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The effect of adsorbed adatoms on the structural stability and electronic properties of monolayer N2P6 have been systematically studied via first-principles simulation methods. It is found that pristine N2P6 is an indirect 0.21 eV band gap semiconductor, with a pleated honeycomb-like structure similar to phosphorene. The calculation results show that adsorbed adatoms can modify the properties of monolayer N2P6 effectively. The degree of local distortion strongly depends on the electronegativity and size of adatoms, also the adsorption energy ranges from 0.3 to 5.8 eV depending on the species of adatoms. The electronic properties show metallic behavior with several adsorbed metal atoms (Li, Na, Al, K, Cu, Ni, and Zn) and some non-metal atoms (H, F, P, and Cl), while adsorbed O, S, Ca, and Si atoms still remain semiconductors. The systems of Ni and Zn adatoms show ferromagnetic behavior, and adsorbed Mg exhibits a half-metallic character. Our theoretical studies indicate that N2P6 possesses potential application in the field of gas sensors.

All-inorganic lead halide perovskites are ideal platforms to investigate the fundamental physics of the light–matter interactions, due to their strong oscillator strength at room temperature and va...

Metamaterial absorbers with tunability have broad prospects for mid-infrared absorption applications. While various methods have been proposed to control absorption, how to analyse and present the physical image of absorption mechanism in depth is still expected and meaningful. Here, we present experimental spatial near-field distributions of a multi-resonant mode induced broadband tunable metamaterial absorber by using near-field optical microscopy. The absorber is constructed by a metal double-sized unit cell and a metallic mirror separated by a thin Ge2Sb2Te5 (GST) spacer. To clearly obtain the physical images, we used a hybrid unit cell consisting of four square resonators to produce two absorption peaks at 7.8 μm and 8.3 μm. The resonance central-wavelength exhibits a redshift while switching the GST thin film from amorphous to crystalline phase. The near-field amplitude and phase optical responses of the absorber are directly observed at absorption frequencies when GST is in both phases, respectively. This work will pave the way for the fundamental science field and inspire potential applications in optical tunable absorption control.

The layer-by-layer buildup of a two-dimensional transition metal dichalcogenide monolayer to form a stack is an important development for these materials, which performs many remarkable properties in the light–matter interaction. Herein, we find clear evidence of exciton–polaritons emerging from WS2/hBN/WS2 heterostructures embedded in a dielectric microcavity under optical pumping. A large Rabi splitting of 15 meV is observed at room temperature, which increases to 25 meV at 5 K. An all-dielectric Fabry–Pérot microcavity provides a simple but effective way to study the room temperature strong coupling between cavity photons and excitons. Our results pave the way for room-temperature polaritonic devices based on quantum-well van der Waals heterostructures.

Hot carrier harvest could save 30% energy loss in solar cells. So far, however, it is still unreachable as the photoexcited hot carriers are short-lived, ∼1 ps, determined by a rapid relaxation process, thus invalidating any reprocessing efforts. Here, we propose and demonstrate a feasible route to reserve hot electrons for efficient collection. It is accomplished by an intentional mix of cubic zinc-blend and hexagonal wurtzite phases in III-V semiconductor nanowires. Additional energy levels are then generated above the conduction band minimum, capturing and storing hot electrons before they cool down to the band edges. We also show the superiority of core/shell nanowire (radial heterostructure) in extracting hot electrons. The strategy disclosed here may offer a unique opportunity to modulate hot carriers for efficient solar energy harvest.

Perovskite quantum dots (QDs) are of interest for solution‐processed lasers; however, their short Auger lifetime has limited lasing operation principally to the femtosecond temporal regime the photoexcitation levels to achieve optical gain threshold are up to two orders of magnitude higher in the nanosecond regime than in the femtosecond. Here the authors report QD superlattices in which the gain medium facilitates excitonic delocalization to decrease Auger recombination and in which the macroscopic dimensions of the structures provide the optical feedback required for lasing. The authors develope a self‐assembly strategy that relies on sodiumd—an assembly director that passivates the surface of the QDs and induces self‐assembly to form ordered three‐dimensional cubic structures. A density functional theory model that accounts for the attraction forces between QDs allows to explain self‐assembly and superlattice formation. Compared to conventional organic‐ligand‐passivated QDs, sodium enables higher attractive forces, ultimately leading to the formation of micron‐length scale structures and the optical faceting required for feedback. Simultaneously, the decreased inter‐dot distance enabled by the new ligand enhances exciton delocalization among QDs, as demonstrated by the dynamically red‐shifted photoluminescence. These structures function as the lasing cavity and the gain medium, enabling nanosecond‐sustained lasing with a threshold of 25 µJ cm–2., The manipulation of the surface properties of quantum dots can be used to control their self‐assembly into macroscopic structures that provide the required optical feedback for lasing. Here the use of a ligand that passivates the quantum dot surface and simultaneously induce self‐assembly into superlattice structures that sustain low‐threshold lasing is reported.

Exciton–polariton Bose–Einstein condensation (EP BEC) is of crucial importance for the development of coherent light sources and optical logic elements, as it creates a new state of matter with coherent nature and nonlinear behaviors. The demand for room temperature EP BEC has driven the development of organic polaritons because of the large binding energies of Frenkel excitons in organic materials. However, the reliance on external high-finesse microcavities for organic EP BEC results in poor compactness and integrability of devices, which restricts their practical applications in on-chip integration. Here, we demonstrate room temperature EP BEC in organic single-crystal microribbon natural cavities. The regularly shaped microribbons serve as waveguide Fabry–Pérot microcavities, in which efficient strong coupling between Frenkel excitons and photons leads to the generation of EPs at room temperature. The large exciton–photon coupling strength due to high exciton densities facilitates the achievement of EP BEC. Taking advantages of interactions in EP condensates and dimension confinement effects, we demonstrate the realization of controllable output of coherent light from the microribbons. We hope that the results will provide a useful enlightenment for using organic single crystals to construct miniaturized polaritonic devices., The use of room temperature exciton–polariton Bose–Einstein condensation is limited by the need for external high-finesse microcavities. The authors generate room temperature EPs with single-crystal microribbons as waveguide Fabry–Pérot microcavities, and demonstrate controllable output of coherent light.

Recently, two-dimensional (2D) materials, especially transition-metal dichalcogenides (TMDCs), have attracted extensive interest owing to their potential applications in optoelectronics. Here, we demonstrate a hybrid 2D-zero-dimensional (0D) photodetector, which consists of a single-layer or few-layer molybdenum disulfide (MoS2) thin film and a thin layer of core/shell zinc cadmium selenide/zinc sulfide (ZnCdSe/ZnS) colloidal quantum dots (QDs). It is worth mentioning that the photoresponsivity of the hybrid 2D-0D photodetector is 3 orders of magnitude larger than the TMDC photodetector (from 10 to 104 A W-1). The detectivity of the hybrid structure detector is up to 1012 Jones, and the gain is up to 105. Due to an effective energy transfer from the photoexcited QD sensitizing layer to MoS2 films, light absorption is enhanced and more excitons are generated. Thus, this hybrid 2D-0D photodetector takes advantage of high charge mobility in the MoS2 layer and efficient photon absorption/exciton generation in the QDs, which suggests their promising applications in the development of TMDC-based optoelectronic devices.

In this work, we present the design method of diffractive beam splitters via two comparative technical routes, the first referred as the direct scheme and the second referred as the indirect scheme. Comparative study is carried on the design procedures and results. The advantages of the direct design scheme include overcoming the limit on the number of phase pixels and being capable of realizing beam shaping and splitting simultaneously. Numerical simulation shows that the uniformity of spots array pattern in the direct design is close to that of the indirect design. These results are helpful for the design and application of diffractive optical elements (DOEs) in modern optical devices.

We demonstrated strong fluorescence blinking on large all-inorganic perovskite (CsPbBr3) nano-spheres. By performing (time-resolved) micro-photoluminescence (μ-PL) measurements, the unique blinking characteristics of the as-grown nano-spheres with diameters of hundred nanometers, are clearly observed. Blinking has no obvious on/off states, which is different from the blinking characteristics of quantum dots. It is believed that the blinking of fluorescence is caused by metastable defect-induced trapping of carriers on the surface of the nano-spheres, because dramatically suppressed fluorescence blinking and the decay rates of ultrafast carriers are realized by surface passivation of the nano-spheres. Surface defects are closely related to the ambient atmosphere, which has been further confirmed by PL measurements of the as-grown nano-spheres in vacuum. Additionally, we also found that the fluorescence blinking was significantly suppressed as the sample size increased, which can be attributed to the large-size induced average effect on fluorescence blinking. These results may be important for understanding the mechanism of the fluorescence blinking of perovskite materials and for developing optical devices with good fluorescence stability.

The band-edge emission lifetime in a single ZnO tetrapod is studied by using the time-resolved confocal micro-photoluminescence (TR- μ PL) spectroscopic technique at room temperature. By performing μ PL and TR- μ PL mapping along the tapered arm of tetrapod, we observe whispering gallery mode (WGM) polaritons and find that the predominant radiative lifetime of exciton polaritons decreases linearly with increasing the surface-to-volume ratio of the sample. This behavior is ascribed to the surface electric field induced enhancement of the radiative decay rate of the exciton-like polaritons coupling with LO phonons.

Obtaining single-mode lasing with excellent stability and beam quality is highly desirable but still challenging. Although microplatelet optical cavities attract great attention because of their important lasing characteristics of directionality and high-power output light, they suffer from weak light confinement, which restricts applications of a single-mode laser. Herein, we increased the vertical thickness of the microplatelet cavity appropriately to achieve 3D light confinement in a CsPbBr3 micro-cubic cavity, from which single-mode lasing with an extreme narrow linewidth of 0.064 nm (Q ∼ 8500) was successfully achieved at room temperature. Besides, the microcavity we prepared exhibits superb capability for the output of continuous stable single-mode lasing. Different growth stages of cavities were found and a related growth mechanism was analyzed, indicating that the micro-cubic cavities evolved from nanospheres. Moreover, interesting multi-mode lasing spectra with higher-order transvers modes were observed in larger micro-cubic cavities. All these results suggest that 3D CsPbBr3 micro-cubic cavities, which provide improved photo-physical properties, are important for fundamental studies and future applications in photonic devices.

The optical waveguides under subwavelength scale are highly desirable for on-chip photonics to link various optical elements or to realize logical operations. In this work, the optical waveguiding along a single buckled CdS (cadmium sulfide) nanowire is comprehensively investigated at room temperature. By carefully scanning excitation along buckled nanowire with fixed PL detection at nanowire end, we present unique waveguide propagation loss strongly modulated by strain effect, which is distinct from the waveguide behavior of straight nanowires. When laser spot moves to buckling part, the light waveguide propagation loss is significantly reduced because band-to-band reabsorption effect during light propagation is greatly suppressed by tensile strain-induced bandgap shrinking. In addition, a dynamic manipulating waveguide propagation based on a controllable buckling of nanowires is also carried out; the solely strain-dependent waveguiding intensity loss and intensity modulation nearly 400% are clearly demo...

Single-mode laser is realized in a cesium lead halide perovskite submicron sphere at room temperature. All-inorganic cesium lead halide (CsPbX3, X = Cl, Br, I) microspheres with tunable sizes (0.2–10 μm) are first fabricated by a dual-source chemical vapor deposition method. Due to smooth surface and regular geometry structure of microspheres, whispering gallery resonant modes make a single-mode laser realized in a submicron sphere. Surprisingly, a single-mode laser with a very narrow line width (∼0.09 nm) was achieved successfully in the CsPbX3 spherical cavity at low threshold (∼0.42 μJ cm–2) with a high cavity quality factor (∼6100), which are the best specifications of lasing modes in all natural nano/microcavities ever reported. By modulating the halide composition and sizes of the microspheres, the wavelength of a single-mode laser can be continuously tuned from red to violet (425–715 nm). This work illustrates that the well-controlled synthesis of metal cesium lead halide perovskite nano/microspher...

Thermal radiation with narrow bandwidth and well-defined emission directions is highly sought after for a variety of applications, ranging from infrared sensing and thermal imaging to thermophotovoltaics. Here, a large-area (4-inch-diameter) long-wavelength infrared thermal emitter is presented, which is spectrally selective, highly directional, and easily fabricated. The basic structure of the proposed thermal emitter is composed of a truncated one-dimensional photonic crystal and a continuous metallic film separated by a dielectric spacer. Experimental results show that the emitter exhibits a narrowband thermal emittance peak of 92% in the normal direction at the wavenumber of 943.4 cm−1 with a bandwidth of 12.5 cm−1 and a narrow angular emission lobe with a limited solid angle of 0.325 sr (0.115 sr) for s (p) polarization. Numerical simulation analyses are performed to corroborate the experimental observations. Temporal coupled-mode theory combined with transfer matrix method is employed to analytically investigate the emission properties of the structure, which not only can be used to understand the experimental results, but also plays a certain guidance role in designing a thermal emitter with the desired properties. The present thermal emitter can be implemented for thermal photonics management, allowing applications in thermal imaging and medical systems, etc.

Rubidium lead halides (RbPbX3 ), an important class of all-inorganic metal halide perovskites, are attracting increasing attention for photovoltaic applications. However, limited by its lower Goldschmidt tolerance factor t≈0.78, all-inorganic RbPbBr3 has not been reported. Now, the crystal structure, X-ray diffraction (XRD) pattern, and band structure of perovskite-phase RbPbBr3 has now been investigated. Perovskite-phase RbPbBr3 is unstable at room temperature and transforms to photoluminescence (PL)-inactive non-perovskite. The structural evolution and mechanism of the perovskite-non-perovskite phase transition were clarified in RbPbBr3 . Experimentally, perovskite-phase RbPbBr3 was realized through a dual-source chemical vapor deposition and annealing process. These perovskite-phase microspheres showed strong PL emission at about 464 nm. This new perovskite can serve as a gain medium and microcavity to achieve broadband (475-540 nm) single-mode lasing with a high Q of about 2100.

Recently, two-dimensional (2D) materials, especially transition-metal dichalcogenides (TMDCs), have attracted extensive interest owing to their potential applications in optoelectronics. Here, we demonstrate a hybrid 2D-zero-dimensional (0D) photodetector, which consists of a single-layer or few-layer molybdenum disulfide (MoS

Magnetic skyrmions have significant potential for applications in storage and logic devices, but the ability to control skyrmion motion is key to their success. To realize controlled skyrmion motion, vertical spin current-driven methods employing, e.g., the spin Hall or inverse spin galvanic effect, are efficient; thus, magnetic heterostructures featuring large spin-orbit torques are appealing. In this paper, we report on the observation of room-temperature magnetic skyrmions in Pt/Co/W multilayers. The interfacial Dzyaloshinskii-Moriya interaction was estimated to be $0.19\ifmmode\pm\else\textpm\fi{}0.05\phantom{\rule{0.16em}{0ex}}\mathrm{mJ}/{\mathrm{m}}^{2}$ based on the asymmetric domain-wall motion occurring upon the application of in-plane magnetic fields. The evolution of the magnetic structures from labyrinth domains to skyrmions with diameters of around 145 nm under magnetic fields was observed by performing Lorentz transmission electron microscopy. The skyrmion nucleation fields could be tuned by varying the repetition number. Large spin Hall angle systems such as Pt/Co/W multilayers are appealing for achieving current-driven skyrmion motion in future racetrack and logic applications.

Semiconductor nanostructures such as nanowires and nanoribbons have shown great potential for fabrication of functional nanoscale lasers due to their high dielectric contrast and bandgap engineering performance. However, these as-grown nanostructures are weak in structural controllability, and the operation of highly desired single-mode lasers currently performed by coupled nanostructural cavities needs a relatively complex fabrication process and lacks flexibility. In this work, a tunable coupled nanoribbon cavity was simply obtained by using a home-made transfer platform. Relying on this, the Vernier effect-driven high performed single-mode laser was realized. Most interestingly, the laser mode can be reversibly tuned between single-mode and multi-mode by adjusting the gap of two coupled nanoribbons. The coupling constant and the optical loss of different gaps were demonstrated by simulation, large diffraction loss, and scattering loss as limiting factors for coupling were clarified. This work offers an alternative route toward realizing mode-tunable nanoscale lasers, which may have great potential in flexible multi-functional optoelectronic devices.

Two-dimensional (2D) semiconductors of graphene, as well as transition–metal dichalcogenides, have performed strong interaction with light. Here the strong light–matter interaction between monolayer tungsten disulphide ( W S 2 ) excitons and microcavity photons at room temperature is well studied by the introduction of a gain material embedded dielectric optical microcavity structure. A Rabi splitting of about 36 meV is observed in angle-resolved reflectance spectra at room temperature, which agrees well with the theoretical results simulated by using the transfer matrix method. Since the cavity structures and 2D semiconductors can be prepared, the cavity and the gain materials, respectively, can be optimized separately in this platform. An all-dielectric Fabry–Pérot microcavity provides a simple but effective way to study the room temperature strong coupling between cavity photons and 2D excitons.

Semiconductor nanowires/nanoribbons have great potential in nanoscale lasers because of their intrinsic laser capabilities and excellent optoelectronic properties. However, these as-grown nanostructures, lacking precise structural controllability, usually show multimode lasing, which hinders their applications in on-chip functional optoelectronic devices. In this work, by using a home-made strain apparatus, we obtained out-of-plane buckled cadmium selenide nanoribbons, resulting in a single-mode lasing at the curved part of the nanoribbons. Taking into consideration the bending structure of nanoribbons, we speculate that deformation-induced light confinement and strain-driven carrier's redistribution contributed mainly to the single-mode lasing. Moreover, a periodic out-of-plane bending of nanoribbons is realized by thermal controlling deformation of the elastic substrate and cadmium selenide, in which single-mode lasing at each crest part can be obtained. Our work opened an alternative avenue to realize nanoscale single-mode lasers, which was quite useful for flexible optoelectronic devices.

International audience; The development of novel approaches that control absorption and emission operating in the long wavelength infrared (LWIR) spectral region is of fundamental importance for many applications, such as remote temperature sensing, thermal imaging, radiation cooling, environmental monitoring, and night vision. A high performance plasmonic metasurface–based absorber for the LWIR spectral region is presented. In the design, a pyroelectric thin film, poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) copolymer, is introduced as spacer, that offers the device not only multiple selective high absorption bands but also promising potential for application in optoelectronics. The angle-resolved optical responses show that the absorption effect is sensitive to the incident angles and can be controlled by the periodicity, indicating that the design can function as optical devices with directional and frequency-selective absorption/emission characteristics. By employing near-field optical microscopy, both the near-field amplitude and phase optical responses of the absorber are investigated at resonant wavelength, thereby providing direct experimental evidence to verify the nature of the absorption effect. To further demonstrate the versatility of the design, a particular metasurface patterned by the building blocks of the absorber is fabricated. 2D hyperspectral images show that such a patterned structure exhibits both frequency and spatially selective absorption.

In this letter, the optical properties of InAs (QDs)/GaInAsP on InP substrate grown by gas source molecular beam epitaxy are investigated. By measuring and analyzing the photoluminescence spectra of InAs (QDs)/GaInAsP/InP at different temperatures and excitation powers, the origin of each emission is verified. And it is found that, with the temperature increasing, the emission intensity of GaInAsP wetting layers decreases firstly (T

© 2017 American Physical Society. Magnetization reversal of interconnected kagome artificial spin ice was studied by the first-order reversal curve (FORC) technique based on the magneto-optical Kerr effect and magnetoresistance measurements. The magnetization reversal exhibits a distinct sixfold symmetry with the external field orientation. When the field is parallel to one of the nano-bar branches, the domain nucleation/propagation and annihilation processes sensitively depend on the field cycling history and the maximum field applied. When the field is nearly perpendicular to one of the branches, the FORC measurement reveals the magnetic interaction between the Dirac strings and orthogonal branches during the magnetization reversal process. Our results demonstrate that the FORC approach provides a comprehensive framework for understanding the magnetic interaction in the magnetization reversal processes of spin-frustrated systems.

Utilizing the magneto-optic Kerr effect and Kerr microscopy measurements, we investigated the antiferromagnetic (AFM) domain switching process at different magnetic fields in a single-crystalline Fe/CoO bilayer grown on MgO(001) substrate. In spite of the zero-net magnetic moment in the CoO layer, we find that the activation energy barrier of CoO AFM domain switching decreased at larger magnetic field. To separate the different behaviors of domain nucleation and domain wall motion during the CoO spin switching process, a new analytical method was developed. Using this method, we found that the CoO domain nucleation energy barrier exhibited a jump at a critical magnetic field while the CoO domain wall motion experienced only a tiny energy barrier variation. The field-dependent behaviors of the energy barriers were attributed to the formation of a spiral domain wall in the Fe layer during its magnetization reversal and this was supported by micromagnetic simulations.

Magnetization excitation in micron sized FeNi disks with different diameters is studied by broadband ferromagnetic resonance (FMR) measurement. Except the main FMR peak, additional adsorption peaks with lower energies are observed. Both micromagnetic simulation and quantum spin wave calculation confirm that the low-energy excitation states are attributed to backward volume magnetostatic (BVM) spin waves. The size dependence of the low-energy states is systematically studied in 50-nm-thick Py disks with diameters larger than 500 nm, and the linewidth of the first BVM state is found to be obviously smaller than that of the FMR absorption peak. Through a quantitative comparison with experimental results, the quantum spin wave calculation is proven to be a reliable method to get the susceptibility and is much faster than the classical micromagnetic simulations.

We systematically compare the active and the passive methods for infrared scattering-type scanning near-field optical microscopy (s-SNOM). The active SNOM makes use of IR lasers or incoherent thermal emitters to illuminate a sample, whereas the passive method directly measures extremely weak fluctuating electromagnetic evanescent fields spontaneously generated at the sample surface without any external illumination. For this reason, our specific version of the passive SNOM is called a scanning noise microscope (SNoiM). In thermal equilibrium, the two methods are shown to be similar, both mapping the nanoscale variation of the complex dielectric constant of the sample. We demonstrate that a significant difference between the two methods emerges when the sample is driven out of thermal equilibrium, viz., the active SNOM is insensitive whereas the SNoiM is extremely sensitive to the electron temperature in locally heated nanoregions.

Strain engineering can be utilized to tune the fundamental properties of semiconductor materials for applications in advanced electronic and photonic devices. Recently, the effects of large strain on the properties of nanostructures are being intensely investigated to further expand our insights into the physics and applications of such materials. In this letter, we present results on controllable buckled cadmium-sulfide (CdS) optical nanowires (NWs), which show extremely large energy bandgap tuning by >250 meV with applied strains within the elastic deformation limit. Polarization and spatially-resolved optical measurements reveal characteristics related to both compressive and tensile regimes, while micro-reflectance spectroscopy clearly demonstrate the effect of strain on the different types of excitons in CdS. Our results may enable strained NWs-based optoelectronic devices with tunable optical responses.

Angle-resolved second harmonic generation (SHG) spectra of ZnO microwires show characteristic Fano resonances in the spectral vicinity of exciton-polariton modes. We observe a resonant peak followed by a strong dip in SHG originating from the constructive and destructive interference of the nonresonant SHG and the resonant contribution of the polariton mode. It is demonstrated that the Fano line shape, and thus the Fano asymmetry parameter $q$, can be tuned by the phase shift of the two channels. We develop a model to calculate the phase-dependent $q$ as a function of the radial angle in the microwire and achieve a good agreement with the experimental results. The deduced phase-to-$q$ relation unveils the crucial information about the dynamics of the system and offers a tool for control on the line shape of the SHG spectra in the vicinity of exciton-polariton modes.

The strong coupling between excitons and Fabry-Pérot (F-P) cavity modes in tungsten sulfide (WS

We report the modulation of emission energy, exciton dynamics and lasing properties in a single buckled CdS nanoribbon (NR) by strain-engineering. Inspired by ordered structure fabrication on elastomeric polymer, we develop a new method to fabricate uniform buckled NRs supported on polydimethylsiloxane (PDMS). Wavy structure, of which compressive and tensile strain periodically varied along the CdS NR, leads to a position-dependent emission energy shift as large as 14 nm in photoluminescence (PL) mapping. Both micro-PL and micro-reflectance reveal the spectral characteristics of broad emission of buckled NR, which can be understood by the discrepancy of strain-induced energy shift of A- and B-exciton of CdS. Furthermore, the dynamics of excitons under tensile strain are also investigated; we find that the B-exciton have much shorter lifetime than that of redshifted A-exciton. In addition, we also present the lasing of buckled CdS NRs, in which the strain-dominated mode selection in multi-mode laser and negligible mode shifts in single-mode laser are clearly observed. Our results show that the strained NRs may serve as new functional optical elements for flexible light emitter or on-chip all-optical devices.

The anti-crossing behavior of exciton polaritons in WS2 thin layers was spectrally observed. Giant Rabi splitting of ~270 meV for A exciton and ~780 meV for B exciton were obtained from the fitting of the cavity polariton dispersions.

Metal-catalyzed chemical vapor deposition (CVD) has been broadly employed for large-scale production of high-quality graphene. However, a following transfer process to targeted substrates is needed, which is incompatible with current silicon technology. We here report a new CVD approach to form nanographene and nanographite films with accurate thickness control directly on non-catalytic substrates such as silicon dioxide and quartz at 800 °C. The growth time is as short as a few seconds. The approach includes using 9-bis(diethylamino)silylanthracene as the carbon source and an atomic layer deposition (ALD) controlling system. The structure of the formed nanographene and nanographite films were characterized using atomic force microscopy, high resolution transmission electron microscopy, Raman scattering, and x-ray photoemission spectroscopy. The nanographite film exhibits a transmittance higher than 80% at 550 nm and a sheet electrical resistance of 2000 ohms per square at room temperature. A negative temperature-dependence of the resistance of the nanographite film is also observed. Moreover, the thickness of the films can be precisely controlled via the deposition cycles using an ALD system, which promotes great application potential for optoelectronic and thermoelectronic-devices.

Strain-induced modulation of perpendicular magnetic anisotropy (PMA) is demonstrated in a wedge-shaped Pt/Co/Pt sandwich grown on PMN-PT(0 1 1) substrate using magnetic torque measurements. An anisotropic in-plane strain is generated by applying an electric field across the PMN-PT substrate and transferred to the ferromagnetic Pt/Co/Pt sandwich. The critical thickness of spin reorientation transition is tuned to the thicker region of the Pt/Co/Pt wedge. The strain-induced change of PMA is quantitatively extracted. Only the first order anisotropy term is tuned by the electric field, while the second order anisotropy term has negligible electric field-dependence. Both of the volume and interface contributions of the first order anisotropy term show tunable electric field modulation. These results may benefit the understanding of strain-mediated magnetoelectric coupling effect in artificial multiferroic structures containing a ferromagnetic layer with PMA.

Ultrafast laser induced magnetization reversal in L10 FePt films with high perpendicular magnetic anisotropy was investigated using single- and double-pulse excitations. Single-pulse excitation beyond 10 mJ cm−2 caused magnetization (M) reversal at the applied fields much smaller than the static coercivity of the films. For double-pulse excitation, both coercivity reduction and reversal percentage showed a rapid and large decrease with the increasing time interval (Δt) of the two pulses in the range of 0–2 ps. In this Δt range, the maximum demagnetization (ΔMp) was also strongly attenuated, whereas the integrated demagnetization signals over more than 10 ps, corresponding to the average lattice heat effect, showed little change. These results indicate that laser induced M reversal in FePt films critically relies on ΔMp. Because ΔMp is determined by spin temperature, which is higher than lattice temperature, utilizing an ultrafast laser instead of a continuous-wave laser in laser-assisted M reversal may reduce the overall deposited energy and increase the speed of recording. The effective control of M reversal by slightly tuning the time delay of two laser pulses may also be useful for ultrafast spin manipulation.

In this Article, we demonstrate a new synthesis route for the construction of rhombohedral In2O3 (rh-In2O3) nanosheets-based three-dimensional flowerlike microspheres (NBFMs). In this route, InOOH NBFMs were first prepared by a convenient and controllable method based on a complex reaction, using InCl3·4H2O as the starting material, oxalic acid as the complexing agent, and a mixture of glycerol and water as solvent at 180 °C for 12 h. The rh-In2O3 NBFMs were then obtained by calcining InOOH NBFMs precursors at 490 °C under ambient pressure. Scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, infrared spectroscopy, and thermogravimetric analysis were adopted to investigate the evolution process of InOOH precursors, and the chemical reactions at each stage were identified. The Ostwald ripening and anisotropic crystal structure are proposed to account for the formation of InOOH NBFMs on the basis of the evaluation of the time-dependent morphology. Furthermore, the influence...

Exchange coupling between a ferromagnet (FM) and an anti-ferromagnet (AFM) in a FM/AFM system has attracted great interests in the last decades due to its great impact on spintronics applications. However, there is a lack of a complete physical picture due to the difficulty of probing the spin structure at the FM/AFM interface. Because the so-called spin frustration at the FM/AFM interface plays a key role in determining the overall magnetic properties of the system, a single-crystalline film system is believed to reveal the intrinsic exchange coupling better by reducing the complicity of the grain boundary in polycrystalline systems.

In contrast to the extensive study of domain reversal in ferromagnetic materials, the domain switching process in antiferromagnets is much less studied due to the difficulty of probing antiferromagnetic spins. Using a combination of hysteresis loop, Kerr microscope, and x-ray magnetic linear dichroism measurements, we investigated the antiferromagnetic (AFM) domain switching process in single crystalline Fe/CoO bilayers on MgO(001). We demonstrate that the CoO AFM switching is a Kolmogorov-Avrami process in which the thermal activation energy creates AFM domain nucleation centers which further expand by domain wall propagation. From the temperature- and thickness-dependent measurements, we are able to retrieve quantitatively the important parameter of the CoO AFM activation energy, which is shown to increase linearly with CoO thickness.

We demonstrate a clear anticrossing between two polarization-orthogonal exciton-polariton modes in ZnO microwires. The strong coupling between exciton polaritons with orthogonal polarization is evidenced by using angle-resolved photoluminescence spectroscopy. The evolution of the coupling strength with the detuning between the two coupled polariton modes is studied by scanning the excitation spot on a tapered ZnO microwire. Steady oscillations are established between the two differently polarized polariton modes with resonant wave vectors and frequencies, which is well described by the plane wave coupling model.

A tunable polariton lasing is realized in a single ZnO tapered whispering gallery (WG) microcavity at room temperature. A tunable range of 100 meV and a minimum lasing threshold appeared at positive detuning of 42 meV are observed.