AVS 70 Session TF1-TuM: Thin Films: Controlling Crystalline Phases
Session Abstract Book
(311KB, Jul 23, 2024)
Time Period TuM Sessions
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Abstract Timeline
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8:00 AM | Invited |
TF1-TuM-1 Peter Mark Memorial Award Talk: Strain-Induced Magnetism and Superconductivity in Single-Crystalline Heusler Membranes
Jason Kawasaki (University of Wisconsin - Madison) Single-crystalline membranes of functional materials enable the tuning of properties via extreme strain states; however, conventional routes for producing membranes require the use of sacrificial layers and chemical etchants, which can both damage the membrane and limit the ability to make them ultrathin. I will describe how the growth of thin films on graphene-terminated substrates enables synthesis of single crystalline, mechanically exfoliatable membranes [1,2]. Using rippled membranes of the Heusler compound GdPtSb, we demonstrate the first experimental example of flexomagnetism, that is, ferro/ferri-magnetism induced by strain gradients [3]. I will also describe evidence of superconductivity induced in another Heusler membrane via strain. More broadly, Heusler membranes provide highly tunable platform for tuning ferroic order, topological states, and correlations [4]. [1] S. Manzo, et. al., Nature Commun., 13, 4014 (2022). https://doi.org/10.1038/s41467-022-31610-y [2] D. Du et. al., Nano Lett. 22, 21, 8647 (2022). https://doi.org/10.1021/acs.nanolett.2c03187 [3] D. Du, et. al., Nature Commun., 12, 2494 (2021). https://doi.org/10.1038/s41467-021-22784-y [4] D. Du, e. al. APL, 122, 170501 (2023). https://doi.org/10.1063/5.0146553 |
8:30 AM |
TF1-TuM-3 Stabilization of P63cm ScFeO3 on (111) Pt Mediated via an Fe3O4 Interlayer
Marshall Frye, Jonathan Chin (Georgia Institute of Technology); Nicholas Parker, Matthew Barone (Cornell University); Lauren Garten (Georgia Institute of Technology) Marshall Frye1, Jonathan Chin1, Nicholas Parker2, Matthew Barone3, Lauren M. Garten1
Ferroelectric photovoltaics are an emerging renewable energy technology where charge separation occurs in a single layer and the open-circuit voltage can be larger than the bandgap. The metastable P63cm phase of ScFeO3 (h-ScFeO3) is an ideal candidate for ferroelectric photovoltaics due to its polar crystal structure and narrow bandgap (1.2 eV). While h-ScFeO3 can be grown on Al2O3 using a layered approach,1 on conductive substrates, such as (111) Pt, only the ground state bixbyite phase of ScFeO3 is stable. h-ScFeO3 growth on a substrate with high conductivity and low epitaxial strain is critically needed for photovoltaic device fabrication. In this work we grew h-ScFeO3 on (111) platinum via molecular beam epitaxy (MBE). The stabilization of the h-ScFeO3 phase was enabled by an Fe3O4 interlayer. This approach is adapted from reports of growth of hexagonal LuFeO3 on oriented Fe3O4 via MBE.2 Epitaxial (111) Pt which was deposited on c-Al2O3 was found to have a narrow (~0.005°) full width at half maximum (FWHM) rocking curve about the (111) peak, indicating a highly crystalline film. After depositing (111) Pt, a Fe3O4 layer was deposited. ScFeO3 was then deposited on the Fe3O4 film with alternating depositions of Sc and Fe.1 The films are solely (0002l) oriented of h-ScFeO3 with clear Laue oscillations. Furthermore, rocking curves about the (0004) hexagonal ScFeO3 peak have a FWHM of 0.07°, indicating a highly crystalline film. Films grown on conductive substrates then enabled measurements of the carrier mobility and dielectric response of the h-ScFeO3. Overcoming the challenge of growing h-ScFeO3 on conductive substrates will allow us to utilize these materials advantageous properties for high-efficiency photovoltaics.
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8:45 AM |
TF1-TuM-4 Thermo-Controlled Defect Engineering in Ceria: An XPS and Raman Spectroscopy Study with In-Situ Heating
Udit Kumar, Corbin Feit, Jeya Prakash Ganesan, S. Novia Berriel, Yifei Fu, Craig Neal, Elayaraja Kolanthai, Parag Banerjee, Sudipta Seal (University of Central Florida) Cerium oxide nanostructures possess unique oxidative recycling properties, enabling their use in various engineering applications. However, predictable and precise defect engineering remains challenging. Ceria thin films offer a method to engineer defects by controlling thickness, albeit with limitations. To further enhance performance, we fabricated 2.9 nm and 0.5 nm CeO2-33 nm VO2 bilayers using atomic layer deposition (ALD), leveraging the low-temperature phase transition of VO2. We established a test vehicle utilizing X-ray Photoelectron Spectroscopy (XPS) with in-situ heating and cooling to study defect levels. The Ce3+/Ce4+ ratio was determined using Ce3d XPS scans during heating and cooling. A remarkable Ce3+/Ce4+ ratio of 5.97 (Ce3+ ~ 85%) was obtained and modulated over a temperature range from room temperature to 90 ºC. Additionally, Raman studies with in-situ heating and cooling were conducted to understand the mechanism behind this phenomenon. |
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9:00 AM |
TF1-TuM-5 Hybrid Pulsed Laser Deposition Growth of Epitaxial Chalcogenides
Mythili Surendran (USC) Chalcogenides such as transition metal dichalcogenides (TMDC) and chalcogenide perovskites (CP) have garnered attention for their electronic and photonic properties. Despite their promising potential for electronic applications, the epitaxial growth of these materials is still in its nascent stages. Adding to the complexity, a most of the emerging chalcogenides are vapor pressure mismatched transition metal compounds. The stark differences in vapor pressures between transition metal cations and chalcogen anions present a great challenge during epitaxial growth. This challenge is particularly pronounced in sulfide thin film growth and exacerbated in CPs due to their complex stoichiometries. Addressing these complexities demands innovative strategies to achieve precise flux control and maintain stoichiometric integrity during epitaxial growth. Sulfides have been mostly grown using CVD, although MBE, MOCVD, pulsed laser deposition (PLD)and several other techniques have been exploited. However, large area and high-quality growth with precise and uniform thickness control and low defect densities still remain a challenge due to a large cation-sulfur vapor pressure mismatch, corrosive and reactive nature of most chalcogen precursors, high synthesis temperatures and the propensity to oxidize easily in the presence of oxygen at these high temperatures. Most growth techniques utilize H2S as the sulfur source. However, H2S is a toxic, hazardous, and flammable gas and require high temperatures for efficient decomposition and sulfurization, resulting in high defect densities. Here, we discuss epitaxial growth of CPs and TMDCs (specifically sulfides) using a novel hybrid PLD (Adv. Mater 2024) approach wherein we employed organo-sulfur precursors as the sulfur source. Large area epitaxial thin films of Group IV 2D chalcogenides such as TiS2 (metallic) and ZrS2 (semiconducting) and CPs such as BaZrS3 and BaTiS3 were successfully grown. This novel method utilizes precursors with optimum vapor pressures and they decompose at a lower temperatures (~250-400°C) to provide dissociated sulfur species. Structural and electrical characterization, along with low temperature transport studies reveal low defect densities and high carrier mobilities in these films. This work emphasizes on low temperature growth of high mobility refractory metal-based sulfides, especially with BEOL compatibility. Although slightly elevated temperatures were required for CPs, the interfacial roughness and optoelectronic performance were improved. The potential of these chalcogenides as candidates for transparent and conducting layers in chalcogenide-based optoelectronic devices will be discussed. |
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9:15 AM |
TF1-TuM-6 Atomic Layer Deposition of Entropy Stabilized ZrxTayOz
Shane Witsell, Jessica Haglund, John Conley (Oregon State University) High entropy oxides (HEOs) can exhibit enhanced mechanical, refractory, catalytic, cryogenic, and dielectric properties over conventional materials [1]. The classic understanding of HEOs is founded on a high degree of configurational disorder as well as a positive enthalpy of formation. It has been thought that five discrete elements were necessary to cause this high degree of disorder (Sconfig >1.6R,J/mol*K). However, it has recently been shown that A6B2O17 perovskites, where A = Zr or Hf and B = Nb or Ta can demonstrate an exceptionally high degree of disorder (Sconfig of 4.50R, J/mol*K) [2]. Though these materials have been synthesized by powder sintering [5] and ternary ZrTaO has been demonstrated with atomic layer deposition (ALD) [3], entropy stabilized ZrxTayOz has yet to be achieved via ALD. Herein we report the successful transformation of ALD ZrxTayOz into the entropy-stabilized form. ZrO2 and Ta2O5 were synthesized via ALD using tantalum ethoxide (Ta(OEt)5) and zirconium chloride (ZrCl4), respectively, with O3 [3]. ZrxTayOz was deposited using modulated ZrCl4/N2/Ta(OEt)5/N2/O3/N2 super cycles [4]. Films were deposited on Si substrates and were amorphous as-deposited. Following annealing at 800°C for 30 minutes in N2, x-ray diffractometry (XRD) spectra (Fig. 1) show a strong overlap between annealed ALD Zr6Ta2O17 and the expected peaks for HEO stabilized A6B2O17 [5], and no overlap with binary ZrO2 or Ta2O5. Metal/insulator/Si (MIS) electrical devices were fabricated using Ag top electrodes. 800 °C annealed entropy stabilized ZrxTayOz devices exhibited unipolar threshold voltage switching when illuminated, with a ON/OFF current ratio of 7x103 and a ~ +0.56 MV/cm SET voltage. Switching did not occur in the dark. Unannealed amorphous ZrxTayOz devices did not exhibit switching in this voltage range but required a +1.8 MV/cm SET voltage and had an ON/OFF ration of only ~102. Switching under illumination is still under investigation and was possibly due to the formation of oxygen vacancies in the entropy stabilized matrix as opposed to the un-annealed amorphous form [6].
View Supplemental Document (pdf) |
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9:30 AM |
TF1-TuM-7 Stabilizing Oriented Barium Nickelate Thin Films
Ian Graham, Marshall Frye, Lauren Garten (Georgia Institute of Technology) Oxygen evolution reaction (OER) is the rate limiting step inhibiting the production of fuel from water.1,2 Barium nickelate (BaNiO3) is a potential candidate for OER catalysis because it has an order of magnitude higher catalytic activity for the OER compared to the current benchmark iridium oxide (IrO2).1 Understanding the impact of crystallographic orientation and oxygen vacancy concentration on OER catalytic activity is critical to enabling BaNiO3 catalysts. 1,2 In this work, we demonstrate the growth of oriented BaNiO3 films via pulsed laser deposition (PLD). Films were deposited from a BaNiO2.36 target onto (0001) Al2O3 substrates over a range of deposition temperatures, laser fluences, and oxygen partial pressures. X-ray diffraction shows that the orientation of BaNiO3 is dependent on the deposition temperature. The (11-20) orientation of BaNiO3 grows at temperatures below 500 °C, whereas increasing the deposition temperature from 400 °C to 500 °C leads to (10-10) BaNiO3. Further increasing the deposition temperature to 700 °C changes the orientation of the film to predominately (0002) oriented. X-ray photoelectron spectroscopy shows the oxidation state of films deposited under different deposition oxygen partial pressures. Reducing deposition pO2 from 1.65 x 10-2 mbar to 1.27 x 10-2 mbar shows a 4% decrease in oxygen atomic percentage. Atomic force microscopy shows that decreasing the laser fluence and oxygen partial pressure decreases the root mean square surface roughness of the deposited films. Reducing the laser fluence from 3.5 J/cm2 to 2.5 J/cm2 shows a 3 nm decrease in the root mean square surface roughness, while decreasing the oxygen partial pressure from 9.1 x 10-2 mbar to 1.65 x 10-2 mbar shows a 1 nm decrease in root mean square surface roughness. Co-planar top electrodes enabled impedance spectroscopy and dielectric measurements. Impedance data shows the migration of oxygen vacancies which play an important role in OER. Elucidating the impact of crystallographic orientation on oxygen vacancy migration gives insight into how crystallographic orientation affects OER catalytic activity. References
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9:45 AM |
TF1-TuM-8 Optimizing Sputter Deposition of Bi2Te3 and Sb2Te3 for Photolithographic Device Fabrication
Rumana Zahir (University of Central Florida); F. Javier Gonzalez (Truventic LLC); Darian Smalley, Akash Hari Bharath, Edgar Nino, Kalpathy Sundaram, Masahiro Ishigami, Robert Peale (University of Central Fllorida) Antenna-coupled thermoelectric junctions have potential for THz and mm-wave detection and energy harvesting. These require patterned deposition of thermoelectric materials with a junction at the feed of a suitable antenna, where the junction is heated by the received radiation. Sb2Te3 and Bi2Te3 thin films have ideal thermoelectric properties for this application, and deposition over patterned photoresist on suitable substrate followed by lift-off is the simplest patterning approach. Our optimization study of unpatterned sputtered films on heated substrates required temperatures exceeding 175 oC to obtain ideal thermoelectric performance. Such temperatures tend to carbonize photoresists, complicating the subsequent lift-off. Here we report the results of a new optimization study using lower substrate temperatures during sputtering followed by annealing. Our approach considers three factors in a two-level full factorial optimization experiment. The three factors are substrate temperature during sputtering, subsequent vacuum annealing temperature, and annealing time. High and low values are selected for each factor giving 8 possible combinations. A mid-point tests for curvature in the main effects. The nine depositions per material were performed on glass substrates in randomized order. Graphs of the response (Seebeck coefficient) averaged over two of the factors plotted vs the third reveal the main effects of varying each factor. Graphs of the response averaged over one of the factors and plotted vs a second factor for each value of the third factor reveal interactions between factors. Examples of device fabrication following the optimized recipe, characterization, and simulation will be presented. View Supplemental Document (pdf) |
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10:00 AM | BREAK - Complimentary Coffee in Exhibit Hall |