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8 Mar 2004

Volume 84, Issue 10, pp. 1623-1807

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 1798 (2004); http://dx.doi.org/10.1063/1.1664019 (3 pages)

Bartosz A. Grzybowski, Michal Radkowski, Christopher J. Campbell, Jessamine Ng Lee, and George M. Whitesides
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Secondary ion mass spectrometry for the identification of polymers with noncharacteristic secondary ions using multivariate statistical analysis

W. J. H. van Gennip, P. C. Thüne, J. B. Dijkstra, and J. W. Niemantsverdriet

Appl. Phys. Lett. 84, 1789 (2004); http://dx.doi.org/10.1063/1.1642278 (3 pages) | Cited 1 time

Online Publication Date: 2 March 2004

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Eleven different, filler-free polymers were depth profiled until all secondary ion signals were stable. Discriminant function analysis and principal components analysis were performed on a dataset containing the intensities of noncharacteristic hydrocarbon secondary ions, measured in this steady state. Discriminant function analysis showed that these secondary ions were sufficient to correctly identify all polymers using leave-one-out correction. Even with principal components analysis, which uses no prior knowledge about the origin of a data point, identification was shown to be possible. © 2004 American Institute of Physics.
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82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
82.35.Lr Physical properties of polymers
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials

Probing ion channel conformational dynamics using simultaneous single-molecule ultrafast spectroscopy and patch-clamp electric recording

Greg Harms, Galya Orr, and H. Peter Lu

Appl. Phys. Lett. 84, 1792 (2004); http://dx.doi.org/10.1063/1.1652228 (3 pages) | Cited 8 times

Online Publication Date: 2 March 2004

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An approach to probing single-molecule ion channel kinetics and conformational dynamics, patch-clamp confocal fluorescence microscopy (PCCFM), uses simultaneous ultrafast fluorescence spectroscopy and single-channel electric current recording. PCCFM is applied to determine single-channel conformational dynamics by probing single-pair fluorescence resonant energy transfer, fluorescence self-quenching, and anisotropy of the dye-labeled gramicidin ion channel incorporated in an artificial lipid bilayer. Hidden conformational changes were observed, which strongly suggests that multiple intermediate conformation states are involved in gramicidin ion channel dynamics. © 2004 American Institute of Physics.
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87.16.D- Membranes, bilayers, and vesicles
82.39.Jn Charge (electron, proton) transfer in biological systems
33.50.Dq Fluorescence and phosphorescence spectra
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Torsional spring constant obtained for an atomic force microscope cantilever

Sangmin Jeon, Yehuda Braiman, and Thomas Thundat

Appl. Phys. Lett. 84, 1795 (2004); http://dx.doi.org/10.1063/1.1667000 (3 pages) | Cited 12 times

Online Publication Date: 2 March 2004

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In this letter, a method to measure the torsional spring constant of a microcantilever is described. The cantilever was twisted laterally without any normal load by inducing the Lorentz force. An electrical current was applied to the cantilever in a magnetic field, and the torsional resonance frequency of the cantilever was obtained. Based on the observation that the torsional resonance frequency is the same as the second resonance peak of the thermally vibrating cantilever, the ratio of deflection spring constant to torsional spring constant is easily obtained from a simple relationship. For the cantilever used here, the torsional spring constant is 11.24 N/m, 28 times greater than the deflection spring constant. © 2004 American Institute of Physics.
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45.05.+x General theory of classical mechanics of discrete systems
07.79.Lh Atomic force microscopes
46.25.-y Static elasticity

Self-assembling fluidic machines

Bartosz A. Grzybowski, Michal Radkowski, Christopher J. Campbell, Jessamine Ng Lee, and George M. Whitesides

Appl. Phys. Lett. 84, 1798 (2004); http://dx.doi.org/10.1063/1.1664019 (3 pages) | Cited 10 times

Online Publication Date: 2 March 2004

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This letter describes dynamic self-assembly of two-component rotors floating at the interface between liquid and air into simple, reconfigurable mechanical systems (“machines”). The rotors are powered by an external, rotating magnetic field, and their positions within the interface are controlled by: (i) repulsive hydrodynamic interactions between them and (ii) by localized magnetic fields produced by an array of small electromagnets located below the plane of the interface. The mechanical functions of the machines depend on the spatiotemporal sequence of activation of the electromagnets. © 2004 American Institute of Physics.
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84.50.+d Electric motors
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
47.65.-d Magnetohydrodynamics and electrohydrodynamics
68.18.-g Langmuir-Blodgett films on liquids

Accurate formulas for interaction force and energy in frequency modulation force spectroscopy

John E. Sader and Suzanne P. Jarvis

Appl. Phys. Lett. 84, 1801 (2004); http://dx.doi.org/10.1063/1.1667267 (3 pages) | Cited 149 times

Online Publication Date: 2 March 2004

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Frequency modulation atomic force microscopy utilizes the change in resonant frequency of a cantilever to detect variations in the interaction force between cantilever tip and sample. While a simple relation exists enabling the frequency shift to be determined for a given force law, the required complementary inverse relation does not exist for arbitrary oscillation amplitudes of the cantilever. In this letter we address this problem and present simple yet accurate formulas that enable the interaction force and energy to be determined directly from the measured frequency shift. These formulas are valid for any oscillation amplitude and interaction force, and are therefore of widespread applicability in frequency modulation dynamic force spectroscopy. © 2004 American Institute of Physics.
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07.79.Lh Atomic force microscopes
68.37.Ps Atomic force microscopy (AFM)

Intense electron emission from graphite nanocraters and their application to time-resolved x-ray radiography

Takahiro Matsumoto and Hidenori Mimura

Appl. Phys. Lett. 84, 1804 (2004); http://dx.doi.org/10.1063/1.1668319 (3 pages) | Cited 12 times

Online Publication Date: 2 March 2004

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A high-density electron emission more than 20 mA/cm2 was achieved from a cold cathode fabricated by simple plasma etching nanocraters onto a graphite substrate. The magnitude of the field enhancement factor was about 30 000, which is similar to that for the highest reported performance for carbon nanotube. The performance of this cathode was demonstrated by obtaining high-intensity pulse x-ray generation. High-speed x-ray radiography images of dynamical processes of the order of 10 μs were successfully shown, thus offering a new technique for nondestructive inspections.© 2004 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
07.85.-m X- and γ-ray instruments
81.65.Cf Surface cleaning, etching, patterning
81.05.U- Carbon/carbon-based materials
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