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Top 20 Most Read Articles
August 2006
The 20 articles with the most full-text downloads during the month, in descending order.
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Flexible ferroelectret field-effect transistor for large-area sensor skins and microphones Appl. Phys. Lett. 89, 073501 (2006); http://dx.doi.org/10.1063/1.2335838 (3 pages) Online Publication Date: 14 August 2006
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Ferroelectrets generate an electric field large enough to modulate the conductance of the source-drain channel of a thin-film field-effect transistor. Integrating a ferroelectret with a thin-film transistor produces a ferroelectret field-effect transistor. The authors made such transistors by laminating cellular polypropylene films and amorphous silicon thin-film transistors on polyimide substrates. They show that these ferrroelectret field-effect transistors respond in a static capacitive or dynamic piezoelectric mode. A touch sensor, a pressure-activated switch, and a microphone are demonstrated. The structure can be scaled up to large-area flexible transducer arrays, such as roll-up steerable compliant sensor skin.
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Evidence for spin injection in a single metallic nanoparticle: A step towards nanospintronics Appl. Phys. Lett. 89, 062502 (2006); http://dx.doi.org/10.1063/1.2236293 (3 pages) Online Publication Date: 7 August 2006
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We have fabricated nanometer-sized magnetic tunnel junctions using a conductive tip nanoindentation technique in order to study the transport properties of a single metallic nanoparticle. Coulomb blockade effects show clear evidence for single-electron tunneling through a single 2.5 nm Au cluster. The observed magnetoresistance is the signature of spin conservation during the transport process through a nonmagnetic cluster.
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Appl. Phys. Lett. 89, 062501 (2006); http://dx.doi.org/10.1063/1.2259813 (3 pages) Online Publication Date: 7 August 2006
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Spin-wave interference is demonstrated in the micromagnetic modeling of a specially designed geometry made of variously shaped magnetic thin-film waveguides. When spin waves are diffracted through two separate openings, corresponding to the two pinholes in the second screen of Young’s apparatus, they interfere constructively or destructively in a magnetic medium, thereby showing distinct interference patterns. Furthermore, the radiation, propagation, transmission, and dispersion behaviors of spin waves as well as the filtering of their lower frequencies are investigated in the present modeling study. These results directly confirm not only the wave characteristics of spin waves traveling at ultrafast speeds in variously shaped magnetic waveguides but also their interference effect, that is similar to that observed in well-known Young’s double slit experiment with light.
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Appl. Phys. Lett. 89, 041116 (2006); http://dx.doi.org/10.1063/1.2236462 (3 pages) Online Publication Date: 26 July 2006
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The InGaN–GaN epitaxial films were grown by low-pressure metal-organic chemical vapor deposition on a sapphire substrate, and then the light-emitting diode (LED) with double roughened (p-GaN and undoped-GaN) surfaces was fabricated by surface-roughening, wafer-bonding, and laser lift-off technologies. It was found that the front side luminance intensity of double roughened LED was 2.77 times higher than that of the conventional LED at an injection current of 20 mA. The backside luminance intensity was 2.37 times higher than that of the conventional LED. This is because the double roughened surfaces can provide photons multiple chances to escape from the LED surface, and redirect photons, which were originally emitted out of the escape cone, back into the escape cone.
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Electrical characterization of ZnO-based homojunctions Appl. Phys. Lett. 89, 053501 (2006); http://dx.doi.org/10.1063/1.2245221 (3 pages) Online Publication Date: 31 July 2006
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Electrical characteristics have been studied for ZnO p-n and p-i-n homojunctions, with optimization of device structures for improved performance. Capacitance-voltage measurements confirm the formation of abrupt junctions. The current-voltage characteristics exhibit their inherent electrical rectification behavior. The p-ZnO:(N,Al)/n-ZnO:Al homojunctions fabricated on sapphire substrates combining with the intrinsic ZnO buffer layer have acceptable p-n diode characteristics, with the forward turn-on voltage of 1.4 V and the reverse breakdown voltage of 5.3 V. By introduction of an intrinsic (Zn,Cd)O layer, the resultant p-ZnO:(N,Al)/i-(Zn,Cd)O/n-ZnO:Al homojunction exhibits a high reverse breakdown voltage of ∼ 18 V.
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Properties of an optical multipass surface plasmon resonance technique Appl. Phys. Lett. 89, 071101 (2006); http://dx.doi.org/10.1063/1.2336625 (3 pages) Online Publication Date: 14 August 2006
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A fiber optic four-pass surface plasmon resonance technique with an approach to increase the number of passes to any arbitrary number is described. Within multipass regime, reflections off the gold sample surface that reduce the reflectivity to less than 0.1% are achieved by using a fiber optic collimator, a reflector, and a corner cube prism. In this case, the optical beam emits from and returns to the collimator. This technique holds the potential for significantly increasing the detection sensitivity of surface plasmon resonance device.
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Visible two-dimensional photonic crystal slab laser Appl. Phys. Lett. 89, 071102 (2006); http://dx.doi.org/10.1063/1.2336721 (3 pages) Online Publication Date: 14 August 2006
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The authors describe the fabrication and performance of photonic crystal lasers fabricated within thin membranes of InGaP/InGaAlP quantum well material and emitting in the visible wavelength range. These lasers have ultrasmall mode volumes, emit red light, and exhibit low threshold powers. They can be lithographically tuned from 650 to 690 nm. Their cavity volumes of approximately 0.01 μm3 are ideally suited for use as spectroscopic sources.
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High performance thin-film flip-chip InGaN–GaN light-emitting diodes Appl. Phys. Lett. 89, 071109 (2006); http://dx.doi.org/10.1063/1.2337007 (3 pages) Online Publication Date: 16 August 2006
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Data are presented on the operation of thin-film flip-chip InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs). The combination of thin-film LED concept with flip-chip technology is shown to provide surface brightness and flux output advantages over conventional flip-chip and vertical-injection thin-film LEDs. Performance characteristics of blue, white, and green thin-film flip-chip 1×1 mm2 LEDs are described. Blue ( ∼ 441 nm) thin-film flip-chip LEDs are demonstrated with radiance of 191 mW/mm2 sr at 1 A drive, more than two times brighter than conventional flip-chip LEDs. An encapsulated thin-film flip-chip blue LED lamp is shown to have external quantum efficiency of 38% at forward current of 350 mA. A white lamp based on a YAG:Ce phosphor coated device exhibits luminous efficacy of 60 lm/W at 350 mA with peak efficiency of 96 lm/W at 20 mA and luminance of 38 Mcd/m2 at 1 A drive current. Green ( ∼ 517 nm) devices exhibit luminance of 37 Mcd/m2 at 1 A.
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Ordering of metallic quantum dots Appl. Phys. Lett. 89, 073105 (2006); http://dx.doi.org/10.1063/1.2337006 (3 pages) Online Publication Date: 15 August 2006
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This letter proposes a mechanism for the ordering of metallic quantum dots without coherent lattice or lattice mismatch with the substrate so that elasticity may not account for the phenomena. The authors show that contact potential induces repulsive charge clouds in the substrate. The size-dependent repulsion and van der Waals attraction lead to ordered nanoscale structures.
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Group velocity measurement using spectral interference in near-field scanning optical microscopy Appl. Phys. Lett. 89, 051101 (2006); http://dx.doi.org/10.1063/1.2243632 (3 pages) Online Publication Date: 31 July 2006
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Near-field scanning optical microscopy provides a tool for studying the behavior of optical fields inside waveguides. In this experiment the authors measure directly the variation of group velocity between different modes of a planar slab waveguide as the modes propagate along the guide. The measurement is made using the spectral interference between pulses propagating inside the waveguide with different group velocities, collected using a near-field scanning optical microscope at different points down the guide and spectrally resolved. The results are compared to models of group velocities in simple guides.
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Appl. Phys. Lett. 89, 061101 (2006); http://dx.doi.org/10.1063/1.2335365 (3 pages) Online Publication Date: 7 August 2006
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A twofold absolute photoluminescence quantum yield (PLQY) enhancement of poly(2-methoxy 5-[2′-ethylhexyloxy]-p-phenylenevinylene) (MEH-PPV) is demonstrated by simple preparation of films where the polymer is blended with the small organic molecule 7,8,10-triphenylfluoranthene (3PF). The photophysical investigation of this particular energy transfer process was carried out using steady state absorption/luminescence spectroscopy and optically detected magnetic resonance techniques. The enhanced PLQY is attributed to direct sensitization of the intrachain emitting state of MEH-PPV by energy transfer from 3PF.
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Appl. Phys. Lett. 89, 051103 (2006); http://dx.doi.org/10.1063/1.2234317 (3 pages) Online Publication Date: 1 August 2006
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This work presents the fabrication of high-brightness (over 30 000 cd/m2) top-emissive polymer light-emitting diodes (PLEDs) using a hybrid semitransparent cathode capable of efficient injection of electrons. The composite cathode is comprised of the organic oxide/Al complex as the injection buffer layer covered by a thin Ag overlayer. The anode is made of Ag:Ag2O coated on the glass substrate. The electroluminescence (EL) efficiency of 8.9 cd/A for phenyl-substituted poly(para-phenylene vinylene) copolymer based top-emissive PLED markedly exceeds that of 4.3 cd/A for the control device with the bottom-emissive configuration. The high performance is attributed to the balanced injection of charge carriers and the effective extraction of EL emission from the top cathode. The optical microcavity effect significantly promotes the EL emission in the direction along the surface normal.
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Green fluorescent organic light-emitting device with external quantum efficiency of nearly 10% Appl. Phys. Lett. 89, 063504 (2006); http://dx.doi.org/10.1063/1.2266452 (3 pages) Online Publication Date: 9 August 2006
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Green fluorescent organic light-emitting device (OLED) exhibiting a high external quantum efficiency of nearly 10% has been developed. The OLED consists of simple three organic layers, using NPB, 0.8% C545T doped TPBA, and DBzA as a hole-transporting layer, an emitting layer, and an electron-transporting layer, respectively, [fluorocarbon coated indium tin oxide/NPB (60 nm)/08% C545T doped TPBA (40 nm)/DBzA (20 nm)/LiF (1 nm/Al], where NPB is 4,4′-bis (N-phenyl-1-naphthylamino)biphenyl, C545T is 10-(2-benzothiazolyl)-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-benzo[l]pyrano[6 7 8-ij]quinolizin-11-one, TPBA is 9,9′,10,10′-tetraphenyl-2,2′-bianthracene, and DBzA is 9,10-bis[4-(6-methylbenzothiazol-2-yl)phenyl]anthracene. The high external quantum efficiency is maintained in the wide range of current density of 2–100 mA/cm2. The current efficiency and power efficiency of the OLED are also very high, 29.8 cd/A and 26.2 lm/W, respectively, at a current density of 20 mA/cm2. The OLED is promising for practical use with high color purity with Commission Internationale de L’Eclairage coordinates of (0.24, 0.62) and long half-lifetime of 71 h at a current density of 80 mA/cm2 (initial luminance of 23 900 cd/m2).
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Highly efficient and stable inverted bottom-emission organic light emitting devices Appl. Phys. Lett. 89, 053503 (2006); http://dx.doi.org/10.1063/1.2268923 (3 pages) Online Publication Date: 1 August 2006
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The authors report the development of highly efficient and stable C545T doped green fluorescent Alq3 inverted bottom-emission organic light emitting device (OLED), with a device configuration of ITO/Mg/Cs2O:Bphen/Alq3/C545T:Alq3/NPB/WO3/Al, that achieved a maximum current efficiency of 23.7 cd/A and a power efficiency of 12.4 lm/W which are two times better than those of the conventional OLED. At a brightness level of 100 cd/m2, the device required driving current density only as low as 0.5 mA/cm2 at a driving voltage of only 5.0 V and its half-lifetime T1/2 in excess of 104 000 h.
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Lasing in high-Q quantum-dot micropillar cavities Appl. Phys. Lett. 89, 051107 (2006); http://dx.doi.org/10.1063/1.2266231 (3 pages) Online Publication Date: 2 August 2006
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We present lasing in optically pumped high-Q micropillar cavity lasers with low thresholds and high β factors. The micropillar cavities with diameters between 1.0 and 4.0 μm contain a single layer of low density In0.3Ga0.7As quantum dots as active region. Cavity Q factors of up to 23.000 for 4.0 μm micropillar cavities and lasing based on less than 70 quantum dots is demonstrated.
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Appl. Phys. Lett. 89, 081101 (2006); http://dx.doi.org/10.1063/1.2337284 (3 pages) Online Publication Date: 21 August 2006
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The authors report the fabrication of high-power strained quantum cascade lasers working in continuous mode above 370 K. The devices, processed in narrow buried heterostructures, were grown by low-pressure metal organic vapor-phase epitaxy. Continuous wave output power as high as 312 mW at 300 K was obtained at a wavelength of 5.29 μm from a 3.25 mm long, 7.5 μm wide laser with a high-reflectivity back facet coating. The slope efficiency was in excess of 1.5 W/A and the power conversion efficiency reached almost 5%.
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Appl. Phys. Lett. 89, 043103 (2006); http://dx.doi.org/10.1063/1.2234293 (3 pages) Online Publication Date: 24 July 2006
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We report intrinsic current-voltage properties of ZnO nanowire measured by a four-tip scanning tunneling microscopy (F-STM). It is found that after bending the nanowire with the F-STM the conductance is reduced by about five orders of magnitude. The cathodoluminescent spectra indicate that the ZnO nanowires contain a sizable amount of defects in the surface region, responsible for their conduction. It is suggested that the observed huge conductance changes are caused by the shifting of the surface defect states in the ZnO nanowires in response to the applied surface strain.
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Enhanced spectral coverage in tandem organic solar cells Appl. Phys. Lett. 89, 073502 (2006); http://dx.doi.org/10.1063/1.2336593 (3 pages) Online Publication Date: 14 August 2006
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In order to realize enhanced spectral coverage in organic photovoltaic devices, the authors have stacked a zinc phthalocyanine:C60 based cell on the top of a poly-3-hexyl-thiophene:[6,6]-phenyl C61-butyric acid methyl ester layer using a 1 nm thick Au intermediate recombination layer. Such tandem devices comprising active materials with complementary absorption spectra exhibit a short circuit current (Isc) of 4.8 mA cm−2, an open circuit voltage (Voc) of 1020 mV, and a fill factor of 0.45. Measurements of the photocurrent versus wavelength of the incident light show that photons are converted into charge carriers from 400 to more than 800 nm. Further optimization of the respective layer thicknesses may lead to high efficiency devices.
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Highly efficient organic light-emitting diodes based on donor-acceptor small molecules Appl. Phys. Lett. 89, 073504 (2006); http://dx.doi.org/10.1063/1.2243864 (3 pages) Online Publication Date: 15 August 2006
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The authors have fabricated highly efficient organic light-emitting diodes from donor-acceptor small molecules, 2-(4-methyl-quinolin-2-yl)-10-phenyl-phenothiazine (MQPTZ) and 2-(4-phenyl-quinolin-2-yl)-10-phenyl-phenothiazine (PQPTZ). Their devices turned on at 4.0 V and emitted strong green light near 510 nm. The maximum luminance of 60 000 and 55 000 cd/m2 at 10.4 V and the maximum power efficiencies of 5.75 and 2.5 lm/W at 5 V were obtained from the MQPTZ and the PQPTZ, respectively. The overall performance of their devices in terms of current-voltage, luminance, and external quantum efficiency were discussed and compared with those from the device with tris-(8-hydroxyquinolineolato) aluminum.
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Efficient fabrication of field electron emitters from the multiwalled carbon nanotube yarns Appl. Phys. Lett. 89, 063101 (2006); http://dx.doi.org/10.1063/1.2236465 (3 pages) Online Publication Date: 7 August 2006
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An efficient method has been developed to fabricate field electron emitters by cutting a continuous multiwalled carbon nanotube (MWNT) yarn into segments. The cross section of each segment was composed of open-ended MWNTs which serve as field emitters. The emission current can reach several milliamperes, and the emitters can work stably for a long time. The excellent field emission properties are attributed to the large enhancement factor over 100 000, dense emitting centers, and the robust structure. The emitters might be easily manipulated and assembled into devices, such as electron guns, x-ray tubes, pixel tubes, etc.
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