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Kryvyi S, Kret S, Domagala JZ, Wojnar P. Reconstruction of three-dimensional strain field in an asymmetrical curved core-shell hetero-nanowire. NANOTECHNOLOGY 2023; 34:445705. [PMID: 37524071 DOI: 10.1088/1361-6528/acebf6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/16/2023] [Accepted: 07/31/2023] [Indexed: 08/02/2023]
Abstract
Crystal orientation and strain mapping of an individual curved and asymmetrical core-shell hetero-nanowire (NW) is performed based on transmission electron microscopy. It relies on a comprehensive analysis of scanning nanobeam electron diffraction data obtained for 1.3 nm electron probe size. The proposed approach also handles the problem of appearing twinning defects on diffraction patterns and allows for the investigation of materials with high defect densities. Based on the experimental maps and their comparison with finite element simulations, the entire core-shell geometry including full three-dimensional strain distribution within the curved core-shell NW are obtained. Our approach represents, therefore, a low-dose quasi-tomography of the strain field within a nanoobject using only a single zone axis diffraction experiment. Our approach is applicable also for electron beam-sensitive materials for which performing conventional tomography is a difficult task.
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Affiliation(s)
- Serhii Kryvyi
- Institute of Physics Polish Academy of Sciences, al. Lotnikow 32/46, 02-668 Warsaw, Poland
| | - Slawomir Kret
- Institute of Physics Polish Academy of Sciences, al. Lotnikow 32/46, 02-668 Warsaw, Poland
| | - Jaroslaw Z Domagala
- Institute of Physics Polish Academy of Sciences, al. Lotnikow 32/46, 02-668 Warsaw, Poland
| | - Piotr Wojnar
- Institute of Physics Polish Academy of Sciences, al. Lotnikow 32/46, 02-668 Warsaw, Poland
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Gas K, Sawicki M. A Simplified Method of the Assessment of Magnetic Anisotropy of Commonly Used Sapphire Substrates in SQUID Magnetometers. MATERIALS (BASEL, SWITZERLAND) 2022; 15:8532. [PMID: 36500027 PMCID: PMC9739591 DOI: 10.3390/ma15238532] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/17/2022] [Revised: 11/24/2022] [Accepted: 11/26/2022] [Indexed: 06/17/2023]
Abstract
Solid-state wafers are indispensable components in material science as substrates for epitaxial homo- or heterostructures or carriers for two-dimensional materials. However, reliable determination of magnetic properties of nanomaterials in volume magnetometry is frequently affected by unexpectedly rich magnetism of these substrates, including significant magnetic anisotropy. Here, we describe a simplified experimental routine of magnetic anisotropy assessment, which we exemplify and validate for epi-ready sapphire wafers from various sources. Both the strength and the sign of magnetic anisotropy are obtained from carefully designed temperature-dependent measurements, which mitigate all known pitfalls of volume SQUID magnetometry and are substantially faster than traditional approaches. Our measurements indicate that in all the samples, two types of net paramagnetic contributions coexist with diamagnetism. The first one can be as strong as 10% of the base diamagnetism of sapphire [-3.7(1) × 10-7 emu/gOe], and when exceeds 2%, it exhibits pronounced magnetic anisotropy, with the easy axis oriented perpendicularly to the face of c-plane wafers. The other is much weaker, but exhibits a ferromagnetic-like appearance. These findings form an important message that nonstandard magnetism of common substrates can significantly influence the results of precise magnetometry of nanoscale materials and that its existence must be taken for granted by both industry and academia.
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Kryvyi S, Kret S, Wojnar P. Precise strain mapping of nano-twinned axial ZnTe/CdTe hetero-nanowires by scanning nanobeam electron diffraction. NANOTECHNOLOGY 2022; 33:195704. [PMID: 34874318 DOI: 10.1088/1361-6528/ac3fe3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/2021] [Accepted: 12/03/2021] [Indexed: 06/13/2023]
Abstract
The occurrence of strain is inevitable for the growth of lattice mismatched heterostructures. It affects greatly the mechanical, electrical and optical properties of nano-objects. It is also the case for nanowires which are characterized by a high surface to volume ratio. Thus, the knowledge of the strain distribution in nano-objects is critically important for their implementation into devices. This paper presents an experimental data for II-VI semiconductor system. Scanning nanobeam electron diffraction strain mapping technique for hetero-nanowires characterized by a large lattice mismatch (>6% in the case of CdTe/ZnTe) and containing segments with nano-twins has been described. The spatial resolution of about 2 nm is 10 times better than obtained in synchrotron nanobeam systems. The proposed approach allows us to overcome the difficulties related to nanowire thickness variations during the acquisition of the nano-beam electron diffraction data. In addition, the choice of optimal parameters used for the acquisition of nano-beam diffraction data for strain mapping has been discussed. The knowledge of the strain distribution enables, in our particular case, the improvement of the growth model of extremely strained axial nanowires synthetized by vapor-liquid solid growth mechanism. However, our method can be applied for the strain mapping in nanowire heterostructures grown by any other method.
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Affiliation(s)
- Serhii Kryvyi
- Institute of Physics Polish Academy of Sciences, al. Lotnikow 32/46, 02-668 Warsaw, Poland
| | - Slawomir Kret
- Institute of Physics Polish Academy of Sciences, al. Lotnikow 32/46, 02-668 Warsaw, Poland
| | - Piotr Wojnar
- Institute of Physics Polish Academy of Sciences, al. Lotnikow 32/46, 02-668 Warsaw, Poland
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Gas K, Sawicki M. In Situ Compensation Method for Precise Integral SQUID Magnetometry of Miniscule Biological, Chemical, and Powder Specimens Requiring the Use of Capsules. MATERIALS 2022; 15:ma15020495. [PMID: 35057212 PMCID: PMC8780521 DOI: 10.3390/ma15020495] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/18/2021] [Revised: 01/05/2022] [Accepted: 01/06/2022] [Indexed: 01/25/2023]
Abstract
Steadily growing interest in magnetic characterization of organic compounds for therapeutic purposes or of other irregularly shaped specimens calls for refinements of experimental methodology to satisfy experimental challenges. Encapsulation in capsules remains the method of choice, but its applicability in precise magnetometry is limited. This is particularly true for minute specimens in the single milligram range as they are outweighed by the capsules and are subject to large alignment errors. We present here a completely new experimental methodology that permits 30-fold in situ reduction of the signal of capsules by substantially restoring the symmetry of the sample holder that is otherwise broken by the presence of the capsule. In practical terms it means that the standard 30 mg capsule is seen by the magnetometer as approximately a 1 mg object, effectively opening the window for precise magnetometry of single milligram specimens. The method is shown to work down to 1.8 K and in the whole range of the magnetic fields. The method is demonstrated and validated using the reciprocal space option of MPMS-SQUID magnetometers; however, it can be easily incorporated in any magnetometer that can accommodate straw sample holders (i.e., the VSM-SQUID). Importantly, the improved sensitivity is accomplished relying only on the standard accessories and data reduction method provided by the SQUID manufacturer, eliminating the need for elaborate raw data manipulations.
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Gas K, Kret S, Zaleszczyk W, Kamińska E, Sawicki M, Wojtowicz T, Szuszkiewicz W. Oxidation of MBE-Grown ZnTe and ZnTe/Zn Nanowires and Their Structural Properties. MATERIALS 2021; 14:ma14185252. [PMID: 34576476 PMCID: PMC8469095 DOI: 10.3390/ma14185252] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/04/2021] [Revised: 09/01/2021] [Accepted: 09/07/2021] [Indexed: 12/23/2022]
Abstract
Results of comparative structural characterization of bare and Zn-covered ZnTe nanowires (NWs) before and after thermal oxidation at 300 °C are presented. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, and Raman scattering not only unambiguously confirm the conversion of the outer layer of the NWs into ZnO, but also demonstrate the influence of the oxidation process on the structure of the inner part of the NWs. Our study shows that the morphology of the resulting ZnO can be improved by the deposition of thin Zn shells on the bare ZnTe NWs prior to the oxidation. The oxidation of bare ZnTe NWs results in the formation of separated ZnO nanocrystals which decorate crystalline Te cores of the NWs. In the case of Zn-covered NWs, uniform ZnO shells are formed, however they are of a fine-crystalline structure or partially amorphous. Our study provides an important insight into the details of the oxidation processes of ZnTe nanostructures, which could be of importance for the preparation and performance of ZnTe based nano-devices operating under normal atmospheric conditions and at elevated temperatures.
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Affiliation(s)
- Katarzyna Gas
- Institute of Physics, Polish Academy of Sciences, Aleja Lotnikow 32/46, PL-02668 Warsaw, Poland; (S.K.); (W.Z.); (M.S.); (W.S.)
- Correspondence:
| | - Slawomir Kret
- Institute of Physics, Polish Academy of Sciences, Aleja Lotnikow 32/46, PL-02668 Warsaw, Poland; (S.K.); (W.Z.); (M.S.); (W.S.)
| | - Wojciech Zaleszczyk
- Institute of Physics, Polish Academy of Sciences, Aleja Lotnikow 32/46, PL-02668 Warsaw, Poland; (S.K.); (W.Z.); (M.S.); (W.S.)
- International Research Centre MagTop, Institute of Physics, Polish Academy of Sciences, Aleja Lotnikow 32/46, PL-02668 Warsaw, Poland;
| | - Eliana Kamińska
- Institute of High Pressure Physics Unipress, Al. Prymasa Tysiaclecia 98, PL-01142 Warsaw, Poland;
| | - Maciej Sawicki
- Institute of Physics, Polish Academy of Sciences, Aleja Lotnikow 32/46, PL-02668 Warsaw, Poland; (S.K.); (W.Z.); (M.S.); (W.S.)
| | - Tomasz Wojtowicz
- International Research Centre MagTop, Institute of Physics, Polish Academy of Sciences, Aleja Lotnikow 32/46, PL-02668 Warsaw, Poland;
| | - Wojciech Szuszkiewicz
- Institute of Physics, Polish Academy of Sciences, Aleja Lotnikow 32/46, PL-02668 Warsaw, Poland; (S.K.); (W.Z.); (M.S.); (W.S.)
- Institute of Physics, College of Natural Sciences, University of Rzeszow, S. Pigonia 1, PL-35310 Rzeszow, Poland
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Cros A, Cristóbal AG, Hestroffer K, Daudin B, Wang J, Demangeot F, Péchou R. Resonant Raman scattering of core-shell GaN/AlN nanowires. NANOTECHNOLOGY 2020; 32:085713. [PMID: 33142269 DOI: 10.1088/1361-6528/abc710] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/25/2020] [Accepted: 11/03/2020] [Indexed: 06/11/2023]
Abstract
We have analyzed the electron-phonon coupling in GaN/AlN core-shell nanowires by means of Raman scattering excited at various wavelengths in the ultraviolet spectral range (335, 325 and 300 nm) and as a function of the AlN shell thickness. The detailed analysis of the multi-phonon spectra evidences important differences with excitation energy. Under 325 and 300 nm excitation the Raman process is mediated by the allowedA1(LO) phonon mode, where the atoms vibrate along the NW axis. Considering its selection rules, this mode is easily accessible in backscattering along the wurtzitecaxis. Interestingly, for 335 nm excitation the scattering process is instead mediated by theE1(LO) phonon mode, where atoms vibrate in thec-plane and that is forbidden in this configuration. This change is ascribed to the band anticrossing caused by the uniaxial strain imposed by the AlN shell and the proximity, at this particular excitation energy, of real electronic transitions separated by the energy of the longitudinal optical phonon modes. The energy and character of the electronic bands can be tuned by varying the AlN shell thickness, a degree of freedom unique to core-shell nanowires. The interpretation of the experimental results is supported by calculations of the electronic transitions of GaN under uniaxial strain performed within the framework of ak · pmodel.
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Affiliation(s)
- A Cros
- Institute of Materials Science (ICMUV), University of Valencia, PO Box 22085, E-46071, Valencia, Spain
| | - A García Cristóbal
- Institute of Materials Science (ICMUV), University of Valencia, PO Box 22085, E-46071, Valencia, Spain
| | - K Hestroffer
- Univ. Grenoble-Alpes, CEA-IRIG, PHELIQS, 17 av. des Martyrs, F-38000 Grenoble, France
| | - B Daudin
- Univ. Grenoble-Alpes, CEA-IRIG, PHELIQS, 17 av. des Martyrs, F-38000 Grenoble, France
| | - J Wang
- CNRS-CEMES, 29 rue J. Marvig, BP. 94347, F-31055 Toulouse, France
| | - F Demangeot
- CNRS-CEMES, 29 rue J. Marvig, BP. 94347, F-31055 Toulouse, France
| | - R Péchou
- CNRS-CEMES, 29 rue J. Marvig, BP. 94347, F-31055 Toulouse, France
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