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- ItemNonlinear optical mechanism of forming periodical nanostructures in large bandgap dielectrics(Les Ulis : EDP Sciences, 2013) Grunwald, R.; Das, S.K.; Debroy, A.; McGlynn, E.; Messaoudi, H.Nonlinear excitation mechanisms of plasmons and their influence on femtosecond-laser induced sub-wavelength ripple generation on dielectric and semiconducting transparent materials are discussed. The agreement of theoretical and experimental data indicates the relevance of the model.
- ItemPolarization-dependent vibrational shifts on dielectric substrates(Cambridge : RSC Publ., 2020) Yang, C.; Wang, W.; Nefedov, A.; Wang, Y.; Mayerhöfer, T.G.; Wo¨ll, C.The interaction of light with matter at surfaces of dielectrics strongly depends on polarization. Here, we present the first infrared spectroscopic evidence for significant polarization effects in the spectroscopic detection of adsorbate vibrational frequencies. In addition to much larger peak intensities for p-polarized light relative to s-polarization, a small but distinct blue shift was identified for CO adsorbed at the surfaces of two prototype dielectric substrates, CeO2(111) and CaCO3(10.4). A simulation using a layer model yields very good agreement with experiment.
- ItemBilayer insulator tunnel barriers for graphene-based vertical hot-electron transistors(Cambridge : Royal Society of Chemistry, 2015) Vaziri, S.; Belete, M.; Dentoni Litta, E.; Smith, A.D.; Lupina, G.; Lemme, M.C.; Östling, M.Vertical graphene-based device concepts that rely on quantum mechanical tunneling are intensely being discussed in the literature for applications in electronics and optoelectronics. In this work, the carrier transport mechanisms in semiconductor–insulator–graphene (SIG) capacitors are investigated with respect to their suitability as electron emitters in vertical graphene base transistors (GBTs). Several dielectric materials as tunnel barriers are compared, including dielectric double layers. Using bilayer dielectrics, we experimentally demonstrate significant improvements in the electron injection current by promoting Fowler–Nordheim tunneling (FNT) and step tunneling (ST) while suppressing defect mediated carrier transport. High injected tunneling current densities approaching 103 A cm−2 (limited by series resistance), and excellent current–voltage nonlinearity and asymmetry are achieved using a 1 nm thick high quality dielectric, thulium silicate (TmSiO), as the first insulator layer, and titanium dioxide (TiO2) as a high electron affinity second layer insulator. We also confirm the feasibility and effectiveness of our approach in a full GBT structure which shows dramatic improvement in the collector on-state current density with respect to the previously reported GBTs. The device design and the fabrication scheme have been selected with future CMOS process compatibility in mind. This work proposes a bilayer tunnel barrier approach as a promising candidate to be used in high performance vertical graphene-based tunneling devices.
- ItemControlling optical trapping of metal–dielectric hybrid nanoparticles under ultrafast pulsed excitation: a theoretical investigation(Cambridge : Royal Society of Chemistry, 2021) Devi, Anita; Nair, Shruthi S.; Yadav, Sumit; De, Arijit K.Crucial to effective optical trapping is the ability to precisely control the nature of force/potential to be attractive or repulsive. The nature of particles being trapped is as important as the role of laser parameters in determining the stability of the optical trap. In this context, hybrid particles comprising of both dielectric and metallic materials offer a wide range of new possibilities due to their tunable optical properties. On the other hand, femtosecond pulsed excitation is shown to provide additional advantages in tuning of trap stiffness through harnessing optical and thermal nonlinearity. Here we demonstrate that (metal/dielectric hybrid) core/shell type and hollow-core type nanoparticles experience more force than conventional core-type nanoparticles under both continuous-wave and, in particular, ultrafast pulsed excitation. Thus, for the first time, we show how tuning both materials properties as well as the nature of excitation can impart unprecedented control over nanoscale optical trapping and manipulation leading to a wide range of applications.
- ItemSurface polarization, field homogeneity, and dielectric breakdown in ordered and disordered nanodielectrics based on gold-polystyrene superlattices(Cambridge : RSC Publ., 2023) Buchheit, Roman; Niebuur, Bart-Jan; González-García, Lola; Kraus, TobiasHybrid dielectrics were prepared from dispersions of nanoparticles with gold cores (diameters from 2.9 nm to 8.2 nm) and covalently bound thiol-terminated polystyrene shells (5000 Da and 11 000 Da) in toluene. Their microstructure was investigated with small angle X-ray scattering and transmission electron microscopy. The particles arranged in nanodielectric layers with either face-centered cubic or random packing, depending on the ligand length and core diameter. Thin film capacitors were prepared by spin-coating inks on silicon substrates, contacted with sputtered aluminum electrodes, and characterized with impedance spectroscopy between 1 Hz and 1 MHz. The dielectric constants were dominated by polarization at the gold-polystyrene interfaces that we could precisely tune via the core diameter. There was no difference in the dielectric constant between random and supercrystalline particle packings, but the dielectric losses depended on the layer structure. A model that combines Maxwell-Wagner-Sillars theory and percolation theory described the relationship of the specific interfacial area and the dielectric constant quantitatively. The electric breakdown of the nanodielectric layers sensitively depended on particle packing. A highest breakdown field strength of 158.7 MV m−1 was found for the sample with 8.2 nm cores and short ligands that had a face-centered cubic structure. Breakdown apparently is initiated at the microscopic maxima of the electric field that depends on particle packing. The relevance of the results for industrially produced devices was demonstrated on inkjet printed thin film capacitors with an area of 0.79 mm2 on aluminum coated PET foils that retained their capacity of 1.24 ± 0.01 nF@10 kHz during 3000 bending cycles.