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6 Aug 2007

Volume 91, Issue 6, Articles (06xxxx)

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Appl. Phys. Lett. 91, 063118 (2007); http://dx.doi.org/10.1063/1.2768861 (3 pages)

Douglas C. Meier, Steve Semancik, Bradley Button, Evgheni Strelcov, and Andrei Kolmakov
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High-flux characterization of ultrasmall multijunction concentrator solar cells

Omer Korech, Baruch Hirsch, Eugene A. Katz, and Jeffrey M. Gordon

Appl. Phys. Lett. 91, 064101 (2007); http://dx.doi.org/10.1063/1.2766666 (3 pages) | Cited 18 times

Online Publication Date: 6 August 2007

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A characterization study of ultrasmall ultraefficient multijunction concentrator solar cells is presented, with emphasis on performance sensitivity to light intensity and distribution. Information of this type is essential in the design and optimization of the latest generations of high-flux photovoltaic systems. Cell miniaturization allows increasing the concentration at which efficiency peaks, facilitates passive heat rejection, and permits the use of all-glass optics. However, few device measurements have been published on ultrasmall cells. Extensive measurements, up to ∼ 5000 suns, on the 1.0 mm2 active region within the busbars are reported and analyzed.
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84.60.Jt Photoelectric conversion
72.40.+w Photoconduction and photovoltaic effects
42.79.Ek Solar collectors and concentrators

Thermodynamics of losses in photovoltaic conversion

Tom Markvart

Appl. Phys. Lett. 91, 064102 (2007); http://dx.doi.org/10.1063/1.2766857 (3 pages) | Cited 15 times

Online Publication Date: 7 August 2007

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This letter presents a thermodynamic analysis of losses in an ideal solar cell. It is shown that the maximum voltage—corresponding to the voltage produced by a hot-carrier solar cell—is equal to the energy of the incident solar photon multiplied by the appropriate Carnot factor. Voltage generated by the usual p-n junction cell is lower on account of entropy generation through kinetic losses, photon cooling, and étendue expansion of the incident beam. Simple expressions can be obtained by an approximation where the energy and entropy changes are modeled by the corresponding expressions for a two-dimensional ideal photon gas.
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65.40.G- Other thermodynamical quantities
88.40.-j Solar energy

Modeling the mechanisms driving ac electro-osmotic flow on planar microelectrodes

Fabrice Olivier Morin, Frédéric Gillot, and Hiroyuki Fujita

Appl. Phys. Lett. 91, 064103 (2007); http://dx.doi.org/10.1063/1.2768907 (3 pages)

Online Publication Date: 8 August 2007

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The authors introduce an electrical model of the electrode-electrolyte interface and use it to discuss the mechanisms responsible for the generation of ac electro-osmotic flows at the surface of planar electrodes. They propose that such flows are generated by two distinct mechanisms: nonuniform diffusion of ionic species from the bulk to the electrode surface and inhomogeneous electrochemical transfer across the electrode surface. They then proceed to explain experimental observations in two situations where one mechanism dominates over the other, in each case validating the inclusion of specific components in their model.
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47.65.-d Magnetohydrodynamics and electrohydrodynamics
47.61.Fg Flows in micro-electromechanical systems (MEMS) and nano-electromechanical systems (NEMS)
47.60.-i Flow phenomena in quasi-one-dimensional systems
82.45.Gj Electrolytes
82.45.Fk Electrodes

Comprehensive model for fine Coulomb fission of liquid droplets charged to Rayleigh limit

Wenhua Gu, Philip Edward Heil, Hyungsoo Choi, and Kyekyoon Kim

Appl. Phys. Lett. 91, 064104 (2007); http://dx.doi.org/10.1063/1.2767774 (3 pages) | Cited 6 times

Online Publication Date: 8 August 2007

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Fine Coulomb fission of liquid droplets charged to the Rayleigh limit is modeled, combining the theories for the flow-limited field-injection electrostatic spraying and the conventional electrostatic spraying. The model gives expressions for the current, flow rate, jet growth rate, and secondary droplet size in the fine Coulomb fission process. The model can explain the reported experimental results and completes the previous model on Coulomb fission.
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47.55.df Breakup and coalescence
47.10.-g General theory in fluid dynamics

Electrochemically induced crystallization in lead fluoroborate glasses below the glass transition temperature

José Ezequiel De Souza, Jean-Claude M’Peko, and Antonio Carlos Hernandes

Appl. Phys. Lett. 91, 064105 (2007); http://dx.doi.org/10.1063/1.2767196 (3 pages) | Cited 4 times

Online Publication Date: 8 August 2007

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Lead fluoroborate (BO1.5–PbO–PbF2) glasses were prepared by melt quenching and studied here in terms of (micro)structural and electrical properties. The results show that electrochemically induced surface crystallization may also occur below the glass transition temperature. As previously proposed elsewhere and shown here, occurrence of this phenomenon arose from a field-induced redox reaction at the electrodes, followed by crystallite nucleation. Once nucleated, growth of β-PbF2 crystallites, with the indication of incorporating reduced lead ions (Pb+), was both (micro)structurally and electrically detectable and was analyzed. In particular, the authors introduce a procedure combining impedance spectroscopy and polarization/depolarization techniques to also monitor this phenomenon.
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64.70.D- Solid-liquid transitions
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
61.43.Fs Glasses
82.45.-h Electrochemistry and electrophoresis

Identifying sudden cardiac death risk and specifying its occurrence time by analyzing electrocardiograms in natural time

P. A. Varotsos, N. V. Sarlis, E. S. Skordas, and M. S. Lazaridou

Appl. Phys. Lett. 91, 064106 (2007); http://dx.doi.org/10.1063/1.2768928 (3 pages) | Cited 7 times

Online Publication Date: 9 August 2007

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Sudden cardiac death (SCD) is a frequent cause of death and may occur even if the electrocardiogram seems to be similar to that of a healthy individual. A method which not only identifies the risk but also provides an estimate of the time of an impending cardiac arrest is proposed. Analyzing 159 electrocardiograms in natural time, the authors find that the key quantity is the entropy change under time reversal. After it becomes maximum at the scale of 13 heartbeats, ventricular fibrillation starts within ∼ 3 h in 16 out of 18 SCDs. The method also distinguishes congestive heart failure patients from SCD.
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87.80.-y Biophysical techniques (research methods)

Dynamics of tapping mode atomic force microscopy in liquids: Theory and experiments

Sudipta Basak and Arvind Raman

Appl. Phys. Lett. 91, 064107 (2007); http://dx.doi.org/10.1063/1.2760175 (3 pages) | Cited 27 times

Online Publication Date: 9 August 2007

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A mathematical model is presented to predict the oscillating dynamics of atomic force microscope cantilevers with nanoscale tips tapping on elastic samples in liquid environments. Theoretical simulations and experiments performed in liquids using low stiffness probes on hard and soft samples reveal that, unlike in air, the second flexural mode of the probe is momentarily excited near times of tip-sample contact. The model also predicts closely the tip amplitude and phase of the tip at different set points.
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68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Analog electronic cochlea with mammalian hearing characteristics

S. Martignoli, J.-J. van der Vyver, A. Kern, Y. Uwate, and R. Stoop

Appl. Phys. Lett. 91, 064108 (2007); http://dx.doi.org/10.1063/1.2768204 (3 pages) | Cited 9 times

Online Publication Date: 9 August 2007

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Systems close to bifurcations can be used as small-signal amplifiers. Biophysical measurements suggest that the active amplifiers present in the mammalian cochlea are systems close to a Hopf bifurcation. The pure tone and transient signal output of our electronic hearing sensor based on this observation provides output that is fully compatible with the electrophysiological data from the mammalian cochlea. In particular, it reproduces all salient nonlinear effects displayed by the cochlea.
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07.64.+z Acoustic instruments and equipment
43.58.+z Acoustical measurements and instrumentation
43.80.-n Bioacoustics
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