Anton Autere

Rapid visualization of grain boundaries in monolayer MoS2 by multiphoton microscopy

Grain boundaries have a major effect on the physical properties of two-dimensional layered materials. Therefore, it is important to develop simple, fast and sensitive characterization methods to visualize grain boundaries. Conventional Raman and photoluminescence methods have been used for detecting grain boundaries; however, these techniques are better suited for detection of grain boundaries with a large crystal axis rotation between neighbouring grains. Here we show rapid visualization of grain boundaries in chemical vapour deposited monolayer MoS2 samples with multiphoton microscopy. In contrast to Raman and photoluminescence imaging, third-harmonic generation microscopy provides excellent sensitivity and high speed for grain boundary visualization regardless of the degree of crystal axis rotation. We find that the contrast associated with grain boundaries in the third-harmonic imaging is considerably enhanced by the solvents commonly used in the transfer process of two-dimensional materials. Our results demonstrate that multiphoton imaging can be used for fast and sensitive characterization of two-dimensional materials.

Rapid and Large-Area Characterization of Exfoliated Black Phosphorus Using Third-Harmonic Generation Microscopy

Black phosphorus (BP) is a layered semiconductor that recently has been the subject of intense research due to its novel electrical and optical properties, which compare favorably to those of graphene and the transition metal dichalcogenides. In particular, BP has a direct bandgap that is thickness-dependent and highly anisotropic, making BP an interesting material for nanoscale optical and optoelectronic applications. Here, we present a study of the anisotropic third-harmonic generation (THG) in exfoliated BP using a fast scanning multiphoton characterization method. We find that the anisotropic THG arises directly from the crystal structure of BP. We calculate the effective third-order susceptibility of BP to be ∼1.64 × 10-19 m2 V-2. Further, we demonstrate that multiphoton microscopy can be used for rapid, large-area characterization indexing of the crystallographic orientations of many exfoliated BP flakes from one set of multiphoton images. This method is therefore beneficial for samples of areas ∼1 cm2 in future investigations of the properties and growth of BP.

Nonlinear Optics with 2D Layered Materials

2D layered materials (2DLMs) are a subject of intense research for a wide variety of applications (e.g., electronics, photonics, and optoelectronics) due to their unique physical properties. Most recently, increasing research efforts on 2DLMs are projected toward the nonlinear optical properties of 2DLMs, which are not only fascinating from the fundamental science point of view but also intriguing for various potential applications. Here, the current state of the art in the field of nonlinear optics based on 2DLMs and their hybrid structures (e.g., mixed-dimensional heterostructures, plasmonic structures, and silicon/fiber integrated structures) is reviewed. Several potential perspectives and possible future research directions of these promising nanomaterials for nonlinear optics are also presented.

Slot waveguide ring resonators coated by an atomic layer deposited organic/inorganic nanolaminate.

In this study, slot waveguide ring resonators patterned on a silicon-on-insulator (SOI) wafer and coated with an atomic layer deposited nanolaminate consisting of alternating layers of tantalum pentoxide and polyimide were fabricated and characterized. To the best of our knowledge, this is the first demonstration of atomic layer deposition (ALD) of organic materials in waveguiding applications. In our nanolaminate ring resonators, the optical power is not only confined in the narrow central air slot but also in several parallel sub-10 nm wide vertical polyimide slots. This indicates that the mode profiles in the silicon slot waveguide can be accurately tuned by the ALD method. Our results show that ALD of organic and inorganic materials can be combined with conventional silicon waveguide fabrication techniques to create slot waveguide ring resonators with varying mode profiles. This can potentially open new possibilities for various photonic applications, such as optical sensing and all-optical signal processing.

Nanowire encapsulation with polymer for electrical isolation and enhanced optical properties

Light management and electrical isolation are essential for the majority of optoelectronic nanowire (NW) devices. Here, we present a cost-effective technique, based on vapor-phase deposition of parylene-C and subsequent annealing, that provides conformal encapsulation, anti-reflective coating, improved optical properties, and electrical insulation for GaAs nanowires. The process presented allows facile encapsulation and insulation that is suitable for any nanowire structure. In particular, the parylene-C encapsulation functions as an efficient antireflection coating for the nanowires, with reflectivity down to <1% in the visible spectrum. Furthermore, the parylene-C coating increases photoluminescence intensity, suggesting improved light guiding to the NWs. Finally, based on this process, a NW LED was fabricated, which showed good diode performance and a clear electroluminescence signal. We believe the process can expand the fabrication possibilities and improve the performance of optoelectronic nanowire devices.

Measurement of Nanowire Optical Modes Using Cross-Polarization Microscopy

A method to detect optical modes from vertical InGaAs nanowires (NWs) using cross-polarization microscopy is presented. Light scattered from the optical modes in the NWs is detected by filtering out the polarized direct reflection with a crossed polarizer. A spectral peak and a valley were seen to red-shift with increasing NW diameter in the measured spectra. The peak was assigned to scattering from the TE01 optical mode and the valley was an indication of the HE11 mode, based on finite-element and scattering matrix method simulations. The cross-polarization method can be used to experimentally determine the spectral positions of the TE01 and HE11 optical modes. The modes are significantly more visible in comparison to conventional reflectance measurements. The method can be beneficial in the characterization of NW solar cells, light-emitting diodes and lasers where precise mode control is required.

High-quality slot waveguide ring resonator based on atomic layer deposition

Slot waveguide based ring resonators filled with atomic layer deposited (ALD) aluminum oxide (Al2O3) were fabricated and characterized. Our results demonstrate that ALD can be used to create slot waveguide ring resonators with relatively high Q-factors, which opens new possibilities for various photonic applications, such as optical sensing and all-optical signal processing.

Nanowire network–based multifunctional all-optical logic gates

Authors develop nanowire-based multifunctional logic gates for all-optical computation used in future nanophotonic devices. All-optical nanoscale logic components are highly desired for various applications because light may enable logic functions to be performed extremely quickly without the generation of heat and cross-talk. All-optical computing at nanoscale is therefore a promising alternative but requires the development of a complete toolbox capable of various logic functionalities. We demonstrate nanoscale all-optical switches by exploiting the polarization-dependent light emission property of crossbar InP and AlGaAs nanowire networks. These networks can perform various logic operations, such as AND, OR, NAND, and NOR binary logic functions. Furthermore, on the basis of these logic operations, our networks successfully enable all-optical arithmetic binary calculations, such as n-bit addition, to be conducted. Our results underscore the promise of assembled semiconductor nanowire networks as a building block of on-chip all-optical logic components for future nanophotonics.