International Workshop on Nanomaterials and Nanodevices
联 系 人：秦志辉
Designing Energy Materials via Atomic-resolution Microscopy and Spectroscopy
主 讲 人：Stephen J. Pennycook，National University of Singapore
讲座摘要：In recent years, the sensitivity of the electron microscope for imaging and spectroscopy has dramatically improved due to aberration correction, greatly assisting the correlation of atomic-scale structure and bonding to materials’ properties. Trial and error materials’ development is increasingly being replaced by atomic scale engineering, informed by the powerful combination of microscopy and theoretical calculations.
In catalysis for example, it has become almost routine to image single atoms and probe their coordination by spectroscopy, greatly aiding the development of so-called single atom catalysts (SACs). Their unique coordination can impart exceptional activity and selectivity, and much effort is ongoing to replace platinum group metals by cheaper, earth abundant metals such as cobalt or nickel. One example is the synthesis of graphene-supported cobalt SACs with a tunable high loading using atomic layer deposition that show exceptional activity and selectivity for the hydrogenation of nitroarenes to azoxy aromatic compounds. Single Co atoms are visible in the Z-contrast image, and electron energy loss (EEL) spectra from them show that whenever Co is detected, so also is O; theory then shows that these proximal O atoms expose partially-filled Co-d orbitals, resulting in the excellent catalytic activity. Another example of a cobalt SAC uses porous nitrogen-doped carbon nanoflake arrays as support. These SACs show a lower oxygen evolution reaction (OER) overpotential and higher oxygen reduction reaction (ORR) saturation current than Co nanoparticle catalysts, showing that Co metal clusters are actually redundant for both the OER and ORR reactions. The well-dispersed Co single atoms are the active sites, attached to the carbon network through N−Co bonding. The electrocatalyst was used as the air cathode in a solid-state Zn−air battery, achieving good cycling stability (2500 min, 125 cycles) and a high open circuit potential (1.411 V).
Single atom sensitivity is also important for developing thermoelectric materials. Whereas nanostructuring has been well appreciated, recently the key role of interstitials and interstitial clusters on thermal and electrical transport properties has also been elucidated. In piezoelectrics, gradual atomic-scale polarization rotation among co-existing phases has been recently found in lead-free piezoelectrics, a feature that seems common to all high-performance piezoelectric systems at phase boundaries.
The Organic-2D Heterointerface
主 讲 人：Andrew Wee，National University of Singapore
讲座摘要：For more than a decade after the discovery of the unique physical properties of graphene, two-dimensional (2D) materials have been attracting the attention of the nanoscale research community. 2D materials can be stacked on top of the other or be interfaced with organic molecules, and this leads to a paradigm shift in the way nanoscale heterostructures can be artificially fabricated.
In this talk, I will introduce our work on the use of high resolution scanning tunneling microscopy/spectroscopy (STM/STS) to study the atomic structure and local electronic properties of 2D graphene and transition metal dichalcogenides (TMDs) monolayers, e.g. MoS2, WSe2, MoSe2. We show that the electronic bandgaps can be tuned by strain at grain boundaries and dislocations. Using monolayers of adsorbed organic molecules, we demonstrate the surface transfer doping of epitaxial graphene and TMDs. We also discuss the fabrication and electronic properties of a lateral doped/intrinsic heterojunction in 2D WSe2, partially covered with a molecular acceptor C60F48 (Fig1). Using PTCDA as a prototype semiconductor organic molecule, we show that a monolayer TMD can effectively screen an organic-inorganic heterointerface. Recent results of DAP on MoSe2 will also be introduced. The use of organic-2D hybrid heterointerfaces is a promising approach to manipulate the electronic properties for flexible and wearable applications.
On the density of racemic and homochiral crystals:Wallach, Liebisch and Sommerfeld in Göttingen
主 讲 人：Karl-Heinz Ernst，EMPA, Swiss Federal Laboratories for Materials Testing &
讲座摘要：Alfred Werner (1866–1919) is the undisputed founder of coordination chemistry, but many years passed before his stereochemical insights were accepted. Only after he proved conclusively that metal complexes can be chiral did his model become accepted and earn him the nickname “Inorganic Kekulé” and the Nobel Prize in Chemistry in 1913. But it took more than ten years from the time he predicted chirality in coordination compounds for his group to succeed in separating enantiomers. During the 1980s, reports appeared stating that some of the compounds originally prepared by one of Werner’s students, Edith Humphrey, resolve spontaneously into the enantiomers during crystallization. This led to the claim that Werner could have proven his theory much earlier if he had only tested a single crystal for optical activity. However, our re-examination of the original samples, which are stored in the Werner collection at the University of Zurich, and perusal of the corresponding doctoral theses of Werner’s students, reveals new aspects of conglomerate crystallization in the old samples.
The first comparison of densities of heterochiral crystals with their homochiral counterparts was given by Otto Wallach (Nobel Prize in Chemistry 1910) in an account on carvone bromide crystals in 1895 in Liebigs Annalen der Chemie. Although the well-known mineralogist Theodor Liebisch, professor in Göttingen from 1887 to 1908, wrote the last four pages of that Annalen paper, his colleague from chemistry, Wallach served as sole author. The tedious density measurements in Liebsch’s laboratory were performed by one of the fathers of theoretical physics, Arnold Sommerfeld! We discuss whether Wallach or Liebisch had the idea of a comparative study of crystal densities of racemates and their homochiral analogues and who of the two should be credited.
Tip and local environment induced manipulation of molecular properties
主 讲 人：Uta Schlickum，Technical University Braunschweig, Germany
时 间：2019年7月5日 11:00-11:30
讲座摘要：Functionalities of organic molecules on surfaces can be manipulated locally using a scanning tunneling microscope or globally by altering the properties of the local environment. In this talk I will demonstrate these capabilities on the example of a single molecular switch and the intercalation of graphene patches to tailor the electronic surface properties.
In the first example we demonstrate a perfect bipolar switch exploiting a bistability of molecular conformations stabilized by different charge transfers between molecule and metal substrate. Single molecular switches can be addressed individually  but also entire ensembles can be switched using the scanning tunneling microscopy tip as a local stimulus. In the latter case hot charge carrier injection into a surface state and the long mean free path of this specific state allows switching for distances of the order of 100 nm.
In the second example we describe a new way to create h-BN/carbon nanostructures. We can alter the electronic and structural properties of hexagonal boron nitride (h-BN) on Rh(111) by the controlled intercalation of carbon between the h-BN and the Rh(111) surface. The carbon atoms – natural impurities in Rh bulk crystals – diffuse to the surface during the h-BN growth and segregate at the surface during cooling. Due to the specific h-BN/Rh(111) interaction, resulting in a strong corrugation of the h-BN superstructure, hexagonal carbon rings are formed situated at specific sites under the h-BN layer. This intercalated carbon rings lead to a modified appearance of the Moiré pattern as well as to altered electronic properties. The observed work-function variations could be shown to affect the local reactivity of the surface by modified preferred adsorption positions of organic molecules.
Low-dimensional Metal Halide Perovskites for Integrated Photonics
主 讲 人：Anlian Pan，Hunan University, China
讲座摘要：Low-dimensional metal halide perovskites (PVK) have attracted enormous attentions due to their superior optical and electronic properties, holding promise for integrated laser and photodetector applications.
High-quality low-dimensional PVK nanostructures with natural optical cavities, are suitable for laser applications. Herein, we systhesised CsPbX3 nanorods through a vapor method, then we achieved tunable lasing and investigated the underlying mechanism. Achieving large-area integration of PVKs is of great significance, highly aligned CsPbBr3 nanowire arrays were successfully grown on annealed M-plane sapphire, showing excellent photodetecting performance and ideal for constructing laser arrays. The instability characteristic of PVK has limited the device fabrication, we constructed devices through directly growing CsPbBr3 nanoplates on ITO electrodes, achieving electroluminescence and visulization of carrier transport.
High-quality PVK films are excellent platforms for integrated photodetection. Flexible photodetector arrays were patterned on CH3NH3PbI3-xClx film, demonstrating real-time photosensing. Combining PVK film with erbium silicate nanosheet is a nice solution to achieve high-performance near-infrared photoresponse. In addition to the film structure, 2D ultrathin PVKs with strong quantum confinement have attracted booming attention. TMDcs were found to be ideal substrates for growing few-nanometer-thick PVK, the obtained ultrathin PVK/TMDc heterostructures show outstanding photodetection performance. The above results suggest that high-quality PVKs may open up new opportunities for various applications in high-performance integrated lasers and optoelectronics. More details about our recent works on PVKs can be found in our review paper.
Programmed assembly of terpyridine derivatives into porous, on-surface networks
主 讲 人：Thomas Jung，Paul Scherrer Institut,Switzerland
讲座摘要：Metal organic frameworks and metal organic networks comprise tunable systems made from chemical linkers with different coordinating metals. We here present the complex behavior of symmetric and slightly asymmetric terpyrimidine building blocks in their van der Waals assembly and in their coordination with Cu. V-shaped terpyridine building blocks self-assemble into hydrogen-bonded domains and upon addition of copper atoms undergo metallation with concomitant transformation into a coordination network. Interestingly multiple, energetically similar, structural motifs are observed in both hydrogen-bonded and adatom-coordinated networks and provide insight into the structure function property relation of these tunable 2D and 3D architectures.
Functional Large Scale, Single Layer Hexagonal Boron Nitride
主 讲 人：Thomas Greber，University of Zürich, Switzerland
讲座摘要：Two-dimensional (2D) van der Waals materials may be stacked layer by layer and thus allow for the realization of unprecedented properties of condensed matter systems. This perspective relies on the availability of inert 2D materials, where boron nitride is expected to play the first violin.
I will report on our recent progress on the exfoliation of centimeter sized single orientation, single layer boron nitride from its metal growth substrate . To demonstrate the quality of the material on a large scale, it was employed as a packing-layer to protect a germanium wafer from oxidation in air at high temperature. A second set of experiments involved the nanoscale engineering of the h-BN layer with the “can opener effect” prior to the transfer. This allowed the realization of boron nitride membranes with 2 nm voids, across which we measured ion transport in aqueous solutions.
The new BN exfoliation process involves in the first step the application of tetraoctylammonium (TOA) from a water free electrochemical reaction with the h-BN/Rh(111) substrate before the standard hydrogen bubbling. With high-resolution x-ray photoelectron spectroscopy, atomic force microscopy and density functional theory we identify the proximity of the metal substrate to enable covalent functionalization of h-BN with TOA constituents.
Tuning the band structures of graphene nanoribbons via functional group edge modification
主 讲 人：Jincheng Li，Nanoscience Cooperative Research Center, Spain
讲座摘要：The tunable electronic structure of Graphene Nanoribbons (GNRs) has provoked great interest due to potential applications in electronic devices as molecular diodes or transistors or as interconnectors or electrodes. On-surface synthesis strategy has been developed to fabricate GNRs with atomic precision . The high precision in the bottom-up synthesis allows to tune their electronic structure via width control, edge topology or chemical doping.
A common strategy for chemical doping of GNRs is through the substitution of carbon atoms by heteroatoms in the organic precursor . However, the on-surface synthesis strategy provides further tuning flexibility, such as the addition of functional groups to the GNR structure. In this talk, I will show you that the functional groups attached to the backbone of GNRs can effectively dope the GNRs. Furthermore, the n-doping or p-doping of GNRs can be precisely controlled through different functional groups. By means of Scanning Tunneling Spectroscopy and Density Functional Theory, I will show you that how the nitrile (CN) functional groups n-dope the GNRs , while the amino (NH2) functional group p-dopes the GNRs. Interestingly, the amino (NH2) functional groups can turn narrow chiral GNRs from semiconducting to metallic by doping.
Tuning charge and spin interactions at hybrid organic/metal and organic/topological insulator interfaces
主 讲 人：Aitor Mugarza Ezpeleta，Catalan Institute of Nanoscience and Nanotechnology, Spain
讲座摘要：Interfacing materials with different functionalities is an efficient way to manipulate their respective properties and promote the emergence of novel phenomena. Controlling interfacial interactions is however a complicated task in most cases. In that respect, the tunability offered by ligand chemistry in organic materials is an interesting asset that can be exploited at hybrid interfaces. Here I will present two examples where the molecular strategy is employed to tune the interactions of localized transition metal ions with underlying spin-degenerated electrons in non-magnetic metals, and with spin-textured electrons in topological insulators. In both cases, we obtain a comprehensive picture of the phenomenology by combining scanning tunnelling microscopy/spectroscopy, atomic manipulation, X-ray absorption and photoelectron spectroscopy, and ab-initio calculations.
On our systematic study of transition metal phthalocyanines on noble metals we show how the molecular charge redistribution can either quench or enhance the molecular magnetic moment depending on the relative ligand/ion interaction strengths, and how the molecular spin and charge can be manipulated by doping them with alkali atoms one by one. This tunability will be employed to study different intramolecular and molecule-metal spin interactions.
For molecular films on topological insulators, the tunability of ligands is exploited to tune the interaction of Co ions with the underlying topological surface state (TSS), going from the strongly interacting regime where the TSS is quenched in the first quintuple layer , to the weakly interacting regime where both the TSS and the Co magnetic moment are preserved.
Tomonaga Luttinger Liquid Hosted by Line Defects in 2D Semiconductors
主 讲 人：Matthias Batzill，University of South Florida, USA
讲座摘要：Mirror twin grain boundaries (MTBs) in MoSe2 or MoTe2 are well-ordered 1D defects, that exhibit metallic properties. The presence of such 1D-metals that are decoupled from the semiconducting host material opens the prospect of studying truly 1D electron systems. We show that dense networks of Mo-rich MTBs can be synthesized by simple incorporation of excess Mo atoms into the lattice structure of Mo-dichalcogenides. The densely packed MTBS enable us to characterize their 1D electronic properties by ARPES . These measurements show signature of spin charge separation consistent with Tomonaga Luttinger Liquid theory and thus prove the true 1D nature of these electron systems.
Structural and Electronic Properties of Germanene
主 讲 人：Lijie Zhang，School of Physics and Electronics, Hunan University
讲座摘要：Germanene, the germanium analogue of graphene, is in many aspects very similar to graphene, but in contrast to the planar graphene lattice, the germanene honeycomb lattice is slightly buckled and composed of two vertically displaced sub-lattices . Frist principles total energy calculations have revealed that freestanding germanene is a two-dimensional Dirac fermion system, i.e. the electrons behave as massless relativistic particles that are described by the Dirac equation, i.e. the relativistic variant of the Schrödinger equation. Recently, it has been shown that germanene can be synthesized on various substrates, including MoS2 and Ge2Pt . As predicted germanene’s honeycomb lattice is indeed buckled and the experimentally measured density of states exhibits a V-shape, which is one of the hall marks of a two-dimensional Dirac system. Spatial maps of the Dirac point of germanene synthesized on MoS2 reveal the presence of charge puddles, which are induced by charged defects of the underlying substrate.