pt atoms on the surface. Our studies point out a possible way to stabilize the favorable shape and composition established on conceptual catalytic models in practical nanoscale catalysts.

High-resolution multicolor printing based on pixelated optical nanostructures is of great importance for promoting advances in color display science. So far, most of the work in this field has been focused on achieving static colors, limiting many potential applications. This inevitably calls for the development of dynamic color displays with advanced and innovative functionalities. In this Letter, we demonstrate a novel dynamic color printing scheme using magnesium-based pixelated Fabry-Pérot cavities by gray scale nanolithography. With controlled hydrogenation and dehydrogenation, magnesium undergoes unique metal and dielectric transitions, enabling distinct blank and color states from the pixelated Fabry-Pérot resonators. Following such a scheme, we first demonstrate dynamic Ishihara plates, in which the encrypted images can only be read out using hydrogen as information decoding key. We also demonstrate a new type of dynamic color generation, which enables fascinating transformations between black/white printing and color printing with fine tonal tuning. Our work will find wide-ranging applications in full-color printing and displays, colorimetric sensing, information encryption and anticounterfeiting.

Negative transconductance (NTC) devices have been heavily investigated for their potential in low power logical circuit, memory, oscillating, and high-speed switching applications. Previous NTC devices are largely attributed to two working mechanisms: quantum mechanical tunneling, and mobility degradation at high electrical field. Herein we report a systematic investigation of charge transport in multilayer two-dimensional semiconductors (2DSCs) with optimized van der Waals contact and for the first time demonstrate NTC and antibipolar characteristics in multilayer 2DSCs (such as MoS 2 , WSe 2 ). By varying the measurement temperature, bias voltage, and body thickness, we found the NTC behavior can be attributed to a vertical potential barrier in the multilayer 2DSCs and the competing mechanisms between intralayer lateral transport and interlayer vertical transport, thus representing a new working mechanism for NTC operation. Importantly, this vertical potential barrier arises from inhomogeneous carrier distribution in 2DSC from the near-substrate region to the bulk region, which is in contrast to conventional semiconductors with homogeneous doping defined by bulk dopants. We further show that the unique NTC behavior can be explored for creating frequency doublers and phase shift keying circuits with only one transistor, greatly simplifying the circuit design compared to conventional technology.

Vertical heterostructures based on graphene have emerged as a unique architecture for novel electronic devices with unusual characteristics. Here we report a new design of vertical ambipolar barristors based on metal-graphene-silicon-graphene sandwich structure, using the bottom graphene as a gate-tunable "active contact", the top graphene as an adaptable Ohmic contact, and the low doping thin silicon layer as the switchable channel. Importantly, with finite density of states and weak screening effect of graphene, we demonstrate, for the first time, that both the carrier concentration and majority carrier type in the sandwiched silicon can be readily modulated by gate potential penetrating through graphene. It can thus enable a new type of ambipolar barristors with an ON-OFF ratio exceeding 10 3 . Significantly, these ambipolar barristors can be flexibly configured into either p-type or n-type transistors and used to create integrated circuits with reconfigurable logic functions. This unconventional device structure and ambipolar reconfigurable characteristics can open up exciting opportunities in future electronics based on graphene or two-dimensional van der Waals heterostructures.

Magnetic resonance imaging (MRI) compatible neural electrodes are important for combining high-resolution electrophysiological measurements with more global MRI mapping of brain activity, which is critical for fundamental neuroscience studies, as well as clinical evaluation and monitoring. Copper is a favorable material to use in MRI because it has magnetic susceptibility close to water and tissues. However, the cytotoxicity of copper precludes its direct implantation for neural recording. Here, we overcome this limitation by developing a graphene encapsulated copper (G-Cu) microelectrode. The toxicity of copper is largely eliminated, as evidenced by the in vitro cell tests and in vivo histology studies. Local field potentials and single-unit spikes were recorded from rodent brains with the G-Cu microelectrodes. Notably, the G-Cu microelectrodes show no image artifacts in a 7.0 T MRI scanner, indicating minimal magnetic field distortion in their vicinity. This high MRI compatibility of our G-Cu probes would open up new opportunities for fundamental brain activity studies and clinical applications requiring continuous MRI and electrophysiological recordings.

Two-dimensional semiconductors (2DSCs) such as molybdenum disulfide (MoS 2 ) have attracted intense interest as an alternative electronic material in the postsilicon era. However, the ON-current density achieved in 2DSC transistors to date is considerably lower than that of silicon devices, and it remains an open question whether 2DSC transistors can offer competitive performance. A high current device requires simultaneous minimization of the contact resistance and channel length, which is a nontrivial challenge for atomically thin 2DSCs, since the typical low contact resistance approaches for 2DSCs either degrade the electronic properties of the channel or are incompatible with the fabrication process for short channel devices. Here, we report a new approach toward high-performance MoS 2 transistors by using a physically assembled nanowire as a lift-off mask to create ultrashort channel devices with pristine MoS 2 channel and self-aligned low resistance metal/graphene hybrid contact. With the optimized contact in short channel devices, we demonstrate sub-100 nm MoS 2 transistor delivering a record high ON-current of 0.83 mA/μm at 300 K and 1.48 mA/μm at 20 K, which compares well with that of silicon devices. Our study, for the first time, demonstrates that the 2DSC transistors can offer comparable performance to the 2017 target for silicon transistors in International Technology Roadmap for Semiconductors (ITRS), marking an important milestone in 2DSC electronics.

Chirality is a highly important topic in modern chemistry, given the dramatically different pharmacological effects that enantiomers can have on the body. Chirality of natural molecules can be controlled by reconfiguration of molecular structures through external stimuli. Despite the rapid progress in plasmonics, active regulation of plasmonic chirality, particularly in the visible spectral range, still faces significant challenges. In this Letter, we demonstrate a new class of hybrid plasmonic metamolecules composed of magnesium and gold nanoparticles. The plasmonic chirality from such plasmonic metamolecules can be dynamically controlled by hydrogen in real time without introducing macroscopic structural reconfiguration. We experimentally investigate the switching dynamics of the hydrogen-regulated chiroptical response in the visible spectral range using circular dichroism spectroscopy. In addition, energy dispersive X-ray spectroscopy is used to examine the morphology changes of the magnesium particles through hydrogenation and dehydrogenation processes. Our study can enable plasmonic chiral platforms for a variety of gas detection schemes by exploiting the high sensitivity of circular dichroism spectroscopy.

The recently emerged organohalide perovskites (e.g., CH3NH3PbI3) have drawn intense attention for high efficiency solar cells. However, with a considerable solubility in many solvents, these perovskites are not typically compatible with conventional lithography processes for more complicated device fabrications that are important for both fundamental studies and technological applications. Here, we report the creation of novel heterojunction devices based on perovskites and two-dimensional (2D) crystals by taking advantage of the layered characteristic of lead iodide (PbI2) and vapor-phase intercalation. We show that a graphene/perovskite/graphene vertical stack can deliver a highest photoresponsivity of ∼950 A/W and photoconductive gain of ∼2200, and a graphene/WSe2/perovskite/graphene heterojunction can display a high on/off ratio (∼10(6)) transistor behavior with distinct gate-tunable diode characteristics and open-circuit voltages. Such unique perovskite-2D heterostructures have significant potential for future optoelectronic research and can enable broad possibilities with compositional tunability of organohalide perovskites and the versatility offered by diverse 2D materials.

Two-dimensional (2D) layered transition metal dichalcogenides (TMDs) have recently emerged as a new class of atomically thin semiconductors for diverse electronic, optoelectronic, and valleytronic applications. To explore the full potential of these 2D semiconductors requires a precise control of their band gap and electronic properties, which represents a significant challenge in 2D material systems. Here we demonstrate a systematic control of the electronic properties of 2D-TMDs by creating mixed alloys of the intrinsically p-type WSe2 and intrinsically n-type WS2 with variable alloy compositions. We show that a series of WS2xSe2-2x alloy nanosheets can be synthesized with fully tunable chemical compositions and optical properties. Electrical transport studies using back-gated field effect transistors demonstrate that charge carrier types and threshold voltages of the alloy nanosheet transistors can be systematically tuned by adjusting the alloy composition. A highly p-type behavior is observed in selenium-rich alloy, which gradually shifts to lightly p-type, and then switches to lightly n-type characteristics with the increasing sulfur atomic ratio, and eventually evolves into highly n-doped semiconductors in sulfur-rich alloys. The synthesis of WS2xSe2-2x nanosheets with tunable optical and electronic properties represents a critical step toward rational design of 2D electronics with tailored spectral responses and device characteristics.

Deterministic placement and dynamic manipulation of individual plasmonic nanoparticles with nanoscale precision feature an important step toward active nanoplasmonic devices with prescribed levels of performance and functionalities at optical frequencies. In this Letter, we demonstrate a plasmonic walker couple system, in which two gold nanorod walkers can independently or simultaneously perform stepwise walking powered by DNA hybridization along the same DNA origami track. We utilize optical spectroscopy to resolve such dynamic walking with nanoscale steps well below the optical diffraction limit. We also show that the number of walkers and the optical response of the system can be correlated. Our studies exemplify the power of plasmonics, when integrated with DNA nanotechnology for realization of advanced artificial nanomachinery with tailored optical functionalities.

Scalable preparation of solution processable graphene and its bulk materials with high specific surface areas and designed porosities is essential for many practical applications. Herein, we report a scalable approach to produce aqueous dispersions of holey graphene oxide with abundant in-plane nanopores via a convenient mild defect-etching reaction and demonstrate that the holey graphene oxide can function as a versatile building block for the assembly of macrostructures including holey graphene hydrogels with a three-dimensional hierarchical porosity and holey graphene papers with a compact but porous layered structure. These holey graphene macrostructures exhibit significantly improved specific surface area and ion diffusion rate compared to the nonholey counterparts and can be directly used as binder-free supercapacitor electrodes with ultrahigh specific capacitances of 283 F/g and 234 F/cm(3), excellent rate capabilities, and superior cycling stabilities. Our study defines a scalable pathway to solution processable holey graphene materials and will greatly impact the applications of graphene in diverse technological areas.

Titanium oxide (TiO2) represents one of most widely studied materials for photoelectrochemical (PEC) water splitting but is severely limited by its poor efficiency in the visible light range. Here, we report a significant enhancement of visible light photoactivity in nitrogen-implanted TiO2 (N-TiO2) nanowire arrays. Our systematic studies show that a post-implantation thermal annealing treatment can selectively enrich the substitutional nitrogen dopants, which is essential for activating the nitrogen implanted TiO2 to achieve greatly enhanced visible light photoactivity. An incident photon to electron conversion efficiency (IPCE) of ∼10% is achieved at 450 nm in N-TiO2 without any other cocatalyst, far exceeding that in pristine TiO2 nanowires (∼0.2%). The integration of oxygen evolution reaction (OER) cocatalyst with N-TiO2 can further increase the IPCE at 450 nm to ∼17% and deliver an unprecedented overall photocurrent density of 1.9 mA/cm(2), by integrating the IPCE spectrum with standard AM 1.5G solar spectrum. Systematic photoelectrochemical and electrochemical studies demonstrated that the enhanced PEC performance can be attributed to the significantly improved visible light absorption and more efficient charge separation. Our studies demonstrate the implantation approach can be used to reliably dope TiO2 to achieve the best performed N-TiO2 photoelectrodes to date and may be extended to fundamentally modify other semiconductor materials for PEC water splitting.

High surface area in h-WO3 has been verified from the intracrystalline tunnels. This bottom-up approach differs from conventional templating-type methods. The 3.67 Å diameter tunnels are characterized by low-pressure CO2 adsorption isotherms with nonlocal density functional theory fitting, transmission electron microscopy, and thermal gravimetric analysis. These open and rigid tunnels absorb H(+) and Li(+), but not Na(+) in aqueous electrolytes without inducing a phase transformation, accessing both internal and external active sites. Moreover, these tunnel structures demonstrate high specific pseudocapacitance and good stability in an H2SO4 aqueous electrolyte. Thus, the high surface area created from 3.67 Å diameter tunnels in h-WO3 shows potential applications in electrochemical energy storage, selective ion transfer, and selective gas adsorption.

Two-dimensional layered semiconductors such as molybdenum disulfide (MoS2) have attracted tremendous interest as a new class of electronic materials. However, there are considerable challenges in making reliable contacts to these atomically thin materials. Here we present a new strategy by using graphene as the back electrodes to achieve ohmic contact to MoS2. With a finite density of states, the Fermi level of graphene can be readily tuned by a gate potential to enable a nearly perfect band alignment with MoS2. We demonstrate for the first time a transparent contact to MoS2 with zero contact barrier and linear output behavior at cryogenic temperatures (down to 1.9 K) for both monolayer and multilayer MoS2. Benefiting from the barrier-free transparent contacts, we show that a metal-insulator transition can be observed in a two-terminal MoS2 device, a phenomenon that could be easily masked by Schottky barriers found in conventional metal-contacted MoS2 devices. With further passivation by boron nitride (BN) encapsulation, we demonstrate a record-high extrinsic (two-terminal) field effect mobility up to 1300 cm(2)/(V s) in MoS2 at low temperature.

Transition metal dichacogenides represent a unique class of two-dimensional layered materials that can be exfoliated into single or few atomic layers. Tungsten diselenide (WSe(2)) is one typical example with p-type semiconductor characteristics. Bulk WSe(2) has an indirect band gap (∼ 1.2 eV), which transits into a direct band gap (∼ 1.65 eV) in monolayers. Monolayer WSe(2), therefore, is of considerable interest as a new electronic material for functional electronics and optoelectronics. However, the controllable synthesis of large-area WSe(2) atomic layers remains a challenge. The studies on WSe(2) are largely limited by relatively small lateral size of exfoliated flakes and poor yield, which has significantly restricted the large-scale applications of the WSe(2) atomic layers. Here, we report a systematic study of chemical vapor deposition approach for large area growth of atomically thin WSe(2) film with the lateral dimensions up to ∼ 1 cm(2). Microphotoluminescence mapping indicates distinct layer dependent efficiency. The monolayer area exhibits much stronger light emission than bilayer or multilayers, consistent with the expected transition to direct band gap in the monolayer limit. The transmission electron microscopy studies demonstrate excellent crystalline quality of the atomically thin WSe(2). Electrical transport studies further show that the p-type WSe(2) field-effect transistors exhibit excellent electronic characteristics with effective hole carrier mobility up to 100 cm(2) V(-1) s(-1) for monolayer and up to 350 cm(2) V(-1) s(-1) for few-layer materials at room temperature, comparable or well above that of previously reported mobility values for the synthetic WSe(2) and comparable to the best exfoliated materials.

Low-temperature solution-processed electronic materials on plastic substrates are of considerable interest for flexible electronics. Solution dispersible inorganic nanostructures (e.g., zero-dimensional (0D) quantum dots or one-dimensional (1D) nanowires) have emerged as interesting ink materials for low-temperature solution processing of electronic thin films on flexible substrates, but usually with limited performance due to the large number of grain boundaries (0D) or incomplete surface coverage (1D). Here, we report two-dimensional (2D) colloidal nanoplates of layered materials as a new ink material for solution assembly of high-performance electronic thin films. The 2D colloidal nanoplates exhibit few dangling bonds and represent an ideal geometry for the assembly of highly uniform continuous thin films with greatly reduced grain boundaries dictated by large-area conformal plane-plane contact with atomically flat/clean interfaces. It can therefore promise efficient charge transport across neighboring nanoplates and throughout the entire thin film to enable unprecedented electronic performance. We show that Bi2Se3 and Bi2Te3 nanoplates can be synthesized with well-controlled thickness (6-15 nm) and lateral dimension (0.5-3 μm) and can be used for the assembly of highly uniform continuous thin films with a full surface coverage and an excellent room temperature carrier mobility >100 cm(2)·V(-1)·s(-1), approaching that of chemical vapor deposition grown materials. Our study demonstrates a general strategy to using 2D nanoplates as a unique building block for the construction of high-performance electronic thin films on plastic substrates for future flexible electronics and optoelectronics.

The p-n diodes represent the most fundamental device building blocks for diverse optoelectronic functions, but are difficult to achieve in atomically thin transition metal dichalcogenides (TMDs) due to the challenges in selectively doping them into p- or n-type semiconductors. Here, we demonstrate that an atomically thin and sharp heterojunction p-n diode can be created by vertically stacking p-type monolayer tungsten diselenide (WSe2) and n-type few-layer molybdenum disulfide (MoS2). Electrical measurements of the vertically staked WSe2/MoS2 heterojunctions reveal excellent current rectification behavior with an ideality factor of 1.2. Photocurrent mapping shows rapid photoresponse over the entire overlapping region with a highest external quantum efficiency up to 12%. Electroluminescence studies show prominent band edge excitonic emission and strikingly enhanced hot-electron luminescence. A systematic investigation shows distinct layer-number dependent emission characteristics and reveals important insight about the origin of hot-electron luminescence and the nature of electron-orbital interaction in TMDs. We believe that these atomically thin heterojunction p-n diodes represent an interesting system for probing the fundamental electro-optical properties in TMDs and can open up a new pathway to novel optoelectronic devices such as atomically thin photodetectors, photovoltaics, as well as spin- and valley-polarized light emitting diodes, on-chip lasers.

Structural defects/grain boundaries in metallic materials can exhibit unusual chemical reactivity and play important roles in catalysis. Bulk polycrystalline materials possess many structural defects, which is, however, usually inaccessible to solution reactants and hardly useful for practical catalytic reactions. Typical metallic nanocrystals usually exhibit well-defined crystalline structure with few defects/grain boundaries. Here, we report the design of ultrafine wavy nanowires (WNWs) with a high density of accessible structural defects/grain boundaries as highly active catalytic hot spots. We show that rhodium WNWs can be readily synthesized with controllable number of structural defects and demonstrate the number of structural defects can fundamentally determine their catalytic activity in selective oxidation of benzyl alcohol by O2, with the catalytic activity increasing with the number of structural defects. X-ray photoelectron spectroscopy (XPS) and cyclic voltammograms (CVs) studies demonstrate that the structural defects can significantly alter the chemical state of the Rh WNWs to modulate their catalytic activity. Lastly, our systematic studies further demonstrate that the concept of defect engineering in WNWs for improved catalytic performance is general and can be readily extended to other similar systems, including palladium and iridium WNWs.

Flexible thin-film transistors (TFTs) are of central importance for diverse electronic and particularly macroelectronic applications. The current TFTs using organic or inorganic thin film semiconductors are usually limited by either poor electrical performance or insufficient mechanical flexibility. Here, we report a new design of highly flexible vertical TFTs (VTFTs) with superior electrical performance and mechanical robustness. By using the graphene as a work-function tunable contact for amorphous indium gallium zinc oxide (IGZO) thin film, the vertical current flow across the graphene-IGZO junction can be effectively modulated by an external gate potential to enable VTFTs with a highest on-off ratio exceeding 10(5). The unique vertical transistor architecture can readily enable ultrashort channel devices with very high delivering current and exceptional mechanical flexibility. With large area graphene and IGZO thin film available, our strategy is intrinsically scalable for large scale integration of VTFT arrays and logic circuits, opening up a new pathway to highly flexible macroelectronics.

The phase formation sequence of silicides in two-dimensional (2-D) structures has been well-investigated due to their significance in microelectronics. Applying high-quality silicides as contacts in nanoscale silicon (Si) devices has caught considerable attention recently for their potential in improving and introducing new functions in nanodevices. However, nucleation and diffusion mechanisms are found to be very different in one-dimensional (1-D) nanostructures, and thus the phase manipulation of silicides is yet to be achieved there. In this work, we report kinetic phase modulations to selectively enhance or hinder the growth rates of targeted nickel (Ni) silicides in a Si nanowire (NW) and demonstrate that Ni31Si12, δ-Ni2Si, θ-Ni2Si, NiSi, and NiSi2 can emerge as the first contacting phase at the silicide/Si interface through these modulations. First, the growth rates of silicides are selectively tuned through template structure modifications. It is demonstrated that the growth rate of diffusion limited phases can be enhanced in a porous Si NW due to a short diffusion path, which suppresses the formation of interface limited NiSi2. In addition, we show that a confining thick shell can be applied around the Si NW to hinder the growth of the silicides with large volume expansion during silicidation, including Ni31Si12, δ-Ni2Si, and θ-Ni2Si. Second, a platinum (Pt) interlayer between the Ni source and the Si NW is shown to effectively suppress the formation of the phases with low Pt solubility, including the dominating NiSi2. Lastly, we show that with the combined applications of the above-mentioned approaches, the lowest resistive NiSi phase can form as the first phase in a solid NW with a Pt interlayer to suppress NiSi2 and a thick shell to hinder Ni31Si12, δ-Ni2Si, and θ-Ni2Si simultaneously. The resistivity and maximum current density of NiSi agree reasonably to reported values.

Direct observation of delithiated structures of LiCoO(2) at atomic scale has been achieved using spherical aberration-corrected scanning transmission electron microscopy (STEM) with high-angle annular-dark-field (HAADF) and annular-bright-field (ABF) techniques. The ordered Li, Co, and O columns for LiCoO(2) nanoparticles are clearly identified in ABF micrographs. Upon the Li ions extraction from LiCoO(2), the Co-contained (003) planes distort from the bulk to the surface region and the c-axis is expanded significantly. Ordering of lithium ions and lithium vacancies has been observed directly and explained by first-principles simulation. On the basis of HAADF micrographs, it is found that the phase irreversibly changes from O3-type in pristine LiCoO(2) to O1-type Li(x)CoO(2) (x ≈ 0.50) after the first electrochemical Li extraction and back to O2-type Li(x)CoO(2) (x ≈ 0.93) rather than to O3-stacking after the first electrochemical lithiation. This is the first report of finding O2-Li(x)CoO(2) in the phase diagram of O3-LiCoO(2), through which the two previously separated LiCoO(2) phases, i.e. O2 and O3 systems, are connected. These new investigations shed new insight into the lithium storage mechanism in this important cathode material for Li-ion batteries.

Compact wavelength-sensitive optical components are desirable for optical information processing and communication in photonic integrated system. In this work, optical waveguiding along single composition-graded CdS(x)Se(1-x) nanowires were systematically investigated. Under a focused laser excitation, the excited light can be guided passively along the bandgap-increased direction of the nanowire, keeping the photonic energy of the guided light almost unchanged during the whole propagation. In comparison, the excited light is guided actively through incessantly repeated band-to-band reabsorption and re-emitting processes along the bandgap-decreased direction, resulting in a gradual wavelength conversion during propagation. On the basis of this wavelength-converted waveguiding, a concept of nanoscale wavelength splitter is demonstrated by assembling a graded nanowire with several composition-uniform nanowires into branched nanowire structure. Our study indicates that composition-graded semiconductor nanowires would open new exciting opportunities in developing new wavelength-sensitive optical components for integrated nanophotonic devices.

We report a facile synthetic strategy to single-crystalline PtPd nanocrystals with controllable shapes and tunable compositions. In the developed synthesis, the molar ratio of the starting precursors determines the composition in the final PtPd nanocrystals, while the halides function as the shape-directing agent to induce the formation of PtPd nanocrystals with cubic or octahedral/tetrahedral morphology. These obtained PtPd nanocrystals exhibit high activity in the hydrogenation of nitrobenzene, and their performance is highly shape- and composition-dependent with Pt in ∼50% showing the optimum activity and the {100}-facet-enclosed PtPd nanocrystals demonstrating a higher activity than the {111}-facet-bounded PtPd nanocrystals.