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, , , , , Peter Cuony, Mathieu Boccard, Grégory Bugnon, Céline Denizot, , et al.
Published: 24 May 2010
Applied Physics Letters, Volume 96; https://doi.org/10.1063/1.3432739

Abstract:
We propose the use of transparent replicated random nanostructures fabricated via nanoimprinting on glass as next-generation superstrates for thin film silicon solar cells. We validate our approach by demonstrating short-circuit current densities for $p-i-n$ hydrogenated microcrystalline silicon solar cells as high as for state-of-the-art nanotextured ZnO front electrodes. Our methodology opens exciting possibilities to integrate a large variety of nanostructures into $p-i-n$ solar cells and allows to systematically investigate the influence of interface morphology on the optical and electronic properties of the device in order to further improve device performance.
Y. Ando, , K. Kasahara, Y. Kishi, K. Ueda, , ,
Published: 4 May 2009
Applied Physics Letters, Volume 94; https://doi.org/10.1063/1.3130211

Abstract:
We demonstrate electrical injection and detection of spin-polarized electrons in silicon (Si) using epitaxially grown $Fe3Si/Si$ Schottky-tunnel-barrier contacts. By an insertion of a $δ$ -doped $n+-Si$ layer $(∼1019 cm−3)$ near the interface between a ferromagnetic $Fe3Si$ contact and a Si channel $(∼1015 cm−3)$ , we achieve a marked enhancement in the tunnel conductance for reverse-bias characteristics of the $Fe3Si/Si$ Schottky diodes. Using laterally fabricated four-probe geometries with the modified $Fe3Si/Si$ contacts, we detect nonlocal output signals that originate from the spin accumulation in a Si channel at low temperatures.
H. X. Guo, B. Yang, L. Chen, Y. D. Xia, , , J. Yin
Published: 10 December 2007
Applied Physics Letters, Volume 91; https://doi.org/10.1063/1.2825273

Abstract:
Resistive switching devices with a sandwich structure $Ag∕(AgI)0.5(AgPO3)0.5∕Pt$ were fabricated on silicon(001) wafer by using the pulsed laser deposition method and the focused ion beam nanofabrication technique. $(AgI)0.5(AgPO3)0.5$ films deposited at room temperature show a nanocrystal structure and the composition of the films was identified by using x-ray photoelectron spectroscopy. The current-voltage characteristics of the $Ag∕(AgI)0.5(AgPO3)0.5∕Pt$ memory units show good switching behaviors. The ratio of the conductance between the “ON” state (high conductance) and the “off” state (low conductance) reaches $1×106$ . The ON and OFF states can be effectively written, read, and erased up to $4×105$ scanning cycles by using a set of voltage pulses with an amplitude less than $3V$ . It also could be observed that the time for the writing and erasing operations could be less than $150ns$ . The switching mechanism of the $Ag∕(AgI)0.5(AgPO3)0.5∕Pt$ memory devices was ascribed to the possible formation and dissolution of Ag filaments in $(AgI)0.5(AgPO3)0.5$ films induced by the applied electrical pulses with different polarities.
Published: 10 December 2007
Applied Physics Letters, Volume 91; https://doi.org/10.1063/1.2823577

Abstract:
Noise in pentacene thin film transistors has been measured as a function of device thickness from well above the effective conduction channel thickness to only two conducting layers. Over the entire thickness range, the spectral noise form is 1 ∕ f , and the noise parameter varies inversely with gate voltage, confirming that the noise is due to mobility fluctuations, even in the thinnest films. Hooge’s parameter varies as an inverse power law with conductivity for all film thicknesses. The magnitude and transport characteristics of the spectral noise are well explained in terms of percolative effects arising from the grain boundary structure.
Published: 10 December 2007
Applied Physics Letters, Volume 91; https://doi.org/10.1063/1.2822420

Abstract:
The statistics of electrical breakdown field ( E bd ) of Hf O 2 and Si O 2 thin films has been evaluated over multiple length scales using macroscopic testing of standardized metal-oxide-semiconductor ( Ti N ∕ Si O 2 ∕ Si ) and metal-insulator-metal ( Ti N ∕ Hf O 2 ∕ Ti N ) capacitors ( 10 − 2 mm 2 – 10 μ m 2 area) on a full 200 mm wafer along with conductive-atomic-force microscopy. It is shown that E bd follows the same Weibull distribution when the data are scaled using the testing area. This overall scaling suggests that the defect density is ∼ 10 15 cm − 2 and E bd is ∼ 40 MV ∕ cm for nanometer-length scales; as such, breakdown in these materials is most likely initiated by bond breaking rather than punctual defects.
Published: 26 March 2007
Applied Physics Letters, Volume 90; https://doi.org/10.1063/1.2717532

Abstract:
The lateral spatial resolution (LSR) in two-photon induced polymerization was improved to 80 nm by using an anthracene derivative (9,10-bis-pentyloxy-2,7-bis[2-(4-dimethylamino-phenyl)-vinyl]anthracene (BPDPA)) as a highly sensitive and efficient photoinitiator. Photocurable resin containing 0.18 mol % BPDPA exhibited a low polymerization threshold of 0.64 mW at 800 nm . Theoretical calculations showed that the LSR can be increased by reducing the laser power, indicating that the LSR could be improved using more sensitive initiators in the future.
, , Ken-Ichi Ueda, Hideki Yagi, Takagimi Yanagitani, Alexander A. Kaminskii
Published: 26 March 2007
Applied Physics Letters, Volume 90; https://doi.org/10.1063/1.2717519

Abstract:
Laser-diode pumped nearly diffraction-limited beam quality ( M 2 < 1.05 ) , high peak power, subnanosecond passively Q -switched Yb : Y 3 Al 5 O 12 ceramic miniature laser with Cr 4 + : Y 3 Al 5 O 12 ceramic as saturable absorber has been achieved. The slope efficiency is as high as 36% for 80% initial transmission of Cr 4 + : Y 3 Al 5 O 12 ceramic. The pulse width of 335 ps and peak power of over 150 kW at repetition rate of 5 kHz were obtained. Laser oscillates at single-longitudinal-mode oscillation and wide-separated multilongitudinal-mode oscillation due to the combined etalon effect of the Cr 4 + : YAG thin plate and thin glass plate as output coupler.
, , E. Kuokštis, K. Liu, , J. P. Zhang,
Published: 26 March 2007
Applied Physics Letters, Volume 90; https://doi.org/10.1063/1.2717145

Abstract:
A set of $Al0.35Ga0.65N∕Al0.49Ga0.51N$ multiple quantum wells (MQWs) with fixed barrier width and well widths varying from $1.65to5.0nm$ has been grown by metal-organic chemical vapor deposition. Carrier dynamics in the MQWs were studied using time-resolved photoluminescence (PL) spectroscopy and light-induced transient grating (four wave mixing) technique. The authors observed that the lifetime of nonequilibrium carriers (excitons) increases with decreasing well width and interpreted the effect by stronger localization preventing their migration to nonradiative recombination centers. Meanwhile the radiative decay time is also influenced by screening of the built-in electric field, which spatially separates the electrons and holes. It is shown that this effect affects the initial part of PL intensity decay after pulsed excitation. It becomes more pronounced with increase in the initial carrier density but saturates when the carrier density is high enough to completely screen the built-in electric field. The screening effect on PL decay is stronger in wider quantum wells.
, L. J. A. Koster,
Published: 26 March 2007
Applied Physics Letters, Volume 90; https://doi.org/10.1063/1.2711534

Abstract:
In organic semiconductors the recombination mechanism is of the Langevin type, controlled by the mobility of the charge carriers. As a result, in organic solar cells the mobility simultaneously controls both the carrier extraction and the losses via carrier recombination. The authors demonstrate that the balance between carrier losses by extraction and by recombination leads to a distinct optimum in the carrier mobility with regard to the efficiency of organic solar cells. For low mobilities recombination losses limit the performance, whereas the efficient extraction at high mobilities leads to a reduction of the open-circuit voltage.
, Jun-Hua Liu, Hai-Dong Liu, Fei Jia, , Jian Zheng
Published: 9 October 2017
Applied Physics Letters, Volume 111; https://doi.org/10.1063/1.5001666

Abstract:
Adding ceramic or conductive fillers into polymers for increasing permittivity is a direct and effective approach to enhance the actuation strain of dielectric elastomer actuators (DEAs). Unfortunately, the major dielectric loss caused by weak interfaces potentially harms the electro-mechanical stability and lifetime of DEAs. Here, we construct a desired macromolecular network with a long chain length and low cross-link density to reduce the elastic modulus of silicone elastomers. Selecting a high molecular weight of polymethylvinylsiloxane and a low dose of the cross-linker leads the soft but tough networks with rich entanglements, poor cross-links, and a low amount of defects. Then, a ductile material with low elastic modulus but high elongation at break is obtained. It accounts for much more excellent actuation strain of Hl in comparison to that of the other silicone elastomers. Importantly, without other fillers, the ultralow dielectric loss, conductivity, and firm networks possibly promote the electro-mechanical stability and lifetime for the DEA application.
Correction
Joakim Vester-Petersen, Rasmus E. Christiansen, , , ,
Published: 9 October 2017
Applied Physics Letters, Volume 111; https://doi.org/10.1063/1.5007855

Weiwei Tang, Changlong Liu, , Xiaoshuang Chen, Man Luo, Wanlong Guo, , Wei Lu
Published: 9 October 2017
Applied Physics Letters, Volume 111; https://doi.org/10.1063/1.5001671

Abstract:
Two-dimensional layered materials, such as molybdenum disulfide, are emerging as an exciting material system for future electronics due to their unique electronic properties and atomically thin geometry. In this work, MoS2-based FETs are fabricated using mechanical cleavage and standard photolithographic and metal evaporation techniques, and the detector exhibits a good ohmic contact. We show that the multilayer molybdenum disulfide photodetector has a fast photoresponse as short as 42 μs. The fast photodetector response is due to the decrease in the trap states in MoS2 flakes compared to monolayer MoS2, making its photoresponse time close to its intrinsic response. The large photocurrent with the responsivity and external quantum efficiency of 59 A/W and 13 800% for the wavelength of 532 nm was also measured. The fast response time, high responsivity, and the ease of fabrication of these devices make them important components for future optoelectronic devices.
Yupeng Cheng, Jianxin Yang, , Debin Zhu, Xiang Cai, Xiaowen Hu, Wen Huang,
Published: 9 October 2017
Applied Physics Letters, Volume 111; https://doi.org/10.1063/1.4995490

Abstract:
A convenient and easily controllable microfluidic system was proposed based on a photothermal device. Here, graphene oxide was assembled on an optical waveguide, which could serve as a miniature heat source to generate a microbubble and to control dynamic behaviors of flow by adjusting optical power at the micrometer scale. Micro/nanoparticles were used to demonstrate the trace of fluid flow around the microbubble, which displayed the ability of the flow to capture, transmit, and rotate particles in thermal convection. Correspondingly, three-dimensional theoretical simulation combining thermodynamics with hydrodynamics analyzed the distribution of the velocity field induced by the microbubble for collection and driving of particles. Furthermore, the photothermal waveguide would be developed into a microbubble-based device in the manipulation or transmission of micro/nanoparticles.
, Hua Ma, , , Zhiqiang Li,
Published: 9 October 2017
Applied Physics Letters, Volume 111; https://doi.org/10.1063/1.4995505

Abstract:
The dispersion curves of spoof surface plasmon polaritons (SSPPs) are typically asymptotically nonlinear, with only one single intersection point with the dispersion curves of couplers. This means that wave-vector matching can be achieved only at a single frequency, leading to a narrow bandwidth of SSPP couplers. In this letter, we propose to achieve broadband SSPP couplers through dispersion engineering of metamaterials. To this end, we investigated the dispersion properties of a metallic patch array (MPA) that supports the propagation of TE-mode SSPPs at microwave frequencies. After this, we designed a planar metamaterial lens that can provide additional tangential wave-vectors to free space waves. By dispersion engineering, the dispersion curve of the coupled waves overlaps with that of SSPPs on the MPA in a broadband, resulting in high-efficiency broadband coupling of SSPPs. As an example, we demonstrated a broadband SSPP coupler with more than a bandwidth of 1 GHz in the X band. The method can be readily extended to millimeter-wave, terahertz, and other higher frequencies.
Published: 9 October 2017
Applied Physics Letters, Volume 111; https://doi.org/10.1063/1.4999206

Abstract:
The ionic transport and dielectric behaviors in NaNbO3 were studied under pressures up to 29.1 GPa by in situ impedance spectroscopy measurements. The transport process consists of the ionic transfer and the Warburg diffusion process between sample/electrode diffusion layers. A dielectric relaxation with a giant dielectric constant at low frequencies is observed, which is attributed to the “Maxwell-Wagner” interfacial polarization. In the Pbcm phase, the increase in the interaction between the Na+ ions and the NbO6 octahedra results in the enhancement of vibration resonance damping. In the high-pressure phases, the decrease in the relative permittivity with pressure indicates the existence of space charge polarization of the interface layer besides the ionic polarization.
Published: 9 October 2017
Applied Physics Letters, Volume 111; https://doi.org/10.1063/1.4989391

Abstract:
Miniaturization of conventional field effect transistors (FETs) approaches the fundamental limits beyond which opening and closing the transistor channel require higher gate voltage swing and cause higher power dissipation and heating. This problem could be eliminated by placing a ferroelectric layer between the FET gate electrode and the channel, which effectively amplifies the gate voltage. The original idea of using a bulk ferroelectric negative capacitor suffers however from irreversible multi-domain ferroelectric switching, which does not allow us to stabilize static negative capacitance, while a recent reversible solution with super-lattices may be difficult to integrate onto FET. Here, we introduce a solution which provides static negative capacitance from a nano-domain nucleus. Phase-field simulations confirm the robustness of this concept, the conveniently achievable small effective negative capacitance and the potentially high compatibility of such a negative nano-capacitor with FET technology.
, Jian Shi, Morris A. Washington,
Published: 9 October 2017
Applied Physics Letters, Volume 111; https://doi.org/10.1063/1.5000704

Abstract:
The interaction at a van der Waals (vdW) epitaxial interface is perceived to be too weak to induce substantial elastic strain in films due to the weak nature of dipole-dipole interactions. Recent research on discovering giant strain in vdW heterostructures in 2D-2D configurations has reformed such an understanding. In this letter, the study on strain was extended to the regime of 3D-2D vdW heterostructures. Using temperature dependent Raman spectroscopy, the strain behaviors were revealed, through the change of phonon frequency, at a vdW epitaxial interface of CdS-mica. Although the interface was free of interactions for relatively thick CdS films, it was found that at least 0.4% strain can be borne at the interface when the film was only 6 nm thick and the strain was estimated to be 1.2% if a two-monolayer can be grown. The finding suggests that non-trivial strain could be enabled in 3D-2D vdW heterostructures if the thickness can be well-controlled, providing an avenue for strain engineering. This work also indicated a different changing tendency in the linewidth of phonon scattering as a function of temperature, which may be related to defects and serve as a reference for studying the linewidth of ultrathin films.
Published: 9 October 2017
Applied Physics Letters, Volume 111; https://doi.org/10.1063/1.4998508

Abstract:
With the negative capacitance (NC) effect of ferroelectric materials, a sub-60-mV/decade sub-threshold slope in a conventional field-effect transistor has been theoretically and experimentally demonstrated. In order to utilize the NC for complementary metal-oxide-semiconductor logic device applications, it is necessary to closely examine various parameters for the device performance. Specifically, the analysis of effective drive current (i.e., Ieff = {IDS@[VDS = 0.5VDD, VG = VDD] + IDS@[VDS =VDD, VG = 0.5VDD]}/2) of the NC device is vital. In this work, Ieff of a NC fin field-effect transistor (FinFET), in which a baseline 70 nm FinFET is electrically integrated with a ferroelectric capacitor, is experimentally measured to explore the correlation between hysteresis and Ieff.
Published: 30 July 2007
Applied Physics Letters, Volume 91; https://doi.org/10.1063/1.2768028

Abstract:
A method of fabricating highly rectifying Schottky contacts on n -type ZnO using silver oxide has been developed and used to compare diode performance on hydrothermal and melt grown, bulk, single crystals. Silver oxide diodes on hydrothermal ZnO have lower ideality factors, lower reverse current voltage dependence, higher series resistance, and larger surface-polarity related differences in barrier height, compared to those on melt ZnO. These effects are explained by the large difference in resistivity between hydrothermal and melt ZnO. Barrier heights of 1.20 eV were achieved on the Zn-polar face of hydrothermal ZnO which are the highest reported for n -type ZnO.
A. B. Campos, , , J. A. Varela, V. M. Longo, A. T. De Figueiredo, , A. C. Hernandes
Published: 30 July 2007
Applied Physics Letters, Volume 91; https://doi.org/10.1063/1.2766856

Abstract:
A combined experimental and theoretical study was conducted to analyze the photoluminescence (PL) properties of ordered and disordered $CaWO4$ (CW) and $CaMoO4$ (CM) powders. Two mechanisms were found to be responsible for photoluminescence emission in CW and CM powders. The first one, in the disordered powders, was caused by oxygen complex vacancies $[MO3∙VOx]$ , $[MO3∙VO•]$ and $[MO3∙VO••]$ , where $M=W$ or Mo, which leads to additional levels in the band gap. The second mechanism, in ordered powders, was caused by an intrinsic slight distortion of the $[WO4]$ or $[MoO4]$ tetrahedral in the short range.
J. Zhong, H. Chen, G. Saraf, , C. K. Choi, J. J. Song, D. M. Mackie, H. Shen
Published: 14 May 2007
Applied Physics Letters, Volume 90; https://doi.org/10.1063/1.2741052

Abstract:
Enhancement of light extraction from an integrated ZnO nanotips/GaN light emitting diode(LED) is demonstrated. The device is composed of a GaNLED with a Ga-doped ZnO (GZO) transparent conductive layer and ZnO nanotips grown on GZO for light extraction. The light output power of a ZnO nanotips/GZO/GaN LED exhibits 1.7 times enhancement, in comparison with a conventional Ni ∕ Au p -metal LED. The higher emission efficiency is attributed to the enhanced light transmission and scattering in the Zn O ∕ Ga N multilayer.
Tao Wang, Jun Wang, , Lu Li, Kai Yuan,
Published: 31 March 2008
Applied Physics Letters, Volume 92; https://doi.org/10.1063/1.2907692

Abstract:
Low roll-off power efficiency ( η p ) organic light-emitting diodes at high current density were fabricated using a nondoped ultrathin bis[2-(4-tertbutylphenyl)benzothiazolato- N , C 2 ′ ] iridium (acetylacetonate) phosphorescent layer and thin N , N ′ -di(naphthalene-2-yl)- N , N ′ -diphenyl-benzidine separate layer. A maximum η p of 8.48 lm ∕ W and luminance efficiency of 20.26 cd ∕ A at 2014 cd ∕ m 2 were obtained from the device. The η p roll-off percentage of ultrathin phosphor layer device was reduced to 20% at a current density of 20 mA ∕ cm 2 , which is about 40% for conventional phosphorescent device. The low roll off of efficiency was attributed to the direct carrier trapping and confining emission zone function of the ultrathin phosphor layer.
Seung Hwan Seo, Gu-Cheol Kang, Kang Seob Roh, Kwan Young Kim, Sunyeong Lee, Kwan-Jae Song, So Ra Park, Kichan Jeon, Jun-Hyun Park, , et al.
Published: 31 March 2008
Applied Physics Letters, Volume 92; https://doi.org/10.1063/1.2905272

Abstract:
Bias temperature-dependent characteristics of nanoscale silicon-oxide-nitride-oxide-silicon memories are investigated under program/erase (P/E) Fowler–Nordheim (FN) stresses. In the erased cell, FN stress time evolution is found to be a similar physical process to the recovery of interface traps ( N IT ) that takes place under the dynamic negative bias temperature instability stress. In addition, anode hole injection induced holes are trapped in the bottom oxide, both in the erase and in the read conditions of the erased cell, and make significant roles in the reverse hysteresis and higher power-law exponent n at higher temperature in P/E cycled erased cells. While the temperature-independent n = 0.3 is observed in the programed cell, the temperature-sensitive n = 0.36 – 0.66 is observed in the erased cell.
Mutsumi Kimura, Takashi Nakanishi, Kenji Nomura, , Hideo Hosono
Published: 31 March 2008
Applied Physics Letters, Volume 92; https://doi.org/10.1063/1.2904704

Abstract:
Trap densities in amorphous-$InGaZnO4$$(α-IGZO)$ are extracted directly from the capacitance-voltage characteristics of thin-film transistors at low frequencies. It is found that the trap densities are flat in the energy gap, and are $1.7×1016cm−3eV−1$ in the deep energy far from the conduction band edge $(Ec)$ , but become larger near $Ec$ . Moreover, postannealing reduces the trap density near $Ec$ , which is associated with the reduction of the hysteresis in the current-voltage characteristics. The annealed $α-IGZO$ does not have a Gaussian-type state and has fewer tail states than amorphous Si.
T. Manago,
Published: 22 July 2002
Applied Physics Letters, Volume 81, pp 694-696; https://doi.org/10.1063/1.1496493

Abstract:
We have succeeded in growingferromagnetic metals (Co, Fe, and NiFe)/Al 2 O 3 / AlGaAs heterostructures with homogeneous flat interfaces. The electroluminescence from a light-emitting diode with a metal/insulator/semiconductor (MIS)structure depends on the magnetization direction of the ferromagnetic electrode. This fact shows that a spin injection from the ferromagnetic metal to the semiconductor is achieved. The spin-injection efficiency is estimated to be the order of 1% at room temperature.
Silvia Famà, , Gianlorenzo Masini, , Hsin-Chiao Luan
Published: 22 July 2002
Applied Physics Letters, Volume 81, pp 586-588; https://doi.org/10.1063/1.1496492

Abstract:
We demonstrate fast and efficient germanium-on-silicon p-i-n photodetectors for optical communications, with responsivities as high as 0.89 and 0.75 A/W at 1.3 and 1.55 μm, respectively, time response 2.5 Gb/s integrated receivers for the second and third fiber spectral windows.
Published: 22 July 2002
Applied Physics Letters, Volume 81, pp 769-771; https://doi.org/10.1063/1.1495881

Abstract:
A photoresponsive organic light-emitting device combining blue-emitting organic electroluminescent (EL)diode with titanyl phthalocyanine as a near-infrared (IR) sensitive layer was fabricated. By irradiating near-IR light to the device, blue emission occurred in the lower drive voltage (between 5 and 12 V). The result indicates that the device acts as a light switch and/or an up-converter from near-IR light (1.6 eV) to blue (2.6 eV). The EL response times of rise and decay using a near-IR light trigger were 260 and 330 μs, respectively. At a higher voltage (above 12 V), enhancement of blue emission was observed with near-IR light irradiation. The ON/OFF ratio reached a maximum of 10 3 .
James C. Booth, R. H. Ono, Kao-Shuo Chang,
Published: 22 July 2002
Applied Physics Letters, Volume 81, pp 718-720; https://doi.org/10.1063/1.1494854

Abstract:
We evaluate dielectric tuning on nanosecond time scales in ferroelectric Ba 0.3 Sr 0.7 TiO 3 thin films by measuring nonlinear harmonic generation at a fundamental frequency of 3 GHz. We compare the form of the distributed nonlinear capacitance per unit length C(V rf ) extracted from a simple model of harmonic generation in coplanar waveguide transmission line structures with the nonlinear capacitance C(V dc ) measured using a dc bias voltage, and obtain excellent agreement for temperatures in the range 235–295 K. This demonstrated agreement implies that full dielectric tuning can be expected in these ferroelectric thin films on nanosecond time scales, and also demonstrates that detrimental high-frequency nonlinear effects in device structures can be accurately predicted based on dc biased measurements.
Guillaume Malpuech, , , Jeremy J. Baumberg, ,
Published: 15 July 2002
Applied Physics Letters, Volume 81, pp 412-414; https://doi.org/10.1063/1.1494126

Abstract:
The critical temperature for Bose condensation of exciton polaritons in an AlGaN microcavity containing 9 GaN quantum wells is calculated to be T=460 K . We have modeled the kinetics of polaritons in such a microcavity device using the two-dimensional Boltzmann equation. Room-temperature lasing is found with a threshold as small as 100 mW. The kinetic blocking of polariton relaxation that prevents formation of the Bose-condensed phase of polaritons at low temperatures disappears at high temperatures, especially in n-doped samples. Thus, GaN microcavities are excellent candidates for realization of room-temperature polariton lasers.
N. Y. Garces, L. Wang, L. Bai, , , G. Cantwell
Published: 22 July 2002
Applied Physics Letters, Volume 81, pp 622-624; https://doi.org/10.1063/1.1494125

Abstract:
Electron paramagnetic resonance(EPR),photoluminescence, and infrared optical absorption have been used to investigate a ZnO crystal before and after a thermal anneal for 1 h in air at 900 °C. The sample was an undoped high quality crystal grown by the chemical vapor transport method. In addition to shallow donor impurities, the crystal contained trace amounts of copper ions. Prior to the thermal anneal, these ions were all in the Cu + (3d 10 ) state and the observed luminescence at 5 K, produced by 364 nm light, consisted of a broad structureless band peaking at 500 nm. After the high-temperature anneal, the Cu 2+ (3d 9 ) EPRspectrum was observed and the luminescence had changed significantly. The emission then peaked near 510 nm and showed structure identical to that reported by Dingle [Phys. Rev. Lett. 23, 579 (1969)]. Our data reaffirm that the structured green emission in ZnO is associated with Cu 2+ ions. We suggest that the unstructured green emission (observed before the high-temperature anneal) is donor–acceptor pair recombination involving the Cu + acceptors.
K. Kim, , T. B. Norris, J. Singh, , P. Bhattacharya
Published: 16 July 2002
Applied Physics Letters, Volume 81, pp 670-672; https://doi.org/10.1063/1.1493665

Abstract:
Using a femtosecond three-pulse pump-probe technique, we investigated spectral hole-burning and gain recovery dynamics in self-organized In(Ga)As quantum dots. The spectral hole dynamics are qualitatively different from those observed in quantum wells, and allow us to distinguish unambiguously the gain recovery due to intradot relaxation and that due to carrier capture. The gain recovery due to carrier–carrier scattering-dominated intradot relaxation is very fast $(∼130 fs),$ indicating that this is not the factor limiting the bandwidth of directly modulated quantum dot lasers.
T. Umebayashi, T. Yamaki, H. Itoh,
Published: 15 July 2002
Applied Physics Letters, Volume 81, pp 454-456; https://doi.org/10.1063/1.1493647

Abstract:
Titanium dioxide ( TiO 2 ) doped with sulfur (S) was synthesized by oxidationannealing of titanium disulfide ( TiS 2 ). According to the x-ray diffraction patterns, TiS 2 turned into anatase TiO 2 when annealed at 600 ° C . The residual S atoms occupied O-atom sites in TiO 2 to form Ti – S bonds. The S doping caused the absorption edge of TiO 2 to be shifted into the lower-energy region. Based on the theoretical analyses using ab initio band calculations, mixing of the S 3p states with the valence band was found to contribute to the band gap narrowing.
, , , , P. Lacorre, M. Zaghrioui
Published: 16 July 2002
Applied Physics Letters, Volume 81, pp 619-621; https://doi.org/10.1063/1.1493645

Abstract:
$Nd0.7Eu0.3NiO3$ thin films are deposited by rf sputtering and subsequent oxygen pressure annealing on (100) oriented silicon substrate. We characterize the thermochromic properties of films by measuring electrical transition, infrared transmittance, and reflectance. The thermochromic effect at room temperature is observed. Resistivity measurements exhibit a sharper hysteresis loop than is usually observed in $NdNiO3$ thin films. Infrared properties in the 8–14 μm wavelength range spectra reveal a contrast of 30% in reflectance and 55% in transmittance.
, S. Kobayashi, S. Haraichi
Published: 15 July 2002
Applied Physics Letters, Volume 81, pp 391-393; https://doi.org/10.1063/1.1493643

Abstract:
Coherent transients of pseudoisocyanine J aggregates in distributed feedback microcavities are reported. Under the resonant excitation of the cavity-mode observed at the low-energy side of the excitonic resonance, the response time is about 0.5 ps, approximately equal to the pump–pulse duration. We find the enhancement of the optical nonlinearity by one order of magnitude in the microcavity. The excitation of the dielectric-band mode is effective to enhance the nonlinearity with the ultrafast response.
Published: 15 July 2002
Applied Physics Letters, Volume 81, pp 490-492; https://doi.org/10.1063/1.1493229

Abstract:
Electroabsorption measurements are reported for wurtzite InGaN/GaN quantum wells. The electroabsorption technique allows exact quantitative analysis of absorption and absorption changes in InGaN quantum wells and barrier layers, with recorded field-induced absorption changes as large as 7000 cm−1 below and almost 20000 cm−1 above the band edge. The technique thus allows precise determination of the strong internal fields that originate from strain-induced polarization and differences in spontaneous polarization. The fields measured on functioning diodes vary between 1.1 and 1.4 MV/cm for indium concentrations in InGaN quantum wells ranging from 7% to 9%.
, S. H. Lim, F. Wu, J. S. Speck,
Published: 2 July 2002
Applied Physics Letters, Volume 81, pp 469-471; https://doi.org/10.1063/1.1493220

Abstract:
In this letter we describe the structural characteristics of nonpolar $(112̄0)$a-plane GaN thin films grown on $(11̄02)$r-plane sapphire substrates via metalorganic chemical vapor deposition. Planar growth surfaces have been achieved and the potential for device-quality layers realized by depositing a low temperature nucleation layer prior to high temperature epitaxial growth. The in-plane orientation of the GaN with respect to the $r$ -plane sapphire substrate was confirmed to be $[0001]GaN‖[1̄101]sapphire$ and $[1̄100]GaN‖[112̄0]sapphire.$ This relationship is explicitly defined since the polarity of the $a$ -GaN films was determined using convergent beam electron diffraction. Threading dislocations and stacking faults, observed in plan-view and cross-sectional transmission electron microscope images, dominated the $a$ -GaN microstructure with densities of $2.6×1010 cm−2$ and $3.8×105 cm−1,$ respectively. Submicron pits and crystallographic terraces were observed on the optically specular $a$ -GaN surface with atomic force microscopy.
, Xiaowei Li, Ismo Vartiainen, Anni Lehmuskero, Guoguo Kang, Jari Turunen, Markku Kuittinen, Pasi Vahimaa
Published: 22 August 2011
Applied Physics Letters, Volume 99; https://doi.org/10.1063/1.3631671

Abstract:
We report on an anomalous polarization-switching extinction effect in a sparse array of goldnanoparticle chains: under normal incidence of light, the array is almost transparent for one polarization; whereas it is fully opaque (with nearly zero transmittance) for the orthogonal polarization within a narrow band, even though the nanoparticles cover only a tiny fraction (say, 3.5%) of the transparent substrate surface. We reveal that the strong polarization-dependent short-range dipolar coupling and long-range radiative coupling of goldnanoparticles in this highly asymmetric array is responsible for this extraordinary effect.
Published: 22 August 2011
Applied Physics Letters, Volume 99; https://doi.org/10.1063/1.3630028

Abstract:
Molecular dynamics simulations of a dislocation based mechanism for void formation in silicon are presented. By studying a moving solid-liquid interface in Si, we observe the formation of dislocation loops on (111) facets consisting of coherency and anticoherency dislocations, which disband within nanoseconds into vacancy clusters of 10 or more vacancies. These vacancy clusters can act as nucleation seeds for the experimentally observed octahedral single and double voids.
Published: 22 August 2011
Applied Physics Letters, Volume 99; https://doi.org/10.1063/1.3630027

Abstract:
We report on differential etching behavior of the different orientations of the polarization in BiFeO3 (BFO), similar to other ferroelectrics, such as LiNbO3. We show how this effect can be used to fabricateepitaxial BiFeO3nanostructures. By means of piezoresponse force microscopy(PFM) domains of arbitrary shape and size can be poled in an epitaxial BiFeO3film, which are then reproduced in the film morphology by differential etching.Structures with a lateral size smaller than 200 nm were fabricated and very good retention properties as well as a highly increased piezoelectric response were detected by PFM.
Published: 22 August 2011
Applied Physics Letters, Volume 99; https://doi.org/10.1063/1.3630005

Abstract:
In direct contrast to recent reports, density functional theory predicts that the most stable structure of Bi2Ti2O7 pyrochlore is a cubic Fd 3 ¯ m space group by accounting for atomic displacements. The displaced Bi occupies the 96g(x,x,z) Wyckoff position with six equivalent sites, which create multiple local minima. Using nudged elastic band method, the transition states of Bi cation hopping between equivalent minima were investigated and an energy barrier between 0.11 and 0.21 eV was determined. Energy barriers associated with the motion of Bi between equivalent sites within the 96g Wyckoff position suggest the presence of dielectric relaxation in Bi2Ti2O7.
, Taisuke Hayashi, Takuya Ohba,
Published: 22 August 2011
Applied Physics Letters, Volume 99; https://doi.org/10.1063/1.3629771

Abstract:
A dielectric constant of over 100 000, with dielectric loss of less than 0.1, was found in 1.0 mol. % Ni-doped KTaO3 (KT:1%Ni) single crystals, showing temperature and frequency stabilities favorable for capacitor applications. The dielectric constant was found to depend on the electrodematerial, and Agelectrodes markedly enhanced the dielectric properties. This result indicates that the giant effective dielectric constant is due to a non-Ohmic electrode contact with a semiconducting KT:1%Ni.
Published: 22 August 2011
Applied Physics Letters, Volume 99; https://doi.org/10.1063/1.3628657

Abstract:
Ion bombardment of the phosphor layer during a sustain discharge was identified as the key factor inducing permanent image sticking and reducing the lifetime of alternating-current (ac) plasma display panels (PDPs). Secondary ion mass spectroscopy(SIMS) confirmed that ion bombardment of the phosphor layer facilitated the re-crystallization of the Mg particles sputtered from the MgO surface during a discharge, thereby degrading the visible conversion of the phosphor layer and eventually lowering the luminance and color temperature. Based on this mechanism, experimental results showed that the re-crystallization of the Mg particles was suppressed when using a positive-biased address electrode to diminish the ion bombardment of the phosphor layer. Consequently, minimizing the ion bombardment of the phosphor layer during a sustain discharge was shown to mitigate permanent image sticking in an ac PDP by suppressing the re-crystallization of the Mg particles.
, Kentaro Fujita, Paul H. Otsuka, , Matt Clark, Oliver B. Wright,
Published: 2 October 2017
Applied Physics Letters, Volume 111; https://doi.org/10.1063/1.4994886

Abstract:
We selectively generate chiral surface-acoustic whispering-gallery modes in the gigahertz range on a microscopic disk by means of an ultrafast time-domain technique incorporating a spatial light modulator. Active chiral control is achieved by making use of an optical pump spatial profile in the form of a semicircular arc, positioned on the sample to break the symmetry of clockwise- and counterclockwise-propagating modes. Spatiotemporal Fourier transforms of the interferometrically monitored two-dimensional acoustic fields measured to micron resolution allow individual chiral modes and their azimuthal mode order, both positive and negative, to be distinguished. In particular, for modes with 15-fold rotational symmetry, we demonstrate ultrafast chiral control of surface acoustic waves in a micro-acoustic system with picosecond temporal resolution. Applications include nondestructive testing and surface acoustic wave devices.
Published: 22 August 2011
Applied Physics Letters, Volume 99; https://doi.org/10.1063/1.3628463

Abstract:
The formation of single-crystaldiamond membranes is an important prerequisite for the fabrication of high-quality optical cavities in this material.Diamond membranes fabricated using lift-off processes involving the creation of a damaged layer through ion implantation often suffer from residual ion damage, which severely limits their usefulness for photonic structures. The current work demonstrates that strategic etch removal of the most highly defective material yields thin, single-crystaldiamond membranes with strong photoluminescence and a Raman signature approaching that of single-crystal bulk diamond. These optically active membranes can form the starting point for fabrication of high-quality optical resonators.
Published: 22 August 2011
Applied Physics Letters, Volume 99; https://doi.org/10.1063/1.3628459

Abstract:
Cathodoluminescence (CL) was used to study the onset of mechanical stress relaxation in low indium composition semipolar $(112¯2)$ InxGa1−xN lattice-mismatched layers grown on bulk GaN substrates. Monochromatic CL of short interfacial misfit dislocation (MD) segments showed a single threading dislocation (TD) associated with each MD segment—demonstrating that the initial stage of MD formation in semipolar III-nitride heterostructures proceeded by the bending and glide of pre-existing TDs on the (0001) slip plane. The state of coherency as determined by panchromatic CL is also compared to that determined by x-ray diffraction analysis based on crystallographic epilayer tilt and Matthew-Blakeslee’s critical thickness calculations.
Published: 22 August 2011
Applied Physics Letters, Volume 99; https://doi.org/10.1063/1.3628333

Abstract:
The optical emission response of a single nano-emitter coupled with a plasmonicnanorod dimer is investigated, where the short and long nanorods in the dimer support dipolar and quadrupolar plasmon resonance, repsectively. Fano resonances are observed with a nano-emitter being placed at either apex of the dimer. However, no Fano resonance is seen when the nano-emitter is placed in the gap of the dimer. Bonding and antibonding dipolar-quadrupolar plasmon couplings are closely related to the Fano resonances in this dimer system.
, D. O'connor, , W. Dickson,
Published: 22 August 2011
Applied Physics Letters, Volume 99; https://doi.org/10.1063/1.3628330

Abstract:
We demonstrate the application of plasmonic crystals for extracting light trapped in the substrate due to total internal reflection (TIR). The broadband transmission properties of one-dimensional plasmonic crystals have been investigated, both experimentally and numerically, beyond the TIR critical angle in order to reveal the role of plasmonic modes in this process. Through optimisation of the traditional square slit unit cell geometry of the crystals, transmission coefficients of up to 47% were obtained in the TIR regime. An U-shaped cell geometry with a few nm thick continuous film was found to significantly modify the plasmonic modes of the crystal in addition to exhibiting highly tuneable, structurally dispersive transmission peaks, further increasing transmission in the TIR regime up to 56%. Such structures exhibit better than glass transparency at the design wavelength when integrated over all incident angles.
, Frederico De Faria Elsner,
Published: 22 August 2011
Applied Physics Letters, Volume 99; https://doi.org/10.1063/1.3627184

Abstract:
The deflection signal of a thermally excited force sensor of an atomic force microscope can be analyzed to gain important information about the detector noise and about the validity of the equipartion theorem of thermodynamics. Here, we measured the temperature dependence of the thermal amplitude of a tuning fork and compared it to the expected values based on the equipartition theorem. In doing so, we prove the validity of these assumptions in the temperature range from 140 K to 300 K. Furthermore, the application of the equipartition theorem to quartztuning forks at liquid helium temperatures is discussed.
Chung-Chiang Wu,
Published: 22 August 2011
Applied Physics Letters, Volume 99; https://doi.org/10.1063/1.3627178

Abstract:
The low quality factor (Q) of single-walled carbon nanotube(SWNT)resonators has limited their sensitivity in sensing application. To this end, we employ the technique of parametric amplification by modulating the spring constant of SWNTresonators at twice the resonant frequency and achieve 10 times Q enhancement. The highest Q obtained at room temperature is around ∼700, which is 3–4 times better than previous Q record reported for doubly clamped SWNTresonators. Furthermore, efficient parametric amplification is found to only occur in the catenary vibration regime. Our results open up the possibility to employ light-weight and high-Qcarbon nanotuberesonators in single molecule and atomic mass sensing.
, Stephen Mutisya, Massimo Bertino
Published: 22 August 2011
Applied Physics Letters, Volume 99; https://doi.org/10.1063/1.3627164

Abstract:
Localization and enhancement of electric field by Ag-coated vertical Ni nanotip arrays were studied by using finite-different time domain calculations. With the 30 nm thick Ag coating, the nanotips can localize and enhance the electric field to more than 103 times under the excitation of TE-polarized light with a 532 nm wavelength. Nanotip-enhanced Raman scattering of cytochrome-c protein was demonstrated in a confocal Raman microscope. Significant enhancement of Raman spectrum was achieved at 1 × 10−9 mol/l concentration of the proteins.
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