Applied Physics Letters

Published by American Institute of Physics
Online ISSN: 0003-6951
Publications
Article
Pb(In(12)Nb(12))O(3)-Pb(Mg(13)Nb(23))O(3)-PbTiO(3) (PIN-PMN-PT) single crystals have been developed recently, which can increase the operating temperature by at least 20 degrees C compared to PMN-PT crystals. We have measured a complete set of material properties of single domain PIN-PMN-PT crystal, which is urgently needed in theoretical studies and electromechanical device designs using this crystal. Because the rotated values of d33*=1122 pCN and k33*=89% along [001](c) calculated using the single domain data obtained here are in good agreement with the [001](c) poled multidomain PIN-PMN-PT crystals, one may conclude that the physical origin of the ultrahigh piezoelectric properties mainly come from orientation effect.
 
and 2 present the value of lnðA=A 0 Þ as a function of propagation distance x for the ultrasonic waves propagating in both [001] c and [011] c poled PMN-0.28PT single crystals. For both cases, the values of a vary considerably with wave propagation directions. For [001] c and [011] c poled crystals, the longitudinal ultrasonic waves propagate along the same pseudo-cubic [100] c direction. But their a values are much different, i.e., 0.09775 cm À1 and 0.04989 cm À1 , respectively, for [001] c and [011] c poled crystals. The former is almost 2 times as large as the latter. This indicates that the domain structure is an important factor for the ultrasonic attenuation. In other words, the domain structure is vital in controlling the ultrasonic attenuation and the mechanical quality factor Q. In [001] c-poled crystals, four degenerated engineered domains exist. The domain structure are less stable under external drive and there is also a large hysteresis. 21 Domain wall movements or breathing motions produce 
Article
Complete sets of elastic, piezoelectric, and dielectric constants of 0.72Pb(Mg(1∕3)Nb(2∕3))O(3)-0.28PbTiO(3) single crystal poled along [111](c) (single domain) as well as non-polar axes [001](c) and [011](c) (multidomain) have been measured under natural conditions. These data allowed us to evaluate accurately the extrinsic contributions to the superior piezoelectric properties. Very large extrinsic contributions to the unusual anisotropies in multidomain crystals are confirmed. We found that the instability of domain structures is the origin of the low mechanical quality factor Q for the multidomain relaxor-based ferroelectric single crystals. Our results can provide useful guidance in future design of domain engineered materials.
 
(a) Bridge electrode configuration for activating the flexural mode; (b) Illustration of the flexural motion of a k 32-type bar.
Article
Rhombohedral phase relaxor-PbTiO(3) solid solution single crystals poled along [011](c) exhibits superior lateral extensional piezoelectric response, which enables the excitation of a pure low frequency flexural mode with a bridge-type electrode configuration. For the ternary 0.24Pb(In(1/2)Nb(1/2)) O(3)-0.46Pb(Mg(1/3)Nb(2/3))O(3)-0.30PbTiO(3) single crystal poled along [011](c), the electromechanical coupling factor of the flexural mode reached as high as 0.66, and the resonance frequency of this mode can be easily made in kHz range, making it possible to fabricate very small size low frequency sensors and actuators. We have delineated theoretically the coupling between flexural mode and other modes and realized a strong pure flexure mode.
 
The hydrostatic pressure dependence of d h for face-plate stabilized 2-2 composites with various epoxy matrixes.
Schematic diagram of 2-2 crystal/epoxy composite comprised of [011] poled PMN-PT crystals, with layers parallel to X axes.
Article
The hydrostatic piezoelectric properties of [011] poled Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) crystals and corresponding 2-2 crystal/epoxy composites were investigated. The crystal volume ratio and compositional dependencies of the hydrostatic charge and voltage coefficients (dh and gh ) and hydrostatic figure of merit (FOM) dh × gh were determined, where large FOM value of 3.2 pm(2)/N with high stability as a function of hydrostatic pressure was achieved for rhombohedral crystal composites. In addition, the stress amplification effects of the face-plate and different epoxy matrixes were investigated, with maximum FOM value being on the order of 92 pm(2)/N, indicating that 2-2 crystal/epoxy composites are promising materials for hydrostatic applications.
 
Article
We have studied the dynamic behavior of nanoparticles in ferrofluids consisting of single-domain, biogenic magnetite (Fe(3)O(4)) isolated from Magnetospirillum magnetotacticum (MS-1). Although dipolar chains form in magnetic colloids in zero applied field, when dried upon substrates, the solvent front disorders nanoparticle aggregation. Using avidin-biotin functionalization of the particles and substrate, we generated self-assembled, linear chain motifs that resist solvent front disruption in zero-field. The engineered self-assembly process we describe here provides an approach for the creation of ordered magnetic structures that could impact fields ranging from micro-electro-mechanical systems development to magnetic imaging of biological structures.
 
Article
The high efficient tandem blue fluorescent organic light emitting diodes (OLEDs) with the transparent interconnection layer (ICL) of fullerence (C60)/Molybdenum oxide (MoO3)-doped N,N'-bis(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (NPB) were presented. A stack consisting of 0.5 nm of LiF and 1 nm of Ca, which is located from C60 to adjacent electron transporting layer is used as an electron injection layer. The experiment results indicate that the luminance of the tandem device is basically equal to that of the traditional single-unit device, but the current density of the tandem device is much less than that of the single-unit device under a same luminance. The current efficiency and the maximal power efficiency of tandem device with LiF/Ca/C60/NPB:MoO3/MoO3-based interconnection layer have been approximately enhanced by 250% and 126%, respectively. In addition, we also analyze that the mechanism of the efficiency enhancement is ascribed to the effective charge separation and transport of the ICL in tandem OLEDs.
 
Color online Mesh scans of 002, 200, 22 ¯ 0, and 220 of PZN-4.5%PT with E =1 kV/ cm applied along 110 at 413 K in the FC condition. 
Color online Mesh scans of 002, 200, 22 ¯ 0, and 220 of PZN-4.5%PT with E =1 kV/ cm applied along 110 at 383 K in the FC condition. 
Color online Mesh scans of 002, 200, 22 ¯ 0, and 220 of PZN-4.5%PT with E =1 kV/ cm applied along 110 at 338 K in the FC condition. 
Color online Temperature dependence of lattice constants and tilt angle of monoclinic phase for PZN-4.5%PT with E =1 kV/ cm along 110. 
Article
We report the finding of a monoclinic M(B) phase in Pb(Zn(13)Nb(23))O(3)-4.5%PbTiO(3) single crystals. High precision x-ray diffraction investigations of [110] field cooled crystals have shown a transformation sequence of cubic(C)-->tetragonal(T)-->orthorhombic(O)-->monoclinic(M(B)), which is different from that previously reported [A.-E. Renault et al., J. Appl. Phys. 97, 044105 (2005)]. Beginning in the zero-field-cooled condition at 383 K, a rhombohedral (R)-->M(B)-->O sequence was observed with increasing field. Coexisting M(B) and O phases were then found upon removal of field, which fully transformed to M(B) on cooling to room temperature.
 
Article
The massively parallel arrays of highly periodic Gd-doped Si nanowires (SiNWs) self-organized on Si(110)-16 × 2 surface were investigated by scanning tunneling microscopy and spectroscopy. These periodic Gd-doped SiNWs are atomically precise and show equal size, periodic positions, and high-integration densities. Surprisingly, the scanning tunneling spectroscopy results show that each metallic-like, Gd-doped SiNW exhibits room-temperature negative differential resistance (RT-NDR) behavior, which can be reproducible with various Gd dopings and is independent of the tips. Such massively parallel arrays of highly ordered and atomically identical Gd-doped SiNWs with one-dimensional laterally confined RT-NDR can be exploited in Si-based RT-NDR nanodevices.
 
Color online a Schematic diagram of graphene as used in our investigations. b LEED pattern at 114 eV showing the diffraction spots due to the SiC111 substrate S1, S2 and the graphene lattice G1, G2. c STM images 27 15 nm 2 of the surface of graphene/3C-SiC111. d Honeycomb type structures 5 5 nm 2 45 mV, 0.2 nA.
Color online a C 1s XPS spectra of the fully grown graphene on 3C-SiC111 for different temperatures. b XPS spectra of the C 1s core level for graphene with a Doniach-Sunjic lineshape analysis red line; Decomposition with bulk and two surfaces components identified by B, G, and I, respectively.
Article
Epitaxial graphene films grown on silicon carbide (SiC) substrate by solid state graphitization is of great interest for electronic and optoelectronic applications. In this paper, we explore the properties of epitaxial graphene films on 3C-SiC(111)Si(111) substrate. X-ray photoelectron spectroscopy and scanning tunneling microscopy were extensively used to characterize the quality of the few-layer graphene (FLG) surface. The Raman spectroscopy studies were useful in confirming the graphitic composition and measuring the thickness of the FLG samples.
 
Article
[This corrects the article on p. 243501 in vol. 97, PMID: 21221250.][This corrects the article on p. 243501 in vol. 97, PMID: 21221250.].
 
Photon counts per second 
Article
We report on controlling the spontaneous emission (SE) rate of a molybdenum disulfide (MoS$_2$) monolayer coupled with a planar photonic crystal (PPC) nanocavity. Spatially resolved photoluminescence (PL) mapping shows strong variations of emission when the MoS$_2$ monolayer is on the PPC cavity, on the PPC lattice, on the air gap, and on the unpatterned gallium phosphide substrate. Polarization dependences of the cavity-coupled MoS$_2$ emission show a more than 5 times stronger extracted PL intensity than the un-coupled emission, which indicates an underlying cavity mode Purcell enhancement of MoS$_2$ SE rate exceeding a factor of 70.
 
(Color online) (a)-(c) FT-IR absorption spectra of GeO 2 after air exposure for 3 months (3 months air expo.), after air exposure for 7 days (air expo.), and after 300 C vacuum annealing (vac. anneal). (d) Moisture desorption curves of GeO 2 (air expo.) and SiO 2 (PE-CVD and thermally grown; see Ref. 12) obtained from TPD-MS. Absorbed H 2 O (2) is assigned to confined H 2 O in GeO 2 .
(Color online) Relative intensities of various secondary ion peaks in TOF-SIMS spectra of GeO 2 after air exposure for 7 days (air expo.), after 300 C vacuum annealing (vac. anneal), and native SiO 2 [SiO 2 (air expo.); see Ref. 14]. Intensities of the ion peaks of GeO 2 and SiO 2 are normalized by 74 Ge þ and 30 Si þ , respectively.
(Color online) SIMS depth profiles of (a) deuterium and (b) carbon in GeO 2 films for different D 2 O moisture exposure times of 0.1, 1, 10, and 60 min. Spectrum calibration is the same as that in Fig. 3. (c) Intensities of deuterium, carbon, and germanium at 10-nm depth depending on the D 2 O exposure time.
(Color online) (a) SIMS depth profiles of hydrogen in thin and thick GeO2 films. The samples without (w/o) and with (w/) 400 °C vacuum annealing were shown, respectively. The samples after the vacuum annealing were stored in analytical chambers with no air exposure by means of the transferring in an inert gas. Spectrum calibration is the same as that in Fig.3. (b) Schematic illustration of hydrogen distribution in GeO2. The hydrogen distribution in GeO2 is restricted by two independent processes, which lead to different behaviors at surface and interface of GeO2/Ge.
Article
Adsorbed species and its diffusion behaviors in GeO(2)∕Ge stacks, which are future alternative metal-oxide-semiconductor (MOS) materials, have been investigated using various physical analyses. We clarified that GeO(2) rapidly absorbs moisture in air just after its exposure. After the absorbed moisture in GeO(2) reaches a certain limit, the GeO(2) starts to absorb some organic molecules, which is accompanied by a structural change in GeO(2) to form a partial carbonate or hydroxide. We also found that the hydrogen distribution in GeO(2) shows intrinsic characteristics, indicative of different diffusion behaviors at the surface and at the GeO(2)∕Ge interface. Because the impurity absorbability of GeO(2) has a great influence on the electrical properties in Ge-MOS devices, these results provide valuable information in realizing high quality GeO(2)∕Ge stacks for the actual use of Ge-MOS technologies.
 
Article
The authors demonstrate an optical manipulation mechanism of gas bubbles for microfluidic applications. Air bubbles in a silicone oil medium are manipulated via thermocapillary forces generated by the absorption of a laser in an amorphous silicon thin film. In contrast to previous demonstrations of optically controlled thermally driven bubble movement, transparent liquids can be used, as the thermal gradient is formed from laser absorption in the amorphous silicon substrate, and not in the liquid. A variety of bubbles with volumes ranging from 19 pl to 23 nl was transported at measured velocities of up to 1.5 mm/s.
 
Rf heating measurement set-up with water-cooled LCR resonator consisting of a parallel plate capacitor and solenoid. 
Magnitude of conservative electric field E z , magnetically induced 
E rf and H rf vector components distribution in (a) parallel plate 
Temperature dependence on time plotted for (a) 28 mg/ml, (b) 1 mg/ml SPIO suspension samples measured in three rf fields configurations. Insets show qm slopes and linear dependence of T on t during first 20 s of heating. The other two insets depict NPs overall size and zeta potential distribution.
Article
We report a method for characterization of the efficiency of radio-frequency (rf) heating of nanoparticles (NPs) suspended in an aqueous medium. Measurements were carried out for water suspended 5 nm superparamagnetic iron-oxide NPs with 30 nm dextran matrix for three different configurations of rf electric and magnetic fields. A 30 MHz high-Q resonator was designed to measure samples placed inside a parallel plate capacitor and solenoid coil with or without an rf electric field shield. All components of rf losses were analyzed and rf electric and magnetic field induced heating of NPs and the dispersion medium was determined and discussed.
 
Article
We combine the characterization techniques of scanning AC nanocalorimetry and x-ray diffraction to study phase transformations in complex materials system. Micromachined nanocalorimeters have excellent performance for high-temperature and high-scanning-rate calorimetry measurements. Time-resolved X-ray diffraction measurements during in-situ operation of these devices using synchrotron radiation provide unprecedented characterization of thermal and structural material properties. We apply this technique to a Fe0.84Ni0.16 thin-film sample that exhibits a martensitic transformation with over 350 K hysteresis, using an average heating rate of 85 K/s and cooling rate of 275 K/s. The apparatus includes an array of nanocalorimeters in an architecture designed for combinatorial studies.
 
Color online The principle of land-contrast interferometry on the BioCD. a Reflection coefficients are 0.383i on 77 nm SiO 2 / Si land and 0.383i on 140 nm SiO 2 / Si mesa, and R = 0.147 for both. A 1 nm water film changes the reflection coefficients by 0.0017 and +0.0017 on the land and the mesa, respectively. b Spot-shaped mesas were etched on silicon thermal-oxide silicon chips by photolithography. The contrast between the spot and the land is sensitive to water accumulation, because the local contrast is self-referenced with common-mode rejection of system fluctuations.  
Color online Water film accumulation on bare and chemicallytreated silica surfaces under differing humidities. a The four surface preparations were dehydrated silica, hydrated silica, silanized silica chlorodimethyl-octadecylsilane, and protein coated silica. The chips were baked after 1800 min and scanned again. b Water accumulation on proteincoated chips is 3 larger on a chip spinning at 5 m/s compared to a static chip. The chips were baked after 600 min and scanned again.
Color online Eight protein spots rabbit IgG were printed on a 140 nm thick silica-on-silicon surface and dried by nitrogen. The sample was scanned by the SDI system exposed to air. Each image frame was acquired every 20 min. The thickness increased over 8 h by approximately 320 pm of water on the protein spots relative to the silanized hydrophobic land.  
Article
Water is a persistent background in virtually all biosensors, yet is difficult to quantify. We apply an interferometric optical balance to measure water film accumulation from air onto several types of prepared silica surfaces. The optical balance uses in-line common-path interferometry with balanced quadratures to measure the real-time accumulation of molecular films. The accumulated water thickness is sensitive to ambient conditions, with thicknesses that vary from picometers up to nanometers, even on hydrophobic silanized surfaces. These results demonstrate that water adsorption contributes an excess signal in dry label-free protein microarray optical biosensors and presents a fundamental limit to assay sensitivity.
 
Tissue sample and experimental configuration for Experiment #1.
Article
Tools that are capable of manipulating micro-sized objects have been widely used in such fields as physics, chemistry, biology, and medicine. Several devices, including optical tweezers, atomic force microscope, micro-pipette aspirator, and standing surface wave type acoustic tweezers have been studied to satisfy this need. However, none of them has been demonstrated to be suitable for in vivo and clinical studies. Single beam acoustic tweezers (SBAT) is a technology that uses highly focused acoustic beam to trap particles toward the beam focus. Its feasibility was first theoretically and experimentally demonstrated by Lee and Shung several years ago. Since then, much effort has been devoted to improving this technology. At present, the tool is capable of trapping a microparticle as small as 1 μm, as well as a single red blood cell. Although in comparing to other microparticles manipulating technologies, SBAT has advantages of providing stronger trapping force and deeper penetration depth in tissues, and producing less tissue damage, its potential for in vivo applications has yet been explored. It is worth noting that ultrasound has been used as a diagnostic tool for over 50 years and no known major adverse effects have been observed at the diagnostic energy level. This paper reports the results of an initial attempt to assess the feasibility of single beam acoustic tweezers to trap microparticles in vivo inside of a blood vessel. The acoustic intensity of SBAT under the trapping conditions that were utilized was measured. The mechanical index and thermal index at the focus of acoustic beam were found to be 0.48 and 0.044, respectively, which meet the standard of commercial diagnostic ultrasound system.
 
(a) Top view of CMUT array zoomed in highlighting the size of one membrane and portion of one element delimitated by the yellow dashed lines. The lighter rectangles running along the element and through the membranes are the top electrodes. (b) Full 1 Â 16 CMUT array with wire bond pads and connections used in experiments. (c) (dimensions not to scale) Electrical schematic of the connections to the CMUT array showing that all elements are biased by V bias via the bottom electrode and the center elements (Elmt. 2-15) can have a different bias through the V biasC connection.
Article
Capacitive Micromachined Ultrasonic Transducers (CMUTs) operating in immersion support dispersive evanescent waves due to the subwavelength periodic structure of electrostatically actuated membranes in the array. Evanescent wave characteristics also depend on the membrane resonance which is modified by the externally applied bias voltage, offering a mechanism to tune the CMUT array as an acoustic metamaterial. The dispersion and tunability characteristics are examined using a computationally efficient, mutual radiation impedance based approach to model a finite-size array and realistic parameters of variation. The simulations are verified, and tunability is demonstrated by experiments on a linear CMUT array operating in 2-12 MHz range.
 
Article
Our recently developed ultrasound-switchable fluorescence (USF) imaging technique showed that it was feasible to conduct high-resolution fluorescence imaging in a centimeter-deep turbid medium. Because the spatial resolution of this technique highly depends on the ultrasound-induced temperature focal size (UTFS), minimization of UTFS becomes important for further improving the spatial resolution USF technique. In this study, we found that UTFS can be significantly reduced below the diffraction-limited acoustic intensity focal size via nonlinear acoustic effects and thermal confinement by appropriately controlling ultrasound power and exposure time, which can be potentially used for deep-tissue high-resolution imaging.
 
Article
The purpose of this paper is to present a rapid and simple method to evaluate the trapping performance of high frequency focused ultrasonic transducers for acoustic tweezer applications. The method takes into consideration the friction between the particle to be trapped and the surface that it resides on. As a result it should be more reliable and accurate than the methods proposed previously. The trapping force produced by a 70-MHz press-focused transducer was measured to evaluate the performance of this approach. This method demonstrates its potential in optimizing the excitation conditions for acoustic tweezer applications and the design of acoustic tweezers.
 
Color online Bubble evolution for different initial nucleation size for droplet size of R o =12 m. 
Color online Time evolution of bubble for a R o = 9.72 m, P a = 10.8, and N = 4, b R o = 11.61 m, P a = 7.7, and N = 13, c R o = 13.84 m, P a = 9.9, and N = 4, and d R o = 18.9 m, P a =7.7, and N=4. 
Color online Bubble evolution for a varying viscosity and b varying surface tension. 
Article
Acoustic droplet vaporization is investigated in a theoretical model. This work is motivated by gas embolotherapy, a developmental cancer treatment involving tumor infarction with gas microbubbles that are selectively formed from liquid droplets. The results indicate that there exists a threshold value for initial droplet size below which the bubble evolution is oscillatory and above which it is smooth and asymptotic, and show that the vaporization process affects the subsequent microbubble expansion. Dampening of the bubble expansion is observed for higher viscosity and surface tension, with effects more pronounced for droplet size less than 6 mum in radius.
 
Rate of occurrence observed in bubble torus formation as a function of number of inputted cycles and PNP for droplets of 9.1 lm (STD ¼ 1.2 lm) droplets vaporized using single pulses from a 7.5 MHz transducer.
Article
Acoustic droplet vaporization (ADV) is the selective vaporization of liquid microdroplets using ultrasound to produce stable gas bubbles. ADV is the primary mechanism in an ultrasound based cancer therapy, called gas embolotherapy, where the resulting bubbles are used to create localized occlusions leading to tumor necrosis. In this investigation, early time scale events including phase change are directly visualized using ultra-high speed imaging. Modulating elevated acoustic pressure or pulse length resulted in toroidal bubbles. For sufficiently short pulses (4 cycles at 7.5 MHz), toroidal bubble formation could be avoided, regardless of acoustic pressures tested.
 
Article
A high frequency ultrasonic phased array is shown to be capable of trapping and translating microparticles precisely and efficiently, made possible due to the fact that the acoustic beam produced by a phased array can be both focused and steered. Acoustic manipulation of microparticles by a phased array is advantageous over a single element transducer since there is no mechanical movement required for the array. Experimental results show that 45 μm diameter polystyrene microspheres can be easily and accurately trapped and moved to desired positions by a 64-element 26 MHz phased array.
 
͑ Color online ͒ ͑ a ͒ ͑ left ͒ Experimental configuration of acoustic traps. ͑ b ͒ ͑ right ͒ LABVIEW interface for three dimensional linear stepping motions. 
͑ Color online ͒ ͑ a ͒ ͑ upper left ͒ Peak pressures from 23 to 37 MHz with different excitation voltages at the focus. ͑ b ͒ ͑ upper right ͒ Illustration of maximum displacement measurement. The droplet ͑ a shaded pink circle ͒ was drawn into the focal spot ͑ a shaded gold area ͒ when trapped. ͑ c ͒ ͑ lower left ͒ Maximum displacements as a function of frequency and excitation voltage. ͑ d ͒ ͑ lower right ͒ Axial pressure distribution when V pp = 41 V at 30 MHz. 
͑ Color online ͒ Trapped droplet motion I ͑ enhanced online ͒ . ͓ URL:  ͔ 
Color online Definition of parameters to calculate the transverse trapping force on a sphere centered at C x c, y c, z c Ref. 7.
Article
A single beam acoustic device, with its relatively simple scheme and low intensity, can trap a single lipid droplet in a manner similar to optical tweezers. Forces in the order of hundreds of nanonewtons direct the droplet toward the beam focus, within the range of hundreds of micrometers. This trapping method, therefore, can be a useful tool for particle manipulation in areas where larger particles or forces are involved.
 
Experimental images of the optofluidic switch. (a) and (b) The device without acoustic excitation. (c) and (d) The device under acoustic excitation where microstreaming is observed. The dotted arrow represents the light path.
A schematic showing the design and working principle of the oscillating bubble-based optofluidic switch. (a) The device under acoustic excitation; (b) the device without acoustic excitation.
Article
Merging acoustofluidic mixing with optofluidic integration, we have demonstrated a single-layer, planar, optofluidic switch that is driven by acoustically excited oscillating microbubbles. The device was found to have a switching speed of 5 Hz, an insertion loss of 6.02 dB, and an extinction ratio of 28.48 dB. With its simplicity, low fluid consumption, and compatibility with other microfluidic devices, our design could lead to a line of inexpensive, yet effective optical switches for many lab-on-a-chip applications.
 
Article
Acoustophoretic separation in microchannels offers a promising avenue for high-throughput, label-free, cell and particle separation for many applications. However, previous acoustophoretic separation approaches have been limited to a single size separation threshold, analogous to a binary filter, (i.e., high-pass or low-pass). Here, we describe a tunable acoustophoretic separation architecture capable of sorting cells and particles based on a range of sizes, analogous to a band-pass filter. The device is capable of sorting an arbitrary range of particle sizes between 3 and 10 mum in diameter with high efficiency (transfer fraction=0.98+/-0.02) at a throughput of approximately 10(8) particleshmicrochannel.
 
Article
Ultrasound-activated microbubbles were used as actuators to deform microvessels for quantifying microvessel relaxation timescales at megahertz frequencies. Venules containing ultrasound contrast microbubbles were insonified by short 1 MHz ultrasound pulses. Vessel wall forced-deformations were on the same microsecond timescale as microbubble oscillations. The subsequent relaxation of the vessel was recorded by high-speed photomicrography. The tissue was modeled as a simple Voigt solid. Relaxation time constants were measured to be on the order of ∼10 μs. The correlation coefficients between the model and 38 data sets were never lower than 0.85, suggesting this model is sufficient for modeling tissue relaxation at these frequencies. The results place a bound on potential numerical values for viscosity and elasticity of venules.
 
Color online Nanodomain manipulation. Image of a dot array with a diameter of 15 nm a before and b after the erase.
Article
A new method to achieve real information recording with a density above 1 Tbit∕in.(2) in ferroelectric data storage systems is proposed. In this system, data bits were written in the form of the polarization direction, and the data were read by scanning nonlinear dielectric microscopy technique. The domain-switching characteristics of the virgin and inversely prepolarized media were compared, and the conditions of the pulse voltage for writing were optimized. As a result, actual data containing 64×64 bits were recorded at an areal density of 4 Tbit∕in.(2). The bit error rate was evaluated to be 1.2×10(-2).
 
Article
The bullfrog sacculus contains mechanically sensitive hair cells whose stereociliary bundles oscillate spontaneously when decoupled from the overlying membrane. Steady-state offsets on the resting position of a hair bundle can suppress or modulate this native motility. To probe the dynamics of spontaneous oscillation in the proximity of the critical point, we describe here a method for mechanical actuation that avoids loading the bundles or contributing to the viscous drag. Magnetite beads were attached to the tips of the stereocilia, and a magnetic probe was used to impose deflections. This technique allowed us to observe the transition from multi-mode to single-mode state in freely oscillating bundles, as well as the crossover from the oscillatory to the quiescent state.
 
Article
We present a method for the numerical correction of optical aberrations based on indirect sensing of the scattered wavefront from point-like scatterers ("guide stars") within a three-dimensional broadband interferometric tomogram. This method enables the correction of high-order monochromatic and chromatic aberrations utilizing guide stars that are revealed after numerical compensation of defocus and low-order aberrations of the optical system. Guide-star-based aberration correction in a silicone phantom with sparse sub-resolution-sized scatterers demonstrates improvement of resolution and signal-to-noise ratio over a large isotome. Results in highly scattering muscle tissue showed improved resolution of fine structure over an extended volume. Guide-star-based computational adaptive optics expands upon the use of image metrics for numerically optimizing the aberration correction in broadband interferometric tomography, and is analogous to phase-conjugation and time-reversal methods for focusing in turbid media.
 
Color The comparison of relative permittivity a and dielectric loss b of the Y = 20: 1 Al / PVDF, Al micrometer / PVDF, and Al nano composites.
Comparison of the experimental and modified model values of the thermal conductivity from different volume fraction of the      Al  ∗  / PVDF    composites.
The comparison of relative permittivity (a) and dielectric loss (b) of the    Y = 20 : 1        Al  ∗  / PVDF   ,      Al  ∗   (  micrometer  )  / PVDF   , and      Al  ∗   (  nano  )     composites.
The thermal conductivity and schematic particle distributions of      Al  ∗  / PVDF    composites as a function of the volume proportion of micrometer size and nanometer size      Al  ∗     filler measured at room temperature.
SEM micrographs of the      Al  ∗  / PVDF    composite with    Y = 20 : 1    and TEM micrographs (the inset of Fig. 1) of the passivation layer thickness of microsize      Al  ∗     particle.
Article
A polymer composite was prepared by embedding fillers made of self-passivated aluminum particles in two kind of sizes, micrometer size and nanometer size with different volume proportions into polyvinylidene fluoride matrix. The thermal conductivity and dielectric properties of the composite were studied. The results showed that the thermal conductivity of composites was significantly increased to 3.258 W∕mK when the volume proportion of micrometer size Al particles to nanometer size Al particles is at 20:1, also the relative permittivity was about 75.8 at 1 MHz. The effective simulation model values were in good accordance with experimental results.
 
Article
Nanomechanical motion of bacteria adhered to a chemically functionalized silicon surface is studied by means of a microcantilever. A non-specific binding agent is used to attach Escherichia coli (E. coli) to the surface of a silicon microcantilever. The microcantilever is kept in a liquid medium, and its nanomechanical fluctuations are monitored using an optical displacement transducer. The motion of the bacteria couples efficiently to the microcantilever well below its resonance frequency, causing a measurable increase in the microcantilever fluctuations. In the time domain, the fluctuations exhibit large-amplitude low-frequency oscillations. In corresponding frequency-domain measurements, it is observed that the mechanical energy is focused at low frequencies with a 1/f(α) -type power law. A basic physical model is used for explaining the observed spectral distribution of the mechanical energy. These results lay the groundwork for understanding the motion of microorganisms adhered to surfaces and for developing micromechanical sensors for bacteria.
 
Article
With a lipid shell containing biotin, micron-sized bubbles bound to avidin on a porous and flexible cellulose boundary were insonified by ultrasound. The oscillation of these targeted microbubbles was observed by high-speed photography and compared to the oscillation of free-floating microbubbles. Adherent microbubbles were observed to oscillate asymmetrically in the plane normal to the boundary, and nearly symmetrically in the plane parallel to the boundary, with a significantly smaller maximum expansion in each dimension for bound than free bubbles. With sufficient transmitted pressure, a jet was produced traveling toward the boundary.
 
Article
In the present study we engineered a micro-machined polyimide cantilever with an embedded sensing element to investigate cellular adhesion, in terms of its relative ability to stick to a cross-linker, 3,3'-dithiobis[sulfosuccinimidylpropionate], coated on the cantilever surface. To achieve this objective, we investigated adhesive properties of three human prostate cancer cell lines, namely, a bone metastasis derived human prostate cancer cell line (PC3), a brain metastasis derived human prostate cancer cell line (DU145), and a subclone of PC3 (PC3-EMT14). We found that PC3-EMT14, which displays a mesenchymal phenotype, has the least adhesion compared to PC3 and DU145, which exhibit an epithelial phenotype.
 
A sketch of the experimental setup is shown. RLC resonator consisting of a parallel plate capacitor and multi-turn solenoid allows for placing the sample in uniform electric or magnetic rf fields. 
Temperature vs. time dependence of 30 nm silica particles in water suspension and in 2% w/v albumin solution is shown. Respective dependencies of control samples such as 2% albumin only solution and DI water are 
Slopes for temperature rise vs. albumin concentrations adsorbed on 
Components of overall rf loss which is converted into heat in the case of SiO 2 /albumin water suspension.
Surface plot of SAR (which is proportional to effective conductivity) of silica NPs is shown as a function of silica size and albumin concentration.
Article
Measurements of specific-absorption-rate (SAR) of silica 30, 50, and 100 nm nanoparticles (NP) suspended in water were carried out at 30 MHz in 7 kV/m radio-frequency (rf) electric field. Size dependent, NP-suspension interface related heating of silica NP was observed. To investigate a possible mechanism of heating, bovine serum albumin was adsorbed on the surface of silica NPs in suspension. It resulted in significant enhancement of SAR when compared to bare silica NPs. A calorimetric and rf loss model was used to calculate effective conductivity of silica NP with/without adsorbed albumin as a function of silica size and albumin concentration.
 
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We study the adsorption of gold nanospheres onto cylindrical and spherical glass surfaces from quiescent particle suspensions. The surfaces consist of tapers and microspheres fabricated from optical fibers and were coated with a polycation, enabling irreversible nanosphere adsorption. Our results fit well with theory, which predicts that particle adsorption rates depend strongly on surface geometry and can exceed the planar surface deposition rate by over two orders of magnitude when particle diffusion length is large compared to surface curvature. This is particularly important for plasmonic sensors and other devices fabricated by depositing nanoparticles from suspensions onto surfaces with non-trivial geometries.
 
Article
This letter describes an experimental test of a simple argument that predicts the scaling of chaotic mixing in a droplet moving through a winding microfluidic channel. Previously, scaling arguments for chaotic mixing have been described for a flow that reduces striation length by stretching, folding, and reorienting the fluid in a manner similar to that of the baker's transformation. The experimentally observed flow patterns within droplets (or plugs) resembled the baker's transformation. Therefore, the ideas described in the literature could be applied to mixing in droplets to obtain the scaling argument for the dependence of the mixing time, t~(aw/U)log(Pe), where w [m] is the cross-sectional dimension of the microchannel, a is the dimensionless length of the plug measured relative to w, U [m s(-1)] is the flow velocity, Pe is the Péclet number (Pe=wU/D), and D [m(2)s(-1)] is the diffusion coefficient of the reagent being mixed. Experiments were performed to confirm the scaling argument by varying the parameters w, U, and D. Under favorable conditions, submillisecond mixing has been demonstrated in this system.
 
Color online Semilogarithmic plot of excitation emission spectra of HSA in a a buffer solution and b in a buffer solution treated with lead Pb 2+ =10 pM.
Article
Comprehensive analysis of fluorescence of albumin shows a weak fluorescence band at 430 nm, whose intensity exhibits a remarkable sensitivity to the presence of heavy ions in water. Using this fluorescence as a marker, as low as 10 pM concentration of lead can be routinely detected. Such a great sensitivity is explained in terms of electrostatic interactions in solution, which promote protein agglomeration. The latter is independently confirmed using dynamic light scattering measurements. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3246792]
 
Article
AlGaN/GaN high electron mobility transistors (HEMTs) were used to measure electrical characteristics of physisorbed gold nanoparticles (Au NPs) functionalized with alkanethiols with a terminal methyl, amine, or carboxyl functional group. Additional alkanethiol was physisorbed onto the NP treated devices to distinguish between the effects of the Au NPs and alkanethiols on HEMT operation. Scanning Kelvin probe microscopy and electrical measurements were used to characterize the treatment effects. The HEMTs were operated near threshold voltage due to the greatest sensitivity in this region. The Au NP/HEMT system electrically detected functional group differences on adsorbed NPs which is pertinent to biosensor applications.
 
(a) Top: Schematics of the growth cone adhesion to the asymmetric nanotextured surface, where β is the angle of the tilted nanorods. The axons extend preferentially in a direction opposite to the direction of the tilted nanorods. The direction of growth is defined as the reference direction (i.e., the 0 radians direction) for the analysis presented in the paper. Fluorescence (middle) and bright field (bottom) images of two different cells growing on the surface are also shown. The length of the axon shown in the figure is 60 microns. (b) Scanning electron microscopy (top) and atomic force microscope (bottom) image of the surface.
Ensembles of 100 trajectories generated from a biased, symmetric (δ = κ = 0) and asymmetric random walk for various values of bias parameter κ and azimuthal anisotropy parameter δ. Starting points are indicated with white circles.
(a) The direction of axon is shown in a schematic as the direction opposite to the direction of the nanotextured surface. Angular distributions for neural growth at (b) glass surface (control), (c) 2000 cells/cm2, (d) 6000 cells/cm2, and (e) 25 000 cells/cm2. All angles are measured with respect to this direction. All plots on (c)-(e) are on the same vertical scale. The bins at π radians for each histogram shown in the middle column collect axon counts from the bins at π and −π of the corresponding histogram shown in third column. The data show weaker preferential growth in the direction of the nanotextured surface (θ = π) than in the opposite direction (θ = 0). Solid lines in the right hand column histograms represent theoretical fits using a model of Brownian motion in constant field.
Article
Axonal growth and the formation of synaptic connections are key steps in the development of the nervous system. Here we present experimental and theoretical results on axonal growth and interconnectivity in order to elucidate some of the basic rules that neuronal cells use for functional connections with one another. We demonstrate that a unidirectional nanotextured surface can bias axonal growth. We perform a systematic investigation of neuronal processes on asymmetric surfaces and quantify the role that biomechanical surface cues play in neuronal growth. These results represent an important step towards engineering directed axonal growth for neuro-regeneration studies.
 
The SEM image of a 50 nm thick aluminum bow-tie antenna which is formed by two equilateral triangles of 100 nm side length with 20 nm apex to apex gap distance.
Article
An aluminum bow-tie nano-antenna is combined with the resonance Raman effect in the deep ultraviolet to dramatically increase the sensitivity of Raman spectra to a small volume of material, such as benzene used here. We further demonstrate gradient-field Raman peaks for several strong infrared modes. We achieve a gain of [Formula: see text] in signal intensity from the near field enhancement due to the surface plasmon resonance in the aluminum nanostructure. The on-line resonance enhancement contributes another factor of several thousands, limited by the laser line width. Thus, an overall gain of hundreds of million is achieved.
 
Article
Photoacoustic spectrum (PA) analysis (PASA) has been found to have the ability to identify the microstructures in phantoms and biological tissues. PASA adopts the procedures in ultrasound spectrum analysis, although the signal generation mechanisms related to ultrasound backscatter and PA wave generation differ. The purpose of this study was to theoretically validate PASA. The analytical solution to the power spectrum of PA signals generated by identical microspheres following discrete uniform random distribution in space was derived. The simulation and experiment validation of the analytical solution include: (i) the power spectrum profile of a single microsphere with a diameter of 300 μm, and (ii) the PASA parameters of the PA signals generated by randomly distributed microspheres 100, 200, 300, 400 and 500 μm in diameter, at concentrations of 30, 60, 120, 240, 480 per 1.5(3) cm(3) in the observation range 0.5-13 MHz. Copyright © 2015 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.
 
Simulated source and gate pressure profiles of valve 2 at the onset of oscillation. Q i is 2 μl/min. Gray region corresponds to valve 2-on state. Atthe bottom panel, P SG-min is a minimum value of P S − P G. If P SG-min is >P th-close at the moment of valve 1-on to valve 2 off, valve 2 stays on. As a result, both valves are on and oscillation stops.
Microfluidic oscillator with two membrane valves. (a) Cross-section of a microfluidic valve showing its on- and off-conditions. P S, P G, and P D are pressures at the source (S), drain (D), and gate (G) terminals, respectively. P th-open and P th-close are opening and closing threshold pressures, respectively. (b) Schematic of the oscillator consisting of two microfluidic membrane valves. The valve has S, D, and inlet and outlet gate terminals (Gi and Go). Gray and blue areas represent the bottom and top channels of the oscillator, respectively. R c and R d are connection and downstream resistance, respectively. (c) Schematic showing oscillating and non-oscillating outflows. The oscillating and non-oscillating outflows are determined by R d/R c and theinflow rate (Q i). Constant Q i is provided by a syringe pump (enhancedonline). [URL: http://dx.doi.org/10.1063/1.4769985.1] [URL: http://dx.doi.org/10.1063/1.4769985.2]10.1063/1.4769985.110.1063/1.4769985.2
Article
This paper reveals a critical limitation in the electro-hydraulic analogy between a microfluidic membrane-valve (μMV) and an electronic transistor. Unlike typical transistors that have similar on and off threshold voltages, in hydraulic μMVs, the threshold pressures for opening and closing are significantly different and can change, even for the same μMVs depending on overall circuit design and operation conditions. We explain, in particular, how the negative values of the closing threshold pressures significantly constrain operation of even simple hydraulic μMV circuits such as autonomously switching two-valve microfluidic oscillators. These understandings have significant implications in designing self-regulated microfluidic devices.
 
(Color online) The optical absorption curves of (a, a 0 ) pure, (b, b 0 ) Si-doped, (c, c 0 ) Eu-doped, (d, d 0 ) Eu/Si-codoped TiO 2. The left and right figures represent the absorption spectra obtained by calculations and experiments, respectively.
(Color online) Calculated TDOS and PDOS of different doped TiO2. The top of the valence band of pure anatase TiO2 is taken as the reference level. Curves above and below the horizontal axis refer to the up-spin and down-spin DOS, respectively.
(Color online) (a) 48-atom supercell model for defective anatase TiO2 shows the location of the dopants. The atom doping sites are marked with Eu and Si. The gray spheres and red spheres represent the Ti and O atoms, respectively. The blue sphere and purple sphere represent Eu and Si atoms, respectively. (b) XRD patterns for the pure and doped TiO2.
Article
The electronic and optical properties of Eu/Si-codoped anatase TiO(2) are investigated using the density functional theory. The calculated results show that the synergistic effects of Eu/Si codoping can effectively extend the optical absorption edge, which can lead to higher visible-light photocatalytic activities than pure anatase TiO(2). To verify the reliability of our calculated results, nanocrystalline Eu/Si-codoped TiO(2) is prepared by a sol-gel-solvothermal method, and the experimental results also indicate that the codoping sample exhibits better absorption performance and higher photocatalytic activities than pure TiO(2).
 
Article
A Talbot-Lau interferometer is demonstrated using micro-periodic gratings inclined at a glancing angle along the light propagation direction. Due to the increase in the effective thickness of the absorption gratings, the device enables differential phase contrast imaging at high x-ray energy, with improved fringe visibility (contrast). For instance, at 28° glancing angle, we obtain up to ∼35% overall interferometer contrast with a spectrum having ∼43 keV mean energy, suitable for medical applications. In addition, glancing angle interferometers could provide high contrast at energies above 100 keV, enabling industrial and security applications of phase contrast imaging.
 
SEM images (obtained from the central area in the 1 Â 1-cm ITO films) of the periodic (a) nanodot and (b) nanoline structures induced by fs laser pulses with fluences (pulse numbers) of F ¼ 0.1 mJ/cm 2 (N ¼ 3 Â 10 6 ) and 0.2 mJ/cm 2 (N ¼ 2 Â 10 7 ), respectively. The red-square insets show the 2D Fourier-transformed patterns and their cross-sectional profiles at locations corresponding to (a) and (b). The arrows indicate the direction of the laser polarization. The size distribution of particles for (c) nanodot structure in (a) and (d) nanoline structure in (b). The solid lines show the fitting curves using a log-normal function.
(a) The optical transmission spectra of as-deposited ITO and fs laser-treated films with two types of nanostructures (nanodot and nanoline); the corresponding SEM images are shown in Figs. 1(a) and 1(b). The inset shows a schematic illustration of the two forms of polarized light (P V and 
b). This dichroic or anisotropic transmission property of the fs laser-treated ITO films can be attributed to the laser-induced periodic nanostructures on their surfaces. The inset of a) shows a schematic illustration for the dichroic optical property of fs laser-treated ITO films with a nanoline structure. The fs laser-treated ITO film blocks the vertically polarized light (P V ), which is parallel to the long 
(a) The optical transmission spectra of as-deposited ITO and fs laser-treated films with two types of nanostructures (nanodot and nanoline); the corresponding SEM images are shown in Figs. 1(a) and 1(b). The inset shows a schematic illustration of the two forms of polarized light (PV and PH) passing through a fs laser-treated ITO film. L: the direction of nanolines. (b) The extinction ratio (T L⊥P/T L//P) for the fs laser treated films with nanodot and nanoline structures. T L⊥P (T L//P) is the transmittance in the configuration, L⊥P (L//P).
(a) The first derivative (dN/dE) of AES peaks, In(MNN), Sn(MNN), and O(KLL), measured for an as-deposited ITO film and a fs laser treated ITO film with a nanoline structure. The point A (outside a nanoline) and point B (inside a nanoline) correspond to the arrows marked in (b), the SEM image of a fs laser treated ITO film. The inset shows the ratio of the areas of the as-deposited (A-area) region and the nanoline (B-area) region.
Article
Two types of periodic nanostructures, self-organized nanodots and nanolines, were fabricated on the surfaces of indium-tin-oxide (ITO) films using femtosecond laser pulse irradiation. Multiple periodicities (approximately 800 nm and 400 nm) were clearly observed on the ITO films with nanodot and nanoline structures and were identified using two-dimensional Fourier transformation patterns. Both nanostructures show the anisotropic transmission characteristics in the visible range, which are strongly correlated with the geometry and the metallic content of the laser-induced nanostructures.
 
Top-cited authors
Steven Denbaars
  • University of California, Santa Barbara
James Speck
  • University of California, Santa Barbara
T. Venkatesan
  • National University of Singapore
H. Morkoç
  • Virginia Commonwealth University
Asif Khan
  • University of South Carolina