Observation of Three-State Nematicity and Domain Evolution in Atomically Thin Antiferromagnetic NiPS.

Nickel phosphorus trisulfide (NiPS), a van der Waals 2D antiferromagnet, has received significant interest for its intriguing properties in recent years. However, despite its fundamental importance in the physics of low-dimensional magnetism and promising potential for technological applications, the study of magnetic domains in NiPS down to an atomically thin state is still lacking. Here, we report the layer-dependent magnetic characteristics and magnetic domains in NiPS by employing linear dichroism spectroscopy, polarized microscopy, spin-correlated photoluminescence, and Raman spectroscopy.

Synthesis of 2D layered transition metal (Ni, Co) hydroxides via edge-on condensation.

Layered transition metal hydroxides (LTMHs) with transition metal centers sandwiched between layers of coordinating hydroxide anions have attracted considerable interest for their potential in developing clean energy sources and storage technologies. However, two-dimensional (2D) LTMHs remain largely understudied in terms of physical properties and applications in electronic devices. Here, for the first time we report > 20 μm α-Ni(OH) 2D crystals, synthesized from hydrothermal reaction.

Rapid, Multianalyte Detection of Opioid Metabolites in Wastewater.

By monitoring opioid metabolites, wastewater-based epidemiology (WBE) could be an excellent tool for real-time information on the consumption of illicit drugs. A key limitation of WBE is the reliance on costly laboratory-based techniques that require substantial infrastructure and trained personnel, resulting in long turnaround times. Here, we present an aptamer-based graphene field effect transistor (AptG-FET) platform for simultaneous detection of three different opioid metabolites.

Electronic Raman scattering in the 2D antiferromagnet NiPS.

Correlated-electron systems have long been an important platform for various interesting phenomena and fundamental questions in condensed matter physics. As a pivotal process in these systems, transitions have been suggested as a key factor toward realizing optical spin control in two-dimensional (2D) magnets. However, it remains unclear how excitations behave in quasi-2D systems with strong electronic correlation and spin-charge coupling.

Graphene-Based Environmental Sensors: Electrical and Optical Devices.

In this review paper, we summarized the recent progress of using graphene as a sensing platform for environmental applications. Especially, we highlight the electrical and optical sensing devices developed based on graphene and its derivatives. We discussed the role of graphene in these devices, the sensing mechanisms, and the advantages and disadvantages of specific devices.

Spin-induced linear polarization of photoluminescence in antiferromagnetic van der Waals crystals.

Antiferromagnets are promising components for spintronics due to their terahertz resonance, multilevel states and absence of stray fields. However, the zero net magnetic moment of antiferromagnets makes the detection of the antiferromagnetic order and the investigation of fundamental spin properties notoriously difficult. Here, we report an optical detection of Néel vector orientation through an ultra-sharp photoluminescence in the van der Waals antiferromagnet NiPS from bulk to atomically thin flakes.

Modulation Doping via a Two-Dimensional Atomic Crystalline Acceptor.

Two-dimensional nanoelectronics, plasmonics, and emergent phases require clean and local charge control, calling for layered, crystalline acceptors or donors. Our Raman, photovoltage, and electrical conductance measurements combined with calculations establish the large work function and narrow bands of α-RuCl enable modulation doping of exfoliated single and bilayer graphene, chemical vapor deposition grown graphene and WSe, and molecular beam epitaxy grown EuS. We further demonstrate proof of principle photovoltage devices, control via twist angle, and charge transfer through hexagonal boron nitride.

A cleanroom in a glovebox.

The exploration of new materials, novel quantum phases, and devices requires ways to prepare cleaner samples with smaller feature sizes. Initially, this meant the use of a cleanroom that limits the amount and size of dust particles. However, many materials are highly sensitive to oxygen and water in the air.

Deep-Learning-Enabled Fast Optical Identification and Characterization of 2D Materials.

Advanced microscopy and/or spectroscopy tools play indispensable roles in nanoscience and nanotechnology research, as they provide rich information about material processes and properties. However, the interpretation of imaging data heavily relies on the "intuition" of experienced researchers. As a result, many of the deep graphical features obtained through these tools are often unused because of difficulties in processing the data and finding the correlations.

Dielectrophoresis assisted rapid, selective and single cell detection of antibiotic resistant bacteria with G-FETs.

The rapid increase in antibiotic resistant pathogenic bacteria has become a global threat, which besides the development of new drugs, requires rapid, cheap, scalable, and accurate diagnostics. Label free biosensors relying on electrochemical, mechanical, and mass based detection of whole bacterial cells have attempted to meet these requirements. However, the trade-off between selectivity and sensitivity of such sensors remains a key challenge.

Enhanced Raman Scattering on Nine 2D van der Waals Materials.

Since the discovery of graphene-enhanced Raman scattering in 2010, other 2D materials have been reported to show a Raman enhancement effect on molecules adsorbed on their surfaces. The mechanism for this phenomenon, however, still remains elusive. Here we performed a comparative investigation of the Raman enhancement effect on nine 2D materials with an identical number of copper phthalocyanine (CuPc) as probe molecules.

Chemical and Bio Sensing Using Graphene-Enhanced Raman Spectroscopy.

Graphene is a two-dimensional (2D) material consisting of a single sheet of sp² hybridized carbon atoms laced in a hexagonal lattice, with potentially wide usage as a Raman enhancement substrate, also termed graphene-enhanced Raman scattering (GERS), making it ideal for sensing applications. GERS improves upon traditional surface-enhanced Raman scattering (SERS), combining its single-molecule sensitivity and spectral fingerprinting of molecules, and graphene's simple processing and superior uniformity. This enables fast and highly sensitive detection of a wide variety of analytes.

Probing the Domain Architecture in 2D α-Mo C via Polarized Raman Spectroscopy.

MXenes are emerging 2D materials with intriguing properties such as excellent stability and high conductivity. Here, a systematic study on the Raman spectra of 2D α-Mo C (molybdenum carbide), a promising member in MXene family, is conducted. Six experimentally observed Raman modes from ultrathin α-Mo C crystal are first assigned with the assistance of phonon dispersion calculated from density functional theory.

Anomalous Phonon Modes in Black Phosphorus Revealed by Resonant Raman Scattering.

Black phosphorus (BP), a layered material with puckered crystalline structure in each layer, has drawn intense interest due to its unique optical and electronic properties. In particular, the intricate Raman scattering effect in BP is intriguing and provides a platform for researchers to probe the physical properties of BP in depth. Here we report the first observation of anomalous modes with the frequency in the range of 100-900 cm in BP due to the resonant Raman effect.