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We investigate the time evolution of ZnO thin film growth in oxygen plasma-enhanced atomic layer deposition using in situ spectroscopic ellipsometry. The recently proposed dynamic-dual-box-model approach [Kilic et al., Sci. Rep. 10, 10392 (2020)] is used to analyze the spectroscopic data post-growth. With the help of this model, we explore the in-cycle surface modifications and reveal the repetitive layer-by-layer growth and surface roughness modification mechanisms during the ZnO ultrathin film deposition. The in situ complex-valued dielectric function of the amorphous ZnO thin film is also determined from the model analysis for photon energies of 1.7–4 eV. The dielectric function is analyzed using a critical point model approach providing parameters for bandgap energy, amplitude, and broadening in addition to the index of refraction and extinction coefficient. The dynamic-dual-box-model analysis reveals the initial nucleation phase where the surface roughness changes due to nucleation and island growth prior to film coalescence, which then lead to the surface conformal layer-by-layer growth with constant surface roughness. The thickness evolution is resolved with Angstrom-scale resolution vs time. We propose this method for fast development of growth recipes from real-time in situ data analysis. We also present and discuss results from x-ray diffraction, x-ray photoelectron spectroscopy, and atomic force microscopy to examine crystallographic, chemical, and morphological characteristics of the ZnO film. 

We report the effect of remote surface optical (RSO) phonon scattering on carrier mobility in monolayer graphene gated by ferroelectric oxide. We fabricate monolayer graphene transistors back-gated by epitaxial (001) Ba0.6Sr0.4TiO3 films, with field effect mobility up to 23 000 cm2 V−1 s−1 achieved. Switching ferroelectric polarization induces nonvolatile modulation of resistance and quantum Hall effect in graphene at low temperatures. Ellipsometry spectroscopy studies reveal four pairs of optical phonon modes in Ba0.6Sr0.4TiO3, from which we extract RSO phonon frequencies. The temperature dependence of resistivity in graphene can be well accounted for by considering the scattering from the intrinsic longitudinal acoustic phonon and the RSO phonon, with the latter dominated by the mode at 35.8 meV. Our study reveals the room temperature mobility limit of ferroelectric-gated graphene transistors imposed by RSO phonon scattering. 

Abstract Nanostructures represent a frontier where meticulous attention to the control and assessment of structural dimensions becomes a linchpin for their seamless integration into diverse technological applications. However, determining the critical dimensions and optical properties of nanostructures with precision still remains a challenging task. In this study, by using an integrative and comprehensive methodical series of studies, the evolution of the depolarization factors in the anisotropic Bruggeman effective medium approximation (AB‐EMA) is investigated. It is found that these anisotropic factors are extremely sensitive to the changes in critical dimensions of the nanostructure platforms. In order to perform a systematic characterization of these parameters, spatially coherent, highly‐ordered slanted nanocolumns are fabricated from zirconia, silicon, titanium, and permalloy on silicon substrates with varying column lengths using glancing angle deposition (GLAD). In tandem, broad‐spectral range Mueller matrix spectroscopic ellipsometry data, spanning from the near‐infrared to the vacuum UV (0.72–6.5 eV), is analyzed with a best‐match model approach based on the anisotropic Bruggeman effective medium theory. The anisotropic optical properties, including complex dielectric function, birefringence, and dichroism, are thereby extracted. Most notably, the research unveils a generalized, material‐independent inverse relationship between depolarization factors and column length. It is envisioned that the presented scaling rules will permit accurate prediction of optical properties of nanocolumnar thin films improving their integration and optimization for optoelectronic and photonic device applications. As an outlook, the highly porous nature and extreme birefringence properties of the fabricated columnar metamaterial platforms are further explored in the detection of nanoparticles from the cross‐polarized integrated spectral color variations.