| 41. |
- Jayathilaka, K. M. D. C., et al.
(författare)
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Surface treatment of electrodeposited n-type Cu2O thin films for applications in Cu2O based devices
- 2014
-
Ingår i: Physica Status Solidi. Rapid Research Letters. - : Wiley. - 1862-6254 .- 1862-6270. ; 8:6, s. 592-595
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Tidskriftsartikel (refereegranskat)abstract
- In this Letter, we report the effects of ammonium sulfide [(NH4)(2)S] surface treatment on electrical and optical characteristics of the electrodeposited n-type Cu2O thin films on Ti substrates. Films characterized structurally and morphologically before and after the surface treatment were compared using conductivity, spectral photoresponse and current-voltage (I-V) measurements. The ammonium sulfide surface treatment time showed an impact on optical and electrical characteristics of the films. Treated Cu2O films exhibited enhanced conductivity giving rise to a 50-fold increase in the photocurrent and improved I-V characteristics. It was found that the sulfur passivation resulted in a nearly ohmic behaviour for Au or Ni contacts made with n-type Cu2O whereas Ag or Cu contacts showed nearly Schottky behaviour. The results showed that ammonium sulfide treatments were very effective to passivate defects and improve the optical and electrical properties of polycrystalline n-type Cu2O thin films that may provide a solid platform for Cu2O based devices of enhanced quality. [GRAPHICS] .
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| 42. |
- Jishiashvili, D., et al.
(författare)
-
Germanium Nitride Nanowires Produced by Thermal Annealing in Hydrazine Vapor
- 2009
-
Ingår i: Advanced Science Letters. - : American Scientific Publishers. - 1936-6612 .- 1936-7317. ; 2:1, s. 40-44
-
Tidskriftsartikel (refereegranskat)abstract
- A simple pyrolytic: technology was developed in this paper for producing Germanium nitride nanowires. Hydrazine was used as the nitriding agent, while the 3 mol.% of water diluted in it served for producing volatile GeO molecules and for the accomplishment of mass transfer. The Ge3N4 nuclei appeared on the surfaces of GeOx clusters, formed after redeposition of GeO molecules. The growth of two types of nanowires was observed. The ball-shaped Ge tip surrounded with the amorphous GeO2 sheath served as a catalyst during the vapor-liquid-solid growth of tapered nanowires. Straight nanowires were produced through the oxide-assisted method. Tentative results on the blue-green photoluminescence of nanowires were obtained.
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| 43. |
- Kapaklis, Vassilios, 1978-
(författare)
-
Magnetizing semiconductors with light
- 2018
-
Ingår i: Nature Nanotechnology. - : Springer Science and Business Media LLC. - 1748-3387 .- 1748-3395. ; 13:6, s. 438-439
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 44. |
- Kapaklis, Vassilios, et al.
(författare)
-
Melting artificial spin ice
- 2012
-
Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 14, s. 035009-
-
Tidskriftsartikel (refereegranskat)abstract
- Artificial spin ice arrays of micromagnetic islands are a means of engineering additional energy scales and frustration into magnetic materials. Here we demonstrate a magnetic phase transition in an artificial square spin ice and use the symmetry of the lattice to verify the presence of excitations far below the ordering temperature. We do this by measuring the temperature dependent magnetisation in different principal directions and comparing with simulations of idealised statistical mechanical models. Our results confirm a dynamical pre-melting of the artificial spin ice structure at a temperature well below the intrinsic ordering temperature of the island material. We thus create a spin ice array that has real thermal dynamics of the artificial spins over an extended temperature range.
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| 45. |
- Kapaklis, Vassilios, 1978-, et al.
(författare)
-
Nanolithographic Templates Using Diblock Copolymer Films on Chemically Heterogeneous Substrates
- 2010
-
Ingår i: Journal of Nanoscience and Nanotechnology. - : American Scientific Publishers. - 1533-4880 .- 1533-4899. ; 10:9, s. 6056-6061
-
Tidskriftsartikel (refereegranskat)abstract
- The orientation of the lamellae formed by the phase separation of symmetric diblock copolymer thin films is strongly affected by the wetting properties of the polymer blocks with respect to the substrate. On bare silicon wafers the lamellae of polystyrene-b-polymethylmethacrylate thin films tend to order parallel to the wafer surface, with the polymethylmethacrylate block preferentially wetting silicon. We have developed a methodology for inducing the arrangement of lamellae perpendicular to the substrate by using chemically modified substrates. This is done by chemisorbing a self-assembled monolayer of thiol-terminated alkane chains on thin gold films deposited on silicon wafers. We also show that it is possible to spatially control the perpendicular orientation of the lamellae at sub-micron length scales by using simple chemical patterns and etch them, in order to produce nanolithographic templates. This method may be of great technological interest for the preparation of well-defined templates using block copolymer thin films.
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| 46. |
- Kapaklis, Vassilios, 1978-, et al.
(författare)
-
Structure and Magnetic Properties of hcp and fcc Nanocrystalline Thin Ni Films and Nanoparticles Produced by Radio Frequency Magnetron Sputtering
- 2010
-
Ingår i: Journal of Nanoscience and Nanotechnology. - : American Scientific Publishers. - 1533-4880 .- 1533-4899. ; 10:9, s. 6024-6028
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the growth of thin Ni films by radio frequency magnetron sputtering in Ar-plasma. The growth temperature was about 350 K and the films were deposited on various substrates such as glass, silicon, sapphire and alumina. The thickness of the thinnest films was estimated by the appearance of Kiessig fringes up to about 2 theta = 8 degrees in the small-angle X-ray diffraction pattern, as expected for high-quality atomically-flat thin films. With the help of this, a quartz balance system was calibrated and used for measuring the thickness of thicker samples with an accuracy of better than 5%. Structural characterization via X-ray diffraction and high resolution transmission electron microscopy revealed an Ar-gas pressure window, where single phase hcp Ni films may be grown. The magnetic response of the Ni films was checked at room temperature via a newly established and fully automatic polar magneto-optic Kerr effect magnetometer. The hcp films show no magnetic response. Interestingly, the magnetic saturation field of fcc films deposited at low Ar pressure is comparable to the one of bulk Ni, while the one of fcc films deposited at high Ar pressures is decreased, revealing the presence of residual strain in the films. Finally, it is shown that it is possible to form films which contain magnetic Ni fcc nanoparticles in a non-magnetic hcp matrix, i.e., a system interesting for technological applications demanding a single Ni target for its production.
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| 47. |
- Kapaklis, Vassilios, et al.
(författare)
-
Temperature dependence of the electrical resistivity and electronic structure of amorphous Fe100-xZrx films and multilayers
- 2012
-
Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 24:49, s. 495402-
-
Tidskriftsartikel (refereegranskat)abstract
- The electrical resistivity of amorphous Fe100-xZrx metal alloy films and multilayers has been investigated in a wide temperature and composition range. The overall behavior of the resistivity is consistent with bulk measurements, exhibiting prominent semiconductor-like changes at low temperatures. The transition from positive (metallic) to negative temperature coefficient of resistivity behavior is accompanied by minute changes in magnetoresistance and we can therefore rule out magnetic phase changes as being the cause for the observed changes in the resistivity. Using x-ray absorption and emission spectroscopies we are able to probe the unoccupied and occupied electronic densities of states. The corresponding spectra are found to significantly overlap, as expected for a metallic-like electronic structure and the absence of a band gap. Besides a broadening of the x-ray emission lines expected from an amorphous material, remarkably small differences are observed in the electronic structures when changing the amount of Zr. The resistivity data were modeled and agreement with the Mott variable range hopping model was found, indicating localized electronic states due the disordered structure of the Fe100-xZrx alloys.
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| 48. |
- Kapaklis, Vassilios, et al.
(författare)
-
Thermal fluctuations in artificial spin ice
- 2014
-
Ingår i: Nature Nanotechnology. - 1748-3387 .- 1748-3395. ; 9:7, s. 514-519
-
Tidskriftsartikel (refereegranskat)abstract
- Artificial spin ice systems have been proposed as a playground for the study of monopole-like magnetic excitations(1,2), similar to those observed in pyrochlore spin ice materials(3). Currents of magnetic monopole excitations have been observed's, demonstrating the possibility for the realization of magnetic-charge-based circuitry. Artificial spin ice systems that support thermal fluctuations can serve as an ideal setting for observing dynamical effects such as monopole propagation and as a potential medium for magnetricity investigations(1,2). Here, we report on the transition from a frozen to a dynamic state in artificial spin ice with a square lattice. Magnetic imaging is used to determine the magnetic state of the islands in thermal equilibrium. The temperature-induced onset of magnetic fluctuations and excitation populations are shown to depend on the lattice spacing and related interaction strength between islands. The excitations are described by Boltzmann distributions with their factors in the frozen state relating to the blocking temperatures of the array. Our results provide insight into the design of thermal artificial spin ice arrays where the magnetic charge density and response to external fields can be studied in thermal equilibrium.
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| 49. |
- Kapaklis, Vassilios, 1978-, et al.
(författare)
-
Violation of Hund’s third rule in structurally disordered ferromagnets
- 2011
-
Ingår i: Physical Review B Condensed Matter. - : American Physical Society. - 0163-1829 .- 1095-3795. ; 84:2, s. 024411-
-
Tidskriftsartikel (refereegranskat)abstract
- Violation of Hund’s third rule caused by structural disorder is observed for the induced magnetic moment of Zr, using X-ray magnetic circular dischroism. The induced spin and orbital magnetic moments are anti-parallel in the crystalline state, but parallel in an amorphous state of the investi- gated Co- and Fe-based materials. First principles calculations are used to provide physical insight into the dependency of the spin-orbit coupling on the interatomic distance and coordination number.
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| 50. |
- Karimipour, Masoud, et al.
(författare)
-
Nanoparticles of Ni/NiO embedded in TiO(2) synthesized by the complex-polymer sol-gel method
- 2011
-
Ingår i: Physica Scripta. - : IOP Publishing. - 0031-8949 .- 1402-4896. ; 84:3, s. 035702-
-
Tidskriftsartikel (refereegranskat)abstract
- Ni-doped TiO(2) nanoparticles were synthesized by the non-hydrous complex-polymer sol-gel method. Titanium isopropoxide was used as precursor and acetyl acetone (AcAc) and citric acid were used as polymer and complex agent, respectively. A series of Ni(x) : Ti(1-x)O(2) samples with x = 0.01, 0.03, 0.05 and 0.10 were prepared and subsequently annealed at 400, 600 and 800 degrees C. The structural and magnetic properties of Ni(x) : Ti(1-x)O(2) were studied by means of x-ray diffraction (XRD) and dc magnetometery. Samples annealed at 400 degrees C attained a particle size of 12 nm with structural phases of anatase, rutile and cubic NiO. From the blocking temperatures of the zero-field-cooled and field-cooled measurements, similar particle sizes (as from XRD) were obtained. The presence of ferro- and antiferromagnetic (AFM) interactions further confirms that the particles have different structural compositions. At 800 degrees C the particles have grown to about 30 nm with either a rutile or NiTiO(3)-type structure. The presence of NiTiO(3) is also seen in the magnetic measurements, which show the characteristic AFM peak at 23 K.
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