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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. Investigation of ALD HfSiOx as gate dielectric on β -Ga2O3 (001)

   https://doi.org/10.1063/5.0179813  

   Zhai, Xin; Wen, Zhuoqun; Odabasi, Oguz; Achamyeleh, Eyosyas; Sun, Kai; Ahmadi, Elaheh (March 2024, Applied Physics Letters)

   The interface and bulk properties of ∼20 nm hafnium-silicon-oxide (HfSiOx) dielectric deposited by atomic layer deposition (ALD) on (001) β-Ga2O3 were investigated systematically using deep ultraviolet photo-assisted capacitance–voltage (C–V) and current–voltage (I–V) measurements. The ALD HfSiOx dielectric constant, bulk, and HfSiOx/Ga2O3 interface quality and breakdown field were determined, and the impact of post-deposition annealing (PDA) on these parameters was studied. PDA reduced near-interface traps resulting in a smaller hysteresis without changing the dielectric constant. An average trap density of 2.72 × 1012 and 1.06 × 1012 cm−2 eV−1 was measured on samples with PDA at 400 and 900 °C, respectively. In addition, a high dielectric constant of 9.28 and breakdown field as high as 8.7 MV/cm were achieved on these devices. 

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4. Comparison of Physical Aging and Glass Transition in Glassy–Rubbery Polymer Bilayer Films

   https://doi.org/10.1021/acs.jpcb.4c07902  

   McGuire, Jennifer A; Merrill, James H; Couturier, Alexander A; Thees, Michael F; Roth, Connie B (March 2025, Journal of Physical Chemistry B)

   In the present work, we use ellipsometry to extract the physical aging response of thin glassy polystyrene (PS) layers from rubbery–glassy bilayer films of poly(n-butyl methacrylate) (PnBMA) atop PS. How the soft interface between rubbery and glassy polymer domains can impact the physical aging response of glassy domains is unclear. Measurements in the literature have shown that the local glass transition temperature Tg of PS is strongly reduced near a PnBMA/PS interface with a magnitude twice as large compared to that imparted by a free surface. As the free surface is known to reduce physical aging, we anticipated large changes in the physical aging response of PS within PnBMA/PS bilayer films. However, surprisingly the aging response remained equivalent to bulk down to 75 nm PS layer thicknesses that were the thinnest we found could be accurately measured given the optical limits of dispersion. With complementary fluorescence measurements, we show that the average Tg(hPS) of such PS layers within 150 nm PnBMA/75 nm PS bilayer films are also still bulk. These findings demonstrate that films with finite domain sizes have interfacial dynamical gradients that are significantly altered from those previously measured in systems with semi-infinite domain sizes. 

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5. 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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