Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:6.2.1.1 (ACS)
 78,556 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Fusing bithiophene units with a benzo moiety, benzo[2,1-b:3,4-b']dithiophene (BDT), was projected by theoretical calculations to lower the highest occupied molecular orbital (HOMO) energy level of the resulting polymers compared with that of the bithiophene unit, which would enhance the open circuit voltage of bulk heterojunction photovoltaic cells fabricated from BDT-based polymers blended with PCBM. The homopolymer of BDT (HMPBDT) and alternating copolymer of BDT with 2,1,3-benzothiadiazole (PBDT-BT) were therefore synthesized and fully characterized. Both the homopolymer (HMPBDT) and the copolymer (PBDT-BT) were experimentally confirmed to have low HOMO energy levels (-5.70 eV for HMPBDT and -5.34 eV for PBDT-BT). Introducing the acceptor moiety (2,1,3-benzothiadiazole) successfully lowered the optical band gap of the copolymer from 2.31 eV (HMPBDT) to 1.78 eV (PBDT-BT). Bulk heterojunction photovoltaic devices were fabricated from blends of these structurally related polymers with PBCM to investigate the photovoltaic performances. The optimized device of HMPBDT:PCBM (1:3, 180 nm) exhibited an improved open circuit voltage (V(oc)) of 0.76 V, a short circuit current (J(sc)) of 0.34 mA/cm(2), and a fill factor (FF) of 0.40, offering an overall efficiency of 0.10%. The observed large phase separation of the thin film by AFM and the large band gap were accountable for the small current. The optimized device of PBDT-BT:PCBM (1:3, 55 nm) demonstrated a better efficiency of 0.6%, with V(oc) = 0.72 V, J(sc) = 2.06 mA/cm(2), and FF = 0.42. The much improved current was attributed to the lower bandgap and better film morphology. However, the low hole mobility limited the thickness of the PBDT-BT:PCBM film, making inaccessible the thicker film which would utilize more light and enhance the current. Further improvements are expected if the mobility and film morphology can be improved by the new materials design, together with low band gap and low HOMO energy level.
ACS Appl Mater Interfaces 2009 Jul
PMID:Conjugated polymers based on benzo[2,1-b:3,4-b']dithiophene with low-lying highest occupied molecular orbital energy levels for organic photovoltaics. 2035 69

Nanocomposite matrices of silver/poly(3-hexylthiophene) (P3HT) were prepared in ultrahigh vacuum through vapor-phase codeposition. Change in microstructure, chemical nature, and electronic properties with increasing filler (Ag) content were investigated using in situ XPS and UPS, and ambient AFM. At least two chemical binding states occur between Ag nanoparticles and sulfur in P3HT at the immediate contact layer, but no evidence of interaction between Ag and carbon (in P3HT) was found. AFM images reveal a change in Ag nanoparticles size with concentration which modifies the microstructure and the average roughness of the surface. Under codeposition, P3HT largely retains its conjugated structures, which is evidenced by the similar XPS and UPS spectra to those of P3HT films deposited on other substrates. We demonstrate here that the magnitude of the barrier height for hole injection (epsilon(v)(F)) and the position of the highest occupied band edge (HOB) with respect to the Fermi level of Ag may be controlled and changed by adjusting the metal (Ag) content in the composite. Furthermore, UPS reveals distinct features related to the C 2p (sigma states) in the 5-12 eV regions, indicating the presence of ordered P3HT, which is different from solution processed films.
ACS Appl Mater Interfaces 2009 Dec
PMID:Photoemission spectroscopy and atomic force microscopy investigation of vapor-phase codeposited silver/poly(3-hexylthiophene) composites. 2035 49

Stimuli-responsive surfaces grafted with thermoresponsive polymers switch from hydrophilic to hydrophobic thermally, making these surfaces attractive in applications such as in microfluidics devices, as antifouling surfaces, and in cell culture and tissue engineering. These materials exhibit changes in wettability as the polymer undergoes a phase transition above its lower critical solution temperature (LCST). Because the presence of salts affects LCSTs in accordance to the Hofmeister series, salt effects on the wettability of these thermoresponsive surfaces will dramatically impact device performance. Prior studies of such effects have focused on the influence of anions. Detailed studies of the effects of cations have not been carried out. Here, the influence of varying cation identity in a series of mono-, di-, and trivalent sulfate salts on the wettability of a stimuli-responsive grafted surface was investigated by measuring advancing water contact angle (Theta(a)) changes. The cation-induced changes in Theta(a) were correlated with corresponding changes in surface morphology examined by AFM. The results showed that the effects of varying cations on surface wettability are as large as the effects of varying anion identity and concentration (i.e., Theta(a) changes of up to 90 degrees). Parallel studies of the effects of varying the cation identity and concentration for these same cation sulfate salts in solution show that cation variation also has a large effect on the LCST of PNIPAM, the stimuli responsive polymer component of the nanocomposite grafts that were studied. Moreover, analyses of the Theta(a) and LCST data using activity showed that the Theta(a) or LCST versus cation activity/concentration could be readily grouped by charge. Such differences are not seen in similar studies where anion identity, charge, and concentration are changed.
ACS Appl Mater Interfaces 2010 Feb
PMID:Parallel effects of cations on PNIPAM graft wettability and PNIPAM solubility. 2035 91

Self-assembled surfactant structures at the solid/liquid interface have been shown to act as nanoparticulate dispersants and are capable of providing a highly effective, self-healing boundary lubrication layer in aqueous environments. However, in some cases in particular, chemical mechanical planarization (CMP) applications the lubrication imparted by self-assembled surfactant dispersants can be too strong, resulting in undesirably low levels of wear or friction disabling material removal. In the present investigation, the influence of calcium cation (Ca(2+)) addition on dodecyl trimethylammonium bromide (C(12)TAB) mediated lubrication of silica surfaces is examined via normal and lateral atomic force microscopy (AFM/LFM), benchtop polishing experiments and surface adsorption characterization methods. It is demonstrated that the introduction of competitively adsorbing cations that modulate the surfactant headgroup surface affinity can be used to tune friction and wear without compromising dispersion stability. These self-healing, reversible, and tunable tribological systems are expected to lead to the development of smart surfactant-based aqueous lubrication schemes, which include designer polishing slurries and devices that take advantage of pressure-gated friction response phenomena.
ACS Appl Mater Interfaces 2010 Apr
PMID:Tailoring silica nanotribology for CMP slurry optimization: Ca(2+) cation competition in C(12)TAB mediated lubrication. 2038 10

A new amorphous semiconducting polymer containing dodecylthiophene rings and a rigid thieno[3,2-b]thiophene ring, poly(2,5-bis(3'-dodecyl-2,2'-bithiophen-5-yl)thieno[3,2-b]thiophene) (NAP), was synthesized via a microwave-assisted Stille coupling reaction. The presence of the flexible unsubstituted thiophene ring units next to the rigid fused thiophene ring caused NAP to have an amorphous structure. This structure was confirmed by XRD, AFM, and computational calculations. In particular, the out-of-plane XRD patterns of NAP thin films exhibited no reflection peaks before or after the annealing process, indicating that the films had amorphous microstructures. In addition, AFM images of the NAP thin films showed amorphous surface morphologies with very small root-mean-square (rms) surface roughnesses of 0.3-0.5 nm, independent of surface treatment or heat treatment. Computational calculations performed to investigate the preferred conformation of the polymer confirmed the amorphous characteristics of the NAP structure. On the basis of these findings, we propose how an amorphous NAP semiconductor can maintain high carrier mobility. A NAP-based TFT device exhibited a very high carrier mobility of 0.02 cm(2) V(-1) s(-1) with an on/off ratio of 1 x 10(5) and a very small threshold voltage of -2.0 V. This carrier mobility is the highest yet reported for TFTs based on amorphous semiconductors. Thus, the present findings suggest that an amorphous semiconductor layer comprised of NAP would be suitable for use in high-performance organic TFTs fabricated via simple processes in which neither surface treatment nor heat treatment is necessary.
ACS Appl Mater Interfaces 2010 Apr
PMID:A new amorphous semiconducting polythiophene for high-performance organic thin-film transistors. 2038 57

In this work, we have studied the adsorption and diffusion of large functionalized organic molecules on an insulating ionic surface at room temperature using a noncontact atomic force microscope (NC-AFM) and theoretical modeling. Custom designed syn-5,10,15-tris(4-cyanophenylmethyl)truxene molecules are adsorbed onto the nanoscale structured KBr(001) surface at low coverages and imaged with atomic and molecular resolution with the NC-AFM. The molecules are observed rapidly diffusing along the perfect monolayer step edges and immobilized at monolayer kink sites. Extensive atomistic simulations elucidate the mechanisms of adsorption and diffusion of the molecule on the different surface features. The results of this study suggest methods of controlling the diffusion of adsorbates on insulating and nanostructured surfaces.
ACS Nano 2010 Jun 22
PMID:Functionalized truxenes: adsorption and diffusion of single molecules on the KBr(001) surface. 2049 57

The adhesion between a micro-object and a microgripper end-effector is an important problem in micromanipulation. Canceling or reducing this force is a great challenge. This force is directly linked to the surface chemical structure of the object and the gripper. We propose to reduce the adhesion force by using a self-assembled monolayer structuring on one surface. The surface was structured by polystyrene latex particles (PS particles) with radii from 100 to 1500 nm. The adhesion force measurements obtained by AFM were compared to a multisphere van der Waals force model. The model suggests the existence of an optimal value of the sphere radius which minimizes the adhesion. In that case, the pull-off force is reduced to 20 nN by the PS particles layer with a radius of 45 nm. A wide range of applications in the field of telecommunications, bioengineering, and more generally speaking, MEMS can be envisaged for these substrates.
ACS Appl Mater Interfaces 2010 Jun
PMID:Reducing the adhesion between surfaces using surface structuring with PS latex particle. 2051 50

We have demonstrated the utility of hollow silica nanoparticles in fabricating conformal thin film nanoporous antireflection (AR) coatings on both poly(methyl methacrylate) (PMMA) and glass substrates. Layer-by-layer (LbL) assembly was successfully used to produce ultrathin AR coatings on planar and textured surfaces. Hollow silica nanoparticles were synthesized to extend the range of apparent refractive indices possible in an AR coating, enabling the design of both single index and graded index AR coatings on PMMA substrates. The diameter and shell thickness of the silica nanoparticles are the two independent, controllable parameters that we manipulated to tune the refractive index of the coating. The AR coatings reduced the minimum reflection of PMMA from 7% to 0.5%, while the maximum transmission increased from 92% to 98% at the optimized wavelength region that could be adjusted from the near UV into the visible. Cross sectional SEM showed that conformal coatings can be achieved on grooved PMMA Fresnel lenses. AFM was used to study surface topography on flat substrates.
ACS Nano 2010 Jul 27
PMID:Hollow silica nanoparticles in UV-visible antireflection coatings for poly(methyl methacrylate) substrates. 2053 11

We investigate the influence of gold nanoparticle addition on the stability, dewetting, and pattern formation in ultrathin polymer-nanoparticle (NP) composite films by examining the length and time scales of instability, morphology, and dynamics of dewetting. For these 10-50 nm thick (h) polystyrene (PS) thin films containing uncapped gold nanoparticles (diameter approximately 3-4 nm), transitions from complete dewetting to arrested dewetting to absolute stability were observed depending on the concentration of the particles. Experiments show the existence of three distinct stability regimes: regime 1, complete dewetting leading to droplet formation for nanoparticle concentration of 2% (w/w) or below; regime 2, partial dewetting leading to formation of arrested holes for NP concentrations in the range of 3-6%; and regime 3, complete inhibition of dewetting for NP concentrations of 7% and above. Major results are (a) length scale of instability, where lambdaH approximately hn remains unchanged with NP concentration in regime 1 (n approximately 2) but increases in regime 2 with a change in the scaling relation (n approximately 3-3.5); (b) dynamics of instability and dewetting becomes progressively sluggish with an increase in the NP concentration; (c) there are distinct regimes of dewetting velocity at low NP concentrations; (d) force modulation AFM, as well as micro-Raman analysis, shows phase separation and aggregation of the gold nanoparticles within each dewetted polymer droplet leading to the formation of a metal core-polymer shell morphology. The polymer shell could be removed by washing in a selective solvent, thus exposing an array of bare gold nanoparticle aggregates.
ACS Nano 2010 Jul 27
PMID:Stability and dewetting of metal nanoparticle filled thin polymer films: control of instability length scale and dynamics. 2056 May 92

The self-limiting reactions which distinguish atomic layer deposition (ALD) provide ultrathin film deposition with superb conformality over the most challenging topography. This work addresses how the shapes (i.e., surface profiles) of nanostructures are modified by the conformality of ALD. As a nanostructure template, we employ a highly scalloped surface formed during the first anodization of the porous anodic alumina (PAA) process, followed by removal of the alumina to expose a scalloped Al surface. SEM and AFM reveal evolution of surface profiles that change with ALD layer thickness, influenced by the way ALD conformality decorates the underlying topography. The evolution of surface profiles is modeled using a simple geometric 3D extrusion model, which replicates the measured complex surface topography. Excellent agreement is obtained between experimental data and the results from this model, suggesting that for this ALD system conformality is very high even on highly structured, sharp features of the initial template surface. Through modeling and experimentation, the benefits of ALD to manipulate complex surface topographies are recognized and will play an important role in the design and nanofabrication of next generation devices with increasingly high aspect ratios as well as nanoscale features.
ACS Nano 2010 Aug 24
PMID:Profile evolution for conformal atomic layer deposition over nanotopography. 2073 45


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>