Home About us Contact
|
Home About us Contact | ||
|
|
||
Increasing Film Thickness (increasing + film_thickness)
Selected AbstractsThickness-Dependent Structural Evolutions and Growth Models in Relation to Carrier Transport Properties in Polycrystalline Pentacene Thin Films,ADVANCED FUNCTIONAL MATERIALS, Issue 17 2007H.-L. Cheng Abstract Thickness-dependent crystal structure, surface morphology, surface energy, and molecular structure and microstructure of a series of polycrystalline pentacene films with different film thickness ranging from several monolayers to the several hundred nanometers have been investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), contact angle meter, and Raman spectroscopy. XRD studies indicate that thin film polymorphs transformation behaviours are from the orthorhombic phase to the thin-film phase and then to the triclinic bulk phase as measured by the increased tilt angle (,tilt) of the pentacene molecule from the c- axis toward the a- axis. We propose a growth model that rationalizes the ,tilt increased along with increasing film thickness in terms of grain size and surface energy varying with film growth using AFM combined with contact angle measurements. The vibrational characterizations of pentacene molecules in different thickness films were investigated by Raman spectroscopy compared to density functional theory calculations of an isolated molecule. In combination with XRD and AFM the method enables us to distinguish the molecular microstructures in different thin film polymorphs. We proposed a methodology to probe the microscopic parameters determining the carrier transport properties based on Davydov splitting and the characteristics of aromatic C,C stretching modes in Raman spectra. When compared to the triclinic bulk phase at a high thickness, we suggest that the first few monolayer structures located at the dielectric surface could have inferior carrier transport properties due to weak intermolecular interactions, large molecular relaxation energy, and more grain boundaries. [source] A comprehensive investigation of the structural properties of ferroelectric PbZr0.2Ti0.8O3 thin films grown by PLDPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2009David Walker Abstract X-Ray diffraction investigations were made of high-quality epitaxial thin films of the ferroelectric material lead zirconate titanate, PbZr0.2Ti0.8O3 (PZT), grown by pulsed laser deposition (PLD). Layers from 7 to 200,nm in thickness were studied, deposited on a 30,nm SrRuO3 (SRO) electrode on a [001] oriented SrTiO3 (STO) substrate. The out-of-plane lattice parameters of the PZT films were measured by high-resolution X-ray diffraction using CuK,1 radiation. A significant enhancement of the c lattice parameter with film thickness was observed, the maximum value of 4.25,Å reached in the 30,50,nm thick films. For film thicknesses greater than 100,nm, the c lattice parameter is relaxed, towards the bulk value of 4.13,Å at this composition. The in-plane lattice parameters were studied by Grazing incidence X-ray scattering (GIXS), using 15,keV synchrotron radiation at I16, Diamond. The a lattice parameter of domains with [001] oriented normal to the sample surface was effectively lattice matched to the SRO layer in the 7,nm ultra-thin film, but relaxed compared to the SRO in thicker films. The tetragonality of the [001] oriented domains decreases with increasing film thickness, approaching the bulk value of 1.05 in the thickest films. Evidence for the presence of [100] oriented a -domains was found in PZT films as thin as 30,nm, the proportion of which increased with increasing film thickness, suggesting they grow in order to relieve stresses that would prevent the epitaxial growth of thicker PZT films. The a -domains in the thicker films were found to be located nearer to the PZT/SRO interface than to the top surface of the PZT. [source] FMR study of ultrahigh vacuum e-beam evaporated Co23Cu77 nanogranular films: Magnetotransport propertiesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2006R. Mustafa Öksüzoglu Abstract The magnetic, magnetotransport and structural properties of Co23Cu77 granular thin films (7,43 nm) have been investigated using ferromagnetic resonance (FMR) and high-resolution XRD techniques. Co particles possess a crystalline fcc structure in the investigated films. A correlation between the GMR effect and the anisotropy field has been found, which increases with increasing film thickness. Temperature-dependent FMR measurements revealed a blocking effect, which results from the competition of long range dipole,dipole interaction and anisotropy fields of Co particles. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Optical characteristics of thin rf sputtered Ta2O5 layersPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 2 2005Tz. Babeva Abstract The optical properties of rf sputtered (30; 52 nm) Ta2O5 before and after O2 annealing at 1173 K have been investigated in the terms of storage capacitor applications for high density dynamic memories. Refractive index and thickness of the films are determined from transmittance and reflectance measurements at normal light incidence in the spectral range 400,800 nm. The film density explored by refractive index is improved with increasing film thickness as well as after annealing. The optical band gap is found to be 4.20 eV for 30 nm and 4.12 eV for 52 nm Ta2O5 regardless of the amorphous status of the layers-amorphous (as-deposited) or polycrystalline (annealed layers). (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effects of film and substrate dimensions on warpage of film insert molded partsPOLYMER ENGINEERING & SCIENCE, Issue 6 2010Seong Yun Kim Three-dimensional flow and structural analyses were carried out for film insert injection molding to investigate warpage of film insert molded (FIM) parts with respect to variation of film and substrate thickness. Asymmetry of temperature distribution in the thickness direction was increased with increasing film thickness but decreased with increasing substrate thickness. Asymmetry of the in-mold residual stress distribution in the FIM specimen was generated by the nonuniform temperature distribution, and it was increased with increasing film thickness but reduced with increasing substrate thickness. Warpage of the ejected FIM specimen was determined by relaxation of the asymmetric in-mold residual stress distribution, and it was increased with increasing film thickness but reduced with increasing substrate thickness. Warpage of FIM specimens annealed at 80°C for 30 min showed complex behavior, and the behavior was understood by using factors such as degree of warpage of the ejected part, thermal shrinkage of the inserted film, and retardation of heat transfer. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers [source] Characteristics of Photoexcitations and Interfacial Energy Levels of Regioregular Poly(3-hexythiophene-2,5-diyl) on Gold,CHEMPHYSCHEM, Issue 13 2007Youngku Sohn Dr. Abstract We have studied characteristics of photoexcitations and interfacial electronic structures of regioregular poly(3-hexlythiophene-2,5-diyl) (P3HT) on gold using two-photon photoemission (2PPE) spectroscopy. The vacuum level threshold is decreased by 1.3 eV from that of bare gold, attributable to interface dipole effects. The 2PPE spectral width narrows as the film thickness increases. We tentatively understand that this is due to destabilization of long-lived localized polaron, attributed to strong interchain interactions. On the basis of the analysis of the 2PPE distribution as a function of photon energy and laser power, the polaron level is located at 3.1 eV below the vacuum level. Using this value and a polaron level of 1.75 eV above the HOMO, we indirectly estimate an ionization potential of 4.85 eV for P3HT. An increase in two-photon photoemission yield with increasing photon energy is attributed to an enhanced electron-hole pair dissociation yield at higher photo-excitation levels. The decrease in power law slope with increasing film thickness is understood by Langevin recombination kinetics and saturation of photoexcitations [source] | ||||||||||