Browsing by Subject "Selected area electron diffraction"

Now showing 1 - 4 of 4

Open Access
Fabrication of flexible polymer–GaN core–shell nanofibers by the combination of electrospinning and hollow cathode plasma-assisted atomic layer deposition
(Royal Society of Chemistry, 2015) Ozgit Akgun, C.; Kayaci, F.; Vempati S.; Haider A.; Celebioglu A.; Goldenberg, E.; Kizir S.; Uyar, Tamer; Bıyıklı, Necmi
Here we demonstrate the combination of electrospinning and hollow cathode plasma-assisted atomic layer deposition (HCPA-ALD) processes by fabricating flexible polymer-GaN organic-inorganic core-shell nanofibers at a processing temperature much lower than that needed for the preparation of conventional GaN ceramic nanofibers. Polymer-GaN organic-inorganic core-shell nanofibers fabricated by the HCPA-ALD of GaN on electrospun polymeric (nylon 6,6) nanofibers at 200 °C were characterized in detail using electron microscopy, energy dispersive X-ray analysis, selected area electron diffraction, X-ray diffraction, X-ray photoelectron spectroscopy, photoluminescence measurements, and dynamic mechanical analysis. Although transmission electron microscopy studies indicated that the process parameters should be further optimized for obtaining ultimate uniformity and conformality on these high surface area 3D substrates, the HCPA-ALD process resulted in a ∼28 nm thick polycrystalline wurtzite GaN layer on polymeric nanofibers of an average fiber diameter of ∼70 nm. Having a flexible polymeric core and low processing temperature, these core-shell semiconducting nanofibers might have the potential to substitute brittle ceramic GaN nanofibers, which have already been shown to be high performance materials for various electronic and optoelectronic applications.
Open Access
Highly monodisperse low-magnetization magnetite nanocubes as simultaneous T1–T2 MRI contrast agents
(Royal Society of Chemistry, 2015) Sharma, V. K.; Alipour, A.; Soran-Erdem, Z.; Aykut, Z. G.; Demir, Hilmi Volkan
We report the first study of highly monodisperse and crystalline iron oxide nanocubes with sub-nm controlled size distribution (9.7 ± 0.5 nm in size) that achieve simultaneous contrast enhancement in both T1- and T2-weighted magnetic resonance imaging (MRI). Here, we confirmed the magnetite structure of iron oxide nanocubes by X-ray diffraction (XRD), selected area electron diffraction (SAED) pattern, optical absorption and Fourier transformed infrared (FT-IR) spectra. These magnetite nanocubes exhibit superparamagnetic and paramagnetic behavior simultaneously by virtue of their finely controlled shape and size. The magnetic measurements reveal that the magnetic moment values are favorably much lower because of the small size and cubic shape of the nanoparticles, which results in an enhanced spin canting effect. As a proof-of-concept demonstration, we showed their potential as dual contrast agents for both T1- and T2-weighted MRI via phantom studies, in vivo imaging and relaxivity measurements. Therefore, these low-magnetization magnetite nanocubes, while being non-toxic and bio-compatible, hold great promise as excellent dual-mode T1 and T2 contrast agents for MRI. © 2014 The Royal Society of Chemistry.
Open Access
Low-temperature self-limiting atomic layer deposition of wurtzite InN on Si(100)
(American Institute of Physics Inc., 2016) Haider, A.; Kizir, S.; Bıyıklı, Necmi
In this work, we report on self-limiting growth of InN thin films at substrate temperatures as low as 200 °C by hollow-cathode plasma-assisted atomic layer deposition (HCPA-ALD). The precursors used in growth experiments were trimethylindium (TMI) and N2 plasma. Process parameters including TMI pulse time, N2 plasma exposure time, purge time, and deposition temperature have been optimized for self-limiting growth of InN with in ALD window. With the increase in exposure time of N2 plasma from 40 s to 100 s at 200 °C, growth rate showed a significant decrease from 1.60 to 0.64 Å/cycle. At 200 °C, growth rate saturated as 0.64 Å/cycle for TMI dose starting from 0.07 s. Structural, optical, and morphological characterization of InN were carried out in detail. X-ray diffraction measurements revealed the hexagonal wurtzite crystalline structure of the grown InN films. Refractive index of the InN film deposited at 200 °C was found to be 2.66 at 650 nm. 48 nm-thick InN films exhibited relatively smooth surfaces with Rms surface roughness values of 0.98 nm, while the film density was extracted as 6.30 g/cm3. X-ray photoelectron spectroscopy (XPS) measurements depicted the peaks of indium, nitrogen, carbon, and oxygen on the film surface and quantitative information revealed that films are nearly stoichiometric with rather low impurity content. In3d and N1s high-resolution scans confirmed the presence of InN with peaks located at 443.5 and 396.8 eV, respectively. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) further confirmed the polycrystalline structure of InN thin films and elemental mapping revealed uniform distribution of indium and nitrogen along the scanned area of the InN film. Spectral absorption measurements exhibited an optical band edge around 1.9 eV. Our findings demonstrate that HCPA-ALD might be a promising technique to grow crystalline wurtzite InN thin films at low substrate temperatures.
Open Access
Preparation of Al 2O 3and AlN nanotubes by atomic layer deposition
(Cambridge University Press, 2012) Ozgit-Akgun, Çagla; Kayacı, Fatma; Dönmez, İnci; Çağatay, Engin; Uyar, Tamer; Bıyıklı, Necmi
Al 2O 3 and AlN nanotubes were fabricated by depositing conformal thin films via atomic layer deposition (ALD) on electrospun nylon 66 (PA66) nanofiber templates. Depositions were carried out at 200°C, using trimethylaluminum (TMAl), water (H 2O), and ammonia (NH 3) as the aluminum, oxygen, and nitrogen precursors, respectively. Deposition rates of Al 2O 3 and AlN at this temperature were ∼1.05 and 0.86 Å/cycle. After the depositions, Al 2O 3- and AlN-coated nanofibers were calcinated at 500°C for 2 h in order to remove organic components. Nanotubes were characterized by using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). AlN nanotubes were polycrystalline as determined by high resolution TEM (HR-TEM) and selected area electron diffraction (SAED). TEM images of all the samples reported in this study indicated uniform wall thicknesses. © 2012 Materials Research Society.