Solubility of Boron, Carbon, and Nitrogen in Transition Metals: Getting Insight into Trends from First-Principles Calculations

Efficient chemical vapor deposition synthesis of two-dimensional (2D) materials such as graphene, boron nitride, and mixed BCN systems with tunable band gaps requires precise knowledge of the solubility and mobility of B/C/N atoms in the transition metals (TMs) used as substrates for the growth. Yet, surprisingly little is known about these quantities either from experiments or simulations. Using first-principles calculations, we systematically study the behavior of B/C/N impurity atoms in a wide range of TMs. We compute formation energies of B/C/N interstitials and demonstrate that they exhibit a peculiar but common behavior for TMs in different rows of the periodic table, as experimentally observed for C. Our simulations indicate that this behavior originates from an interplay between the unit cell volume and filling of the d-shell electronic states of the metals. We further assess the vibrational and electronic entropic contributions to the solubility, as well as the role of anharmonic effects. Finally, we calculate the migration barriers, an important parameter in the growth kinetics. Our results not only unravel the fundamental behavior of interstitials in TMs but also provide a large body of reference data, which can be used for optimizing the growth of 2D BCN materials

All-Graphene Three-Terminal-Junction Field-Effect Devices as Rectifiers and Inverters

We present prominent tunable and switchable room-temperature rectification performed at 100 kHz ac input utilizing micrometer-scale three-terminal junction field-effect devices. Monolayer CVD graphene is used as both a channel and a gate electrode to achieve all-graphene thin-film structure. Instead of ballistic theory, we explain the rectification characteristics through an electric-field capacitive model based on self-gating in the high source–drain bias regime. Previously, nanoscale graphene three-terminal junctions with the ballistic (or quasi-ballistic) operation have shown rectifications with relatively low efficiency. Compared to strict nanoscale requirements of ballistic devices, diffusive operation gives more freedom in design and fabrication, which we have exploited in the cascading device architecture. This is a significant step for all-graphene thin-film devices for integrated monolithic graphene circuits

Young’s Modulus of Wurtzite and Zinc Blende InP Nanowires

The Young’s modulus of thin conical InP nanowires with either wurtzite or mixed “zinc blende/wurtzite” structures was measured. It has been shown that the value of Young’s modulus obtained for wurtzite InP nanowires (<i>E</i>_[0001] = 130 ± 30 GPa) was similar to the theoretically predicted value for the wurtzite InP material (<i>E</i>_[0001] = 120 ± 10 GPa). The Young’s modulus of mixed “zinc blende/wurtzite” InP nanowires (<i>E</i>_[111] = 65 ± 10 GPa) appeared to be 40% less than the theoretically predicted value for the zinc blende InP material (<i>E</i>_[111] = 110 GPa). An advanced method for measuring the Young’s modulus of thin and flexible nanostructures is proposed. It consists of measuring the flexibility (the inverse of stiffness) profiles 1/<i>k</i>(<i>x</i>) by the scanning probe microscopy with precise control of loading force in nanonewton range followed by simulations

Atomic Layer Engineering of Er-Ion Distribution in Highly Doped Er:Al₂O₃ for Photoluminescence Enhancement

For the past decade, erbium-doped integrated waveguide amplifiers and lasers have shown excellent potential for on-chip amplification and generation of light at the important telecommunication wavelength regime. However, Er-based integrated devices can only provide small gain per unit length due to the severe energy-transfer between the Er-ions at high concentration levels. Therefore, active ion concentrations have been limited to <1% levels in these devices for optimal performance. Here, we show an efficient and practical way of fabricating Er-doped Al₂O₃ with Er-concentration as high as ∼3.5% before concentration quenching starts to limit the C-band emission in our material. The Er-doped Al₂O₃ was fabricated by engineering the distribution of the Er-ions in Al₂O₃ with the atomic layer deposition (ALD) technique. By choosing a proper precursor for the fabrication of Er₂O₃, the steric hindrance effect was utilized to increase the distance between the Er-ions in the lateral direction. In the vertical direction, the distance was controlled by introducing subsequent Al₂O₃ layers between Er₂O₃ layers. This atomic scale control of the Er-ion distribution allows us to enhance the photoluminescence of our Er:Al₂O₃ material by up to 16 times stronger when compared to the case where the Er-concentration is ∼0.6%. In addition, long lifetime of approximately 5 ms is preserved in the Er-ions even at such high concentration levels. Thus, our optimized ALD process shows very promising potential for the deposition of optical gain media for integrated photonics structures

Fabrication of Dual-Type Nanowire Arrays on a Single Substrate

A novel method for fabricating dual-type nanowire (NW) arrays is presented. Two growth steps, selective-area epitaxy (SAE) in the first step and vapor–liquid–solid (VLS) in the second step, are used to grow two types of NWs on the same GaAs substrate. Different precursors can be used for the growth steps, resulting in sophisticated compositional control, as demonstrated for side-by-side grown GaAs and InP NWs. It was found that parasitic growth occurs on the NWs already present on the substrate during the second growth step and that the SAE NWs shadow the growth of the VLS NWs. Optical reflectance measurements revealed the dual-type array having improved light trapping properties compared to single-type arrays. Dual-type NW arrays could be practical for thermoelectric generation, photovoltaics and sensing where composition control of side-by-side NWs and complex configurations are beneficial

Visualization 4: Nonlinear microscopy using cylindrical vector beams: Applications to three-dimensional imaging of nanostructures

Visualization 4. 3D SHG images of the vertically-aligned semiconductor nanowires using azimuthal polarization Originally published in Optics Express on 29 May 2017 (oe-25-11-12463

Visualization 1: Nonlinear microscopy using cylindrical vector beams: Applications to three-dimensional imaging of nanostructures

Visualization 1. 3D SHG images of the vertically-aligned semiconductor nanowires using linear x polarization Originally published in Optics Express on 29 May 2017 (oe-25-11-12463

Visualization 3: Nonlinear microscopy using cylindrical vector beams: Applications to three-dimensional imaging of nanostructures

Visualization 3. 3D SHG images of the vertically-aligned semiconductor nanowires using radial polarization Originally published in Optics Express on 29 May 2017 (oe-25-11-12463

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

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