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1. In situ observation of fast surface dynamics during the vapor-deposition of a stable organic glass

   https://doi.org/10.1039/d0sm01916j  

   Thoms, E.; Gabriel, J. P.; Guiseppi-Elie, A.; Ediger, M. D.; Richert, R. (December 2020, Soft Matter)

   null (Ed.)

   By measuring the increments of dielectric capacitance (Δ C ) and dissipation (Δtan  δ ) during physical vapor deposition of a 110 nm film of a molecular glass former, we provide direct evidence of the mobile surface layer that is made responsible for the extraordinary properties of vapor deposited glasses. Depositing at a rate of 0.1 nm s −1 onto a substrate at T dep = 75 K = 0.82 T g , we observe a 2.5 nm thick surface layer with an average relaxation time of 0.1 s, while the glass growing underneath has a high kinetic stability. The level of Δtan  δ continues to decrease for thousands of seconds after terminating the deposition process, indicating a slow aging-like increase in packing density near the surface. At very low deposition temperatures, 32 and 42 K, the surface layer thicknesses and mobilities are reduced, as are the kinetic stabilities. 

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2. Observation of MOSFET-like behavior of a TFT based on amorphous oxide semiconductor channel layer with suitable integration of atomic layered deposited high-k gate dielectrics

   https://doi.org/10.1063/5.0136037  

   Yarbrough, Kelsea_A; Behera, Makhes_K; Beckford, Jasmine; Pradhan, Sangram_K; Bahoura, Messaoud (February 2023, AIP Advances)

   A series of different high κ dielectrics such as HfO2, ZrO2, and Al2O3 thin films were studied as an alternative material for the possible replacement of traditional SiO2. These large areas, as well as conformal dielectrics thin films, were grown by the atomic layer deposition technique on a p-type silicon substrate at two different deposition temperatures (150 and 250 °C). Atomic force microscopic study reveals that the surface of the films is very smooth with a measured rms surface roughness value of less than 0.4 nm in some films. After the deposition of the high κ layer, a top metal electrode was deposited onto it to fabricate metal oxide semiconductor capacitor (MOSCAP) structures. The I–V curve reveals that the sample growth at high temperatures exhibits a high resistance value and lower leakage current densities. Frequency-dependent (100 kHz to 1 MHz) C–V characteristics of the MOSCAPs were studied steadily. Furthermore, we have prepared a metal oxide semiconductor field-effect transistor device with Al-doped ZnO as a channel material, and the electrical characteristic of the device was studied. The effect of growth temperature on the structure, surface morphology, crystallinity, capacitance, and dielectric properties of the high κ dielectrics was thoroughly analyzed through several measurement techniques, such as XRD, atomic force microscopy, semiconductor parameter analysis, and ultraviolet-visible spectroscopy. 

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3. Effects of elevated-temperature deposition on the atomic structure of amorphous Ta2O5 films

   https://doi.org/10.1063/5.0170100  

    Prasai, K.; Lee, K.; Baloukas, B.;  Cheng, H-P; Fazio, M.; Martinu, L.; Mehta, A.; Menoni, C_S; Schiettekatte, F.; Shink, R.; et al (December 2023, APL Materials)

   Brownian thermal noise as a result of mechanical loss in optical coatings will become the dominant source of noise at the most sensitive frequencies of ground-based gravitational-wave detectors. Experiments found, however, that a candidate material, amorphous Ta2O5, is unable to form an ultrastable glass and, consequently, to yield a film with significantly reduced mechanical loss through elevated-temperature deposition alone. X-ray scattering PDF measurements are carried out on films deposited and subsequently annealed at various temperatures. Inverse atomic modeling is used to analyze the short and medium range features in the atomic structure of these films. Furthermore, in silico deposition simulations of Ta2O5 are carried out at various substrate temperatures and an atomic level analysis of the growth at high temperatures is presented. It is observed that upon elevated-temperature deposition, short range features remain identical, whereas medium range order increases. After annealing, however, both the short and medium range orders of films deposited at different substrate temperatures are nearly identical. A discussion on the surface diffusion and glass transition temperatures indicates that future pursuits of ultrastable low-mechanical-loss films through elevated temperature deposition should focus on materials with a high surface mobility, and/or lower glass transition temperatures in the range of achievable deposition temperatueres. 

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4. Vapor-to-glass preparation of biaxially aligned organic semiconductors

   https://doi.org/10.1063/5.0174819  

   Ju, Jianzhu; Chatterjee, Debaditya; Voyles, Paul M.; Bock, Harald; Ediger, Mark D. (December 2023, The Journal of Chemical Physics)

   Physical vapor deposition (PVD) provides a route to prepare highly stable and anisotropic organic glasses that are utilized in multi-layer structures such as organic light-emitting devices. While previous work has demonstrated that anisotropic glasses with uniaxial symmetry can be prepared by PVD, here, we prepare biaxially aligned glasses in which molecular orientation has a preferred in-plane direction. With the collective effect of the surface equilibration mechanism and template growth on an aligned substrate, macroscopic biaxial alignment is achieved in depositions as much as 180 K below the clearing point TLC−iso (and 50 K below the glass transition temperature Tg) with single-component disk-like (phenanthroperylene ester) and rod-like (itraconazole) mesogens. The preparation of biaxially aligned organic semiconductors adds a new dimension of structural control for vapor-deposited glasses and may enable polarized emission and in-plane control of charge mobility. 

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5. Parametric Control of Melting Gel Morphology and Chemistry via Electrospray Deposition

   https://doi.org/https://doi.org/10.1115/MSEC2021-63347  

   1. Grzenda, M.; Gamboa, A. R.; Mercado, J.; Lei, L.; Guzman, J.; Klein, L. C.; Jitianu, A.; Singer, J. P (August 2021, ASME 2021 16th International Manufacturing Science and Engineering Conference)

   null (Ed.)

   Melting gels are a class of hybrid organic-inorganic silica based gels prepared via the sol-gel process that are solid below their glass transition temperatures, near room temperature, but show thermoplastic behavior when heated. While this phase change can be repeated multiple times, heating the gel past its consolidation temperatures, typically above 130 oC initiates an irreversible reaction that produces highly crosslinked glassy organic-inorganic materials via hydrolysis and poly-condensation. This ability makes melting gels uniquely compatible with processing techniques inaccessible to other sol-gels. By properly tuning their properties, it should be possible to create protective coatings for electronics and anti-corrosive coatings for metals that are highly hydrophobic and insulating. However, melting gel consolidation reactions are highly dependent on charge interactions, raising the question of how these materials will respond to a processing technique, like electrospray deposition (ESD), which is dependent on charge delivery. In this study, we focus on the role that substrate temperature and charge polarity play on film morphology, consolidation chemistry, and surface properties. Optical images, film thickness measurements, nanoindentation, and FTIR were used to characterize the sprayed melting gel with the goal of developing a robust processing space for producing highly cross linked, hydrophobic, dielectric coatings. 

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