Title Participants "A double-sided surface scanning platform for sapphire substrate quality assessment" "Tegoeh Tjahjowidodo" "Nucleation Mechanism during WS2 Plasma Enhanced Atomic Layer Deposition on Amorphous Al2O3 and Sapphire Substrates" "Benjamin Groven, Ankit Nalin Mehta, Johan Meersschaut, Wilfried Vandervorst, Marc Heyns, Iuliana Radu, Annelies Delabie" "The structure, crystallinity and properties of as-deposited two-dimensional (2D) transition metal dichalcogenides are determined by nucleation mechanisms in the deposition process. 2D materials grown by atomic layer deposition (ALD) in absence of a template, are polycrystalline or amorphous. Little is known about their nucleation mechanisms. Therefore, we investigate the nucleation behavior of WS2 during plasma enhanced ALD from WF6, H2 plasma and H2S at 300 °C on amorphous ALD Al2O3 starting surface and on monocrystalline, bulk sapphire. Preferential interaction of the precursors with the Al2O3 starting surface promotes fast closure of the WS2 layer. The WS2 layers are fully continuous at WS2 content corresponding to only 1.2 WS2 monolayers. On amorphous Al2O3, (0002) textured and polycrystalline WS2 layers form with grain size of 5 nm to 20 nm due to high nucleation density (~1014 nuclei/cm2). The WS2 growth mode changes from 2D (layer-by-layer) growth on the initial Al2O3 surface to three-dimensional (Volmer-Weber) growth after WS2 layer closure. Further growth proceeds from both WS2 basal planes in register with the underlying WS2 grain, and from or over grain boundaries of the underlying WS2 layer with different in-plane orientation. In contrast, on monocrystalline sapphire, WS2 crystal grains can locally align along a preferred in-plane orientation. Epitaxial seeding occurs locally albeit a large portion of crystals remain randomly oriented, presumably due to the low deposition temperature. The WS2 sheet resistance is 168 MΩµm suggesting that charge transport in the WS2 layers is limited by grain boundaries." "Scanning tunneling microscopy for imaging and quantification of defects in as-deposited MoS₂ monolayers on sapphire substrates" "Renan Villarreal De La Fuente, Lino da Costa Pereira, Valeri Afanasiev" "This paper quantitatively assessed the intrinsic defectivity of as-deposited molybdenum disulfide (MoS₂) monolayers on sapphire substrates using atomically resolved scanning tunneling microscopy and spectroscopy. We observed two types of point defects — protrusion-like and depression-like with average densities of (2.4 ± 2) · 10¹³ cm¯² and (1.9 ± 1.4) · 10¹² cm¯², respectively. The position of the electron state within the MoS₂ bandgap suggests that the protrusion-like defect associates with a sulfur mono-vacancy." "In situ bow monitoring: towards uniform blue and green InGaN/GaN quantum well structures grown on 100mm sapphire substrates by MOVPE" "Kai Cheng, Stefan Degroote, Maarten Leys, Liyang Zhang, Joff Derluyn, Marianne Germain, Gustaaf Borghs" "Scanning tunneling microscopy for imaging and quantification of defects in as-deposited MoS2 monolayers on sapphire substratesâ" "Thomas Hantschel, Yevhenii Rybalchenko, Albert Minj, Valeri Afanasiev, Dennis Lin, Pierre Morin, Henry Medina Silva, Benjamin Groven" "This paper quantitatively assessed the intrinsic defectivity of as-deposited molybdenum disulfide (MoS2) monolayers on sapphire substrates using atomically resolved scanning tunneling microscopy and spectroscopy. We observed two types of point defects - protrusion-like and depression-like with average densities of (2.4 +/- 2) center dot 1013 cm-2 and (1.9 +/- 1.4) center dot 1012 cm-2, respectively. The position of the electron state within the MoS2 bandgap suggests that the protrusion-like defect associates with a sulfur mono-vacancy." "Heat-transfer based characterization of DNA on synthetic sapphire chips" "Mohammed Sharif MURIB, Weng Siang YEAP, Y. Eurlings, Bart VAN GRINSVEN, Hans-Gerd BOYEN, Bert CONINGS, Luc MICHIELS, Marcel AMELOOT, Robert CARLEER, J. Warmer, P. Kaul, Ken HAENEN, M.J. Schoening, Ward DE CEUNINCK, Patrick WAGNER" "In this study, we show that synthetic sapphire (Al2O3), an established implant material, can also serve as a platform material for biosensors comparable to nanocrystalline diamond. Sapphire chips, beads, and powder were first modified with (3-aminopropyl) triethoxysilane (APTES), followed by succinic anhydride (SA), and finally single-stranded probe DNA was EDC coupled to the functionalized layer. The presence of the APTES-SA layer on sapphire powders was confirmed by thermogravimetric analyis and Fourier-transform infrared spectroscopy. Using planar sapphire chips as substrates and X-ray photoelectron spectroscopy (XPS) as surface-sensitive tool, the sequence of individual layers was analyzed with respect to their chemical state, enabling the quantification of areal densities of the involved molecular units. Fluorescence microscopy was used to demonstrate the hybridization of fluorescently tagged target DNA to the probe DNA, including denaturation- and re-hybridization experiments. Due to its high thermal conductivity, synthetic sapphire is especially suitable as a chip material for the heat-transfer method, which was employed to distinguish complementary- and non-complementary DNA duplexes containing single-nucleotide polymorphisms. These results indicate that it is possible to detect mutations electronically with a chemically resilient and electrically insulating chip material." "Synthesis of Few-Layered Transition-Metal Dichalcogenides by Ion Implantation of Chalcogen and Metal Species into Sapphire" "Lino da Costa Pereira" "The growth of transition-metal dichalcogenides (TMDCs) has been performed so far using most established thin-film growth techniques (e.g., vapor phase transport, chemical vapor deposition, molecular beam epitaxy, etc.). However, because there exists no self-limiting mechanism for the growth of TMDCs, none of these techniques allows precise control of the number of TMDC layers over large substrate areas. Here, we explore the ion implantation of the parent TMDC atoms into a chemically neutral substrate for the synthesis of TMDC films. The idea is that once all of the ion-implanted species have reacted together, the synthesis reaction stops, thereby effectively stopping growth. In other words, even if there is no self-limiting mechanism, growth stops when the nutrients are exhausted. We have co-implanted Mo and S ions into c-oriented sapphire substrates using various doses corresponding to 1- to 5-layer atom counts. We find that the subsurface region of the sapphire substrates is amorphized by the ion implantation process, at least for implanted doses of 2-layer atom counts and over. For all doses, we have observed the formation of MoS2 material inside the sapphire after postimplantation annealing between 800 and 850 °C. We report that the order of implantation (i.e., whether S or Mo is implanted first) is an important parameter. More precisely, samples for which S is implanted first tend to yield thin crystals with a large lateral extension (more than 200 nm for 5-layer doses) and mainly located at the interface between the amorphized and crystalline sapphire. When Mo is first implanted, the MoS2 crystals still predominantly appear at the amorphous-crystalline interface (which is much rougher), but they are much thicker, suggesting a different nucleation mechanism." "Peculiar alignment and strain of 2D WSe2 grown by van der Waals epitaxy on reconstructed sapphire surfaces" "Wouter Mortelmans, Johan Meersschaut, Stefan De Gendt, Marc Heyns, Clement Merckling" "The increasing scientific and industry interest in 2D MX2 materials within the field of nanotechnology has made the single crystalline integration of large area van der Waals (vdW) layers on commercial substrates an important topic. The c-plane oriented (3D crystal) sapphire surface is believed to be an interesting substrate candidate for this challenging 2D/3D integration. Despite the many attempts that have been made, the yet incomplete understanding of vdW epitaxy still results in synthetic material that shows a crystallinity far too low compared to natural crystals that can be exfoliated onto commercial substrates. Thanks to its atomic control and in situ analysis possibilities, molecular beam epitaxy (MBE) offers a potential solution and an appropriate method to enable a more in-depth understanding of this peculiar 2D/3D hetero-epitaxy. Here, we report on how various sapphire surface reconstructions, that are obtained by thermal annealing of the as-received substrates, influence the vdW epitaxy of the MBE-grown WSe2 monolayers (MLs). The surface chemistry and the interatomic arrangement of the reconstructed sapphire surfaces are shown to control the preferential in-plane epitaxial alignment of the stoichiometric WSe2 crystals. In addition, it is demonstrated that the reconstructions also affect the in-plane lattice parameter and thus the in-plane strain of the 2D vdW-bonded MLs. Hence, the results obtained in this work shine more light on the peculiar concept of vdW epitaxy, especially relevant for 2D materials integration on large-scale 3D crystal commercial substrates." "Crystal plane dependent growth of aligned single-walled carbon nanotubes on sapphire" "Kostya Iakoubovskii" "On single-crystal substrates, such as sapphire (alpha-Al 2O 3) and quartz (SiO 2), single-walled carbon nanotubes (SWNTs) align along specific crystallographic axes of the crystal, indicating that the SWNT growth is influenced by the crystal surface. Here, we show that not only the orientation, but also the diameter and chirality of SWNTs are affected by the crystal plane of the sapphire substrate. The aligned SWNTs grown on the A- and R-planes of sapphire have narrower diameter distributions than randomly oriented tubes produced on the C-plane sapphire and amorphous SiO 2. Photoluminescence measurements reveal a striking difference between the aligned SWNTs: near-zigzag tubes are observed on the A-plane and near-armchair tubes on the R-plane. This study shows the route for the diameter and chirality control of SWNTs by surface atomic arrangements of a single-crystal substrate." "Chemical Vapor Deposition of a Single-Crystalline MoS2 Monolayer through Anisotropic 2D Crystal Growth on Stepped Sapphire Surface" "Iryna Kandybka, Sreetama Banerjee, Stefanie Sergeant, Ankit Nalin Mehta, Annelies Delabie, Pierre Morin, Henry Medina Silva, Yuanyuan Shi, Benjamin Groven, Serkan Koylan" "Recently, a step-flow growth mode has been proposed to break the inherent molybdenum disulfide (MoS2 ) crystal domain bimodality and yield a single-crystalline MoS2 monolayer on commonly employed sapphire substrates. This work reveals an alternative growth mechanism during the metal-organic chemical vapor deposition (MOCVD) of a single-crystalline MoS2 monolayer through anisotropic 2D crystal growth. During early growth stages, the epitaxial symmetry and commensurability of sapphire terraces rather than the sapphire step inclination ultimately govern the MoS2 crystal orientation. Strikingly, as the MoS2 crystals continue to grow laterally, the sapphire steps transform the MoS2 crystal geometry into diamond-shaped domains presumably by anisotropic diffusion of ad-species and facet development. Even though these MoS2 domains nucleate on sapphire with predominantly bimodal 0 and 60 degrees azimuthal rotation, the individual domains reach lateral dimensions of up to 200 nm before merging seamlessly into a single-crystalline MoS2 monolayer upon coalescence. Plan-view transmission electron microscopy reveals the single-crystalline nature across 50 mu m by 50 mu m inspection areas. As a result, the median carrier mobility of MoS2 monolayers peaks at 25 cm2 V-1 s(-1) with the highest value reaching 28 cm2 V-1 s(-1). This work details synthesis-structure correlations and the possibilities to tune the structure and material properties through substrate topography toward various applications in nanoelectronics, catalysis, and nanotechnology. Moreover, shape modulation through anisotropic growth phenomena on stepped surfaces can provide opportunities for nanopatterning for a wide range of materials."