Articles you may be interested inEffects of annealing on electronic and structural characteristics of pentacene thin-film transistors on polyimide gate dielectrics Appl. Phys. Lett. 95, 023302 (2009); 10.1063/1.3179166 Effect of rubbed polyimide layer on the field-effect mobility in pentacene thin-film transistors Appl. Phys. Lett. 92, 052107 (2008); 10.1063/1.2830694Effect of surface free energy in gate dielectric in pentacene thin-film transistors
Single-crystal silicon films grown at 400°C on Si(l 1 l):B(V3x V5) are rotated 180° about the surface normal with respect to the substrate. We discuss a mechanism based on chemical effects due to the boron (VJx VJ) reconstruction that favors the film to grow with a ZMype (twin) orientation. Films grown on the SiCl 1 l)-(7x7) reconstruction under identical conditions have the ^-type (untwinned) orientation. PACS numbers: 68.35.Bs, 61.16.Di, 68.35.DvIn all prior cases of homoepitaxy, the epilayer has been crystallographically aligned with the substrate, irrespective of the surface reconstruction, impurity segregation, or other effects at the substrate surface. The original surface reconstruction has always reordered into an unreconstructed interface between the substrate and film, since epitaxy requires a sufficiently high temperature for surface diffusion to occur. Here, we describe Si homoepitaxial growth on the boron VJxVJ surface of SiC111) with j monolayer of boron. At low temperature, the surface reconstruction is partly preserved, buried under an epilayer, and the homoepitaxial layer grows rotated by 180° with respect to the substrate. Tung et al. x have demonstrated rotated heteroepitaxial films. We will use their notation; if the substrate orientation is denoted as "^-type," the "ZMype" orientation corresponds to a layer rotated by 180° about the normal (111) direction.To our knowledge this is the first example of homoepitaxial growth with the overlayer not crystallographically aligned with the substrate. We show experimentally that this phenomenon is critically sensitive to the presence of boron at the original interface during growth, although after growth boron may be in-diffused with no change in film orientation. Modeling suggests that strain effects cannot account for this phenomena. We suggest that the stabilization of the twin boundary interface is related to chemical (electronic) effects which favor a wurtzite stacking at the VJxVJ interface.Samples were prepared in a molecular-beam-epitaxy (MBE) chamber equipped with a quartz-crystal thickness monitor, an electron-gun evaporator to deposit silicon, and a Knudsen cell to deposit boron from HBO2. Low-energy electron diffraction (LEED) and Auger analysis were performed in situ, and x-ray diffraction, transmission electron microscopy (TEM), Rutherford backscattering spectroscopy, nuclear reaction analysis, and Hall-effect measurements were done after removing samples from the MBE chamber. Surfaces were prepared by chemical growth of a thin protective oxide layer before transferring into the vacuum system. The boron VJxVJ surface reconstruction was prepared either by surface segregation of y monolayer (ML) of boron from boron-implanted samples at 900-1000°C, or by deposition of boron onto /?-type samples from HBO2 while the sample was held at 750°C. The surface structure thus formed is unique to the SiCl 11)/B system since boron occupies a subsurface site in a fivefold-coordinated substitutional site under a silicon adatom. 2 " 4 Silicon films of 350...
We report a boron δ-doping layer in crystalline silicon with an electrically active concentration of 1×1022 cm−3 and a mobility of ∼20 cm2/V s. This structure was fabricated by low-temperature molecular-beam epitaxy with boron confined to 3 monolayers in the silicon growth direction. Complete electrical activation is observed, showing metallic conduction down to 4 K. This two-dimensional doped layer, incorporated into the crystal lattice, represents a volume concentration exceeding the solid solubility of boron in silicon by two orders of magnitude. These high-concentration structures fill an unexplored region of the mobility versus concentration curve.
Grazing incidence small-angle x-ray scattering and atomic force microscopy have been used to systematically investigate the evolution of Si͑100͒ surface morphology during normal-incidence Ar ϩ sputtering as a function of ion energy in the range of 100-500 eV. For ion energy ranges of 100-300 eV, two structures with distinct individual length scales and behaviors form on the surface. There is a smaller scale ͑lateral size of 20-50 nm͒ morphology that grows in scattering intensity and coarsens with time. There is also a larger scale ͑lateral size of approximately 100 nm͒ morphology that grows in scattering intensity but does not coarsen significantly in the time scales studied. At higher energies ͑400-500 eV͒, sputtering causes the Si͑100͒ surface to become smoother on length scales smaller than 200 nm.
At least two different routes lead to conical structures on laser ablated polymer surfaces. These were investigated by studying laser ablation on the surfaces of different classes of polymers. Cones appeared readily in strongly absorbing polymers such as poly(ethylene terephthalate) (PET) and polyimide (PI), but only within narrow laser parameters in nylon 6, and rarely in poly(chlorotrifluoroethylene), the last two being weak ultraviolet (UV) absorbers. Self-assembled, close-packed cones occurred in PET, in which heat generated due to absorbed laser energy creates a thin, chemically stable, viscoelastic, highly compliant layer (above the glass transition temperature). Surface structure in such polymers evolves from nodules through donuts into ripples and finally to cones as the energy deposited per unit area on the surface (total fluence) is increased using a combination of single pulse fluence and number of pulses. A phase transition from a ripple phase to a cone phase is thought to occur as the thickness of the viscoelastic surface layer increases above a critical value. Cones began to appear from almost the beginning of the irradiation process at random locations in PI, a polymer whose surface irreversibly turns into a hard solid upon exposure to either or both UV and heat. It is proposed that the radiation hardened spots serve as nuclei, a cone “grows” out of this as the material surrounding this nuclei is ablated. The initial sparse occurrence of cones in PI-like polymers, and the increase in their number density with total fluence until the surface is densely packed with cones can be explained by a nucleation and growth model.
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