Matching Items (4)
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- All Subjects: Thin films
- Creators: Friesen, Cody
- Member of: Theses and Dissertations
Description
There is an inexorable link between structure and stress, both of which require study in order to truly understand the physics of thin films. To further our knowledge of thin films, the relationship between structure and stress development was examined in three separate systems in vacuum. The first was continued copper thin film growth in ultra-high vacuum after adsorption of a sub-monolayer quantity of oxygen. Results showed an increase in compressive stress generation, and theory was proposed to explain the additional compressive stress within the films. The second system explored was the adsorption of carbon monoxide on the platinum {111} surface in vacuum. The experiments displayed a correlation between known structural developments in the adsorbed carbon monoxide adlayer and the surface stress state of the system. The third system consisted of the growth and annealing stresses of ice thin films at cryogenic temperatures in vacuum. It was shown that the growth stresses are clearly linked to known morphology development from literature, with crystalline ice developing compressive and amorphous ice developing tensile stresses respectively, and that amorphous ice films develop additional tensile stresses upon annealing.
ContributorsKennedy, Jordan (Author) / Friesen, Cody (Thesis advisor) / Sieradzki, Karl (Committee member) / Crozier, Peter (Committee member) / Arizona State University (Publisher)
Created2011
Description
This research focuses on the stress and structure evolution observed in-situ during the earliest stages of thin film growth in Cu on Au(111)-reconstruction. For the research, an ultra high vacuum-scanning tunneling microscopy (UHV-STM) system was modified to have the additional capabilities of in-situ deposition and in-situ stress evolution monitoring. The design and fabrication processes for the modifications are explained in detail. The deposition source enabled imaging during the deposition of Cu thin films, while also being columnar enough to avoid negatively impacting the function of the microscope. It was found that the stress-induced changes in piezo voltage occurred over a substantially longer time scale and larger piezo scale than used during imaging, allowing for the deconvolution of the two sources of piezo voltage change. The intrinsic stress evolution observed at the onset of Cu growth was tensile in character and reached a maximum of 0.19 N/m at approximately 0.8ML, with an average tensile slope of 1.0GPa. As the film thickness increased beyond 0.8 ML, the stress became less tensile as the observation of disordered stripe and trigon patterns of misfit dislocations began to appear. The transport of atoms from the surface of enlarged Cu islands into the strained layer played an important role in this stage, because they effectively reduce the activation barrier for the formation of the observed surface structures. A rich array of structures were observed in the work presented here including stripe, disordered stripe and trigon patterns co-existing in a single Cu layer. Heteroepitaxial systems in existing literature showed a uniform structure in the single layer. The non-uniform structures in the single layer of this work may be attributed to the room temperature Cu growth, which can kinetically limit uniform pattern formation. The development of the UHV-STM system with additional capabilities for this work is expected to contribute to research for the stress and structure relationships of many other heteroepitaxial systems.
ContributorsNah, Jungwoo (Author) / Friesen, Cody (Thesis advisor) / Sieradzki, Karl (Committee member) / Bennett, Peter (Committee member) / Arizona State University (Publisher)
Created2012
Description
Over the last decade copper electrodeposition has become the dominant process by which microelectronic interconnects are made. Replacing ultra-high vacuum evaporative film growth, the technology known as the Cu damascene process has been widely implemented in the microelectronics industry since the early 2000s. The transition from vacuum film growth to electrodeposition was enabled by solution chemistries that provide "bottom-up" or superfilling capability of vias and trenches. While the process has been and is used widely, the actual mechanisms responsible for superfilling remain relatively unknown. This dissertation presents and discusses the background and results of experimental investigations that have been done using in situ electrochemical surface stress monitoring techniques to study the evolution of stress on Cu{111} thin film electrodes. Because of its extreme sensitivity to the structure on both the electrode and solution sides of the interface, surface stress monitoring as analytical technique is well suited for the study of electrodeposition. These ultra-high resolution stress measurements reveal the dynamic response of copper electrodes to a number of electrochemical and chemical experimental variables. In the case of constant current pulsed deposition and stripping, the surface stress evolution depends not only on the magnitude of the current pulse, but also shows a marked response to plating bath composition. The plating bath chemistries used in this work include (1) additive free, (2) deposition suppressing solutions that include polyethylene glycol (PEG) and sodium chloride (NaCl) as well as (3) full additive solution combinations which contain PEG, NaCl, and a one of two deposition accelerating species (bis-(sodiumsulfopropyl)disulfide (SPS) or mercaptopropane sulfonic acid (MPS)). The development of thin film stress is further investigated through a series of solution exchange experiments that correlate the magnitude of electrode exchange current density and the stress state of the film. Remarkably, stress changes as large as ~8.5 N/m are observed during solution exchanges at the open circuit potential. Overall, this research demonstrates that solution chemistry can have a large impact on thin film stress evolution, even for very small deposition thicknesses (e.g. <10 ML) or in the absence of net addition or removal of material from the electrode.
ContributorsHeaton, Thomas Stanley (Author) / Friesen, Cody (Thesis advisor) / Buttry, Daniel (Committee member) / Sieradzki, Karl (Committee member) / Arizona State University (Publisher)
Created2011
Description
Multifunctional oxide thin-films grown on silicon and several oxide substrates have been characterized using High Resolution (Scanning) Transmission Electron Microscopy (HRTEM), Energy-Dispersive X-ray Spectroscopy (EDX), and Electron Energy-Loss Spectroscopy (EELS). Oxide thin films grown on SrTiO3/Si pseudo-substrate showed the presence of amorphised SrTiO3 (STO) at the STO/Si interface. Oxide/oxide interfaces were observed to be atomically clean with very few defects.
Al-doped SrTiO3 thin films grown on Si were of high crystalline quality. The Ti/O ratio estimated from EELS line scans revealed that substitution of Ti by Al created associated O vacancies. The strength of the crystal field in STO was measured using EELS, and decreased by ~1.0 eV as Ti4+ was substituted by Al3+. The damping of O-K EELS peaks confirmed the rise in oxygen vacancies. For Co-substituted STO films grown on Si, the EDS and EELS spectra across samples showed Co doping was quite random. The substitution of Ti4+ with Co3+ or Co2+ created associated oxygen vacancies for charge balance. Presence of oxygen vacancies was also confirmed by shift of Ti-L EELS peaks towards lower energy by ~0.4 eV. The crystal-field strength decreased by ~0.6 eV as Ti4+ was partially substituted by Co3+ or Co2+.
Spinel Co3O4 thin films grown on MgAl2O4 (110) were observed to have excellent crystalline quality. The structure of the Co3O4/MgAl2O4 interface was determined using HRTEM and image simulations. It was found that MgAl2O4 substrate is terminated with Al and oxygen. Stacking faults and associated strain fields in spinel Co3O4 were found along [111], [001], and [113] using Geometrical Phase Analysis.
NbO2 films on STO (111) were observed to be tetragonal with lattice parameter of 13.8 Å and NbO films on LSAT (111) were observed to be cubic with lattice parameter of 4.26 Å. HRTEM showed formation of high quality NbOx films and excellent coherent interface. HRTEM of SrAl4 on LAO (001) confirmed an island growth mode. The SrAl4 islands were highly crystalline with excellent epitaxial registry with LAO. By comparing HRTEM images with image simulations, the interface structure was determined to consist of Sr-terminated SrAl4 (001) on AlO2-terminated LAO (001).
Al-doped SrTiO3 thin films grown on Si were of high crystalline quality. The Ti/O ratio estimated from EELS line scans revealed that substitution of Ti by Al created associated O vacancies. The strength of the crystal field in STO was measured using EELS, and decreased by ~1.0 eV as Ti4+ was substituted by Al3+. The damping of O-K EELS peaks confirmed the rise in oxygen vacancies. For Co-substituted STO films grown on Si, the EDS and EELS spectra across samples showed Co doping was quite random. The substitution of Ti4+ with Co3+ or Co2+ created associated oxygen vacancies for charge balance. Presence of oxygen vacancies was also confirmed by shift of Ti-L EELS peaks towards lower energy by ~0.4 eV. The crystal-field strength decreased by ~0.6 eV as Ti4+ was partially substituted by Co3+ or Co2+.
Spinel Co3O4 thin films grown on MgAl2O4 (110) were observed to have excellent crystalline quality. The structure of the Co3O4/MgAl2O4 interface was determined using HRTEM and image simulations. It was found that MgAl2O4 substrate is terminated with Al and oxygen. Stacking faults and associated strain fields in spinel Co3O4 were found along [111], [001], and [113] using Geometrical Phase Analysis.
NbO2 films on STO (111) were observed to be tetragonal with lattice parameter of 13.8 Å and NbO films on LSAT (111) were observed to be cubic with lattice parameter of 4.26 Å. HRTEM showed formation of high quality NbOx films and excellent coherent interface. HRTEM of SrAl4 on LAO (001) confirmed an island growth mode. The SrAl4 islands were highly crystalline with excellent epitaxial registry with LAO. By comparing HRTEM images with image simulations, the interface structure was determined to consist of Sr-terminated SrAl4 (001) on AlO2-terminated LAO (001).
ContributorsDhamdhere, Ajit (Author) / Smith, David J. (Thesis advisor) / McCartney, Martha R. (Committee member) / Chamberlin, Ralph (Committee member) / Ponce, Fernando (Committee member) / Arizona State University (Publisher)
Created2015