Remote Surface Optical Phonon Scattering in Ferroelectric Ba0.6_{0.6}Sr0.4_{0.4}TiO3_{3} Gated Graphene

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) Ba$_{0.6}$Sr$_{0.4}$TiO$_{3}$ films, with field effect mobility up to 23,000 cm$^{2}$V$^{-1}$s$^{-1}$ achieved. Switching the 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 Ba$_{0.6}$Sr$_{0.4}$TiO$_{3}$, from which we extract the 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.Comment: 15 pages, 6 figure

Remote surface optical phonon scattering in ferroelectric Ba\u3csub\u3e0.6\u3c/sub\u3eSr\u3csub\u3e0.4\u3c/sub\u3eTiO\u3csub\u3e3\u3c/sub\u3e gated graphene

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

Nanocolumnar Material Platforms:Universal structural parameters revealed from optical anisotropy

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. By using integrative and comprehensive methodical series of studies, we investigate the evolution of the depolarization factors in the anisotropic Bruggeman effective medium approximation, that are extremely sensitive to the changes in critical dimensions of the nanostructure platforms. To this end, we fabricate spatially coherent highly-ordered slanted nanocolumns from zirconia, silicon, titanium, and permalloy on silicon substrates with varying column lengths using glancing angle deposition. In tandem, broad-spectral range Mueller matrix spectroscopic ellipsometry data, spanning from the near-infrared to the vacuum ultraviolet (0.72 eV to 6.5 eV), is analyzed with a best-match model approach based on the anisotropic Bruggeman effective medium theory. We thereby extracted the anisotropic optical properties including complex dielectric function, birefringence, and dichroism. Most notably, our research unveils a universal, material-independent inverse relationship between depolarization factors and column length. We envision that the presented universal relationship will permit accurate prediction of optical properties of nanocolumnar thin films improving their integration and optimization for optoelectronic and photonic device applications.Comment: 20 pages, 10 figure

BIREFRINGENCE IMAGING CHROMATOGRAPHY BASED ON HIGHLY ORDERED 3D NANOSTRUCTURES

Ellipsometers and polarimeters or the like to investigate analyte containing fluids applied to a substrate - stage having a multiplicity of nano - structures that project non - normal to a surface thereof , including dynamics of interaction there with , to the end of evaluating and presenting at least partial Jones or Mueller Matricies corresponding to a multiplicity of locations over an imaged area

INTEGRATED MID-INFRARED, FAR INFRARED AND TERAHERTZ OPTICAL HALL EFFECT (OHE) INSTRUMENT, AND METHOD OF USE

System Stage, and Optical Hall Effect (OHE) system method for evaluating such as free charge carrier effective mass, concentration, mobility and free charge carrier type in a (51) Int. Ci. sample utilizing a permanent magnet at room temperature

The relationship between perceived social support and depressive symptoms in informal caregivers of community-dwelling older persons in Chile

AIM: Depression among caregivers of older persons is a serious concern, but it is often overlooked and neglected in developing countries. The aim of this study was to examine the relationship between perceived social support and depression in informal caregivers of community-dwelling older persons in Chile. Methods: We analyzed cross-sectional secondary data on 377 dyads of community-dwelling older persons and their informal caregivers from a nationwide survey in Chile. The Duke-UNC Functional Social Support Questionnaire (FSSQ) was used to measure caregivers’ perceived social support, and the Center for Epidemiologic Studies Depression Scale assessed their depression. Results: In this study, 76.9% of the caregivers perceived a high level of social support, and 46.9% were assessed as having depression. Based on multivariable analysis, factors that decrease the likelihood of being depressed are a high level of social support (odds ratio (OR) = 0.311, 95% confidence interval (CI): 0.167–0.579) and having taken holidays in the past 12 months (OR = 0.513, 95%CI: 0.270–0.975). Factors that increase the likelihood of being depressed are being a female caregiver (OR = 2.296, 95%CI: 1.119–4.707), being uninsured (OR = 4.321, 95%CI: 1.750–10.672), being the partner or spouse of the care recipient (OR = 3.832, 95%CI: 1.546–9.493), and the number of hours of care (OR = 1.053, 95%CI: 1.021–1.085). Conclusion: Higher levels of perceived social support and holidays were associated with lower levels of depression. However, being female, being the care recipient's partner or spouse, being uninsured, and having long care periods had detrimental effects. Interventions to preserve and enhance perceived social support could help improve depressive symptoms in informal caregivers. Additionally, support should be available to caregivers who are women, uninsured, and the care recipient's partner or spouse, as well as those who provide care for long hours, to ensure they have respite from their caregiving role

Phonon and free-charge carrier properties in group-III nitride heterostructures investigated by spectroscopic ellipsometry and optical Hall effect

The material class of group-III nitrides gained tremendous technological importance for optoelectronic and high-power/high-frequency amplification devices. Tunability of the direct band gap from 0.65 eV (InN) to 6.2 eV (AlN) by alloying, high breakthrough voltages and intrinsic mobilities, as well as the formation of highly mobile 2d electron gases (2DEG) at heterointerfaces make these compounds ideal for many applications. GaN and Ga-rich alloys are well studied and current research is mainly device-oriented. For example, choice and quality of the gate dielectric significantly influence device performance in high-electron mobility transistors (HEMT) which utilize highly mobile 2DEGs at heterointerfaces. Experimental access to the 2DEG channel properties without influence from parasitic currents or contact properties are desirable. In- and Al-rich ternary alloys are less explored than Ga-rich compounds. For InN and In-rich alloys, while many material parameters such as stiffness constants or effective mass values are largely unknown, reliable p-type doping is a major challenge, also because p-type conducting channels are buried within highly conductive n-type material formed at the surface and interfaces preventing electrical characterization. For AlN and high-Al content alloys, doping mechanisms are not understood and reliable fabrication of material with high free-charge carrier (FCC) concentrations was achieved just recently. Difficulties to form ohmic contacts impair electrical measurements and optical characterization is impeded by lack of high-energy excitation sources. In this work, spectroscopic ellipsometry over the wide spectral range from the THz to VUV in combination with optical Hall effect (generalized ellipsometry with applied magnetic field) from THz to MIR are applied in order to investigate the phonon modes and FCC properties in group-III nitride heterostructures. Adequate model descriptions and analysis strategies are introduced which allow contact-less characterization of the anisotropic IR dielectric function tensor and phonon mode parameters in arbitrarily oriented uniaxial compounds often used as substrate material such as bulk single-crystalline rutile TiO 2, to characterize the phonon and FCC parameters in Al-rich AlGaN:Si thin films including effective mass tensor, and to identify and characterize buried p-type conducting channels within InN:Mg samples. THz optical Hall effect is introduced as novel, contactless method to investigate sheet density, in-plane effective mass, and in-plane mobility parameters for 2DEGs formed within group-III nitride based HEMT structures. The theory is outlined and simple measurement schemes which dispense with the need of complex model analysis are proposed

Effective structural chirality of beetle cuticle determined from transmission Mueller matrices using the Tellegen constitutive relations

Several beetle species in the Scarabaeoidea superfamily reflect left-handed polarized light due to a circular Bragg structure in their cuticle. The right-handed polarized light is transmitted. The objective here is to evaluate cuticle chiral properties in an effective medium approach using transmission Mueller matrices assuming the cuticle to be a bianisotropic continuum. Both differential decomposition and nonlinear regression were used in the spectral range of 500-1690nm. The former method provides the sample cumulated birefringence and dichroic optical properties and is model-free but requires a homogeneous sample. The materials chirality is deduced from the circular birefringence and circular dichroic spectra obtained. The regression method requires dispersion models for the optical functions but can also be used in more complex structures including multilayered and graded media. It delivers the material properties in terms of model functions of materials permittivity and chirality. The two methods show excellent agreement for the complex-valued chirality spectrum of the cuticle.Funding Agencies|Knut and Alice Wallenberg FoundationKnut &amp; Alice Wallenberg Foundation; Swedish Government Strategic Research Area in Materials Science on Advanced Functional Materials at Linkoping University [SFO-Mat-LiU, 2009-00971]</p