Tuning the Transconductance of Organic Electrochemical Transistors

Organic electrochemical transistors (OECTs) operate at very low voltages, transduce ions into electronic signals, and reach extremely large transconductance values, making them ideally suited for bio-sensing applications. However, despite their promising performance, the dependence of their maximum transconductance on device geometry and applied voltages are not correctly captured by current capacitive device models. Here, current scaling laws are revised in the light of a recently developed 2D device model that adequately accounts for drift and diffusion of ions inside the polymer channel. It is shown that the maximum transconductance of the devices is found at the transition between the depletion and accumulation region of the transistors, which as well provides an explanation for the observed shift of the transconductance peak with geometric dimensions and the drain potential. Overall, the results provide a better understanding of the working mechanisms of OECTs, and facilitate design rules to optimize OECT performance further.     

An Electrical Rectifier Based on Au Nanoparticle Array Fabricated Using Direct‐Write Electron Beam Lithography

Close‐packed arrays of Au nanoparticles are produced in patterned regions by electron beam (e‐beam) lithography using a highly sensitive direct–write resist, N⁺AuCl₄^?(C₈H₁₇)₄Br. While the e–beam causes dewetting of the resist to nucleate Au nanoparticles, the following step of thermolysis aids particle growth and removal of the organic part. Thus formed arrays contain Au nanoparticles. Such arrays are patterned into ≈10 μm wide stripes between Au contact pads on SiO₂/Si substrates to realize electrical rectification. Under forward bias, the device exhibits a threshold voltage of +4.3 V and a high current rectification ratio of 3 × 10⁵, which are stable over many repetitive measurements. The threshold voltage of the rectifier can be reduced by applying an electric stress or by varying the electron dosage used for array formation. The nanoparticle rectifier element could be transferred onto flexible substrates such as PDMS, where the nanoparticle coupling is influenced by swelling of the substrate. Obviously, the nanoparticle size, shape, and the spacing in array are all important for the rectifier device performance. Based on the electrical measurements the mechanism of rectification is found to be due to switching of electrical conduction with applied bias, from short–distance tunneling to F–N type tunneling followed by transient filament formation.     

Structural,Mechanical and Biological Insights on Reduced Graphene Nanosheets Reinforced Sonochemically Processed Nano‐Hydroxyapatite Ceramics

In this study, we have attempted to prepare reduced graphene nanosheets (RGNS) reinforced nano-hydroxyapatite (nHAp) nanocomposites via different sonochemical treatments of nHAp. Structural properties of RGNS-nHAp nanocomposites were investigated by XRD and Raman analysis. In vitro bioactivity of RGNS-nHAp nanocomposites were examined by immersing them in hank's balanced salt solution and further in vitro apatite layer formation was confirmed by systematic investigations using FESEM and ICP-OES analyses. Interactions of RGNS, pure nHAp and their nanocomposites with human erythrocytes were explored. Hemocompatibility of BGO-nHAp nanocomposites were found to be superior to pristine RGNS. The nanocomposites were mechanically improved when compared to nHAp through effective load transfer onto their 2D lattice of RGNS. However, 20PGO-nHAp nanocomposites were mechanically weaker than 20BGO-nHAp due to the formation of β-TCP as an additional phase, thus decreases its mechanical strength.     

Investigating illusions of agreement in group requirements determination

The success of information systems development efforts hinges largely on eliciting accurate requirements from users and other stakeholders. Requirements determination is difficult due to the complexity of the systems to be built, analysts’ and users’ cognitive and motivational challenges, and the highly politicized nature of many development efforts. The present research addresses a problem that arises from users’ motivations during the requirements determination process. Most past studies have focused on explicit conflicts that arise between systems analysts, users, and other organizational stakeholders. The present research is concerned instead with the opposite problem—illusions of agreement between participants in the systems development environment. Our study investigates a type of illusion of agreement known as the Abilene Paradox in requirements determination. The Abilene Paradox refers to situations in which each member of a group believes (incorrectly) that the other group members want to pursue a particular course of action, which leads everyone to avoid conflict by agreeing to the action publicly while disagreeing privately. We first provide theory underlying the paradox and review past literature. We then build theory to motivate our investigation and generate hypotheses. We then report results of a laboratory experiment utilizing group requirements determination efforts. Results indicated behavior consistent with the presence of the paradox and an illusion of agreement. These results have important implications for research and practice in requirements determination specifically and systems development in general. Our results contribute to both the requirements determination literature and the literature on illusions of agreement and social conformity.     

Direct micromolding of Pd micro-stripes for electronic applications

A simple, one-step direct micromolding process has been realised to produce highly conducting Pd micro-stripes over large areas on various substrates including flexible polyimide. Under a PDMS micromold, Pd octanethiolate served as a precursor at 250 degrees C, a temperature at which the precursor gets neatly metallised. Thus produced micro-stripes are robust under bending and can be utilised for flexible electronics. Hydrogen sensing by Pd micro-stripes is demonstrated. By electrolessly depositing Cu on the stripes, they can be made to peel off to form free standing Cu-Pd micro-ribbons.     

Flexible and semitransparent strain sensors based on micromolded Pd nanoparticle-carbon μ-stripes

Flexible resistive strain sensors have been fabricated by micromolding Pd alkanethiolate on polyimide substrates and subjecting to thermolysis in air. Thus produced stripes were ～1 μm wide with spacing of ～0.5 μm and contained Pd nanoparticles in carbon matrix. The nanoparticle size and the nature of carbon are much dependent on the thermolysis temperature as is also the resistance of the microstripes. Generally, lower thermolysis temperatures (<230 °C) produced stripes containing small Pd nanoparticles with significant fraction of carbon from the precursor decomposition. The stripes were poorly conducting yet interestingly, exhibited change of resistance under tensile and compressive strain. Particularly noteworthy are the stripes produced from 195 °C thermolysis, which showed a high gauge factor of ～390 with strain sensitivity, 0.09%. With molding at 230 °C, the stripes obtained were highly conducting, and amazingly did not change the resistance with strain even after several bending cycles. The latter are ideal as flexible conduits and interconnects. Thus, the article reports a method of producing flexible sensitive strain sensors on one hand and on the other, flexible conduits with unchanging resistance, merely by fine-tuning the precursor decomposition under the molding conditions.     

Recycling of Poly(phenylene ether) Blends

The effects of postindustry recycling of polymer blends composed of poly(phenylene ether) (PPE) on the properties of the PPE blends were investigated by simulated recycling with multiple molding cycles. Two compositions with different concentrations of PPE were reprocessed with an injection‐molding machine. Mechanical, thermal, rheological, and morphological characterizations were carried out on as‐produced and reprocessed samples to examine the influence of the number of molding cycles on the two specific PPE blends. Efforts were made to determine the effect of each molding cycle on the specific properties of the two PPE blends, including the Elastic (E), modulus, stress at break, strain at break, multiaxial impact, and melt viscosity. The results are discussed in detail. The retention of the properties correlated well with the unperturbed morphology of the compositions before and after recycling, as observed by transmission electron microscopy analyses on fractured tensile samples. However, more in‐depth microanalyses are required to identify the effect of recycling on the individual components present in the studied compositions. In this study, we aimed to establish structure–property relations upon recycling using several characterization techniques. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011