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Here, we report the growth of (Sr, Ca) Nd2Fe2O7 single crystals with the Ruddlesden–Popper structure using an optical floating-zone method. A significantly anisotropic magneto-dielectric effect (MD), ab-plane and c-axial MD coefficients reaching −12.3% and −8.4% measured at 103 Hz in a 1 T magnetic field, can be obtained in a SrNd2Fe2O7 crystal at room temperature. The corresponding anisotropic MD ratio can be reached as high as 1.46. With an increase in the Ca concentration, the MD effect decreases dramatically and is eventually completely suppressed in both directions. Analysis of magnetic properties and 57Fe Mössbauer spectra suggests that the anisotropic MD effects in SrNd2Fe2O7 can be attributed to polaronic hopping between two neighboring Fe3+ ions through oxygen vacancies in an anisotropically antiferromagnetic matrix; the disappearance of the MD effect in Ca-doped SrNd2Fe2O7 is a consequence of the suppression of the antiferromagnetism. Our work suggests that the significantly anisotropic MD effect in SrNd2Fe2O7 crystals at room temperature can be used in magneto-dielectric controlled devices.

As an emerging approach to charge storage phosphors, upconversion charging (UCC) is attracting increased attention owing to its fundamental and practical perspectives. Despite the potential, further development of the UCC technology is restricted by the limited types of excitation light sources. Here, we use a white flashlight as excitation to investigate the UCC performance of storage phosphors. We demonstrate, as an example, that a Y3Al2Ga3O12:Pr3+ phosphor exhibits long-lasting emissions in the ultraviolet and visible regions after intense illumination from the flashlight. Thermoluminescence investigations reveal that both excited-state absorption and energy-transfer upconversion are involved in the UCC process. Based on the luminescence performance of the white-light charged phosphor, a conceptual thermometry approach is introduced, which can remotely sense the local temperature by monitoring the afterglow intensity ratio. Considering the wide use of flashlight, such a white-light excitability and the associated glow emission may potentially revolutionize the way to utilize storage phosphors.

Due to its attractive interaction with light, negative photoconductivity (NPC) has received widespread attention and has been used in optoelectronic logic devices with excellent performance. However, long negative response time triggered by photogenerated carriers trapping mechanism became a bottleneck in further application. Therefore, an enhanced strategy that can speed up negative response is urgently needed. Herein, we prepared a zinc oxide microwire (ZnO MW)–silver nanowires (Ag NWs)–methylammonium lead halide perovskite (CH3NH3PbBr3) heterostructure with enhanced negative response than the previous NPC device. The Ag NWs with high mobility at the interface of ZnO and CH3NH3PbBr3 accelerate the photoresponse time from 50 to 5.4 s and improve the dark current recovery time by two orders of magnitude. This work provides a strategy to improve the negative response speed with simple operation, which represents a step toward applications in the field of fast NPC optoelectronics.

Sound absorption is important for room acoustics and remediation of noise. Acoustic metamaterials have recently emerged as one of the most promising platforms for sound absorption. However, the working bandwidth is severely limited because of the strong dispersion in the spectrum caused by local resonance. Utilizing the coupling effect among resonators can improve the absorbers' performance, but the requirement of collecting coupling effects among all resonators, not only the nearest-neighbor coupling, makes the system too complex to explore analytically. This Letter describes deep learning based acoustic metamaterials for achieving broadband sound absorption with no visible oscillation in a targeted frequency band. We numerically and experimentally achieve an average absorption coefficient larger than 97% within the ultra-broadband extending from 860 to 8000 Hz, proving the validity of the deep learning based acoustic metamaterials. The excellent ultra-broadband and near-perfect absorption performance allows the absorber for versatile applications in noise-control engineering and room acoustics. Our work also reveals the significance of modulating coupling effects among resonators, and the deep learning approach may blaze a trail in the design strategy of acoustic functional devices.

Transition metal dichalcogenides (TMDs) have attracted broad interest in photonics owing to their unique electric band structures, which triggers various applications for functional devices. However, the optical absorbance of TMDs is relatively low because of the atomic-scale thickness, limiting further development of TMDs-based nonlinear optical devices. Here, we propose an effective method to enhance the nonlinear optical properties of TMDs using plasmons, which are from embedded silver (Ag) nanoparticles (NPs) inside the fused silica substrate. In such a configuration, the third-order nonlinear absorption coefficient of MoS2 with non-contact Ag NPs is one order of magnitude higher than that of pure monolayer MoS2 under excitation of 515 nm light, and at 1030 nm, the reverse saturable absorption switches to the saturable absorption due to the plasmonic implication. In addition, the mechanism of plasmon-enhanced nonlinear optical properties is confirmed by results of both transient absorption spectroscopy and near-field electromagnetic field simulation. This study on plasmon-enhanced third-order nonlinearity of MoS2 expands the boundaries of TMDs-based optical nonlinearity engineering.

Recently, ion-doped HfO2 thin films are highly desirable for the next-generation nonvolatile memories due to excellent compatibility with current complementary metal-oxide-semiconductor processes and robust ferroelectricity persisted down to the nanoscale. In this work, we study conduction mechanisms of 4 and 8 nm-thick La:HfO2 ultrathin films sandwiched between Pt and (La0.67,Sr0.33)MnO3 (LSMO) electrodes based on band alignments of the Pt/La:HfO2/LSMO, measured by x-ray photoelectron spectroscopy, and temperature-dependent current-voltage curves from 50 to 300 K. In a 4 nm-thick La:HfO2 thin-film capacitor, the conduction mechanism is found to be governed by direct tunneling at 50–100 K and phonon-assisted indirect tunneling when the temperature is further increased to 300 K in which the [Formula: see text] acceptors are served as localized states, facilitating hole hopping through the La:HfO2 barrier. When the thickness is increased to 8 nm, the tunneling through a La:HfO2 layer is suppressed, and the current-voltage character becomes rectifying, which is regulated by the dominated La:HfO2/LSMO interfacial barrier. The transport for a forward bias of the La:HfO2/LSMO barrier is found to be governed by thermionic-field emission, exhibiting a temperature-independent build-in potential of ∼2.77 V. For the reverse bias, the Fowler–Nordheim tunneling is observed. The revealing of conduction mechanisms in terms of band alignments sheds light on leakage problems and facilitates the design of HfO2-based ferroelectric devices with excellent insulating character for high-performance memory applications.

Efficient nonlinear frequency conversion, such as second-harmonic generation in ultracompact structures, is essential for the development of modern nanophotonic devices. Here, we demonstrate intense second-harmonic emission in scalable embedded Ag nanoparticle arrays fabricated by ion implantation into BK7 glass. The interparticle coupling effect significantly enhances the local field at the nanogap (gap size ∼1 nm) of two neighboring Ag nanoparticles and finally amplifies second-harmonic emission generated at the surface of plasmonic nanoparticles. Notably, the intensity of second-harmonic emission in embedded Ag nanoparticle arrays is comparable to that of two-dimensional transition metal dichalcogenides under the excitation of a fundamental wave at 1064 nm and independent of the incident polarization angles. Our work offers a promising strategy on the rapid fabrication of low-cost nonlinear optical nanostructures with great environmental stability. Published version This work was supported by National Natural Science Foundation of China (Grant No. 11535008) and Taishan Scholars Program of Shandong Province (No. tspd20210303).

Developing efficient methods for boosting light–matter interactions is critical to improve the functionalities of two-dimensional (2D) transition metal dichalcogenides toward next-generation optoelectronic devices. Here, we demonstrate that the light–matter interactions in tungsten disulfide (WS2) monolayer can be significantly enhanced by introducing an air-stable functional substrate (fused silica with embedded plasmonic Ag nanoparticles). Distinctive from conventional strategies, the Ag nanoparticles are embedded under the surface of fused silica via ion implantation, forming a functional substrate for WS2 monolayer with remarkably environmental stability. A tenfold photoluminescence enhancement in WS2 monolayer has been achieved due to the plasmonic effect of Ag nanoparticles. This work offers a strategy to fabricate the plasmon-2D hybrid system at low cost and large scale and paves the way for their applications in optoelectronics and photonics.

To explore the bandgap tunability in strain-compensated superlattices, we have grown a series of InAs/AlAs strain-compensated short-period superlattices (SPSs) with different period lengths by molecular beam epitaxy. Although the average indium composition of the InAs/AlAs SPS samples remains the same, the bandgaps of these SPSs measured by photoluminescence show a strong dependence on the period length, ranging from 1.41 to 1.01 eV as the period length varies from 4 ML to 10 ML. This fine control on the period length can extend the cutoff wavelength of this digital-alloy-like InAlAs (lattice matched to InP) material up to 1230 nm at room temperature. Multiple transitions are observed in Fourier transform infrared spectra, which agree well with the calculation and confirm the confinement in this structure. The strain effect in tuning the band structures and the band alignments is demonstrated, showing that longer period length together with smaller conduction band offset has led to the smaller effective bandgap of the InAs/AlAs SPS.

Understanding the interfacial charge transfer process and its dynamical mechanism is crucial to design efficient photoelectric devices. Methylammonium lead halide perovskite and zinc oxide (ZnO) have been demonstrated as promising candidates for excellent solar cells and photodetectors. However, the carrier transport process has not yet been fully explored on the perovskite surface and the perovskite/ZnO interface. Herein, a CH3NH3PbBr3-ZnO heterojunction was constructed as a quasi-phototransistor, where an apparent negative photoconductance was observed under illumination. Based on electrical and optical characterization, the photogenerated carrier transfer dynamics at CH3NH3PbBr3, ZnO, and their interface were investigated in detail. It can be assigned that the photogenerated electrons transfer toward the CH3NH3PbBr3 surface and the holes transfer to interior, so that the light-induced built-in electric field change would serve as the photogate to control the current flowing in the CH3NH3PbBr3-ZnO channel. These results provide clear images on the charge diffusion and drift process in the CH3NH3PbBr3-ZnO heterostructure. The study on the dynamics of negative photoconductivity of CH3NH3PbBr3-ZnO has great value for understanding the carrier transport properties and constructing perovskite heterostructure memory and optical switching devices.

We report on optical waveguides produced by a femtosecond laser in 6H–SiC crystals. Their guiding properties have been investigated at a wavelength of 1064 nm, and confocal micro-Raman images have been obtained at an excitation wavelength of 532 nm. The results demonstrate that mode profiles can be tailored by the adjustment of writing parameters, and the blueshift of the spectrum (at around 787.05 cm−1) mainly takes place in the irradiated areas. From images of Raman intensity and spectral shift, it is obvious that optical properties in guiding regions are well preserved. These waveguides may have potential applications in integrated optics and quantum photonics.

A series of reverberating shock experiments on the precompressed hydrogen-deuterium (H-D) mixture were performed by using a two-stage light gas gun, and an elaborately designed diagnostic configuration was presented to probe the multishock states of dense fluid H-D mixtures. The particular diagnostics allowed multiple physical parameters, including the equation of state (EOS), refractive index, reflectivity, molecular polarizability, and energy gap, of H-D mixtures under double-shock compression to be simultaneously determined in a single shot. The multiple parameters obtained provide a comprehensive evaluation for existing theoretical models from multiple perspectives. It is found that, compared with the semilocal Perdew–Burke–Ernzerhof xc functional, the EOS data predicted by a nonlocal van der Waals exchange-correlation (xc) functional (vdW-DF1) are in much better agreement with the experimental results. Furthermore, the commonly used Gladstone–Dale relation is not appropriate for describing the refractive index in high-pressure-temperature regions, and the refractive index and reflectivity can be well reproduced by the Heyd–Scuseria–Ernzerhof hybrid xc functional. These observations may provide insights into future theoretical developments and a better understanding of material properties under extreme pressure-temperature conditions.

The effects of epitaxial strain on the properties of 0.95(K0.49Na0.49Li0.02)(Ta0.2Nb0.8)O3-0.05CaZrO3 (KNNLT-CZ) thin films are investigated. La0.07Sr0.93SnO3 and SrRuO3 are used as bottom electrodes to provide in-plane tensile and compressive stress, respectively. Our results show that the La0.07Sr0.93SnO3-buffered KNNLT-CZ films are mostly strain-relaxed with an orthorhombic (O) and tetragonal (T) mixed phase and a tetragonality of 1.002, which have a twice remnant polarization (2Pr) of 14.29 μC/cm2, an effective piezoelectric strain coefficient (d33*) of ∼60 pm/V, and an O to T phase transition temperature (TO-T) of 140 °C, while the SrRuO3-buffered KNNLT-CZ films are only partially strain-relaxed with a pure O phase and a larger tetragonality of 1.011, resulting in an increased 2Pr value of 33.63 μC/cm2, an improved d33* value of ∼80 pm/V, and an enhanced TO-T value of 200 °C. Both films show a high Curie temperature above 380 °C and stable hysteresis loops from room temperature to 225 °C. These results highlight the feasibility to improve the performance of KNN-based materials via epitaxial strain.

Surface-enhanced Raman scattering (SERS) spectroscopy with unparalleled sensitivity for fingerprint detection of aromatic dyes is demonstrated by loading highly dense Au@Ag core/shell nanoparticles (NPs) on carbon nanotubes (CNTs). The Raman spectrum of crystal violet molecules adsorbed on the optimal CNT/Au@Ag NPs (8.4% Au and 8.6% Ag) can be distinguished as low as 10−14 M, achieving ultralow SERS detection. Besides electromagnetic enhancement originating from the Au@Ag core-shell, the strong electron-phonon coupling effect in CNTs is highlighted by the formation of more defects via doping bimetallic NPs, further improving SERS activity. Thus, this finding will offer a strategy for boosting SERS performance in widespread applications.

Spin relaxation properties of π-conjugated organic semiconductors are key indicators of the performance of organic spintronic devices. However, reliable determination of spin relaxation parameters in organic materials is hindered by complex interfacial phenomena at organic/ferromagnetic metal interfaces that couple spin injection with charge injection. Here, we study the spin pumping induced pure spin transport in Permalloy/rubrene/Pt trilayers and determine the spin diffusion length λs = 132 ± 9 nm and the spin relaxation time τs = 3.8 ± 0.5 ms in rubrene films at room temperature by using the inverse spin Hall effect. The determined spin diffusion length λs is found to be almost two times larger than that of ∼46.3 nm at 100 K extracted from rubrene spin valve devices in which charge carrier injection/detection occurs at organic/ferromagnetic metal interfaces. Our results demonstrate experimentally that the efficiency and the rate of spin polarized charge transport through the organic/ferromagnetic metal interface play a dominant role in determining the spin relaxation process of spin valve devices in which charge and spin currents are coupled.

Electron-electron (e-e) correlation and spin-orbit coupling (SOC) are two essential control parameters that determine the physical properties of transition-metal-oxide-based thin films and heterostructures. Here, by harnessing these two parameters, we report the systematic control of both ferromagnetism and in-plane magnetic anisotropy in La0.67Ca0.33MnO3/CaIr1-xRuxO3 (LCMO/CIRO) superlattices grown on NdGaO3 substrates. In these all-oxide epitaxial systems, we demonstrate that the e-e correlation and the SOC depend strongly on the chemical composition of CIRO layers. By simply increasing the Ru doping level x, we can significantly suppress the degradation of ferromagnetism in ultrathin LCMO layers and enhance the TC by ∼90 K. Moreover, we observe a clear reorientation of the magnetic easy axis from orthorhombic [010] to [100] as x decreased to 0, which may originate from the enhanced SOC. Our work provides an insight for utilizing the 4d/5d transition-metal-oxides to tune the functionality of magnetic heterostructures.

The intrinsically low thermal conductivity is fundamentally important for the development of high-performance thermoelectric and thermal insulating materials. Here, we observed ultra-low cross-plane thermal conductivities of naturally misfit layered single crystals Bi2[AE]2Co2Oy (AE = Ca, Ca0.5Sr0.5, Sr, and Ba) using the time-domain thermoreflectance method. These low values are comparable to the lowest conductivity in crystalline oxides and approaching the theoretical conductivity minimum of disordered crystals. Besides, these samples show the amorphous-like temperature dependence at cryogenic temperatures and the effective mean free paths are in the same magnitudes as the lattice constants.

In this paper, a characterization method has been developed in situ to study the microstructural changes of tungsten oxide nanowires induced by thermal effects, in which the Eu3+ rare earth ions are pre-doped into the WO3 nanowires (Eu@WO3 nanowires). The thermal effect in the Eu@WO3 nanowires have been studied by increasing the sample temperature in a nitrogen gas environment, and the results indicate the microstructural changes induced by the thermal effect could be not detected by the micro-Raman spectrum, but could be obviously detected by the fluorescence spectrum of Eu3+ fluorescence centers. The most notable effect of the increasing temperature is the appearance of two new fluorescence emissions related with a broad band emission at 675 nm and two sharp peaks at 525 and 530 nm, respectively. The understanding picture for the relationship between the new fluorescence emissions and the microstructural changes of the Eu@WO3 nanowires has also been proposed in this paper.

Recently, transition metal dichalcogenide (TMD) materials have shown promise in electronics and optoelectronics applications. Most of their properties are closely related to their abundant structural phases and phase transitions. For more practical applications in the future, it is necessary to tune the phase transitions in this material system. Here, we demonstrate the modulation of phase transitions in miscible WxMo1−xTe2 samples by appropriate alloying. The temperature dependent thermal conductivity along the c-axis, which strongly relates to the phase structures and the defect level, has been measured using the time-domain thermoreflectance method. In addition, a tunable hysteretic effect, induced by phase transitions, is observed in both thermal and electrical transport properties and confirmed by the consistent hysteresis in the Raman spectroscopic study. This hysteretic effect can be applied to realize phase-change storage devices. Furthermore, we provide a phase diagram to illustrate the compositi...

An unambiguous antiferromagnetic interlayer exchange coupling (IEC) is realized in all-perovskite oxide La0.7Sr0.3MnO3(LSMO)/SrRu1-xTixO3(SR1-xTxO) (x

Phonon-polaritons are studied both theoretically and experimentally in a one-dimensional two-component generalized quasiperiodic piezoelectric superlattice. The experimental observation of phonon-polaritons through dielectric abnormality is carried out at the microwave region. Some potential applications are discussed.

Applying a combinatorial methodology, (1−x)Na0.5Bi0.5TiO3−xBaTiO3 (NBT-BT) thin-film chips were fabricated on (001)-LaAlO3 substrates by pulsed laser deposition with a few quaternary masks. A series of NBT-BT library with the composition of BT ranged from 0 to 44% was obtained with uniform composition and well crystallinity. The relation between the concentration of NBT-BT and their structural and dielectric properties were investigated by x-ray diffraction (XRD), evanescent microwave probe, atomic force microscopy, and Raman spectroscopy. An obvious morphotropic phase boundary (MPB) was established to be about 9% BT by XRD, Raman frequency shift, and dielectric anomaly, different from the well-known MPB of the materials. The result shows the high efficiency of combinatorial method in searching new relaxor ferroelectrics.

The planar waveguides have been fabricated in z-cut β-BaB2O4 crystal by 2.2MeV O+ ion implantation at doses ranging from 5×1012 to 5×1014ions∕cm2 at room temperature. The waveguides were characterized by the prism-coupling method. Monomode, nonleaky planar waveguides at λ=633nm in β-BBO single crystals were fabricated at doses from 5×1012 to 2×1013ions∕cm2, and two mode and three mode waveguides were fabricated at doses from 4×1013 to 5×1014ions∕cm2, respectively. The refractive index profiles of the waveguides are reconstructed using reflectivity calculation method. The propagation loss of the measured ion implanted waveguide was about 1.6dB∕cm. It was found that positive changes of extraordinary refractive indices happened in the guiding regions, and such changes increased with the doses, which were different from most of the observed ion-implanted waveguides.

Thin films of A-site substituted, B-site substituted, and both A- and B-sites cosubstituted Bi4Ti3O12 (BTO) by La3+ and Zr4+, i.e., Bi3.25La0.75Ti3O12 (BLT), Bi4Ti2.8Zr0.2O12 (BTZ), and Bi3.25La0.75Ti2.8Zr0.2O12 (BLTZ), were fabricated on Pt/Ti/SiO2/Si substrates by pulsed laser deposition. Structures of the films are investigated by x-ray diffraction, Raman spectroscopy, and scanning electron microscopy. Compared to the well known BLT films, both the BTZ and BLTZ films have larger remanent polarization (Pr) but smaller coercive field (Ec). It is shown experimentally that the oxygen vacancy is the predominant factor determining ferroelectric fatigue. The effects of substitution on structural and ferroelectric properties of BTO are discussed in detail. As a result, the A- and B-sites cosubstitution might be one of the promising ways to improve ferroelectric properties of BTO.

We report a direct fabrication of an omnidirectional negative microlens array on a curved substrate by a femtosecond laser enhanced chemical etching process, which is utilized as a molding template for duplicating bioinspired compound eyes. The femtosecond laser treatment of the curved glass substrate employs a common x-y-z stage without rotating the sample surface perpendicular to the laser beam, and uniform, omnidirectional-aligned negative microlenses are generated after a hydrofluoric acid etching. Using the negative microlens array on the concave glass substrate as a molding template, we fabricate an artificial compound eye with 3000 positive microlenses of 95-μm diameter close-packed on a 5-mm polymer hemisphere. Compared to the transferring process, the negative microlenses directly fabricated on the curved mold by our method are distortion-free, and the duplicated artificial eye presents clear and uniform imaging capabilities. This work provides a facile and efficient route to the fabrication of microlenses on any curved substrates without complicated alignment and motion control processes, which has the potential for the development of new microlens-based devices and systems.

Optical structures with balanced loss and gain provide an efficient platform to study the features of light propagation under non-Hermitian parity-time symmetry. Here, we report a feasible design of one-dimensional parity-time symmetric diffraction grating, where the real and imaginary parts of refractive index are separately modulated. Due to the spontaneous breaking of parity-time symmetry at the exceptional point, asymmetric diffractions are observed between a pair of oblique incident light. This asymmetric phenomenon, determined by the modulation direction of the introduced parity-time symmetry, is also polarization-dependent. The coupled-mode theory is implemented to theoretically analyze the polarization dependent asymmetric diffraction, showing consistence with numerical simulations. Our findings may provide a feasible way for manipulating light and instructively inspire the development of diffraction optics.

Recently, the extremely large magnetoresistance observed in transition metal telluride, like WTe$_2$, attracted much attention because of the potential applications in magnetic sensor. Here we report the observation of extremely large magnetoresistance as 3.0$\times$10$^4$ % measured at 2 K and 9 T magnetic field aligned along [001]-ZrSiS. The significant magnetoresistance change (~1.4$\times$10$^4$ %) can be obtained when the magnetic field is titled from [001] to [011]-ZrSiS. These abnormal magnetoresistance behaviors in ZrSiS can be understood by electron-hole compensation and the open orbital of Fermi surface. Because of these superior MR properties, ZrSiS may be used in the novel magnetic sensors., Comment: 18 pages, 5 figures, 21 references

We report a design of topological phononic states for underwater sound using arrays of acoustic coupled ring resonators. In each individual ring resonator, two degenerate acoustic modes, corresponding to clockwise and counter-clockwise propagation, are treated as opposite pseudospins. The gapless edge states arise in the bandgap resulting in protected pseudospin-dependent sound transportation, which is a phononic analogue of the quantum spin Hall effect. We also investigate the robustness of the topological sound state, suggesting that the observed pseudospin-dependent sound transportation remains unless the introduced defects facilitate coupling between the clockwise and counter-clockwise modes (in other words, the original mode degeneracy is broken). The topological engineering of sound transportation will certainly promise unique design for next generation of acoustic devices in sound guiding and switching, especially for underwater acoustic devices.

High-quality c-axis epitaxial ferroelectric thin films of Bi4Ti3O12 (BTO) and Nd-substituted BTO, Bi3.15Nd0.85Ti3O12 (BNT), were prepared on (001)-LaNiO3-coated (001) LaAlO3 substrates by pulsed-laser deposition. The epitaxial alignments were established by the x-ray diffraction, including θ–2θ and φ scans. Compared to the BTO films, the BNT films have significantly improved electrical properties with about 2 times larger remanent polarization, 0.6 times lower coercive field, better fatigue-resisting characteristics, and 1.7 times larger dielectric constant. These results showed experimentally that Nd substitution could enhance the c-axis electrical properties of BTO. The reason for the improved properties of BNT films was discussed.

The first four members of Bi-layered Srm−3Bi4TimO3m+3 homologous series with m=3, 4, 5, and 6, i.e., Bi4Ti3O12, SrBi4Ti4O15, Sr2Bi4Ti5O18, and Sr3Bi4Ti6O21, were grown on SrTiO3 (001) single-crystal substrates by pulsed-laser deposition. X-ray diffraction and high-resolution transmission electron microscopy (HRTEM) reveal that the films grew epitaxially with in-plane epitaxial alignment of [110]Srm−3Bi4TimO3m+3‖[010]SrTiO3. HRTEM cross-sectional images show that the films with m=3, 4, and 5 are nearly free of intergrowth, whereas a number of growth defects were observed in the film with m=6. Using an evanescent microwave probe, the room-temperature dielectric constants of these epitaxial films are measured to be 221±13, 205±15, 261±29, and 249±17 for films with m=3, 4, 5, and 6, respectively.

We report the temperature dependence of thermopower (S) in the ab plane of Bi2Sr2Co2O9 (BC-222) single crystalline whiskers under high pressure up to 1.2 GPa. Special modifications were made to our high-pressure transport measurement system to improve the measurement accuracy of S for whiskers with high resistance. Pressure improved the contact resistance dramatically. We observed a slight decrease of S and four-wire electrical conductivity (σ) under high pressure. As a result, the power factor (S2σ) was decreased less than 20% by pressure. From the temperature dependence of σ, the band gap of BC-222 whiskers increase very slightly under high pressure.

The planar waveguide has been fabricated in a Nd:YVO4 crystal by 3.0 MeV Si+ ion implantation at a dose of 1×1015 ions/cm2 at room temperature. The waveguide was characterized by the prism-coupling method. The dark modes are measured before and after the annealing at 240 °C for 60 min in air. The refractive index profile is reconstructed using reflectivity calculation method. It is found that relatively large positive change of ordinary refractive index happens in the guiding region, which is quite different from most of the observed ion-implanted waveguides. The TRIM’98 code is carried out to simulate the energy loss during the implantation in order to obtain a better understanding for the waveguide formation.

Optically transparent Sb-doped SrTiO3 thin films with a transmittance higher than 95% in most of the visible region have been grown on SrTiO3 (001) substrate by pulsed laser deposition. The films behave as an n-type semiconductor between 10 K and room temperature. The carrier concentration and mobility of the films at room temperature are ∼5.8×1017 cm−3 and ∼6.4 cm2/V s, respectively. X-ray photoelectron spectroscopy measurement reveals that the delocalized electrons from the Sb dopants give rise to deep impurity levels within the band gap of the parent compound, which are responsible for the electrical conduction observed. The wide band gap and low density of states in the conduction band account for transparency of the films.

Bi-based layered ferroelectric thin films of Sr2Bi4Ti5O18 (SBTi) were prepared by pulsed-laser deposition. The c-axis-oriented SBTi films were grown on SrRuO3 seeded Pt/TiO2/SiO2/Si substrates while polycrystalline SBTi films were grown on Pt/TiO2/SiO2/Si substrates. The measurements of ferroelectricity revealed that the direction of spontaneous polarization was not along the c axis since the polarization of c-axis-oriented films was much less than that of randomly oriented films. There was no significant degradation of switchable charge at least up to 1011 cycles for the randomly oriented films, suggesting that, even with Ti which was widely accepted to contribute to the fatigue of Pb(Zr, Ti)O3, SBTi showed superior fatigue characteristics. The randomly oriented films also showed excellent retention characteristics after 105 s.

In this work, acoustic phase-reconstruction is studied and experimentally demonstrated in a triangular lattice two-dimensional phononic crystal (PnC) composed of steel rods in air. Owning to the fact that two bands of this triangular lattice PnC touch at the K/K′ point and thus give rise to a conical Dirac cone, acoustic waves transmitting through this PnC can exhibit a pseudo-diffusion transportation feature, producing a reconstructed planar wavefront in the far field away from the interface of the PnC. Such phase reconstruction effect can be utilized in many applications, and here we demonstrate experimentally two important applications: an acoustic collimator and an acoustic cloak operating at a Dirac frequency of 41.3 kHz.

Low-temperature growth and subsequent rapid thermal anneal were used to intermix Al and Ga atoms in AlGaAs/GaAs multiple quantum wells (QWs). The intermixed samples were characterized by photoluminescence (PL) spectroscopy, and the observed blue shifts in PL energies are interpreted as the result of modification of the QW shape due to the enhanced Al-Ga interdiffusion in the samples. The enhancement of interdiffusion was found to be strongly dependent on the growth and annealing conditions. In addition, the saturation behavior of Al-Ga interdiffusion was also observed.

An electric poling method has been used to prepare microstructured LiTaO3 crystals with periodically inverted-ferroelectric domains. By using these crystals as acoustic superlattices, both an “in-line” scheme and a “cross-field” scheme for acoustic excitation have been realized. The experimental results are in good agreement with the theoretical analysis. It is expected that these results may be applied to a bulk-acoustic device operating at a frequency high above 450 MHz.

We have investigated the effect of thermal annealing on optical emission properties of low‐temperature (LT) grown AlGaAs/GaAs multiple quantum wells (MQWs) by using photoluminescence (PL) spectroscopy. For comparison, the results on normal‐temperature (NT) grown MQWs implanted with protons are also presented. The LT sample was grown by molecular beam epitaxy at 310 °C. The as‐grown LT‐MQWs show moderately strong PL. Upon annealing at 600 °C, the PL intensity of the LT‐MQWs is dramatically quenched, in sharp contrast to the large increase in PL intensity of the implanted NT‐MQWs. The quenching of PL intensity in the LT‐MQWs is attributed to the formation of arsenic clusters that fast trap photoexcited carriers. In addition, an enhancement in the interface intermixing and roughening induced by thermal annealing has also been observed in the LT‐MQWs.

Epitaxial near‐stoichiometric ferroelectric Pb(Zr0.53Ti0.47)O3 thin films were fabricated on epitaxial metallic LaNiO3 electrodes deposited on (001) SrTiO3 and (001) LaAlO3 single crystal substrates by pulsed laser ablation. The P–E hysteresis loop of PZT in the trilayer of Ag/PZT/LNO/STO was measured using the Sawyer–Tower circuit. The remnant polarization Pr and coercive field Ec at room temperature were 30 μC/cm2 and 69.3 kV/cm (peak‐to‐peak voltage=30 V, 50 Hz), respectively.

Studies on the polycrystalline PbTiO3 thin films deposited on (001) redoped n‐Si substrates by metalorganic chemical vapor deposition (MOCVD) under reduced pressure indicated the evidence of ferroelectricity weakening [Appl. Phys. Lett. 65, 1906 (1994)] when the grain size of PbTiO3 was down to the scale of ∼1100 A. X‐ray diffraction patterns demonstrated that the perovskite unit cells have a contraction along the c‐axis direction. All transverse optical phonon modes in the films were observed shift downward in the Raman spectrum measured at 300 K. And the spontaneous polarization of PbTiO3 is determined to be 52 μC/cm2 by using Si substrates as the bottom electrodes. The three related experimental observations are conjected to be attributable to the finite size effect and the surface conditions in the ferroelectric thin film.

Single‐crystalline and single‐domain PbTiO3 films with thickness of 3000 A have been prepared by metalorganic chemical vapor deposition (MOCVD), using metalorganic precursors of tetra‐ethyl‐lead and iso‐propoxide titanium. The nature of single‐crystalline epitaxy and single domain of as‐grown films was characterized by x‐ray diffraction (XRD), synchrotron radiation (SR), and Rutherford backscattering (RBS). Using atomic force microscopy (AFM), the evidence of layer‐by‐layer growth was observed. The growth steps on the surface may be attributable to the formation of single‐crystalline and single‐domain PbTiO3 film with 3000‐A thickness.

High‐quality PbTiO3 thin films have been grown on LaAlO3 substrates by metalorganic chemical vapor deposition, using purified metalorganic precursors titanium‐iso‐propoxide and tetra‐ethyl‐lead. The results of the cross‐section scanning electron microscopy and x‐ray diffraction (XRD), including theta and phi scan, show that the films are epitaxy, and a domains and c domains may align alternately in the thin films. The experiments of high‐temperature XRD reveal the nature of the phase transition of grown PbTiO3 thin films from tetragonal to cubic phase. The transition temperature is around 460 °C which is far lower than that of bulk PbTiO3 and the thin films deposited on fused quartz substrates.

We demonstrate a compact passively Q-switched channel waveguide laser based on the interaction of the evanescent-field and the graphene coated surface. The graphene layer is transferred onto the surface of a femtosecond laser inscribed Nd:YAG surface waveguide for a simple integration of the saturable absorber and waveguide structure. The passive Q-switching configuration is based on the evanescent-field interaction with graphene. A 1064 nm pulsed waveguide laser with a maximum repetition rate of 10.4 MHz has been achieved, reaching an output power of 48 mW. The shortest pulse duration of the channel waveguide laser is 52 ns.

This Letter demonstrates a simple method to achieve underwater anisotropic oil-wetting using silicon surfaces with a microgroove array produced by femtosecond laser ablation. The oil contact angles along the direction perpendicular to the grooves are consistently larger than those parallel to the microgroove arrays in water because the oil droplet is restricted by the energy barrier that exists between the non-irradiated domain and the trapped water in the laser-ablated microgrooves. This underwater anisotropic oil-wetting is able to be controlled, and the anisotropy can be tuned from 0° to ∼20° by adjusting the period of the microgroove arrays.