Amit Banerjee

Electron- and ion-beam-induced maneuvering of nanostructures: phenomenon and applications

Electron-and ion-induced bending (EIB/IIB) phenomena have been studied in self-supported polycrystalline metallic and metal-amorphous bilayered nanocantilevers. The experiments reveal many interesting facts regarding electron/ion-matter interaction, which builds a proper foundation for the understanding of the phenomenon. The mechanism for bending of metallic cantilevers has been proposed to be primarily due to void-induced stress generation during ion beam irradiation. On the other hand, thermal effects have been found to play the dominant role in the case of bending of bilayer (amorphous-metal) nanocantilevers. The instantaneous, reversible, highly controllable and permanent nature of the process has been exploited to fabricate several complicated nanostructures in three dimensions. IIB of the fabricated cantilevers is shown to have a high precession mass sensing aptitude, capable of detecting a change in mass of the order of femtograms.

The measurement of attogram mass accumulation on nanostructures during e-beam scanning, using carbon nanopillars in resonant mode

We present a universal phenomenon of mass accumulation and its sensing on nanostructures due to electron beam cracking of residual gas molecules during electron beam scanning. Though the extent of this phenomenon is limited to a very small increment in mass or thickness, it has significant implications for both the scientific and technological aspects of almost all processes in the nanodomain. Mass accumulation in every frame scan (or per second) is of the order of a few attograms and the thickness of deposition is of the order of picometre (fraction of a monolayer) only. Direct measurement of a mass or thickness of this order is difficult. Nanopillars having a high resonance Q-factor have been successfully exploited for such high precision measurements. The mass accumulation rate has been characterized with respect to (i) electron energy and beam current, (ii) environment within the chamber (presence or absence of a precursor gas) and (iii) partial exposure of the nanopillars to the e-beam.

Ultralarge elastic deformation of nanoscale diamond

Small, smooth, and bendable diamonds If you manage to deform a diamond, it usually means you have broken it. Diamonds have very high hardness, but they do not deform elastically. This limits their usefulness for some applications. However, Banerjee et al. discovered that diamond nanoneedles can deform elastically after all (see the Perspective by LLorca). The key was in their small size (300 nm), which allowed for very smooth-surfaced, defect-free diamonds. The deformation was close to the theoretical limit for diamond, which opens up the potential for applications in microelectronics and drug delivery. Science, this issue p. 300; see also p. 264 Diamond nanoneedles have smooth surfaces and are defect-free, allowing them to deform elastically. Diamonds have substantial hardness and durability, but attempting to deform diamonds usually results in brittle fracture. We demonstrate ultralarge, fully reversible elastic deformation of nanoscale (~300 nanometers) single-crystalline and polycrystalline diamond needles. For single-crystalline diamond, the maximum tensile strains (up to 9%) approached the theoretical elastic limit, and the corresponding maximum tensile stress reached ~89 to 98 gigapascals. After combining systematic computational simulations and characterization of pre- and postdeformation structural features, we ascribe the concurrent high strength and large elastic strain to the paucity of defects in the small-volume diamond nanoneedles and to the relatively smooth surfaces compared with those of microscale and larger specimens. The discovery offers the potential for new applications through optimized design of diamond nanostructure, geometry, elastic strains, and physical properties.

Fracto-emission in lanthanum-based metallic glass microwires under quasi-static tensile loading

Plastic deformation in metallic glasses is highly localized and often associated with shear banding, which may cause momentary release of heat upon fracture. Here, we report an explosive fracture phenomenon associated with momentary (∼10u2009ms) light emission (flash) in Lanthanum-based (LaAlNi) metallic glass microwires (dia. ∼50u2009μm) under quasi-static tensile loading. The load-displacement data as well as the visual information of the tensile deformation process were acquired through an in situ measurement set-up, which clearly showed nonlinear stress (σ)–strain ( ϵ) curves prior to yielding and also captured the occurrence of the flash at high fracture stresses (∼1u2009GPa). Through the postmortem fractographic analysis, it can be revealed that the fracto-emission upon quasi-static loading could be mainly attributed to the localized adiabatic work accumulated at a very large elastic strain confined within the microscale sample volume, followed by a localized high temperature rise up to ∼1000u2009K at the fracture ...

Unusual dimensional dependence of resonance frequencies of Au nanocantilevers fabricated with self-organized microstructure

Metallic nanocantilevers of gold are fabricated from self-supporting polycrystalline thin film (100 nm) by focused ion beam assisted milling and ion induced manipulation processes. The surfactant assisted growth of the thin film leads to self-organized dendrite like morphology. This self-organized dendrite like morphology of the gold film imposes a new characteristic length scale corresponding to the mean size of gold grains present within the branches of the dendrite pattern in the film. The resonance characteristic investigated on cantilevers having different widths shows a significant drop in energy dissipation and hence an enhancement in the resonance amplitude at a characteristic width. At this width the resonance frequency of a vibrating cantilever approaches the theoretically expected value anticipated from an ideal cantilever treated like an elastic continuum.

Fabrication of single and coupled metallic nanocantilevers and their nanomechanical response at resonance

We fabricate and explore the resonance characteristics of self-supporting thin film based metallic nanocantilever systems. Nanocantilevers of Au and Ag are fabricated from self-supporting (polycrystalline) thin films (∼100 nm) grown via a surfactant mediated process. Focused ion beam assisted milling and manipulation techniques are used to fabricate the nanocantilevers. The resonance characteristics of the cantilevers are investigated by the piezoelectric base excitation method and the frequencies of their first resonance modes are determined by digitally processing and analysing scanning electron microscopy images captured during the study. The resonance characteristics of the nanocantilevers are observed to deviate from the Euler-Bernoulli description. We suggest a polynomial expression to describe the peculiar dimensional dependence of resonance frequency of a mechanically vibrating nanocantilever, where the zeroth order term in the polynomial expression represents an Euler-Bernoulli like form. We also demonstrate a fabrication and measurement technique for an elastically coupled Au nanocantilever system and analysis of its vibration characteristics by means of an analogous mass-spring system.

P1–18: I-V Characteristics of nanogap electrodes formed by thermally assisted electromigration

Electrodes with nano-scale gaps have been fabricated using metallic nano-wires, derived via milling of thin films with focused ion beam (FIB) and passing current ~10¹²A/m². Their I-V characteristics measured at a pressure ~10⁻⁶ mbar are shown to follow Child-Langmuir law or Fowler-Nordheim field emission depending upon the gap.

Detecting sub-nanometer transverse vibrations on a piezo crystal oscillator surface, using time series tunneling current measurements

Vibration characteristics of a piezo crystal oscillator surface are studied using time series measurements of tunneling current. Using this technique, the fluctuations in the tunneling current between a scanning tunneling microscopy tip and the surface of a piezo crystal oscillator are studied, which reveal sub-nanometer vibrations with a sensitivity of 10−2 A°Hzu2009. As the excitation frequency applied to the crystal is varied, the vibrations on the oscillator surface exhibit a resonant response. Furthermore, we detected unconventional sub-nanometer perpendicular vibration modes excited on the crystal surface. These vibrations are in a direction transverse to the surface of the crystal oscillator, whose conventional vibration mode is in a horizontal plane parallel to the surface. We also find near resonance higher harmonics of the perpendicular mode. Thus, the piezo crystal oscillator together with the time series tunneling current measurements offer a convenient simultaneous drive and detection system with...

Growing gold fractal nano-structures and studying changes in their morphology as a function of film growth rate

We investigate the formation of fractal like nano-structures on free standing gold films grown via surfactant mediated thin film growth process. We determine these structures to be confined within the first few monolayers of the thin film. Their chemical composition is identical to that of the Au film, although their density is different from the surrounding film. We observe changes in the morphology of these fractal structures by controlling the film growth rate, which spans across three orders of magnitude. From our study, we quantify the morphological changes in the fractal structure via a roundness parameter and we suggest an empirical relation between the roundness parameter and the growth rate. The study shows an inverse relationship between the roundness parameter and the growth rate and also that the fractal to compact morphological transition is continuous.

Spatially resolved energy dispersive x-ray spectroscopic method for in-situ evaluation of mechanical properties during the growth of a C - Pt composite nanowire

A core-shell type C-Pt composite nanowire is fabricated using focused ion and electron beam induced chemical vapor deposition techniques. Using information from spatially resolved energy dispersive x-ray spectra, we detect the resonance vibration in the C-Pt composite nanowire. We use this method to measure the Youngs moduli of the constituents (C, Pt) of the composite nanowire and also estimate the density of the FEB CVD grown Pt shell surrounding the C core. By measuring the resonance characteristics of the composite nanowire we estimate a Pt shell growth rate of ∼0.9 nms−1. The study is analyzed to suggest that the Pt shell growth mechanism is primarily governed by the sticking coefficient of the organometallic vapor on the C nanowire core.