16,880 research outputs found
Elastomeric carbon nanotube circuits for local strain sensing
We use elastomeric polydimethylsiloxane substrates to strain single-walled
carbon nanotubes and modulate their electronic properties, with the aim of
developing flexible materials that can sense local strain. We demonstrate
micron-scale nanotube devices that can be cycled repeatedly through strains as
high as 20% while providing reproducible local strain transduction by via the
device resistance. We also compress individual nanotubes, and find they undergo
an undulatory distortion with a characteristic spatial period of 100-200 nm.
The observed period can be understood by the mechanical properties of nanotubes
and the substrate in conjunction with continuum elasticity theory. These could
potentially be used to create superlattices within individual nanotubes,
enabling novel devices and applications
Nanoscale Bandgap Tuning across an Inhomogeneous Ferroelectric Interface
We report nanoscale bandgap engineering via a local strain across the
inhomogeneous ferroelectric interface, which is controlled by the
visible-light-excited probe voltage. Switchable photovolatic effects and the
spectral response of the photocurrent were explore to illustrate the reversible
bandgap variation (~0.3eV). This local-strain-engineered bandgap has been
further revealed by in situ probe-voltage-assisted valence electron energy-loss
spectroscopy (EELS). Phase-field simulations and first-principle calculations
were also employed for illustration of the large local strain and the bandgap
variation in ferroelectric perovskite oxides. This reversible bandgap tuning in
complex oxides demonstrates a framework for the understanding of the
opticallyrelated behaviors (photovoltaic, photoemission, and photocatalyst
effects) affected by order parameters such as charge, orbital, and lattice
parameters
Dynamics of Bulk vs. Nanoscale WS_2: Local Strain and Charging Effects
We measured the infrared vibrational properties of bulk and nanoparticle
WS in order to investigate the structure-property relations in these novel
materials. In addition to the symmetry-breaking effects of local strain,
nanoparticle curvature modifies the local charging environment of the bulk
material. Performing a charge analysis on the \emph{xy}-polarized E
vibrational mode, we find an approximate 1.5:1 intralayer charge difference
between the layered 2H material and inorganic fullerene-like (IF)
nanoparticles. This effective charge difference may impact the solid-state
lubrication properties of nanoscale metal dichalcogenides.Comment: 6 pages, 5 figure
A nanoindentation investigation of local strain rate sensitivity in dual-phase Ti alloys
Using nanoindentation we have investigated the local strain rate sensitivity in dual-phase Ti alloys, Ti-6Al-2Sn-4Zr-xMo (x=2 and 6), as strain rate sensitivity could be a potential factor causing cold dwell fatigue. Electron backscatter diffraction (EBSD) was used to select hard and soft grain orientations within each of the alloys. Nanoindentation based tests using the continuous stiffness measurement (CSM) method were performed with variable strain rates, on the order of 10â1 to 10â3sâ1. Local strain rate sensitivity is determined using a power law linking equivalent flow stress and equivalent plastic strain rate. Analysis of residual impressions using both a scanning electron microscope (SEM) and a focused ion beam (FIB) reveals local deformation around the indents and shows that nanoindentation tested structures containing both α and ÎČ phases within individual colonies. This indicates that the indentation results are derived from averaged α/ÎČ properties. The results show that a trend of local rate sensitivity in Ti6242 and Ti6246 is strikingly different; as similar rate sensitivities are found in Ti6246 regardless of grain orientation, whilst a grain orientation dependence is observed in Ti6242. These findings are important for understanding dwell fatigue deformation modes, and the methodology demonstrated can be used for screening new alloy designs and microstructures
Measuring Spatial Distribution of Local Elastic Modulus in Glasses
Glasses exhibit spatially inhomogeneous elastic properties, which can be
investigated by measuring their elastic moduli at a local scale. Various
methods to evaluate the local elastic modulus have been proposed in the
literature. A first possibility is to measure the local stress-local strain
curve and to obtain the local elastic modulus from the slope of the curve, or
equivalently to use a local fluctuation formula. Another possible route is to
assume an affine strain and to use the applied global strain instead of the
local strain for the calculation of the local modulus. Most recently a third
technique has been introduced, which is easy to be implemented and has the
advantage of low computational cost. In this contribution, we compare these
three approaches by using the same model glass and reveal the differences among
them caused by the non-affine deformations
Random local strain effects in homovalent-substituted relaxor ferroelectrics: a first-principles study of BaTi0.74Zr0.26O3
We present first-principles supercell calculations on BaTi0.74Zr0.26O3, a
prototype material for relaxors with a homovalent substitution. From a
statistical analysis of relaxed structures, we give evidence for four types of
Ti-atom polar displacements: along the , , or
directions of the cubic unit cell, or almost cancelled. The type of a Ti
displacement is entirely determined by the Ti/Zr distribution in the adjacent
unit cells. The underlying mechanism involves local strain effects that ensue
from the difference in size between the Ti4+ and Zr4+ cations. These results
shed light on the structural mechanisms that lead to disordered Ti
displacements in BaTi(1-x)Zr(x)O3 relaxors, and probably in other BaTiO3-based
relaxors with homovalent substitution.Comment: 5 pages, 4 figure
A quantum phase transition from triangular to stripe charge order in NbSe
The competition between proximate electronic phases produces a complex
phenomenology in strongly correlated systems. In particular, fluctuations
associated with periodic charge or spin modulations, known as density waves,
may lead to exotic superconductivity in several correlated materials. However,
density waves have been difficult to isolate in the presence of chemical
disorder, and the suspected causal link between competing density wave orders
and high temperature superconductivity is not understood. Here we use scanning
tunneling microscopy to image a previously unknown unidirectional (stripe)
charge density wave (CDW) smoothly interfacing with the familiar
tri-directional (triangular) CDW on the surface of the stoichiometric
superconductor NbSe. Our low temperature measurements rule out thermal
fluctuations, and point to local strain as the tuning parameter for this
quantum phase transition. We use this discovery to resolve two longstanding
debates about the anomalous spectroscopic gap and the role of Fermi surface
nesting in the CDW phase of NbSe. Our results highlight the importance of
local strain in governing phase transitions and competing phenomena, and
suggest a new direction of inquiry for resolving similarly longstanding debates
in cuprate superconductors and other strongly correlated materials.Comment: PNAS in pres
Gradient Photonic Materials Based on OneâDimensional Polymer Photonic Crystals
In nature, animals such as chameleons are wellâknown for the complex color patterns of their skin and the ability to adapt and change the color by manipulating sophisticated photonic crystal systems. Artificial gradient photonic materials are inspired by these color patterns. A concept for the preparation of such materials and their function as tunable mechanochromic materials is presented in this work. The system consists of a 1D polymer photonic crystal on a centimeter scale on top of an elastic poly(dimethylsiloxane) substrate with a gradient in stiffness. In the unstrained state, this system reveals a uniform red reflectance over the entire sample. Upon deformation, a gradient in local strain of the substrate is formed and transferred to the photonic crystal. Depending on the magnitude of this local strain, the thickness of the photonic crystal decreases continuously, resulting in a positionâdependent blue shift of the reflectance peak and hence the color in a rainbowâlike fashion. Using more sophisticated hardâsoftâhardâsoftâhard gradient elastomers enables the realization of stripeâlike reflectance patterns. Thus, this approach allows for the tunable formation of reflectance gradients and complex reflectance patterns. Envisioned applications are in the field of mechanochromic sensors, telemedicine, smart materials, and metamaterials
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