Ferroelectricity and Dipolar Interactions in Mesocrystalline NH4TiOF3
Explore the source record for details and available documents.
Wang, John↗
Engineering topics
Kumar, Amit
Publications and source records attributed to Kumar, Amit.
Nanoscale Probing of Voltage Activated Oxygen Reduction/Evolution Reactions in Nanopatterned (LaxSr1-x)CoO3- Cathodes
Explore the source record for details and available documents.
Biegalski, Michael D↗
Electrochemical Strain Microscopy: Probing Electrochemical Transformations in Nanoscale Volumes
Electrochemical and electrocatalytic phenomena underpin a broad spectrum of energy, chemical, and information technologies. Examples range from electrocatalytic activation of oxygen reduction reactions in fuel cells, gas-solid reactions, and ionic transport in gas sensors and oxygen pumps, to a wide gamut of electrochemical and transport phenomena in primary and secondary batteries. Equally important is the role of ionic phenomena in information technologies, as exemplified by a recent wave of interest in memristive and electroresisitive information storage and logic devices. Finally, this article examines a new type of scanning probe microscopy (SPM), referred to as electrochemical strain microscopy (ESM), that can provide a better understanding of these complex phenomena.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Linker-Induced Anomalous Emission of Organic-Molecule Conjugated Metal-Oxide Nanoparticles
Semiconductor nanoparticles conjugated with organic- and dye-molecules to yield high efficiency visible photoluminescence (PL) hold great potential for many future technological applications. We show that folic acid (FA)-conjugated to nanosize TiO2 and CeO2 particles demonstrates a dramatic increase of photoemission intensity at wavelengths between 500 and 700 nm when derivatized using aminopropyl trimethoxysilane (APTMS) as spacer-linker molecules between the metal oxide and FA. Using density-functional theory (DFT) and time-dependent DFT calculations we demonstrate that the strong increase of the PL can be explained by electronic transitions between the titania surface oxygen vacancy (OV) states and the low-energy excited states of the FA/APTMS molecule anchored onto the surface oxygen bridge sites in close proximity to the OVs. We suggest this scenario to be a universal feature for a wide class of metal oxide nanoparticles, including nanoceria, possessing a similar band gap (3 eV) and with a large surface-vacancy-related density of electronic states. We demonstrate that the molecule-nanoparticle linker can play a crucial role in tuning the electronic and optical properties of nanosystems by bringing optically active parts of the molecule and of the surface close to each other.
Environmental Molecular Sciences Laboratory↗
Myotonic Dystrophy Type 1 RNA Crystal Structures Reveal Heterogeneous 1 × 1 Nucleotide UU Internal Loop Conformations
RNA internal loops often display a variety of conformations in solution. Herein, we visualize conformational heterogeneity in the context of the 5'CUG/3'GUC repeat motif present in the RNA that causes myotonic dystrophy type 1 (DM1). Specifically, two crystal structures of a model DM1 triplet repeating construct, 5'r[{und UU}GGGC(C{und U}G){sub 3}GUCC]{sub 2}, refined to 2.20 and 1.52 {angstrom} resolution are disclosed. Here, differences in the orientation of the 5' dangling UU end between the two structures induce changes in the backbone groove width, which reveals that noncanonical 1 x 1 nucleotide UU internal loops can display an ensemble of pairing conformations. In the 2.20 {angstrom} structure, CUGa, the 5' UU forms a one hydrogen-bonded pair with a 5' UU of a neighboring helix in the unit cell to form a pseudoinfinite helix. The central 1 x 1 nucleotide UU internal loop has no hydrogen bonds, while the terminal 1 x 1 nucleotide UU internal loops each form a one-hydrogen bond pair. In the 1.52 {angstrom} structure, CUGb, the 5' UU dangling end is tucked into the major groove of the duplex. While the canonically paired bases show no change in base pairing, in CUGb the terminal 1 x 1 nucleotide UU internal loops now form two hydrogen-bonded pairs. Thus, the shift in the major groove induced by the 5' UU dangling end alters noncanonical base patterns. Collectively, these structures indicate that 1 x 1 nucleotide UU internal loops in DM1 may sample multiple conformations in vivo. This observation has implications for the recognition of this RNA, and other repeating transcripts, by protein and small molecule ligands.
08 HYDROGEN↗
Diospyrin derivative, an anticancer quinonoid, regulates apoptosis at endoplasmic reticulum as well as mitochondria by modulating cytosolic calcium in human breast carcinoma cells
Highlights: Black-Right-Pointing-Pointer Diospyrin diethylether (D7) caused oxidative stress-dependent activation of PC-PLC. Black-Right-Pointing-Pointer Activated PC-PLC induced a sustained-release of Ca{sup 2+} from endoplasmic reticulum. Black-Right-Pointing-Pointer The elevated cytosolic Ca{sup +2} led to the calpain-caspase12 dependent apoptosis. Black-Right-Pointing-Pointer D7-Induced Ca{sup +2} also found to accentuate the mitochondrial pathway of apoptosis. -- Abstract: Diospyrin diethylether (D7), a bisnaphthoquinonoid derivative, exhibited an oxidative stress-dependent apoptosis in several human cancer cells and tumor models. The present study was aimed at evaluation of the increase in cytosolic calcium [Ca{sup 2+}]{sub c} leading to the apoptotic cell death triggered by D7 in MCF7 human breast carcinoma cells. A phosphotidylcholine-specific phospholipase C (PC-PLC) inhibitor, viz. U73122, and an antioxidant, viz. N-acetylcysteine, could significantly prevent the D7-induced rise in [Ca{sup 2+}]{sub c} and PC-PLC activity. Using an endoplasmic reticulum (ER)-Ca{sup 2+} mobilizer (thapsigargin) and an ER-IP3R antagonist (heparin), results revealed ER as a major source of [Ca{sup 2+}]{sub c} which led to the activation of calpain and caspase12, and cleavage of fodrin. These effects including apoptosis were significantly inhibited by the pretreatment of Bapta-AM (a cell permeable Ca{sup 2+}-specific chelator), or calpeptin (a calpain inhibitor). Furthermore, D7-induced [Ca{sup 2+}]{sub c} was found to alter mitochondrial membrane potential and induce cytochrome c release, which was inhibited by either Bapta-AM or ruthenium red (an inhibitor of mitochondrial Ca{sup 2+} uniporter). Thus, these results provided a deeper insight into the D7-induced redox signaling which eventually integrated the calcium-dependent calpain/caspase12 activation and mitochondrial alterations to accentuate the induction of apoptotic cell death.
60 APPLIED LIFE SCIENCES↗
Radiation-Induced Reduction of Ceria in Single and Polycrystalline Thin Films
Ceria (CeO{sub 2}) is a technologically important ceramic material with a wide range of neoteric applications in catalysis, solid oxide fuel cells, oxygen gas sensors, hydrogen production, and ultraviolet shielding. Recent research has revealed promising biomedical applications of ceria. Nanoparticles of ceria have been shown to protect healthy cells from radiation-induced cellular damage. The mechanisms governing the radioprotection characteristics of ceria nanoparticles are not well understood and it has been hypothesized that reversible switching between Ce{sup 4+} and Ce{sup 3+} states may enable ceria nanoparticles to mop up free radicals.
08 HYDROGEN↗
Nanoscale origins of nonlinear behavior in ferroic thin-films
The nonlinear response of a ferroic to an applied stimulus (e.g. electric field, mechanical stress) is a fundamental characteristic that underpins a number of technologically significant applications[1-3]. It is also the driving feature in numerous physical phenomena, such as interfacial motion[4,5], spin glasses[6], relaxors[7] and phase transitions[8]. In particular, nonlinearity associated with minor hysteresis loops is an extremely useful avenue to explore energy dissipation and losses in such systems. This knowledge is necessary for the design of future materials with enhanced low-field properties. Quantitatively, the macroscopic nonlinear response of ferroic systems at low to mid-range amplitudes of driving fields is given by the phenomenological Rayleigh law[9], first conceived in 1887 for magnetic materials. Yet, the applicability of the Rayleigh law at small length scales has not been extensively studied. Here, we show using a combination of scanning probe techniques and phase field modeling, that nanoscale response appears to follow a non-Rayleigh regime. However, through statistical analysis, we find that a distribution in the individual responses can lead to directly to Rayleigh-like behavior of the strain on a macroscale. The studies shed light on the nanoscale origins of nonlinear behavior in disordered ferroics.
ferroelectric↗
Switchable Induced Polarization in LaAlO3/SrTiO3 Heterostructures
Demonstration of a tunable conductivity of the LaAlO3/SrTiO3 interfaces drew significant attention to the development of oxide electronic structures where electronic confinement can be reduced to the nanometer range. While the mechanisms for the conductivity modulation are quite different and include metal insulator phase transition and surface charge writing, generally it is implied that this effect is a result of electrical modification of the LaAlO3 surface (either due to electrochemical dissociation of surface adsorbates or free charge deposition) leading to the change in the twodimensional electron gas (2DEG) density at the LaAlO3/SrTiO3 (LAO/STO) interface. In this paper, using piezoresponse force microscopy we demonstrate a switchable electromechanical response of the LAO overlayer, which we attribute to the motion of oxygen vacancies through the LAO layer thickness. These electrically induced reversible changes in bulk stoichiometry of the LAO layer are a signature of a possible additional mechanism for nanoscale oxide 2DEG control on LAO/STO interfaces.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Probing surface and bulk electrochemical processes on the LaAlO3-SrTiO3 interface
Local electrochemical phenomena on the surfaces of LaAlO3-SrTiO3 heterostructure are explored using unipolar and bipolar dynamic electrochemical strain microscopy (D-ESM). The D-ESM suggests the presence of at least two distinct electrochemical processes, including fast reversible low-voltage process and slow high-voltage process. The latter process is associated with static surface deformations in the sub-nm regime. These behaviors are compared with Kelvin Probe Force Microscopy hysteresis data. The possible origins of observed phenomena are discussed and these studies suggest that charge-writing behavior in LAO-STO include strong surface/bulk electrochemical component and are more complicated than simple screening by surface adsorbates.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Ionically-mediated electromechanical hysteresis in transition metal oxides
Electromechanical activity, remanent polarization states, and hysteresis loops in paraelectric TiO2 and SrTiO3 are observed. The coupling between the ionic dynamics and incipient ferroelectricity in these materials is analyzed using extended Ginsburg Landau Devonshire (GLD) theory. The possible origins of electromechanical coupling including ionic dynamics, surface-charge induced electrostriction, and ionically-induced ferroelectricity are identified. For the latter, the ionic contribution can change the sign of first order GLD expansion coefficient, rendering material effectively ferroelectric. These studies provide possible explanation for ferroelectric-like behavior in centrosymmetric transition metal oxides.
Kim, Yunseok↗
Controlling magnetoelectric coupling by nanoscale phase transformation instrain engineered bismuth ferrite
The magnetoelectric coupling in multiferroic materials is promising for a wide range of applications, yet manipulating magnetic ordering by electric field proves elusive to obtain and difficult to control. In this paper, we explore the prospect of controlling magnetic ordering in misfit strained bismuth ferrite (BiFeO3, BFO) films, combining theoretical analysis, numerical simulations, and experimental characterizations. Electric field induced transformation from a tetragonal phase to a distorted rhombohedral one in strain engineered BFO films has been identified by thermodynamic analysis, and realized by scanning probe microscopy (SPM) experiment. By breaking the rotational symmetry of a tip-induced electric field as suggested by phase field simulation, the morphology of distorted rhombohedral variants has been delicately controlled and regulated. Such capabilities enable nanoscale control of magnetoelectric coupling in strain engineered BFO films that is difficult to achieve otherwise, as demonstrated by phase field simulations.
42 ENGINEERING↗
Dynamic piezoresponse force microscopy: Spatially resolved probing of polarization dynamics in time and voltage domains
An approach for probing dynamic phenomena during hysteresis loop measurements in piezoresponse force microscopy (PFM) is developed. Dynamic PFM (D-PFM) necessitates development of 5-dimensional (5D) data acquisition protocols and associated methods for analysis and visualization of multidimensional data. Using a combination of multivariate statistical analysis and phenomenological fitting, we explore dynamic behavior during polarization switching in model ferroelectric films with dense ferroelastic domain structures and in ferroelectric capacitors. In polydomain films, multivariate analysis of the switching data suggests that ferroelectric and ferroelastic components can be decoupled and time dynamics can be explored. In capacitors, a strong correlation between polarization dynamics and microstructure is observed. The future potential of D-PFM for probing time-dependent hysteretic phenomena in ferroelectrics and ionic systems is discussed.
Dynamic piezoresponse force microscopy↗
The partially reversible formation of Li-metal particles on a solid Li electrolyte: applications toward nanobatteries
The feasibility of large-scale implementation of Li-air batteries (LABs) hinges on understanding the thermodynamic and kinetic factors that control charge-discharge rates, efficiency and life times. Here, the kinetics of bias-induced reactions is explored locally on the surface of Li-ion conductive glass ceramics, a preferred electrolyte for LABs, using direct current-voltage and strain spectroscopies. Above a critical bias, particle growth kinetics were found to be linear in both the bias and time domains. Partial reversibility was observed for Li particles as evidenced by the presence of anodic peaks following the Li{sup +} reduction, as well an associated reduction in particle height. The degree of reversibility was highest for the smallest particles formed. These observations thus suggest the possibility of producing nanobatteries with an active anode volume of the order of 0.1 al.
77 NANOSCIENCE AND NANOTECHNOLOGY↗
Electrochemical strain microscopy: Probing ionic and electrochemical phenomena in solids at the nanometer level
Atomistic and nanometer scale mechanisms of electrochemical reactions and ionic flows in solids in the nanometer-micron range persist as terra incognito in modern science. While structural and electronic phenomena are now accessible to electron and scanning probe microscopy (SPM) techniques, probing nanoscale electrochemistry requires the capability to probe local ionic currents. Here, we discuss principles and applications of electrochemical strain microscopy (ESM), a technique based on probing minute deformations induced by electric bias applied to an SPM tip. ESM imaging and spectroscopy are illustrated for several energy storage and conversion materials. We further argue that down-scaling of physical device structures based on oxides necessitates ionic and electrochemical effects to be taken into account. Future pathways for ESM development are discussed
Jesse, Stephen↗
Li-ion dynamics and reactivity on the nanoscale
Explore the source record for details and available documents.
catalysis (heterogeneous)↗
A phosphate-dependent shift in redox state of cerium oxide nanoparticles and its effects on catalytic properties
Cerium oxide nanoparticles (CeNPs) have shown promise as catalytic antioxidants in cell culture and animal models as both superoxide dismutase and catalase mimetics. The reactivity of the cerium (Ce) atoms at the surface of its oxide particle is critical to such therapeutic properties, yet little is known about the potential for a protein or small molecule corona to form on these materials in vivo. Moreover Ce atoms in these active sites have the potential to interact with small molecule anions, peptides, or sugars when administered in culture or animal models. Several nanomaterials have been shown to alter or aggregate under these conditions, rendering them less useful for biomedical applications. In this work we have studied the change in catalytic properties of CeNPs when exposed to various biologically relevant conditions in vitro. We have found that CeNPs are resistant to broad changes in pH and also not altered by incubation in cell culture medium. However to our surprise phosphate anions significantly altered the characteristics of these nanomaterials and shifted the catalytic behavior due to the binding of phosphate anions to cerium. Given the abundance of phosphate in biological systems in an inorganic form, it is likely that the action of CeNPs as a catalyst may be strongly influenced by the local concentration of phosphate in the cells and/or tissues in which it has been introduced.
59 BASIC BIOLOGICAL SCIENCES↗