List of Abstracts 2022: SESSION E - ADVANCED METHODS OF PREPARATION AND CHARACTERIZATION OF NANOMATERIALS
Date: October 21, 2022
The Plasma-Assisted Vapour Thermal Deposition (PAVTD) is thin-film deposition technique utilizing a classical polymer as a source of material. The polymer is heated to fragmentation/evaporation under low pressure. The released fragments (effective a "monomer") with molar mass of 102 to 103 g/mol are then repolymerized in the RF plasma. The high molar mass of the film building blocks offers an opportunity to tune the structure and properties of the films in an exceptionally broad range for a plasma polymer, effectively bridging the gap between classical polymers and PECVD films.
Currently, the PAVTD method has several drawbacks compared with PECVD. The deposition must be done as a batch process, governed by the capacity of the crucible. The thermal release of the precursor fragments is highly temperature-and history- sensitive. The resulting fluctuations in deposition rate make retaining good reproducibility of the process rather tricky. To overcome these technical limitations, a modification of the setup utilizing a filament for FDM 3D-printing fed into a modified filament heater/extruder was made.
In this contribution, overview of the possibilities of PAVTD using PLA as the source material will be given along with the first results obtained using an improved deposition setup with continuous material feed. Significant improvements in deposition rate and control of stability of the deposition will be presented.
Acknowledgments
This contribution is supported by the grant GA22-21007S of the Czech Science Foundation.
Temporal stability of the Haberland type of the Gas Aggregation Source (GAS) of nanoparticles (NPs) is together with the low target usage limiting factor any industrial application. The target usage is typically around 2 % due to very narrow erosion zone which is created in case of magnetron sputtering at the pressures of several tens of Pa. Formation of such narrow erosion zone affects the process of the NPs formation. It was shown that increasing depth of the erosion trench leads first to the broadening of the size distribution of the NPs and to the increase of the mean size. The production rate of the NPs also decreases with increasing depth of the erosion trench and at certain point the deposition of the NPs stops. One possible solution of this issue is employment of the full-face erosion (FFE) magnetron. It is the magnetron which sputters the material homogeneously from the whole target. Commercially available FFE magnetrons are usually optimized for deposition of homogeneously thick films rather than for maximal target usage. Moreover, they are typically too big for common GAS where 2” or 3” magnetrons are typically used.
Simple construction of 3” FFE magnetron together with the theoretical model of the erosion zone and target usage will be presented in this study. It was found that the target usage can be improved from about 2 % for classical stationary magnetic circuit of the magnetron up to almost 20 % for the same circuit rotating eccentrically in the planar magnetron. The stable production rate of Cu NPs was reached for the whole lifetime of the target. It was proven that the size distribution remained constant with the deposition rate of Cu NPs 10 mg/h.
ACKNOWLEDGEMENTS: This work was supported by the Czech Science Foundation via grant GAČR 21-05030K and by the National Science Centre, Poland via grant no 2020/02/Y/ST8/00030 and by the grant Vakuum Praha.
The fine control of mono- or bi-metallic nanoparticles (NPs) chemical composition is one of the most critical concerns in nanomaterial manufacturing; however, when metals holding dissimilar characteristics form bi-metallic NPs, this becomes an unresolved matter. Herein we present the successful control of bismuth doping in two different magnetic NPs - nickel and iron- for producing magnetic NPs with optical characteristics of semiconductors. For this, we have employed reactive laser ablation in liquids (RLAL) employing a magnetic foil (either nickel or iron) as the ablation target, which was immersed in an acetone solution with a hard-to-dissolve Bi(NO3)3 salt.
The employment of various Bi(NO3)3 concentrations showed that values between 0.01 and 0.1 mM are optimal for manipulating the Bi doping degree on Ni or Fe NPs, which was verified by scanning electron microscopy. Moreover, their magnetic manipulation testing and inspection by ultraviolet-visible spectroscopy allowed assessing that both types of magnetic NPs display the desired optical properties. Furthermore, the minimal Bi salt employment resulted in chemical waste suppression verified by inductively coupled plasma spectroscopy. Since room conditions and no hazardous reducing agents were required for this synthetic procedure, the presented alternative represents an up-and-coming practice for producing Ni and Fe NPs doped by Bi.
In spite of advanced research of functional colloidal inorganic nanoparticles and their reactivity, room temperature reactive interaction between two different colloids has remained so far challenging. Laser ablation of titanium monoxide and silicon monoxide in ethanol and water allows generation of TiO-derived and SiO-derived colloidal nanoparticles which were characterized for their stability, size distribution and zeta potentials with dynamic light scattering and after evaporation of solvent examined for their morphology, chemical and phase composition by scanning electron microscopy, Raman spectroscopy, high resolution transmission electron microscopy and electron diffraction and small angle X-ray scattering. Aqueous and ethanolic TiO-derived colloids consist of anatase and monoclinic TiO, while ethanolic SiO-derived colloids are composed of crystalline and amorphous Si, nanocrystalline Si and SiO2 and aqueous SiO-derived colloids contain, in addition to these phases, high pressure form of cristobalite. Simple room temperature mixing of ethanolic TiO- and SiO-derived colloids allows formation of TiSi2, which is a case of so far unreported room temperature reactive interaction between two colloidal species. All colloids absorb solar light and act as photocatalysts for methylene blue degradation. These findings present a challenge for further search of feasible room-temperature reactions between distinct colloidal particles and open the potential for green synthesis of another desirable and hardly achievable phases.
Atomic force microscopy (AFM) is a valuable tool for investigating a variety of biological systems, from single molecules to cells. However, biological samples can be especially challenging for AFM imaging, because the samples may be weakly adhered or easily damaged, often need imaging in physiological conditions, or are dynamic processes that require higher imaging rates. Thus, for biological samples especially, there is a need for AFM imaging modes that combine simplicity and robustness of operation, fast imaging ability and low imaging forces.
In off-resonance imaging modes, the tip-sample distance is modulated well-below the cantilever resonance. These modes are generally simple and robust in operation and capable of very gentle imaging. However, their speed of operation has been limited because they have used the AFM piezo scanner to generate the tip-sample modulation. Towards this aim, we have recently developed an off-resonance AFM imaging mode, WaveMode, that modulates the tip-sample distance directly by photohermally-induced bending of the cantilever. This direct actuation approach brings significant benefit in speed and stability of operation.
We will discuss the necessary technical basis for WaveMode imaging, in particular the advantages that photothermal excitation brings towards AFM and demonstrate examples of how WaveMode enables simple and rapid imaging of delicate samples, such as virus capsids bound to intact nuclei.
Nowadays, atomic force microscopy (AFM) and scanning electron microscopy (SEM) are two of the most utilized techniques in the analysis of nano-sized structures and topography features. However, both techniques possess several disadvantages when used separately. In order to overcome these issues, we propose the idea to implement the AFM into the SEM. The combination of AFM-in-SEM opens new opportunities in the characterization of nanomaterials applied in Materials Science, Nanotechnology, Semiconductors, and Life Science.
Our company Nenovision developed a unique and compact AFM called LiteScope 2.0 that can be easily integrated into most SEMs. Using LiteScope and our technology of Correlative Probe and Electron Microscopy (CPEM), it effectively enables combining benefits of AFM (analysis of 3D topography, mechanical, electrical, and magnetic properties) and SEM (precise imaging with high resolution, chemical analysis, and surface modification), resulting in a 3D multi-channel in-situ analysis providing true data of the analyzed sample.
As an example of the benefits of the AFM-in-SEM combination, we would like to present an investigation of the Mo2C chemical vapor deposited (CVD) 2D flakes. Mo2C is a well-known material that found application in automotive and semiconductor fields due to its unique combination of mechanical and electrical properties. The AFM-in-SEM was used to (i) carry out a complex pack of analyses on topography, structure and elemental distribution from AFM, SEM and EDX signals resulting in a 3D CPEM illustration; to (ii) perform all the analyses at the same time, place and conditions; and to (iii) enable fast and easy navigation to the region of interest.
s-SNOM has become a key technology to study the optical properties and chemical composition of materials at the nanoscale. This AFM-based technology exploits the strong confinement of light at the end of a sharp, metallic AFM tip to generate a nanoscale optical hotspot at the sample surface. The use of broadband or tunable vis-IR-THz sources combined with interferometric detection enables optical spectroscopy with <10 nanometer precision, as well as nanoscale mapping of the sample chemical composition.
With tremendous sensitivity compared to classical spectroscopy and microscopy techniques, s-SNOM allows chemical identification of nanocomposites based on their spectroscopic fingerprint. It further reveals optical and electronic properties of low dimensional materials with impact on recent applications development.
Nanoscale Infrared spectroscopy [1] has been successfully demonstrated in an expanding range of applications in recent years due to significant increases in capability. One method of nanoscale infrared spectroscopy, atomic force microscope based infrared spectroscopy (AFM-IR) uses the tip of an AFM as a nanoscale detector of the expansion caused by absorption of IR radiation. AFM-IR can be used to obtain IR absorption spectra and chemical imaging with resolution as fine as the AFM tip radius, >100X smaller than spatial resolution limits of conventional infrared spectroscopy. The photothermal AFM-IR technique has demonstrated improvements in sensitivity, down to the scale of single monolayers, and speed with spectral acquisition times dropping by an order of magnitude. This presentation will describe the underlying technology and complementary techniques for nano-mechanical/nano-electrical and nano-thermal analysis. Additionally, we will also highlight numerous applications of nanoscale spectroscopy and chemical imaging in physics, materials and life sciences. Applications include nanoscale chemical analysis of polymers, composites, semiconductors, biological cells, proteins, tissue, and other areas. REFERENCES: [1] J. Mathurin, A. Deniset-Besseau, D. Bazin, E. Dartois, M. Wagner, A. Dazzi, J. Appl. Phys. 131, 010901 (2022).
Attractive tip-to-sample interactions are used in non-contact non-resonant (NCNR) AFM mode to measure surface morphology. Here we report a trigger-based NCNR mode realization using self-sensing cantilevers on LiteScope™ AFM. This method is based on 4 criteria, which are used to stop the tip approach toward the surface in each studied point. The method was implemented using a script. We analyzed various scripting approaches and applied them for measurements on a grid calibration standard sample. We observe how the tip approach stops after reaching negative setpoint value and thus before establishing direct tip-to-sample contact. This is expected to allow gentler measurement on sensitive samples with less sample modification and tip contamination compared to other AFM methods. We analyze long-term stability of such measurements. We also compare and discuss the NCNR measurements with conventional contact non-resonant AFM mode.