Browsing by Subject "CVD"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Strongly-Bound Excitons In Transition Metal Dichalcogenides And Organic Semiconductors(2020-05) Schulzetenberg, AaronAtomically-thin, semiconducting transition metal dichalcogenides (TMDs) and organic semiconductors such as rubrene hold exceptional promise for unique and niche electronic applications which cannot be solved with conventional semiconducting crystalline materials. In particular, the process by which excitons relax in thin TMDs controls device engineering considerations including charge carrier mobility and exciton diffusion length. The decay mechanism and time scales can critically depend on interfaces, method of sample preparation and temperature. Here, I present ultrafast transient reflectivity studies of several chemical vapor deposition (CVD) grown TMD structures, including few-layer 2H MoTe2 on SiO2, MoTe2 1T’-2H homojunctions and monolayer MoS2-WS2 lateral heterojunctions on sapphire. The transient reflectivity of CVD-grown, few-layer (5-10 layers) 2H MoTe2 carried out a both room temperature and cryogenic temperatures demonstrates a temperature and fluence dependence consistent with defect-mediated exciton decay. The optical properties of MoTe2 were additionally found to be stable over the course of 8 months air exposure. The biexponential decay dynamics of monolayer MoS2 and WS2 were shown to be consistent with previous investigations. Both studies of interfaces, including the 2H-1T’ MoTe2 homojunctions and the MoS2-WS2 heterojunction were unable to observe signatures of interfacial charge transfer due to lack of sufficient spatial resolution near the interface crossover. In addition to studies on TMDs, the low-wavenumber Raman modes of both isotopically substituted 13C Rubrene and those of a structural analog to rubrene, fm-rubrene, were measured and compared to native rubrene. The 13C rubrene demonstrated a uniform shift to lower energy intermolecular mode vibrations. The modes of fm-rubrene were characterized for the first time and compared to a predicted computational Raman spectrum showing large (~4%) deviations with theory at low vibrational energies (<200cm-1), suggesting intermolecular coupling becomes influential at this threshold.Item Understanding cominatorial atomic layer deposition and chemical vapor deposition.(2009-01) Moersch, Tyler LeightonThe transformation of molecular precursor to solid film begins with an understanding of molecular structure, proceeds through delivery of the molecule to the surface and ends with the decomposition of precursor on the surface to form a deposit. An understanding of the physical and chemical processes leading from molecule to film enables the utilization of chemical precursors in effective deposition processes. Single crystal X-ray crystallography was used to study the structure of [NO]0.5[NO2]0.5[Zr(NO3)5] and [NO]0.5[NO2]0.5[Hf(NO3)5]. Infrared spectroscopy was employed to identify the nature of the cation in the crystal structure, and characteristic absorptions of both nitronium and nitrosonium cations were observed. Fluidized bed reactor technology has been used to study the sublimation behavior of solid-state chemicals. Fluidization behavior, precursor mass transfer rates and delivery uniformity for aluminum trichloride were studied and the results reported. Mixed metal oxide nanolaminate films of hafnium oxide and zirconium oxide interspersed with layers of silicon oxide have been deposited on silicon substrates by a combinatorial atomic layer deposition (ALD) technique. Exposure of repeated cycles of co-dosed alkoxide precursors Hf[OC(CH3)3]4 and Zr[OC(CH3)3]4 with counter-reactant pulses of Si[OC(CH3)3]3(OH) formed films of uniform thickness (±5%) and uniform silicon oxide concentration (85% per total metals basis). The hafnium and zirconium concentrations exhibited smooth gradation across the film from 18% - 82% (per Hf and Zr metals basis). Self-limiting deposition rates of 1.5 nm / cycle were measured, and a linear relationship of film thickness to number of deposition cycles was observed, both consistent with a true ALD process. Rutherford backscattering spectrometry, ellipsometry and X-ray reflectivity results were used to map the composition and determine the film microstructure. Single precursor depositions have been performed and compared to computational models created using CFD-ACE in order to further the understanding of the interaction of fluid dynamics and chemistry in the combinatorial chemical vapor deposition process. The physical and chemical processes contributing to film growth in combinatorial chemical vapor deposition were evaluated.