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Two-dimensional (2D) PtSe2 shows the most prominent layer-dependent electrical properties among various 2D materials and high catalytic activity for hydrogen evolution reaction (HER), and therefore, it is an ideal material for exploring the structure-activity correlations in 2D systems. Here, starting with the synthesis of single-crystalline 2D PtSe2 with a controlled number of layers and probing the HER catalytic activity of individual flakes in micro electrochemical cells, we investigated the layer-dependent HER catalytic activity of 2D PtSe2 from both theoretical and experimental perspectives. We clearly demonstrated how the number of layers affects the number of active sites, the electronic structures, and electrical properties of 2D PtSe2 flakes and thus alters their catalytic performance for HER. Our results also highlight the importance of efficient electron transfer in achieving optimum activity for ultrathin electrocatalysts. Our studies greatly enrich our understanding of the structure-activity correlations for 2D catalysts and provide new insight for the design and synthesis of ultrathin catalysts with high activity.

Trivalent praseodymium (Pr3+) is the most established rare-earth ion for the direct generation of visible light. In our work, based on Pr-doped Lu3Al5O12 (LuAG) single crystal, cladding waveguides are fabricated by applying femtosecond laser inscription with different parameters. The main characteristics of the waveguides such as mode distributions, propagation losses are investigated. The investigations on confocal micro-photoluminescence enable us to illustrate femtosecond laser induced modifications in Pr:LuAG matrix. The waveguides are further pumped at a wavelength of 450 nm with an InGaN laser diode. Guided fluorescence emissions in visible range covering green, yellow-green, orange and red are obtained with a maximum slope efficiency of 4 × 10−4.

Electrical stimulations have demonstrated positive effects in improving the survival rates of retinal cells and restoring the visual acuity in patients with ophthalmic diseases. However, optimal application parameters of electrical stimulations still need further exploration for better clinical efficacy. In this paper, a simulation study was performed for the electrical eyes stimulation with the stimulating electrode placed at six different positions on the eyelids. The results showed that the induced electric field was mainly distributed around front parts in the eye, while back position near retina had only strongly attenuated induced fields. Additionally, stimulating electrodes located at upper and outer positions on eyelid tended to produce stronger electric fields in eye than located at the opposite positions. This simulation study demonstrated that electrode positions played an important role in retina cell activities modulation in electrical eyes stimulation, and appropriate configurations that can increase retina stimulation efficiency are of great concern in practical clinical application, which need further exploration and investigation.

Two-dimensional (2D) MoS2, which has great potential for optoelectronic and other applications, is thermodynamically stable and hence easily synthesized in its semiconducting 2H phase. In contrast, growth of its metastable 1T and 1T' phases is hampered by their higher formation energy. Here we use theoretical calculations to design a potassium (K)-assisted chemical vapour deposition method for the phase-selective growth of 1T' MoS2 monolayers and 1T'/2H heterophase bilayers. This is realized by tuning the concentration of K in the growth products to invert the stability of the 1T' and 2H phases. The synthesis of 1T' MoS2 monolayers with high phase purity allows us to characterize their intrinsic optical and electrical properties, revealing a characteristic in-plane anisotropy. This phase-controlled bottom-up synthesis offers a simple and efficient way of manipulating the relevant device structures, and provides a general approach for producing other metastable-phase 2D materials with unique properties.

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) with layered structures provide a unique platform for exploring the effect of number of layers on their fundamental properties. However, the thickness scaling effect on the chemical properties of these materials remains unexplored. Here, we explored the chemically induced phase transition of 2D molybdenum disulfide (MoS2) from both experimental and theoretical aspects and observed that the critical electron injection concentration and the duration required for the phase transition of 2D MoS2 increased with decreasing number of layers. We further revealed that the observed dependence originated from the layer-dependent density of states of 2H-MoS2, which results in decreasing phase stability for 2H-MoS2 with increasing number of layers upon electron doping. Also, the much larger energy barrier for the phase transition of monolayer MoS2 induces the longer reaction time required for monolayer MoS2 as compared to multilayer MoS2. The layer-dependen...

Optical channel waveguides with depressed cladding configurations have been produced in Nd,Gd:CaF2 laser crystals by using ultrafast laser inscription. Waveguide properties are investigated in terms of guiding behaviors and localized laser-induced lattice damages. Under an optical pump of 808 nm light, continuous-wave waveguide lasing at 1.06 µm is achieved, with a single-mode operation and a minimum lasing threshold of 98.8 mW. Furthermore, the visible emissions of Nd3+ with short wavelengths ranging from 415 nm to 550 nm and long wavelengths from 550 nm to 625 nm are observed upon 808 nm laser excitation via the up-converted process. The intensity ratios of two wavelength ranges are proved to be tunable through changing the pumping polarizations.

Chirality-specific growth of single-walled carbon nanotubes (SWNTs) remains a challenge for their practical applications in electronics. Here, we explored the surface growth of SWNTs by utilizing the atomic-precise silver cluster complex [Ag15{1,3,5–(C≡C)3–C6H3}2(Py[8])3–(CF3SO3)3] (CF3SO3)6 (Py[8] is abbreviation for octamethylazacalix[8] pyridine) as a catalyst precursor. The diameters of most acquired SWNTs distributed in the range of 1.2–1.4 nm, which is suitable for making high performance field-effect transistors. The high quality of the obtained SWNTs was evidenced by Raman spectroscopy and electrical measurements. Successful growth of high quality SWNTs in this study foresees that rational design of metal-organic complexes as growth catalysts can open up a new avenue for the controllable synthesis of SWNTs.

Single-crystal graphene domains grown by chemical vapor deposition (CVD) intrinsically tend to have a six-fold symmetry; however, several factors can influence the growth kinetics, which can in turn lead to the formation of graphene with different shapes. Here we report the growth of oriented large-area pentagonal single-crystal graphene domains on Cu foils by CVD. We found that high-index Cu planes contributed selectively to the formation of pentagonal graphene. Our results indicated that lattice steps present on the crystalline surface of the underlying Cu promoted graphene growth in the direction perpendicular to the steps and finally led to the disappearance of one of the edges forming a pentagon. In addition, hydrogen promoted the formation of pentagonal domains. This work provides new insights into the mechanism of graphene growth.

We report on the fabrication of dual-line waveguides with low propagation losses and single-mode guidance in Pr:CaF2 crystals by applying femtosecond laser inscription. In contrast to the typical highly elliptic modes previously reported in dual-line waveguides, the guiding mode obtained in our work is highly-localized with a near-circular profile at wavelength of 633 nm. The investigations on confocal micro-photoluminescence and micro-Raman imaging enable us to illustrate the effect of different femtosecond laser filamentations on the localized refractive index change in Pr:CaF2 crystals. In company with the mode simulation by finite element method, we further reconstruct the refractive index distribution of the fabricated waveguides. Our results indicate that highly-localized refractive-index increment caused by compressive stress between the lower parts of the filaments is the main mechanism for waveguiding, whereas the damage-induced refractive-index reductions at filaments and in the region between the upper parts of the filaments are responsible for the strong light confinement in both horizontal and vertical directions.

Edge effects are predicted to significantly impact the properties of low dimensional materials with layered structures. The synthesis of low dimensional materials with copious edges is desired for exploring the effects of edges on the band structure and properties of these materials. Here we developed an approach for synthesizing MoS2 nanobelts terminated with vertically aligned edges by sulfurizing hydrothermally synthesized MoO3 nanobelts in the gas phase through a kinetically driven process; we then investigated the electrical and magnetic properties of these metastable materials. These edge-terminated MoS2 nanobelts were found to be metallic and ferromagnetic, and thus dramatically different from the semiconducting and nonmagnetic two-dimensional (2D) and three-dimensional (3D) 2H-MoS2 materials. The transitions in electrical and magnetic properties elucidate the fact that edges can tune the properties of low dimensional materials. The unique structure and properties of this one-dimensional (1D) MoS2 material will enable its applications in electronics, spintronics, and catalysis.

Controlled stacking of different two-dimensional (2D) atomic layers will greatly expand the family of 2D materials and broaden their applications. A novel approach for synthesizing MoS2 /WS2 heterostructures by chemical vapor deposition has been developed. The successful synthesis of pristine MoS2 /WS2 heterostructures is attributed to using core-shell WO3-x /MoO3-x nanowires as a precursor, which naturally ensures the sequential growth of MoS2 and WS2 . The obtained heterostructures exhibited high crystallinity, strong interlayer interaction, and high mobility, suggesting their promising applications in nanoelectronics. The stacking orientations of the two layers were also explored from both experimental and theoretical aspects. It is elucidated that the rational design of precursors can accurately control the growth of high-quality 2D heterostructures. Moreover, this simple approach opens up a new way for creating various novel 2D heterostructures by using a large variety of heteronanomaterials as precursors.

To ensure the practical application of atomically thin transition metal dichalcogenides, it is essential to characterize their structural stability under external stimuli such as electric fields and currents. Using vacancy monolayer islands on TiSe2 surfaces as a model system, for the first time we have observed a shape evolution and growth from triangular to hexagonal driven by scanning tunneling microscopy (STM) electrical stressing. The size of islands shows linear growth with a rate of (3.00 +- 0.05) x 10-3 nm/s, when the STM scanning parameters are held fixed at Vs = 1.0 V and I = 1.8 nA. We further quantified how the growth rate is related to the tunneling current magnitude. Our simulations of monolayer island evolution using phase-field modeling are in good agreement with our experimental observations, and point towards preferential edge atom dissociation under STM scanning driving the observed growth. The results could be potentially important for device applications of ultrathin transition metal dichalcogenides and related 2D materials subject to electrical stressing under device operating conditions., Comment: 24 pages, 5 figures

Nerve conduction blocking by high frequency biphasic (HFB) electrical stimulations would cause injuries to nerves. This study aimed to investigate whether laser irradiations could reduce this kind of injuries as an assistant method. Compound action potentials (CAPs) were recorded on isolated bullfrog's sciatic nerve before and following HFB electrical stimulations in each experimental trial, and the laser irradiations of 650 nm or 850 nm at various power were applied in testing trials. The parameters of injury rates and effectiveness ratios were computed from the CAPs to identify how many axons were influenced in respect of conductibility and how effective the laser irradiations were for the neural recoveries. The results showed that the laser irradiations of 650 nm and 75 mW reduced nerve injury rates following HFB electrical blocking stimulation and improved neural recovering speed by an average rate of 0.145. With the power of 50 mW, the 650 nm laser irradiation resulted in more significant (P

Chemical vapor deposition (CVD) has shown great potential in synthesizing various high-quality two-dimensional (2D) transition metal dichalcogenides (TMDCs). However, the nondestruction transfer of these CVD-grown 2D TMDCs at a high yield remains a key challenge for applying these emerging materials in various aspects. To address this challenge, we designed a water-soluble transfer mediator consisting of two polymers, polyvinylpyrrolidone (PVP) and poly(vinyl alcohol) (PVA), which can form strong interactions with CVD-grown 2D TMDCs for the nondestruction transfer of these materials. With this mediator, we realized the physical transfer of CVD-grown MoS2 flakes and several other 2D TMDCs, including 2D alloys and heterostructures to a wide range of substrates at a high yield of90% with well-retained properties as evidenced by various microscopic, spectroscopic, and electrical measurements. Field-effect transistors (FETs) made on thus-transferred CVD-grown MoS2 monolayers exhibited obviously higher mobility than those transferred by chemical method. We also constructed several artificial 2D crystals showing very strong interlayer coupling by the multiple transfer of CVD-grown 2D TMDCs monolayers with this approach. This transfer approach will make versatile CVD-grown 2D materials and their artificial stacks with pristine qualities easily accessible for both fundamental studies and practical applications.

Nerve injuries found in previous studies need to be explained with appropriate simulation studies. This study employed an axonal model based on the Frankenhaeuser-Huxley (FH) equations to investigate the changes of membrane potentials and sodium currents during high frequency (HF) electrical stimulation. The HF electrical stimulation induced continuously changing high-amplitude membrane responses different from the normal action potentials (APs). The phenomena of steady state depolarization and hyper polarization were observed at relatively low (1 kHz) and high (10 kHz) frequency HF currents respectively, for which overall inward and outward sodium fluxes occurred. Although only inward sodium flux occurred at low amplitude (1 mA) HF current, both inward and outward sodium fluxes were observed at high amplitude (5 mA) HF current. Higher frequencies (10 kHz) of HF currents caused more inward sodium fluxes and had bigger inward-to-outward ratio values. The results suggested the existence of an optimal HF frequency for HF electrical nerve stimulation. Successful verification of this would promote the design of safe HF electrical nerve stimulation protocols.

One of the issues met in nerve block implemented with high frequency (HF) electrical stimulation is the safety problem. This study aimed to investigate the applicability of conducting velocity distribution (CVD) in detecting nerve injuries induced by HF electrical stimulation. Deconvolution algorithm was adopted for CVD calculation. Both a simulation study and an in vitro experiment were performed to verify the applicability of this method. The results showed that deconvolution algorithm successfully calculated the single fiber action potential (SFAP) and CVDs. And changes of the obtained CVDs provided intuitive information about nerve function injuries induced by HF electrical stimulation. Nerve injury rates, denoted by normalized number of fibers losing their original conducting function, was apparently observed following HF electrical stimulation. Using CVDs to detect nerve injuries would help to design more safe electrical nerve stimulation strategies.