Browsing by Author "Doumani, Jacques"

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    Characterizations of two-photon absorption process induced by defects in aluminum nitride using Z-scan method
    (IOP Publishing, 2024) Zhou, Jingan; Li, Tao; Zhao, Xuan; Zhang, Xiang; Doumani, Jacques; Xu, Mingfei; He, Ziyi; Luo, Shisong; Mei, Zhaobo; Chang, Cheng; Robinson, Jacob T.; Ajayan, Pulickel M.; Kono, Junichiro; Zhao, Yuji; Smalley-Curl Institute
    In this work, we reported two-photon absorption (TPA) measurements for aluminum vacancies in Aluminum nitride single crystals. We measured the linear transmission and identified the defect levels. Using the Z-scan method, we measured the TPA coefficients of the transitions between defect levels from 380 nm to 735 nm. The transition occurs between the aluminum vacancies defect levels. Furthermore, the power dependence shows good linear fitting, confirming the TPA mechanism. These results will be helpful for the design and fabrication of ultra-low loss waveguides and integrated photonics in the ultraviolet spectral range.
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    Engineering chirality at wafer scale with ordered carbon nanotube architectures
    (Springer Nature, 2023) Doumani, Jacques; Lou, Minhan; Dewey, Oliver; Hong, Nina; Fan, Jichao; Baydin, Andrey; Zahn, Keshav; Yomogida, Yohei; Yanagi, Kazuhiro; Pasquali, Matteo; Saito, Riichiro; Kono, Junichiro; Gao, Weilu; Carbon Hub; Smalley-Curl Institute
    Creating artificial matter with controllable chirality in a simple and scalable manner brings new opportunities to diverse areas. Here we show two such methods based on controlled vacuum filtration - twist stacking and mechanical rotation - for fabricating wafer-scale chiral architectures of ordered carbon nanotubes (CNTs) with tunable and large circular dichroism (CD). By controlling the stacking angle and handedness in the twist-stacking approach, we maximize the CD response and achieve a high deep-ultraviolet ellipticity of 40 ± 1 mdeg nm−1. Our theoretical simulations using the transfer matrix method reproduce the experimentally observed CD spectra and further predict that an optimized film of twist-stacked CNTs can exhibit an ellipticity as high as 150 mdeg nm−1, corresponding to a g factor of 0.22. Furthermore, the mechanical rotation method not only accelerates the fabrication of twisted structures but also produces both chiralities simultaneously in a single sample, in a single run, and in a controllable manner. The created wafer-scale objects represent an alternative type of synthetic chiral matter consisting of ordered quantum wires whose macroscopic properties are governed by nanoscopic electronic signatures and can be used to explore chiral phenomena and develop chiral photonic and optoelectronic devices.
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    Harnessing Chirality in Ordered Carbon Nanotube Architectures at Wafer Scale
    (2024-08-09) Doumani, Jacques; Kono, Junichiro
    Harnessing chirality can advance diverse technologies, encompassing displays, quantum light sources, secured communication, and biosensing. This thesis explores harnessing chirality in carbon nanotubes (CNTs) at wafer scales, focusing on molecular intrinsic and structurally engineered chirality. Significant advancements were made in alignment techniques, second harmonic generation (SHG) from aligned and chiral CNT films, and engineering structural chirality in CNTs. We developed techniques to enhance CNT alignment using controlled vacuum filtration, including linear reciprocating shaking, and introduced a novel SEM-based method for characterizing nematic order parameters. The AquaGold process was developed for monolayer precision thinning, achieving a wafer-scale aligned CNT film with a thickness of 2.3 nm and a packing factor of 1000 CNTs/μm. Through SHG measurements, we discovered significant second-order optical nonlinearity in wafer-scale, enantiomer-pure, aligned, and densely packed chiral (6,5)- CNT thin films. The only non-zero element of the second-order nonlinear optical susceptibility tensor reached approximately 1.5 nm/V, the highest value for 1D systems. We also fabricated wafer-scale chiral architectures of ordered CNTs with tunable and large circular dichroism. By controlling the stacking angle and handedness, we achieved a high deep-ultraviolet ellipticity of 40 mdeg/nm. These findings pave the way for applications in chiral photonics and opto-electronics.