Volume 77, Issue 2, February 2006
Index of content:
77(2006); http://dx.doi.org/10.1063/1.2163973View Description Hide Description
We present an approach by which submicrometer-spaced electrical contacts can be fabricated on virtually any surface under ultrahigh-vacuum conditions. The metallic contacts are formed by subsequent deposition through a macroscopic mask and a nanostructured stencil mask. The stencil mask with a high aspect ratio was obtained by nanopatterning of suspended low-stress membranes with a focused ion-beam system. The fabricated contacts can be electrically connected in situ by simply exchanging the mask carrier by a second, spring-loaded, carrier.
77(2006); http://dx.doi.org/10.1063/1.2169502View Description Hide Description
Some organic light-emitting devices(OLEDs) behave better and longer when driven with alternating bias. It is believed that the reverse bias helps to remove the trapped charges and prevents permanent drift of ionic dopants or ion migration from electrodes. OLEDs behave much like diodes. When driven with a voltage source, the highly asymmetrical exponential curve of diodes makes the accurate control of the forward current difficult. Using a voltage-controlled current source, the voltage can constantly adjust to maintain the desired current through the device. The reverse resistance of a diode is large. Using a current source to reverse bias can produce a large reverse voltage that would destroy the junction. In this article we present an electronic device used to drive and characterize organic light-emitting devices. It consists of a high voltage hybrid source, which alternatively generates direct voltage-controlled current pulses, up to 200 mA, and reverse voltage-controlled voltage pulses. Furthermore, it allows simultaneous measurement of both, direct and reverse, current and voltage. This hybrid source, driven by an arbitrary wave form generator, makes possible the dynamical characterization of OLED when submitted to a wide variety of current and voltage signals.
77(2006); http://dx.doi.org/10.1063/1.2170080View Description Hide Description
A system to measuretemperatures in the fused quartz liner of a research combustor is discussed. A standard black/white charge-coupled devicecamera was used with an bandpass filter to thermally image high-emissivity paint strips on the inside and outside surfaces of the liner, a requirement for heat-flow model evaluations. Signals were viewed in real time with a framegrabber and simultaneously recorded to videotape for postrun analysis. This system is inexpensive compared to commercial mid- and long-wave IR thermal imagers and more sensitive to temperature differences through the use of bandpass filters for spectral selection of near-infrared wavelengths.
Methodology for determining the influence of soft surface layers in porous solids on compressive behavior: Application to NASA’s lightweight ceramic ablator77(2006); http://dx.doi.org/10.1063/1.2173067View Description Hide Description
A methodology is presented for determining the compressive response of a porous material’s surface layer. Microscopic strain measurements are combined with an analytical model that describes the strain in the surface layer, at a given compressive stress, as a nonlinear function of surface depth. The model yields the effective thickness of the surface layer, explains quantitatively an increase in apparent material stiffness with increasing sample thickness, and yields accurate stress-strain curves (prior to yielding) for samples of arbitrary thickness. The methodology is applied successfully to silicone impregnated reusable ceramic ablator, a thermal protection system material developed and used by NASA for planetary missions, including the Mars rovers.
77(2006); http://dx.doi.org/10.1063/1.2173069View Description Hide Description
The ultrafast imaging methods in sliced sampling streak cameras are investigated. It is shown that the sampling-image x-ray streak camera has potential advantages in highly time-resolved and space-resolved imaging for imploded core plasmas. An optimized sampling method is presented to acquire two-dimensional spatial resolutions and temporal resolution , within a field of view and a time range .