Browsing by Subject "Hollow nanofibers"

Now showing 1 - 3 of 3

Open Access
Fabrication of hafnia hollow nanofibers by atomic layer deposition using electrospun nanofiber templates
(Elsevier, 2013) Donmez, I.; Kayaci, F.; Akgun, C. O.; Uyar, Tamer; Bıyıklı, Necmi
Hafnia (HfO2) hollow nanofibers (HNs) were synthesized by atomic layer deposition (ALD) using electrospun nylon 6,6 nanofibers as templates. HfO2 layers were deposited on polymeric nanofibers at 200 °C by alternating reactant exposures of tetrakis(dimethylamido)hafnium and water. Polymeric nanofiber templates were subsequently removed by an ex situ calcination process at 500 °C under air ambient. Morphological and structural characterizations of the HN samples were conducted by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. Freestanding network of HfO2 HNs was found to be polycrystalline with a monoclinic crystal structure. Elemental composition and chemical bonding states of the resulting HfO2 HNs were studied by using X-ray photoelectron spectroscopy. The presence of HfO2 was evidenced by high resolution scans of Hf 4f and O 1s with binding energies of 16.3-17.9 and 529.6 eV, respectively. Combination of electrospinning and ALD processes provided an opportunity to precisely control both diameter and wall thickness of the synthesized HfO2 HNs. © 2013 Elsevier B.V. All rights reserved.
Open Access
Hollow-cathode plasma-assisted atomic layer deposition: A novel route for low-temperature synthesis of crystalline III-nitride thin films and nanostructures
(IEEE, 2015) Bıyıklı, Necmi; Ozgit-Akgun, Çağla; Goldenberg, Eda; Haider, Ali; Kızır, Seda; Uyar, Tamer; Bolat, Sami; Tekcan, Burak; Okyay, Ali Kemal
Hollow cathode plasma-assisted atomic layer deposition is a promising technique for obtaining III-nitride thin films with low impurity concentrations at low temperatures. Here we report our efforts on the development of HCPA-ALD processes for III-nitrides together with the properties of resulting thin films and nanostructures. The content will further include nylon 6,6/GaN core/shell and BN/AlN bishell hollow nanofibers, proof-of-concept thin film transistors and UV photodetectors fabricated using HCPA-ALD-grown GaN layers, as well as early results for InN thin films deposited by HCPA-ALD technique. © 2015 IEEE.
Open Access
Transformation of polymer-ZnO core-shell nanofibers into ZnO hollow nanofibers: Intrinsic defect reorganization in ZnO and its influence on the photocatalysis
(Elsevier, 2015) Kayaci, F.; Vempati S.; Ozgit Akgun, C.; Donmez, I.; Bıyıklı, Necmi; Uyar, Tamer
Photocatalytic activity (PCA) on semiconductors is known to be majorly influenced by specific surface area and intrinsic lattice defects of the catalyst. In this report, we tested the efficiencies of 1D ZnO catalysts of varying fiber diameter (80. nm and 650. nm of inner diameter) in two formats, viz. core-shell and hollow nanofibers, where the former is calcined to yield the latter. These nanofibrous catalysts were produced by combining electrospinning and atomic layer deposition processes which were then subjected to thorough characterization including photoluminescence (PL) unveiling the details of intrinsic defects/densities. During the thermal treatment, intrinsic defects are reorganized and as a result a new PL band is observed apart from some significant changes in the intensities of other emissions. The densities of various intrinsic defects from PL are compared for all samples and juxtaposed with the PCA. Careful scrutiny of the various results suggested an anti-correlation between surface area and PCA; i.e., higher surface area does not necessarily imply better PCA. Beyond a limit, the most deterministic factor would be the density of surface defects rather than the specific surface area. The results of this study enable the researchers to fabricate 1D semiconductor photocatalysts while striking the balance between surface area and density of defects.