Sung-Reol Lee

Gating effect in the I-V characteristics of iodine doped polyacetylene nanofibers

The I-V characteristics of iodine doped polyacetylene (PA) nanofibers were measured as function of temperature. Platinum electrodes on top of SiO 2 substrates were used to prevent reaction with iodine dopant. The distance between the two electrodes is approximately 100 nm. Upon iodine doping, non-ohmic I-V characteristics are observed. The gate dependence shows the charge carrier to be hole with a mobility μ FET ∼ 4.4×10 -5 cm 2 /Vs at 233K.

The analysis of thermal stress effect on electromigration failure time in Al alloy thin-film interconnects

Microfailure of thin-film interconnects by electromigration is one of the primary causes of degradation of the reliability of microelectronic circuits. This study analyzed the electromigration failure time considering the thermal stress effect in the interconnect. The thermal stress is generated by the difference of thermal expansion coefficients between the metal interconnect and the oxidized silicon substrate. This thermal stress, which is developed during fabrication, produces defects, such as microvoids which accelerate the electromigration. The effect of thermal stress on the electromigration failure time was analyzed via kinetic considerations. For those, after applying different thermal cycles to develop various thermal stresses in the test specimens, the MTF (mean time to failure) was evaluated by measuring the change of electrical resistance during the electromigration test. Then, the apparent activation energy for electromigration was calculated. The experimental results show that the apparent activation energy and MTF tend to decrease with increasing thermal stress. Microvoids due to thermal stress are an important factor in accelerating the electromigration failure. The presence of stress-induced microvoids was ascertained by the fact that the initial resistance increased with increasing thermal stress.

Tunneling conduction in polyacetylene nanofiber

We report the first low temperature measurements of I-V characteristics of polyacetylene nanofibers. Our data provide (i) no temperature dependence below 10-30K, (ii) no significant change of MR in magnetic field up to H=6T, to within the accuracy of the data. These are signatures of a novel conduction mechanism: the creation of charged soliton-antisoliton pairs by quantum-mechanical tunneling.

Quantum transport in low-dimensional organic nanostructures

We have studied three low-dimensional systems with sub-micron dimensions: a single polyacetylene (PA) nanofiber; a single-walled carbon nanotube (SWNT)-rope; and a lithographically prepared stripe of poly(2-methoxy-5-(2-ethyl hexyloxy)-p-phenylene vinylene) (MEH-PPV). In each case, the sample was contacted to four-probe electrodes, with 100-nm spacing and various electronic transport properties such as the I-V characteristics, the temperature dependence of resistivity and the gate voltage dependence of the transport current were measured. The PA nanofiber was found to be non-ohmic with a room temperature conductivity of ∼ 0.1 S/cm. Its carriers were found to be hole-like with charge carrier mobility of μ = 7.76 × 10 -2 cm 2 /Vs. For the SWNT-rope, the temperature-dependence of resistivity exhibited signatures of a Luttinger liquid for temperatures below 30 K. With varying gate voltage, periodic peaks were seen in the nanotube current which would normally be attributed to the effects of Coulomb blockade. Interestingly, these peaks show three-way splitting, similar to observations in triple quantum dot experiments. The MEH-PPV stripe, which was produced using electron beam lithography, had I-V characteristics similar to that of a large band-gap semiconductor. In the high field region, these characteristics could be explained in terms of a single carrier device model which considers the field-dependent mobility along with space charge limited conduction (SCLC). All three samples can be considered as field-effect transistors (FETs), with potential use in future high density integrated electronic devices.

Solid–solid transformation mechanism for nanocrystalline sodalite from pillared clay

We here report the synthesis of nanocrystalline sodalite by a solid-solid transformation from a solid gel mixture of Al2O3 pillared montmorillonite (Al2O3-PILM) and NaOH under an ambient atmosphere at 80 degrees C. HR-TEM clearly shows both the formation of sodalite nuclei by the solid-solid transformation of the montmorillonite matrix and the crystal growth of nanocrystalline sodalite through the rearrangement of delocalized nuclei.

2D→3D transformation of layered aluminosilicate upon base treatment

Abstract The present study describes a novel preparative route to sodalite from layered aluminosilicates such as kaolinite, montmorillonite, and Al 2 O 3 -pillared montmorillonite (Al-PILC), those which are subjected to react directly with sodium hydroxide as low as 100 °C under an ambient atmosphere. Powder X-ray diffraction (XRD) analysis, infrared absorption (IR) spectra and 27 Al and 29 Si magic-angle-spinning nuclear magnetic resonance (MAS NMR) spectra reveal that the resulting solid products are crystalline sodalites with cubic symmetry ( a =8.92±0.05 A) consisted of zeolitic Al–O–Si networks with an alternating ordering of Al and Si tetrahedra. Scanning electron microscopy (SEM) indicates that the sodalites derived from the two-dimensional aluminosilicates consist of nano-sized sodalite particles (30–50 nm) with preserved lamellar characters of the pristine layer silicates. Among the starting aluminosilicates, Al 2 O 3 -pillared montmorillonite is found to be an active precursor to zeolitic sodalite because of the high microporosity and the compositional and structural similarities.

Non-linear I–V characteristics of MEH-PPV patterned on sub-micrometer electrodes

A sub-micrometer-wide line of a conjugated polymer MEH-PPV [poly(2-methoxy-5-(2-ethyl hexyloxy)-p-phenylene vinylene)] was patterned using a scanning electron microscope (SEM). The spin-coated thin MEH-PPV film was exposed to the electron beam in SEM, resulting in an increase in cross-linking, which reduced the solubility of the MEH-PPV film. The polymer was developed in p-xylene to dissolve the non-irradiated part of the polymer. The width, length and thickness of the active patterned area, determined by the atomic force microscopy (AFM) image, was 500, 200 and 20 nm, respectively. The two-probe current-voltage characteristics of the patterned MEH-PPV line were measured as a function of temperature. The higher field data of the non-linear I-V curves were fitted using the single carrier device model which considered the field and temperature dependent mobility with space charge limited conduction (SCLC). The estimated zero-field hole mobility was of the order of 10 -3 cm 2 /Vs with an activation energy of 0.038 eV.

Variation with temperature of the I–V characteristics of polyacetylene nanofibres☆

The current–voltage (I–V) characteristics of individual nanofibres of doped polyacetylene show a dramatic change from very strong nonlinearities for lightly-doped samples at low temperatures, to nearly ohmic behaviour for higher temperatures and doping levels. At low temperatures (below 10–30 K), the I–V characteristics are independent of temperature and follow the expression for Zener-type tunnelling, as predicted for field-induced tunnelling of the conjugated bond system. At higher temperatures, the I–V characteristics deviate from Zener-type behaviour and the current increases with temperature as thermally-assisted conduction mechanisms become important. The I–V characteristics for the most conductive sample are consistent with our calculations of fluctuation-induced tunnelling.

Non-linear I–V characteristics of polypyrrole micro-line synthesized using scanning probe microscope

AbstractWemeasuredtemperaturedependenceofvoltage–currentcharacteristicsofelectrochemicallypolymerizedpolypyrroleinmicronscaleusingscanningprobemicroscope.Themorphologyandthemagnitudeofroomtemperatureresistivity,q RT ¼ 0:016Xcm,aresimilartootherelectrochemicallysynthesizedpolypyrrole.I–Vcharacteristicsbecamenon-linearforT < 100Kandcanbefittedtofluctuation-inducedtunnelingconductionmodel. 2002ElsevierScienceB.V.Allrightsreserved. PACS:72.80.-r;72.80.Le;73.63.-b;73.63.NmKeywords:Polypyrrole;Micor-line;Electrochemicalsynthesis;Scanningprobemicroscope;Non-linearI-Vcharacteristics 1.IntroductionConjugatedpolymerhasinterestingphysicalproper-tiesincludingmetallicbehaviourandeventhesuper-conductivity [1] as well as applicability to electronicdevices such as LED [2] or field-effect transistor orconductivewireetc.Conductingpolymersuchaspoly-acetylene (PA), polypyrrole (PPy), polythiophen (PT)andpolyaniline(PANI)haslongbeeninvestigatedtoelucidate their intrinsictransport properties owing totheirlowdimensionality.Thelocalexcitationssuchassoliton [3], polaron and bipolaron are suggestedfor their conducting carriers. However the transportmechanisminconductingpolymerinnanoscaleisnotunderstoodwellyet.Recentlywehavereportedtrans-portmeasurementsofPAnanofibernetworkinmicronscale[4]andthatofPAsinglenanofiberin100nmscale[5].ContrarytothefibrillarstructureofPA,thegranularstructureofelectrochemicallypolymerizedconductingpolymermakesitdifficulttoapplythenanopatternedarrayofelectrodesfortheelectricalmeasurement.Inthecaseofusingtemplatesuchasanodicaluminumoxide(AAO) or zeolite, we can polymerize the conductingpolymer inside the template [6] and then separate itfromthetemplate.Othermethodstosynthesizealinearstructure of conducting polymer is using SPM localoxidation[7],e-beamirradiationtoPANI[8]orpoly-octylthiophene [9], self-assembled monolayer (SAM)pattern [10] and Langmuir–Bloddgett (LB) technique[11].STMlocaloxidationhassomedifficultiestomakealinearstructureinnarrowscaleduetotherandomnessofthegrowthdirection.UsingaSAMhaslimitationonthestamptogeneratetheSAMpatternanditisali-thography dependent technique. Here we present thetransport measurements of PPy line that is electro-chemicallypolymerizedbybiasingtothemetalcoatedSPMtipontopofthepatternedelectrodes.2.ExperimentalMicron and submicron electrodes for transportmeasurement were patterned using JEOL JBX5D-IIe-beamlithographysystem.300nmSiO