The scanning tunneling microscope has been used to image a reduced TiO(2)(110) surface in ultrahigh vacuum. Structural units with periodicities rangng from 21 to 3.4 angstroms have been clearly imaged, demonstrating that atomic resolution imaging of an ionic, wide band gap (3.2 electron volts) semiconductor is possible. The observed surface structures can be explained by a model involving ordered arrangements of two-dimensional defects known as crystallographic shear planes and indicate that the topography of nonstoichiometric oxide surfaces can be complex.

https://science.sciencemag.org/content/sci/250/4985/1239.full.pdf

Structure of the Reduced TiO2(110) Surface Determined by Scanning Tunneling Microscopy

The theory and applications of scanned probe microscopies in chemistry are reviewed. The review includes scanning tunneling microscopy (STM), atomic force microscopy (AFM), near-field scanning optical microscopy (NSOM), and other related techniques. Applications to chemical and biochemical imaging, molecular identification, and other systems of importance in chemistry are described.

Scanned Probe Microscopies in Chemistry

This review describes work presented in the 2014 inaugural Tsinghua University Press-Springer Nano Research Award lecture, as well as current and future opportunities for nanoscience research at the interface with brain science. First, we briefly summarize some of the considerations and the research journey that has led to our focus on bottom-up nanoscale science and technology. Second, we recapitulate the motivation for and our seminal contributions to nanowire-based nanoscience and technology, including the rational design and synthesis of increasingly complex nanowire structures, and the corresponding broad range of “applications” enabled by the capability to control structure, composition and size from the atomic level upwards. Third, we describe in more detail nanowire-based electronic devices as revolutionary tools for brain science, including (i) motivation for nanoelectronics in brain science, (ii) demonstration of nanowire nanoelectronic arrays for high-spatial/high-temporal resolution extracellular recording, (iii) the development of fundamentally-new intracellular nanoelectronic devices that approach the sizes of single ion channels, (iv) the introduction and demonstration of a new paradigm for innervating cell networks with addressable nanoelectronic arrays in three-dimensions. Last, we conclude with a brief discussion of the exciting and potentially transformative advances expected to come from work at the nanoelectronics-brain interface.

/pdf/nanoscience-and-the-nano-bioelectronics-frontier-3bh02fn76c.pdf

Nanoscience and the nano-bioelectronics frontier

The formation of superconducting phases in the Bi(Pb)─Sr─Ca─Cu─O system has been systematically investigated using DTA/TG, XRD, SEM/EDAX, TEM, EPMA, ICP-AES, fourprobe dc resistance, and ac susceptibility. Starting compositions, firing temperature, and the duration of heat treatment, together with the atmosphere, were found to be critical in determining the preferred formation of the 2223 phase. This paper reports the effect of the initial chemical composition, emphasizing the importance of compositional control in the synthesis of the single 2223 phase. It has been shown that, with a correct starting composition and predetermined synthesis conditions, single 2223 phase can be obtained without intergrowth by the 2212 and other impurity crystalline phases. The optimum starting composition for the preferred growth of the 2223 phase was identified as being Bi1.7Pb0.3+ySr2Ca2Cu3Ox (y= 0.1), with excess Pb added in order to compensate for its loss at high temperatures. The effect of Pb doping and excess Cu on the phase formation in the Bi oxide based superconducting system is discussed.

2223 Phase Formation in Bi(Pb)─Sr─Ca─Cu─O: I, The Role of Chemical Composition

Pure and Nb2O5 added Bi1.6Pb0.4NbxSr2Ca2Cu3O? superconductors (x varies up to 0.30) were synthesized by the solid state reaction method. Structural and superconducting properties of the samples were investigated. The fraction of the high-Tc phase (2223) increases with Nb addition up to x = 0.10, for which a nearly single 2223 phase was obtained. The critical temperature of the samples increases from 96 to 104?K with doping up to x = 0.20 and a further increase in Nb decreases the Tc sharply. Similarly, there is a considerable enhancement in the critical current density (jc) of the samples in the same doping range. Both AC susceptibility and transport measurements showed that the optimum Nb concentration is x = 0.20. The out-of-phase component of the AC susceptibility measurements showed that inter-grain coupling was enhanced up to the same doping level. Nb additions above x = 0.30 decrease the fraction of the high-Tc phase and degrade the superconducting properties. Present measurements indicate that x = 0.20 is the optimum Nb concentration in the BSCCO superconductor to enhance phase purity, inter-grain coupling and superconducting parameters (Tc and jc).

Enhancement in the high-Tc phase of BSCCO superconductors by Nb addition

The structural and electronic effects of lead substitution in the high-temperature superconducting materials PbxBi2-xSr2CaCu2O8 have been characterized by scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Large-area STM images of the Bi(Pb)—O layers show that lead substitution distorts and disorders the one-dimensional superlattice found in these materials. Atomic-resolution images indicate that extra oxygen atoms are present in the Bi(Pb)—O layers. STS data show that the electronic structure of the Bi(Pb)—O layers is insensitive to lead substitution within ±0.5 electron volt of the Fermi level; however, a systematic decrease in the density of states is observed at ≈1 electron volt above the Fermi level. Because the superconducting transition temperatures are independent of x(Pb) (x ≤ 0.7), these microscopic STM and STS data suggest that the lead-induced electronic and structural changes in the Bi(Pb)—O layer do not perturb the electronic states critical to forming the superconducting state in this system.

https://science.sciencemag.org/content/sci/248/4960/1211.full.pdf

Structural and Electronic Role of Lead in (PbBi)2Sr2CaCu2O8 Superconductors by STM.

Scanning tunneling microscopy has been used to characterize the electronic and structural effects of oxygen doping in ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{\mathit{x}}$ materials. Bias-voltage-dependent images of oxygen-deficient nonsuperconducting crystals show that reversible oxygen loss leads to nonperiodic variations in the electronic states near the Fermi level (\ifmmode\pm\else\textpm\fi{}300 mV). Variations in the electronic states near the Fermi level are not observed, however, in images of superconducting samples. In addition, high-resolution images of the BiO layer of oxygen-deficient samples do not exhibit vacancies or strongly perturbed sites, but rather appear similar to images of the BiO layer of superconducting crystals. These data indicate that suppression of ${\mathit{T}}_{\mathit{c}}$ in ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{\mathit{x}}$ may not be due to oxygen loss from the BiO layer.

Electronic and structural effects of oxygen doping in Bi2Sr2CaCu2Ox superconductors characterized by tunneling microscopy.

Scanning tunneling microscopy has been used to characterize directly the surface electronic structure of a series of single-crystal ${\mathrm{Pb}}_{\mathit{x}}$${\mathrm{Bi}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8}$ superconductors. High-resolution spectroscopic measurements show that within \ifmmode\pm\else\textpm\fi{}0.5 eV of the Fermi level the Bi(Pb)-O electronic structure is independent of the Pb concentration (x\ensuremath{\le}0.7). Extended spectroscopic measurements demonstrate that the density of unfilled states at +1 eV systematically decrease as the concentration of Pb increases, although the filled states between 0 and -2 eV are essentially independent of the concentration of Pb. In addition, analysis of the differential conductivity indicates that the surface conductivity varies from weakly metallic to semiconducting as the tip-surface separation increases.

Electronic effect of lead substitution in single-crystal Bi(Pb)-Sr-Ca-Cu-O superconductors determined by scanning tunneling microscopy

The effect of metal substitution on the critical current densities of single-crystal PbxBi2-xSr2CaCu2O8 (x = 0 or x = 0.7) superconductors has been investigated. Substitution of lead was found to increase the average critical current density from 1 x 10(5) A/cm2 to 2 x 10(6) A/cm2 at 5 K in an applied magnetic field of 10 kilooersteds (1 oersted = 80 A/m). The order of magnitude increase in the critical current density was observed for temperatures up to the flux vortex lattice melting point; the flux lattice melting point was also found to increase to 30 K (from 22 K) in the lead-substituted materials. Diffraction and microscopy investigations of the structural parameters indicate that the fundamental atomic lattices are virtually the same for both materials. Scanning tunneling microscopy images demonstrate, however, that lead substitution causes significant disorder (or defects) in the one-dimensional superstructure found in Bi2Sr2CaCu2O8. Since crystal defects can increase the critical current density by pinning the motion of flux vortices, it is likely that this lead-induced disorder enhances vortex pinning. The lead-induced disorder is specific to the nonsuperconducting Bi-O layers, and thus our results suggest that chemical substitutions may be utilized to control selectively flux pinning and the critical current density in these materials.

Enhancement of the critical current density in single-crystal Bi2Sr2CaCu2O8 superconductors by chemically induced disorder

Brassinosteroids (BRs) are essential plant growth- and development-regulating phytohormones. When applied exogenously, BRs ameliorate heat shock (HS)-induced cell damage and enhance plant thermotolerance; however, the molecular mechanism by which BRs regulate plant thermotolerance is unknown. In this study, by analyzing the thermotolerance of a series of BR signaling mutants and plants that overexpressed different BR signaling components, we obtained comprehensive data showing that BRASSINOSTEROID INSENSITIVE 2 (BIN2) plays a major role in mediating the crosstalk between BR signaling and plant HS responses. By RNA-Seq, 608 HS- and BIN2-regulated genes were identified. An analysis of the 1-kb promoter sequences of these genes showed enrichment of an abscisic acid (ABA) INSENSITIVE 5 (ABI5)-binding cis-element. Physiological studies showed that thermotolerance was reduced in bin2-1 mutant and ABI5-OX plants but increased in the abi5 mutant, and that the abi5 mutation could recover the thermotolerance of bin2-1 plants to a wild-type level, suggesting that ABI5 functions downstream of BIN2 in regulating plant thermotolerance. Further, HS treatment increased the cellular abundance of BIN2. Both bin2-1 mutant and BIN2-OX plants showed early flowering, while the BIN2 loss-of-function mutant bin2-3 bil1 bil2 flowered late. Given these findings, we propose that under HS conditions plants increase BIN2 activity to promote early flowering and ensure species survival; however, this reduces the thermotolerance and survivability of individual plants partially by activating ABI5.

/pdf/heat-shock-induced-accumulation-of-the-glycogen-synthase-3k3iv2uf.pdf

Heat Shock-Induced Accumulation of the Glycogen Synthase Kinase 3-Like Kinase BRASSINOSTEROID INSENSITIVE 2 Promotes Early Flowering but Reduces Thermotolerance in Arabidopsis

Yue Li Wang

Papers

Structural and Electronic Role of Lead in (PbBi)2Sr2CaCu2O8 Superconductors by STM.

Electronic and structural effects of oxygen doping in Bi2Sr2CaCu2Ox superconductors characterized by tunneling microscopy.

Electronic effect of lead substitution in single-crystal Bi(Pb)-Sr-Ca-Cu-O superconductors determined by scanning tunneling microscopy

Enhancement of the critical current density in single-crystal Bi2Sr2CaCu2O8 superconductors by chemically induced disorder

Heat Shock-Induced Accumulation of the Glycogen Synthase Kinase 3-Like Kinase BRASSINOSTEROID INSENSITIVE 2 Promotes Early Flowering but Reduces Thermotolerance in Arabidopsis