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- ItemGraphene Q-switched Yb:KYW planar waveguide laser(New York, NY : American Inst. of Physics, 2015) Kim, Jun Wan; Young Choi, Sun; Aravazhi, Shanmugam; Pollnau, Markus; Griebner, Uwe; Petrov, Valentin; Bae, Sukang; Jun Ahn, Kwang; Yeom, Dong-Il; Rotermund, FabianA diode-pumped Yb:KYW planar waveguide laser, single-mode Q-switched by evanescent-field interaction with graphene, is demonstrated for the first time. Few-layer graphene grown by chemical vapor deposition is transferred onto the top of a guiding layer, which initiates stable Q-switched operation in a 2.4-cm-long waveguide laser operating near 1027 nm. Average output powers up to 34 mW and pulse durations as short as 349 ns are achieved. The measured output beam profile, clearly exhibiting a single mode, agrees well with the theoretically calculated mode intensity distribution inside the waveguide. As the pump power is increased, the repetition rate and pulse energy increase from 191 to 607 kHz and from 7.4 to 58.6 nJ, respectively, whereas the pulse duration decreases from 2.09 μs to 349 ns.
- ItemAtomically controlled CVD processing of group IV semiconductors for ultra-large-scale integrations(Bristol : IOP Publishing, 2012) Murota, Junichi; Sakuraba, Masao; Tillack, BerndOne of the main requirements for ultra-large-scale integrations (ULSIs) is atomic-order control of process technology. Our concept of atomically controlled processing is based on atomic-order surface reaction control by CVD. By ultraclean low-pressure CVD using SiH4 and GeH4 gases, high-quality low-temperature epitaxial growth of Si1−xGex (100) (x=0–1) with atomically flat surfaces and interfaces on Si(100) is achieved. Self-limiting formation of 1–3 atomic layers of group IV or related atoms in the thermal adsorption and reaction of hydride gases on Si1-xGex (100) are generalized based on the Langmuir-type model. By the Si epitaxial growth on top of the material already-formed on Si(100), N, B and C atoms are confined within about a 1 nm thick layer. In Si cap layer growth on the P atomic layer formed on Si1−xGex (100), segregation of P atoms is suppressed by using Si2H6 instead of SiH4 at a low temperature of 450 °C. Heavy C atomic-layer doping suppresses strain relaxation as well as intermixing between Si and Ge at the Si1−xGex/Si heterointerface. It is confirmed that higher carrier concentration and higher carrier mobility are achieved by atomic-layer doping. These results open the way to atomically controlled technology for ULSIs.
- ItemInN nanowires: Growth and optoelectronic properties(Basel : MDPI AG, 2012) Calarco, R.An overview on InN nanowires, fabricated using either a catalyst-free molecular beam epitaxy method or a catalyst assisted chemical vapor deposition process, is provided. Differences and similarities of the nanowires prepared using the two techniques are presented. The present understanding of the growth and of the basic optical and transport properties is discussed.
- ItemGraphene mode-locked Tm,Ho-codoped crystalline garnet laser producing 70-fs pulses near 21 µm(Washington, DC : OSA, 2019) Zhao, Yongguang; Chen, Weidong; Wang, Li; Wang, Yicheng; Pan, Zhongben; Dai, Xiaojun; Yuan, Hualei; Cai, Huaqiang; Zhang, Yan; Bae, Ji Eun; Park, Tae Gwan; Rotermund, Fabian; Loiko, Pavel; Serres, Josep Maria; Mateos, Xavier; Shen, Deyuan; Griebner, Uwe; Petrov, ValentinBilayer graphene synthesized by chemical vapor deposition is successfully applied as a saturable absorber (SA) for the passive mode-locking of a Tm,Ho:CLNGG laser at 2093nm. Near transform-limited pulses as short as 70 fs, i.e., 10 optical cycles, are produced at a 89 MHz repetition rate with 69 mW average output power. To the best of our knowledge, these are the shortest pulses ever reported from graphene-SA mode-locked Tm, or Ho-lasers in the 2 µm spectral region, including bulk and fiber lasers.
- ItemControl of etch pit formation for epitaxial growth of graphene on germanium(Melville, NY : American Inst. of Physics, 2019) Becker, Andreas; Wenger, Christian; Dabrowski, JarekGraphene epitaxy on germanium by chemical vapor deposition is a promising approach to integrate graphene into microelectronics, but the synthesis is still accompanied by several challenges such as the high process temperature, the reproducibility of growth, and the formation of etch pits during the process. We show that the substrate cleaning by preannealing in molecular hydrogen, which is crucial to successful and reproducible graphene growth, requires a high temperature and dose. During both substrate cleaning and graphene growth, etch pits can develop under certain conditions and disrupt the synthesis process. We explain the mechanisms how these etch pits may form by preferential evaporation of substrate, how substrate topography is related to the state of the cleaning process, and how etch pit formation during graphene growth can be controlled by choice of a sufficiently high precursor flow. Our study explains how graphene can be grown reliably on germanium at high temperature and thereby lays the foundation for further optimization of the growth process. © 2019 Author(s).
- ItemCVD-Grown CNTs on Basalt Fiber Surfaces for Multifunctional Composite Interphases(Basel : MDPI, 2016) Förster, Theresa; Hao, Bin; Mäder, Edith; Simon, Frank; Wölfel, Enrico; Ma, Peng-ChengChemical vapor deposition (CVD) is used as a method for the synthesis of carbon nanotubes (CNT) on substrates, most commonly pre-treated by a metal-catalyst. In this work, the capability of basalt fiber surfaces was investigated in order to stimulate catalyst-free growth of carbon nanotubes. We have carried out CVD experiments on unsized, sized, and NaOH-treated basalt fibers modified by growth temperature and a process gas mixture. Subsequently, we investigated the fiber surfaces by SEM, AFM, XPS and carried out single fiber tensile tests. Growth temperatures of 700 °C as well as 800 °C may induce CNT growth, but depending on the basalt fiber surface, the growth process was differently affected. The XPS results suggest surficial iron is not crucial for the CNT growth. We demonstrate that the formation of a corrosion shell is able to support CNT networks. However, our investigations do not expose distinctively the mechanisms by which unsized basalt fibers sometimes induce vertically aligned CNT carpets, isotropically arranged CNTs or no CNT growth. Considering data from the literature and our AFM results, it is assumed that the nano-roughness of surfaces could be a critical parameter for CNT growth. These findings will motivate the design of future experiments to discover the role of surface roughness as well as surface defects on the formation of hierarchical interphases.
- ItemSubstrate Developments for the Chemical Vapor Deposition Synthesis of Graphene(Weinheim : Wiley-VCH Verlag, 2020) Shi, Q.; Tokarska, K.; Ta, H.Q.; Yang, X.; Liu, Y.; Ullah, S.; Liu, L.; Trzebicka, B.; Bachmatiuk, A.; Sun, J.; Fu, L.; Liu, Z.; Rümmeli, M.H.Since the isolation of graphene and numerous demonstrations of its unique properties, the expectations for this material to be implemented in many future commercial applications have been enormous. However, to date, challenges still remain. One of the key challenges is the fabrication of graphene in a manner that satisfies processing requirements. While transfer of graphene can be used, this tends to damage or contaminate it, which degrades its performance. Hence, there is an important drive to grow graphene directly over a number of technologically important materials, viz., different substrate materials, so as to avoid the need for transfer. One of the more successful approaches to synthesis graphene is chemical vapor deposition (CVD), which is well established. Historically, transition metal substrates are used due to their catalytic properties. However, in recent years this has developed to include many nonmetal substrate systems. Moreover, both solid and molten substrate forms have also been demonstrated. In addition, the current trend to progress flexible devices has spurred interest in graphene growth directly over flexible materials surfaces. All these aspects are presented in this review which presents the developments in available substrates for graphene fabrication by CVD, with a focus primarily on large area graphene.
- ItemScalable Functionalization of Optical Fibers Using Atomically Thin Semiconductors(Weinheim : Wiley-VCH Verlag, 2020) Ngo G.Q.; George A.; Schock R.T.K.; Tuniz A.; Najafidehaghani E.; Gan Z.; Geib N.C.; Bucher T.; Knopf H.; Saravi S.; Neumann C.; Lühder T.; Schartner E.P.; Warren-Smith S.C.; Ebendorff-Heidepriem H.; Pertsch T.; Schmidt M.A.; Turchanin A.; Eilenberger F.Atomically thin transition metal dichalcogenides are highly promising for integrated optoelectronic and photonic systems due to their exciton-driven linear and nonlinear interactions with light. Integrating them into optical fibers yields novel opportunities in optical communication, remote sensing, and all-fiber optoelectronics. However, the scalable and reproducible deposition of high-quality monolayers on optical fibers is a challenge. Here, the chemical vapor deposition of monolayer MoS2 and WS2 crystals on the core of microstructured exposed-core optical fibers and their interaction with the fibers’ guided modes are reported. Two distinct application possibilities of 2D-functionalized waveguides to exemplify their potential are demonstrated. First, the excitonic 2D material photoluminescence is simultaneously excited and collected with the fiber modes, opening a novel route to remote sensing. Then it is shown that third-harmonic generation is modified by the highly localized nonlinear polarization of the monolayers, yielding a new avenue to tailor nonlinear optical processes in fibers. It is anticipated that the results may lead to significant advances in optical-fiber-based technologies. © 2020 The Authors. Published by Wiley-VCH GmbH
- ItemStudies towards synthesis, evolution and alignment characteristics of dense, millimeter long multiwalled carbon nanotube arrays(Frankfurt, M. : Beilstein-Institut zur Förderung der Chemischen Wissenschaften, 2011) Mahanandia, P.; Schneider, J.J.; Engel, M.; Stühn, B.; Subramanyam, S.V.; Nanda, K.K.We report the synthesis of aligned arrays of millimeter long carbon nanotubes (CNTs), from benzene and ferrocene as the molecular precursor and catalyst respectively, by a one-step chemical vapor deposition technique. The length of the grown CNTs depends on the reaction temperature and increases from ~85 μm to ~1.4 mm when the synthesis temperature is raised from 650 to 1100°C, while the tube diameter is almost independent of the preparation temperature and is ~80 nm. The parallel arrangement of the CNTs, as well as their tube diameter can be verified spectroscopically by small angle X-ray scattering (SAXS) studies. Based on electron diffraction scattering (EDS) studies of the top and the base of the CNT films, a root growth process can be deduced.
- ItemMagnetization Dynamics of an Individual Single-Crystalline Fe-Filled Carbon Nanotube(Weinheim : Wiley-VCH, 2019) Lenz, Kilian; Narkowicz, Ryszard; Wagner, Kai; Reiche, Christopher F.; Körner, Julia; Schneider, Tobias; Kákay, Attila; Schultheiss, Helmut; Weissker, Uhland; Wolf, Daniel; Suter, Dieter; Büchner, Bernd; Fassbender, Jürgen; Mühl, Thomas; Lindner, JürgenThe magnetization dynamics of individual Fe-filled multiwall carbon-nanotubes (FeCNT), grown by chemical vapor deposition, are investigated by microresonator ferromagnetic resonance (FMR) and Brillouin light scattering (BLS) microscopy and corroborated by micromagnetic simulations. Currently, only static magnetometry measurements are available. They suggest that the FeCNTs consist of a single-crystalline Fe nanowire throughout the length. The number and structure of the FMR lines and the abrupt decay of the spin-wave transport seen in BLS indicate, however, that the Fe filling is not a single straight piece along the length. Therefore, a stepwise cutting procedure is applied in order to investigate the evolution of the ferromagnetic resonance lines as a function of the nanowire length. The results show that the FeCNT is indeed not homogeneous along the full length but is built from 300 to 400 nm long single-crystalline segments. These segments consist of magnetically high quality Fe nanowires with almost the bulk values of Fe and with a similar small damping in relation to thin films, promoting FeCNTs as appealing candidates for spin-wave transport in magnonic applications. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim