150 research outputs found
Atomic Step Organization in Homoepitaxial Growth on GaAs(111)B Substrates
When homoepitaxial growth is performed on exactly oriented (singular) (111) GaAs substrates, while maintaining the √19 x √19 surface reconstruction, the originally flat surface spontaneously evolves vicinal (111) facets that are tilted approximately 2.5° toward the \u3c 211 \u3e azimuthal directions. These facets form pyramid-like structures where the distance between adjacent peaks can be varied from as little as 1 μm to tens of μm. When these surfaces are observed with atomic force microscopy (AFM), we find that they are extremely smooth with the observed tilt resulting from atomic steps which are spaced at approximately 7.5 nm. We have also studied growth on vicinal GaAs(111) substrates. Our results are interpreted as indicating that the 2.5° vicinal (111) surface has a minimum free energy for the √19 x √19 reconstruction (i.e., that 10 nm spacing of \u3c 011 \u3e steps is thermodynamically preferred). Exactly oriented (111) facets are only observed when their facet width is less than a couple of micrometers implying a minimum nucleation size. This is a surprising result since conventional wisdom argues the surfaces with low Miller indexes are preferred. A possible explanation is an anisotropy in the surface in the two degenerate phases of √19 x √19 reconstruction which are rotated ±23° from the unreconstructed surface
Electroless deposition of Fe-Ni alloys from acidic and alkaline solutions using hypophosphite as a reducing agent
The deposition of Fe–Ni alloys from acidic and alkaline solutions, using hypophosphite as a reducing agent, is studied in this work. The experimental results confirm the autocatalytic nature of this process. The composition of alloys is practically independent of the temperature deposition. Fe–Ni alloys produced from acidic solutions contained less than 1% Fe. The amount of Fe in Fe–Ni alloys produced from alkaline solutions was estimated to be about 15 %. The deposition of Fe–Ni alloys was significantly faster in the alkaline than in the acidic solutions, due to more pronounced hydrolysis of Fe(II) and Ni(II) ions under the alkaline conditions. The Fe–Ni alloys produced from both acidic and alkaline solutions contain phosphorus and as such have amorphous structure. © 2019 Serbian Chemical Society. All rights reserved
Effect of interface on mid-infrared photothermal response of MoS2 thin film grown by pulsed laser deposition
Here we report mid infrared (mid-IR) photothermal response of multi layer
MoS2 thin film grown on crystalline (p-type silicon and c-axis oriented single
crystal sapphire) and amorphous substrates (Si/SiO2 and Si/SiN) by pulsed laser
deposition (PLD) technique. The photothermal response of the MoS2 films was
measured as changes in the resistance of MoS2 films when irradiated with mid IR
(7 to 8.2 {\mu}m) source. We show that it is possible to enhance the
temperature coefficient of resistance (TCR) of the MoS2 thin film by
controlling the interface through proper choice of substrate and growth
conditions. The thin films grown by PLD were characterized using XRD, Raman,
AFM, XPS and TEM. High-resolution transmission electron microscopy (HRTEM)
images show that the MoS2 films grow on sapphire substrate in a layer-by-layer
manner with misfit dislocations. Layer growth morphology is disrupted when
grown on substrates with diamond cubic structure such as silicon due to growth
twin formation. The growth morphology is very different on amorphous substrates
such as Si/SiO2 or Si/SiN. The MoS2 film grown on silicon shows a very high TCR
(-2.9% K-1), mid IR sensitivity (delR/R=5.2 %) and responsivity (8.7 V/W) as
compared to films on other substrates
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