Mikhail Ladanov

Structure and opto-electrochemical properties of ZnO nanowires grown on n-Si substrate.

Zinc oxide (ZnO) nanostructures have attracted great attention as a promising functional material with unique properties suitable for applications in UV lasers, light emitting diodes, field emission devices, sensors, field effect transistors, and solar cells. In the present work, ZnO nanowires have been synthesized on an n-type Si substrate using a hydrothermal method where surfactant acted as a modifying and protecting agent. The surface morphology, electrochemical properties, and opto-electrochemical properties of ZnO nanowires are investigated by using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), cyclic voltammetry, and impedance spectroscopy techniques. The cycling characteristics and rate capability of the ZnO nanowires are explored through electrochemical studies performed under varying electrolytes. The photo response is observed using UV radiation. It is demonstrated that crystallinity, particle size, and morphology all play significant roles in the electrochemical performance of the ZnO electrodes.

Microfluidic hydrothermal growth of ZnO nanowires over high aspect ratio microstructures

A hydrothermal synthesis of densely packed ZnO nanowires was realized in a confined space via forced circulation of the heated growth solution through microfluidic channels formed primarily by a set of high aspect ratio trenches in a Si substrate. A uniform and conformal seeding layer of ZnO was deposited to cover the entire surface of the trenches by means of atomic layer deposition (ALD). Densely packed ZnO nanowires were formed inside the trenches with particularly good coverage over the sidewalls, where they would not grow effectively through a conventional hydrothermal method. The strategy for controlled growth of densely packed ZnO nanowires over such high aspect ratio microstructures is deemed beneficial when these microstructures are employed as electrodes with high specific surface areas for devices such as supercapacitors or any other electrochemical devices.

Dynamic visualization of photothermal heating by gold nanocages using thermoresponsive elastin like polypeptides.

Understanding how plasmonic nanoparticles collectively generate heat upon exposure to light and thus increase the local temperature of the surrounding medium is critical for many applications such as plasmon-assisted microfluidics, plasmonic tweezers, and photothermal cancer therapy. Reliable temperature manipulation requires the capability to spatially and dynamically analyze local temperature profiles as a function of nanoparticle concentration and laser intensity. In this work, we present a novel method for visualization of local temperature increase using elastin-like polypeptides (ELP). We also propose a robust algorithm that allows the construction of reliable calibration curves using known boundary conditions and Boltzmann sigmoid fit applied to the ELP solutions temperature-absorption transfer function. Using this technique, for the first time, we successfully demonstrated how surface and volume distribution of the nano-heaters affect collective heat generation. This approach allows the visualization of dynamic 2D-temperature profiles and simultaneously enables the measurement of specific temperature at any point in a 2D-map. The experimental setup is compatible with conventional optical microscopy and requires no specialized hardware or complex sample preparation. Finally, the real time visualization of plasmonic heating offers an opportunity to control outcomes of thermo-plasmonics which enables a myriad of practical applications.

Optimization of light delivery by a nanowire-based single cell optical endoscope

Here we present a new design and FDTD simulations of light delivery by a nanowire-based intracellular endoscope. Nanowires can be used for minimally invasive and very local light delivery inside cells. One of the main challenges is coupling of light into the nanowire. We propose a new plasmonic coupler interface between cleaved optical fiber and a nanowire, and optimize light coupling efficiency and contrast.

Resonant Raman Scattering by Strained and Relaxed Ge Quantum Dots

Fundamental vibrations in Ge/Si structures with strained and relaxed Ge quantum dots (QDs) grown by molecular beam epitaxy were investigated using resonant Raman spectroscopy. Transmission electron microscopy experiments show that the strained Ge QDs are typical “hut clusters” with base size of 15nm and a height of 2nm. A two mode distribution in size (100200nm and 3-6nm) is found for relaxed QDs. The Raman efficiencies of the Ge optical phonons as a function of excitation energy reveal maxima at 2.35-2.41eV attributed to the E0 resonance in Ge QDs due to electronic confinement. The frequency positions of optical phonons localized in Ge “hut clusters” under non-resonant conditions correspond to fully strained Ge QDs while the frequency position of optical phonons in relaxed Ge QDs corresponds to the value in bulk Ge. With increasing excitation energy (2.5-2.7eV) the position of the Ge optical phonons shifts downwards due to size-confinement effect of optical phonons in strained and relaxed Ge QDs, indicating the presence of a QD size distribution in Ge dot structures.

Plasmono-magnetic material for precise photothermal heating

Noble metal nanoparticles have been extensively studied as photo-sensitive agents for photothermal cancer therapy. Precise control over the size and shape of the nanoparticles allowed strong optical absorption and efficient heat generation necessary for destroying a tumor to be achieved. However, one of the fundamental challenges of application of the nanoparticles towards photothermal cancer therapy is low specificity in the targeting tumor tissue in comparison with the healthy tissue and the resulting unfavorable biodistribution of the nanoparticles. Additional levels of control over particle distribution can be achieved by making the particles magnetic and using external magnets to control their accumulation in a tumor. Since the direct synthesis of particles with a magnetic core and a metallic shell limits the options for design and fine-tuning of plasmonic properties, the alternative approaches to the design of such materials have to be investigated. Here we propose and demonstrate a new design of a hybrid plasmono-magnetic material for photothermal heating created by grafting Au nanocages onto a surface of magnetic micro-beads. Next, we confirm its dual functionality in in vitro studies and show that individual hybrid particles can be magnetically controlled with a precision of a few micrometers and precisely destroy individual cells using plasmonic heating.