Fachgebiet 3D-Nanostrukturierung, Institut für Physik Contact: Office: Heliosbau 1102, Prof. Schmidt-Straße 26 (Tel: 3748) Vorlesung:Tuesday 15:00 – 16:30, C 110 Übung: Friday 9:00 – 10:30, C 110 (U) Stefan Bösemann Übung Nanostrukturphysik (Nanostructure Physics)
What are atomically-thick 2D crystals? What’s special about them?
What’s atomically-thick 2D crystals? Atomic or molecular thickness Infinite planar length Microscopic superior optical, electronic, and magnetic features Macroscopic ultrathinness, flexibility, and transparency Maximizing functionality with a minimized size
Why is XRD not suitable to characterize atomically-thick 2D crystals? Why is XAFS suitable?
Structure characterization Traditional X-ray diffraction (XRD) Based on the long-range order of atomic positions in a crystal Unable to identify the spatial atomic distribution: the lack of long-range order in the third dimension
When a X-ray travels through matter, part of it will be absorbed. If the X-ray is absorbed by a core-level electron of one absorbing atom, a photoelectron will be excited and goes away from this atom. The excited photoelectron will be scattered back to the absorbing atom via the electrons of its neighboring atom. The interference between the excited and scattered photoelectron waves can thus give birth to the oscillation in the X-ray absorption coefficient and this is the origin of synchrotron radiation XAFS. X-ray absorption fine structure spectroscopy (XAFS)
Sensitivity to the chemical state and short-range order (typically several Å): based on short-range effect of several nearest neighbor coordination shells of the absorbing atoms Element-specificity: local atomic geometry and chemical state of atoms in almost any type of substance Information: coordination number, bond length, disorder degree
Please use an example to introduce the information about the structures of atomically-thick 2D crystals that we can obtain from XAFS.
Structural characteristics of atomically-thick 2D layered crystals using XAFS Exfoliation: loss of the interplanar interaction from the adjacent layers 5-atom-thick 2D Bi 2 Se 3 crystals Slightly elongated Bi-Se and Se-Bi distances Increased disorder degree Slightly reduced coordination numbers Exfoliation process didn’t damage the structure of 5-atom-thick 2D Bi 2 Se 3 crystals, but resulted in a slight intra-layer structural distortion.
Structural characteristics of atomically-thick 2D non-layered crystals using XAFS Lamellar hybird intermediate strategy: (Zn 2 Se 3 )(pa) (pa stands for n-propylamine) Stability of 2D ZnSe crystals with many dangling bonds at ambient condition. Slight expansion of surface Zn-Se bond- lengths eminently contracted the next nearest Zn-Zn distances obviously elongated the Se-Se distances Apparent surface distortion
Please give an example of the applications of atomically-thick 2D crystals, except for the application areas that are introduced in the class.
Sandwich-like carbon-anchored ultrathin TiO 2 nanosheets for ultrafast lithium storage Lamellar hybrid intermediate
Please explain how to characterize graphene using optical measurement, scanning probe microscopy, and Raman spectroscopy.
optical measurement Optical absorbance: 2.3% per layer Science 2008, 320, 1308.
AFM
Raman spectroscopy
Please explain the structural differences among graphite, graphene oxide, reduced graphene oxide, and graphene. How do you estimate the differences of their physical and chemical properties?
structural differences GraphiteGraphene oxide (GO) Reduced grahpene oxide (rGO)Graphene
Differences in properties Elctrical conductivity Less oxygen-bonds better conductivity Chemical reactivity Reactivity increase with functional groups Themal properties Optical properties
Please give an example of using graphene for energy-related device application and explain the advantages.
Opto-electronics Solar applications Display technology transparent (transmit up to 97.7 % of light) conductive Energy storage Supercapacitors Batteries Graphene as anode material better longevity, charge rate, capacity