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In this study, the surface acoustic wave device combined with an oscillator circuit was used as the excitation platform to explore the photoluminescence responses of the two-dimensional atomic layers of MoS2. The MoS2 layers were prepared using the mechanical exfoliation method, and then transferred onto the SAW delay line area of the platform. Under the varied servo driving voltages of the excitation platform, various power intensities of the oscillator were obtained. It represented that the various energy levels of acoustic waves were propagated underneath the MoS2 layers. From the observation by multiphoton excitation microscopy, the excited fluorescent intensities of the MoS2 species were detected at various levels. Studies have proved that as the driving voltage of the oscillator increases, the interaction between the MoS2 species and the acoustic wave is also enhanced. [ABSTRACT FROM AUTHOR]

A flat plate in the deposition stage is designed to be tilted flexibly to form an inclination angle (θ) between an ion beam and the direction normal to a polyethylene terephthalate ( PET) substrate. Five kinds of PET/aluminum-doped zinc oxide specimens were prepared to examine the effects of inclination angle on the microstructures, crystals, chemical compositions, and electrical properties. An increase in the inclination angle results in X-ray diffraction peak intensity variations in ZnO and a reduction in the composite d-spacing. As the measure of the oxygen vacancies, the O2-peak intensity ratio ( IRO2) obtained using the X-ray photoelectron spectrometry ( XPS) is evaluated. The IRO2 value increased with increasing the inclination angle, and it is proportional to the porosity integration over the visible light wavelengths. An increase in IRO2 is favorable for the reduction in composite grain size ( gComposite). A smaller composite grain size ( gComposite) of ZnO particles and a larger energy gap (Eg) can be obtained from applications of nonzero inclination angle. An appropriate nonzero inclination angle increases hardness and reduced elastic modulus and decreases the carrier concentration and carrier mobility of the specimen significantly. [ABSTRACT FROM AUTHOR]

TiO2/poly(ethylene terephthalate) ( PET) specimens with various PET substrate prestrains are prepared to investigate the effect of the deposition conditions of the TiO2 film on the geometries of TiO2 film porosities and the effect of these void geometries on three optical parameters. The response surface methodology is used to express these three geometric parameters and three optical parameters as functions of the substrate prestrain and four deposition parameters. An increase in the O2/Ar flow ratio increases the mean width of voids. The trends of the curved surface of optical transmittance with L* and L*/ W* are opposite to those of reflection. The highest transmittance is obtained with the largest L*/ W* and the smallest L*. A nonzero flow rate of O2 gas in the deposition process reduces the optical band gap and increases the TiO2 film thickness generally, thus resulting in a reduction in transmittance and an increase in absorption. An increase in the prestrain of the PET substrate decreases the TiO2 film thickness. Both the mean index of refraction ( n)mean and the mean extinction coefficient ( k)mean due to the provision of the O2 gas are reduced. The n and k parameters for various wavelengths vary in a narrow range. [ABSTRACT FROM AUTHOR]

Abstract: A mold is designed to create a prestrain in a poly(ethylene terephthalate) (PET) substrate before the deposition of TiO2 film to imitate the deposition process on a cylindrical partial-arc drum. Four prestrain levels, namely 0%, 2%, 4%, and 6%, are adopted in the preparation of TiO2/PET specimens to investigate their effects on the stress/strain formed in the PET substrate and the film morphology. The contact pressure distribution between the PET substrate and the partial-arc drum is first theoretically derived as the boundary condition. Finite element analyses for stress/strain in the PET substrate are then carried out. A significant increase in the average stress/strain is produced by increasing the prestrain of the PET substrate. The increase in the prestrain leads to a decrease of the contact angle and an increase of the mean size of the TiO2 particles deposited at the interface of the TiO2 film and the PET substrate. The mean length (L ⁎) and width (W ⁎) of the voids in the TiO2/PET specimens strongly depend on the specimen position. An increase in the prestrain, and thus the mean stress/strain, results in a nonlinear increase in the mean width and length of voids. The porosity pattern shows that the average slenderness ratio (average L ⁎/W ⁎ value) of voids increases with decreasing average tilt angle ( ) of the lateral surfaces in the porous TiO2 film. Slimmer voids generally form with a larger void depth. The light absorption (Ab) significantly increases when the prestrain is increased from 0% to 2%; it then becomes asymptotic to a constant value as the prestrain is further increased. The reflectance decreases slightly with increasing substrate prestrain. If is fixed, the absorption decreases with increasing average slenderness ratio of voids. The reflectance behavior is exactly opposite to that of the absorption. [Copyright &y& Elsevier]

Interest in bringing p- and n-type monolayer semiconducting transition metal dichalcogenides (TMD) into contact to form rectifying pn diode has thrived since it is crucial to control the electrical properties in two-dimensional (2D) electronic and optoelectronic devices. Usually this involves vertically stacking different TMDs with pn heterojunction or, laterally manipulating carrier density by gate biasing. Here, by utilizing a locally reversed ferroelectric polarization, we laterally manipulate the carrier density and created a WSe2 pn homojunction on the supporting ferroelectric BiFeO3 substrate. This non-volatile WSe2 pn homojunction is demonstrated with optical and scanning probe methods and scanning photoelectron micro-spectroscopy. A homo-interface is a direct manifestation of our WSe2 pn diode, which can be quantitatively understood as a clear rectifying behavior. The non-volatile confinement of carriers and associated gate-free pn homojunction can be an addition to the 2D electron-photon toolbox and pave the way to develop laterally 2D electronics and photonics. Bringing together p- and n-type monolayers of semiconducting transition metal dichalcogenides results in the formation of atomically thin pn junctions. Here, the authors laterally manipulate carrier density to create a WSe2 pn homojunction on a supporting ferroelectric BiFeO3 substrate. [ABSTRACT FROM AUTHOR]

Abstract: A mold is designed to create various pre-strain levels in poly(ethylene) terephthalate (PET) substrates before the deposition of TiO2 film to imitate the deposition process on a cylindrical drum. Four pre-strain levels, namely 0%, 2%, 4%, and 6%, are used in the preparations of TiO2/PET specimens to investigate the effects of pre-strain on the film morphology and the stress/strain formed in the PET substrate on the contact angle. Finite element analyses for stress/strain in the PET substrate are carried out, including that for the contact pressure distribution over the contact surface between the PET substrate and the partial-arc cylindrical drum. A significant increase in the stress/strain is produced with increasing pre-strain of the PET substrate. The mean length and width of the voids formed in the TiO2/PET specimens strongly depend on the specimen position. An increase in the pre-strain, and thus the stress/strain, results in an increase of the mean width and length of voids. The contact angle increases with decreasing stress/strain of the PET substrate. An increase in the pre-strain of the PET substrate leads to a reduction in the contact angle. Bent PET specimens have wavier surface profiles compared to that of the as-received PET. The mean amplitude value decreases with increasing pre-strain. The effect of stress on the contact angle formed on the wavy surface can be explained by the Wenzel equation. The decrease in the contact angle can enhance the absorption of the TiO2 film, and thus increase the distance between two adjacent valleys in the porous TiO2 film. The extrusions/intrusions in the porous PET after bending and the different stress/strain distributions over the PET substrate cause drastic changes in the local morphology of the TiO2/PET specimen. [Copyright &y& Elsevier]

Interest in bringing p- and n-type monolayer semiconducting transition metal dichalcogenides (TMD) into contact to form rectifying pn diode has thrived since it is crucial to control the electrical properties in two-dimensional (2D) electronic and optoelectronic devices. Usually this involves vertically stacking different TMDs with pn heterojunction or, laterally manipulating carrier density by gate biasing. Here, by utilizing a locally reversed ferroelectric polarization, we laterally manipulate the carrier density and created a WSe 2 pn homojunction on the supporting ferroelectric BiFeO 3 substrate. This non-volatile WSe 2 pn homojunction is demonstrated with optical and scanning probe methods and scanning photoelectron micro-spectroscopy. A homo-interface is a direct manifestation of our WSe 2 pn diode, which can be quantitatively understood as a clear rectifying behavior. The non-volatile confinement of carriers and associated gate-free pn homojunction can be an addition to the 2D electron-photon toolbox and pave the way to develop laterally 2D electronics and photonics.

This study focused on the fabrication and the theoretical analysis of solidly mounted resonators (SMR) concerning dual-mode frequency responses and their frequency shift of bulk acoustic wave (BAW) resonance. For this device fabrication, RF/DC magnetron sputtering and photolithography were employed to constitute the required multilayer structure. For the theoretical analysis, the dualmode frequency shift was characterized by the Sauerbrey's formula, and a modified formula was carried out following the trend for the large frequency shift. In the fabrication of the SMR device, Mo/SiO2 was chosen to construct the Bragg reflector as the high/low acoustic impedance materials, respectively, and aluminum nitride (AlN) was used as a piezoelectric layer. To investigate the characteristics of BAW on the dual-mode frequency shift, the c-axis tilted angle of AlN was altered as well as the various mass loading on the SMR. Based on the experimental results, the dual-resonance frequencies showed a nonlinear decreasing trend with a linear increase of the mass loading. Therefore, a modified formula was carried out. Furthermore, the ratio of the longitudinal-resonant frequency to the shear-resonant frequency remained at a range around 1.76 despite the various c-axis tilted angles of AlN and gradual mass loading on the SMR. The electromechanical coupling coefficient, k2(eff), of the shear resonance rose with the increase of the c-axis tilted angle of AlN.