Session H34: Focus Session: Nano II: Nanoscale Materials and Properties I

Nanoelectronics Meets Biology

Nanoscale materials enable unique opportunities at the interface between the physical and life sciences, and the interface between nanoelectronic devices and biological systems makes possible communication between these two diverse systems at the length scale relevant to biological function. In this presentation, the development of nanowire nanoelectronic devices and their application as powerful tools for the life sciences will be discussed. First, a brief introduction to nanowire nanoelectronic devices as well as comparisons to other electrophysiological tools will be presented to illuminate the unique strengths and opportunities enabled at the nanoscale. Second, illustration of detection capabilities including signal-to-noise and applications for real-time label-free detection of biochemical markers down to the level of single molecules will be described. Third, the use of nanowire nanoelectronics for building interfaces to cells and tissue will be reviewed. Multiplexed measurements made from nanowire devices fabricated on flexible and transparent substrates recording signal propagation across cultured cells, acute tissue slices and intact organs will be illustrated, including quantitative analysis of the high simultaneous spatial and temporal resolution achieved with these nanodevices. Specific examples of subcellular and near point detection of extracellular potential will be used to illustrate the unique capabilities, such as recording localized potential changes due to neuronal activities simultaneously across many length scales, which provide key information for functional neural circuit studies. Last, emerging opportunities for the creation of powerful new probes based on controlled synthesis and/or bottom-up assembly of nanomaterials will be described with an emphasis on nanowire probes demonstrating the first intracellular transistor recordings, and the development of ``cyborg'' tissue. The prospects for blurring the distinction between nanoelectronic and living systems in the future will be highlighted.   

Charge Retention by Monodisperse Gold Clusters on Surfaces Prepared Using Soft Landing of Mass Selected Ions

Monodisperse gold clusters have been prepared on surfaces in different charge states through soft landing of mass-selected ions. Gold clusters were synthesized in methanol solution by reduction of a gold precursor with a weak reducing agent in the presence of a diphosphine capping ligand. Electrospray ionization was used to introduce the clusters into the gas-phase and mass-selection was employed to isolate a single ionic cluster species which was delivered to surfaces at well controlled kinetic energies. Using in-situ time of flight secondary ion mass spectrometry (SIMS) it is demonstrated that the cluster retains its 3+ charge state when soft landed onto the surface of a fluorinated self assembled monolayer on gold. In contrast, when deposited onto carboxylic acid terminated and conventional alkyl thiol surfaces on gold the clusters exhibit larger relative abundances of the 2+ and 1+ charge states, respectively. The kinetics of charge reduction on the surface have been investigated using in-situ Fourier Transform Ion Cyclotron Resonance SIMS. It is shown that an extremely slow interfacial charge reduction occurs on the fluorinated monolayer surface while an almost instantaneous neutralization takes place on the surface of the alkyl thiol monolayer. Our results demonstrate that the size and charge state of small gold clusters on surfaces, both of which exert a dramatic influence on their chemical and physical properties, may be tuned through soft landing of mass-selected ions onto selected substrates.   

Transitioning the Superfluid Helium Droplet Assembly into a Technology: Synthesis of Nanometer Scale Energetic Films using SHeDA

Since the pioneering work of the Toennies, Scoles, and Northby groups in the early 1990's, dozen of instruments around the world have been constructed to produce and study beams of superfluid helium nanodroplets. The technique has been exploited to shed light on a wide range of topics in chemical physics such as atomic scale manifestations of superfluidity, chemistry at ultra-low temperatures, and the assembly of exotic Van der Waals complexes to name a few. The helium droplet method has been considered for more applied use as a tool for isotope enrichment, low-fragmentation ionization mass spectrometry, and synthesizing/depositing core-shell spintronic nanoparticles. Indeed, the helium droplet methodology is in the midst of transitioning from a novel cryogenic nano-scale matrix in which to perform fundamental research into a technology for synthesizing, characterizing, and manipulating material. This talk describes our efforts to engineer a robust, user-friendly, broadly-tunable helium droplet apparatus capable of synthesizing composite nanoparticles and depositing them into films. This device is now being used to assemble and deposit metallic nanoparticles, and the efficiency of the process is being investigated. The physical details of the design, performance of the instrument, and our progress at understanding the deposition process will be presented. Distro 96ABW-2011-0266.   

Screened Charge Model in the Treatment of Electrostatic Interactions

Partial atomic charges play an important role in molecular simulations of complex systems, and they are widely used to compute the electrostatic interactions in various methods. We propose a screened charge model to include charge penetration and screening effects in electrostatic modeling. In the screened charge model, the atomic charge density of an atom in a molecule is represented by a spherical smeared charge plus a point charge at the nucleus. The new model is illustrated for the electronically embedded combined quantum mechanical and molecular mechanical (QM/MM) calculations and for the electrostatically embedded many-body (EE-MB) method. For a test set of 40 complexes, the mean unsigned error of QM/MM electrostatic interactions between QM and MM regions is reduced from 8.1 to 2.8 kcal/mol and that for QM/MM induction interactions from 1.9 to 1.4 kcal/mol. In a test of five water hexamers, the mean unsigned error of the EE-MB binding energies of the clusters is decreased by a factor of 2 at both the pairwise additive (PA) and three-body (3B) levels. Moreover, we have found that the charges derived by fitting electrostatic potentials with the screened charge method are less sensitive to the positions of the fitting points, and the quality of the fit to the electrostatics is improved.   

Magnetic Superatom Assemblies and their Transport Properties

We had recently shown that magnetic superatoms can be formed by embedding 3d transition metal atoms in metallic clusters of otherwise non-magnetic elements. The hybridization between the localized exchange split atomic orbitals in 3d elements with superatomic orbitals can help stabilize the magnetic state. Through first principles studies on the electronic structure and magnetic moment of Mg$_{n}$TM (TM = Sc, Ti, V, Cr, Mn, Fe, Co, and Ni) clusters, we had identified Mg$_{8}$Fe to be a stable magnetic superatom. In this work, we will present our investigations on the magnetic properties of the assemblies of such superatoms and the nature of electronic transport through such assemblies with various electrodes. The effects of the contact geometry and gate voltage on the conductance are also studied.   

Fabrication and Characterization of Electrodeposited Nanoporous Alloys

Nanoporous Ni and NiFe thin films were created by electrodeposition of NiCu and NiFeCu followed by electrochemical dealloying to remove the Cu component. The structure and composition of the resulting materials, before and after the dealloying step, was characterized using scanning electron microscopy and energy dispersive spectroscopy. The electrochemical double-layer capacitance was measured to estimate the active surface area. The catalytic behavior of these complex nanoporous materials was investigated using hydrogen evolution as a model reaction.   

Strongly Size-Dependent High-Temperature Behavior of Bismuth Oxide Nanoparticles

Oxide nanostructures show very strong size-dependent changes in their thermal and chemical stability and reactivity. The degree of these changes depends on the type and strength of bonds at the surface: The higher the surface energy the stronger the size-dependence. Inorganic compounds are governed by strong and long ranging bonds which result e.g. in generally high melting points and surface energies. So the properties of such nanostructures could shed more light on the role that the material's surface plays. This is demonstrated here by experiments with size-selected bismuth oxide nanoparticles between 5 and 60 nm ($\pm$5\%). Characterization of the particles revealed a metastable $\beta-Bi_2O_3$ structure. That testifies a size-driven crossover in phase stability below a critical particle size. Heating experiments up to the evaporation point were performed inside the synthesis-chamber as well as with in-situ TEM, in-situ XRD and a high-temperature nanocalorimeter. Different atmospheres were used. For the first time a melting point reduction in oxide nanoparticles was directly shown: For example 10 nm particles melted max. 40\% and evaporated 12\% below the bulk values which is a considerably stronger size-effect than for metals ($\leq$5\%).   

Borane derivatives: A New Class of Superhalogens

Halogens have the largest electron affinities of all elements in the periodic table, that of Cl being the highest, namely 3.6 eV. Superhalogens have electron affinities that far exceed that of halogens. Based on density functional theory calculations, we show that the Wade-Mingo's rule, well known for describing the stability of \textit{closo}-boranes (B$_{n}$H$_{n}^{2-})$, can be used to design a new class of superhalogens by tailoring the size and composition of borane derivatives. These superhalogens do not have to have either a metal or a halogen atom unlike conventional superhalogens. We show this by taking B$_{12}$H$_{13}$ and CB$_{11}$H$_{12}$ as examples. Also, these superhalogens can be used as building blocks of hyperhalogens of the form M(B$_{12}$H$_{13})_{2}$ and M(CB$_{11}$H$_{12})_{2}$ (M=Li, Na, K, Rb, Cs). This finding opens the door to an untapped source of superhalogens and weakly coordinating anions with potential applications.   

Configurational thermodynamics of alloyed nanoparticles: a first-principles cluster expansion study

Transition-metal, alloyed core-shell nanoparticles (NPs) continue to be studied as heterogeneous catalysts because they are found to improve catalytic activity and selectivity for many energy-conversion processes. However, thermodynamic investigations have been limited mostly to NP core-shell preference, rather than both geometric structure and its chemical decoration. Here, by extending cluster expansion methods to treat alloyed nanoparticles, we study the configurational thermodynamics of bimetallic NPs, using databases from density functional theory calculations. We find that the interplay between the ordering tendency and the core-shell segregation tendency can induce site-specific preferences around the NP, as we exemplify, e.g., in AgAu. Such simulations will provide information needed for further understanding of the structure-function relationships in NP catalysis.   

Sintering of multi-metallic nanoparticles

During the thermal treatment employed to activate the Pt-based nano catalysts used in fuel cell applications, the particles undergo structural transformations that affects their chemical performance. The mechanisms of coalescence and grain growth in bimetallic/trimetallic nanoparticles supported on planar silica on silicon are investigated using in-situ synchrotron based X-ray diffraction in the temperature regime 400-900C. The sintering process was found to be accompanied by lattice contraction and L10 chemical ordering. The mass transport involved in sintering is attributed to grain boundary diffusion and its corresponding activation energy is estimated from data analysis.   

Temperature dependence of Raman spectroscopy of molecular iodine trapped in zeolite crystals

Molecular iodine has been pursued for many practical applications, such as molecular clock, molecule-based quantum information processing, due to its narrow-linewidth hyperfine optical transitions. But because of its low vapor pressure, the experimental setup employing a free-space-based iodine vapor cell is very space-consuming. Recently, it is reported that the iodine molecule can be loaded into the channels of zeolite crystals, the density there could be orders improved and its space orientation can be precisely controlled. It may drastically reduce the size of molecular iodine experiment setup, and have many potential applications in microchip technology. We have studied the Raman spectroscopy of iodine molecule confined in zeolite crystals, AlPO4-5 (AFI) and AlPO4-11 (AEL), under different temperatures. The results show that in AEL, where the molecules are intensely confined, the ground vibrational states are close to that of an ideal 1D harmonic oscillator, while in AFI, where the molecules have a bit more freedom, they vibrate like in the free space, but with a loosened spring. And we come up a reasonable theoretical model to explain the Raman width dependence on temperature for these systems   

Single molecule thermodynamics and nanopore-based thermometry

The nanopore-based resistive pulse method measures the reduction in ionic current caused by the interaction of single molecules with the pore. It has great promise in addressing problems across a range of fields that include biomedicine and genomics. The technique requires the residence time of the molecules in the pore to exceed the inverse bandwidth of the detection system ($\sim $ 10 $\mu $s). Efforts are underway to improve this by molecular modification of the pore wall, but little effort has focused on modifying the solution conditions in and around the pore. We address this issue by precisely controlling the solution temperature around a protein ion channel (alpha hemolysin) via laser-induced heating of gold nanoparticles. In this technique, the nanopore serves dual roles as both a highly local thermometer and single molecule sensor. Preliminary data suggests that the solution temperature can be controlled over a wide range, the nanopore conductance can be used to directly measure rapid changes in temperature, and the temperature change can dramatically alter the interaction kinetics of single molecules with the nanopore. The method will improve the development of biochip sensors and lead to a new platform for single molecule thermodynamic studies.   

On the Stability and Dynamics of Atmospheric Pre-Nucleation Clusters

Atmospheric new-particle formation is a complex physical phenomenon with far-reaching consequences: currently, the role of aerosols is one of the main uncertainties in predicting the climate change. However, the molecular-level particle formation mechanisms are poorly understood. It is believed that sulfuric acid is the key player with possible contributions from various base molecules, ions or organics. Here we present results from first-principles molecular dynamics simulations of molecular clusters of sulfuric acid and two atmospherically relevant bases, ammonia and dimethylamine. The dynamics and stability of the studied clusters (sulfuric acid)$_n \bullet$(ammonia)$_{n-1}$ and (sulfuric acid)$_n \bullet$ (dimethylamine)$_n$ where $n=2,3,4$ were probed for 45 ps at T=300K at BPE/TZV2P level of theory. The stability of the clusters is largely dependent on the H-bonding patterns and in most cases the equilibrium patterns emerged within the first 10 ps. Curiously, even after the equilibrium was reached the clusters showed pronounced bond rearrangement: the number of bonds remained the same, but the individual atoms forming the bonds changed. Regardless of this behavior, the clusters remained bound together.