Optical imaging and spectroscopy of atomically precise armchair graphene nanoribbons

S. Zhao, G. Borin Barin, T. Cao, J. Overbeck, R. Darawish, T. Lyu, S. Grant Drapcho, S. Wang, T. Dumslaff, A. Narita, M. Calame, K. Müllen, S. G. Louie, P. Ruffieux, R. Fasel, and F. Wang

Nano Letters (2020)

https://pubs.acs.org/doi/pdf/10.1021/acs.nanolett.9b04497

Abstract

We report the optical imaging and absorption spectroscopy on atomically precise armchair graphene nanoribbons (GNRs) on insulating fused silica substrates. This is achieved by controlling light polarization on macroscopically aligned GNRs, which greatly enhances the sub-monolayer GNR optical contrast on the insulating substrates. We measured the linear absorption spectra of 7-armchair and 9-armchair GNRs in this study, and the experimental data agree qualitatively with ab inito calculation results. The polarization spectroscopy technique enables an unambiguous optical identification of GNR samples and provides a rapid tool to characterize the transferred film over large area.


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Influence of helium ion irradiation on the structure and strength of diamond

Chen M, Best JP, Shorubalko I, Michler J, Spolenak R & Wheeler JM

Carbon. (2019)

https://doi.org/10.1016/j.carbon.2019.10.078

Abstract
Microfabrication of synthetic single crystal diamond using accelerated helium ions beams has significant potential for functional applications, such as high precision optical devices, through tailoring of the optical properties via diamond graphitization. The use of helium ion microscopes (HIM) with nano-scaled focused ion beam spot sizes also allows for precision nano-patterning of the diamond surface through post-exposure selective etching of the generated graphitic phase. Here, single-crystalline diamonds with ⟨100⟩, ⟨110⟩, ⟨111⟩ and ⟨123⟩ orientations are exposed to He ion radiation from a HIM at a range of acceleration voltages and fluences. It is observed that ⟨123⟩ orientation was notably more sensitive to ion irradiation as sp3 bonds transition to sp2 bonds at lower fluence (1015 ions/cm2) compared to other orientations. In situ uniaxial compression of SC diamond micro-pillars revealed the strength of ⟨123⟩-oriented pillars is strongly dependent on the ion fluence, and thus is tunable by ion irradiation. Notably, ⟨100⟩-oriented pillars exhibit a better damage resistance as a small strength degradation due to its higher ion channeling efficiency. The irradiation damage of energetic helium ions on the structure and strength of diamond is therefore highly orientation-dependent. Such results provide the critical knowledge for precise patterning and designing of diamond-based functional structures in nano-fabrication.

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Stable ultra-concentrated and ultra-dilute colloids of CsPbX3 (X=Cl, Br) nanocrystals using natural lecithin as a capping ligand

Krieg F, Ong QK, Burian M, Rainò G, Naumenko D, Amenitsch H, Süess A, Grotevent MJ, Krumeich F, Bodnarchuk MI, Shorubalko I, Stellacci F & Kovalenko MV

Journal of the American Chemical Society, 141(50), 19839-19849.

https://doi.org/10.1021/jacs.9b09969

Abstract

Attaining thermodynamic stability of colloids in a broad range of concentrations had long been a major thrust in the field of colloidal ligand-capped semiconductor nanocrystals (NCs). This challenge is particularly pressing for the novel NCs of cesium lead halide perovskites (CsPbX3; X=Cl, Br) owing to their highly dynamic and labile surfaces. Herein we demonstrate that soy-lecithin, a mass-produced natural phospholipid, serves as a tightly-binding surface capping ligand, suited for a high-reaction yield synthesis of CsPbX3 NCs (6-10 nm) and allowing for the long-term retention of colloidal and structural integrity of CsPbX3 NCs in a broad range of concentrations – from a few ng/mL to >400 mg/mL (inorganic core mass). The high colloidal stability achieved with this long-chain zwitterionic ligand can be rationalized with the Alexander-De Gennes model that considers the increased particle-particle repulsion due to branched chains and ligand polydispersity. The versatility and immense practical utility of such colloids is showcased by the single NC spectroscopy on ultra-dilute samples and, conversely, by obtaining micron-thick, optically homogeneous dense NC films in a single spin-coating step from ultra-concentrated colloids.