This PDF file contains the front matter associated with SPIE Proceedings Volume 10725, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

GaN nanowire LEDs with radial p-i-n junctions were grown by molecular beam epitaxy using N-polar selective area growth on Si(111) substrates. The N-polar selective area growth process facilitated the growth of isolated and highaspect-ratio n-type NW cores that were not subject to self-shadowing effects during the subsequent growth of a conformal low-temperature Mg:GaN shell. LED devices were fabricated from single-NW and multiple-NW arrays in their as-grown configuration by contacting the n-type core through an underlying conductive GaN layer and the p-type NW shell via a metallization layer. The NW LEDs exhibited rectifying I-V characteristics with a sharp turn-on voltage near the GaN bandgap and low reverse bias leakage current. Under forward bias, the NW LEDs produced electroluminescence with a peak emission wavelength near 380 nm and exhibited a small spectral blueshift with increasing current injection, both of which are consistent with electron recombination in the p-type shell layer through donor-acceptor-pair recombination. These core-shell NW devices demonstrate N-polar selective area growth as an effective technique for producing on-chip nanoscale light sources.

Site-selectively growth and small footprint on Si techniques make GaN-based core-shell nanowires to be potential building blocks for fabricating devices such as laser diodes, solar cells, and field-effect transistors. Drift is fundamental in electronic devices, and can eventually determine their performance. It is well known that the optical phonons (OPs) play the main role on the electron mobility (EM) at room temperature. In this talk, we report a theoretically study on the OPs-limited EM in InxGa1-xN/GaN CSNWs and its ternary and size effects, based on the theory of force-balance and energy-balance equations.1 The results show that the quasi-confined OPs are much more important than the interface (IF) and propagating (PR) OPs. This is caused by the strong quantum confinement effects that can push the electrons to distribute in the core of InGaN layer. The total EM reaches its peak value at a certain composition. It is the critical composition for PR OPs transforming to IF OPs due to the anisotropy phonon dispersions in wurtzite nitrides. It is also found that EM increases as the core radius due to a weakened scattering by confined OPs. The total EM shows an obvious enhancement when decreases the temperature or increases the electron density.2 These theoretical results are expected to be helpful for design of CSNWs structure devices. 1 X. L. Lei and C. S. Ting, Phys. Rev. B 30, 4809 (1984) 2 W. H. Liu, Y. Qu and S. L. Ban, J. Appl. Phys. 122, 115104 (2017).

Ultra-thin ZnO films were grown by atomic layer deposition (ALD) at a temperature of 60C on Si substrates and Si substrates coated with ~20nm of Al2O3 also deposited via ALD at 60C. Ellipsometry indicated ZnO films ranging in thickness from ~0.5 nm to ~7 nm. Atomic force microscopy results showed ZnO nano-islands formed prior to the completion of conformal atomic layers. AFM scans of 1um and 10um areas were employed in this study. This low dimensional ZnO islanding phenomenon was observed in both substrate types but with different incubation periods. The ZnO nano-islands on both substrates varied in diameter from ~20nm to ~100nm, island height variation ranged from ~2nm to ~9nm. ZnO nano-island formation had little to no incubation period on the Si substrates treated with ~20nm of Al2O3, and island formation was observed within 10 ZnO ALD cycles and nano-island density peaked around 20 to 30 ZnO ALD cycles. The highest rms roughness measurement obtained was of 0.7756 nm and is attributed to high nano-island density. While on bare Si the incubation period is significantly longer with nano-islands taking greater than 50 ZnO ALD cycles to form and achieving highest rms roughness of 0.25 nm around 60-70 ZnO ALD cycles. These results demonstrate non-conformal ultra-thin film growth by ALD, a deposition method expected to yield conformal thin films.

A new atomic layer deposition (ALD) tool, named the meter-scale ALD system (MSAS), has been designed, constructed, and tested to apply uniform protective coatings over a substrate 36” in diameter. The novel chamber design utilizes a large substrate to be coated as a wall of the chamber. We discuss conceptual design and implementation of this new tool with potential applications to large astronomical optics, specifically protective coatings for silver telescope mirrors, and other large structures. In this work, trimethylaluminum and water was used to deposit aluminum oxide at a low reaction temperature of 60°C. Growth rates, dependent on precursor pulse times and chamber purge times, show that the two half-reactions occur in a saturated regime, which demonstrates typical characteristics of ideal ALD behavior. Thickness uniformity across a 36” substrate is within 2.5% of the average film thickness. MSAS aluminum oxide deposition process parameters are compared with those of a conventional 4” wafer-scale ALD tool. The results show promising application of transparent robust dielectric films as uniform barriers across large optical components.

Aluminum nitride (AlN) thin films were studied to assess the dependence of their optical properties on their chemical and structural characteristics. The AlN thin films used for the study were deposited by RF magnetron sputtering with an aluminum nitride target reactively sputtered with a mixture of Ar and N2 gases.Resulting AlN thin films were further studied in the form of Distributed Bragg Reflector (DBR) that consists of stoichiometric AlN thin films (high-n layer) and an off-stoichiometric AlN thin films (low-n layer). The DBR was designed for the UV-A spectrum region exploiting negligible extinction coefficient of these AlN thin films, demonstrating the fabrication of DBR with a single sputtering target. By incrementally adding a high-n/low-n pair, the evolution of optical properties of the DBR was studied with respect to its structural transformation.

Development of cost-effective and power-efficient optical interconnects is required to meet high demand of data transfer in the era of Internet of Things (IoT) that is expected to connect billions of sensors with different functionalities. The cost of optical links must be reduced for a wide adoption of optical interconnects in the fast data transmission systems. Monolithic integration of ultra-fast photodetectors (PDs), one of the major components of optical receivers-with CMOS/BiCMOS circuits, can reduce the cost dramatically. However, expensive material systems and non-CMOS-compatible processing utilized in the current high-speed photodetectors do not promise a monolithic integration to the required circuitry in the near future. On the other hand, high speed PDs with CMOS-compatible material systems such as silicon (Si), germanium (Ge) or SiGe alloys have poor responsivity for the wavelengths of interest at data rates 10 Gb/s or higher. Our solution to this problem is to increase the optical absorption properties of the semiconductor by introducing micro-/nanoscale air holes to the material. Such micro/nanoholes support an ensemble of modes that propagate laterally inside in a very thin layer of semiconductor (<2µm) which is required for high speed operations. The recent demonstration of surface-illuminated high-speed (>25Gb/s) and high efficiency (>50%) Si PDs with integrated micro-/nanoholes proved that light bending can enable ultra-fast Si-based PDs for monolithic integration with CMOS/BiCMOS circuits to realize cost-effective all-Si optical receivers. In this talk, a review of state-of-the art ultra-fast Si PDs for short-reach data communication will be presented and high speed and high efficiency PDs with alternative Si-based material systems will be demonstrated for the applications in long-reach optical links. Future opportunities that light-bending phenomenon can offer in high performance PD design for various applications such as single photon detection, LIDAR and high-performance computing will be discussed.

This paper presents a novel approach for the design and fabrication of graphene-based and fully printed single patch antennas. Graphene ink for inkjet printing is prepared by dispersing graphene nano flakes (12 nm) into terpineol and cyclohexanone solvents, and ethyl cellulose surfactant. The viscosity of the as-synthesized graphene ink is found to be 5.5 cP which is compatible with the inkjet printing. Raman spectroscopy is used to provide a structural fingerprint of the printed graphene flakes. Additionally, the printed graphene patterns become conductive for 35-40 printed layers. The physical structure of the single patch antenna consists of a printed transmission line and a single patch. The resonant frequency for the inkjet-printed graphene single patch antenna on DuPont Kapton FPC Polyimide substrate is 5 GHz, which is consistent with the design. The performance of printed graphene antenna is compared with the transferred graphene and printed silver antennas. The printed graphene antenna shows a better gain of 4.47 dBi and efficiency of 70%.

Quantum well devices can be investigated through the use of computational predictions of the electron-electron subband scattering rates. A high-accuracy prediction requires the calculation of the quantum well electron polarizability. An approximation is sometimes made that renders the integral in the polarizability equation analytically solvable. This study comprehensively quantifies the error and the limitations introduced through the use of this approximation. The approximate polarizability equation is found to introduce significant error for certain scenarios. Furthermore, the approximate polarizability equation is found to fail to give any numeric answer at all for relatively high temperatures and low electron densities.

The implementation of ultra-thin and highly efficient photodetectors and photovoltaic devices is crucial to realize flexible and wearable products in the era of Internet of Things (IoT). CMOS-compatible processing and well-established manufacturing makes Silicon (Si) a great material of choice in many applications but thin crystalline-Si is not as efficient as bulk Si in absorbing light. Light bending phenomenon enabled by micro-/nanoscale holes have been recently demonstrated to achieve high speed Si photodiodes and high efficiency thin crystalline-Si solar cells. Such small-scale devices can be released and transferred from mother substrate to various platforms such as the tips of fiber optic cables for realizing fiber receivers and probing applications in vivo studies. In this study, preliminary results of morphological and electrical characterization of transferred devices are demonstrated and details of the transfer techniques are presented. The quantum efficiency of devices transferred to aluminum coated glass were observed to get enhanced compared to the ones on Si substrate.

Localized surface plasmon resonances (LSPR) occur in certain metals where electrons confined to the metal surface oscillate with similar frequency as the perturbation source, giving rise to localized electromagnetic fields. In this study we employ experimental and theoretical analyses to characterize LSPR in Alcore(Al2O3)shell nanoparticles with controlled morphologies. We perform simulations of LSPR using Boundary Element Methods, where the electron beam is passing at a 2.5 nm distance from the surface of an icosahedron-shaped Alcore(Al2O3)shell nanoparticles. The energy loss probability spectra show that for the mode located at an energy around 7 eV, the LSPR energy and intensity have lower values compared to other modes, when the impact factor is placed near a facet, edge and corner of the nanoparticle respectively. This agrees with our experiment, where we collected electron energy-loss spectroscopy-LSPR measurements near the surface of the nanoparticles using a monochromated 80 KeV electron source with 100 meV energy resolution. The experimental spectra appertaining to the edge and corner of the nanoparticle display an energy shift as a function of position of the electron beam with respect to the nanoparticle. By applying a Non-Negative Matrix Factorization algorithm, we de-coupled convoluted LSPR signals and attribute them to the geometry of the nanoparticle. This allowed us to map the coupling coefficient of the electron beam with the LSPR revealing the energy transfer path from the excitation source to the plasmonic nanoparticles. This study paves the way for a better understanding of the localization of LSPR in nanocatalysts with nano-engineered morphologies.

Hexagonal boron nitride (hBN) is a natural hyperbolic material that supports both volume-confined hyperbolic polaritons (HPs) and sidewall-confined hyperbolic surface polaritons (HSPs). In this work, we demonstrate efficient excitation, control and steering of HSPs in hBN through engineering the geometry and orientation of hBN sidewalls. By combining infrared (IR) nano-imaging and numerical simulations, we investigate the reflection, transmission and scattering of HSPs at the hBN corners with various apex angles. We show that the sidewall-confined nature of HSPs enables a high degree of control over their propagation by designing the geometry of hBN nanostructures.

The emerging class of low symmetry 2D materials, which include black phosphorus, its isoelectronic materials such as the monochalcogenides of Group IV elements and other layered materials with reduced in-plane symmetry, exhibit strong in-plane anisotropy in their optical and phonon properties that allow for the realization of conceptually new electronic and photonic devices. High mobility, narrow gap BP thin film (0.3 eV in bulk), for example, fill the energy space between zero-gap graphene and large-gap transition metal dichalcogenides, making it a promising material for mid-infrared wavelength infrared optoelectronics. Here, we will first present our work in understanding the fundamental electronic and optical properties of low-symmetry 2D materials such as black phosphorus and rhenium diselenide using a newly developed scanning ultrafast electron microscopy (SUEM) technique and photoluminescence spectroscopy. A few novel photonic device concepts will then be discussed that utilize these new materials, particularly for applications in the infrared wavelength range. We will also discuss about promising future research directions of low-symmetry optoelectronic devices based on anisotropic 2D materials and how their novel properties is expected to benefit the next-generation photonics technologies.

During last 15 years significant attention of the research community was devoted to 2D materials, first-carbon based and recently- broad class of 2D semiconductors such as transition metal dichalcogenides ( TMDC), black phosphorous etc. Amazing wealth of physical and optoelectronic phenomena in TMDC make them an extremely attractive object of research both from the fundamental and applied points of view. Raman and photoluminescence spectroscopy proved to be powerful tools for characterization of 2D semiconductors. Unfortunately, spatial resolution of these techniques, on the order of few hundreds of nanometers is not sufficient to address important heterogeneities in these materials. STEM, to the contrary, provides true atomic resolution and allows addressing defects at single atom scale, but lacks to great extent correlation with physical properties of the materials in question. Luckily, recent advances in tip enhanced Raman spectroscopy ( TERS) and tip enhanced photoluminescence ( TEPL) and cross-correlation of these near-filed spectroscopic data with other properties probed by scanning probe microscopy, provide scientific community with a powerful and relatively easy-to-use characterization method that address the properties of 2D materials at proper scale. We’ll demonstrate application of cross-correlated TERS, TEPL, Kelvin probe microscopy, photocurrent mapping, friction etc for characterization of grain boundaries, physical defects, nanoscale doping heterogeneities in TMDCs and exciton population heterogeneities in the vicinity of the crystal edges in 2D semiconductors.

The limited Photoluminescence (PL) quantum yield of monolayer Transition metal dichalcogenides (1L-TMDs) are surprisingly shown to increase up to ~ 100 % by defect passivation mechanism i.e. suppressing the exciton quenching caused by the structural defects by simple chemical treatment. However, the mechanism behind it is in veil due to lack of experimental results in atomic level. In this work, we carried out bis(trifluoromethane) sulfonimide (TFSI) treatment of 1L-MoS2 and 1L-WS2 with different defects domains grown by chemical vapor deposition (CVD) and found drastically enhanced PL intensity in case of 1L-MoS2 while about 5 fold enhancement in case of 1L-WS2. Similarly the Raman intensity of both 1L-TMDs were increased and the intensity ratio of 2LA(M) to A1g peaks for 1L-WS2 were increased in different defect domains after TFSI treatment which are the strong evidence of defect passivation. We directly observed the atomic healing of 1L-TMDs by TFSI molecules under scanning transmission electron microscopy (STEM) analysis of pristine and TFSI treated 1L-TMDs and found that about ~ 90 % sulfur vacancies of 1L-TMDs were filled after treatment. The direct anchoring of dissociated sulfur atoms from TFSI molecules to the sulfur vacancies of 1L-TMDs was found to be energetically favorable by density functional theory calculations. Our observation shed light on the mechanism of intriguing healing process of lattice defects of 1L-TMDs and suggests that 1L-TMDs can be made defect-free which widens and prompts the practical uses of 1L-TMDs in nanophotonics applications. Furthermore, correlated experimental results and details will be presented.

Van der Waals epitaxy (vdWE) is an approach to grow crystal materials of high quality on the substrates even under a poor lattice matching condition. Graphene has been investigated to be a desirable buffer layer between substrates and layered materials to achieve vdWE. In this work, BiI3, a layered semiconducting material with high light-harvesting capability in the visible range, is successfully grown on graphene substrates via vdWE and presents highly orientated and ordered film. This is attributed to weak van der Waals interactions at the graphene/BiI3 heterojunction, which is verified by photoemission spectroscopy. In addition, the highly sensitive photodetectors with graphene/BiI3 hybrid channels perform a negative photocurrent response and an ultrahigh photoresponsivity of ~106 A W−1 under dim light, which is comparable to most previously reported photodetectors with graphene/semiconductor vertical heterostructures. Furthermore, due to nearly free interfacial traps and dangling bonds at graphene/BiI3 van der Waals heterojunctions, the graphene−BiI3 hybrid photodetectors exhibit significantly faster photocurrent rise time (<10 ms) and fall time (~500 ms) as compared with graphene-based hybrid photodetectors with CH3NH3PbI3 perovskite absorber layer (rise (fall) time of ~2 s (~1s)).

Supercapacitors (SCs) have got much attention in energy storage devices because of their higher power densities, fast charge-discharge processes, and extended cycle life. Conjugated polymers such as polyaniline (PANI) are widely used for the supercapacitor electrode applications due to its chemical stability, high conductivity, cost-effectiveness and ease of synthesis. PANI/multiwalled carbon nanotube (MWCNT) composite was synthesized via in-situ polymerization method. Morphological studies confirmed the formation of PANI/MWCNT composite. Detailed electrochemical characterization was carried out with aluminum and carbon cloth (CC) as a current collector for the fabrication of SC. PANI/MWCNT composite shows a specific capacitance of 0.02 F/g and 158.4 F/g using aluminum and carbon cloth as current collector, respectively, at a current density of 1 A/g within the potential range of 0 to 1 V in 1M lithium perchlorate electrolyte. The Charge storage in PANI/MWCNT composite SC is a combination of pseudocapacitance and electrical double layer capacitance. PANI/MWCNT composite with CC as current collector reaches a specific capacitance of ~174 F/g at a current density of 0.5 A/g. With the CC current collector, the composite electrode shows high cycling stability for more than 1000 cycles. Fiber-like 3D structure improves the surface area of the electrode and thereby increases the performance of the electrode in terms of cycling stability. The result shows that the synthesized binary composite is a promising electrode material for supercapacitor applications.

Hydrogen is an environmentally friendly energy carrier and its one of the most promising alternatives to the current traditional fossil-fuel based technologies. Hydrogen economy is currently hindered by a set of issues regarding production, distribution and end use and its storage has become one of the most arduous issues in the past few years. In this work, we report a novel synthesis routine for mesoporous monolythic boron nitride (BN) nanostructures based on a template assisted polymer-derived ceramic route. Polyborazylene has been used in order to impregnate monolithic activated carbon used as templates. After pyrolysis and template removal, BN polyhedral have been obtained, with controlled crystallinity and tunable textural properties, which highly depend on the annealing temperature. High-resolution Transmission Electron Microscopy analysis has shown that our synthesis routine has resulted in monoliths with an interconnected mesoporous network as well as high surface areas ranging from 584 to 728 m2·g-1, high pore volumes (0.75 to 0.93 cm3 · g-1) and high compressive strengths. Furthermore, we demonstrate the use of these highly porous compounds as nanoscaffolds to confine ammonia borane with the objective to enhance its dehydrogenation properties. The as formed composites are able to release pure H2 at low temperatures (1000 C) and show a remarkable effective gravimetric hydrogen storage capacity up to 8.1 wt. % based on measurement of ammonia borane. This demonstrates the remarkable potential of this system as a potential hydrogen storage material.

Chemical pre-intercalation is a low-temperature, scalable synthesis method that utilizes a sol-gel process to form layered oxides with positively-charged species inserted between the layers. We have shown that this approach can be used to successfully intercalate Li⁺ , Na⁺ , K⁺ , Mg²⁺, and Ca²⁺ ions into the crystal structure of bilayered vanadium oxide (δV₂O₅).1 Through this ion-intercalation, the interlayer spacing of the δ-Mg_xV₂O₅ (M=Li, Na, K, Mg, and Ca) structure can be controlled between 9.6 Å (δ-K_xV₂O₅) and 13.4 Å (δ-Mg_xV₂O₅).1 Moreover, the expanded spacing achieved for the δ-Mg_xV₂O₅ phase corresponded to increased electrochemical stability in both Li- and Na-ion cells.[1] While this study identified a correlation between expanded interlayer spacing and improved electrochemical stability over cycling, chemical pre-intercalation of ions does not allow for expansion beyond that exhibited by the δ-MgxV2O5 structure. In this work, we show that further expansion of the interlayer spacing can be achieved via pre-intercalation of positivelycharged linear, organic cations. We report synthesis of hybrid inorganic/organic materials with a 1D nanobelt morphology. The layered structure of the hybrids is confirmed by both XRD and TEM analysis. δ-V₂O₅ preintercalated with cetyltrimethylammonia ions, CTA⁺ , demonstrated the interlayer spacings of all samples (31 Å), more than twice larger than the largest interlayer spacing achieved via pre-intercalation of inorganic ions. The effects of carbon chainlength and positively charged nitrogen termini on the interlayer spacing and electrochemical stability is investigated, with two N-termini on the cation (DMO⁺) resulting in increased electrochemical stability of the preintercalated phase.

The medical prosthesis components made from (ZrO₂)-based ceramics present a good biocompatibility as well as especially mechanical properties. Much more, the problems of nondestructive evaluation for these elements, which assure both comfort and maximum safety to the patient, are imperative for these medical implants. In this study, we investigate the structure and the mechanical properties of Zr_1-x(Ce/Y)_xO₂ , (x=0.0;0.09;0.13;0.17) materials as well as the modification of their crystallographic structure due to various thermal treatments and variation of Ce/Y concentrations in the samples. The substitution of Zr with Ce and the thermal treatment at 1000°C produced important transformation in the phase composition and the microstructure of the sample. A large decrease of the microstrains was observed at the treated samples. Combining characterization techniques based on XRD and ND with non-destructive evaluation methods based on Resonant Ultrasound Spectroscopy (RUS) and Acoustic Emission (AE), we emphasize a unique approach on evaluating the physical properties of these ceramics. Performed evaluation tests of Zr_1-x(Ce/Y)_xO₂ ceramics have shown big influence of composition on their fracture behavior and resulting strength due to different damage mechanisms.

The low cost, environmental friendliness, and high electrochemical activity of manganese oxides make them attractive candidates for electrodes in intercalation-based battery systems. Tunnel manganese oxides are a subset of this materials family built from corner and edge sharing MnO₆ octahedra arranged around stabilizing cations and water molecules to form tunnels of various size and shape. Here, we synthesize three tunnel manganese oxides with different 1D diffusion channel size and ionic content. The apparent Li⁺ ion and Na⁺ ion diffusion coefficients are calculated from the galvanostatic intermittent titration technique to understand the effect of tunnel size and ionic content on diffusion of charge-carrying ions through the one-dimensional structural tunnels. In LIBs, the material with the largest tunnels demonstrated the highest Li⁺ ion diffusion coefficient, while in SIBs the material stabilized by Na⁺ ions (the same as the charge-carrying ions) demonstrated the highest rate performance, revealing the significance of ionic content in the structural tunnels. These results highlight the importance of the relationship between tunnel size and charge-carrying ion size and provide insight into the design and selection of tunnel manganese oxides for improved diffusion of charge carrying species.

Carbon material derived from biomass is used to modify the sulfur cathode. The modified sulfur cathode composite (ACS) together with PEDOT: PSS-CNT interlayer is used to visualize high performance Li-S cells. The Li-S cells with the interlayer inserted between the separator and ACS cathode shows remarkably improved electrochemical activity with an initial discharge capacity of 950 mA h g^-1 at 0.2 C. The improved performance for the interlayer assisted Li-S cells is due to the conductivity of the interlayer, also it can hold back the migrating polysulfides with in the cathode region and hindering the polysulfide shuttling phenomenon.

This work explores the ion removal performance of Na-birnessite and Mg-buserite during extended cycling in NaCl and MgCl₂ solutions in a hybrid capacitive deionization (HCDI) cell. These two layered manganese oxides (LMOs) contain two-dimensional diffusion pathways and thus present the potential for enhanced ion diffusion and higher performance in HCDI. Correlation between stabilizing ions and ions removed from solution are investigated. In NaCl solution, Mgbuserite shows the largest ion removal capacity of 37.2 mg g^-1 while the reverse is true in MgCl₂ solution, where Nabirnessite delivers a capacity of 50.2 mg g^-1. Furthermore, ex-situ XRD after 200 cycles revealed the changes in the structures of the two materials after repeated ion removal-ion release. These results demonstrate that materials with twodimensional crystal structures can demonstrate high capacities in HCDI and show that interlayer content and spacing can dramatically impact material stability in electrochemical water desalination.

In this study, electronic properties of field-effect transistors (FETs) fabricated from exfoliated MoTe₂ single crystals are investigated as a function of channel thickness. The conductivity type in FETs gradually changes from n-type for thick MoTe₂ layers (above ≈ 65 nm) to ambipolar behavior for intermediate MoTe₂ thickness (between ≈ 60 and 15 nm) to ptype for thin layers (below ≈ 10 nm). The n-type behavior in quasi-bulk MoTe₂ is attributed to doping with chlorine atoms from the TeCl₄ transport agent used for the chemical vapor transport (CVT) growth of MoTe₂. The change in polarity sign with decreasing channel thickness may be associated with increasing role of surface states in ultra-thin layers, which in turn influence carrier concentration and dynamics in the channel due to modulation of Schottky barrier height and band-bending at the metal/semiconductor interface.