Substrate-Independent Growth of Atomically Precise Chiral Graphene Nanoribbons
Dimas G. de Oteyza, Aran Garcia-Lekue, Manuel Vilas-Varela, Nestor Merino, Eduard Carbonell-Sanromà, Martina Corso, Guillaume Vasseur, Celia Rogero, Enrique Gui… 展开作者
Dimas G. de Oteyza, Aran Garcia-Lekue, Manuel Vilas-Varela, Nestor Merino, Eduard Carbonell-Sanromà, Martina Corso, Guillaume Vasseur, Celia Rogero, Enrique Guitian, Jose Ignacio Pascua, J. Enrique Ortega, Yutaka Wakayama, Diego Peña
Contributing to the need of new graphene nanoribbon (GNR) structures that can be synthesized with atomic precision, we have designed a reactant that renders chiral (3,1) - GNRs after a multi-step reaction including Ullmann coupling and cyclodehydrogenation. The nanoribbon synthesis has been successfully proved on different coinage metals, and the formation process, together with the fingerprints associated to each reaction step, has been studied combining scanning tunnelling microscopy, core-level spectroscopy and density functional calculations. In addition to the GNR chiral edge structure, the substantial GNR lengths achieved and the low processing temperature required to complete the reaction grant this reactant extremely interesting properties for potential applications.
One-dimensional (1D) materials have attracted significant research interest due to their unique quantum confinement effects and edge-related properties. Atomically thin 1D nanoribbon is particularly interesting because it is a valuable platform with physical limits of both thickness and width. Here, we develop a catalyst-free growth method and achieves the growth of Bi2O2Se nanostructures with tunable dimensionality. Significantly, Bi2O2Se nanoribbons with thickness down to 0.65 nm, corresponding to monolayer, are successfully grown for the first time. Electrical and optoelectronic measurement…
The fabrication of atomically precise structures with designer electronic properties is one of the emerging topics in condensed matter physics. The required level of structural control can either be reached through atomic manipulation using the tip of a scanning tunneling microscope (STM) or by bottom-up chemical synthesis. In this review, we focus on recent progress in constructing novel, atomically precise artificial materials: artificial lattices built through atom manipulation and graphene nanoribbons (GNRs) realized by on-surface synthesis. We summarize the required theoretical background…
We study the band gap of finite $N_A=7$ armchair graphene nanoribbons (7-AGNRs) on Au(111) through scanning tunneling microscopy/spectroscopy combined with density functional theory calculations. The band gap of 7-AGNRs with lengths of 6 nm and more is converged to within 0.1 eV of its bulk value of 2.3 eV, while the band gap opens by several hundred meV in very short 7-AGNRs. The termination has a significant effect on the band gap, doubly hydrogenated termini yielding a lower band gap than singly hydrogenated ones.
Monolayer materials are strongly affected by their potential fluctuations, which are induced by an intrinsic corrugation or the surface roughness of the substrate. We compare the effective exciton-exciton annihilation (EEA) rate constants of monolayer WS2 on substrates with different surface topographies. We show that monolayer WS2 on the substrate with atomically flat terraces displays small effective EEA rate constant deviating from the overall tendency and multiple exciton decay components, which cannot be accounted for by a conventional EEA model. To obtain a correct description, we use a …
The on-surface synthesis of graphene nanoribbons (GNRs) allows for the fabrication of atomically precise narrow GNRs. Despite their exceptional properties which can be tuned by ribbon width and edge structure, significant challenges remain for GNR processing and characterization. In this contribution, we use Raman spectroscopy to characterize different types of GNRs on their growth substrate and to track their quality upon substrate transfer. We present a Raman-optimized (RO) device substrate and an optimized mapping approach that allows for acquisition of high-resolution Raman spectra, achiev…
Recent progress in the on-surface synthesis of graphene nanoribbons (GNRs) has given access to atomically precise narrow GNRs with tunable electronic band gaps that makes them excellent candidates for room-temperature switching devices such as field-effect transistors (FET). However, in spite of their exceptional properties, significant challenges remain for GNR processing and characterization. This contribution addresses some of the most important challenges, including GNR fabrication scalability, substrate transfer, long-term stability under ambient conditions and ex situ characterization. W…
Excitonic emission from atomically precise graphene nanoribbons (GNRs) synthesised on a metal surface is probed with atomic-scale spatial resolution using a scanning tunneling microscopy (STM) approach. A STM-based strategy to transfer the GNRs to a partially insulating surface is used to prevent light emission quenching of the ribbons by the metal substrate. Sub-nanometer resolved STM-induced fluorescence spectra reveal emission from localized dark excitons build upon the topological end states of the GNRs. A low frequency vibronic emission comb whose characteristics change with the GNR lengt…
Atomically-abrupt interfaces in transition metal oxide (TMO) heterostructures could host a variety of exotic condensed matter phases that may not be found in the bulk materials at equilibrium. A critical step in the development of such atomically-sharp interfaces is the deposition of atomically-smooth TMO thin films. Optimized deposition conditions exist for the growth of perovskite oxides. However, the deposition of rutile oxides, such as VO$_2$, with atomic-layer precision has been challenging. In this work, we used pulsed laser deposition (PLD) to grow atomically-smooth VO$_2$ thin films on…
The challenge of synthesizing graphene nanoribbons (GNRs) with atomic precision is currently being pursued along a one-way road, based on the synthesis of adequate molecular precursors that react in predefined ways through self-assembly processes. The synthetic options for GNR generation would multiply by adding a new direction to this readily successful approach, especially if both of them can be combined. We show here how GNR synthesis can be guided by an adequately nanotemplated substrate instead of by the traditionally designed reactants. The structural atomic precision, unachievable to da…
We report successful deposition of high quantum efficiency (QE) bialkali antimonide K2CsSb photocathodes on graphene films. The results pave a pathway towards an ultimate goal of encapsulating technologically-relevant photocathodes for accelerator technology with an atomically-thin protecting layer to enhance lifetime while minimizing QE losses. A QE of 17 % at ~3.1 eV (405 nm) is the highest value reported so far on graphene substrates and is comparable to that obtained on stainless steel and nickel reference substrates. The spectral responses of the photocathodes on graphene exhibit signatur…
Strain engineering in single-layer semiconducting transition metal dichalcogenides aims to tune their bandgap energy and to modify their optoelectronic properties by the application of external strain. In this paper we study transition metal dichalcogenides monolayers deposited on polymeric substrates under the application of biaxial strain, both tensile and compressive. We can control the amount of biaxial strain applied by letting the substrate thermally expand or compress by changing the substrate temperature. After modelling the substrate-dependent strain transfer process with a finite ele…
On-surface synthesis has recently emerged as an effective route towards the atomically precise fabrication of graphene nanoribbons of controlled topologies and widths. However, whether and to which degree structural disorder occurs in the resulting samples is a crucial issue for prospective applications that remains to be explored. Here, we experimentally identify missing benzene rings at the edges, which we name "bite" defects, as the most abundant type of disorder in armchair nanoribbons synthesized by the bottom-up approach. First, we address their density and spatial distribution on the ba…
Graphene nanoribbons (GNRs) have attracted considerable interest as their atomically tunable structure makes them promising candidates for future electronic devices. However, obtaining detailed information about the length of GNRs has been challenging and typically relies on low-temperature scanning tunneling microscopy. Such methods are ill-suited for practical device application and characterization. In contrast, Raman spectroscopy is a sensitive method for the characterization of GNRs, in particular for investigating their width and structure. Here, we report on a length-dependent, Raman ac…
We extensively characterize the electronic structure of ultra-narrow graphene nanoribbons (GNRs) with armchair edges and zig-zag termini that have 5 carbon atoms across their width (5-AGNRs), as synthesised on Au(111). Scanning tunnelling spectroscopy measurements on the ribbons, recorded on both the metallic substrate and a decoupling NaCl layer, show well-defined dispersive bands and in-gap states. In combination with theoretical calculations, we show how these in-gap states are topological in nature and localised at the zig-zag termini of the nanoribbons. Besides rationalising the driving f…
Atomically thin layers of transition metal dichalcogenides (TMDCs) exhibit exceptionally strong Coulomb interaction between charge carriers due to the two-dimensional carrier confinement in connection with weak dielectric screening. The van der Waals nature of interlayer coupling makes it easy to integrate TMDC layers into heterostructures with different dielectric or metallic substrates. This allows to tailor electronic and optical properties of these materials, as Coulomb interaction inside atomically thin layers is very susceptible to screening by the environment. Here we theoretically inve…
2D abrupt nano-junctions blending sp-sp2 bonds on atomically precise heterostructures
Politecnico di Milano（米兰理工大学）；Università degli Studi di Milano（米兰大学）；INFN Sezione di Milano（意大利国家核物理研究所米兰分部）；Università di Pavia（帕维亚大学）；Università Degli Studi Di Padova（帕多瓦大学）；Instituto de Nanociencia y Materiales de Aragon (INMA), CSIC-Universidad de Zaragoza（阿拉贡纳米科学与材料研究所（INMA），西班牙国家科学研究委员会-萨拉戈萨大学）
Graphene nanoribbons (GNRs) with widths of a few nanometres are promising candidates for future nano-electronic applications due to their structurally tunable bandgaps, ultrahigh carrier mobilities, and exceptional stability. However, the direct growth of micrometre-long GNRs on insulating substrates, which is essential for the fabrication of nano-electronic devices, remains an immense challenge. Here, we report the epitaxial growth of GNRs on an insulating hexagonal boron nitride (h-BN) substrate through nanoparticle-catalysed chemical vapor deposition (CVD). Ultra-narrow GNRs with lengths of…
We study numerically the adsorption of a mixture of CO$_2$ and CH$_4$ on a graphite substrate covered by graphene nanoribbons (NRs). The NRs are flat and parallel to the graphite surface, at a variable distance ranging from 6 Å to 14 Å. We show that the NRs-graphite substrate acts as an effective filter for CO$_2$. Our study is based on Molecular Dynamics (MD) simulations. Methane is considered a spherical molecule, and carbon dioxide is represented as a linear rigid body. Graphite is modeled as a continuous material, while the NRs are approached atomistically. We observe that when the NRs are…
We report quantum efficiency (QE) enhancements in accelerator technology relevant antimonide photocathodes (K2CsSb) by interfacing them with atomically thin two-dimensional (2D) crystal layers. The enhancement occurs in a reflection mode, when a 2D crystal is placed in between the photocathodes and optically reflective substrates. Specifically, the peak QE at 405 nm (3.1 eV) increases by a relative 10 percent, while the long wavelength response at 633 nm (2.0 eV) increases by a relative 36 percent on average and up to 80 percent at localized hot spot regions when photocathodes are deposited on…
Mott transition has been realized in atomically thin monolayer (ML) of two dimensional semiconductors (WS$_2$) via optically excited carriers above a critical carrier density through many body interactions. The above nonlinear optical transition occurs when excited electron hole pairs in ML WS2 continuum heavily interact with each other followed by transformation into a collective electron hole plasma phase (EHP), by losing their identity as individual quasiparticles. This is manifested by the alluring red-shift-blue-shift crossover (RBC) phenomena of the excitonic peaks in the emission spectr…
Understanding the nature and hierarchy of on surface reactions is a major chal- lenge for designing coordination and covalent nanostructures by means of multistep synthetic routes. In particular, intermediates and final products are hard to predict since reaction paths and their activation windows depend on the choice of both the molecular precursor design and the substrate. Here we report a systematic study of the effect of the catalytic metal surface to reveal how a single precursor can give rise to very distinct polymers that range from coordination and covalent non planar polymer chains of…
