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Near-Infrared Tunable Reflection and Absorption Using Nanostructured Thin Film Structures Employing Phase-Change Material

100%
Ozdemir A., Kocer H.
Acta Physica Polonica A
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2016
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vol. 129
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issue 4
464-467
EN
We present the design of a polarization-dependent tunable nanostructured thin film absorber in the near-infrared region. Germanium antimonide tellurite (GST) was employed as the phase change material in the designed structure. Our structure is composed of a periodic grating-type array of 150 nm thick Au buried with 50 nm thick GST layer from the top of the Au layer. The period of the gratings is 2 µm and in each period, GST width is 1 µm. GST was selected as the active phase change material because its optical properties undergo a substantial change during a structural transition from amorphous to crystalline phase. The optical absorption and reflection properties of the designed structure with respect to the geometric and material parameters were systematically investigated using the finite difference time domain computations. It was shown that absorption peak or reflection dip at the resonant wavelengths in the near-infrared region was red shifted from 2039 nm to 2143 nm wavelength by switching the phase change material from its amorphous to crystalline states. The distributions of the electric field and absorbed power at the resonant wavelengths with respect to different phases of the GST were investigated to further explain the physical origin of the absorption. Our study provides a path toward the realization of tunable infrared absorbers for applications, such as selective infrared emitters, infrared camouflage, sensors, and photovoltaic devices.
2
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Boriding of Binary Ni-Ti and Ternary Ni-Ti-Cu Shape Memory Alloys

81%
Ucar N., Turku N., Ozdemir A., Calik A.
|
EN
In this work, the boriding of binary (Ni-Ti) and ternary (Ni-Ti-Cu) shape memory alloys was carried out in a solid medium at 1173 K for 8 h using the powder pack method with Ekabor-Ni powders. Characterization of boride layer formed on the surface of alloys was identified by optical microscopy and scanning electron microscopy. TiB₂, NiB₂ and SiC phases in the boride layer of borided binary (Ni-Ti) and ternary (Ni-Ti-Cu) shape memory alloys was confirmed by X-ray diffraction analysis. The microhardness and thickness of the boride layers were measured. The obtained hardness values show a hardness anomaly due to porosity and structural defects with increase of Cu content, while a decrease in the value of hardness moving from the boride layer to main structure was observed.
3
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Diffusion Kinetics of Binary Ti-Ni Shape Memory Alloys

71%
Ucar N., Dogan S., Ozdemir A., Karakas S., Calik A.
Acta Physica Polonica A
|
2017
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vol. 132
|
issue 3
524-526
EN
In this work, the boriding of binary Ti-Ni shape memory alloys was carried out in a solid medium at 1173 and 1273 K for 2, 4, and 8 h using the powder pack method with Ekabor-Ni powders. The boride layer was characterized by optical microscopy and scanning electron microscopy. The obtained results show that boride layer thickness increases with the increasing boriding temperature and time. Depending on temperature and boride layer thickness, the diffusion process is thermally activated, with the mean value of the activation energy being close to 67 kJ/mol.
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