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January 2008 - present
August 1997 - December 2005
Publications
Publications (506)
Stretchable electronics capable of conforming to nonplanar and dynamic human body surfaces are central for creating implantable and on‐skin devices for high‐fidelity monitoring of diverse physiological signals. While various strategies have been developed to produce stretchable devices, the signals collected from such devices are often highly sensi...
Van der Waals materials display rich structural polymorphs with distinct physical properties. An atomistic understanding of the phase-transition dynamics, propagation pathway and associated evolution of physical properties is essential for capturing their potential in practical technologies. However, direct visualization of the rapid phase-transiti...
Aqueous rechargeable batteries (ARBs) offer a low‐cost, high‐safety, and fast‐reacting alternatives for large‐scale energy storage. However, their further practical applications are limited by challenges in achieving satisfactory energy density, long cycling lifetime, and cost‐effectiveness. In this study, an aqueous rechargeable aluminum‐ammonium...
Directly probing deep tissue activities from body surfaces offers a noninvasive approach to monitoring essential physiological processes1-3. However, this method is technically challenged by rapid signal attenuation toward the body surface and confounding motion artifacts4-6 primarily due to excessive contact impedance and mechanical mismatch with...
The platinum (Pt) catalyzed hydrogen evolution and oxidation reactions (HER/HOR) usually show considerable slower kinetics in alkaline electrolytes than that in acidic environment. The fundamental origin of such distinct kinetics has been a topic of considerable interest. In general, the electrode-electrolyte (Pt-water) interface in alkaline electr...
Crystalline solids typically show robust long-range structural ordering, vital for their remarkable electronic properties and use in functional electronics, albeit with limited customization space. By contrast, synthetic molecular systems provide highly tunable structural topologies and versatile functionalities but are often too delicate for scala...
Stretchable electronics capable of conforming to nonplanar and dynamic human body surfaces are central for creating implantable and on-skin devices for high-fidelity monitoring of diverse physiological signals. While various strategies have been developed to produce stretchable devices, the signals collected from such devices are often highly sensi...
The mechanical interactions among integrated cellular structures in soft tissues dictate the mechanical behaviors and morphogenetic deformations observed in living organisms. However, replicating these multifaceted attributes in synthetic soft materials remains a challenge. In this work, we develop a smart hydrogel system featuring engineered stiff...
Microbial fuel cells utilize exoelectrogenic microorganisms to directly convert organic matter into electricity, offering a compelling approach for simultaneous power generation and wastewater treatment. However, conventional microbial fuel cells typically require thick biofilms for sufficient metabolic electron production rate, which inevitably co...
The performance of electrocatalysts is critical for renewable energy technologies. While the electrocatalytic activity can be modulated through structural and compositional engineering following the Sabatier principle, the insufficiently explored catalyst-electrolyte interface is promising to promote microkinetic processes such as physisorption and...
Two-dimensional transition metal dichalcogenides, which feature atomically thin geometry and dangling-bond-free surfaces, have attracted intense interest for diverse technology applications, including ultra-miniaturized transistors towards the subnanometre scale. A straightforward exfoliation-and-restacking approach has been widely used for nearly...
Copper-doped Bi2Se3 (CuxBi2Se3) is of considerable interest for tailoring its electronic properties and inducing exotic charge correlations while retaining the unique Dirac surface states. However, the copper dopants in CuxBi2Se3 display complex electronic behaviors and may function as either electron donors or acceptors depending on their concentr...
Alcohol-assisted water electrolysis offers an attractive path for on-demand hydrogen generation while concurrently producing value added carboxylates. However, the anodic alcohol oxidation reaction (AOR) often requires precious metal-based catalysts, yet is still plagued with high overpotential or limited mass activity. Herein we report a facile sy...
Lithium–sulfur (Li–S) battery is attracting increasing interest for its potential in low‐cost high‐density energy storage. However, it has been a persistent challenge to simultaneously realize high energy density and long cycle life. Herein, we report a synergistic strategy to exploit a unique nitrogen‐doped three‐dimensional graphene aerogel as bo...
Platinum (Pt) nanocatalysts are essential for facilitating the cathodic oxygen reduction reaction in proton exchange membrane fuel cells but suffer from a trade-off between activity and durability. Here we present the design of a fine nanocatalyst comprising Pt nanoparticles with sparsely embedded cobalt oxide clusters (CoOx@Pt). This design exploi...
Chiral superconductors, a unique class of unconventional superconductors in which the complex superconducting order parameter winds clockwise or anticlockwise in the momentum space¹, represent a topologically non-trivial system with intrinsic time-reversal symmetry breaking (TRSB) and direct implications for topological quantum computing2,3. Intrin...
Microbial fuel cells (MFCs) utilize exoelectrogenic microorganisms to directly convert organic matter into electricity, offering a compelling approach for simultaneous power generation and wastewater treatment. However, conventional MFCs typically require thick biofilms for sufficient metabolic electron production rate, which inevitably compromises...
Platinum nanocatalysts facilitate the hydrogen evolution reaction (HER) for renewable chemical fuel generation. These nanostructures encompass diverse surface sites, including (111) and (100) facets and edge sites between them. Identifying the exact active sites is essential for optimal catalyst design, but remains challenging. Here, combining elec...
Monolayer molybdenum disulfide (MoS2) features exceptional sec- ond-order nonlinear optical (NLO) susceptibility, while being atom- ically thin limits its efficiency in second harmonic generation (SHG). The naturally existing 2H-phase MoS2 may offer a larger optical cross section in its bulk form but is inactive for SHG due to the restored centrosy...
The intermittent nature of renewable energy sources sets a requirement for efficient energy storage to mitigate the conflict between energy supply and demand. Hydrogen is a promising choice for energy storage due to its high energy density. However, the conversion of electrical energy to chemical energy stored in hydrogen through water electrolysis...
Nonlinear optical processing of ambient natural light is highly desired for computational imaging and sensing. Strong optical nonlinear response under weak broadband incoherent light is essential for this purpose. By merging 2D transparent phototransistors (TPTs) with liquid crystal (LC) modulators, we create an optoelectronic neuron array that all...
The Tafel slope represents a critical kinetic parameter for mechanistic studies of electrochemical reactions, including the hydrogen evolution reaction (HER). Linear fitting of the polarization curve in a N2-saturated electrolyte is commonly used to determine Tafel slopes, which is, however, frequently plagued with inconsistencies. Our systematic s...
The sulfur reduction reaction (SRR) plays a central role in high-capacity lithium sulfur (Li-S) batteries. The SRR involves an intricate, 16-electron conversion process featuring multiple lithium polysulfide intermediates and reaction branches1–3. Establishing the complex reaction network is essential for rational tailoring of the SRR for improved...
Ru decorated Ag nanoparticles are designed as highly effective bifunctional electrocatalysts for hydrazine oxidation and hydrogen evolution reactions, enabling a hydrazine assisted water electrolyser with greatly increased current density.
Molybdenum disulfide (MoS2) is an extensively studied two-dimensional layered semiconductor with interesting electronic and optical properties. Monolayer MoS2 features strong light–matter interactions due to its direct bandgap, whereas multilayer MoS2 is an indirect bandgap semiconductor and optically inactive. The molecular intercalation of MoS2 w...
Electrochemical molecular intercalation of layered semiconducting crystals with organic cations followed by ultrasonic exfoliation has proven to be an effective approach to producing a rich family of organic/inorganic hybrid superlattices and high-quality, solution-processable 2D semiconductors. A traditional method for exfoliating 2D crystals reli...
Extensive macroscale two-dimensional (2-D) platinum (Pt) nanowire network (NWN) sheets are created through a hierarchical self-assembly process with the aid of biomolecular ligands. The Pt NWN sheet is assembled from the attachment growth of 1.9 nm-sized 0-D nanocrystals into 1-D nanowires featuring a high density of grain boundaries, which then in...
In analogy to natural enzymes, an elaborated design of catalytic systems with a specifically tailored local chemical environment could substantially improve reaction kinetics, effectively combat catalyst poisoning effect and boost catalyst lifetime under unfavourable reaction conditions. Here we report a unique design of ‘Ni(OH)2-clothed Pt-tetrapo...
Nonlinear optical processing of ambient natural light is highly desired in computational imaging and sensing applications. A strong optical nonlinear response that can work under weak broadband incoherent light is essential for this purpose. Here we introduce an optoelectronic nonlinear filter array that can address this emerging need. By merging 2...
Hydrazine assisted water electrolysis offers a feasible path for low-voltage green hydrogen production. Herein w e report the design and synthesis of ultrathin RhRu0.5 alloy wavy nanowires as bifunctional electrocatalysts for both anodic hydrazine oxidation reaction (HzOR) and cathodic hydrogen evolution reaction (HER). W e show that the RhRu0.5 al...
Two-dimensional semiconductors (2DSCs) have attracted considerable interests for optoelectronic devices, but are often plagued by the difficulties in tailoring the charge doping type and poor optical absorption due to their atomically thin geometry. Herein, we report a methylammonium lead iodide perovskite (CH 3 NH 3 PbI 3 )/2DSC heterojunction dev...
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 synth...
Two-dimensional (2D) semiconductors such as molybdenum disulfide (MoS2) have attracted tremendous interest for transistor applications. However, the fabrication of 2D transistors using traditional lithography or deposition processes often causes undesired damage and contamination to the atomically thin lattices, partially degrading the device perfo...
Humans rely increasingly on sensors to address grand challenges and to improve quality of life in the era of digitalization and big data. For ubiquitous sensing, flexible sensors are developed to overcome the limitations of conventional rigid counterparts. Despite rapid advancement in bench-side research over the last decade, the market adoption of...
Chiral superconductors, a unique class of unconventional superconductors in which the complex superconducting order parameter winds clockwise or counter-clockwise in the momentum space, represent a topologically non-trivial system with direct implications for topological quantum computing. Intrinsic chiral superconductors are extremely rare, with o...
The success of the lead halide perovskites in diverse optoelectronics has motivated considerable interest in their fundamental photocarrier dynamics. Here we report the discovery of photocarrier-induced persistent structural polarization and local ferroelectricity in lead halide perovskites. Photoconductance studies of thin-film single-crystal CsPb...
Most of the current methods for the synthesis of two-dimensional materials (2DMs) require temperatures not compatible with traditional back-end-of-line (BEOL) processes in semiconductor industry (450 °C). Here, we report a general BiOCl-assisted chemical vapor deposition (CVD) approach for the low-temperature synthesis of 27 ultrathin 2DMs. In part...
We integrate two-dimensional transparent photodetectors with liquid crystal modulators to form a nonlinear filter-array, allowing self-amplitude-modulation of light at low-intensity levels (<100 mW/cm ² ). We fabricated 10,000 devices over 1 cm ² to demonstrate glare reduction.
Compared with layered materials such as graphite and transitional metal dichalcogenides with highly anisotropic in-plane covalent bonds, freestanding metallic two-dimensional (2D) films with atomic thickness are intrinsically more difficult to achieve. The omnidirectional nature of typical metallic bonds prevents the formation of highly anisotropic...
The integration of dissimilar materials into heterostructures has become a powerful tool for engineering interfaces and electronic structure. The advent of 2D materials has provided unprecedented opportunities for novel heterostructures in the form of van der Waals stacks, laterally stitched 2D layers and more complex layered and 3D architectures....
Integrating light-harvesting materials with microbial biochemistry is a viable approach to produce chemicals with high efficiency from air, water and sunlight. Yet it remains unclear whether all photons absorbed in the materials can be transferred through the material–biology interface for solar-to-chemical production and whether the presence of ma...
Two‐dimensional (2D) semiconductor crystals offer the opportunity to further extend Moore's law to the atomic scale. For practical and low‐cost electronic applications, directly printing devices on substrates is advantageous compared to conventional microfabrication techniques that utilize expensive photolithography, etching, and vacuum metallizati...
The miniaturization of silicon-based electronics has motivated considerable efforts in exploring new electronic materials, including two-dimensional semiconductors and halide perovskites, which are usually too delicate to maintain their intrinsic properties during the harsh device fabrication steps. Here we report a convenient plug-and-probe approa...
The platinum-catalysed hydrogen evolution reaction (HER) generally shows poorer kinetics in alkaline electrolyte and represents a key challenge for alkaline water electrolysis. In the presence of alkali metal cations and hydroxyl anions, the electrode–electrolyte (platinum–water) interface in an alkaline electrolyte is far more complex than that in...
The recent blossom in 2D atomic crystals (2DACs) has ignited intense interest in a new type of bond-free van der Waals heterostructures (vdWHs), in which distinct material components are physically brought together within a vdW distance and held together by weak vdW interactions. Without direct chemical bonding between the constituent materials, th...
Electrocatalytic hydrogen evolution reaction (HER) is critical for green hydrogen generation and exhibits distinct pH-dependent kinetics that have been elusive to understand. A molecular-level understanding of the electrochemical interfaces is essential for developing more efficient electrochemical processes. Here we exploit an exclusively surface-...
Heteroepitaxial growth of single-crystal films typically requires stringent matching of the specific lattice ordering with the underlying substrate. Now, amorphous MoTe2 thin films are shown to transform into wafer-scale 2D single-crystals through seeded growth on the surface of any arbitrary substrate.
Two-dimensional semiconductors such as layered transition metal dichalcogenides can offer superior immunity to short-channel effects compared with bulk semiconductors such as silicon. As a result, these materials can be used to create highly scaled transistors. However, on-state current densities of two-dimensional semiconductor transistors are sti...
Miniaturized spectrometers are of considerable interest for their portability. Most designs to date employ a photodetector array with distinct spectral responses or require elaborated integration of micro & nano optic modules, typically with a centimeter-scale footprint. Here, we report a design of a micron-sized near-infrared ultra-miniaturized sp...
Urinalysis is attractive in non‐invasive early diagnosis of bladder cancer compared with clinical gold standard cystoscopy. However, the trace bladder tumor biomarkers in urine and the particularly complex urine environment pose significant challenges for urinalysis. Here, we report a clinically adoptable urinalysis device that integrates molecular...
The proton exchange membrane fuel cell (PEMFC) as an attractive clean power source can promise a carbon-neutral future, but the widespread adoption of PEMFCs requires a substantial reduction in the usage of the costly platinum group metal (PGM) catalysts. Ultrafine nanocatalysts are essential to provide sufficient catalytic sites at a reduced PGM l...
The use of organic, oxide and low-dimensional materials in field-effect transistors has now been studied for decades. However, properly reporting and comparing device performance remains challenging due to the interdependency of multiple device parameters. The interdisciplinarity of this research community has also led to a lack of consistent repor...
Thermal insulation under extreme conditions requires materials that can withstand complex thermomechanical stress and retain excellent thermal insulation properties at temperatures exceeding 1,000 degrees Celsius1–3. Ceramic aerogels are attractive thermal insulating materials; however, at very high temperatures, they often show considerably increa...
The discovery of chiral-induced spin selectivity (CISS) opens up the possibility to manipulate spin orientation without external magnetic fields and enables new spintronic device designs1–4. Although many approaches have been explored for introducing CISS into solid-state materials and devices, the resulting systems so far are often plagued by high...
Single-atom catalysts represent a unique catalytic system with high atomic utilization and tunable reaction pathway. Despite current successes in their optimization and tailoring through structural and synthetic innovations, there is a lack of dynamic modulation approach for the single-atom catalysis. Inspired by the electrostatic interaction withi...
A critical technological roadblock to the widespread adoption of proton-exchange membrane fuel cells is the development of highly active and durable platinum-based catalysts for accelerating the sluggish oxygen reduction reaction, which has largely relied on anecdotal discoveries so far. While the oxygen binding energy ∆EO has been frequently used...
The controllable growth of two-dimensional (2D) heterostructure arrays is critical for exploring exotic physics and developing novel devices, yet it remains a substantial synthetic challenge. Here we report a rational synthetic strategy to fabricate mosaic heterostructure arrays in monolayer 2D atomic crystals. By using a laser-patterning and an an...
Charge-coupled devices are widely used imaging technologies. However, their speed is limited due to the complex readout process, which involves sequential charge transfer between wells, and their spectral bandwidth is limited due to the absorption limitations of silicon. Here we report graphene charge-injection photodetectors. The devices have a de...
Emerging low-dimensional nanomaterials have been studied for decades in device applications as field-effect transistors (FETs). However, properly reporting and comparing device performance has been challenging due to the involvement and interlinking of multiple device parameters. More importantly, the interdisciplinarity of this research community...
Graphene with linear energy dispersion and weak electron–phonon interaction is highly anticipated to harvest hot electrons in a broad wavelength range. However, the limited absorption and serious backscattering of hot‐electrons result in inadequate quantum yields, especially in the mid‐infrared range. Here, we report a macroscopic assembled graphen...
The conformal integration of electronic systems with irregular, soft objects is essential for many emerging technologies. We report the design of van der Waals thin films consisting of staggered two-dimensional nanosheets with bond-free van der Waals interfaces. The films feature sliding and rotation degrees of freedom among the staggered nanosheet...
A grand family of two-dimensional (2D) materials and their heterostructures have been discovered through the extensive experimental and theoretical efforts of chemists, material scientists, physicists, and technologists. These pioneering works contribute to realizing the fundamental platforms to explore and analyze new physical/chemical properties...
As cancer is increasingly considered a metabolic disorder, it is postulated that serum metabolite profiling can be a viable approach for detecting the presence of cancer. By multiplexing mass spectrometry fingerprints from two independent nanostructured matrixes through machine learning for highly sensitive detection and high throughput analysis, w...
Silicon monoxide (SiO) is an attractive anode material for next-generation lithium-ion batteries for its ultra-high theoretical capacity of 2680 mAh g-1. The studies to date have been limited to electrodes with a relatively low mass loading (< 3.5 mg cm-2), which has seriously restricted the areal capacity and its potential in practical devices. Ma...
Alkaline direct alcohol fuel cells (ADAFCs) represent an attractive alternative to hydrogen fuel cells for the more convenient storage, transportation, and lower cost of alcohols (e.g., methanol and ethanol) when compared with compressed hydrogen. However, the anode alcohol oxidation reaction (AOR) is generally plagued with high overpotential and s...
Hydrogen production through water electrolysis is of considerable interest for converting the intermittent electricity generated by renewable energy sources into storable chemical energy, but the typical water electrolysis process requires a high working voltage (>1.23 V) and produces oxygen at the anode in addition to hydrogen at the cathode. Here...
Monolayer materials are endowed with an additional degree of freedom to modulate electronic structures and catalytic performances. Here, we report a direct synthesis of monolayer Ni(OH)2 on electrodes by in situ electrochemical conversion and a fundamental investigation of their catalytic activity. The monolayer structure greatly promotes hydrogen...
Two-dimensional (2D) semiconductors have attracted intense interest for their unique photophysical properties, including large exciton binding energies and strong gate tunability, which arise from their reduced dimensionality1–5. Despite considerable efforts, a disconnect persists between the fundamental photophysics in pristine 2D semiconductors a...
The high cost of platinum (Pt)-group metal (PGM)-based catalysts used in proton-exchange membrane fuel cells (PEMFCs) poses a critical roadblock to their widespread adoption. Although using low PGM loading PEMFCs can largely address this challenge, high current density performance will be severely compromised consequently. To overcome this dilemma,...
Low‐dose, high‐resolution X‐ray imaging is vital for medical diagnostics and material/device analyses. Current X‐ray imagers are dominated by expensive inorganic materials via high‐temperature solid processes (up to 1700 °C, e.g., CsI:Tl) with heavy metal elements. It is essential to search for new materials as X‐ray imagers with low growth tempera...
Graphene with linear energy dispersion and weak electron-phonon interaction is highly anticipated to harvest hot-electrons in a broad wavelength range from ultraviolet to terahertz. However, the limited absorption (~2.3%) and serious backscattering of hot-electrons associated with single-layer graphene result in inadequate quantum yields, impeding...
The development of pressure sensor arrays capable of distinguishing the shape and texture details of objects is of considerable interest in the emerging fields of smart robots, prostheses, human-machine interfaces, and artificial intelligence (AI). Here we report an integrated pressure sensor array, by combining solution-processed two-dimensional (...
This perspective explores the development of van der Waals superlattices, which are manipulated and constructed at atomic thick level, and points out potential applications and possible future directions of this new class of materials.
The continued scaling of silicon-based electronics is quickly approaching its fundamental material limit, which has motivated worldwide efforts in exploring new electronic materials and unconventional device architectures. In particular, two-dimensional (2D) atomic crystals, halide perovskites, and self-assembled molecular monolayers represent prom...
The discovery of intrinsic ferromagnetism in ultrathin two-dimensional van der Waals crystals opens up exciting prospects for exploring magnetism in the ultimate two-dimensional limit. Here, we show that environmentally stable CrSe2 nanosheets can be readily grown on a dangling-bond-free WSe2 substrate with systematically tunable thickness down to...
Perovskites are highly promising candidates in future energy conversion and storage due to their rich diversities and readily tunable electronic properties. However, the poor morphology controllability and limited surface areas have severely limited their applications. We present a generalizable synthesis strategy to fabricate a library of one-dime...
Recently, the rapid development of the anion exchange membrane (AEM) shows a promising future in the commercialization of low cost and long-term stable AEM based fuel cells and water electrolyzers. AEM features an alkaline electrolyte, where non-precious metal ORR catalysts possess high ORR activity and can replace Pt catalysts. However, Pt is stil...
2D layered materials typically feature strong in‐plane covalent chemical bonding within each atomic layer and weak out‐of‐plane van der Waals (vdW) interactions between adjacent layers. The non‐bonding nature between neighboring layers naturally results in a vdW gap, in which various foreign species may be inserted without breaking the in‐plane cov...
The scalable preparation of high-purity monolayers is essential for practically integrating two-dimensional (2D) semiconductors in diverse technologies but remains a persistent challenge. Previous efforts to exfoliate 2D layered crystals by the organic ammonium intercalation usually produce few-layer nanosheets owing to a self-retarding effect that...
Room-temperature sodium-sulfur batteries (RT-Na-S batteries) are attractive for large-scale energy storage applications owing to their high storage capacity as well as the rich abundance and low cost of the materials. Unfortunately, their practical application is hampered by severe challenges, such as low conductivity of sulfur and its reduced prod...
Two-dimensional (2D) materials1,2 and the associated van der Waals (vdW) heterostructures3–7 have provided great flexibility for integrating distinct atomic layers beyond the traditional limits of lattice-matching requirements, through layer-by-layer mechanical restacking or sequential synthesis. However, the 2D vdW heterostructures explored so far...
The extraordinary mass activity of jagged Pt nanowires can substantially improve the economics of the hydrogen evolution reaction (HER). However, it is a great challenge to fully unveil the HER kinetics driven by the jagged Pt nanowires with their multiscale morphology. Herein we present an end-to-end framework that combines experiment, machine lea...
Downscaling catalyst size has long been used to promote the atomic utilization efficiency of catalysts. Single-atom catalysts (SACs) are the current end of this downscaling road, offering the potential of 100% metal atom utilization and excellent catalytic behavior compared with traditional nanoparticle catalysts. However, most development of SACs...
Two-dimensional (2D) semiconductors have attracted tremendous interest as atomically thin channels that could facilitate continued transistor scaling. However, despite many proof-of-concept demonstrations, the full potential of 2D transistors has yet to be determined. To this end, the fundamental merits and technological limits of 2D transistors ne...
