Development of a 20-MHz wide-bandwidth PMN-PT single crystal phased-array ultrasound transducer.

In this study, a 20-MHz 64-element phased-array ultrasound transducer with a one-wavelength pitch is developed using a PMN-30%PT single crystal and double-matching layer scheme. High piezoelectric (d33>1000pC/N) and electromechanical coupling (k33>0.8) properties of the single crystal with an optimized fabrication process involving the photolithography technique have been demonstrated to be suitable for wide-bandwidth (⩾70%) and high-sensitivity (insertion loss ⩽30dB) phased-array transducer application. A -6dBbandwidth of 91% and an insertion loss of 29dBfor the 20-MHz 64-element phased-array transducer were achieved. This result shows that the bandwidth is improved comparing with the investigated high-frequency (⩾20MHz) ultrasound transducers using piezoelectric ceramic and single crystal materials. It shows that this phased-array transducer has potential to improve the resolution of biomedical imaging, theoretically. Based on the hypothesis of resolution improvement, this phased-array transducer is capable for small animal (i.e. mouse and zebrafish) studies.

Suppressing the Coffee-Ring Effect in Semitransparent MnO2 Film for a High-Performance Solar-Powered Energy Storage Window.

We introduce a simple and effective method to deposit a highly uniform and semitransparent MnO2 film without coffee-ring effect (CRE) by adding ethanol into MnO2 ink for transparent capacitive energy storage devices. By carefully controlling the amount of ethanol added in the MnO2 droplet, we could significantly reduce the CRE and thus improve the film uniformity. The electrochemical properties of supercapacitor (SC) devices using semitransparent MnO2 film electrodes with or without CRE were measured and compared. The SC device without CRE shows a superior capacitance, high rate capability, and lower contact resistance. The CRE-free device could achieve a considerable volumetric capacitance of 112.2 F cm(-3), resulting in a high volumetric energy density and power density of 10 mWh cm(-3) and 8.6 W cm(-3), respectively. For practical consideration, both flexible SC and large-area rigid SC devices were fabricated to demonstrate their potential for flexible transparent electronic application and capacitive energy-storage window application. Moreover, a solar-powered energy storage window which consists of a commercial solar cell and our studied semitransparent MnO2-film-based SCs was assembled. These SCs could be charged by the solar cell and light up a light emitting diode (LED), demonstrating their potential for self-powered systems and energy-efficient buildings.

Low voltage and high ON/OFF ratio field-effect transistors based on CVD MoS2 and ultra high-k gate dielectric PZT.

MoS2 and other atomic-level thick layered materials have been shown to have a high potential for outperforming Si transistors at the scaling limit. In this work, we demonstrate a MoS2 transistor with a low voltage and high ON/OFF ratio. A record small equivalent oxide thickness of ∼1.1 nm has been obtained by using ultra high-k gate dielectric Pb(Zr0.52Ti0.48)O3. The low threshold voltage (<0.5 V) is comparable to that of the liquid/gel gated MoS2 transistor. The small sub-threshold swing of 85.9 mV dec(-1), the high ON/OFF ratio of ∼10(8) and the negligible hysteresis ensure a high performance of the MoS2 transistor operating at 1 V. The extracted field-effect mobility of 1-10 cm(2) V(-1) s(-1) suggests a high crystalline quality of the CVD-grown MoS2 flakes. The combination of the two-dimensional layered semiconductor and the ultra high-k dielectric may enable the development of low-power electronic applications.

Morphology-controlled synthesis of self-assembled LiFePO4/C/RGO for high-performance Li-ion batteries.

Novel architectured LiFePO4 (LFP) that consisted of ordered LFP nanocubes was prepared through a facile hydrothermal method using polyethylene glycol (PEG) as a surfactant. The micro/nanostructured LFP with various morphologies ranging from cube cluster to rugby-like structure was synthesized via controlling the pH values of the precursor. A reasonable assembly process elucidating the formation of the hierarchical structure is also provided based on the experimental results. After a combination of carbon (C) coating and reduced graphene oxide (RGO) wrapping, the obtained LFP/C/RGO composites exhibit enhanced electrochemical performance compared to that of blank LFP synthesized under the same condition. Among as-synthesized cube-cluster-like, dumbbell-like, rod-like, and rugby-like composites, the rugby-like LFP/C/RGO reveal the best electrochemical properties with the discharge specific capacity of ∼150 mA h g(-1) after 100 cycles and a high reversible specific capacity of 152 mA h g(-1) at 0.1 C. The prepared LFP/C/RGO composite can be a promising cathode material for high energy, low cost, and environmentally friendly lithium-ion batteries.

Highly sensitive gas sensor by the LaAlO3 /SrTiO3 heterostructure with Pd nanoparticle surface modulation.

The palladium nanoparticle (Pd NP)-decorated LaAlO3 /SrTiO3 (LAO/STO) heterostructure is for the first time used as a hydrogen-gas sensor with very high sensitivity and workability at room temperature. The outstanding gas-sensing properties are due to the Pd NPs' catalytic effect to different gases, resulting in charge coupling between the gas molecules and the two-dimensional electron gas (2DEG) through the Pd NPs by either a direct charge exchange or a change of the electron affinity. These results provide insight into the emerging properties at LAO/STO interfaces.

Broad-band and high-temperature ultrasonic transducer fabricated using a Pb(In(1∕2)Nb(1∕2))-Pb(Mg(1∕3)Nb(2∕3))-PbTiO3 single crystal∕epoxy 1-3 composite.

In this paper, 1-3 composites based on Pb(In(1∕2)Nb(1∕2))-Pb(Mg(1∕3)Nb(2∕3))-PbTiO(3) (PIMNT) single crystal and high-temperature epoxy were fabricated with various volume fractions of PIMNT single crystal ranging from 0.4 to 0.9. The electrical properties were studied as functions of PIMNT volume fraction and temperature, and it revealed that the nature of ultrahigh electromechanical coupling coefficient (0.82-0.93) and low acoustic impedance (17-19 MRayl) of the composites can be retained within a wide temperature range from room temperature to 185 °C. Single element ultrasonic transducer using the PIMNT 1-3 composite was fabricated and characterized as a function of temperature. It was found that the transducer can still work normally at high temperatures, such as 165 °C, possessing a bandwidth of 95% and insertion loss of -27 dB.

Fabrication and performance of endoscopic ultrasound radial arrays based on PMN-PT single crystal/epoxy 1-3 composite.

In this paper, 0.7Pb(Mg(¹/3)Nb(²/3)O3-0.3PbTiO3 (PMN-PT) single crystal/epoxy 1/3 composite was used as the active material of the endoscopic ultrasonic radial array transducer, because this composite exhibited ultrahigh electromechanical coupling coefficient (k(t) = 0.81%), very low mechanical quality factor (Q(m) = 11) and relatively low acoustic impedance (Z(t) = 12 MRayls). A 6.91 MHz PMN-PT/epoxy 1/3 composite radial array transducer with 64 elements was tested in a pulseecho response measurement. The -6-dB bandwidth of the composite array transducer was 102%, which was ~30% larger than that of traditional lead zirconate titanate array transducer. The two-way insertion loss was found to be -32.3 dB. The obtained results show that this broadband array transducer is promising for acquiring high-resolution endoscopic ultrasonic images in many clinical applications.

Monitoring of dopamine release in single cell using ultrasensitive ITO microsensors modified with carbon nanotubes.

The study of single cell dynamics has been greatly adapted in biological and medical research and applications. In this work a novel microfluidic electrochemical sensor with carbon nanotubes (CNTs) modified indium tin oxide (ITO) microelectrode was developed for single cells release monitoring. The sensitivity of the electrochemical sensor after CNTs surface modification was improved by 2.5-3 orders of magnitude. The developed CNTs modified ITO sensor was successfully employed to monitor the dopamine release from single living rat pheochromocytoma (PC 12) cells. Its ultrahigh sensitivity, transparency and need for fewer agents enable this smart electrochemical sensor to become a powerful tool in recording dynamic release from various living tissues and organs optically and electrically.

Magnetic field-induced strain and magnetoelectric effects in sandwich composite of ferromagnetic shape memory Ni-Mn-Ga crystal and piezoelectric PVDF polymer.

A sandwich composite consisting of one layer of ferromagnetic shape memory Ni-Mn-Ga crystal plate bonded between two layers of piezoelectric PVDF polymer film was fabricated, and its magnetic field-induced strain (MFIS) and magnetoelectric (ME) effects were investigated, together with a monolithic Ni-Mn-Ga crystal, as functions of magnetic fields and mechanical load. The load-free dc- and ac-MFISs were 0.35 and 0.05% in the composite, and 5.6 and 0.3% in the monolithic crystal, respectively. The relatively smaller load-free MFISs in the composite than the monolithic crystal resulted from the clamping of martensitic twin-boundary motion in the Ni-Mn-Ga plate by the PVDF films. The largest ME coefficient (α(E)) was 0.58 V/cm·Oe at a magnetic bias field (H(Bias)) of 8.35 kOe under load-free condition. The mechanism of the ME effect originated from the mechanically mediated MFIS effect in the Ni-Mn-Ga plate and piezoelectric effect in the PVDF films. The measured α(E)-H(Bias) responses under different loads showed good agreement with the model prediction.

Towards pure near-infrared to near-infrared upconversion of multifunctional GdF(3):Yb(3+),Tm(3+) nanoparticles.

Nearly pure near-infrared to near-infrared (NIR-to-NIR) upconversion in GdF(3) host with 23% Yb(3+) and 1% Tm(3+) under 980 nm excitation is firstly reported. The ratio of the intensity of the emission at 807 nm to that at 478 nm can reach to 105, and the intensity of the emission at 807 nm is preserved. Moreover, the excitation and the emission at 980 and 807 nm are away from the visible region. These are beneficial to deeper tissue penetration and reduced autofluorescence. Raman spectroscopy measurements suggest the high probability of NIR emission in GdF(3) host. Our results indicate that the reported multifunctional nanoparticles are promising in bio-imaging and bio-separation.

All wavelengths and directions hybrid-guidance photonic crystal fiber and its property of Bragg grating resonance.

We propose a hybrid-guidance photonic crystal fiber (HG-PCF) that can guide light by the simultaneous effect of index guidance and photonic bandgap guidance at all wavelengths and directions. Index guidance is the dominant guidance mechanism at short wavelengths and photonic bandgap guidance is the dominant guidance mechanism at long wavelengths. The transmission spectrum of the Bragg grating in such a HG-PCF is also investigated.

Performances of one-dimensional sonomyography and surface electromyography in tracking guided patterns of wrist extension.

Electromyography (EMG) and ultrasonography have been widely used for skeletal muscle assessment. Recently, it has been demonstrated that the muscle thickness change collected by ultrasound during contraction, namely sonomyography (SMG), can also be used for assessment of muscles and has the potential for prosthetic control. In this study, the performances of one-dimensional sonomyography (1D SMG) and surface EMG (SEMG) signal in tracking the guided patterns of wrist extension were evaluated and compared, and the potential of 1D SMG for skeletal muscle assessment and prosthetic control was investigated. Sixteen adult normal subjects including eight males and eight females participated in the experiment. The subject was instructed to perform the wrist extension under the guidance of displayed sinusoidal, square and triangular waveforms at movement rates of 20, 30, 50 cycles per min. SMG and SEMG root mean squares (RMS) were collected from the extensor carpi radialis, respectively, and their RMS errors in relation to the guiding signals were calculated and compared. It was found that the mean RMS tracking errors of SMG under different movement rates were 18.9% +/- 2.6% (mean+/-SD), 18.3% +/- 4.5%, and 17.0% +/- 3.4% for sinusoidal, square and triangular guiding waveforms, while the corresponding values for SEMG were 30.3% +/- 0.4%, 29.0% +/- 2.7% and 24.7% +/- 0.7%, respectively. Paired t test showed that the RMS errors of SMG tracking were significantly smaller than those of SEMG. Significant differences in RMS tracking errors of SMG among the three movement rates (p<0.01) for all the guiding waveforms were also observed using one-way analysis of variance (ANOVA). The results suggest that SMG signal, based on further improvement, has great potential to be an alternative method to SEMG to evaluate muscle function and control prostheses.

Fabrication and characterization of epitaxial Ba0.7Sr0.3TiO3 thin films for optical waveguide applications.

The optical properties of barium strontium titanate (Ba0.7Sr0.3TiO3; BST) thin films are described. The BST thin films were epitaxially grown upon MgO (001) substrates by pulsed laser deposition. The crystallographic properties of the BST thin films were examined by x-ray diffraction. The BST thin films were highly optically transparent in the visible region. The optical waveguide properties were characterized by a prism coupling technique. An inverse-WBK method was employed to determine the refractive-index profile along the thickness of the BST films. Optical losses were measured by a moving fiber method, and the optical losses were found to be 0.93 dB/cm for the TE0 mode and 1.29 dB/cm for the TM0 mode at 1550 nm. Electro-optic (E-O) properties were measured by a phase-modulation detection method at 632.8 nm, and the BST films exhibited a predominantly quadratic E-O effect with a quadratic E-O coefficient of 6.64 x 10(-18) m2/V2.