PacSurf2022 Session NM-WeM1: Nanocharacterization

Quantum computing is the next great frontier of science. It has the potential to revolutionise many aspects of modern technology, including digital communications, “quantum-safe” cryptography, as well as incredibly accurate time measurements.

Single impurity atoms in semiconductors are receiving attention as potential quantum technologies, and proof-of-concept devices have shown promise. However, such devices are incredibly challenging to manufacture, as single atoms must be placed within ~ 20 nm of each other within a pure ²⁸Si matrix.

All working devices thus far have been fabricated using hydrogen lithography with an STM followed by atomic layer deposition. It is labour-intensive and requires several days of meticulous preparation to create just a single quantum bit (qubit). Real-world devices will require arrays of hundreds or thousands of impurity atoms, highlighting the requirement for a scalable method of positioning single atoms with nanometre precision.

We report on a new commercial instrument for the fabrication of quantum materials and devices via ion implantation. A well-established technique in the semiconductor industry, ion implantation is both flexible and highly scalable. The instrument features a high-resolution mass-filtered focused ion beam (FIB), a high-sensitivity deterministic implantation system, 6-inch wafer handling, and a high-precision stage.

The ion dose delivered to the sample can be adjusted across a wide range, providing several materials engineering capabilities in a single tool. The deterministic implantation system allows single ion implantation with confidence levels as high as 98%. Operating in a high beam current mode provides direct-write capabilities such as isotopic enrichment and targeted ion-implantation of nanomaterials such as nanowires and graphene.

The liquid metal ion source and mass filtered column can implant many different elements with isotopic resolution. Available sources include silicon, erbium, gold, and bismuth, while many others of technological interest are in development.

Two-dimensional (2D) transition metal dichalcogenides (TMDs) are a family of layered materials with an X-M-X structure, where M and X are transition metal and chalcogen, respectively. TMDs have attracted tremendous interest due to their unique electronic, magnetic, and optical properties with an atomic layer limit depending upon structural elements. The stacking sequence of layers leads to the formation of polytypes such as 1T, 2H, 4H, and 3R, sometimes resulting in significantly different electronic and optical properties.

NbSe₂ is one of the attractive 2D TMDs. Itis a superconducting material with a high-superconducting-transition temperature (Tc) of about 7.0 K and shows metallic characteristics at room temperature. The weak van der Waals force between layers allows superconductivity and charge density wave (CDW) with a transition temperature of about 33K. Interestingly, its phase alters its magnetic and electrical properties. However, its thermal stability, which is important for phase engineering and synthesis, has not been intensively examined.

This study investigated the defect dynamics and thermal evolution of NbSe₂ under vacuum by in-situ heating Scanning Transmission Electron Microscopy (STEM). Low thermal stability of the NbSe₂ was confirmed by direct observation of 2H to 1T phase transition and defects induced by inversion domain boundaries. Interlayer gap expansion, Se atom desorption, and intercalation to the atomic layer gap were also observed. Experimental details will be presented and discussed considering its potential applications.

Nanocomposite film based on chitosan and nanocrystal cellulose (CNCs) was developed as matrices for incorporation of essential oils as antimicrobial compounds. The addition of CNCs in chitosan based-film has permitted to reinforced the physico-chemical properties of the films. An optimal concentration of 5% (w/w) NNCs improved by 26% the the tensile strength (TS) and decreased by 27% the water vapor permeability of the films. A three factor central composite design (CNCs concentration ; microfluidization pressure ; number of cycle of microfluidization) with five levels was designed to optimize the microfluidization process. Microfluidization has permitted to reduce the CNC–chitosan aggregates and improved the mechanical properties of the nanocomposite films by 43%. Two antifungal formulations based on tea tree or on mint in combination with thyme essential oils (Eos) under nano emulsion were developed. When encapsulation under nanoscale, the size of the drop of the antimicrobial formulation was reduced from 219 to 71 nm. The encapsulation efficiency improved from 37 to 83% and the antifungal efficiency was improved from 32 for 3 days to 81% for over one month showing, that the doses required to ensure the biological activity was reduced significantly. The film also showed an effectiveness and slow release of EOs during storage. Combination of active films with γ-irradiation (750 Gy) was synergistic and caused 4 log UFC/gr reduction of fungi for more than 8 weeks of storage. These results showed that the bioactive films and γ-irradiationin combination has commercial potentiality to extend shelf life of rice products.

Atomic Force Microscopy (AFM) is a powerful, and critical technology to characterize a diversity of nanomaterials across many interdisciplinary research fields.The use of AFM is rapidly evolving into a myriad of different modes for highly localized (<30nm) property measurement techniques in addition to roughness, and topography with sub-nm spatial resolution.In order to support the momentum of quantum materials research, advanced modes of Scan Probe Microscopy (SPM) techniques are being used to measure electrical, magnetic, and optical properties of new materials as well as Scan Probe Lithography (SP-L) methods for device fabrication.A highly active area of quantum materials research is the characterization and device fabrication of 2d materials (Graphene and TMDs).The goal of this talk is to provide an overview of how SPM is applied for the advancement of 2d materials research, utilizing Kelvin Force (KPFM), Electrostatic Force (EFM), Piezo Force (PFM), and Scattering Near Field Microscopy (s-SNOM) and other advanced modes. The main focus will be on the exquisite, direct imaging of Moire lattice patterns in twisted bi-layer (t-BL) materials by SPM technologies.Each of the imaging modes used to demonstrate direct visualization and angle measurements of t-BL will be discussed.Furthermore, the impact of a closed cell environmental chamber with Ar/N2 gas flow for each of these modes will be demonstrated. Some examples of direct writing and patterning of 2d structures using a lithography mode for device fabrication will also be presented.