Maksym Demydenko

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Demydenko

First Name

Maksym

ORCID

0000-0003-4637-1272

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Publications 1 - 8 of 8

Magnetic Analysis of Ultrathin Fe Films on W(011) with SFEMPA
Thamm, Ann-Katrin; Wei, Jiapeng; Demydenko, Maksym; et al. (2020)
2020 33rd International Vacuum Nanoelectronics Conference (IVNC)
An ultra-high vacuum Scanning Tunneling Microscope (STM) is converted into a lens-less low-energy Scanning Electron Microscope when the tip-target distance is some tens of nanometers and the tip acts as a source of field emitted electrons. This primary electron beam excites locally secondary electrons out of the sample. Those escaping the tip-target junction are analyzed according to their spin. We use this technology to measure the local magnetization versus applied magnetic field in ultrathin Fe films on W(011) at room temperature. The resulting hysteresis loop is square. The coercive field has its maximum strength between 2.2 monolayers (0.07 T) and 3 monolayers (0.025 T), being larger than 0.1 T at 2.7 monolayers and decreasing to 0.0075 T at 6 monolayers. Rotation of the magnetization, domain wall pinning at incomplete layers and lattice misfits within the Fe films are discussed as possible explanations of this “singular” behavior. © 2020 IEEE.
Low-temperature scanning field emission microscope with polarization analysis
Thamm, Ann-Katrin; Demydenko, Maksym; Michlmayr, Thomas; et al. (2020)
2020 33rd International Vacuum Nanoelectronics Conference (IVNC)
The design of the low-temperature scanning probe microscope, which works in field emission regime with spin polarization analysis, is proposed. A performance at temperature of 77 K has been achieved. The first result of STM imaging with atomic resolution is demonstrated. © 2020 IEEE.
The effect of work function during electron spectroscopy measurements in Scanning Field-Emission Microscopy
Bodik, Michal; Walker, Christopher; Demydenko, Maksym; et al. (2022)
Ultramicroscopy
Electron spectroscopy proves to be a handy tool in material science. Combination of electron spectroscopy and scanning probe microscopy is possible through Scanning Field Emission Microscopy (SFEM), where a metallic probe positioned close to the surface is used as an electron source. However, using this not too much technologically demanding technique, it looks like the compromise between the lateral resolution and spectroscopic clarity must be considered. Here, we demonstrate, using experimental and simulation data, that the spectroscopic information can be understood without the need to grossly deteriorate the potential spatial resolution of the microscope. We prepared a three-section sample with clean W(110), sub-monolayer Cs on W(110) and monolayer of Cs on W(110) on which electron energy loss spectra are obtained via Scanning Probe Energy Loss Spectroscopy (SPELS) measurements. To explain the detected spectra a new model describing SPELS measurements in a SFEM is developed which aids to uncover the origin of spectral features typically detected during experiments. Experimental and simulation data are in a mutual agreement and observed spectral features on different surfaces could be explained. This novel understanding of SPELS can solve the main issue previously related to this technique, and good spatial resolution can be accompanied by the understanding of the measured spectra.
Hallmark of quantum skipping in energy filtered lensless scanning electron microscopy
Thamm, Ann-Katrin; Wei, Jiapeng; Zhou, Jiangtao; et al. (2022)
Applied Physics Letters
We simulate the electronic system of ejected electrons arising when a tip, positioned few 10 nm away from a surface, is operated in the field emission regime. We find that, by repeated quantum reflections (“quantum skipping”), electrons produced at the nanoscale primary site are able to reach the macroscopic environment surrounding the tip-surface region. We observe the hallmark of quantum skipping in an energy filtered experiment that detects the spin of the ejected electrons.
Scanning Field Emission Microscopy with Spin and Energy Analysis
Thamm, Ann-Katrin; Wei, J.; Demydenko, Maksym; et al. (2021)
2021 34th International Vacuum Nanoelectronics Conference (IVNC)
Scanning Field Emission Microscopy with Polarization Analysis was recently introduced to detect the spin polarization of electrons excited in the field emission regime of Scanning Tunnelling Microscopy. In this work, a miniature electron energy analyzer, called Bessel Box, is implemented into the Scanning Field Emission Microscope with Polarization Analysis setup. It is used to filter electrons according to their energy before they reach the spin detector. The Bessel Box allows, e.g., the spin polarization of elastically scattered electrons to be compared with the spin polarization obtained with the full energy spectrum. We use this technology to measure the local in-plane polarization signal as a function of the magnetic field B at room temperature for 10 monolayers Fe deposited on top of a W(011)-single crystal surface through a half mask (half of the surface is covered with Fe, the other half is uncovered). The spin polarization at the Fe-W crossing drops sharply from 9 % above Fe to 0 % above W(011) only if the elastically scattered electrons are selected for spin analysis. The mechanism of signal generation in Scanning Field Emission Microscope with Polarization Analysis including the formation of cascade of inelastically scattered electrons is discussed as an explanation for the different spin polarization profiles observed with and without Bessel Box (energy filtered).
Collapse Mechanism in Few-Layer MoS2 Langmuir Films
Bodik, Michal; Demydenko, Maksym; Shabelnyk, Tetiana; et al. (2020)
The Journal of Physical Chemistry C
Recent advances in the liquid-phase exfoliation enabled large-scale production of two-dimensional (2D) materials, including few-layer graphene and transition metal dichalcogenides. The exfoliated flakes of 2D materials allow cost-effective deposition of continuous films for various applications ranging from optoelectronics to lubrication technology. The self-assembly of 2D materials on water subphase and subsequent transfer of such a Langmuir film onto a solid substrate offers an unprecedented layer quality in terms of spatial homogeneity as it proceeds in thermodynamic equilibrium. However, while the formation of conventional organic molecular Langmuir films has been widely studied, the application of the Langmuir technique to rigid inorganic 2D materials is still rather unexplored. Here, we study the underlying mechanism behind the formation and collapse at the critical surface pressure of the Langmuir film composed of few-layer MoS2 flakes. The in situ wide-angle X-ray scattering measured in real time and other supportive techniques applied ex situ after the film transfer onto a Si/SiO2 substrate were employed. We identify all principal compression stages up to the Langmuir monolayer collapse and beyond, relying on the texture, surface pressure, and elastic modulus temporal evolution. The results obtained and the conclusions drawn can be extended to a large family of the inorganic Langmuir films of other 2D materials to optimize the deposition process for envisaged application.
Electron energy analysis in Scanning Field Emission Microscopy using a Bessel box energy analyzer
Bodik, Michal; Demydenko, Maksym; Walker, Chris G.H.; et al. (2021)
In this study, we use Scanning Field Emission Microscopy (SFEM) combined with a miniature electron energy analyzer known as a Bessel box to measure electron energy spectra emitted from a sample. Previous studies using SFEM have revealed that the work function (ϕ) of the material under study has a significant role to play in the formation of the signal intensity. Hence, in order to understand the role of ϕ in greater detail, a sample of W(110) (ϕ = 5.25 eV) and a sample of Cs deposited on W(110) (ϕ ≈ 1.7 eV) were investigated. STM images show that the Cs covered surface has a speckled appearance indicating small Cs islands. The electron energy loss spectra obtained (which are the first using the Bessel box in SFEM) show differing structure in the elastic peak region. Monte Carlo (MC) simulations including quantum mechanical "bouncing" have been carried out. The results are consistent with MC simulations of the electrons escaping from the tip-sample junction.
Scanning Field Emission Microscopy using a miniature Bessel box electron energy analyser
Bodik, Michal; Demydenko, Maksym; Walker, Christopher; et al. (2021)
Proceedings of the Microscience Microscopy Congress 2021 incorporating EMAG 2021

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Maksym Demydenko

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