15 research outputs found
Probing thermal expansion of graphene and modal dispersion at low-temperature using graphene NEMS resonators
We use suspended graphene electromechanical resonators to study the variation
of resonant frequency as a function of temperature. Measuring the change in
frequency resulting from a change in tension, from 300 K to 30 K, allows us to
extract information about the thermal expansion of monolayer graphene as a
function of temperature, which is critical for strain engineering applications.
We find that thermal expansion of graphene is negative for all temperatures
between 300K and 30K. We also study the dispersion, the variation of resonant
frequency with DC gate voltage, of the electromechanical modes and find
considerable tunability of resonant frequency, desirable for applications like
mass sensing and RF signal processing at room temperature. With lowering of
temperature, we find that the positively dispersing electromechanical modes
evolve to negatively dispersing ones. We quantitatively explain this crossover
and discuss optimal electromechanical properties that are desirable for
temperature compensated sensors.Comment: For supplementary information and high resolution figures please go
to http://www.tifr.res.in/~deshmukh/publication.htm
Orientation-dependent solid solution strengthening in zirconium: a nanoindentation study
Orientation-dependent solid solution strengthening was explored through a combined microtexture plus nanoindentation study. Pure zirconium (6N purity crystal-bar Zr) and commercial Zircaloy-2 were investigated for comparison. Local mechanical properties were estimated through finite element (FE) simulations of the unloading part of the nanoindentation load–displacement response. Combinations of ‘averaging’ scheme and constitutive relationship were used to resolve uncertainty of FE-extracted mechanical properties. Comparing the two grades, non-basal oriented grains showed an overall hardening and increase in elastic modulus. In contrast, insignificant change was observed for basal (or near-basal) oriented grains. The strengthening of non-basal orientations appeared via elimination of the lowest hardness/stiffness values without a shift in the peak value. Such asymmetric development brought out the clear picture of orientation-dependent solid solution strengthening in zirconium
Characterization of multiferroic thin films directly deposited on silicon for novel device applications
We have investigated the multiferroic and dielectric properties in Dy modified BiFeO<SUB>3</SUB> thin films deposited directly on silicon using pulsed laser deposition (PLD) technique. The results support the usability of these films in multiferroic based MEMS devices as well as gate dielectrics for future CMOS applications
Wrinkling of Atomic Planes in Ultrathin Au Nanowires
A detailed understanding of structure and stability of nanowires is critical for applications. Atomic resolution imaging of ultrathin single crystalline Au nanowires using aberration-corrected microscopy reveals an intriguing relaxation whereby the atoms in the close-packed atomic planes normal to the growth direction are displaced in the axial direction leading to wrinkling of the (111) atomic plane normal to the wire axis. First-principles calculations of the structure of such nanowires confirm this wrinkling phenomenon, whereby the close-packed planes relax to form saddle-like surfaces. Molecular dynamics studies of wires with varying diameters and different bounding surfaces point to the key role of surface stress on the relaxation process. Using continuum mechanics arguments, we show that the wrinkling arises due to anisotropy in the surface stresses and in the elastic response, along with the divergence of surface-induced bulk stress near the edges of a faceted structure. The observations provide new understanding on the equilibrium structure of nanoscale systems and could have important implications for applications in sensing and actuation
Wrinkling of Atomic Planes in Ultrathin Au Nanowires
A detailed
understanding of structure and stability of nanowires
is critical for applications. Atomic resolution imaging of ultrathin
single crystalline Au nanowires using aberration-corrected microscopy
reveals an intriguing relaxation whereby the atoms in the close-packed
atomic planes normal to the growth direction are displaced in the
axial direction leading to wrinkling of the (111) atomic plane normal
to the wire axis. First-principles calculations of the structure of
such nanowires confirm this wrinkling phenomenon, whereby the close-packed
planes relax to form saddle-like surfaces. Molecular dynamics studies
of wires with varying diameters and different bounding surfaces point
to the key role of surface stress on the relaxation process. Using
continuum mechanics arguments, we show that the wrinkling arises due
to anisotropy in the surface stresses and in the elastic response,
along with the divergence of surface-induced bulk stress near the
edges of a faceted structure. The observations provide new understanding
on the equilibrium structure of nanoscale systems and could have important
implications for applications in sensing and actuation