Browsing by Author "Topalli K."

Now showing 1 - 4 of 4

Open Access
Atomic layer deposition synthesized TiOx thin films and their application as microbolometer active materials
(AVS Science and Technology Society, 2016) Tanrikulu, M. Y.; Rasouli, H. R.; Ghaffari, M.; Topalli K.; Okyay, Ali Kemal
This paper demonstrates the possible usage of TiOx thin films synthesized by atomic layer deposition as a microbolometer active material. Thin film electrical resistance is investigated as a function of thermal annealing. It is found that the temperature coefficient of resistance values can be controlled by coating/annealing processes, and the value as high as -9%/K near room temperature is obtained. The noise properties of TiOx films are characterized. It is shown that TiOx films grown by atomic layer deposition technique could have a significant potential to be used as a new active material for microbolometer-based applications. © 2016 American Vacuum Society.
Open Access
Complementary spiral resonators for ultrawideband suppression of simultaneous switching noise in high-speed circuits
(Electromagnetics Academy, 2014) Ghobadi, A.; Topalli K.; Bıyıklı, Necmi; Okyay, Ali Kemal
In this paper, a novel concept for ultra-wideband simultaneous switching noise (SSN) mitigation in high-speed printed circuit boards (PCBs) is proposed. Using complementary spiral resonators (CSRs) etched on only a single layer of the power plane and cascaded co-centrically around the noise port, ultra-wideband SSN suppression by 30 dB is achieved in a frequency span ranging from 340MHz to beyond 10 GHz. By placing a slit in the co-centric rings, lower cut-off frequency is reduced to 150 MHz, keeping the rest of the structure unaltered. Finally, the power plane structure with modified complementary spiral resonators (MCSRs) is designed, fabricated, and evaluated experimentally. Measurement and simulation results are in well-agreement.
Open Access
Controlling luminescent silicon nanoparticle emission produced by nanosecond pulsed laser ablation: role of interface defect states and crystallinity phase
(Royal Society of Chemistry, 2016) Ghobadi, T. G. U.; Ghobadi, A.; Okyay, T.; Topalli K.; Okyay, Ali Kemal
In this study, we provide a systematic study on the origin of green and blue emission from luminescent silicon nanoparticles (Si-NPs) synthesized in water using a nanosecond pulsed laser ablation methodology. Here we report a direct one-step process to make ultra-small Si-NPs (∼3 nm mean size) by utilizing spiral beam scanning. In each ablation cycle, this scanning scheme collects generated nanoparticles towards the center and ablates them in subsequent cycles. Therefore, the resultant Si-NPs can reach very small sizes in a short time with high uniformity in their size distribution. Further, we investigate the effect of laser fluence on the emission properties of the obtained nanoparticles. For this aim, two different values of 60 mJ cm−2 and 30 mJ cm−2 laser fluences are employed to achieve green and blue emitting Si-NPs, respectively. Our results show that the emission spectrum for both blue and green Si-NPs has two main peaks at 426 nm and 520 nm, but their relative intensity ratios are different for these two cases. The findings of this study suggest that the blue emission originates from oxide related surface defects at the Si/SiOx interface, while the green emission stems from grain boundaries existing at the NP surface. We found that these two types of disorders can be controlled by tuning the laser power. © The Royal Society of Chemistry.
Open Access
High-conductivity silicon based spectrally selective plasmonic surfaces for sensing in the infrared region
(Institute of Physics Publishing, 2017) Gorgulu, K.; Gok, A.; Yilmaz, M.; Topalli K.; Okyay, Ali Kemal
Plasmonic perfect absorbers have found a wide range of applications in imaging, sensing, and light harvesting and emitting devices. Traditionally, metals are used to implement plasmonic structures. For sensing applications, it is desirable to integrate nanophotonic active surfaces with biasing and amplification circuitry to achieve monolithic low cost solutions. Commonly used plasmonic metals such as Au and Ag are not compatible with standard silicon complementary metal-oxide-semiconductor (CMOS) technology. Here we demonstrate plasmonic perfect absorbers based on high conductivity silicon. Standard optical lithography and reactive ion etching techniques were used for the patterning of the samples. We present computational and experimental results of surface plasmon resonances excited on a silicon surface at normal and oblique incidences. We experimentally demonstrate our absorbers as ultra-low cost, CMOS-compatible and efficient refractive index sensing surfaces. The experimental results reveal that the structure exhibits a sensitivity of around 11 000 nm/RIU and a figure of merit of up to 2.5. We also show that the sensing performance of the structure can be improved by increasing doping density.