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Many applications of graphene can benefit from the enhanced mechanical robustness of graphene-based components. We report how the stiffness of vertical graphene (VG) sheets is affected by the introduction of defects and fluorination, both separately and combined. The defects were created using a high-energy ion beam while fluorination was performed in a XeF2 etching system. After ion bombardment alone, the average effective reduced modulus (E r), equal to â¼4.9 MPa for the as-grown VG sheets, approximately doubled to â¼10.0 MPa, while fluorination alone almost quadrupled it to â¼18.4 MPa. The maximum average E r of â¼32.4 MPa was achieved by repeatedly applying fluorination and ion bombardment. This increase can be explained by the formation of covalent bonds between the VG sheets due to ion bombardment, as well as the conversion from sp2 to sp3 and increased corrugation due to fluorination.
RESUMO
Ionic liquids (ILs) have received considerable interest for use in electrostatic gating in complex oxide systems. Understanding the ionic liquid/oxide interface, and any bias-induced electrochemical degradation, is critical for the interpretation of transport phenomena. The integrity of the interface between ionic liquid 1-ethyl-3-methylimidazolium hexafluorophosphate and La1/3Sr2/3FeO3 under various biasing conditions was examined by analytical transmission electron microscopy, and we report film degradation in the form of an irreversible chemical reaction regardless of the applied bias. This results in an intermixing region of 4-6 nm at the IL/oxide interface. Electron energy loss spectroscopy shows La and Fe migration into the ionic liquid, resulting in secondary phase formation under negative bias. Our approach can be extended to other ionic liquid/oxide systems in order to better understand the electrochemical stability window of these device structures.
RESUMO
The electrical properties of boron nitride (BN) nanostructures, particularly BN nanotubes (NTs), have been studied less in comparison to the counterpart carbon nanotubes. The present work investigates the field emission (FE) behavior of BNNTs under multiple cycles of FE experiments and demonstrates a strain-engineering pathway to tune the electronic properties of BNNTs. The electrical probing of individual BNNTs were conducted inside a transmission electron microscope (TEM) using an in situ electrical holder capable of applying a bias voltage of up to 110 V. Our results indicate that in the first cycle a single BNNT can exhibit the current density of â¼1 mA cm(-2) at 110 V and the turn-on voltage of 325 V µm(-1). However, field emission properties reduced considerably in subsequent cycles. Real-time imaging revealed the structural degradation of individual BNNTs during FE experiments. The electromechanical measurements show that the conductivity of BNNTs can be tuned by means of mechanical straining. The resistance of individual BNNTs reduced from 2000 to 769 MΩ and the carrier concentration increased from 0.35 × 10(17) to 1.1 × 10(17) cm(-3) by straining the samples up to 2.5%.
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As the applications for inorganic nanowires continuously grow, studies on the stability of these structures under high electrical/thermal stress conditions are needed. ZnTe nanowires are grown by the vapor-liquid-solid technique and their breakdown under Joule heating is studied through in situ monitoring in a transmission electron microscope (TEM). The experimental setup, consisting of a scanning tunneling microscope (STM) and a movable piezotube inside the TEM, allows the manipulation of a single nanowire. A voltage applied to the STM tip in contact with a ZnTe nanowire leads to the breakdown of the nanowire into Zn and Te particles or balls which is observed in real time. These balls grow by Ostwald ripening, rendering the surface morphology of the ZnTe nanowire progressively rough. Diffraction patterns along the stem of the wire after the partial breakdown showed substantially smaller lattice spacing compared to 0.35 nm for pristine ZnTe nanowires.
RESUMO
One-dimensional nanostructures such as ZnTe, CdTe, Bi(2)Te(3) and others have attracted much attention in recent years for their potential in thermoelectric devices among other applications. A better understanding of their mechanical properties is important for the design of devices. A combined experimental and computational approach has been used here to investigate the size effects on the Young's modulus of ZnTe nanowires (NWs). The mechanical properties of individual ZnTe nanowires in a wide diameter range (50-230 nm) were experimentally measured inside a high resolution transmission electron microscope using an atomic force microscope probe with the ability to record in situ continuous force-displacement curves. The in situ observations showed that ZnTe NWs are flexible nanostructures with the ability to withstand relatively high buckling forces without becoming fractured. The Young's modulus is found to be independent of nanowire diameter in the investigated range, in contrast to reported results for ZnO NWs and carbon nanotubes where the modulus increases with a decrease in diameter. Molecular dynamics simulations performed for nanowires with diameters less than 20 nm show limited size dependence for diameters smaller than 5 nm. The surface atoms present lower Young's modulus according to the simulations and the limited size dependency of the cylindrical ZnTe NWs is attributed to the short range covalent interactions.
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We report growth and characterization of CdTe wires 30400 nm in diameter by the vaporliquidsolid technique. Individual nanowires were placed on a movable piezotube, which allowed three-dimensional motion toward a scanning tunneling microscope (STM). A bias was applied to the STM tip in contact with the nanowire, and the morphological changes due to Joule heating were observed in situ using a transmission electron microscope (TEM) in real time. For thick CdTe wires (d > ~150 nm), the process results in the growth of superfine nanowires (SFNWs) of 24 nm diameter on the surface of the wire. Smaller diameter nanowires, in contrast, disintegrate under the applied bias before the complete evolution of SFNWs on the surface.
RESUMO
In situ electrochemical lithiation and delithiation processes inside a nanobattery consisting of an individual amorphous Si nanorod and ionic liquid were explored. Direct formation of the crystalline Li(22)Si(5) phase due to the intercalation of Li ions was observed. In addition, the role of the electrolyte-nanorod interface was examined. It was observed that the lithiation of Si nanorods is dominated by surface diffusion. Upon the delithiation process, partial decomposition of Li(22)Si(5) particles was observed which can explain the irreversible capacity loss that is generally seen in Si anodes. This study shows that the radial straining due to lithiation does not cause cracking in nanorods as small in diameter as 26 nm, whereas cracks were observed during the lithiation of 55 nm Si nanorods.
RESUMO
The recent observation of high flexibility in buckled boron nitride nanotubes (BNNTs) contradicts the pre-existing belief about BN nanotube brittleness due to the partially ionic character of bonding between the B and N atoms. However, the underlying mechanisms and relationships within the nanotube remained unexplored. This study reports for the first time the buckling mechanism in multi-walled BNNTs upon severe mechanical deformation. Individual BNNTs were deformed inside a transmission electron microscope (TEM) equipped with an in situ atomic force microscopy holder. High-resolution TEM images revealed that bent BNNTs form multiple rippling upon buckling. The critical strain to form the first ripple was measured as 4.1% and the buckling process was reversible up to 26% strain. As opposed to carbon nanotubes, the BNNTs buckled into V-shaped ripples rather than smooth wavy shapes. The rippling wavelength was quantified in terms of the outer diameter and thickness of the nanotubes. The BNNTs showed a larger rippling wavelength compared to that of CNTs with the same number of walls. This difference was explained by the tendency of BN structures to reduce the number of thermodynamically unfavorable B-B and N-N bonds at the sharp corners in the rippling regions. The BNNTs' structure also exhibited a higher fracture strain compared to their counterpart.