Smooth Dielectric Surface Research Articles

Effects of a Gate-Electrode/Gate-Dielectric Interlayer on Carrier Mobility for Pentacene Organic Thin-Film Transistors

Bottom-gated pentacene organic thin-film transistors with LaTiON gate dielectrics annealed at two different temperatures are fabricated on n+Si wafers. Although atomic-force microscopyresults indicate a smoother dielectric surface and larger pentacene grains for the sample annealed at 400 °C, this sample shows lower carrier mobility than the one annealed at 200 °C. Moreover, the crystallinity of the gate dielectrics is not a key factor in the degradation of the carrier mobility because both dielectrics remain amorphous according to TEM. However, the TEM results show that the sample annealed at 400 °C has a thicker dielectric/Si-gate interlayer. The resultant increase in gate electrode-to-dielectric distance weakens the gate screening of the remote phonon scattering, thereby degrading the mobility of the carriers in the pentacene channel. This effect can be further supported by two similar samples fabricated on n-Si wafers, in which the gate electrode with lower electron concentration has a reduced screening effect on the remote phonon scattering and results in a larger reduction in mobility for the 400 °C-annealed sample with thicker interlayer.

Mapping the Refractive Index of Dielectric Surfaces with Spherical Plasmonic Nanoantenna

Here we demonstrate successful mapping the variations of the refractive index of a smooth dielectric surface by detecting spectral response of a single spherical-shape Ag nanoparticle optically aligned with a supporting optical fiber axicon microlens. We propose and examine various excitation schemes of the plasmonic nanoantenna to provide efficient interaction of its dipolar and quadrupolar modes with the underlying sample surface and to optimize the mapping resolution and sensitivity. Supporting finite-difference time-domain calculations are undertaken to tailor the interaction of the plasmonic nanoantenna and the underlying dielectric substrate upon various excitation conditions demonstrating good agreement with our experimental findings and explaining the obtained results.

Mapping the refractive index with single plasmonic nanoantenna

As the size of the state-of-the-art optical devices shrinks to nanoscale, the need for tools allowing mapping the local optical properties at deep sub-diffraction resolution increases. Here we demonstrate successful mapping the variations of the refractive index of a smooth dielectric surface by detecting spectral response of a single spherical-shape Ag nanoparticle optically aligned with a supporting optical fiber axicon microlens. We propose and examine various excitation schemes of the plasmonic nanoantenna to provide efficient interaction of its dipolar and quadrupolar modes with the underlying sample surface and to optimize the mapping resolution and sensitivity. Moreover, we demonstrate an lithography-free approach for fabrication of the scanning probe combining the high-quality fiber microaxicon with the Ag spherical nanoparticle atop. Supporting finite-difference time-domain calculations are undertaken to tailor the interaction of the plasmonic nanoantenna and the underlying dielectric substrate upon various excitation conditions demonstrating good agreement with our experimental findings and explaining the obtained results.

High-performance organic thin-film transistor by using LaNbO as gate dielectric

Pentacene organic thin-film transistors (OTFTs) using LaxNb(1−x)Oy as gate dielectric with different La contents (x = 0.347, 0.648) have been fabricated and compared with those using Nb oxide or La oxide. The OTFT with La0.648Nb0.352Oy as gate dielectric can achieve a high carrier mobility of 1.14 cm2V−1s−1 (about 1000 times and 2 times those of the devices using Nb oxide and La oxide, respectively), and has negligible hysteresis of −0.130 V, small sub-threshold swing of 0.280 V/dec, and low threshold voltage of −1.35 V. AFM and XPS reveal that La can suppress the formation of oxygen vacancies in Nb oxide while Nb can alleviate the hygroscopicity of La oxide, which results in a more passivated and smoother dielectric surface, leading to larger pentacene grains grown and thus higher carrier mobility. The OTFT with Nb oxide has an anticlockwise hysteresis but the device with La oxide shows an opposite direction. This can be explained in terms of donor-like traps due to oxygen vacancies and acceptor-like traps originated from hydroxyl ions formed after La2O3 absorbing water moisture.

Invited Presentation: Logic Devices with Graphene PN Junctions

Graphene p-n junctions (GPNJs) can be configured as logic devices that can meet the scaling challenges of CMOS devices. In the present context, GPNJs are not rectifying diodes since graphene is gapless. Instead, they exhibit unique angle dependent transport properties that allow the development of new type of electron-optics devices. This angle dependence has been used to predict novel devices, including the Veselago effect, steep subthreshold slope devices, and wave guiding structures.Here, we describe the fabrication and characterization of GPNJs. We use buried gates to electrostatically dope the graphene to form the p- and n-doped regions. The buried gates are fabricated in CNSE’s advanced 300mm wafer line, which is used to obtain an atomically smooth dielectric surface above the gates to preserve the intrinsic electronic structure of graphene.Using the split gates, we study different angled GPNJs and perform electrical measurements to extract the junction resistance. We observe a strong angle dependent junction resistance and confirm Klein tunneling, the normal tunneling component with unity transmission. By blocking the Klein tunneling component, we observe high on/off ratio devices.

Frequency‐ and polarization‐dependent optical response of asymmetric spheroidal silver nanoparticles on dielectric substrate

AbstractWe report theoretical simulations of plasmonic near‐field enhancement and polarization in a system consisting of an asymmetric spheroidal Ag nanoparticle on a smooth dielectric surface. Finite‐difference time‐domain (FDTD) simulations reveal resonant optical extinction bands whose near‐field is concentrated at the metal–substrate contact point with intensity enhancement by a factor of 103 and predominant polarization along the normal to the surface. These features may help explain enhanced photo‐catalytic activity observed for colloidal Au and Ag nanoparticles on titania substrates.magnified imageElectron microscopy image of Ag‐nanoparticles on titania and the used model for numerical FDTD simulations.(© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Organic Thin-Film Transistors with Low-Temperature AlN Film as Gate Insulator

RF-ICP sputtered AlN film was used as the gate insulator in pentacene-based organic thin-film transistors TFTs . With thedielectric breakdown field larger than 5 MV/cm and the relative electrical permittivity as 7 in the AlN film, the proposed TFTsexhibit low operation voltage, low subthreshold swing 0.4 V/decade 6and high on/off current ratio 10 . By adjusting theAlN sputtering process, it was found that smooth morphology of AlN film surface roughness 2A can be obtained by loweringdown the process temperature. This atomically smooth dielectric surface leads to the growth of large pentacene grains andimproves the leakage current and also the field effect mobility.© 2006 The Electrochemical Society. DOI: 10.1149/1.2372227 All rights reserved.Manuscript submitted March 22, 2006; revised manuscript received August 29, 2006. Available electronically November 1, 2006.

Recovery of surface orientation from diffuse polarization

When unpolarized light is reflected from a smooth dielectric surface, it becomes partially polarized. This is due to the orientation of dipoles induced in the reflecting medium and applies to both specular and diffuse reflection. This paper is concerned with exploiting polarization by surface reflection, using images of smooth dielectric objects, to recover surface normals and, hence, height. This paper presents the underlying physics of polarization by reflection, starting with the Fresnel equations. These equations are used to interpret images taken with a linear polarizer and digital camera, revealing the shape of the objects. Experimental results are presented that illustrate that the technique is accurate near object limbs, as the theory predicts, with less precise, but still useful, results elsewhere. A detailed analysis of the accuracy of the technique for a variety of materials is presented. A method for estimating refractive indices using a laser and linear polarizer is also given.