Eugenii U. Donev

Electron-beam-induced deposition of platinum from a liquid precursor.

We demonstrate here the first focused electron-beam-induced deposition (EBID) of nanostructures using a liquid precursor. We have deposited sub-50 nm platinum (Pt) wires and dots from a dilute, aqueous solution of chloroplatinic acid. Existing EBID processes rely on the electron-beam stimulated decomposition of gaseous precursors; as a result, the deposits are highly contaminated (up to 75 at. % carbon or 60 at. % phosphorus for Pt processes). In contrast, we show that deposition of platinum by electron-beam reduction of platinum ions from solution leads to high-purity deposits (approximately 10 at. % chlorine contamination) at rates at least ten times higher than those obtained with other platinum precursors. Liquid-phase EBID offers a new route to deterministic, three-dimensional, nanometer-scale structures composed of multiple materials without complex multistep processing. Thus, it may prove important for prototyping and low-volume production of nanoscale devices and for repair and modification of nanoscale masks and templates used in high-volume production.

Modulation of the gold particle–plasmon resonance by the metal–semiconductor transition of vanadium dioxide

We report experimental observations of relative blue-shifts in the particle?plasmon resonance of gold nanoparticles (Au NPs) covered with a vanadium dioxide (VO2) film as the VO2 material undergoes a semiconductor-to-metal transition at approximately 67??C. Although the extinction spectra of the Au NPs exhibit significant red-shifts in the presence of the surrounding VO2 film as compared to the same particles in air, the key result of this work is the dynamically controlled blue-shift of the Au-NP dipole resonance upon thermal switching of the VO2 overlayer from the semiconducting to the metallic state. We also report on the size and polarization dependence of the extinction spectra for both states, and present Mie theory calculations that confirm in a semi-quantitative way the observed trends in the VO2-induced modulation of the Au-NP plasmon resonance, and their origin in the VO2 dielectric function.

Electron-beam-induced deposition of gold from aqueous solutions

Focused electron-beam-induced deposition (EBID) using bulk liquid precursors is a novel approach to nanofabrication that has shown improvements in purity compared to EBID with gas-phase precursors. Here we report the first EBID of gold using bulk liquid precursors. We study the differences in gold deposited from three different aqueous solutions containing chloroauric acid (HAuCl(4)), sodium tetrachloroaurate (NaAuCl(4)), and the disulfitoaurate complex ([Au(SO(3))(2)](3-)). We also examine the dependence of threshold dose upon precursor concentration and demonstrate high-resolution patterning with a pitch as small as 50 nm. Finally, we show that the purity of gold deposited using these liquid precursors is significantly improved in comparison with deposits from metal-organic gaseous precursors.

Structural colors: from natural to artificial systems.

Structural coloration has attracted great interest from scientists and engineers in recent years, owing to fascination with various brilliant examples displayed in nature as well as to promising applications of bio-inspired functional photonic structures and materials. Much research has been done to reveal and emulate the physical mechanisms that underlie the structural colors found in nature. In this article, we review the fundamental physics of many natural structural colors displayed by living organisms as well as their bio-inspired artificial counterparts, with emphasis on their connections, tunability strategies, and proposed applications, which aim to maximize the technological benefits one could derive from these photonic nanostructures. WIREs Nanomed Nanobiotechnol 2016, 8:758-775. doi: 10.1002/wnan.1396 For further resources related to this article, please visit the WIREs website.

X-ray diffraction studies of the growth of vanadium dioxide nanoparticles

We have characterized for the first time in situ the growth of vanadium dioxide nanoparticulate films prepared by pulsed-laser deposition, using a five-circle x-ray diffractometer, in order to provide structural information as the films are grown. A vanadium metal target was ablated in the presence of a pulsed N2O reactive gas source, and films were grown on Si(001) and Al2O3(0001) substrates. Optical measurements confirmed that the films deposited in this way exhibit the well-known VO2 metal–insulator transition at approximately 70 °C. The VO2 films grown at room temperature on silicon substrates are amorphous and extremely smooth. These become considerably rougher upon thermal annealing, as the VO2 phase crystallizes out in the form of hemispherical islands. These films also contain traces of a V2O5 nanoparticle phase in the first few monolayers, although the degree of VO2 crystallinity in the nanoparticles is quite high. In contrast, the VO2 nanoparticles grown on the sapphire substrates are in the for...

Liquid-precursor electron-beam-induced deposition of Pt nanostructures: dose, proximity, resolution.

While electron-beam-induced deposition (EBID) from various gaseous precursors has been known and studied for decades, EBID from bulk liquid precursors is very much in its infancy and the following is only the second report on this technique. Here we present liquid-precursor (LP-)EBID of platinum (Pt) nanostructures from a dilute aqueous solution of chloroplatinic acid (H(2)PtCl(6)). We investigate how the lateral size of Pt nanoparticles (NPs) varies with charge dose, and how already deposited Pt NPs are affected by the subsequent deposition of their neighbors (proximity effect). We also demonstrate LP-EBID of dense arrays of small Pt dots (60 nm pitch, 30 nm diameter) and thin Pt lines (60 nm pitch, 25 nm width), which compare favorably with the typical resolution of resist-based electron-beam lithography.

Dynamic Optical Gratings Accessed by Reversible Shape Memory

Shape memory polymers (SMPs) have been shown to accurately replicate photonic structures that produce tunable optical responses, but in practice, these responses are limited by the irreversibility of conventional shape memory processes. Here, we report the intensity modulation of a diffraction grating utilizing two-way reversible shape changes. Reversible shifting of the grating height was accomplished through partial melting and recrystallization of semicrystalline poly(octylene adipate). The concurrent variations of the grating shape and diffraction intensity were monitored via atomic force microscopy and first order diffraction measurements, respectively. A maximum reversibility of the diffraction intensity of 36% was repeatable over multiple cycles. To that end, the reversible shape memory process is shown to broaden the functionality of SMP-based optical devices.

Effects of a silicon probe on gold nanoparticles on glass under evanescent illumination

We have numerically investigated the influence of a nanoscale silicon tip in proximity to an illuminated gold nanoparticle. We describe how the position of the high-permittivity tip and the size of the nanoparticle impact the absorption, peak electric field and surface plasmon resonance wavelength under different illumination conditions. We detail the finite element method (FEM) approach we have used, whereby we specify a volume excitation field analytically and calculate the difference between this source field and the total field (i.e., scattered-field formulation). We show that a nanoscale tip can locally enhance the absorption of the particle as well as the peak electric field at length scales far smaller than the wavelength of the incident light.

Differentiating surface and bulk interactions using localized surface plasmon resonances of gold nanorods

We demonstrate a novel localized surface-plasmon resonance sensor that can distinguish surface binding interactions from interfering bulk effects. This is accomplished by utilizing the longitudinal and transverse plasmon modes of gold nanorods. We have investigated, both numerically and experimentally, the effect of change in background refractive index and surface binding on the two resonances of a gold nanorod on an indium tin oxide coated glass substrate.

Silver patterning using an atomic force microscope tip and laser-induced chemical deposition from liquids

This article presents a new direct patterning technique in which laser photoreduction of silver from a liquid is controlled by a scanning atomic force microscope tip. Contrary to expectations, the tip suppresses, rather than enhances, deposition on the underlying substrate, and this suppression persists in the absence of the tip. Experiments presented here exclude three potential mechanisms: purely mechanical material removal, depletion of the silver precursor, and preferential photoreduction on existing deposits. These results represent a first step toward direct, negative tone, tip-based patterning of functional materials.