Andrew Thye Shen Wee

• Doctor of Philosophy
• Professor at National University of Singapore

The synthesis of atomically precise carbon nanostructures in ultra‐high vacuum has seen extensive progress on metal surfaces. However, this remains challenging on chemically inert surfaces. It is because the thermally activated C−C coupling encounters a severe “desorption problem” on weakly interacting substrates. In this study, we report an extrao...

The synthesis of atomically precise carbon nanostructures in ultra‐high vacuum has seen extensive progress on metal surfaces. However, this remains challenging on chemically inert surfaces. It is because the thermally activated C‐C coupling encounters a severe “desorption problem” on weakly interacting substrates. In this study, we report an extrao...

Researchers pursuing advanced photoelectric devices have discovered near room-temperature metal–insulator transitions (MIT) in nonvolatile VO2. Despite theoretical investigations suggesting that polaron dynamics mediate the MIT, direct experimental evidence remains scarce. In this study, we present direct evidence of the polaron state in insulating...

Porous materials play an important role in molecular adsorption and separation. However, understanding the mechanisms of molecular adsorption and separation into the pores remains a challenge. Herein, the adsorption of 1,3,5-tris(4-iodophenyl) benzene (TIPB) molecules onto a 2D covalent organic framework (COF) monolayer is studied by low-temperatur...

Materials with flat bands can serve as a promising platform to investigate strongly interacting phenomena. However, experimental realization of ideal flat bands is mostly limited to artificial lattices or moiré systems. Here, a general way is reported to construct 1D flat bands in phosphorene nanoribbons (PNRs) with a pentagonal nature: penta‐hexa‐...

In the past decades, the invention of scanning probe microscopy (SPM) as the versatile surface-based characterization of organic molecules has triggered significant interest throughout multidisciplinary fields. In particular, the bond-resolved imaging acquired by SPM techniques has extended its fundamental function of not only unraveling the chemic...

The kagome lattice is a versatile platform for investigating correlated electronic states. However, its realization in two-dimensional (2D) semiconductors for tunable device applications is still challenging. An alternative strategy to create kagome-like bands is to realize a coloring-triangle (CT) lattice in semiconductors through a distortion of...

The development of advanced electronic devices is contingent upon sustainable material development and pioneering research breakthroughs. Traditional semiconductor-based electronic technology faces constraints in material thickness scaling and energy efficiency. Atomically thin two-dimensional (2D) transition metal dichalcogenides (TMDs) have emerg...

The interaction of atomic orbitals at the interface of perovskite oxide heterostructures has been investigated for its profound impact on the band structures and electronic properties, giving rise to unique electronic states and a variety of tunable functionalities. In this study, we conducted an extensive investigation of the optical and electroni...

Flat bands and Dirac cones in materials are the source of the exotic electronic and topological properties. The Lieb lattice is expected to host these electronic structures, arising from quantum destructive interference. Nevertheless, the experimental realization of a 2D Lieb lattice remained challenging to date due to its intrinsic structural inst...

Conformational arrangements within nanostructures play a crucial role in shaping the overall configuration and determining the properties, for example in covalent/metal organic framework (COF/MOF) synthesis. In on-surface synthesis, conformational diversity often leads to uncontrollable or disordered structures. Therefore, exploration on controllin...

Phase engineering strategies in two-dimensional transition metal dichalcogenides (2D-TMDs) have garnered significant attention due to their potential applications in electronics, optoelectronics, and energy storage. Various methods, including direct synthesis, pressure control, and chemical doping, have been employed to manipulate structural transi...

Structural topology and symmetry of a two‐dimensional (2D) network play pivotal roles in defining its electrical properties and functionalities. Here, a binary buckled honeycomb lattice with C3v symmetry, which naturally hosts topological Dirac fermions and out‐of‐plane polarity, is proposed. It is successfully achieved in a group IV‐V compound, na...

Materials with topological flat bands can serve as a promising platform to investigate strongly interacting phenomena. However, experimental realization of ideal flat bands is mostly limited to artificial lattices or moir\'e systems. Here we report a general way to construct one-dimensional (1D) flat bands in phosphorene nanoribbons (PNRs) with pen...

Interactions among various electronic states such as CDW, magnetism, and superconductivity are of high significance in strongly correlated systems. While significant progress has been made in understanding the relationship between CDW and superconductivity, the interplay between CDW and magnetic order remains largely elusive. Kagome lattices, which...

The formation of plasmons through the collective excitation of charge density has generated intense discussions, offering insights into fundamental sciences and potential applications. While the underlying physical principles have been well-established, the effects of many-body interactions and orbital hybridization on plasmonic dynamics remain und...

The formation of plasmons through the collective excitation of charge density has generated intense discussions, offering insights to fundamental sciences and potential applications. While the underlying physical principles have been well-established, the effects of multibody interactions and orbital hybridization on plasmonic dynamics remain under...

Flat bands and Dirac cones in materials are at the source of the exotic electronic and topological properties. The Lieb lattice is expected to host these electronic structures, arising from quantum destructive interference. Nevertheless, the experimental realization of a two-dimensional Lieb lattice remained challenging to date due to its intrinsic...

The interaction of atomic orbitals at the interface of perovskite oxide heterostructures has been investigated for its profound impact on the band structures and electronic properties, giving rise to unique electronic states and a variety of tunable functionalities. In this study, we conducted an extensive investigation of the optical and electroni...

Conformational arrangements within nanostructures play a crucial role in shaping the overall configuration and determining the properties, for example in covalent/metal organic frameworks. In on-surface synthesis, conformational diversity often leads to uncontrollable or disordered structures. Therefore, the exploration of controlling and directing...

Phase engineering of two-dimensional transition metal dichalcogenides (2D-TMDs) offers opportunities for exploring unique phase-specific properties and achieving new desired functionalities. Here, we report a phase-selective in-plane heteroepitaxial method to grow semiconducting H-phase CrSe2. The lattice-matched MoSe2 nanoribbons are utilized as t...

On‐site diagnostic tests that accurately identify disease biomarkers lay the foundation for self‐healthcare applications. However, these tests routinely rely on single‐mode signals and suffer from insufficient accuracy, especially for multiplexed point‐of‐care tests (POCTs) within a few minutes. Here, this work develops a dual‐mode multiclassificat...

The availability of an ever‐expanding portfolio of 2D materials with rich internal degrees of freedom (spin, excitonic, valley, sublattice, and layer pseudospin) together with the unique ability to tailor heterostructures made layer by layer in a precisely chosen stacking sequence and relative crystallographic alignments, offers an unprecedented pl...

Combinations of phosphorus with main group III, IV, and V elements are theoretically predicted to generate 2D binary phosphides with extraordinary properties and promising applications. However, experimental synthesis is significantly lacking. Here, a general approach for preparing 2D binary phosphides is reported using single crystalline surfaces...

This year marks the 20th anniversary of the discovery of LaAlO 3 /SrTiO 3 (LAO/STO) oxide heterointerfaces. Since their discovery, transition metal oxide (TMO) interfaces have emerged as a fascinating and fast‐growing area of research, offering a variety of unique and exotic physical properties which has provided a strong impetus for the rapid adva...

In the pursuit of advanced photoelectric devices, researchers have uncovered near room-temperature metal-insulator transitions (MIT) in non-volatile VO2. Although theoretical investigations propose that polaron dynamics mediate the MIT, direct experimental evidence remains scarce. In this study, we present direct evidence of the polaron state in in...

MXenes, a class of two-dimensional materials, have garnered significant attention due to their versatile surface chemistry and customizable properties. In this study, we investigate the work function (WF) tuning capabilities of MXene Ti 3 C 2 T x , where T x denotes the surface termination, synthesized via both conventional hydrogen fluoride-etched...

Spin‐polarized two‐dimensional materials with large and tunable spin‐splitting energy promise the field of 2D spintronics. While graphene has been a canonical 2D material, its spin properties and tunability are limited. Here, we demonstrate the emergence of robust spin‐polarization in graphene with large and tunable spin‐splitting energy of up to 1...

Test‐and‐go” single‐nucleotide variation (SNV) detection within several minutes remains challenging, especially in low‐abundance samples, since existing methods face a trade‐off between sensitivity and testing speed. Sensitive detection usually relies on complex and time‐consuming nucleic acid amplification or sequencing. Here, we develop a graphen...

Advances in research of magnetic two-dimensional van der Waals (2D vdW) materials have opened up new opportunities in miniaturization of spintronic devices at the atomically thin limit. One major research thrust, which is the subject of this review, is that the magnetism of 2D vdW materials and their derived hetero-interface may be significantly af...

Rational design is an important approach to consider in the development of low-dimensional hybrid organic−inorganic perovskites (HOIPs). In this study, 1-butyl-1-methyl pyrrolidinium (BMP), 1-(3-aminopropyl)imidazole (API), and 1-butyl-3-methyl imidazolium (BMI) serve as prototypical ionic liquid components in bismuth-based HOIPs. Element-sensitive...

The intricate role of temperature in the structure–property relationship of manganese oxide nanoparticles (Mn3O4 NPs) remains an open question. In this study, we successfully synthesized Mn3O4 NPs using the hydrothermal method with two differing temperatures, namely, 90 and 150 °C. Interestingly, a smaller average particle size is found when Mn3O4...

Phase engineering in two-dimensional transition metal dichalcogenides (2D-TMDs) offers opportunities for exploring their unique properties of different phases and achieving new desired functionalities. Here, we report a selective synthetic strategy for the molecular beam epitaxy growth of the H-phase CrSe 2 induced by an in-plane heteroepitaxial te...

Precision chemistry demands miniaturized catalytic systems for sophisticated reactions with well-defined pathways. An ideal solution is to construct a nanoreactor system functioning as a chemistry laboratory to execute a full chemical process with molecular precision. However, existing nanoscale catalytic systems fail to in situ control reaction ki...

Two-dimensional (2D) perovskite oxide interfaces are ideal systems to uncover diverse emergent properties, such as the arising polaronic properties from short-range charge–lattice interactions. Thus, a technique to detect this quasiparticle phenomenon at the buried interface is highly coveted. Here, we report the observation of 2D small-polarons at...

The supermoiré lattice, built by stacking two moiré patterns, provides a platform for creating flat mini-bands and studying electron correlations. An ultimate challenge in assembling a graphene supermoiré lattice is in the deterministic control of its rotational alignment, which is made highly aleatory due to the random nature of the edge chirality...

Compared with traditional assay techniques, field-effect transistors (FETs) have advantages such as fast response, high sensitivity, being label-free, and point-of-care detection, while lacking generality to detect a wide range of small molecules since most of them are electrically neutral with a weak doping effect. Here, we demonstrate a photo-enh...

Covalent organic framework nanosheets (COF nanosheets) are two-dimensional crystalline porous polymers with in-plane covalent bonds and out-of-plane Van der Waals forces. Owing to the customizable structure, chemical modification, and ultra-high porosity, COF nanosheets show many fascinating properties unique to traditional two-dimensional material...

Ferroelectric materials are fascinating for their non-volatile switchable electric polarizations induced by the spontaneous inversion-symmetry breaking. However, in all of the conventional ferroelectric compounds, at least two constituent ions are required to support the polarization switching1,2. Here, we report the observation of a single-element...

Two-dimensional (2D) materials provide a platform for developing novel spintronic devices and circuits for low-power electronics. In particular, inducing magnetism and injecting spins in graphene have promised the emerging field of graphene spintronics. This review focuses on the magnetic proximity effect at the interface of 2D materials and magnet...

For epidemic prevention and control, molecular diagnostic techniques such as field‐effect transistor (FET) biosensors is developed for rapid screening of infectious agents, including Mycobacterium tuberculosis, SARS‐CoV‐2, rhinovirus, and others. They obtain results within a few minutes but exhibit diminished sensitivity (<75%) in unprocessed biolo...

The supermoir\'e lattice, built by stacking two moir\'e patterns, provides a platform for creating flat mini-bands and studying electron correlations. An ultimate challenge in assembling a graphene supermoir\'e lattice is in the deterministic control of its rotational alignment, which is made highly probabilistic due to the random nature of the edg...

Liquid methanol has the potential to be the hydrogen energy carrier and storage medium for the future green economy. However, there are still many challenges before zero-emission, affordable molecular H 2 can be extracted from methanol with high performance. Here, we present noble-metal-free Cu–WC/W plasmonic nanohybrids which exhibit unsurpassed s...

Interlayer electronic coupling in two-dimensional materials enables tunable and emergent properties by stacking engineering. However, it also results in significant evolution of electronic structures and attenuation of excitonic effects in two-dimensional semiconductors as exemplified by quickly degrading excitonic photoluminescence and optical non...

Owing to its inherent non‐trivial geometry, the unique structural motif of the recently discovered Kagome topological superconductor AV3Sb5 (A = K, Rb, Cs) is an ideal host of diverse topologically non‐trivial phenomena, including giant anomalous Hall conductivity, topological charge order, charge density wave (CDW), and unconventional superconduct...

The upsurge of low-dimensional Dion–Jacobson (DJ) phase perovskites brought significant interests in view of their appealing stability against harsh environmental conditions as well as their promising performance in optoelectronic applications. Few reports to date have concentrated on the fundamental relationship of fine-tuning control of diamine-b...

The kagome lattice has attracted intense interest with the promise of realizing topological phases built from strongly interacting electrons. However, fabricating two-dimensional (2D) kagome materials with nontrivial topology is still a key challenge. Here, we report the growth of single-layer iron germanide kagome nanoflakes by molecular beam epit...

Two-dimensional (2D) perovskite oxide interfaces are ideal systems where diverse emergent properties can be uncovered.The formation and modification of polaronic properties due to short-range strong charge-lattice interactions of 2D interfaces remains hugely intriguing.Here, we report the direct observation of small-polarons at the LaAlO3/SrTiO3 (L...

Owing to its inherent non-trivial geometry, the unique structural motif of the recently discovered Kagome topological superconductor AV3Sb5 is an ideal host of diverse topologically non-trivial phenomena, including giant anomalous Hall conductivity, topological charge order, charge density wave, and unconventional superconductivity. Despite possess...

Valleytronics is a promising candidate to address low-energy signal transport on chip, leveraging the valley pseudospin of electrons as a new degree of freedom to encode, process and store information1–7. However, valley-carrier nanocircuitry is still elusive, because it essentially requires valley transport that overcomes three simultaneous challe...

Exciton is a bosonic quasiparticle consisting of a pair of electron and hole, with promising potentials for optoelectronic device applications, such as exciton transistors, photodetectors and light emitting devices. However, the charge-neutral nature of excitons renders them challenging to manipulate using electronics. Here we present the generatio...

The tunable control in the inorganic octahedral framework of hybrid perovskites offers potential applications in photovoltaics, solid-state lighting, and radiation detection. However, the implication of the structure and optoelectronic properties pose challenges due to competition between organic− inorganic coupling and intraoctahedral interactions...

Ferroelectric materials play an important role in a wide spectrum of semiconductor technologies and device applications. Two-dimensional (2D) van der Waals (vdW) ferroelectrics with surface-insensitive ferroelectricity that is significantly different from their traditional bulk counterparts have further inspired intensive interest. Integration of f...

The effects of atomic-scale disorder and charge (de)localization hold significant importance, and they provide essential insights to unravel the role that strong and weak correlations play in condensed matter systems. In the case of perovskite oxide heterostructures, while disorders introduced via various external stimuli have strong influences ove...

Monochromators for synchrotron radiation beamlines typically use perfect crystals for the hard X-ray regime and gratings for soft X-rays. There is an intermediate range, typically 1–3 keV (tender X-rays), which common perfect crystals have difficulties covering and gratings have low efficiency, although some less common crystals with high d-spacing...

The effects of atomic-scale disorder and charge (de)localization holds significant importance,and they provide essential insights in unravelling the role that strong and weak correlations play in condensed matter systems.For perovskite oxide heterostructures,while disorders introduced via various external stimuli have strong influences on the (de)l...

Positive magnetoresistance (PMR) and negative magnetoresistance (NMR) describe two opposite responses of resistance induced by a magnetic field. Materials with giant PMR are usually distinct from those with giant NMR due to different physical natures. Here, we report the unusual photomagnetoresistance in the van der Waals heterojunctions of WSe 2 /...

2D materials with common hexagonal crystal structures, such as graphene, hexagonal boron nitride, and transition metal dichalcogenides have attracted great interest due to their novel physical and chemical properties. Pentagonal transition metal dichalcogenides (TMDs) exhibit distinct optical, electrical, and chemical properties, with valuable func...

Complex correlated states emerging from many-body interactions between quasiparticles (electrons, excitons and phonons) are at the core of condensed matter physics and material science. In low-dimensional materials, quantum confinement affects the electronic, and subsequently, optical properties for these correlated states. Here, by combining photo...

Epitaxial growth is a powerful tool for synthesizing heterostructures and integrating multiple functionalities. However, interfacial mixing can readily occur and significantly modify the properties of layered structures, particularly for those containing energy storage materials with smaller cations. Here, we show a two-step sequence involving the...

The chemical bond is of central interest in chemistry, and it is of significance to study the nature of intermolecular bonds in real‐space. Herein, non‐contact atomic force microscopy (nc‐AFM) and low‐temperature scanning tunneling microscopy (LT‐STM) are employed to acquire real‐space atomic information of molecular clusters, i.e., monomer, dimer,...

Many-body interactions between quasiparticles (electrons, excitons, and phonons) have led to the emergence of new complex correlated states and are at the core of condensed matter physics and material science. In low-dimensional materials, unique electronic properties for these correlated states could significantly affect their optical properties....

Monolayer VSe2, featuring both charge density wave and magnetism phenomena, represents a unique van der Waals magnet in the family of metallic two-dimensional transition-metal dichalcogenides (2D-TMDs). Herein, by means of in-situ microscopic and spectroscopic techniques, including scanning tunneling microscopy/spectroscopy, synchrotron X-ray and a...

Magnetism in monolayer (ML) VSe2 has attracted broad interest in spintronics while existing reports have not reached consensus. Using element-specific X-ray magnetic circular dichroism, a magnetic transition in ML VSe2 has been demonstrated at the contamination-free interface between Co and VSe2. Via interfacial hybridization with Co atomic overlay...

Polycyclic hydrocarbons (PHs) share the same hexagonal structure of sp2 carbons as graphene but possess an energy gap due to quantum confinement effect. PHs can be synthesized by a bottom-up strategy starting from small building blocks covalently bonded into large 2D organic sheets. Further investigation of the role of the covalent bonding/coupling...

We report direct measurement of spin-splitting energy in magnetic graphene using Landau fan shifts. The magnetic graphene is realized by stacking graphene on a magnetic insulating oxide Tm3Fe5O12, and its Landau fan shift shows a strong spin splitting energy of 132 meV at 2 K. Strikingly, the spin splitting energy can be tuned over a broad range be...

2D platinum ditelluride (PtTe2) has received significant attention for 2D photodetector applications due to its novel physical properties. One of the critical factors that affect device performance is the film quality. Here, using molecular beam epitaxy, we investigate the role of growth temperature in determining the film quality of PtTe2 on highl...

Well-ordered spin arrays are desirable for next-generation molecule-based magnetic devices, yet their synthetic method remains a challenging task. Herein, we demonstrate the realization of two-dimensional supramolecular spin arrays on surfaces via halogen-bonding molecular self-assembly. A bromine-terminated perchlorotriphenylmethyl radical with ne...

Room-temperature (RT) ferromagnetic atomically thin transition metal chalcogenides (TMCs) provide a novel platform for discovering new physical phenomena in the two-dimensional (2D) limit and developing the next-generation spintronic applications. Recent progress in exploring the RT ferromagnetism in 2D TMCs have attracted significant interest from...

Alloying offers an efficient strategy to tune the bandgap of two‐dimensional (2D) layered materials, enabling them to tailor the optical and electronic attributes without compromising the structural integrity. Here the authors report the synthesis of a series of ternary InSe1−xSx and InSe1−yTey alloys possessing ε‐polymorph and single crystalline s...

Two-dimensional (2D) materials provide a platform for developing novel spintronic devices and circuits for low-power electronics. In particular, inducing magnetism and injecting spins in graphene have promised the emerging field of graphene spintronics. This review focuses on the magnetic proximity effect at the interface of 2D materials and magnet...

The recent emergence of two-dimensional transition metal dichalcogenides (2D TMDs) has led to a rapid burgeoning of the field due to their novel electronic and optical properties with potential electronics/photonics applications. Many organic materials have also exhibited great success in the field of flexible electronics. The integration of 2D TMD...

A one-of-a-kind text offering an introduction to the use of spectroscopic ellipsometry for novel material characterization In Introduction to Spectroscopic Ellipsometry of Thin Film Materials: Instrumentation, Data Analysis and Applications, a team of eminent researchers delivers an incisive exploration of how the traditional experimental techniqu...