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As a two-dimensional semiconductor with many physical properties, including, notably, layer-controlled electronic bandgap and coupled spin-valley degree of freedom, monolayer MoSe2 is a strong candidate material for next-generation opto- and valley-electronic devices. However, due to substrate effects such as lattice mismatch and dielectric screening, preserving the monolayer's intrinsic properties remains challenging. This issue is generally significant for metallic substrates whose active surfaces are commonly utilized to achieve direct chemical or physical vapor growth of the monolayer films. Here, we demonstrate high-temperature-annealed Au foil with well-defined (100) facets as a weakly interacting substrate for atmospheric pressure chemical vapor deposition of highly crystalline monolayer MoSe2. Low-temperature scanning tunneling microscopy/spectroscopy measurements reveal a honeycomb structure of MoSe2 with a quasi-particle bandgap of 1.96 eV, a value comparable with other weakly interacting systems such as MoSe2/graphite. Density functional theory calculations indicate that the Au(100) surface exhibits the preferred energetics to electronically decouple from MoSe2, compared with the (110) and (111) crystal planes. This weak coupling is critical for the easy transfer of monolayers to another host substrate. Our study demonstrates a practical means to produce high-quality monolayers of transition-metal dichalcogenides, viable for both fundamental and application studies.

Graphene nanostructures with specified edge terminations has attracted considerable attention owing to their unique electronic properties induced by the edges. However, an efficient way to controllably fabricate such nanostructures is still highly desired. Here, we show that graphene nanostructures with zigzag edge terminations can be easily and efficiently constructed at room-temperature by tip manipulation of a scanning tunneling microscope (STM). Though intentionally increasing the tip-graphene interaction, we controllably tear and fold graphene sheets against step edges and successfully fabricate nanoscale graphene islands such as quantum dots and nanoribbon-like structures on graphite. Interestingly, the tearing directions are found to mainly along the zigzag orientations of graphene hexagonal lattice, leading to the generated graphene nanostructures possessing the same specified edges with well zigzag terminations. Theoretical modelling demonstrates that the enhanced tip-graphene repulsive force can account for the tearing and folding processes, whereas the preferential zigzag-tearing is attributed to the predicted lowest bond-breaking energy of the zigzag orientation in graphene. Our experiment provides a simple and controllable method for fabrication of graphene nanostructures with precise zigzag edge terminations. The obtained zigzag-edge-terminated graphene nanostructures also provide a platform for engineering novel quantum properties.

Developing highly active and stable nonprecious metal catalysts for electrochemical reactions is desirable but remains a great challenge. Herein, we report a novel metal-ion adsorption-pyrolysis strategy for the controllable zeolitic imidazolate framework-8 derived synthesis of individual high-quality N-doped carbon nanotubes embedded with well-dispersed nonprecious metal nanoparticles, which exhibit superior electrocatalytic activity and stability for electrochemical CO2 reduction reaction, oxygen reduction reaction, and oxygen evolution reaction. Experimental analysis and density functional theory calculations indicate that the remarkable electrocatalytic activities are mainly attributed to the interface effects for the efficient electron transfer from metal nanoparticles to the N-doped carbon shell, as well as the large specific areas, unique tube structures, appropriate doping, high graphitization degree, and robust frameworks. The high reaction stability is attributed to the multiwalled graphitic car...

An efficient heterogeneous photocatalytic system for high-purity hydrogen evolution from formate or aldehyde-water solution were developed using IrCp*Cl (Cp* = η5-pentamethylcyclopentadienyl) complex anchored onto the robust bipyridine-based organosilica nanotubes as a solid catalyst. This system can be conducted at the room temperature with a visible light (λ > 420 nm) illumination. The heterogeneous molecular photocatalyst displayed much improved catalytic activity and recyclability compared to the analogous homogeneous catalyst, benefiting from the isolated photoactive sites as well as the efficient transport of substrates and products in the nanotube channels. A detailed characterization for the solid catalyst after the reactions by UV/vis, XPS and 13C CP MAS NMR testified the molecular nature of the active species. This work provides an easy method to construct the heterogeneous molecular photocatalysts for the high-purity hydrogen generation under mild conditions.

The rational design and control of electrocatalysts at single-atomic sites could enable unprecedented atomic utilization and catalytic properties, yet it remains challenging in multimetallic alloys. Herein, the first example of isolated Rh atoms on ordered PtBi nanoplates (PtBi-Rh1 ) by atomic galvanic replacement, and their subsequent transformation into a tensile-strained Pt-Rh single-atom alloy (PtBi@PtRh1 ) via electrochemical dealloying are presented. Benefiting from the Rh1 -tailored Pt (110) surface with tensile strain, the PtBi@PtRh1 nanoplates exhibit record-high and all-round superior electrocatalytic performance including activity, selectivity, stability, and anti-poisoning ability toward ethanol oxidation in alkaline electrolytes. Density functional theory calculations reveal the synergism between effective Rh1 and tensile strain in boosting the adsorption of ethanol and key surface intermediates and the CC bond cleavage of the intermediates. The facile synthesis of the tensile-strained single-atom alloy provides a novel strategy to construct model nanostructures, accelerating the development of highly efficient electrocatalysts.

Despite recent transport studies of ABC-stacked multilayer graphene systems revealed various unusual quantum phenomena which arise from the nearly flat electronic bands, their quantum tunneling properties have rarely been addressed. Here we investigate the local tunneling characteristics of a gapped ABC-stacked trilayer graphene (TLG) and report the experimental observation of the nearly flat band induced atomic-site-dependent negative differential conductivity (NDC, characterized by a current drop with increasing voltage) via scanning tunneling spectroscopy (STS) measurements. We show that strong NDC emerges in the gap region next to a sharp STS peak induced by the very flat low-energy dispersion of ABC TLG. The NDC is found to mainly reside on one atomic sublattice of the surface layer due to the strong sublattice and layer localization of the nearly flat bands. The observed NDC behavior is explained by the tunnel-diode mechanism, namely, the coexistence of a sharp flat-dispersion STS peak in which tunneling is strongly enhanced and a subsequent gap region in which tunneling is forbidden. Furthermore, we also find that a local defect could effectively switch off the NDC over a large spatial range. Our result highlights a quantum tunneling effect unique to the graphene-based nearly flat band system and expands the potential application scope of ABC TLG.

It is a great challenge to fabricate a metal-free oxygen reduction reaction (ORR) electrocatalyst that can operate well in the acidic medium and fuel cells system. Here, a metal-free carbon material C-900 with abundant defect sites is fabricated by a self-sacrificed template and a solid-state reaction strategy. C-900 shows a superior performance to 20% Pt/C in alkaline medium and a performance closer to 20% Pt/C in acidic condition. It can thus be applied in air-breathing fuel cell (without extra operation pressure) as the cathode catalyst, which shows a high performance (1160 W L-1; ∼62% of 20% Pt/C) with excellent stability. By using oxygen temperature-programmed desorption, the strong selective chemisorption of O2 on C-900 has been revealed. The excellent chemisorption property of C-900 may originate from the large amounts of carbon defect sites, which have been confirmed by synchrotron radiation-based X-ray absorption spectroscopy. The rich defect sites and excellent chemisorption property can thus induce reversible carbon-oxygen interface for the excellent ORR activity.

It is of critical importance to design and fabricate highly active and stable catalysts for CO2 conversion. Herein, we synthesize a kind of novel porous heterobimetallic catalyst by manipulating the structural evolution of metal–organic framework (MOF) nanocrystals. The starting material, homometallic ZIF-8 nanoparticles, transforms in solution by cation exchange with Au3+ ions into heterobimetallic Au/Zn-MOF nanocages that favor the enhancement of active sites. With the use of regular hexahedral (RH) ZIF-8 and rhombic dodecahedral (RD) ZIF-8 nanoparticles as the templates, we obtain RH and RD Au/Zn-MOF nanocages with controllable shell thickness, respectively. The resulting Au/Zn-MOF nanocages are employed to catalyze the cycloaddition of CO2 and epoxides under mild reaction conditions. The excellent catalytic performance is demonstrated by high yields of 95–99% along with easy recyclability of the Au/Zn-MOF nanocages, which outperform most of the reported MOF-based catalysts and a homogeneous Au catalyst due to the synergetic effect of the two metallic components and the unique hollow structures. Impressively, these Au/Zn-MOF nanocages exhibit remarkable catalytic activity for CO2 conversion even at room temperature and atmospheric pressure. These nanomaterials thus hold great promise as catalysts for CO2 conversion in terms of facile preparation, abundant multiple active sites, and enhanced catalytic activity and stability.

Defective carbon-based materials (DCMs) have recently been considered as one of the most promising alternatives to precious metal electrocatalysts owing to their irreplaceable advantages, such as environmentally friendly, low cost and high structural tunability. Despite remarkable progress has been achieved, grand challenges of their further development are still remained by the traditional “trial-and-error” approaches, mainly due to the lack of precise synthetic methodologies as well as in-depth understandings of active centers and underlying electrocatalytic mechanisms. Herein, this review will provide a comprehensive overview and perspective on the critical issues and possible solutions regarding the controllable synthesis of DCMs, with special emphasis on the theoretical guidance in designing complex carbon defect structures and operando characterizations in exploring “dynamic” active centers. More importantly, it will also highlight recent advances in the applications of DCMs for the cutting-edge “E-Refinery”, focusing on the electrochemical conversion of electricity into fuels and chemical building blocks (e.g., H2, O2, CH4, C2H4, CH3OH, C2H5OH, NH3 and other organic compounds). Finally, further challenges and opportunities are summarized to shed some light on the unexploited area and future directions in expectation of stimulating the broad interest of interdisciplinary researchers.

Two-dimensional (2D) Dirac materials have attracted intense research efforts due to their promise for applications ranging from field-effect transistors and low-power electronics to fault-tolerant quantum computation. One key challenge is to fabricate 2D Dirac materials hosting Dirac electrons. Here, monolayer germanene is successfully fabricated on a Ag2Ge surface alloy. Scanning tunneling spectroscopy measurements revealed a linear energy dispersion relation. The latter was supported by density functional theory calculations. These results demonstrate that monolayer germanene can be realistically fabricated on a Ag2Ge surface alloy. The finding opens the door to exploration and study of 2D Dirac material physics and device applications.

Platinum is the most effective metal for a wide range of catalysis reactions, but it fails in the formic acid electrooxidation test and suffers from severe carbon monoxide poisoning. Developing highly active and stable catalysts that are capable of oxidizing HCOOH directly into CO2 remains challenging for commercialization of direct liquid fuel cells. A new class of PtSnBi intermetallic nanoplates is synthesized to boost formic acid oxidation, which greatly outperforms binary PtSn and PtBi intermetallic, benefiting from the synergism of chosen three metals. In particular, the best catalyst, atomically ordered Pt45 Sn25 Bi30 nanoplates, exhibits an ultrahigh mass activity of 4394 mA mg-1 Pt and preserves 78% of the initial activity after 4000 potential cycles, which make it a state-of-the-art catalyst toward formic acid oxidation. Density functional theory calculations reveal that the electronic and geometric effects in PtSnBi intermetallic nanoplates help suppress CO* formation and optimize dehydrogenation steps.

Engineering novel Sn-based bimetallic materials could provide intriguing catalytic properties to boost the electrochemical CO2 reduction. Herein, the first synthesis of homogeneous Sn1- x Bix alloy nanoparticles (x up to 0.20) with native Bi-doped amorphous SnOx shells for efficient CO2 reduction is reported. The Bi-SnOx nanoshells boost the production of formate with high Faradaic efficiencies (>90%) over a wide potential window (-0.67 to -0.92 V vs RHE) with low overpotentials, outperforming current tin oxide catalysts. The state-of-the-art Bi-SnOx nanoshells derived from Sn0.80 Bi0.20 alloy nanoparticles exhibit a great partial current density of 74.6 mA cm-2 and high Faradaic efficiency of 95.8%. The detailed electrocatalytic analyses and corresponding density functional theory calculations simultaneously reveal that the incorporation of Bi atoms into Sn species facilitates formate production by suppressing the formation of H2 and CO.

Herein, a gas-sensitive functional nanomaterial was constructed by confining Tb(acac)3(H2O)2 (acac = acetylacetone) in the space of the metal organic framework ZIF-8. This functional nanomaterial can realize a gas–solid state aldol condensation reaction, even at room temperature and without the use of a catalyst. In the reaction process, formaldehyde (FA) gas molecules can invalidate the antenna effect of the acac ligands, and it can therefore act as an ultrasensitive FA gas remover and detector (limit of detection value = 49 ppb).

Human telomerase RNA (hTR), a template of telomerase for telomeric repeat synthesis, was used to reflect the telomerase activity and act as a potential target of antitumor therapy. Here, we report a novel DNA-conjugated AuNP probe termed sticky-flares for the in situ detection of intracellular human telomerase RNA. The sticky-flares probe is capable of entering living cells directly without any auxiliary and recognizing the binding domain of human telomerase RNA. On recognition, the fluorophore-modified recognition flares can specifically bind to the target, separate from the sticky-flares and act as a fluorescent reporter to quantify and dynamically profile human telomerase RNA in living cells. We envision that the sticky-flares probe would be a valuable platform to investigate the function and regulation of hTR in antitumor therapy and hTR-related drug invention.

This paper presents a novel die attach material that withstands high working temperature of at least 415 °C after low temperature liquid bonding at 250 °C. The die attach material was preform compressed with Cu@Sn core-shell microparticles, which were produced using an electroless process. When the reflow temperature reached Sn melting point, the outer Sn layer melted and connected the inner Cu cores. After reflow soldering at 250 °C for 4 min, the outer Sn completely transformed into tri-dimensional network-like structure intermetallic compounds (IMCS) Cu 6 Sn 5 and Cu 3 Sn, the inner Cu cores were interconnected by the formed network-like Cu-Sn IMCS, with a high remelting temperature (415°C for Cu 6 Sn 5 and 676°C for Cu 3 Sn). With reflow time increased, more Cu 6 Sn 5 layer transformed into Cu 3 Sn, and voids increased with Cu atom diffusing to Cu 6 Sn 5 layer. Consequently, the joint with little Cu 3 Sn has the potential to fulfill the requirements of high temperature die attach. The surface morphology of the produced Cu@Sn microparticles and cross section morphology of the joint was characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis was performed to investigate the structure and phases of Cu@Sn particles and the joint. The voids rate of the joint was studied by X-ray.

This study compared the effects of chemical aging on the polyvinylidene fluoride (PVDF) membranes fabricated with the methods of non-solvent induced phase separation (NIPS) (named NIPS-PVDF) and thermally induced phase separation (TIPS) (named TIPS-PVDF). The chemical solutions of sodium hypochlorite (NaClO) and sodium hydroxide (NaOH) were chosen at the concentration of 5000mg/L. The equivalence of 5 and 10years was respectively selected as the time of aging. The physicochemical evolutions of membrane aging are characterized on the base of morphology analysis, chemical components, permeation ability and mechanical properties. The aging of NIPS-PVDF membrane led to the elimination of surface hydrophilic additives, while NaOH focused on the dehydrofluorination process resulting in the formation of conjugated chains of polyene on the skeleton structure. The chemical components of the surface of TIPS-PVDF membrane were removed continuously during the aging processes of both NaClO and NaOH, which was caused by the saponification of surface additives and the chain scissions of skeleton structure, but without producing any obvious conjugated chains of polyene. All the aging processes led to the increase of contact angle and the decrease of mechanical properties, and the permeability was reduced first and increased later due to the enlargement of surface membrane pores and membrane block. With the influence of membrane aging, selectivity of membrane was decreased (except coliform bacteria). At the beginning of filtration, the turbidity and particle count were at relatively high levels and declined with the filtration process.