Research Project: Horizon Europe Excellent Science ERC POC Grant şablonu
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Contributors
Funders
ID
EC.00176
Authors
Onbaşlı, Mehmet Cengiz
Faculty Member
Publications
Quantifying polycrystallinity effects on skyrmion dynamics and device performance
(Royal Society of Chemistry, 2025) Cheghabouri, Arash Mousavi; Onbaşlı, Mehmet Cengiz; Cheghabouri, Arash Mousavi; Trabzon, Ahmet Bahadır; Department of Physics; Department of Electrical and Electronics Engineering; Yes; College of Sciences; College of Engineering
Skyrmion-based devices promise energy-efficient spintronic functionalities, but polycrystalline magnetic films can degrade performance by inducing skyrmion pinning. Here, we use micromagnetic modeling to quantify the impact of polycrystallinity-induced variability in key material parameters such as saturation magnetization, Dzyaloshinskii–Moriya interaction, and uniaxial anisotropy on skyrmion stability, dynamics, and hysteresis loops in Co/Pt films and device geometries. We demonstrate that variations exceeding 5% in these parameters across grains significantly increase the likelihood of pinning, with the effects depending on both grain size and distribution. Our findings establish quantitative tolerance thresholds and highlight the importance of fabricating films with narrow grain size distributions and stringent control over material uniformity to enable robust, pinning-free operation in skyrmion-based spintronic devices.
Defect dependent electronic properties of two-dimensional transition metal dichalcogenides (2H, 1T, and 1T′ phases)
(Royal Society of Chemistry, 2024) Onbaşlı, Mehmet Cengiz; Akgenç Hanedar, Berna; Department of Electrical and Electronics Engineering; Department of Physics; Yes; College of Engineering; College of Sciences
Transition metal dichalcogenides (TMDs) exhibit a wide range of electronic properties due to their structural diversity. Understanding their defect-dependent properties might enable the design of efficient, bright, and long-lifetime quantum emitters. Here, we use density functional theory (DFT) calculations to investigate the 2H, 1T, and 1T ' phases of MoS2, WS2, MoSe2, WSe2 and the effect of defect densities on the electronic band structures, focusing on the influence of chalcogen vacancies. The 2H phase, which is thermodynamically stable, is a direct band gap semiconductor, while the 1T phase, despite its higher formation energy, exhibits metallic behavior. 1T phases with spin-orbit coupling show significant band inversions of 0.61, 0.77, 0.24 and 0.78 eV for MoS2, MoSe2, WS2 and WSe2, respectively. We discovered that for all four MX2 systems, the energy difference between 2H, 1T and 1T phases decreases with increasing concentration of vacancies (from 3.13% to 21.88%). Our findings show that the 2H phase also has minimum energy values depending on vacancies. TMDs containing W were found to have a wider bandgap compared to those containing Mo. The band gap of 2H WS2 decreased from 1.81 eV (1.54 eV with SOC included) under GGA calculations to a range of 1.37 eV to 0.79 eV, while the band gap of 2H MoSe2 reduced from 1.43 eV (1.31 eV with SOC) under GGA to a range of 0.98 eV to 0.06 eV, depending on the concentration. Our findings provide guidelines for experimental screening of 2D TMD defects, paving the way for the development of next-generation spintronic, electronic, and optoelectronic devices.
Advances in biosensor technologies for infectious diseases detection
(Elsevier, 2024) Onbaşlı, Mehmet Cengiz; Akbari Nakhjavani, Sattar; Mirzajani, Hadi; Carrara, Sandro; KUTTAM (Koç University Research Center for Translational Medicine); Department of Electrical and Electronics Engineering; Department of Physics; KUISCID (Koç University İşbank Center for Infectious Diseases); Yes; College of Engineering; College of Sciences; Research Center
Being responsible for almost 15 % of the deaths globally, infectious diseases (IDs) are considered as a major health challenge, which was lately emphasized by the COVID-19 pandemic once again. Data form COVID pandemic revealed that early and timely detection of pathogens plays an undeniable role in controlling the spread of the disease and provides a time-effective medical interventions and more efficient disease management. To address the shortcomings of the traditional methods, the emergence of biosensors facilitated fast, accurate, robust, real-time, and on-site detection of various pathogens. In this paper, the recent advances in the development of biosensing technologies for detection of IDs are comprehensively explored considering their both detection methods (electrochemical, electrochemiluminescence, and capacitive) as well as proposed biorecognition elements (antibodies, aptamers, natural DNA fragments). Furthermore, the role of nanomaterials in enhancing the biosensors' performance are highlighted, while other innovative fluidics, such as paper-based microfabricated systems, are also considered.
Rational control of combined photothermal and photodynamic therapy for effective eradication of biofilms
(Royal Soc Chemistry, 2025) Koç, İrem; Ataç, Nazlı; Çam, Kübra; Çakır, Ece; Yağan, Rawana; Can, Füsun; Sennaroğlu, Alphan; Onbaşlı, Mehmet Cengiz; Acar, Havva Funda Yağcı; Kurt, Cem; Cooper, Francis Korshe; Yağan, Rawana; School of Medicine; Graduate School of Sciences and Engineering; Department of Electrical and Electronics Engineering; KUISCID (Koç University İşbank Center for Infectious Diseases); Department of Physics; KUYTAM (Koç University Surface Science and Technology Center); Department of Chemistry; Yes; Çam, Kübra; Çakır, Ece; Cooper, Francis Korshe; Koç, İrem; College of Engineering; College of Sciences; GRADUATE SCHOOL OF SCIENCES AND ENGINEERING; SCHOOL OF MEDICINE; Research Center; Kurt, Cem
New therapies are essential for eliminating antibiotic-resistant bacteria and their biofilms, which are a major global health threat, causing millions of deaths annually. Here, we demonstrate a combination of photodynamic therapy (PDT) and photothermal therapy (PTT) for the inhibition of biofilms of Pseudomonas aeruginosa and Staphylococcus epidermidis using aminolevulinic acid (ALA)-loaded polyacrylic acid-coated superparamagnetic iron oxide nanoparticles (PAA-SPIONs) at 200, 600 and 1000 mu g mL-1 Fe concentrations under 640 nm (0.75 W cm-2), 808 nm (2.6 W cm-2) and 640 + 808 nm (0.75 + 2.6 W cm-2, 20 min) irradiation. PTT experiments indicate ALA/PAA-SPION concentration-dependent heating up to 10.2 degrees C for PAA-SPIONs and 9.3 degrees C for ALA/PAA-SPIONs under combined 640 + 808 nm laser excitation. Bacterial growth inhibition by ALA/PAA-SPIONs was investigated with and without laser irradiation for 10 min using 150 and 600 mu g Fe per mL or 0.5 mM and 2 mM ALA on both bacterial types. These experiments indicate a 3 to 6-log reduction in P. aeruginosa compared to control samples (without nanoparticles or a laser) with increasing Fe and ALA concentrations. Growth was completely inhibited by ALA/PAA-SPIONs under 640 + 808 nm irradiation. ALA/PAA-SPIONs caused growth inhibition of S. epidermidis between 2-log and 4-log with increasing wavelengths, Fe and ALA doses. PAA-SPIONs and a laser together inhibited the biofilms of P. aeruginosa with 3 to 11-log reductions with increasing laser wavelengths. The reduction of the biofilm with ALA/PAA-SPIONs and a laser reaches 8-log for 640 nm and 13-log for 808 nm excitation. We accurately model the wavelength, time, and nanoparticle concentration dependence of PTT for the first time. These results pave the way for effective PDT/PTT elimination of biofilms of P. aeruginosa and S. epidermidis.
Ultrahigh mobility and Rashba spin splitting in Sb-substituted bismuth telluride and bismuth selenide
(Royal Society of Chemistry, 2026) Akgenç Hanedar, Berna; Şahin, Akile İlknur; Onbaşlı, Mehmet Cengiz; Kavkhani, Roya; Anar, Kerem; Kavkhani, Roya; Anar, Kerem; Johansson, Annika; Department of Physics; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; Yes; College of Engineering; College of Sciences; GRADUATE SCHOOL OF SCIENCES AND ENGINEERING; Şahin, Akile İlknur
Topological insulators (TIs) such as Sb-doped Bi2Te3 and Bi2Se3 exhibit promising phenomena for advanced spintronics. While previous studies explored isolated doping levels; a systematic understanding of how Sb concentration influences topological behavior, Rashba-type spin splitting, and surface state formation is lacking. Here, we use density functional theory to investigate the structural, electronic, topological and transport properties of (Bi1-xSbx)2Te3 and (Bi1-xSbx)2Se3 thin films across 0 <= x <= 1. We identify pronounced Rashba spin splitting in Bi2Te3 at x = 0.5, 0.6, and 0.9 with in-plane helical spin textures. We identified the orbital origins of topological surface states and demonstrate that band inversion persists across the Sb doping range. At x = 0.2, 0.4, and 0.8, calculated surface electron mobilities are consistent with experiments and increase an order of magnitude over Sb2Te3, with minimal impact on bulk mobilities. These insights advance our understanding of TIs for spintronic and quantum device applications.
