Marianne Kräuter
Solvent-free methods for fabrication of nanoporous materials have been on the rise with the aim of facile processing and accessing new application fields. To establish nanoporous metal-oxides and metal-organic thin films in crucial fields, such as microelectronics or energy conversion, an inexpensive synthesis technique is needed, which excels at scalability and controllability. These requirements are met by chemical vapor deposition methods, which allow for the synthesis of highly conformal layers with precise thickness control and excellent conformality.
This talk will focus on the vapor deposition of the prototypical metal-organic framework ZIF-8, and of nanoporous ZnO thin films.
ZIF-8 is synthesized via a two-step chemical vapor deposition process, termed “MOF-CVD”. First, an ultrathin ZnO seed layer is deposited via plasma-enhanced atomic layer deposition (PE-ALD). ZIF-8 layers are subsequently grown by subjecting the ZnO-layer to a 2-methyl imidazole vapor at elevated temperatures. To gain better control over the novel deposition technique, the impact of the conversion time in combination with different thicknesses (1 to 10 nm) and densities (4.6 g/cm3 and 5.2 g/cm3) of the ZnO precursor onto the resulting ZIF-8 layers was investigated.
To obtain nanoporous ZnO, metal-organic “zincone” thin films are deposited via molecular layer deposition (MLD). Subsequently these layers are calcinated to remove their organic contents, thus introducing cavities in the resulting ZnO thin films. The influence of the calcination temperature as well as the influence of the MLD deposition temperature onto the porosity of the ZnO thin films was explored via porosimetric ellipsometry, a technique which has already shown its usefulness for the determination of porosity in polymer-derived oxides.
Michael Pusterhofer
Compared to edge-emitting LASERs, vertical cavity surface emitting LASERs have many advantages that make them preferable for fiber-based telecommuni- cation [1], and compact sensor systems [2, 3]. The introduction of oxide con- finement was able to further increase this lead by producing emitters with very high power conversion ratios. [4] This improvement, however, also comes with some drawbacks. The oxide used in the process was found to be the source of various defects, which in part can be attributed to the volume change caused by the wet oxidation process. [5, 6] Therefore investigations of the oxide in respect to its deformation were conducted. In this talk, these investigations are pre- sented, which include mechanical simulations, electro-thermal simulations and modeling of the oxidation. In addition, experimental results from Nano-beam precession electron diffraction and thermal resistance measurements are shown to support the simulation.
[1] N. Ledentsov et al. “Development of VCSELs and VCSEL-based Links for Data Communication beyond 50Gb/s”. In: Optical Fiber Communication Conference (OFC) 2020. OSA Technical Digest. San Diego, California: Op- tical Society of America, Mar. 2020, M2A.3. doi: 10.1364/OFC.2020.M2A. 3.
[2] Serdal Okur et al. “High-Power VCSEL Arrays with Customized Beam Divergence for 3D-sensing Applications”. In: Proc.SPIE. Vol. 10938. Mar. 2019.
[3] Jean-Franc ̧ois P. Seurin. “High-Power VCSEL Arrays”. In: VCSELs: Fundamentals, Technology and Applications of Vertical-Cavity Surface-Emitting Lasers. Ed. by Rainer Michalzik. Springer Series in Optical Sciences. Berlin, Heidelberg: Springer, 2013, pp. 263–290. isbn: 978-3-642-24986-0. doi: 10. 1007/978-3-642-24986-0_8.
[4] K. L. Lear et al. “Selectively Oxidised Vertical Cavity Surface Emitting Lasers with 50% Power Conversion Efficiency”. In: Electronics Letters 31.3 (Feb. 1995), pp. 208–209. issn: 0013-5194. doi: 10.1049/el:19950125.
[5] Christopher J. Helms et al. “Reliability of Oxide VCSELs at Emcore”. In: Integrated Optoelectronic Devices 2004. Ed. by Chun Lei, Kent D. Cho- quette, and Sean P. Kilcoyne. San Jose, CA, United States, June 2004, p. 183. doi:10.1117/12.539282.
[6] David T. Mathes et al. “Nanoscale Materials Characterization of Degrada- tion in VCSELs”. In: Integrated Optoelectronics Devices. Ed. by Chun Lei and Sean P. Kilcoyne. San Jose, CA, June 2003, p. 67. doi: 10.1117/12. 482858.
Elisabeth Schöffmann
At Wood K plus in St. Veit an der Glan the main research focus lies on wood and paper surface technologies. This includes surface characterization, determination of correlations and interactions between technological properties and surface appearance and development of new surface characterization methods. Therefore, the overall goal of this PhD research project is to investigate the correlation of macroscopic, microscopic and nanoscopic properties for coated wood-based panels, paper and composites by combining Atomic Force Microscopy (AFM) with infrared spectroscopy and microscopy. Different coated wood-based panels, paper and composite samples with different numbers of coating layers and coating material curing-grades were examined and their influence on the samples were investigated through experimental validation. The used coated wood- based panels consisted of particle boards or MDF boards and were coated with impregnates as well as with lacquer layers. The investigated papers were raw, as well as impregnated and coated. The research project is separated into three main research topics, where the invention of an appropriate sample preparation strategy for the investigated coated wood-based materials, papers and impregnates was the first important step. Challenging was the possibility to extract representative sample pieces and to get them into appropriate sample sizes for ultra microtomy. Also, how all layers could be determined, was challenging. A major problem was that the substrates with wood were soaked with water and that parts of particles broke out of the particle boards. With paper and impregnate samples also swelling and cracking between embedding media and samples were problems to solve. The second part aims at investigating which characteristic chemical and physical information of these materials can be obtained with AFM and IR-microscopy. Therefore, the main goal was to identify how the ideal sample area could be found. Due to the different measurement area size of AFM and IR-microscopy it was also important to investigate how a representative overview of the observed cross- section or over the surface part could be obtained. The otherwise difficult evaluation of the large dataset of about 4000 spectra for one IR-microscopy image could be overcome with multivariate data analysis. Afterwards, the last topic is to examine systematically produced samples and investigate what significant differences on the macroscopic to nanoscopic level could be found. Finally, the correlation between the current state-of-the-art destructive testing methods on macroscopic level, like scratch resistance and acid test, and the proposed testing procedure with AFM and IR-microscopy is started in 2021 and will be further continued in 2022. In this part, the main challenges are to produce macroscopic differing samples and to get representative parts for the microscopic to nanoscopic investigation, as well as the further step to obtain more information with AFM from force distance curve recording.