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Dr Jasmin-Clara Bürger
Feodor Lynen Research Fellow
Clarendon Laboratory Room 245
Phone (office): +44 (0) 1865 272339
Phone (lab): +44 (0) 1865 282649
Email:
jasmin.buerger@physics.ox.ac.uk
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Research interests
Semiconductor-based THz devices
Publications
- High-resolution nanoanalytical insights into particle formation in SnO2/ZnO core/shell nanowire lithium-ion battery anodes,
JC Bürger, S Lee, J Büttner, S Gutsch, M Kolhep, A Fischer, FM Ross, M Zacharias
ACS Appl. Mater. Interfaces, 15:28387–28397 (2023)
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pdf | doi:10.1021/acsami.3c03025 ]
Tin oxide (SnO2)/zinc oxide (ZnO) core/shell nanowires as anode materials in lithium-ion batteries (LIBs) were investigated using a combination of classical electrochemical analysis and high-resolution electron microscopy to correlate structural changes and battery performance. The combination of the conversion materials SnO2 and ZnO is known to have higher storage capacities than the individual materials. We report the expected electrochemical signals of SnO2 and ZnO for SnO2/ZnO core/shell nanowires as well as unexpected structural changes in the heterostructure after cycling. Electrochemical measurements based on charge/discharge, rate capability, and electrochemical impedance spectroscopy showed electrochemical signals for SnO2 and ZnO and partial reversibility of lithiation and delithiation. We find an initially 30% higher capacity for the SnO2/ZnO core/shell NW heterostructure compared to the ZnO-coated substrate without the SnO2 NWs. However, electron microscopy characterization revealed pronounced structural changes upon cycling, including redistribution of Sn and Zn, formation of similar to 30 nm particles composed of metallic Sn, and a loss of mechanical integrity. We discuss these changes in terms of the different reversibilities of the charge reactions of both SnO2 and ZnO. The results show stability limitations of SnO2/ZnO heterostructure LIB anodes and offer guidelines on material design for advanced next-generation anode materials for LIBs. - Defect location in laterally aligned tin oxide nanowires: the role of growth direction, interface dimensionality, and catalyst,
JC Bürger, S Gutsch, V Wollersen, D Wang, B Christian, Z Fu, O Ambacher, C Kübel, M Zacharias
J. Phys. Chem. C, 127:10871-10877 (2023)
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pdf | doi:10.1021/acs.jpcc.3c02405 ]
Laterally aligned SnO2 nanowires, which exhibitplanargrowth along crystallographically defined directions of a sapphiresubstrate surface, are superior for bio- and gas-sensing applications.Little is known about their cross-sectional geometry and the defectdistribution within the nanowire cross section, although this substantiallydetermines the electronic properties of the nanowires. In this study,SnO2 nanowires were grown on r-plane sapphire substrates.Scanning electron microscopy (SEM) and atomic force microscopy (AFM)reveal the highly oriented growth of the SnO2 nanowirestoward the substrate edges. High-resolution transmission electronmicroscopy (HRTEM) of the NW cross section and strain mapping allowedfor analyzing the crystallographic alignment of the SnO2 NW to the sapphire substrate and the defect distribution withinthe SnO2 nanowire cross section. These techniques revealeda defect-free SnO2-Al2O3 interfaceand a high alignment of the SnO2 NW lattice toward thesapphire substrate along the NW width. The determined high defectdensity close to the nanowire surface will be discussed in comparisonto freestanding SnO2 nanowires and SnO2 thinfilms on sapphire substrates considering the differences in the growthdirection and the interface dimensionality. - Size effect in SnO2/Al2O3 core/shell nanowires after battery cycling,
JC Bürger, S Lee, A Penn, S Gutsch, M Kolhep, J Büttner, A Fischer, FM Ross, M Zacharias
Adv. Energy Sustainability Res., 3:2200098 (2022)
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pdf | doi:10.1002/aesr.202200098 ]
Full utilization of the high storage capacity of conversion electrode materials as tin oxide (SnO2) in lithium-ion batteries is hindered by the high volumetric expansion due to the high lithium storability which can lead to major cell damage and consequent safety issues. To overcome this issue, two promising approaches, nanostructures and buffer layers, are combined and evaluated. SnO2 nanowires (NWs) are coated with an aluminum oxide (Al2O3) buffer layer to investigate the combination SnO2-Al2O3. Strong differences in the crystallinity after cycling between the SnO2/Al2O3 core/shell NW-based heterostructure and uncoated SnO2 NWs based on detailed structural analysis are shown via transmission electron microscopy (TEM) and determination of the elemental distribution of tin, oxygen, lithium, and aluminum via energy-dispersive X-Ray spectroscopy and energy-filtered TEM in the as-prepared and postmortem nanostructures. The core/shell NWs exhibit two different states after charge/discharge cycling, amorphous or crystalline, depending on the NW diameter; for the uncoated SnO2 NWs, only an amorphous postmortem structure is found. Additionally, differences in the elemental distribution for the amorphous and crystalline postmortem SnO2/Al2O3 core/shell NWs, especially for tin, are measured. Consequently, the structures and effects of the Al2O3 coating on the lithiation behavior of SnO2 NW-based heterostructures are discussed. - Analysis of the growth of laterally aligned SnO2 nanowires by thermodynamic considerations and experiments,
JC Bürger, S Gutsch, Y Thomann, R Thomann, B Christian, O Ambacher, M Zacharias
Cryst. Growth Des., 21:191-199 (2021)
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pdf | doi:10.1021/acs.cgd.0c00983 ]
Recently, we reported the experimental tuning of the growth of freestanding SnO2 nanowires to a laterally aligned nanowire grovvth mode. Here, we present thet-modynamic considerations taking into account the previously reported influencing parameters determining the experiments, i.e., the total pressure, the Sn/O ratio at the sample sites, the nanowire diameter, and the substrate type. We will discuss process parameters which will prefer a laterally aligned growth mode. We show that a continuous gold film used as catalyst inhibits the laterally aligned growth. Only at the edges the lateral growth can proceed, whereas the area region is covered by freestanding wires. The reason for that will be explained in a model. Furthernore, the laterally aligned nanowire surface faceting is analyzed by means of transmission electron microscopy and atomic force microscopy and explained. - Transition from freestanding SnO2 nanowires to laterally aligned nanowires with a simulation-based experimental design,
JC Bürger, S Gutsch, M Zacharias
Beilstein J. Nanotechnol., 11:843-853 (2020)
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pdf | doi:10.3762/bjnano.11.69 ]
In this study, we used simulations as a guide for experiments in order to switch freestanding nanowire growth to a laterally aligned growth mode. By means of finite element simulations, we determined that a higher volumetric flow and a reduced process pressure will result in a preferred laterally aligned nanowire growth. Furthermore, increasing the volumetric flow leads to a higher species dilution. Based on our numerical results, we were able to successfully grow laterally aligned SnO2 nanowires out of gold film edges and gold nanoparticles on a-plane sapphire substrates. In our experiments a horizontal 2-zone tube furnace was used. The generation of Sn gas was achieved by a carbothermal reduction of SnO2 powder. However, we observed no elongation of the nanowire length with an increase of the process time. Nevertheless, an alternating gas exchange between an inert gas (Ar) and an oxygen-containing process atmosphere yielded an elongation of the laterally aligned nanowires, indicating that the nanowire growth takes place in a transient period of the gas exchange. - Extended view on the vapor-liquid-solid mechanism for oxide compound nanowires: the role of oxygen, solubility, and carbothermal reaction,
JC Bürger, S Gutsch, M Zacharias
J. Phys. Chem. C, 122:24407-24414 (2018)
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pdf | doi:10.1021/acs.jpcc.8b07332 ]
The Si nanowire growth can be well explained by the classical vapor-liquid-solid (VLS) process taking into account the respective Au-Si phase diagram. For oxide-based compound materials, no phase diagram with gold exists because of the insolubility of these materials into the Au catalyst material. Hence, it is not correct to claim a simple VLS mechanism for the respective growth. In this study, a more complex model for the growth of oxide nanowires (NWs) is proposed by analyzing the influence of oxygen concentration and timing of oxygen inflow into the furnace while growing SnO2 NWs by a carbothermal chemical vapor deposition process. It is shown that a controlled amount of oxygen is mandatory to grow the SnO2 NWs. However, either too low or too high oxygen concentration strongly suppresses the nanowire growth. On the basis of the here-presented experiments, we propose the formation of solid oxide flakes on the catalyst surface and their respective concurrence as guided by the Sn/O balance feeding the liquid catalyst surface. A new model is discussed, taking into account the effect of surface transport and the respective transport of SnO2 solid flakes, the effect of the Sn gradient in the catalyst droplet, and a possible viscosity gradient at the droplet-solid nanowire interface.
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