ADHESION TEST OF CARBON NANOTUBE FILM COATED ONTO TRANSPARENT CONDUCTING SUBSTRATES

Sang Won Lee,이영희,Ki Kang Kim,Yan Cui,Seong Chu Lim,Young Woo cho,김수민 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2010 NANO Vol.5 No.3

We examined the adhesion of carbon nanotube films coated on transparent substrates. Single-walled carbon nanotubes (SWCNTs) dispersed with sodium dodecylbenzene sulfonate (NaDDBS) in water were sprayed onto polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) substrates to form thin films. Scotch™ tape was then used to detach some loosely bound SWCNTs. Conventional peel-off method to measure adhesion fails in carbon nanotube (CNT) film mainly due to ill-defined detached area of entangled CNTs. We propose here a new adhesion factor which is defined by using transmittance before and after detachment. The adhesion factor was strongly correlated to film thickness. We also found that the SWCNT adhesion to the substrate was strongly dependent on the surface roughness of the substrate due to mechanical interlocking effects.

ENERGY TRANSDUCTION IN MOLECULAR MACHINES

CHENG-HUNG CHANG,TIAN YOW TSONG 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2007 NANO Vol.2 No.5

An applied force may cause the conformation and thus, the activity of a biological molecule to change. Here we consider a system in which an oscillating or fluctuating electric field is used to actuate membrane protein activities. Most proteins have electric dipoles and net charges in the structure and their conformations are susceptible to the electric and magnetic perturbation. The shape of a cell may also amplify an electric field across its plasma membrane. Therefore, a membrane integral protein such as an ion channel, an ion pump, or a molecular motor, is especially amenable to electric perturbation. The theory of electroconformational coupling addresses the functional implication of this field effect. When an alternating electric field or a fluctuating electric field is employed to actuate a two-state protein oscillator, the dynamics of the conformational change of the protein can be synchronized with the applied field. Through this two-state protein oscillator, we construct a four-state catalytic wheel by coupling an energy transducer mechanism to the two-state protein oscillator. Analysis shows that the catalytic wheel can extract energy from a disordered external energy source, be it electrical, mechanical, or chemical, and convert this stochastic energy source to a usable energy format. The catalytic wheel is tested with the experimental data on the electric field-stimulated cation pumping of Na, K-ATPase. A dipole ratchet model based on the electroconformational coupling concept will also be discussed and compared with the ATP-dependent rotation of a rotary motor F1-ATPase. Since the working principle of this model is simpler than that of F1-ATPase, it provides an easier way to realize a nanoscale rotary motor than artificially reconstructing a F1-ATPase.

CHARGE TRANSPORT THROUGH CARBON NANOTUBE OR FULLERENE–MOLECULE–SILICON JUNCTIONS

FU-REN F. FAN,BO CHEN,AUSTEN K. FLATT,JAMES M. TOUR,ALLEN J. BARD 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2007 NANO Vol.2 No.5

We report here the current–voltage (i–V) characteristics of several (n++-Si/MNOPE/C60/Pt-tip) or (n++-Si/MNOPE/SWCNT/Pt-tip) junctions, where MNOPE = 2'-mononitro-4, 4'-bis(phenylethynyl)-1-phenylenediazonium and SWCNT = single wall carbon nanotube. A layer of C60 or SWCNT-derivatized MNOPE has strong effect on the i–V behavior of the junctions, including rectification, negative differential resistance (NDR) and switching behaviors. The i–V curve of a grafted molecular monolayer (GMM) of MNOPE atop n++-Si shows NDR behavior, whereas those of C60- and SWCNT-derivatized GMMs of MNOPE on n++-Si show strong rectifying behavior with opposite rectification polarities. With C60, larger currents were found with negative tip bias, while with SWCNT, the forward top bias was positive. Because C60 tends to be a good electron acceptor and SWCNTs tend to be good electron donors, they show different i–V behavior, as observed. Some of the (n++-Si/MNOPE/SWCNT/Pt-tip) junctions also show reversible bistable switching behavior.

SYNTHESIS OF DOUBLE-WALL CARBON NANOTUBES ON MESOPOROUS SILICA: INFLUENCES OF CATALYST PRETREATMENT ON THE NANOTUBE GROWTH

H. SHINOHARA,P. RAMESH,K. SATO,Y. OZEKI,N. KISHI,T. SUGAI 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2006 NANO Vol.1 No.1

Experimental conditions that govern the double-wall carbon nanotube (DWNT) growth during alcohol catalytic chemical vapor deposition (CCVD) have been optimized for mesoporous silica (MCM41) support materials. Catalyst pretreatment and preparation methods influence the quality of as-grown carbon nanotubes (CNTs). Catalyst pretreatment at low pressure leads to high-quality CNTs concomitant with an increase in the DWNT yield. Impregnation of metal precursors using methanol as the solvent is found to be more suitable than the aqueous solution. Influence of the precursor anion/metal ion on the DWNT yield is also studied under these optimized conditions. Thermogravimetric analysis (TGA), transmission electron microscopy (TEM) and Raman spectroscopic methods have been employed to estimate the quality of the CNTs. It is observed that the present optimized method yields high-quality DWNTs with low amounts of side-wall defects and other carbon impurities.

CONTROLLED ELECTRIC FIELD-ASSISTED JETTING FROM VISCOUS AND NANOSUSPENSION MEDIA DROPLETS

S. N. JAYASINGHE 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2006 NANO Vol.1 No.3

This paper reports a study into forming a jet-on-demand to continuous microthreads by subjecting electric fields on high viscosity and low conducting media (concentrated nanosuspensions and dielectric mediums) droplets, placed on a conducting copper plate, which has a similar plate above at a distance of ~ 10 mm. The media used in this investigation has a viscosity ≫ 1000 mPa s and an electrical conductivity ≪ 10-6 Sm-1 and in the case of nanomaterial loading in suspension is 003E; 15 wt.%. The investigation illustrates both the ability to form jets in this configuration and the importance of the volume of media placed as a droplet which has a direct result on the formation of a jet subsequently fragmentating to droplets. At a droplet volume of < Q0, the resting droplet when under the influence of an applied electric field deforms forming a cone, much like those referred to as the "Taylor Cones". On increasing the volume of the droplet to Q0 and applying a voltage of ~ 4.6 kV across the plates, the apex of the cone was observed to pulsate. On further increasing the applied voltage, giving rise to an electric field strength of ~ 0.55 kV/mm, the pulsating apex stabilizes to evolve a stable jet which undergoes instabilities promoting the generation of droplets. Consequently, a fine jet-on-demand is obtained. On increasing the droplet volume to > Q0, forms jets on both plates. The study elucidates the importance of this jetting approach for forming droplet relics containing self-assembled nanoparticles to continuous microthreads from concentrated nanosuspensions and dielectric media for forming structures by deposition that are most useful and have widespread applications in materials science and engineering. Hence, the physical behavior of this droplet deformation — jetting — forming droplets under an imposed field, outlines the discussion presented in this paper.

THE EFFECT OF SINGLE WALL CARBON NANOTUBES ON THE DIPOLE ORIENTATION AND PIEZOELECTRIC PROPERTIES OF POLYMERIC NANOCOMPOSITES

JIN HO KANG,JOYCELYN S. HARRISON,CHEOL PARK,STEVEN J. GAIK,SHARON E. LOWTHER 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2006 NANO Vol.1 No.1

Recently, a series of single wall carbon nanotube (SWNT) polyimide nanocomposites were developed since the demand of electroactive polymeric materials as sensors and actuators for use in high temperature applications has been growing. Adding SWNTs into electroactive polyimides enhanced their electrostrictive strain as well as their mechanical integrities and chemical stability. Although an increase in piezoelectricity resulting from the incorporation of SWNTs could be expected, there has been no systematic study detailing the effect of SWNTs on piezoelectricity. In this article, the effects of various types and concentrations of SWNT on the dipole orientation and piezoelectricity were investigated using a thermally stimulated current (TSC) technique and a modified Rheovibron. It was found that the barely modified SWNTs led to a more substantial increase in the remanent polarization (Pr) than the highly modified SWNTs did. As the loading level of SWNTs increased, Pr increased.However, excessive loading of SWNTs showed a reduction in Pr since the actual poling field decreased due to a large leakage of current. The trend of the piezoelectric strain coefficient, d31, was consistent with that of Pr. The increase in interfacial polarization caused by adding SWNT was believed to be primarily responsible for the increase of Pr and d31.

PHOTON-ASSISTED INTERSUBBAND TRANSITIONS IN A QUANTUM WIRE

VINOD PRASAD,PRADEEP KUMAR JHA,MAN MOHAN,MONICA GUDWANI 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2006 NANO Vol.1 No.3

We investigate the response of electrons confined in a quantum wire in the presence of intense terahertz (THz) electric field. An exact and powerful nonperturbative fundamental approach of Floquet theory is employed to solve the equation of motion for resonantly driven intersubband transitions. Several interesting features namely dynamic Stark shift, power broadening and hole-burning are observed with the variation in electric field strength. In addition, the degeneracy between several excited states is found to be removed in the presence of high electric field.

MAGNETIC FORCE MICROMANIPULATION SYSTEMS FOR THE BIOLOGICAL SCIENCES

R. SUPERFINE,J. K. FISHER,L. VICCI,J. CRIBB,E. T. O'BRIEN,R. M. TAYLOR II 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2006 NANO Vol.1 No.3

Manipulation systems using magnetic field gradients have the ability to apply a large range of forces noninvasively to a specific target. Depending on the requirements of a given experiment, the systems may be as simple as a single electromagnet for unidirectional manipulation or as complex as a high-frequency three-dimensional manipulator with force feedback. Here, we discuss the motivation for developing such systems, theory and design considerations, and give examples of the broad range of manipulators that has been put to use. In addition, we discuss a variety of applications demonstrating the range of experiments for which such a system is applicable.

PHOTON-ASSISTED TRANSPORT CHARACTERISTICS THROUGH QUANTUM DOT COUPLED TO SUPERCONDUCTING RESERVOIRS

A. H. PHILLIPS,A. S. ATALLAH,A. F. AMIN,M. A. SEMARY 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2006 NANO Vol.1 No.3

The influence of time-varying fields on the transport through a mesoscopic device has been investigated. This mesoscopic device is modeled as a quantum dot coupled to superconducting reservoirs via quantum point contact. The effect of a magnetic field and the Andreev reflection process were taken into account. The conductance was deduced by using Landuaer–Buttiker equation. A numerical calculation has been performed that shows a resonant tunneling behavior. Such investigation is important for fabricating photoelectron mesoscopic devices.

CRYSTAL STRUCTURE OF BRANCHED EPITAXIAL III–V NANOTREES

L. REINE WALLENBERG,LISA S. KARLSSON,MAGNUS W. LARSSON,JAN-OLLE MALM,KIMBERLY A. DICK,KNUT DEPPERT,WERNER SEIFERT,LARS SAMUELSON 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2006 NANO Vol.1 No.2

In this review we discuss the morphology and crystal structure of branched epitaxial III–V semiconductor structures, so called nanotrees, based on our own work with GaP, InAs and GaP/InP. These structures are formed by epitaxial growth in a step-wise procedure where each level can be individually controlled in terms of diameter, length and composition. Poly-typism is commonly observed for III–Vs with zinc blende, wurtzite or combinations thereof as the resulting crystal structure. Here we review GaP as an example of zinc blende and InAs of wurtzite type of growth in terms of nanotrees with two to three levels of growth. Included are also previously unpublished results on the growth of GaP/InP nanotrees to demonstrate effects of heteroepitaxial growth with substantial mismatch. For these structures a topotaxial growth behavior was observed with InP wires crawling along or spiraling around the GaP nanowires acting as a free-standing substrates.