In this Article, we report the successful fabrication of large-area ordered Si nanowire arrays (NWAs) by a cost-effective and scalable wet-etching process in combination with nanospheres lithography technique. The periodical Si NWAs are further investigated as photocathode for water splitting, with excellent hydrogen evolution performances with a maximum photocurrent density of 27 mA cm(-2) achieved, which is ?2.5 times that of planar Si and random Si nanowires electrode. The greatly improved PEC performance can be attributed to the patterned and ordered NWs structure as a result of enhancement of the light harvesting as well as charge transportation and collection efficiency.
Amyloid deposits are implicated in the pathogenesis of many neurodegenerative diseases such as Alzheimer's disease (AD). The inhibition of ?-sheet formation has been considered as the primary therapeutic strategy for AD. Increasing data show that nanoparticles can retard or promote the fibrillation of amyloid-? (A?) peptides depending on the physicochemical properties of nanoparticles, however, the underlying molecular mechanism remains elusive. In this study, our replica exchange molecular dynamics (REMD) simulations show that fullerene nanoparticle - C60 (with a fullerene?:? peptide molar ratio greater than 1?:?8) can dramatically prevent ?-sheet formation of A?(16-22) peptides. Atomic force microscopy (AFM) experiments further confirm the inhibitory effect of C60 on A?(16-22) fibrillation, in support of our REMD simulations. An important finding from our REMD simulations is that fullerene C180, albeit with the same number of carbon atoms as three C60 molecules (3C60) and smaller surface area than 3C60, displays an unexpected stronger inhibitory effect on the ?-sheet formation of A?(16-22) peptides. A detailed analysis of the fullerene-peptide interaction reveals that the stronger inhibition of ?-sheet formation by C180 results from the strong hydrophobic and aromatic-stacking interactions of the fullerene hexagonal rings with the Phe rings relative to the pentagonal rings. The strong interactions between the fullerene nanoparticles and A?(16-22) peptides significantly weaken the peptide-peptide interaction that is important for ?-sheet formation, thus retarding A?(16-22) fibrillation. Overall, our studies reveal the significant role of fullerene hexagonal rings in the inhibition of A?(16-22) fibrillation and provide novel insight into the development of drug candidates against Alzheimer's disease.
The aggregation processes of amyloid-?-(16-22) peptides (A?16-22) are investigated by atomic force microscopy (AFM). It is found that A?16-22 peptides quickly aggregate from monomers to oligomers and flakelike structures and finally to fibrils. In particular, unusual morphology change is observed in an early stage of aggregation; that is, the originally formed flakelike structures would disappear in the following aggregation processes. To determine the evolution of the flakelike structures, in situ AFM imaging is carried out in liquid to reveal the real-time morphology change of A?16-22. The results provide clear evidence that the flakelike structures are in an unstable intermediate state, which would be dissolved into oligomers or short protofibrils for reorganization. Further fluorescence and attenuated total reflectance Fourier transform infrared (ATR-FTIR) experiments on thioflavin T(ThT) suggest that those flakelike structures contain ?-sheet components.
Photogenerated charging properties of single Si nanorods (Si NRs) are investigated by electrostatic force microscopy (EFM) combined with laser irradiation. Under laser irradiation, Si NRs are positively charged. The amount of the charges trapped in single NRs as well as the contact potential difference between the tip and NRs' surface is achieved from an analytical fitting of the phase shift - voltage curve. Both of them significantly vary with the laser intensity and the NR's size and construction. The photogenerated charging and decharging rates are obtained at a timescale of seconds or slower, indicating that the Si NRs are promising candidates in photovoltaic applications.
Fabrication of semiconductor single and double quantum dot (QD) nanostructures is of utmost importance due to their promising applications in the study of advanced cavity quantum electrodynamics, quantum optics and solid-state spin qubits. We present results about the controllable growth of self-assembled single and double SiGe QD arrays with an ultra-low areal density of 1 × 10(7) cm(-2) on nanohole-patterned Si substrates via molecular beam epitaxy. The two dots in a double QD (DQD) aligned along the elongation direction of the nanoholes and show unsymmetrical features in both size and composition due to the asymmetric nanohole profiles after Si buffer layer growth. The interdot spacing between the two dots in a DQD could well be adjusted by changing the elongation ratio of nanoholes. Moreover, whether a single or a double QD formed in a given nanohole was found to be determined by the growth temperature of the Si buffer layer, the reason of which is given by the calculation of the surface chemical potential around the nanoholes after the buffer layer growth.
The influence of Au nanoparticles (Au NPs) on the aggregation of amyloid-?-(25-35) peptides (A?25-35) is investigated by atomic force microscopy and Thioflavin T fluorescence measurements. It is found that, without Au NPs, the A?25-35 peptides aggregate gradually from monomers and oligomers to long fibrils with the incubation time. In contrast, short protofibrils are formed quickly after Au NPs are added to the A?25-35 solution, which can be further aggregated to form short fibril bundles or even bundle conjunctions. To reveal the origin of Au NPs on the aggregation of A?25-35, electrostatic force microscopy and scanning Kelvin microscopy are employed to investigate the electrical properties of the A?25-35 fibrils with and without Au NPs. Due to the significant difference of the electrical properties between the A?25-35 fibrils and Au NPs, the locations of Au NPs inside the A?25-35 fibril bundles can be revealed and hence a possible influence mechanism of Au NPs on the aggregation of A?25-35 is suggested.
The nanoscale electrical properties of single-layer graphene (SLG), bilayer graphene (BLG) and multilayer graphene (MLG) are studied by scanning capacitance microscopy (SCM) and electrostatic force microscopy (EFM). The quantum capacitance of graphene deduced from SCM results is found to increase with the layer number (n) at the sample bias of 0 V but decreases with n at -3 V. Furthermore, the quantum capacitance increases very rapidly with the gate voltage for SLG, but this increase is much slowed down when n becomes greater. On the other hand, the magnitude of the EFM phase shift with respect to the SiO2 substrate increases with n at the sample bias of +2 V but decreases with n at -2 V. The difference in both quantum capacitance and EFM phase shift is significant between SLG and BLG but becomes much weaker between MLGs with a different n. The layer-dependent quantum capacitance behaviors of graphene could be attributed to their layer-dependent electronic structure as well as the layer-varied dependence on gate voltage, while the layer-dependent EFM phase shift is caused by not only the layer-dependent surface potential but also the layer-dependent capacitance derivation.
The nanoscale electrical properties of individual self-assembled GeSi quantum rings (QRs) were studied by scanning probe microscopy-based techniques. The surface potential distributions of individual GeSi QRs are obtained by scanning Kelvin microscopy (SKM). Ring-shaped work function distributions are observed, presenting that the QRs rim has a larger work function than the QRs central hole. By combining the SKM results with those obtained by conductive atomic force microscopy and scanning capacitance microscopy, the correlations between the surface potential, conductance, and carrier density distributions are revealed, and a possible interpretation for the QRs conductance distributions is suggested.
Novel crystal ?-Si(3)N(4)/Si-SiO(x) core-shell/Au-SiO(x) peapod-like axial double heterostructural nanowires were obtained by directly annealing a Au covered SiO(2) thin film on a Si substrate. Our extensive electron microscopic investigation revealed that the ?-Si(3)N(4) sections with a mathematical left angle bracket 101 mathematical right angle bracket growth direction were grown first, followed by growth of the Si-SiO(x) core-shell sections and finally growth of the Au-SiO(x) peapod-like sections. Through a series of systematically comparative experiments, a temperature-dependent multi-step vapor-liquid-solid growth mechanism is proposed. Room temperature photoluminescence measurement of individual nanowires reveals two emission peaks (410 and 515 nm), indicating their potential applications in light sources, laser or light emitting display devices.
The conductive properties of individual self-assembled GeSi quantum dots (QDs) are investigated by conductive atomic force microscopy on single-layer (SL) and bi-layer (BL) GeSi QDs with different dot densities at room temperature. By comparing their average currents, it is found that the BL and high-density QDs are more conductive than the SL and low-density QDs with similar sizes, respectively, indicating the existence of both vertical and lateral couplings between GeSi QDs at room temperature. On the other hand, the average current of the BL QDs increases much faster with the bias voltage than that of the SL QDs does. Our results suggest that the QDs conductive properties can be greatly regulated by the coupling effects and bias voltages, which are valuable for potential applications.
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