Tuesday, March 21, 2006

Joel's Journal Update

Similar to Cory, I have added my journals to the same folder he created on Purcell. I have also made a new folder for the articles from the beginning of January to March 7, 2006. In the main folder, i have added files containing the usual article information (title, author, abstract etc.) for all of the journal articles that I have collected. You can have a glance at these and see what may be of interest to you (I've put names to the articles to whom it may be most relevant to). But for now, here are a few articles that some of you may be interested in from 2006.

Nanopatterning and Nanochange Writing in Layer-by-Layer Quinquethiophene/Phthalocyanine Ultrathin Films.
A. Baba, J. Locklin, R.S. Xu, R. Advincula
J.Phys.Chem.B (2006)110, 24.

Nanometer-scale patterning and charging in layer-by-layer (LbL) ultrathin films of quinquethiophene (5TN)/ phthalocyanine (CuPS) provides a novel write-read device using a standard current-sensing atomic force microscopy (CS-AFM). The AFM height images showed dented or raised morphological features that could be selectively manipulated by changing the direction of the bias voltages. The conductivity was repeatedly changed between a conductive and insulating state, originating from an electrochemical charging-discharging effect. This was attributed to electrochemical ion transport and the residual mobile ions present in LbL films. Finally, the nanocharge pattern was written by CS-AFM and read out in a conductivity map image.

Ultrafast Excitation Dynamics in CdSe Quantum Dots Studied from Bleaching Recovery and Fluorescence Transients.
H. Wang, C. De Donega, A. Meijerink, M. Glasbeek.
J.Phys.Chem.B (2006)110, 733.

We have performed ultrafast absorption bleach recovery and fluorescence upconversion measurements (~100 fs time resolution) for three CdSe samples, with nanoparticle diameters of 2.7, 2.9, and 4.3 nm. The two types of experiments provide complementary information regarding the contributions of the different processes involved in the fast relaxation of electrons and holes in the CdSe quantum dots. Transient absorption and emission experiments were conducted for the 1S [1S(e) - 1S3/2(h)] transition, S(e) and 1S3/2(h) representing the lowest electron (e) and hole (h) levels. The bleach recovery of the 1S transition shows a ~400-500 fs initial rise, which is followed by a size-dependent ~10-90 ps decay and finally a long-lived (~ns) decay. The fluorescence upconversion signal for the 1S transition shows quite different temporal behavior: a two times slower rise time (~700-1000 fs) and, when the fluorescence upconversion signal has risen to about 20% of its maximum intensity, the signal displays a slight leveling off (bend), followed by a continued rise until the maximum intensity is reached. This bend is well reproducible and power and concentration independent. Simulations show that the bend in the rise is caused by a very fast decay component with a typical time of about 230-430 fs. Considering that the 1S quantum dot excitation is comprised of five exciton substates (F =±2, ±1L, 0L, ±1U, and 0U), we attribute the disparity in the rise of the bleaching and emission transients to the results from the dynamics of the different excitons involved in respectively the bleaching and fluorescence experiments. More specifically, in transient absorption, population changes of the F =±1U excitons are probed, in mission population effects for the F =±2 ("dark") and the F =±1L ("bright") exciton states are monitored. It is discussed that the fast (~400-500 fs) rise of the bleach recovery is representative of the feeding of the F =±1U exciton (by filling of the 1S(e) electron level) and that the slower (~700-1000 fs) feeding of the emissive ±2, ±1L excitons is determined by the relaxation of the hole levels within the 1S3/2 fine structure. Finally, the ~230-430 fs component, typical of the bend in the fluorescence transient, is attributed to the thermalization of the close-lying ±2 ("dark") and ±1L ("bright") excitons.

Preparation and Third-Order Optical Nonlinearity of Self-Assembled Chitosan/CdSe-ZnS Core-Shell Quantum Dots Multilayer Films.
X. Wang, Y. Du, S. Ding, Q. Wang, G. Xiong, M. Xie, X. Shen, D. Pang
J.Phys.Chem.B (2006)110, 1566.

The self-assembed chitosan CdSe quantum dots (QDs) and chitosan CdSe-ZnS core-shell QDs films have been prepared by using layer-by-layer electrostatic technique. The well-ordered nanostructure and the layerby- layer deposition of the QDs are revealed by AFM and exciton absorption spectra, respectively. The optical nonlinearity of the composite films were studied by using Z-scan technique with femtosecond pulses at the wavelength of 790 nm, the value of third-order susceptibility of core-shell QDs are measured to be about 1.1 ×10-8 esu, which is about 200% larger than that of CdSe QDs of 5.3×10-9 esu. This has potential applications in all-optical switches in optical information processing.

Two-Dimensional Crystal Growth and Stacking of Bis(phthalocyaninato) Rare Earth Sandwich Complexes as the 1-Phenyloctane/Graphite Interphace.
T. Takami, D.P. Arnold, A.V. Fuchs, G.D. Will, R. Goh, E.R. Waclawik, J.M. Bell, P.S. Weiss, K. Sugiura, W. Liu, J. Jiang.
J.Phys.Chem.B (2006)110, 1661.

Initial stages of two-dimensional crystal growth of the double-decker sandwich complex Lu(Pc*)2 [Pc* ) 2,3,9,10,16,17,23,24-octakis(octyloxy)phthalocyaninato] have been studied by scanning tunneling microscopy at the liquid/solid interface between 1-phenyloctane and highly oriented pyrolytic graphite. High-resolution images strongly suggest alignment of the double-decker molecules into monolayers with the phthalocyanine rings parallel to the surface. Domains were observed with either hexagonal or quadrate packing motifs, and the growing interface of the layer was imaged. Molecular resolution was achieved, and the face of the phthalocyanine rings appeared as somewhat diffuse circular features. The alkyl chains are proposed to be interdigitating to maintain planar side-by-side packing.

Communication: Conducting-Polymer Nanotubes for Controlled Drug Release
M.R. Abidian, D.H. Kim, D.C. Martin
Advan. Mat. (2006)18, 405.

Controlled release of an anti-inflammatory drug from PEDOT nanotubes using electrical stimulation is demonstrated (see Figure and Inside Cover). The fabrication process includes electrospinning of a biodegradable polymer into which the drug has been incorporated, followed by electrochemical deposition of the conducting polymer around the drug-loaded electrospun nanoscale fibers.

Pentaporphyrin as a Switching Device Activated by Proton and Redox Stimuli.
P. Ceroni, G. Bergamini, N. Aubert, V. Troiani and N. Solladie.
ChemPhysChem (2005) 10, 2120.

The authors investigate the electron charge transfer capabilities of a metalloporphyrin. The porphyrin of interest contains a peptidic backbone with flexible peptidic spacers having either PH2, PZn and PMg on the end (see pic). The aim is to determine if the electron transfer is efficient and if the emission can be controlled by electron or chemical stimuli. What they found was that the the light emitted can be tuned by protonation of the free-base unit and that it can be turned off by a redox in put which quenches the free-base porphyrin emission.

(Kurt's Paper on Fuel Cells if anyone's interested)
The Use of 1H NMR Microscopy to Study Proton-Exchange Membrane Fuel Cells
K.W. Feindel, S.H. Bergens, R.E. Wasylishen
ChemPhysChem (2006) 7(1), 67.

To understand proton-exchange membrane fuel cells (PEMFCs) better, researchers have used several techniques to visualize their internal operation. This Concept outlines the advantages of using 1H NMR microscopy, that is, magnetic resonance imaging, to monitor the distribution of water in a working PEMFC. We describe what a PEMFC is, how it operates, and why monitoring water distribution in a fuel cell is important. We will focus on our experience in constructing PEMFCs, and demonstrate how 1H NMR microscopy is used to observe the water distribution throughout an operating hydrogen PEMFC. Research in this area is briefly reviewed, followed by some comments regarding challenges and anticipated future developments.

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