Atomic water channel controlling remarkable properties of a single brain microtubule: Correlating single protein to its supramolecular assembly

Microtubule nanotubesarefoundineverylivingeukaryoticcells;theseareformedbyreversible polymerizationofthetubulinprotein,andtheirhollow fibersare filledwithuniquelyarrangedwater molecules.Herewemeasuresingletubulinmoleculeandsinglebrain-neuronextractedmicrotubule nanowirewithandwithoutwaterchannelinsidetounraveltheiruniqueelectronicandopticalproperties for the firsttime.Wedemonstratethattheenergylevelsofasingletubulinproteinandsinglemicrotubule madeof40,000tubulindimersareidenticalunlikeconventionalmaterials.Moreover,thetransmittedac powerandthetransient fluorescencedecay(singlephotoncount)areindependentofthemicrotubule length.Evenmoreremarkableisthefactthatthemicrotubulenanowireismoreconductingthanasingle proteinmoleculethatconstitutesthenanowire.Microtubule's vibrationalpeakscondensetoasinglemode thatcontrolstheemergenceofsizeindependentelectronic/opticalproperties,andautomatednoise alleviation,whichdisappearwhentheatomicwatercoreisreleasedfromtheinnercylinder.Wehave carriedoutseveraltrickystate-of-the-artexperimentsandidentified theelectromagneticresonancepeaksof singlemicrotubulereliably.Theresonantvibrationsestablishedthatthecondensationofenergylevelsand periodicoscillationofuniqueenergyfringesonthemicrotubulesurface,emergeastheatomicwatercore resonantlyintegratesallproteinsarounditsuchthatthenanotubeirrespectiveofitssizefunctionslikea singleproteinmolecule.Thus,amonomolecularwaterchannelresidinginsidetheprotein-cylinderdisplays an unprecedentedcontrolingoverningthetantalizingelectronicandopticalpropertiesofmicrotubule

All-Inorganic Red-Light Emitting Diodes Based on Silicon Quantum Dots

We report herein an all-inorganic quantum dot light emitting diode (QLED) where an optically active layer of crystalline silicon (Si) is mounted. The prototype Si-QLED has an inverted device architecture of ITO/ZnO/QD/WO3/Al multilayer, which was prepared by a facile solution process. The QLED shows a red electroluminescence, an external quantum efficiency (EQE) of 0.25%, and luminance of 1400 cd/m2. The device performance stability has been investigated when the device faces different humidity conditions without any encapsulation. The advantage of using all inorganic layers is reflected in stable EQE even after prolonged exposure to harsh conditions

Influence of Oxidation on Temperature-Dependent Photoluminescence Properties of Hydrogen-Terminated Silicon Nanocrystals

In this study, we investigate temperature-dependent photoluminescence (PL) in three samples of hydrogen-terminated silicon nanocrystals (ncSi-H) with different levels of surface oxidation.ncSi-H was oxidized by exposure to ambient air for 0 h, 24 h, or 48 h. The PL spectra as a function of temperature ranging between room temperature (~297 K) and 4 K are measured to elucidate the underlying physics of the PL spectra influenced by the surface oxidation of ncSi-H. There are striking differences in the evolution of PL spectra according to the surface oxidation level. The PL intensity increases as the temperature decreases. ForncSi-H with a smaller amount of oxide, the PL intensity is nearly saturated at 90 K. In contrast, the PL intensity decreases even below 90 K for the heavilyoxidized ncSi-H. For all the samples, full-width at half maxima (FWHM)decreases as the temperature decreases. The plots of the PL peak energy as a function of temperature can be reproduced with an equation where the average phonon energy and other parameters are calculated

Conductance switching in TiO<SUB>2</SUB> nanorods is a redox-driven process: evidence from photovoltaic parameters

We study the effect of conductance switching of TiO2 nanorods on photovoltaic parameters. We fabricate devices with varied concentration of TiO2 nanorods in a poly(3-hexylthiophene) (P3HT) matrix with two electrodes. From the change in photovoltaic parameters upon switching, we have inferred that the conductance switching process of TiO2 nanorods is a redox-driven one. The electroreduction process changes the electronic energy levels of TiO2 that in turn modify the band diagram of P3HT:TiO2 devices. Under illumination, the open-circuit voltage of the device has hence become a parameter to probe the conducting state of TiO2 nanorods. We show that the open-circuit voltage can act as a probe parameter to evidence read-only and random-access memory applications

Transport gap vis-a-vis electrical bistability of alloyed Zn<SUB>x</SUB>Cd<SUB>1-x</SUB>S (x = 0 to 1) quantum dots

We study a correlation between electrical bistability and transport gap of II-VI semiconducting quantum dots. We first grow alloyed ZnxCd1-xS (x = 0 to 1) quantum dots for different values of x, functionalize them with suitable (anionic) stabilizers, and form their monolayer on an electrode surface via electrostatic assembly. We characterize the monolayers of the quantum dots by scanning tunneling microscopy. Current-voltage characteristics of the monolayers evidence electrical bistability and memory phenomena that depend on composition or Zn-content of the quantum dots. The dependence is due to the fact that an addition of Zn in ZnxCd1-xS introduces trap-states, which assist the process of electrical bistability and play a major role in the conduction process of high-conducting states of quantum dots. Transport gap, which depends on the composition of the quantum dots, also responds to the electrical bistability; for all the quantum dots, the gap decreases during the transition from a low- to a high-conducting state. We here correlate the transport gap of ZnxCd1-x (x = 0 to 1) and its change upon conductance-switching with the electrical bistability of quantum dots

Controlled electrostatic assembly of quantum dots vis-à-vis their electronic coupling and transport gap

We correlate the electronic coupling between quantum dots and the transport gap of nanoparticle-passivated Si substrates. We vary the length of the stabilizers of CdS nanoparticles, which in turn alters the particle-to-particle separation and hence the electronic coupling between them. We also control the electronic coupling using time-restricted electrostatic-assembly of quantum dots, using short periods of time so that an incomplete monolayer or a sub-monolayer of CdS forms. In such a sub-monolayer, the nanoparticles remain isolated from each other with a controllable particle-to-particle separation. From electronic absorption spectroscopy of multilayer films and atomic force microscopy of a monolayer, we evidenced sub-monolayer formation in the controlled electrostatic assembly process. We measure the current-voltage characteristics of nanoparticle-passivated substrates with a scanning tunnelling microscope; we show that the transport gap of nanoparticle-passivated substrates depends on the electronic coupling between CdS particles in the monolayer

Al-doped ZnO nanocrystals: electronic states through scanning tunneling spectroscopy

We form a monolayer of undoped and Al-doped ZnOnanocrystals and measure tunneling current with a scanning tunneling microscope tip. From the density of states, we determine the location of conduction and valence band edges with respect to the Fermi energy. We show that with n-doping, Fermi energy of ZnOnanoparticles shifts toward the conduction band edge. The difference between the electronic states, that is, the bandgap of the nanocrystals does not change upon doping. This is in agreement with the optical absorption spectra of the nanomaterials. We also find that inhomogeneity of doping in nanoparticles is reflected in density of states. With an increase in doping concentration, the distribution of dopants among particles becomes broader. We characterize the monolayers also with Hgelectrodes to comment on electrical conductivity versus doping concentration behavior

Core-shell nanoparticles: an approach to enhance electrical bistability

CdS/PbS core-shell nanoparticles are grown via ion-exchange reaction route. Devices based on such nanoparticles exhibit electrical bistability and memory phenomena. We show that the bistability is due to charge confinement in the nanoparticles. Here, although the low-bandgap material allows facile carrier injection from the electrodes, the high-bandgap one traps and confines charges to yield high-conducting state. The results show that the degree of electrical bistability or On/Off ratio in some of the CdS/PbS core-shell nanoparticles is several orders higher in magnitude than that in the individual components. We show how the shell/core ratio controls charge confinement and hence electrical bistability. Core-shell nanoparticles hence provide a newer route to optimize electrical bistability and memory phenomena

Core- shell nanotubes to enhance electrical bistability for 2-bit memory

We have grown core-shell nanotubes with CNTs in the core and CdS as the shell. The thickness of the shell has been varied by controlling the reaction parameters. In devices based on such core-shell nanotubes, the nanotubes act as carrier-transporting channels to augment charge confinement in the shell. Increasing the density of confined carriers results in enhanced electrical bistability and memory phenomena in CdS. With widely separated low- and high-conducting states, we were able to scale the high-state, so that different high-conducting states could be achieved for multi-level memory applications

Transport gap of nanoparticle-passivated silicon substrates

The transport gap of nanoparticle-passivated Si substrates is measured by scanning tunneling microscopy. Passivation is achieved using a monolayer of CdSe nanoparticles. It is shown that the transport gap and conduction-band edge of the system change upon passivation. The size of the nanoparticles that passivate the Si substrate is varied to study its effect on the transport gap of the system. Plots of the tunneling current versus voltage show that the transport gap of the system can be tuned by the binding of just a monolayer of suitable nanoparticles. From the normalized density of states, it is shown that the conduction-band edge of the system responds to the size of the nanoparticles. Here, a monolayer of the nanoparticles, which were capped with suitable functional groups, has been formed via electrostatic adsorption with the substrate