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The metastable semiconductor phase allows for the exploration of unusual properties and functionalities of abnormal structures, although it is often difficult to prevent thermodynamic transformations to lower energy structures from higher, unfavored energy states. Here, we show for the first time the preparation of high-quality ultralong metastable zincblende (ZB)-MnSe nanowires with a four-coordinate structure via solution-solid-solid (SSS) growth in a mild solution-phase synthetic environment (120-220 °C) in the presence of a trace amount of Ag(I). The metastable ZB-MnSe nanowires are stabilized kinetically due to the catalysis of early formed body-centered cubic (bcc) fast-ionic (superionic) Ag2Se nanocrystals from the Ag(I) source, and the ZB-MnSe nanowires grow epitaxially along the ⟨110⟩ axis rather than the ⟨111⟩ axis, as commonly observed for typical four-coordinate Grimm-Sommerfeld bonding solids. Our method provides a new route for the growth of metastable nanostructures. [ABSTRACT FROM AUTHOR]

Controlled manipulation of individual micro- and nanoscaleobjectsrequires the use of trapping forces that can be focused and translatedwith high spatial and time resolution. We report a new strategy thatuses the flow of mobile microvortices to trap and manipulate singleobjects in fluid with essentially no restrictions on their materialproperties. Fluidic trapping forces are generated toward the centerof microvortices formed by magnetic microactuators, that is, rotatingnanowire or self-assembled microbeads, actuated by a weak rotatingmagnetic field (|B|< 5 mT). We demonstrate precisemanipulation of single microspheres and microorganisms near a solidsurface in water. [ABSTRACT FROM AUTHOR]

Capacitance−voltage characteristics of individual germanium nanowire field effect transistors were directly measured and used to assess carrier mobility in nanowires for the first time, thereby removing uncertainties in calculated mobility due to device geometries, surface and interface states, and gate dielectric constants and thicknesses. Direct experimental evidence showed that surround-gated nanowire transistors exhibit higher capacitance and better electrostatic gate control than top-gated devices, and are the most promising structure for future high performance nanoelectronics. [ABSTRACT FROM AUTHOR]

Core-shell germanium nanowires (GeNW) are formed with a single-crystalline Ge core and concentric shells of nitride and silicon passivation layer by chemical vapor deposition (CVD), an Al2O3gate dielectric layer by atomic layer deposition (ALD), and an Al metal surround-gate (SG) shell by isotropic magnetron sputter deposition. Surround-gate nanowire field-effect transistors (FETs) are then constructed using a novel self-aligned fabrication approach. Individual SG GeNW FETs show improved switching over GeNW FETs with planar gate stacks owing to improved electrostatics. FET devices comprised of multiple quasi-aligned SG GeNWs in parallel are also constructed. Collectively, tens of SG GeNWs afford on-currents exceeding 0.1 mA at low source-drain bias voltages. The self-aligned surround-gate scheme can be generalized to various semiconductor nanowire materials. [ABSTRACT FROM AUTHOR]

The fabrication of nanohelices by the scrolling of strained bilayers is investigated. It is shown that structure design is dominated by edge effects rather than bulk crystal properties such as the Young's modulus when the dimensions of the structures are reduced below 400 nm. SiGe/Si/Cr, SiGe/Si, and Si/Cr helical nanobelts are used as test structures. Dimensions of the belt width are reduced from 1.30 μm to 300 nm, and parameters controlling helicity angle, chirality, diameter, and pitch of the nanohelices are investigated. An anomalous scrolling direction deviating from the preferred 〈100〉 scrolling direction has been found for small structures. Making use of the anomalous scrolling, it is possible to fabricate three-dimensional helices with helicity angles less than 45°, which is advantageous for micro- and nanoelectromechanical systems. [ABSTRACT FROM AUTHOR]

With the continuing development of bottom-up nanotechnology fabrication processes, spot welding can play a role similar to its macro counterpart for the interconnection of nano building blocks for the assembly of nanoelectronics and nanoelectromechanical systems (NEMS). Spot welding using single-crystalline copper-filled carbon nanotubes (CNTs) is investigated experimentally using nanorobotic manipulation inside a transmission electron microscope (TEM). Controlled melting and flowing of copper inside nanotube shells are realized by applying bias voltages between 1.5 and 2.5 V. The average mass flow rate of the copper was found to be 120 ag/s according to TEM video imaging (measured visually at approximately 11.6 nm/s through the CNT). Successful soldering of a copper-filled CNT onto another CNT shows promise for nano spot welding and thermal dip-pen lithography. [ABSTRACT FROM AUTHOR]

Brillouin measurements have been made of the spin dynamics of high-density two-dimensional hexagonally ordered 20 nm diameter Fe48Co52 nanowire arrays, with various interwire spacings, as a function of longitudinal magnetic field. The experimental data are analyzed within the Arias−Mills theory based on interwire dipolar couplings in the arrays. The results provide conclusive evidence of collective spin waves arising from the dipolar coupling which is manifested as a reduction in spin wave frequency with decreasing interwire spacing. [ABSTRACT FROM AUTHOR]

In response to environmental variations, living cells need to arrange the conformational changes of macromolecules to achieve the specific biofunctions. Inspired by natural molecular machines, artificial macromolecular assemblies with controllable nanostructures and environmentally responsive functions can be designed. By assembling macromolecular nanostructures with noble metal nanoparticles, environmental information could be significantly amplified and modulated. However, manufacturing dynamic plasmonic nanostructures that are efficiently responsive to different stimuli is still a challenging task. Here we demonstrate a stimulus-responsive plasmonic nanosystem based on DNA origami-organized gold nanorods (GNRs). L-shaped GNR dimers were assembled on rhombus-shaped DNA origami templates. The geometry and chiral signals of the GNR nanoarchitectures respond to multiple stimuli, including glutathione reduction, restriction enzyme action, pH change, or photoirradiation. While the glutathione reduction or restriction enzyme caused irreversible changes in the plasmonic circular dichroism (CD) signals, both pH and light irradiation triggered reversible changes in the plasmonic CD. Our system transduces external stimuli into conformational changes and circular dichroism responses in near-infrared (NIR) wavelengths. By this approach, programmable optical reporters for essential biological signals can be fabricated. [ABSTRACT FROM AUTHOR]

Cells sense and respond to the surrounding microenvironment through binding of membranous integrin to ligands such as the Arg-Gly-Asp (RGD) peptide. Previous studies show that the RGD tether properties on substrate influence cell adhesion and spreading, but few studies have reported strategies to control the tether mobility of RGD on substrate via a physical and noncontact approach. Herein, we demonstrate a novel strategy to tune the tether mobility of RGD on substrate via magnetic force. We conjugate a monolayer of RGD-bearing magnetic nanoparticles (MNPs) on a glass substrate via the flexible and coiled poly(ethylene glycol) linker of large molecular weight (PEG, average MW: 2000), and this increases the RGD tether mobility, which can be significantly reduced by applying magnetic attraction on MNPs. Our data show that high RGD tether mobility delays the early adhesion and spreading of human mesenchymal stem cells (hMSCs), leading to compromised osteogenic differentiation at later stage. In contrast, hMSCs cultured on substrate with restricted RGD tether mobility, achieved either via a shorter PEG linker (MW: 200) or magnetic force, show significantly better adhesion, spreading, and osteogenic differentiation. The control utilizing RGD-bearing nonmagnetic nanoparticles shows no such enhancing effect of magnetic field on cellular events, further supporting our conjecture of magnetic tuning of RGD tether mobility. We hypothesize that high tether mobility of RGD entails additional time and effort by the cells to fully develop traction force and mechanical feedback, thereby delaying the maturation of FAs and activation of subsequent mechanotransduction signaling. Our staining results of vinculin, a critical component of FAs, and Yes-associated protein (YAP), an important mechanosensitive transcriptional factor, support our hypothesis. We believe that our work not only sheds light on the impact of dynamic presentation of cell adhesive ligands on cellular behaviors, which should be taken into consideration for designing novel biomaterials, but also formulate an effective noncontact strategy that enables further investigation on the mechanobiological mechanisms underlying such cellular responses. [ABSTRACT FROM AUTHOR]

Substrate stiffness has been shownto regulate the differentiation fate of human mesenchymal stem cells(hMSCs). hMSCs sense and respond to substrate rigidity by exertingtraction forces upon the binding between integrins and integrin-specificligands present on the substrate surface. However, in previous studies,integrin-specific ligands such as Arg–Gly–Asp (RGD)peptides are always grafted to the substrate by a permanent covalentbond. Whether the coupling strength of integrin-specific ligands onsubstrate will influence cell behaviors has not been explored. Inthis work, we have developed a facile platform to investigate theeffects of varied coupling strength between the RGD peptide and theglass substrate on stem cell behaviors. Glass coverslips are decoratedwith positive charges by silanization using (3-aminopropyl) triethoxysilane(APTES) to immobilize negatively charged citrate-capped gold nanoparticles(cit-AuNPs) solely via electrostatic interactions. The monolayer ofelectrostatically immobilized cit-AuNPs is further conjugated withthe thiolated RGD peptides through the sulfur–gold bond. Thesubstrate coupling strength of the RGD peptides, which is dependenton the electrostatic interactions between the APTES-treated glasssubstrate and the cit-AuNPs, is simply tuned by changing the APTESdosage and, hence, the resultant positive charge density on the surface.A total of 0.5% and 12.5% of APTES are used to fabricate low-coupling-strengthsurfaces (namely, LCS0.5 and LCS12.5), whereas 25% and 50% of APTESare used to fabricate high-coupling-strength surfaces (namely, HCS25and HCS50). Fluorescence microscopy shows that hMSCs spread well andform stable actin filamentous structure on HCS surfaces but not onLCS surfaces. Remarkably, hMSCs exhibit enhanced osteogenesis on HCSsurfaces as revealed by the immunostaining results of multiple earlyosteogenic markers. These differential behaviors may be governed byYes-associated protein (YAP), a mechanosensitive transcriptional regulatorof stem cells. Our findings highlight the importance of the substratecoupling strength of integrin-binding ligands on regulating adhesion,spreading, and differentiation of hMSCs. [ABSTRACT FROM AUTHOR]

We report an experimental and theoretical investigation into mass transport between individual carbon nanotubes (CNTs) via their central cores. These CNT fluidic junctions can serve as basic elements for more complex nanofluidic systems and can also provide a structure for testing theories of fluid flow at the nanoscale. Controlled melting, evaporation, and flowing of copper and tin within and between nanotube shells are investigated experimentally. Cap-to-wall and wall-to-cap mass flow are realized by electric current driven heating, diffusion, and electromigration under low bias voltages between 1.5 and 1.8 V. A comparison shows that the mass loss for the cap-to-wall architecture is much smaller than that for the wall-to-cap junction. A molecular dynamics simulation is presented that provides further insight into the transport mechanism. [ABSTRACT FROM AUTHOR]