1
|
Basha A, Levi G, Amrani T, Li Y, Ankonina G, Shekhter P, Kornblum L, Goldfarb I, Kohn A. Elastic and inelastic mean free paths for scattering of fast electrons in thin-film oxides. Ultramicroscopy 2022; 240:113570. [PMID: 35700667 DOI: 10.1016/j.ultramic.2022.113570] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2022] [Revised: 05/23/2022] [Accepted: 06/03/2022] [Indexed: 10/18/2022]
Abstract
Quantitative transmission electron microscopy (TEM) often requires accurate knowledge of sample thickness for determining defect density, structure factors, sample dimensions, electron beam and X-ray photons signal broadening. The most common thickness measurement is by Electron Energy Loss Spectroscopy which can be applied effectively to crystalline and amorphous materials. The drawback is that sample thickness is measured in units of Inelastic Mean Free Path (MFP) which depends on the material, the electron energy and the collection angle of the spectrometer. Furthermore, the Elastic MFP is an essential parameter for selecting optimal sample thickness to reduce dynamical scatterings, such as for short-range-order characterization of amorphous materials. Finally, the Inelastic to Elastic MFP ratio can predict the dominant mechanism for radiation damage due to the electron beam. We implement a fast and precise method for the extraction of inelastic and elastic MFP values in technologically important oxide thin films. The method relies on the crystalline Si substrate for calibration. The Inelastic MFP of Si was measured as a function of collection semi-angle (β) by combining Energy-Filtered TEM thickness maps followed by perpendicular cross-sectioning of the sample by Focused-Ion-Beam. For example, we measured a total Inelastic MFP (β∼157 mrad) in Si of 145 ± 10 nm for 200 keV electrons. The MFP of the thin oxide films is determined by their ratio at their interface with Si or SiO2. The validity of this method was verified by direct TEM observation of cross-to-cross sectioning of TEM samples. The high precision of this method was enabled mainly by implementing a wedge preparation technique, which provides large sampling areas with uniform thickness. We measured the Elastic and Inelastic Mean Free Paths for 200 keV and 80 keV electrons as a function of collection angle for: SiO2 (Thermal, CVD), low-κ SiOCH, Al2O3, TiO2, ZnO, Ta2O5 and HfO2. The measured MFP values were compared to calculations based on models of Wenzel, Malis and Iakoubovskii. These models deviate from measurements by up to 30%, especially for 80 keV electrons. Hence, we propose functional relations for the Elastic MFP and Inelastic MFP in oxides with respect to the mass density and effective atomic number, which reduce deviations by a factor of 2-3. In addition, the effects of sample cooling on the measurements and sample stability are examined.
Collapse
Affiliation(s)
- Adham Basha
- Department of Materials Science and Engineering, The Iby and Aladar Fleischman Faculty of Engineering, Tel Aviv University, Ramat Aviv, Tel Aviv 6997801, Israel
| | - George Levi
- Department of Materials Science and Engineering, The Iby and Aladar Fleischman Faculty of Engineering, Tel Aviv University, Ramat Aviv, Tel Aviv 6997801, Israel
| | - Tamir Amrani
- Department of Materials Science and Engineering, The Iby and Aladar Fleischman Faculty of Engineering, Tel Aviv University, Ramat Aviv, Tel Aviv 6997801, Israel
| | - Yang Li
- Andrew and Erna Viterbi Faculty of Electrical and Computer Engineering, Technion - Israel Institute of Technology, Haifa 3200003, Israel
| | - Guy Ankonina
- Andrew and Erna Viterbi Faculty of Electrical and Computer Engineering, Technion - Israel Institute of Technology, Haifa 3200003, Israel
| | - Pini Shekhter
- Tel Aviv University Center for Nanoscience and Nanotechnology, Tel Aviv University, Ramat Aviv, Tel Aviv 6997801, Israel
| | - Lior Kornblum
- Andrew and Erna Viterbi Faculty of Electrical and Computer Engineering, Technion - Israel Institute of Technology, Haifa 3200003, Israel
| | - Ilan Goldfarb
- Department of Materials Science and Engineering, The Iby and Aladar Fleischman Faculty of Engineering, Tel Aviv University, Ramat Aviv, Tel Aviv 6997801, Israel
| | - Amit Kohn
- Department of Materials Science and Engineering, The Iby and Aladar Fleischman Faculty of Engineering, Tel Aviv University, Ramat Aviv, Tel Aviv 6997801, Israel.
| |
Collapse
|
2
|
Tran DT, Svensson G, Tai CW. SUePDF: a program to obtain quantitative pair distribution functions from electron diffraction data. J Appl Crystallogr 2017; 50:304-312. [PMID: 28190994 PMCID: PMC5294395 DOI: 10.1107/s160057671601863x] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2016] [Accepted: 11/21/2016] [Indexed: 11/10/2022] Open
Abstract
SUePDF is a graphical user interface program written in MATLAB to achieve quantitative pair distribution functions (PDFs) from electron diffraction data. The program facilitates structural studies of amorphous materials and small nanoparticles using electron diffraction data from transmission electron microscopes. It is based on the physics of electron scattering as well as the total scattering methodology. A method of background modeling is introduced to treat the intensity tail of the direct beam, inelastic scattering and incoherent multiple scattering. Kinematical electron scattering intensity is scaled using the electron scattering factors. The PDFs obtained after Fourier transforms are normalized with respect to number density, nanoparticle form factor and the non-negativity of probability density. SUePDF is distributed as free software for academic users.
Collapse
Affiliation(s)
- Dung Trung Tran
- Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University , Svante Arrhenius väg 16C, Stockholm, S-10691, Sweden
| | - Gunnar Svensson
- Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University , Svante Arrhenius väg 16C, Stockholm, S-10691, Sweden
| | - Cheuk-Wai Tai
- Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University , Svante Arrhenius väg 16C, Stockholm, S-10691, Sweden
| |
Collapse
|
3
|
Gammer C, Burak Ozdol V, Liebscher CH, Minor AM. Diffraction contrast imaging using virtual apertures. Ultramicroscopy 2015; 155:1-10. [DOI: 10.1016/j.ultramic.2015.03.015] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2014] [Revised: 02/18/2015] [Accepted: 03/18/2015] [Indexed: 10/23/2022]
|