scispace - formally typeset
Search or ask a question

Showing papers in "Applied Physics Letters in 2009"


Journal ArticleDOI
TL;DR: ABF swimmers represent the first demonstration of microscopic artificial swimmers that use helical propulsion and are of interest in fundamental research and for biomedical applications.
Abstract: Inspired by the natural design of bacterial flagella, we report artificial bacterial flagella (ABF) that have a comparable shape and size to their organic counterparts and can swim in a controllable fashion using weak applied magnetic fields. The helical swimmer consists of a helical tail resembling the dimensions of a natural flagellum and a thin soft-magnetic “head” on one end. The swimming locomotion of ABF is precisely controlled by three orthogonal electromagnetic coil pairs. Microsphere manipulation is performed, and the thrust force generated by an ABF is analyzed. ABF swimmers represent the first demonstration of microscopic artificial swimmers that use helical propulsion. Self-propelled devices such as these are of interest in fundamental research and for biomedical applications.

1,040 citations


Journal ArticleDOI
TL;DR: In this paper, dual-gated graphene field effect transistors using Al2O3 as top-gate dielectric were constructed using a thin Al film as a nucleation layer to enable the atomic layer deposition of Al 2O3.
Abstract: We fabricate and characterize dual-gated graphene field-effect transistors using Al2O3 as top-gate dielectric. We use a thin Al film as a nucleation layer to enable the atomic layer deposition of Al2O3. Our devices show mobility values of over 8000 cm2/V s at room temperature, a finding which indicates that the top-gate stack does not significantly increase the carrier scattering and consequently degrade the device characteristics. We propose a device model to fit the experimental data using a single mobility value.

904 citations


Journal ArticleDOI
TL;DR: In this article, the authors describe a metaloxide-semiconductor MOS transistor concept in which there are no junctions and the channel doping is equal in concentration and type to the source and drain extension doping.
Abstract: This paper describes a metal-oxide-semiconductor MOS transistor concept in which there are no junctions. The channel doping is equal in concentration and type to the source and drain extension doping. The proposed device is a thin and narrow multigate field-effect transistor, which can be fully depleted and turned off by the gate. Since this device has no junctions, it has simpler fabrication process, less variability, and better electrical properties than classical MOS devices with source and drain PN junctions.

903 citations


Journal ArticleDOI
TL;DR: In this paper, an advanced image reconstruction algorithm for pseudothermal ghost imaging, based on compressed sensing, is presented. But the algorithm is limited to pseudothermal images and cannot be applied to images taken from other pseudothermal imaging experiments.
Abstract: We describe an advanced image reconstruction algorithm for pseudothermal ghost imaging, reducing the number of measurements required for image recovery by an order of magnitude. The algorithm is based on compressed sensing, a technique that enables the reconstruction of an N-pixel image from much less than N measurements. We demonstrate the algorithm using experimental data from a pseudothermal ghost-imaging setup. The algorithm can be applied to data taken from past pseudothermal ghost-imaging experiments, improving the reconstruction’s quality.

793 citations


Journal ArticleDOI
TL;DR: In this article, a metamorphic Ga0.35In0.17As/Ge triple-junction solar cell is shown to provide current-matching of all three subcells and thus composes a device structure with virtually ideal band gap combination.
Abstract: A metamorphic Ga0.35In0.65P/Ga0.83In0.17As/Ge triple-junction solar cell is shown to provide current-matching of all three subcells and thus composes a device structure with virtually ideal band gap combination. We demonstrate that the key for the realization of this device is the improvement of material quality of the lattice-mismatched layers as well as the development of a highly relaxed Ga1−yInyAs buffer structure between the Ge substrate and the middle cell. This allows the metamorphic growth with low dislocation densities below 106 cm−2. The performance of the approach has been demonstrated by a conversion efficiency of 41.1% at 454 suns (454 kW/m2, AM1.5d ASTM G173–03).

691 citations


Journal ArticleDOI
TL;DR: In this paper, the structural and electronic properties of Cu2ZnSnS4 and Cu2znSnSe4 were studied using first-principles calculations and it was shown that the low energy crystal structure obeys the octet rule and is the kesterite structure.
Abstract: The structural and electronic properties of Cu2ZnSnS4 and Cu2ZnSnSe4 are studied using first-principles calculations. We find that the low energy crystal structure obeys the octet rule and is the kesterite (KS) structure. However, the stannite or partially disordered KS structures can also exist in synthesized samples due to the small energy cost. We find that the dependence of the band structure on the (Cu,Zn) cation ordering is weak and predict that the band gap of Cu2ZnSnSe4 should be on the order of 1.0 eV and not 1.5 eV as was reported in previous absorption measurements.

662 citations


Journal ArticleDOI
TL;DR: In this article, the adsorption of several common gas molecules over boron-, nitrogen-, aluminum-, and sulfur-doped graphene was theoretically studied using density functional theory.
Abstract: The adsorption of several common gas molecules over boron-, nitrogen-, aluminum-, and sulfur-doped graphene was theoretically studied using density-functional theory. B- and N-doped graphene retain a planar form, while Al and S atoms protrude out of the graphene layer. We find that only NO and NO2 bind to B-doped graphene, while only NO2 binds to S-doped graphene. Al-doped graphene is much more reactive and binds many more gases, including O2. We suggest that B- and S-doped graphene could be a good sensor for polluting gases such as NO and NO2.

657 citations


Journal ArticleDOI
TL;DR: In this paper, the electron affinity and ionization energy of vacuum-deposited molybdenum trioxide (MoO3) and of a typical MoO3/hole transport material (HTM) interface were determined via ultraviolet and inverse photoelectron spectroscopy.
Abstract: The electronic structures of vacuum-deposited molybdenum trioxide (MoO3) and of a typical MoO3/hole transport material (HTM) interface are determined via ultraviolet and inverse photoelectron spectroscopy. Electron affinity and ionization energy of MoO3 are found to be 6.7 and 9.68 eV, more than 4 eV larger than generally assumed, leading to a revised interpretation of the role of MoO3 in hole injection in organic devices. The MoO3 films are strongly n-type. The electronic structure of the oxide/HTM interface shows that hole injection proceeds via electron extraction from the HTM highest occupied molecular orbital through the low-lying conduction band of MoO3.

640 citations


Journal ArticleDOI
TL;DR: In this paper, the optical constants of graphene in the visible range can be estimated by means of a very simple procedure involving their consistence with universal optical conductivity and experimentally measured optical spectra, within the framework of Fresnel coefficients calculation.
Abstract: We show that the optical constants of graphene in the visible range can be estimated by means of a very simple procedure involving their consistence with universal optical conductivity and experimentally measured optical spectra, within the framework of Fresnel coefficients calculation. The obtained complex refractive index allows for accurate prediction of the optical behavior of graphene in the visible range, from the two-dimensional limit (single atomically thick graphene layer) to the bulk limit (graphite). Therefore, it may result very useful for quantitative optical analysis of graphene layers and graphitic structures in general.

565 citations


Journal ArticleDOI
TL;DR: In this paper, an approach to achieve simultaneous measurement of refractive index and temperature is proposed by using a Mach-Zehnder interferometer realized on tapered single-mode optical fiber.
Abstract: An approach to achieve simultaneous measurement of refractive index and temperature is proposed by using a Mach–Zehnder interferometer realized on tapered single-mode optical fiber. The attenuation peak wavelength of the interference with specific order in the transmission spectrum shifts with changes in the environmental refractive index and temperature. By utilizing S-band and C/L-band light sources, simultaneous discrimination of refractive index and temperature with the tapered fiber Mach–Zehnder interferometer is demonstrated with the corresponding sensitivities of −23.188 nm/RIU (refractive index unit) and 0.071 nm/ °C, and −26.087 nm/RIU (blueshift) and 0.077 nm/°C (redshift) for the interference orders of 169 and 144, respectively.

551 citations


Journal ArticleDOI
TL;DR: By utilizing Schottky contact instead of Ohmic contact in device fabrication, the UV sensitivity of the ZnO nanowire nanosensor has been improved by four orders of magnitude, and the reset time has been drastically reduced.
Abstract: UV response of ZnO nanowire nanosensor has been studied under ambient condition. By utilizing Schottky contact instead of Ohmic contact in device fabrication, the UV sensitivity of the nanosensor has been improved by four orders of magnitude, and the reset time has been drastically reduced from 417 to 0.8 s. By further surface functionalization with function polymers, the reset time has been reduced to 20 ms even without correcting the electronic response of the measurement system. These results demonstrate an effective approach for building high response and fast reset UV detectors. © 2009 American Institute of Physics. DOI: 10.1063/1.3133358 Ultraviolet UV photon detectors have a wide range of applications from environmental monitoring, missile launching detection, space research, high temperature flame detection to optical communications. 1 For these applications, fast response time, fast reset time, high selectivity, high responsivity, and good signal-to-noise ratio are commonly desired characteristics. 2 For UV photon detector based on polycrystalline ZnO thin film, a slow response time ranging from a few minutes to several hours is commonly observed. 3,4 Due

Journal ArticleDOI
TL;DR: In this paper, a melt spinning technique followed by a quick spark plasma sintering procedure was used to fabricate high performance p-type Bi0.52Sb1.48Te3 bulk material with unique microstructures.
Abstract: We report a melt spinning technique followed by a quick spark plasma sintering procedure to fabricate high-performance p-type Bi0.52Sb1.48Te3 bulk material with unique microstructures. The microstructures consist of nanocrystalline domains embedded in amorphous matrix and 5–15 nm nanocrystals with coherent grain boundary. The significantly reduced thermal conductivity leads to a state-of-the-art dimensionless figure of merit ZT∼1.56 at 300 K, more than 50% improvement of that of the commercial Bi2Te3 ingot materials.

Journal ArticleDOI
TL;DR: In this paper, the authors report broadband visible photoluminescence from solid graphene oxide, and modifications of the emission spectrum by progressive chemical reduction, suggesting a gapping of the two-dimensional electronic system by removal of π-electrons.
Abstract: We report broadband visible photoluminescence from solid graphene oxide, and modifications of the emission spectrum by progressive chemical reduction. The data suggest a gapping of the two-dimensional electronic system by removal of π-electrons. We discuss possible gapping mechanisms, and propose that a Kekule pattern of bond distortions may account for the observed behavior.

Journal ArticleDOI
TL;DR: In this article, the linear absorption spectrum of regioregular poly(3-hexylthiophene) films was analyzed to probe directly the film microstructure and how it depends on processing conditions.
Abstract: We analyze the linear absorption spectrum of regioregular poly(3-hexylthiophene) films spun from a variety of solvents to probe directly the film microstructure and how it depends on processing conditions. We estimate the exciton bandwidth and the percentage of the film composed of aggregates quantitatively using a weakly interacting H-aggregate model. This provides a description of the degree and quality of crystallites within the film and is in turn correlated with thin-film field-effect transistor characteristics.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the design, fabrication, and experimental characterization of high quality factor photonic crystal nanobeam cavities in silicon using a five-hole tapered one-dimensional photonic mirror and precise control of the cavity length.
Abstract: We investigate the design, fabrication, and experimental characterization of high quality factor photonic crystal nanobeam cavities in silicon. Using a five-hole tapered one-dimensional photonic crystal mirror and precise control of the cavity length, we designed cavities with theoretical quality factors as high as 1.4×107. By detecting the cross-polarized resonantly scattered light from a normally incident laser beam, we measure a quality factor of nearly 7.5×105. The effect of cavity size on mode frequency and quality factor was simulated and then verified experimentally.

Journal ArticleDOI
TL;DR: In this paper, the authors proposed a simple model for the lattice thermal conductivity of graphene in the framework of Klemens approximation, and the Gruneisen parameters were introduced separately for the longitudinal and transverse phonon branches through averaging over phonon modes obtained from the first principles.
Abstract: The authors proposed a simple model for the lattice thermal conductivity of graphene in the framework of Klemens approximation. The Gruneisen parameters were introduced separately for the longitudinal and transverse phonon branches through averaging over phonon modes obtained from the first principles. The calculations show that Umklapp-limited thermal conductivity of graphene grows with the increasing linear dimensions of graphene flakes and can exceed that of the basal planes of bulk graphite when the flake size is on the order of a few micrometers. The obtained results are in agreement with experimental data and reflect the two-dimensional nature of phonon transport in graphene.

Journal ArticleDOI
TL;DR: In this article, the photovoltaic effect in ferroelectric BiFeO3 thin films was reported and the all-oxide heterostructures with SrRuO3 bottom and tin doped indium oxide top electrodes were characterized by open-circuit voltages ∼08-09V and external quantum efficiencies up to ∼10% when illuminated with the appropriate light.
Abstract: We report a photovoltaic effect in ferroelectric BiFeO3 thin films The all-oxide heterostructures with SrRuO3 bottom and tin doped indium oxide top electrodes are characterized by open-circuit voltages ∼08–09 V and external quantum efficiencies up to ∼10% when illuminated with the appropriate light Efficiencies are at least an order of magnitude larger than the maximum efficiency under sunlight (AM 15) thus far reported for ferroelectric-based devices The dependence of the measured open-circuit voltage on film thickness suggests contributions to the large open-circuit voltage from both the ferroelectric polarization and band offsets at the BiFeO3/tin doped indium oxide interface

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the heat generation in gold nanoparticles when illuminated at their plasmonic resonance using the Green's dyadic method and showed that a wide range of morphologies can be used to design optimized plasmoric nanoheaters.
Abstract: Using the Green’s dyadic method, we investigated numerically the heat generation in gold nanoparticles when illuminated at their plasmonic resonance Two kinds of structures are discussed—colloidal-like nanoparticles and lithographic planar nanostructures—putting special emphasis on the influence of the object’s morphology at a constant metal volume The mechanism of heating is explained and discussed by mapping the heating power density inside the structures This work aims at giving an intuitive and original understanding of the relative heating efficiency of a wide set of morphologies and could stand for a basis recipe to design optimized plasmonic nanoheaters

Journal ArticleDOI
TL;DR: In this paper, the authors developed an approach to broad-band omnidirectional light absorption, based on light propagation in a metamaterial structure forming an effective "black hole".
Abstract: We develop an approach to broad-band omnidirectional light absorption, based on light propagation in a metamaterial structure forming an effective “black hole.” The proposed system does not rely on magnetic response, is nonresonant, and can be fabricated from existing materials.

Journal ArticleDOI
TL;DR: In this paper, a dual-band metamaterial absorber with two distinct and strong absorption points near 0.45 and 0.92 THz has been designed and analyzed.
Abstract: We report the design, simulation, and measurement of a dual-band metamaterial absorber in the terahertz region. Theoretical and experimental results show that the absorber has two distinct and strong absorption points near 0.45 and 0.92 THz, both which are related to the LC resonance of the metamaterial. The distributions of the power flow and the power loss indicate that the absorber is an excellent electromagnetic wave collector: the wave is first trapped and reinforced in certain specific locations and then completely consumed. This dual-band absorber has applications in many scientific and technological areas.

Journal ArticleDOI
TL;DR: In this article, a graphene-polymer nanocomposite membrane was fabricated and first used to mode lock a fiber laser, and stable mode-locked solitons with 3 nJ pulse energy, 700 fs pulse width at the 1590 nm wavelength have been directly generated from the laser.
Abstract: Due to its unique electronic property and the Pauli blocking principle, atomic layer graphene possesses wavelength-independent ultrafast saturable absorption, which can be exploited for the ultrafast photonics application. Through chemical functionalization, a graphene-polymer nanocomposite membrane was fabricated and first used to mode lock a fiber laser. Stable mode locked solitons with 3 nJ pulse energy, 700 fs pulse width at the 1590 nm wavelength have been directly generated from the laser. We show that graphene-polymer nanocomposites could be an attractive saturable absorber for high power fiber laser mode locking.

Journal ArticleDOI
TL;DR: In this paper, both hardening and softening response within the quadratic potential field of a power generating piezoelectric beam (with a permanent magnet end mass) is invoked by tuning nonlinear magnetic interactions.
Abstract: We model and experimentally validate a nonlinear energy harvester capable of bidirectional hysteresis. In particular, both hardening and softening response within the quadratic potential field of a power generating piezoelectric beam (with a permanent magnet end mass) is invoked by tuning nonlinear magnetic interactions. Not only is this technique shown to increase the bandwidth of the device but experimental results additionally verify the capability to outperform linear resonance. Engaging this nonlinear phenomenon is ideally suited to efficiently harvest energy from ambient excitations with slowly varying frequencies.

Journal ArticleDOI
TL;DR: In this paper, the micro-Raman investigation of changes in the single and bilayer graphene crystal lattice induced by low and medium energy electron-beam irradiation (5-20 keV) was conducted.
Abstract: The authors report micro-Raman investigation of changes in the single and bilayer graphene crystal lattice induced by the low and medium energy electron-beam irradiation (5–20 keV). It was found that the radiation exposures result in the appearance of the strong disorder D band around 1345 cm−1, indicating damage to the lattice. The D and G peak evolution with increasing radiation dose follows the amorphization trajectory, which suggests graphene’s transformation to the nanocrystalline and then to amorphous form. The results have important implications for graphene characterization and device fabrication, which rely on the electron microscopy and focused ion beam processing.

Journal ArticleDOI
TL;DR: In this article, the power conversion efficiency (PCE) of a control device based on indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/poly (3-hexyl)thiophene: phenyl-C61-butyric acid methyl ester/LiF/Al electrodes (PCE=3.1%).
Abstract: Large-area, continuous, transparent, and highly conducting few-layered graphene films produced by chemical vapor deposition method were used as anode for application in photovoltaic devices. The noncovalent modification of the graphene films with pyrene buanoic acid succidymidyl ester improved the power conversion efficiency (PCE) to 1.71%. This performance corresponds to ∼55.2% of the PCE of a control device based on indium tin oxide (ITO)/poly(3,4–ethylenedioxythiophene):poly(styrenesulfonate)/poly(3-hexyl)thiophene: phenyl-C61-butyric acid methyl ester/LiF/Al electrodes (PCE=3.1%). This finding paves the way for the substitution of ITO in photovoltaic and electroluminescent devices with low cost graphene films.

Journal ArticleDOI
TL;DR: In this article, spatial control in the heterogeneous nucleation of water can be achieved by manipulating the local nucleation energy barrier and nucleation rate via modification of the local intrinsic wettability of a surface.
Abstract: Heterogeneous nucleation of water plays an important role in a wide range of natural and industrial processes. Though heterogeneous nucleation of water is ubiquitous and an everyday experience, spatial control of this important phenomenon is extremely difficult. Here we show for the first time that spatial control in the heterogeneous nucleation of water can be achieved by manipulating the local nucleation energy barrier and nucleation rate via the modification of the local intrinsic wettability of a surface. Such ability to control water nucleation could address the condensation-related limitations of superhydrophobic surfaces and has implications for efficiency enhancements in energy and desalination systems.

Journal ArticleDOI
TL;DR: In this paper, the authors have fabricated 6.5 in. flexible full-color top-emission active matrix organic light-emitting diode display on a polyimide (PI) substrate driven amorphous indium gallium zinc oxide thin-film transistors (a-IGZO TFTs).
Abstract: We have fabricated 6.5 in. flexible full-color top-emission active matrix organic light-emitting diode display on a polyimide (PI) substrate driven amorphous indium gallium zinc oxide thin-film transistors (a-IGZO TFTs). The a-IGZO TFTs exhibited field-effect mobility (μFE) of 15.1 cm2/V s, subthreshold slope of 0.25 V/dec, threshold voltage (VTH) of 0.9 V. The electrical characteristics of TFTs on PI substrate, including a bias-stress instability after 1 h long gate bias at 15 V, were indistinguishable from those on glass substrate and showed high degree of spatial uniformity. TFT samples on 10 μm thick PI substrate withstood bending down to R=3 mm under tension and compression without any performance degradation.

Journal ArticleDOI
TL;DR: In this paper, the thermal conductivity of graphene nanoribbons with different edge shapes was investigated as a function of length, width, and strain using nonequilibrium molecular dynamics method.
Abstract: We have investigated the thermal conductivity of graphene nanoribbons (GNRs) with different edge shapes as a function of length, width, and strain using nonequilibrium molecular dynamics method. The initial GNR for the functional variations has dimensions of 2×11 nm2. Strong length dependence of thermal conductivity is obtained, indicating high thermal conductivities of GNRs, which is consistent with the experimental results for graphene. A tensile/compressive uniaxial strain can remarkably decrease the thermal conductivity of GNR.

Journal ArticleDOI
TL;DR: In this article, the authors demonstrate a high-performance gas sensor using partially reduced graphene oxide (GO) sheets obtained through low-temperature step annealing in argon flow at atmospheric pressure.
Abstract: We demonstrate a high-performance gas sensor using partially reduced graphene oxide (GO) sheets obtained through low-temperature step annealing (300 °C at maximum) in argon flow at atmospheric pressure. The electrical conductance of GO was measured after each heating cycle to interpret the level of reduction. The thermally reduced GO showed p-type semiconducting behavior in ambient conditions and were responsive to low-concentration NO2 diluted in air at room temperature. The sensitivity is attributed to the electron transfer from the reduced GO to adsorbed NO2, which leads to enriched hole concentration and enhanced electrical conduction in the reduced GO sheet.

Journal ArticleDOI
TL;DR: In this article, the electrical switching behavior of GeTe-based phase change memory devices is characterized by time resolved experiments, and the minimum SET pulse duration can even be reduced down to 1 ns.
Abstract: The electrical switching behavior of GeTe-based phase change memory devices is characterized by time resolved experiments. SET pulses with a duration of less than 16 ns are shown to crystallize the material. Depending on the resistance of the RESET state, the minimum SET pulse duration can even be reduced down to 1 ns. This finding is attributed to the increasing impact of crystal growth upon decreasing switchable volume. Using GeTe or materials with similar crystal growth velocities, hence promises nonvolatile phase change memories with dynamic random access memorylike switching speeds.

Journal ArticleDOI
TL;DR: In this paper, the impinging droplets on superhydrophobic textured surfaces are studied and a design guideline for nonwetting surfaces under droplet impingement is proposed.
Abstract: This paper studies the impinging droplets on superhydrophobic textured surfaces and proposes a design guideline for nonwetting surfaces under droplet impingement. A new wetting pressure, the effective water hammer pressure, is introduced in the study to clearly define wetting states for the impinging droplets. This approach establishes the design criteria for nonwetting surfaces to impinging droplets. For impingement speed higher than raindrop speed, the surfaces need to have sub-100-nm features to generate a large enough antiwetting pressure for the droplets to take a nonwetting state after impingement.