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8 May 2006

Volume 88, Issue 19, Articles (19xxxx)

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Appl. Phys. Lett. 88, 193113 (2006); http://dx.doi.org/10.1063/1.2202003 (3 pages)

Fa-Quan He and Ya-Pu Zhao
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Detection of subsurface defects using a hybrid heating and cooling imaging technique

C. Wang, G. C. Tang, W. B. Wang, M. Zevallos, R. R. Alfano, and M. K. Kassir

Appl. Phys. Lett. 88, 194101 (2006); http://dx.doi.org/10.1063/1.2202189 (3 pages) | Cited 1 time

Online Publication Date: 10 May 2006

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A middle infrared imaging technique combining sequential heating and cooling of the material is shown to detect internal defects in composite materials. A low power flash lamp is used as the heat source to raise the temperature of the material above the ambient temperature. Alcohol is spread on the front surface of the heated sample to cause rapid cooling and removal of the thermal wall. This technique induces thermal waves in the composite material, reduces the diffusive photons, and enables recording better images of internal defects by a mid-infrared camera. The technique provides substantial improvement over existing methodologies currently in use for nondestructive evaluation of subsurface defects and cracks in materials.
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81.70.Pg Thermal analysis, differential thermal analysis (DTA), differential thermogravimetric analysis

Fluid viscosity determination by means of uncalibrated atomic force microscopy cantilevers

Massimiliano Papi, Giuseppe Arcovito, Marco De Spirito, Massimo Vassalli, and Bruno Tiribilli

Appl. Phys. Lett. 88, 194102 (2006); http://dx.doi.org/10.1063/1.2200588 (3 pages) | Cited 15 times

Online Publication Date: 11 May 2006

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In this letter it has been proved that the vibrating resonance frequency of an atomic force microscope cantilever is strictly characterized by its thickness (α), while its width/thickness ratio (β) appears to be a less sensitive parameter that can be approximated to a constant. We therefore propose a data analysis method that, by accounting for a constant β, allows for the determination of the value of α and consequently to calculate η. This method of monitoring viscosity has the advantage of requiring short measurement times on very small sample volumes, thereby avoiding laborious, time-consuming cantilever calibration.
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47.80.-v Instrumentation and measurement methods in fluid dynamics
07.79.Lh Atomic force microscopes

Remote chemical sensing and recognition by acoustic mapping of photothermal fields

Ming Su and Thomas Thundat

Appl. Phys. Lett. 88, 194103 (2006); http://dx.doi.org/10.1063/1.2201555 (3 pages)

Online Publication Date: 11 May 2006

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A remote chemical sensing and recognition approach is developed based on the acoustic mapping of photothermal fields, which has been verified in transmission and reflection modes using a system with ultrasonic transducers, a light source, and light filters. Light absorption increases sample temperature, which changes the phase angle of reflected or transmitted ultrasonic waves. The chemical natures of samples are determined from the wavelength dependent phase change spectrum. The method does not require resonance chambers to amplify photogenerated signals. The light source and ultrasonic transducers can be arranged to enable compact device construction and remote field operation in stand-off manner.
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42.79.Qx Range finders, remote sensing devices; laser Doppler velocimeters, SAR, and LIDAR
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
43.60.Rw
43.35.Yb
42.79.Ci Filters, zone plates, and polarizers
43.38.-p

Enhanced field emission of thin multiwall carbon nanotubes by electron multiplication from microchannel plate

Raghunandan Seelaboyina, Jun Huang, and Won Bong Choi

Appl. Phys. Lett. 88, 194104 (2006); http://dx.doi.org/10.1063/1.2203218 (3 pages) | Cited 13 times

Online Publication Date: 11 May 2006

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We report on a method to amplify electron emission from thin multiwall carbon nanotube (MWCNTs) field emitters using an electron multiplier microchannel plate. High density thin MWCNTs were synthesized by thermal chemical vapor deposition. Density of thin MWCNTs was increased by decreasing the amount of Al2O3 in the catalyst solution. The high density of nanotubes led to their vertical orientation. The thin MWCNTs showed low turn-on electric field and high electron emissivity which could be attributed to their wall thinness and high aspect ratio ( ∼ 1500) resulting in high field enhancement factor ( ∼ 9300). Emission current was stable with an average fluctuation of 2%. A microchannel plate positioned between cathode and anode increased the total emission current by 7.5 times.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.07.De Nanotubes
85.60.Ha Photomultipliers; phototubes and photocathodes
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Single shot positron annihilation lifetime spectroscopy

D. B. Cassidy, S. H. M. Deng, H. K. M. Tanaka, and A. P. Mills

Appl. Phys. Lett. 88, 194105 (2006); http://dx.doi.org/10.1063/1.2203336 (3 pages) | Cited 12 times

Online Publication Date: 11 May 2006

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Recent developments in positron trapping technology have made possible experimentation with dense interacting positronium gases. Along with these capabilities comes a need for suitable measurement techniques, and accordingly we have developed a method to measure positronium lifetimes from a single intense burst of positrons. Our method is based on recording the anode signal from a photomultiplier with a fast oscilloscope following a short-time positron burst which allows us to measure transitory effects as well as high density positronium interactions.
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78.70.Bj Positron annihilation
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