Quantitatively controlled electrophoretic deposition of nanocrystal films from non-aqueous suspensions.

This study presents a novel method to correlate the mass and charge transfer kinetics during the electrophoretic deposition of nanocrystal films by using a purpose-built double quartz crystal microbalance combined with simultaneous current-measurement. Our data support a multistep process for film formation: generation of charged nanocrystal flux, charge transfer at the electrode, and polarization of neutral nanocrystals near the electrode surface. The polarized particles are then subject to dielectrophoretic forces that reduce diffusion away from the interface, generating a sufficiently high neutral particle concentration at the interface to form a film.

Calcium vapor synthesis of extremely coercive SmCo.

Exceptionally coercive SmCo particles are produced through calcium vapor reduction of SmCoO powders synthesized by flame spray pyrolysis. The resulting powders are composed of oblate hexagonal particles approximately 2 microns across with smooth surfaces. This microstructure yields record-breaking room temperature coercivity >80 kOe, or >60 kOe when combined with advanced manufacturing approaches such as electrophoretic deposition or molding with tetraglyme inks.

A Bioinspired Artificial Injury Response System Based on a Robust Polymer Memristor to Mimic a Sense of Pain, Sign of Injury, and Healing.

Flexible electronic skin with features that include sensing, processing, and responding to stimuli have transformed human-robot interactions. However, more advanced capabilities, such as human-like self-protection modalities with a sense of pain, sign of injury, and healing, are more challenging. Herein, a novel, flexible, and robust diffusive memristor based on a copolymer of chlorotrifluoroethylene and vinylidene fluoride (FK-800) as an artificial nociceptor (pain sensor) is reported.

Suppression of low temperature magnetic ordering in samarium nanoparticles.

The role of finite size effects on magnetic order has been investigated in samarium nanoparticles prepared by physical vapor deposition. A dense layer composed of distinct nanoparticles with a mean particle diameter of 26 nm was deposited on a diamagnetic substrate. M(T) measurements identify the expected pair of antiferromagnetic ordering temperatures in the bulk Sm precursor, at 113 K and 14 K, where the magnetic unit cell for the lower ordering temperature is 10.

Space- and time-resolved small angle X-ray scattering to probe assembly of silver nanocrystal superlattices.

The structure of nanocrystal superlattices has been extensively studied and well documented, however, their assembly process is poorly understood. In this work, we demonstrate an in situ space- and time-resolved small angle X-ray scattering measurement that we use to probe the assembly of silver nanocrystal superlattices driven by electric fields. The electric field creates a nanocrystal flux to the surface, providing a systematic means to vary the nanocrystal concentration near the electrode and thereby to initiate nucleation and growth of superlattices in several minutes.

Reversible, Tunable, Electric-Field Driven Assembly of Silver Nanocrystal Superlattices.

Nanocrystal superlattices are typically fabricated by either solvent evaporation or destabilization methods that require long time periods to generate highly ordered structures. In this paper, we report for the first time the use of electric fields to reversibly drive nanocrystal assembly into superlattices without changing solvent volume or composition, and show that this method only takes 20 min to produce polyhedral colloidal crystals, which would otherwise need days or weeks. This method offers a way to control the lattice constants and degree of preferential orientation for superlattices and can suppress the uniaxial superlattice contraction associated with solvent evaporation.

Ultralow Density, Monolithic WS2, MoS2, and MoS2/Graphene Aerogels.

We describe the synthesis and characterization of monolithic, ultralow density WS2 and MoS2 aerogels, as well as a high surface area MoS2/graphene hybrid aerogel. The monolithic WS2 and MoS2 aerogels are prepared via thermal decomposition of freeze-dried ammonium thio-molybdate (ATM) and ammonium thio-tungstate (ATT) solutions, respectively. The densities of the pure dichalcogenide aerogels represent 0.

Improving nanoparticle dispersion and charge transfer in cadmium telluride tetrapod and conjugated polymer blends.

The dispersion of CdTe tetrapods in a conducting polymer and the resulting charge transfer is studied using a combination of confocal fluorescence microscopy and atomic force microscopy (AFM). The results of this work show that both the tetrapod dispersion and charge transfer between the CdTe and conducting polymer (P3HT) are greatly enhanced by exchanging the ligands on the surface of the CdTe and by choosing proper solvent mixtures. The ability to experimentally probe the relationship between particle dispersion and charge transfer through the combination of AFM and fluorescence microscopy provides another avenue to assess the performance of polymer/semiconductor nanoparticle composites.

Thermally induced phase separation in supported bilayers of glycosphingolipid and phospholipid mixtures.

The authors have studied microstructure evolution during thermally induced phase separation in a class of binary supported lipid bilayers using a quantitative application of imaging ellipsometry. The bilayers consist of binary mixtures consisting of a higher melting glycosphingolipid, galactosylceramide (GalCer), which resides primarily in the outer leaflet, and a lower melting, unsaturated phospholipid, 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC). Three different bilayer compositions of GalCer/DLPC mixtures at 35:65, 20:80, and 10:90 molar ratios were cooled at controlled rates from their high-temperature homogeneous phase to temperatures corresponding to their phase coexistence regime and imaged in real time using imaging ellipsometry.

Molecular mechanisms of crystallization impacting calcium phosphate cements.

The biomineral calcium hydrogen phosphate dihydrate (CaHPO(4).2H(2)O), known as brushite, is a malleable material that both grows and dissolves faster than most other calcium minerals, including other calcium phosphate phases, calcium carbonates and calcium oxalates. Within the body, this ready formation and dissolution can play a role in certain diseases, such as kidney stone and plaque formation.

Raman spectroscopy of DNA packaging in individual human sperm cells distinguishes normal from abnormal cells.

Healthy human males produce sperm cells of which about 25-40% have abnormal head shapes. Increases in the percentage of sperm exhibiting aberrant sperm head morphologies have been correlated with male infertility, and biochemical studies of pooled sperm have suggested that sperm with abnormal shape may contain DNA that has not been properly repackaged by protamine during spermatid development. We have used micro-Raman spectroscopy to obtain Raman spectra from individual human sperm cells and examined how differences in the Raman spectra of sperm chromatin correlate with cell shape.

An understanding of renal stone development in a mixed oxalate-phosphate system.

The in vivo formation of calcium oxalate concretions having calcium phosphate nidi is simulated in an in vitro (37 degrees C, pH 6.0) dual constant composition (DCC) system undersaturated (sigma DCPD = -0.330) with respect to brushite (DCPD, CaHPO 4 .

Direct visualization of phase transition dynamics in binary supported phospholipid bilayers using imaging ellipsometry.

Via imaging ellipsometry, we study the phase transition dynamics induced by selective gelation of one component in a binary supported phopholipid bilayer. We find the modulation of two attendant morphological features: emergence of extended defect chains due to a net change in the molecular areas and fractal-like domains suggesting weak line tension. A time-lapse analysis of the ellipsometric images reveals the cluster size of 4-20 molecules undergoing gelation indicating weak cooperativity.

Domain nucleation rates and interfacial line tensions in supported bilayers of ternary mixtures containing galactosylceramide.

Domains within the plane of the plasma membrane, referred to as membrane rafts, have been a topic of considerable interest in the field of membrane biophysics. Although model membrane systems have been used extensively to study lipid phase behavior as it relates to the existence of rafts, very little work has focused on either the initial stage of lipid domain nucleation, or the relevant physical parameters such as temperature and interfacial line tension which control nucleation. In this work, we utilize a method in which the kinetic process of lipid domain nucleation is imaged by atomic force microscopy and modeled using classical theory of nucleation to map interfacial line tension in ternary lipid mixtures.

Quantifying growth of symmetric and asymmetric lipid bilayer domains.

Here, we examine by atomic force microscopy (AFM) the kinetics and morphology of lipid domain growth during lipid phase separation by rapid thermal cooling of fully mixed two-component supported lipid bilayers. At the undercooled temperatures chosen, symmetric 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC)-rich domains favored slower reaction-limited growth whereas asymmetric galactosylceramide (GalCer)-rich domains favored faster diffusion-limited growth, indicated by shape factors and kinetic exponents. Because kinetically limited conditions could be accessed, we were able to estimate the activation energy barrier (approximately 16kT) and lateral diffusion coefficient (approximately 0.

Control of curvature in highly compliant probe cantilevers during carbon nanotube growth.

Direct growth of a sharp carbon nanotube (CNT) probe on a very thin and highly flexible cantilever by plasma-enhanced chemical vapor deposition (PECVD) is desirable for atomic force microscopy (AFM) of nanoscale features on soft or fragile materials. Plasma-induced surface stresses in such fabrication processes, however, tend to cause serious bending of these cantilevers, which makes the CNT probe unsuitable for AFM measurements. Here, we report a new tunable CNT growth technique that controls cantilever bending during deposition, thereby enabling the creation of either flat or deliberately curved AFM cantilevers containing a CNT probe.

Using nucleation rates to determine the interfacial line tension of symmetric and asymmetric lipid bilayer domains.

This work presents a novel method for experimentally quantifying interfacial line tension, which can be readily applied to study a wide variety of different lipid mixtures exhibiting phase coexistence. The method combines AFM imaging of lipid domain nucleation with classical nucleation theories. The results, using symmetric and asymmetric domains, permit the prediction of key physical parameters (critical nuclei size and nucleation rate) in multicomponent bilayer systems with implications toward understanding the dynamic nature of submicrometer domains (i.

A new model for nanoscale enamel dissolution.

The dissolution kinetics of human tooth enamel surfaces was investigated using nanomolar-sensitive constant composition (CC) and in situ atomic force microscopy (AFM) under simulated caries formation conditions (relative undersaturation with respect to hydroxyapatite = 0.902, pH = 4.5).

Dissolution of crystallites: surface energetic control and size effects.

Traditional understanding of dissolution assumes that the reaction is spontaneous and continues until equilibrium is reached. This paper presents theoretical and experimental data to support a dissolution mechanism that involves the existence of critical conditions for dissolution, in which the reaction is accompanied by the formation of pits and the subsequent displacement of pit steps. The accompanying increase in surface roughness leads to changes in surface energy with losses of crystal mass that are positive rather than negative and the existence of critical dissolution conditions.

Effect of hydrogen peroxide on titanium surfaces: in situ imaging and step-polarization impedance spectroscopy of commercially pure titanium and titanium, 6-aluminum, 4-vanadium.

To analyze titanium's response to representative surgical wound environments, a study was conducted on commercially pure titanium (CPTi) and titanium, 6-aluminum, 4-vanadium (Ti-6Al-4V) exposed to phosphate-buffered saline (PBS) with 30 mM of hydrogen peroxide (H(2)O(2)) added. The study was characterized by simultaneous electrochemical atomic force microscopy (EC AFM) and step-polarization impedance spectroscopy (SPIS). Surfaces were covered with protective oxide domes that indicated topography changes with potential and time of immersion.