Zhepeng Zhang

Long-term green tea catechin administration prevents spatial learning and memory impairment in senescence-accelerated mouse prone-8 mice by decreasing Aβ1-42 oligomers and upregulating synaptic plasticity–related proteins in the hippocampus

The senescence-accelerated mouse prone-8 (SAMP8) is characterized by early onset of learning and memory deficits along with spontaneous overproduction of soluble beta-amyloid peptide (Abeta) in the brain. In our study, 4 month old male SAMP8 mice were orally administered 0.05% and 0.1% green tea catechins (GTC, w/v) in drinking water for 6 months. We found that a supplementation with 0.05% or 0.1% GTC prevented spatial learning and memory impairments of mice in the Morris water maze. Better performance of GTC-treated mice was associated with decreased levels of Abeta(1-42) oligomers in the hippocampus. The activity of the protein kinase A/cAMP-response element binding protein (PKA/CREB) pathway, one of the molecular targets of Abeta oligomers which is crucial for late long-term potentiation and long-term memory formation, was significantly increased after GTC administration. We also found that chronic 0.05% or 0.1% GTC consumption prevented the reductions of three representative proteins of synaptic function and synaptic structure, including brain-derived neurotrophic factor(BDNF), post-synaptic density protein-95 (PSD95) and Ca(2+)/calmodulin-dependent protein kinase II (CaMKII). These results demonstrated that long-term 0.05% or 0.1% green tea catechin administration may prevent spatial learning and memory decline of SAMP8 mice by decreasing Abeta(1-42) oligomers and upregulating synaptic plasticity-related proteins in the hippocampus.

Long-term administration of green tea catechins prevents age-related spatial learning and memory decline in C57BL/6 J mice by regulating hippocampal cyclic amp-response element binding protein signaling cascade.

Flavonoid-rich foods have been shown to be effective at reversing age-related deficits in learning and memory in both animals and humans. However, little investigation of the preventative effects of flavonoids on the naturally aged animals was reported. In our study, 14-month-old female C57BL/6 J mice were orally administered 0.025%, 0.05% and 0.1% green tea catechins (GTC, w/v) in drinking water for 6 months; we found that a supplementation with 0.05% or 0.1% GTC prevented age-related spatial learning and memory decline of mice in the Morris water maze. Better performance of GTC-treated mice was associated with increased levels of cAMP-response element binding protein (CREB) phosphorylation in the hippocampus. The expressions of brain-derived neurotrophic factor (BDNF) and Bcl-2, two target genes of CREB which can exhibit long-term regulatory roles in synaptic plasticity and synaptic structure, were also increased. We also found that long-term 0.05% or 0.1% GTC administration prevented age-related reductions of two representative post-synaptic density proteins PSD95 and Ca(2+)/calmodulin-dependent protein kinase II, suggesting that synaptic structural changes may be involved. These results demonstrated that long-term 0.05% or 0.1% green tea catechin administration may prevent age-related spatial learning and memory decline of female C57BL/6 J mice by regulating hippocampal CREB signaling cascade.

Temperature-Mediated Selective Growth of MoS2/WS2 and WS2/MoS2 Vertical Stacks on Au Foils for Direct Photocatalytic Applications

A growth-temperature-mediated two-step chemical vapor deposition strategy is designed to synthesize MoS2 /WS2 and WS2 /MoS2 stacks on Au foils. Predominantly A-A stacked MoS2 /WS2 and A-B stacked WS2 /MoS2 are selectively achieved and confirmed. Relative enhancements or reductions in photocatalytic activities of MoS2 /WS2 or WS2 /MoS2 are observed under illumination, because the type-II band alignment enables directional electron flow from electrode to active site.

Metallic Vanadium Disulfide Nanosheets as a Platform Material for Multifunctional Electrode Applications

Nanothick metallic transition metal dichalcogenides such as VS2 are essential building blocks for constructing next-generation electronic and energy-storage applications, as well as for exploring unique physical issues associated with the dimensionality effect. However, such two-dimensional (2D) layered materials have yet to be achieved through either mechanical exfoliation or bottom-up synthesis. Herein, we report a facile chemical vapor deposition route for direct production of crystalline VS2 nanosheets with sub-10 nm thicknesses and domain sizes of tens of micrometers. The obtained nanosheets feature spontaneous superlattice periodicities and excellent electrical conductivities (∼3 × 103 S cm-1), which has enabled a variety of applications such as contact electrodes for monolayer MoS2 with contact resistances of ∼1/4 to that of Ni/Au metals, and as supercapacitor electrodes in aqueous electrolytes showing specific capacitances as high as 8.6 × 102 F g-1. This work provides fresh insights into the delicate structure-property relationship and the broad application prospects of such metallic 2D materials.

Periodic Modulation of the Doping Level in Striped MoS2 Superstructures

Although the recently discovered monolayer transition metal dichalcogenides exhibit novel electronic and optical properties, fundamental physical issues such as the quasiparticle bandgap tunability and the substrate effects remain undefined. Herein, we present the report of a quasi-one-dimensional periodically striped superstructure for monolayer MoS2 on Au(100). The formation of the unique striped superstructure is found to be mainly modulated by the symmetry difference between MoS2 and Au(100) and their lattice mismatch. More intriguingly, we find that the monolayer MoS2 is heavily n-doped on the Au(100) facet with a bandgap of 1.3 eV, and the Fermi level is upshifted by ∼0.10 eV on the ridge (∼0.2 eV below the conduction band) in contrast to the valley regions (∼0.3 eV below the conduction band) of the striped patterns after high-temperature sample annealing process. This tunable doping effect is considered to be caused by the different defect densities over the ridge/valley regions of the superstructure. Additionally, an obvious bandgap reduction is observed in the vicinity of the domain boundary for monolayer MoS2 on Au(100). This work should therefore inspire intensive explorations of adlayer-substrate interactions, the defects, and their effects on band-structure engineering of monolayer MoS2.

Direct Chemical Vapor Deposition Growth and Band-Gap Characterization of MoS2/h-BN van der Waals Heterostructures on Au Foils

Stacked transition-metal dichalcogenides on hexagonal boron nitride (h-BN) are platforms for high-performance electronic devices. However, such vertical stacks are usually constructed by the layer-by-layer polymer-assisted transfer of mechanically exfoliated layers. This inevitably causes interfacial contamination and device performance degradation. Herein, we develop a two-step, low-pressure chemical vapor deposition synthetic strategy incorporating the direct growth of monolayer h-BN on Au foil with the subsequent growth of MoS2. In such vertical stacks, the interactions between MoS2 and Au are diminished by the intervening h-BN layer, as evidenced by the appearance of photoluminescence in MoS2. The weakened interfacial interactions facilitate the transfer of the MoS2/h-BN stacks from Au to arbitrary substrates by an electrochemical bubbling method. Scanning tunneling microscope/spectroscopy characterization shows that the central h-BN layer partially blocks the metal-induced gap states in MoS2/h-BN/Au foils. The work offers insight into the synthesis, transfer, and device performance optimization of such vertically stacked heterostructures.

Two-dimensional metallic tantalum disulfide as a hydrogen evolution catalyst

Two-dimensional metallic transition metal dichalcogenides are emerging as prototypes for uncovering fundamental physical phenomena, such as superconductivity and charge-density waves, as well as for engineering-related applications. However, the batch production of such envisioned transition metal dichalcogenides remains challenging, which has hindered the aforementioned explorations. Herein, we fabricate thickness-tunable tantalum disulfide flakes and centimetre-sized ultrathin films on an electrode material of gold foil via a facile chemical vapour deposition route. Through temperature-dependent Raman characterization, we observe the transition from nearly commensurate to commensurate charge-density wave phases with our ultrathin tantalum disulfide flakes. We have obtained high hydrogen evolution reaction efficiency with the as-grown tantalum disulfide flakes directly synthesized on gold foils comparable to traditional platinum catalysts. This work could promote further efforts for exploring new efficient catalysts in the large materials family of metallic transition metal dichalcogenides, as well as exploiting their applications towards more versatile applications.Metallic transition metal dichalcogenides are important materials for catalysis, but scalable and controllable preparation methods are scarce. Here, the authors synthesize 2H-TaS2 as centimetre-scale films of tunable thickness and show they are an efficient catalyst for hydrogen evolution.

Fast and uniform growth of graphene glass using confined-flow chemical vapor deposition and its unique applications

Fast and uniform growth of high-quality graphene on conventional glass is of great importance for practical applications of graphene glass. We report herein a confined-flow chemical vapor deposition (CVD) approach for the high-efficiency fabrication of graphene glass. The key feature of our approach is the fabrication of a 2–4 μm wide gap above the glass substrate, with plenty of stumbling blocks; this gap was found to significantly increase the collision probability of the carbon precursors and reactive fragments between one another and with the glass surface. As a result, the growth rate of graphene glass increased remarkably, together with an improvement in the growth quality and uniformity as compared to those in the conventional gas flow CVD technique. These high-quality graphene glasses exhibited an excellent defogging performance with much higher defogging speed and higher stability compared to those previously reported. The graphene sapphire glass was found to be an ideal substrate for growing uniform and ultra-smooth aluminum nitride thin films without the tedious pre-deposition of a buffer layer. The presented confined-flow CVD approach offers a simple and low-cost route for the mass production of graphene glass, which is believed to promote the practical applications of various graphene glasses.

Batch production of 6-inch uniform monolayer molybdenum disulfide catalyzed by sodium in glass

Monolayer transition metal dichalcogenides (TMDs) have become essential two-dimensional materials for their perspectives in engineering next-generation electronics. For related applications, the controlled growth of large-area uniform monolayer TMDs is crucial, while it remains challenging. Herein, we report the direct synthesis of 6-inch uniform monolayer molybdenum disulfide on the solid soda-lime glass, through a designed face-to-face metal-precursor supply route in a facile chemical vapor deposition process. We find that the highly uniform monolayer film, with the composite domains possessing an edge length larger than 400 µm, can be achieved within a quite short time of 8 min. This highly efficient growth is proven to be facilitated by sodium catalysts that are homogenously distributed in glass, according to our experimental facts and density functional theory calculations. This work provides insights into the batch production of highly uniform TMD films on the functional glass substrate with the advantages of low cost, easily transferrable, and compatible with direct applications.Growth of large-area monolayer transition metal dichalcogenides is critical for their application but remains challenging. Here Yang et al. report rapid chemical vapor deposition of 6-inch monolayer molybdenum disulfide by sufficiently uniformly supplying the precursors and catalysts.

Nickelocene‐Precursor‐Facilitated Fast Growth of Graphene/h‐BN Vertical Heterostructures and Its Applications in OLEDs

The direct growth of high-quality, large-area, uniform, vertically stacked Gr/h-BN heterostructures is of vital importance for applications in electronics and optoelectronics. However, the main challenge lies in the catalytically inert nature of the hexagonal boron nitride (h-BN) substrates, which usually afford a rather low decomposition rate of carbon precursors, and thus relatively low growth rate of graphene. Herein, a nickelocene-precursor-facilitated route is developed for the fast growth of Gr/h-BN vertical heterostructures on Cu foils, which shows much improved synthesis efficiency (8-10 times faster) and crystalline quality of graphene (large single-crystalline domain up to ≈20 µm). The key advantage of our synthetic route is the utilization of nickel atoms that are decomposed from nickelocene molecules as the gaseous catalyst, which can decrease the energy barrier for graphene growth and facilitate the decomposition of carbon sources, according to our density functional theory calculations. The high-quality Gr/h-BN stacks are proved to be perfect anode/protecting layers for high-performance organic light-emitting diode devices. In this regard, this work offers a brand-new route for the fast growth of Gr/h-BN heterostructures with practical scalability and high crystalline quality, thus should propel its wide applications in transparent electrodes, high-performance electronic devices, and energy harvesting/transition directions.