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12 May 2008

Volume 92, Issue 19, Articles (19xxxx)

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Appl. Phys. Lett. 92, 193301 (2008); http://dx.doi.org/10.1063/1.2920199 (3 pages)

Wei Chen, Hong Liang Zhang, Han Huang, Lan Chen, and Andrew Thye Shen Wee
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Ordering and lyotropic behavior of a silicon-supported cationic and neutral lipid system studied by neutron reflectivity

F. Domenici, C. Castellano, A. Congiu, G. Pompeo, and R. Felici

Appl. Phys. Lett. 92, 193901 (2008); http://dx.doi.org/10.1063/1.2917807 (3 pages) | Cited 4 times

Online Publication Date: 13 May 2008

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Self-assembling of amphipathic lipid films on solid support allows the structural investigation of important biological model systems, such as the vectorlike lipid membranes, in order to improve DNA transfection in nonviral gene therapy. We present a neutron reflectivity study of a binary lipid system composed of dioleoylphosphatidylcholine (DOPC) and dimethyldioctadecylammonium bromide (DDAB) deposited on [100] silicon support by means of spin coating technique. We underline their lyotropic behavior under saturated deuterium oxide (D2O) vapor thus pointing out that the lipid mixture is organized in ordered domains composed of plane lamellar bilayers of noninteractive DOPC and DDAB.
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87.16.D- Membranes, bilayers, and vesicles
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology

Surface-directed differentiation of embryonic stem cells

E. Hanley, J. L. Lauer, B. K. Micales, G. E. Lyons, and J. L. Shohet

Appl. Phys. Lett. 92, 193902 (2008); http://dx.doi.org/10.1063/1.2929387 (3 pages)

Online Publication Date: 14 May 2008

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Here, we explore how embryonic stem-cell (ESC) differentiation patterns on surfaces are affected by changes in the processing parameters of plasma-polymerized materials. Mouse ESCs were plated on plasma-polymerized tetraethylene glycol dimethyl ether (tetraglyme) surfaces on glass. Depending on the processing conditions, the plated ESCs precociously express the platelet endothelial cell adhesion molecule and von Willebrand Factor genetic markers which indicate directed differentiation of some ESCs into endothelial cells. The surface properties show that a larger fraction of directed differentiation takes place when the plasma-induced surface chemistry includes a branched ether bond and higher carbon-to-oxygen ratios.
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87.15.rp Polymerization
82.35.Gh Polymers on surfaces; adhesion

Detection of chloride ions using an integrated Ag/AgCl electrode with AlGaN/GaN high electron mobility transistors

S. C. Hung, Y. L. Wang, B. Hicks, S. J. Pearton, D. M. Dennis, F. Ren, J. W. Johnson, P. Rajagopal, J. C. Roberts, E. L. Piner, K. J. Linthicum, and G. C. Chi

Appl. Phys. Lett. 92, 193903 (2008); http://dx.doi.org/10.1063/1.2927372 (3 pages) | Cited 8 times

Online Publication Date: 14 May 2008

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AlGaN/GaN high electron mobility transistors (HEMTs) with an Ag/AgCl gate exhibit significant changes in channel conductance upon exposing the gate region to various concentrations of chloride (Cl−) ion. The Ag/AgCl gate electrode, prepared by potentiostatic anodization, changes electrical potential when it encounters Cl− ions. This gate potential changes lead to a change of surface charge in the gate region of the HEMT, inducing a higher positive charge on the AlGaN surface, and increasing the piezoinduced charge density in the HEMT channel. These anions create an image positive charge on the Ag gate metal for the required neutrality, thus increasing the drain current of the HEMT. The HEMT source-drain current was highly dependent on Cl− ion concentration. The limit of detection achieved was 1×10−8M using a 20×50 μm2 gate sensing area.
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85.30.Tv Field effect devices
81.65.-b Surface treatments

Nanoscale thickness double-gated field effect silicon sensors for sensitive pH detection in fluid

Oguz H. Elibol, Bobby Reddy, Jr., and Rashid Bashir

Appl. Phys. Lett. 92, 193904 (2008); http://dx.doi.org/10.1063/1.2920776 (3 pages) | Cited 11 times

Online Publication Date: 15 May 2008

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In this work, we report on the optimization of a double-gate silicon-on-insulator field effect device operation to maximize pH sensitivity. The operating point can be fine tuned by independently biasing the fluid and the back gate of the device. Choosing the bias points such that device is nearly depleted results in an exponential current response—in our case, 0.70 decade per unit change in pH. This value is comparable to results obtained with devices that have been further scaled in width, reported at the forefront of the field, and close to the ideal value of 1 decade/pH. By using a thin active area, sensitivity is increased due to increased coupling between the two conducting surfaces of the devices.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
85.30.Tv Field effect devices
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