Aniruddha Dutta

Nanoscale characterization of gold nanoparticles created by in situ reduction at a polymeric surface

Transmission Electron Microscopy is used as a quantitative method to measure the shapes, sizes and volumes of gold nanoparticles created at a polymeric surface by three different in situ synthesis methods. The atomic number contrast (Z‐contrast) imaging technique reveals nanoparticles which are formed on the surface of the polymer. However, with certain reducing agents, the gold nanoparticles are additionally found up to 20 nm below the polymer surface. In addition, plan‐view high‐angle annular dark‐field scanning transmission electron microscopy images were statistically analyzed on one sample to measure the volume, height and effective diameter of the gold nanoparticles and their size distributions. Depth analysis from high‐angle annular dark‐field scanning transmission electron microscopy micrographs also gives information on the dominant shape of the nanoparticles.

Aging of nano-morphology, resistivity, and far-infrared absorption in gold-black

Gold black is a highly porous, extremely fragile, infrared-absorbing film used primarily as a coating for bolometers. Long term stability of its absorbance is a significant practical concern. This paper reports on the aging of morphological, electrical, and optical properties of gold black samples prepared with different initial porosities. An observed two-fold decrease in electrical resistance after 90 days at room-temperature is correlated with an increase in nano-crystalline grain size. Much larger resistance drops were observed after isothermal annealing at temperatures up to 100 °C. Aging and annealing tended to improve the far-infrared absorption. Samples with the highest initial porosity have the fastest structural relaxation.

Interfacial Atomic Number Contrast in Thick Samples

A quantitative method to simulate the electron scattering at the interface of two material layers in thick samples is presented here. The samples are analyzed by Scanning Transmission Electron Microscopy (STEM) in a Tecnai F30 using a High Angle Annular Dark-Field (HAADF) detector with a collection range 55 mrad to 245 mrad. At the interface of a high-density and low-density material an increase in the HAADF signal for thick TEM samples can be observed. We report here the simulated HAADF detector intensity across the interface of two materials using Python programming language and its comparison with experimental results. The electron atomic scattering factor f e (s) for a complex potential is given by:

Quantitative Measurement of Volumes for Nanoparticles by High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy

A quantitative method to determine sample thicknesses in Transmission Electron Microscopy (TEM) using the Scanning (STEM) mode is presented. A High-Angle Annular Dark-Field (HAADF) detector collects electrons scattered to high angles with its intensity proportional to the sample thickness and increasing with atomic number. Multilayered samples provided by TriQuint Semiconductors in Apopka (FL) are used for calibration yielding data on the interaction cross section per atom. Multislice simulations in C# .NET 3.5 are used for comparison with experimental results. The calibrations were used to determine concentration gradients in nanoscale Fe-Pt multilayers as well as thicknesses and volumes of individual Ag nanoparticles. Volumes of nanoparticles with known composition can be determined with an accuracy better than 15%.