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The bulk phase of transition metal nitrides (TMNs) has long been a subject of extensive investigation due to their utility as coating materials, electrocatalysts, and diffusion barriers, attributed to their high conductivity and refractory properties. Downscaling TMNs into two-dimensional (2D) forms would provide valuable members to the existing 2D materials repertoire, with potential enhancements across various applications. Moreover, calculations have anticipated the emergence of uncommon physical phenomena in TMNs at the 2D limit. In this study, we use the atomic substitution approach to synthesize 2D W 5 N 6 with tunable thicknesses from tens of nanometers down to 2.9 nm. The obtained flakes exhibit high crystallinity and smooth surfaces. Electrical measurements on 15 samples show an average electrical conductivity of 161.1 S/cm, which persists while thickness decreases from 45.6 to 2.9 nm. The observed weak gate-tuning effect suggests the semimetallic nature of the synthesized 2D W 5 N 6 . Further investigation of the conversion mechanism elucidates the crucial role of chalcogen vacancies in the precursor for initiating the reaction and strain in propagating the conversion. Our work introduces a desired semimetallic crystal to the 2D material library with mechanistic insights for future design of the synthesis.

Resonant Raman spectra of a two-dimensional (2D) non-van der Waals (vdW) material, molybdenum nitride (Mo 5 N 6 ), are measured across varying thicknesses, ranging from a few to tens of nanometers. Fifteen distinct Raman peaks are observed experimentally, and their assignments are made using first-principles calculations for the most stable AABB-stacking structure of Mo 5 N 6 . The assignments are further supported by angular-dependent Raman measurements for all peaks, except the most intense one at 215 cm -1 . Calculations reveal that the 215 cm -1 peak does not appear for three-dimensional molybdenum nitrides and is not a first-order Raman-active mode. We further investigated the origin of the 215 cm -1 peak and assigned it as a defect-induced double-resonance peak. Moreover, thickness-dependent Raman measurements reveal that both the 215 and 540 cm -1 peaks─assigned to out-of-plane and in-plane modes, respectively─blue shift as thickness increases, reaching a plateau around 20 nm. This thickness-dependent Raman shift over a wide thickness range is nontrivial compared to other common vdW 2D materials and is attributed to the much stronger stacking interaction between the constituent layers in non-vdW materials. This finding highlights Raman spectroscopy as a valuable tool for characterizing the thickness of 2D non-vdW materials.

Defects around the surface and grain boundaries of perovskite films normally cause severe nonradiative recombination and imbalanced charge carrier transport, further limiting both the efficiency and stability of perovskite solar cells (PSCs). To tackle this critical issue, we propose a chemical bridge strategy to reconstruct the interface using organometallic molecules. The commercially available molecule bis(diphenylphosphino)ferrocene (FcP 2 ), with a unique bridge molecular structure, anchors and chelates Pb atoms by forming strong Pb-P bonds and further passivates both surfaces and grain boundaries. Detailed characterization revealed that bridge molecule FcP 2 reconstruction can effectively suppress nonradiative recombination, and the electron delocalization properties of the ferrocene core can further achieve more balanced interfacial carrier transport. The resultant N-i-P PSC device outputs close to 25% efficiency together with one of the best reported operational stabilities, maintaining over 95% of the initial efficiency after 1000 h of continuous operation at the maximum power point under 1-sun illumination.

Extending the inventory of two-dimensional (2D) materials remains highly desirable, given their excellent properties and wide applications. Current studies on 2D materials mainly focus on the van der Waals (vdW) materials since the discovery of graphene, where properties of atomically thin layers have been found to be distinct from their bulk counterparts. Beyond vdW materials, there are abundant non-vdW materials that can also be thinned down to 2D forms, which are still in their early stage of exploration. In this review, we focus on the downscaling of non-vdW materials into 2D forms to enrich the 2D materials family. This underexplored group of 2D materials could show potential promise in many areas such as electronics, optics, and magnetics, as has happened in the vdW 2D materials. Hereby, we will focus our discussion on their electronic properties and applications of them. We aim to motivate and inspire fellow researchers in the 2D materials community to contribute to the development of 2D materials beyond the widely studied vdW layered materials for electronic device applications. We also give our insights into the challenges and opportunities to guide researchers who are desirous of working in this promising research area.

Nanomaterials with unique structures and components play a crucial role in nanomedicine. In this study, we discovered that the inhomogeneous Au 2 S constructed by cation exchange and acid etching could dissipate energy in different forms after absorbing multichromatic light, which could be used to achieve the integrated diagnosis and treatment of tumors, respectively. Folic acid modified Au 2 S ringed nanoparticles (FA-Au 2 S RNs) with an assembly-like structure were demonstrated to result in better PA imaging performance and generate more reactive oxygen species (O2· - , ·OH, and 1 O 2 ) than folic acid modified Au 2 S triangular nanoparticles (FA-Au 2 S TNs). Finite element analyses determined the reason for the high absorbance properties and synergistic enhancement of plasma resonance in the assembly-like structure of Au 2 S RNs. Both FA-Au 2 S nanostructures were modified with folic acid and injected into 4T1 tumor-bearing mice via the tail vein. The best PA imaging contrast was obtained under 700 nm laser illumination, and the most effective PDT antitumor activity was achieved under 1064 nm laser illumination. The PA average of the tumor in the FA-Au 2 S RN group was approximately 2 times higher than that of the FA-Au 2 S TN group at 24 h of injection. The PA imaging results of intratumorally injected FA-Au 2 S RNs proved that they were still able to show better PA signal enhancement at 24 h postinjection. Our study demonstrates that FA-Au 2 S nanomaterials with unique structures and special properties can be reliably produced using strictly controlled chemical synthesis. It further provides a strategy for the construction of highly sensitive PA imaging platforms and efficient PDT antitumor agents that exploit wavelength-dependent energy dissipation mechanisms.

Lateral confinement of layered, two-dimensional (2D) materials has uniquely enabled the exploration of several topological phenomena in electron transport due to the well-defined nanoscale cross-sections and perimeters. At present, research on laterally confined 2D materials is constrained by the lack of synthesis methods that can reliably and controllably produce nanostructures with narrow widths and high aspect ratios. We demonstrate the use of thermomechanical nanomolding (TMNM) to fabricate nanowires of six layered materials (Te, In 2 Se 3 , Bi 2 Te 3 , Bi 2 Se 3 , GaSe, and Sb 2 Te 3 ) with widths of 40 nm and aspect ratios above 100. During molding, the van der Waals (vdW) layers rotate by 90° from the horizontal direction in the bulk feedstock to the vertical direction in the molded nanowire, such that the layers are aligned along the nanowire length. We find that interfacial diffusion and surface energy minimization drive nanowire formation during TMNM, often resulting in single-crystalline nanowires with consistent crystallographic orientation.

Nanoscale strain control of exciton funneling is an increasingly critical tool for the scalable production of single photon emitters (SPEs) in two-dimensional materials. However, conventional far-field optical microscopies remain constrained in spatial resolution by the diffraction limit and thus can provide only a limited description of nanoscale strain localization of SPEs. Here, we quantify the effects of nanoscale heterogeneous strain on the energy and brightness of GaSe SPEs on nanopillars with correlative cathodoluminescence, photoluminescence, and atomic force microscopy, supported by density functional theory simulations. We report the strain-localized SPEs have a broad range of emission wavelengths from 620 to 900 nm. We reveal substantial strain-controlled SPE wavelength tunability over a ∼100 nm spectral range and 2 orders of magnitude enhancement in the SPE brightness at the pillar center due to Type-I exciton funneling. In addition, we show that radiative biexciton cascade processes contribute to observed CL photon superbunching. Also, the GaSe SPEs show excellent stability, where their properties remain unchanged after electron beam exposure. We anticipate that this comprehensive study on the nanoscale strain control of two-dimensional SPEs will provide key insights to guide the development of truly deterministic quantum photonics.

Oxidative stress accompanying the reactive oxygen species (ROS) burst governs immunocyte infiltration, activation, and differentiation in tumor microenvironments and thus can elicit robust antitumor immunity. Here, we identify a photoactive metal-organic coordination polymer (MOCP), composed of an organometallic core formed by cytotoxic mitoxantrone (MTX) acylates and photosensitive Ru(BIQ)-HDBB [BIQ = 2,2'-biquinoline, HDBB = 4,4'-di(4-benzoato)-2,2'-bipyridine] linked by Fe(II) ions via coordinate covalent bonds and an amphipathic shell encapsulating cholesterol-modified siRNA against GPX4 (siGPX4) via hydrophobic force, to precisely amplify intracellular oxidative storm. MOCPs simultaneously encapsulated MTX, Ru, and siGPX4 with efficiencies >98% and loaded Fe with efficiencies of ∼0.49%. With longer blood circulation and higher tumor accumulation, MOCPs with a 670 nm LED irradiation generate abundant ROS to induce biomembrane dysfunction and subsequently contribute to ferroptotic and immunogenic cell death, which drive tumor-associated antigen-specific immunity. MTX analogs contributed to Type I immunogenic cell death (ICD), while oxidative storm served as a damager for endo/lysosomal escape, an initiator for ferroptosis, and an inducer for type II ICD. Moreover, the blockade of CD73 that reduces extoATP catabolism unleashes immunosuppression, finally enhancing antitumor immune stimulation of MOCPs to promote orthotopic mammary cancer regression and prevent postoperative advanced cancer from recurrence and metastasis. MOCPs by exposing sufficient antigenicity thus provide a platform to synergize immune checkpoint inhibitors for the treatment of immunologically cold tumors.

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. This platform provides a reliable, rapid, and inexpensive method for quantitative analysis of opioid metabolites in wastewater. The platform delivers a limit of detection 2-3 orders of magnitude lower than previous reports, but in line with the concentration range (pg/mL to ng/mL) of these opioid metabolites present in real samples. To enable multianalyte detection, we developed a facile, reproducible, and high-yield fabrication process producing 20 G-FETs with integrated side gate platinum (Pt) electrodes on a single chip. Our devices achieved the selective multianalyte detection of three different metabolites: noroxycodone (NX), 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP), and norfentanyl (NF) in wastewater diluted 20× in buffer.

The combination of antiangiogenesis and chemotherapy regimens with cancer immunotherapy has the potential to synergistically boost antitumor immunity. Herein, we report the construction of two bioresponsive nanoparticles, namely, Podo-NP and CbP-NP, comprising prodrugs of podophyllotoxin (Podo) and carboplatin, respectively. Sequential treatment with esterase-responsive Podo-NP, redox-sensitive CbP-NP, and a CD40 agonist promotes antitumor T cell response. Podo-NP suppresses angiogenesis by preventing proliferation and migration of endothelial cells, sprouting of neovessels, formation of tubules, and stabilization of newly formed vessels. Vascular endothelial growth factor blockade and endostatin stimulation normalize tortuous tumor vasculatures to allow efficient infiltration of effector immune cells. Subsequent treatment with CbP-NP arrests the cell-division cycle and elicits the apoptosis of tumor cells. CD40 agonist activates antigen-presenting cells to process the released tumor-associated antigens from dying tumor cells, thus reversing immunosuppressive tumor microenvironments. Sequential delivery of antiangiogenic and chemotherapeutic agents with bioresponsive NPs activates tumor microenvironments and synergizes with CD40 agonist to regress transplanted tumors and inhibit disseminated tumors in a lung cancer mouse model.

We report a temperature-dependent Raman spectroscopy study of few-layer black phosphorus (BP) with varied incident polarization and sample thickness. The Raman-active modes A g 1 , B 2g , and A g 2 exhibit a frequency downshift, while their line width tends to increase with increasing temperature. To understand the details of these phenomena, we perform first-principles density functional theory calculations on freestanding monolayer BP. The effect of thermal expansion is included by constraining the temperature-dependent lattice constant. The study of the temperature-induced shift of the phonon frequencies is carried out using ab initio molecular dynamics simulations. The normal-mode frequencies are calculated by identifying the peak positions from the magnitude of the Fourier transform of the total velocity autocorrelation. Anharmonicity induces a frequency shift for each individual mode, and the three- and four-phonon process coefficients are extracted. These results are compared with those obtained from many-body perturbation theory, giving access to phonon lifetimes and lattice thermal conductivity. We establish that the frequency downshift is primarily due to phonon-phonon scattering while thermal expansion only contributes indirectly by renormalizing the phonon-phonon scattering. Overall, the theoretical results are in excellent agreement with experiment, thus showing that controlling phonon scattering in BP could result in better thermoelectric devices or transistors that dissipate heat more effectively when confined to the nanoscale.

Spurred by recent progress in medicinal chemistry, numerous lead compounds have sprung up in the past few years, although the majority are hindered by hydrophobicity, which greatly challenges druggability. In an effort to assess the potential of platinum (Pt) candidates, the nanosizing approach to alter the pharmacology of hydrophobic Pt(IV) prodrugs in discovery and development settings is described. The construction of a self-assembled nanoparticle (NP) platform, composed of amphiphilic lipid-polyethylene glycol (PEG) for effective delivery of Pt(IV) prodrugs capable of resisting thiol-mediated detoxification through a glutathione (GSH)-exhausting effect, offers a promising route to synergistically improving safety and efficacy. After a systematic screening, the optimized NPs (referred to as P6 NPs) exhibited small particle size (99.3 nm), high Pt loading (11.24%), reliable dynamic stability (∼7 days), and rapid redox-triggered release (∼80% in 3 days). Subsequent experiments on cells support the emergence of P6 NPs as a highly effective means of transporting a lethal dose of cargo across cytomembranes through macropinocytosis. Upon reduction by cytoplasmic reductants, particularly GSH, P6 NPs under disintegration released sufficient active Pt(II) metabolites, which covalently bound to target DNA and induced significant apoptosis. The PEGylation endowed P6 NPs with in vivo longevity and tumor specificity, which were essential to successfully inhibiting the growth of cisplatin-sensitive and -resistant xenograft tumors, while effectively alleviating toxic side-effects associated with cisplatin. P6 NPs are, therefore, promising for overcoming the bottleneck in the development of Pt drugs for oncotherapy.

Transition-metal dichalcogenides (TMDs) have emerged in recent years as a special group of two-dimensional materials and have attracted tremendous attention. Among these TMD materials, molybdenum disulfide (MoS 2 ) has shown promising applications in electronics, photonics, energy, and electrochemistry. In particular, the defects in MoS 2 play an essential role in altering the electronic, magnetic, optical, and catalytic properties of MoS 2 , presenting a useful way to engineer the performance of MoS 2 . The mechanisms by which lattice defects affect the MoS 2 properties are unsettled. In this work, we reveal systematically how lattice defects and substrate interface affect MoS 2 electronic structure. We fabricated single-layer MoS 2 by chemical vapor deposition and then transferred onto Au, single-layer graphene, hexagonal boron nitride, and CeO 2 as substrates and created defects in MoS 2 by ion irradiation. We assessed how these defects and substrates affect the electronic structure of MoS 2 by performing X-ray photoelectron spectroscopy, Raman and photoluminescence spectroscopies, and scanning tunneling microscopy/spectroscopy measurements. Molecular dynamics and first-principles based simulations allowed us to conclude the predominant lattice defects upon ion irradiation and associate those with the experimentally obtained electronic structure. We found that the substrates can tune the electronic energy levels in MoS 2 due to charge transfer at the interface. Furthermore, the reduction state of CeO 2 as an oxide substrate affects the interface charge transfer with MoS 2 . The irradiated MoS 2 had a faster hydrogen evolution kinetics compared to the as-prepared MoS 2 , demonstrating the concept of defect controlled reactivity in this phase. Our findings provide effective probes for energy band and defects in MoS 2 and show the importance of defect engineering in tuning the functionalities of MoS 2 and other TMDs in electronics, optoelectronics, and electrochemistry.

Plasmons in graphene nanostructures show great promise for mid-infrared applications ranging from a few to tens of microns. However, mid-infrared plasmonic resonances in graphene nanostructures are usually weak and narrow-banded, limiting their potential in light manipulation and detection. Here, we investigate the coupling among graphene plasmonic nanostructures and further show that, by engineering the coupling, enhancement of light-graphene interaction strength and broadening of spectral width can be achieved simultaneously. Leveraging the concept of coupling, we demonstrate a hybrid two-layer graphene nanoribbon array which shows 5-7% extinction within the entire 8-14 μm (∼700-1250 cm -1 ) wavelength range, covering one of the important atmosphere "infrared transmission windows". Such coupled hybrid graphene plasmonic nanostructures may find applications in infrared sensing and free-space communications.

Layered gallium telluride (GaTe) has attracted much attention recently, due to its extremely high photoresponsivity, short response time, and promising thermoelectric performance. Different from most commonly studied two-dimensional (2D) materials, GaTe has in-plane anisotropy and a low symmetry with the C2h(3) space group. Investigating the in-plane optical anisotropy, including the electron-photon and electron-phonon interactions of GaTe is essential in realizing its applications in optoelectronics and thermoelectrics. In this work, the anisotropic light-matter interactions in the low-symmetry material GaTe are studied using anisotropic optical extinction and Raman spectroscopies as probes. Our polarized optical extinction spectroscopy reveals the weak anisotropy in optical extinction spectra for visible light of multilayer GaTe. Polarized Raman spectroscopy proves to be sensitive to the crystalline orientation of GaTe, and shows the intricate dependences of Raman anisotropy on flake thickness, photon and phonon energies. Such intricate dependences can be explained by theoretical analyses employing first-principles calculations and group theory. These studies are a crucial step toward the applications of GaTe especially in optoelectronics and thermoelectrics, and provide a general methodology for the study of the anisotropy of light-matter interactions in 2D layered materials with in-plane anisotropy.

Black phosphorus (BP) is a highly anisotropic allotrope of phosphorus with great promise for fast functional electronics and optoelectronics. We demonstrate the controlled structural modification of few-layer BP along arbitrary crystal directions with sub-nanometer precision for the formation of few-nanometer-wide armchair and zigzag BP nanoribbons. Nanoribbons are fabricated, along with nanopores and nanogaps, using a combination of mechanical-liquid exfoliation and in situ transmission electron microscopy (TEM) and scanning TEM nanosculpting. We predict that the few-nanometer-wide BP nanoribbons realized experimentally possess clear one-dimensional quantum confinement, even when the systems are made up of a few layers. The demonstration of this procedure is key for the development of BP-based electronics, optoelectronics, thermoelectrics, and other applications in reduced dimensions.