Browsing by Author "Demir, Ahmet Kemal"
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Item Open Access Fabrication of flexible, cost-effective, and scalable silver substrates for efficient surface enhanced Raman spectroscopy based trace detection(Elsevier BV, 2021-06-20) Khan, G. A.; Demirtaş, Ö.; Aytekin, Ö.; Demir, Ahmet Kemal; Bek, A.; Bhatti, A. S.; Ahmed, W.The fabrication and optimization of cost-effective, eco-friendly, uniform and flexible SERS platforms by facile synthesis routes has recently attracted great attention for trace detection of various analytes. Herein, we report the fabrication of interconnected Ag nanostructures on the unmodified filter paper-based flexible substrates by a facile recipe, which involves evaporation of Ag precursor solution on the filter paper followed by its reduction with a strong reducing agent, NaBH4. The fabrication process is time-efficient, reproducible, and has the potential of being scaled up. The presence of inter-connected nanostructures results in high concentration of uniformly distributed hotspots on the substrate, which in turn provide excellent and reproducible SERS sensitivity. The finite element simulation results showed that fabricated nanostructures are much more effective for field enhancement as compared to the agglomerated spherical nanoparticles. Crystal violet (CV) concentration of 10−8 M was easily detected with these substrates both via solution drying and swabbing. Similarly, AgFPS have proven effective for swab-based detection of urea nitrate (UN), a well-known constituent of homemade explosives. The C-N and NO3- symmetric stretching modes of UN are detectable down to 1 µM and 100 µM concentrations, respectively. Moreover, these substrates showed SERS signal uniformity both from different spots of a single substrate, and substrates from different batches, with spot-to-spot relative standard deviation (RSD) of 15% and sample-to-sample RSD of 15–19%. This makes them excellent for reliable and quick quantitative detection. The simple synthesis strategy, flexibility, cost-effectiveness, and quantitative detection makes these substrates ideal for SERS based trace detection, especially for on-site analysis, and various sensing applications.Item Open Access Laser photochemical nanostructuring of silicon for surface enhanced raman spectroscopy(Wiley-VCH Verlag GmbH & Co. KGaA, 2022-07-18) Akbıyık, A.; Avishan, N.; Demirtaş, Ö.; Demir, Ahmet Kemal; Yüce, E.; Bek, A.In this work, a novel method of fabricating large-area, low-cost surface-enhanced Raman spectroscopy (SERS) substrates is explained which yields nanostructured surface utilizing laser-induced chemical etching of crystalline silicon (Si) in an hydrofluoric acid solution. Nanostructuring of Si surface is followed by deposition of a thin noble metal layer to complete the fabrication procedure. A 50 nm thick silver (Ag) layer is shown to maximize the SERS performance. The SERS effect is attributed to the electromagnetic field enhancement originating from the nanoscale surface roughness of Si that can be controlled by the illumination power, etch duration, and the spot size of the laser beam. The SERS substrates are found to be capable of detecting a Raman analyte dye molecule down to 10−11 m. SERS performance of the Ag deposited substrates are compared to gold (Au) deposited substrates at 660 and 532 nm excitation. Nanostructured Si surface with Ag exhibits stronger SERS than with Au under 532 nm excitation exhibiting an enhancement factor as high as 109. Raman enhancement factor is calculated both by SERS spectra experimentally, and using finite-elements simulation of the electric field enhancement. The applicability of the fabricated substrates is examined by adsorbing different analytes.Item Open Access LIPSS for SERS: Metal coated direct laser written periodic nanostructures for surface enhanced raman spectroscopy(Wiley-VCH Verlag GmbH & Co. KGaA, 2022-11-18) Erkızan, S. N.; İdikut, F.; Demirtaş, Ö.; Goodarzi, A.; Demir, Ahmet Kemal; Borra, M.; Pavlov, I.; Bek, A.A novel method of fabricating large-area, low-cost surface-enhanced Raman spectroscopy (SERS) substrates is introduced which yields densely nanostructured surfaces utilizing laser-induced periodic surface structuring (LIPSS) of crystalline silicon (Si). Two different interaction regimes yield low spatial frequency (LSFL) and high spatial frequency (HSFL) LIPSS patterns. Nanostructuring of Si surface is followed by deposition of a thin noble metal layer to complete the fabrication procedure. A 50–70 nm thick Ag layer is shown to maximize the SERS performance. The SERS effect is attributed to the electromagnetic field enhancement originating from the nanoscale surface roughness of Si that can be controlled by LSFL and HSFL nature of the structure. The SERS substrates are found to be capable of detecting a Raman analyte down to 10−11 m. SERS performance of the Ag deposited substrates at 532, 660, and 785 nm excitation wavelengths is compared. Both LSFL and HSFL Si surfaces with 70 nm thick Ag are found to exhibit the strongest SERS under 660 nm excitation exhibiting Raman enhancement factors (EFs) as high as 109. The Raman EFs are calculated both by SERS spectra experimentally, and using finite-elements method simulation of the electric field enhancement where a good agreement is found.Item Open Access Nanosphere concentrated photovoltaics with shape control(Wiley, 2020-12) Esmaeilzad, N. S.; Demir, Ahmet Kemal; Hajivand, J.; Çiftpınar, H.; Turan, R.; Kurt, H.; Bek, A.Dielectric colloidal nanospheres (NSs) are promising candidates for light management in photonic devices such as solar cells (SCs). NS arrays can direct the broad incident solar radiation into a set of tighter foci, at which light intensity becomes considerably concentrated, enabling higher photovoltaic conversion efficiency. Furthermore, the NS arrays acting as an effective medium on the SC surface can reduce reflectance and facilitate improved forward scattering. Therefore, uniform arrays of NSs located on top of the SC can behave as antireflection coatings or as microlenses, which can be regarded as a surface distributed light concentrator within the framework of concentrated photovoltaics. Fabrication of NS‐based light‐trapping structures is low‐cost and less complicated than common alternatives such as vacuum evaporated multilayer antireflection coatings. In this work, experimental demonstration and computational confirmation on the shape adjustment of such NS structures for improved light harvesting and efficiency enhancement in Si SCs are studied. The light conversion efficiency of Si solar cells is shown to improve by more than 27% with shape adjustment of NS arrays.Item Open Access SERS-based trace detection by size and shape controlled noble metal particles with high benefit-cost ratio(Digital Library, 2021-08-01) Demirtaş, Özge; Khan, Ghazanfar Ali; Esmaeilzad, Nasim Seyedpour; Iftikhar, R. M. Faheem; Öztürk, İ. Murat; Demir, Ahmet Kemal; Ahmed, Waqqar; Bek, AlpanSERS has become a highly preferred method with the effect of advances in instrument technology and potential for application to many areas from medicine to art conservation for the detection of trace-level environmental and biological analytes. However, the effects of substrate variation and the details of the enhancement mechanism still of concern even much progress has been achieved in recent years. Therefore, it is important to control the size and shape of the materials for maximize the enhancement factor and ensure the reproducibility of the substrates by considering SERS uncertainty principle. In this study, we present novel SERS substrate preparation methods that are highly promising in terms of both signal enhancement and reproducibility with high benefit-cost ratio.Item Open Access Shape and deposition angle control of silver film-over-nanosphere SERS substrates(Institute of Physics Publishing, 2021-10-06) Esmaeilzad, Nasim Seyedpour; Demirtaş, Özge; Demir, Ahmet Kemal; Bek, AlpanThin metallic films on dielectric nanospheres are demonstrated to have a high potential for the fabrication of cost-effective SERS substrates. In addition to the morphological advantages that nanospheres offer for attaining a high density of hot spots, possessing shape adjustability by uncomplicated thermal treatment makes them an attractive platform for tuneable SERS substrates. Furthermore, when combined with the oblique angle metal deposition technique, adjustable gaps at a high density and adjustable shape of metal films, such as Ag films, can be achieved on nanospheres. Applying small changes in deposition angle can provide means for fine adjustment of the Raman enhancement factor (EF), resulting in EF up to 108 measured using crystal violet dye molecule as a Raman analyte. This practice paves the way for the fabrication of high EF SERS substrates at a reasonable cost using a monolayer of self-organized nanosphere patterns. An ultra-thin Ag film coated at 5° tilt is shown to be an excellent substitute for a film deposited at 0° with double the thickness. There is a strong agreement between the experimental results and finite-elements-method-based Maxwell simulations exhibiting expected field enhancements up to 109 at a tilt angle of 5°.Item Restricted Tülomsaş ve gelişen Eskişehir'deki payı(Bilkent University, 2020) Demir, Ahmet Kemal; Yelesti, Efe; Diner, Melodi; Yıldız, Oya; Güneş, Muhammed HüseyinBu çalışmada Türkiye Lokomotif ve Motor Sanayii A.Ş.nin kurulumundan itibaren Eskişehir'in ekonomik, kültürel ve sosyal motifine katkıları incelenmiştir. Araştırmada sorulan sorular sadece fabrikanın çalıştırdığı işçileri ve geliştirdiği teknolojiyi anlama amacıyla değil; aynı zamanda TÜLOMSAŞ'ın sıradan bir Eskişehirlinin hayatında neleri nasıl değiştirdiğini de kavrama amacıyla tasarlanmıştır. TÜLOMSAŞ'ın yeni Türk Cumhuriyeti'nin ilk ağır sanayi fabrikası olarak yaptığı atılımların, geliştirdiği ve koruduğu değerlerin Eskişehir için nasıl sonuçları olduğu araştırılmıştır. Araştırmada TÜLOMSAŞ'ın bünyesinde kurulan Çırak Okulu'ndan mezun olan, TÜLOMSAŞ'ta 20'den fazla yıl bilfiil çalışan, fabrikada çalışırken eskrimde Türkiye'yi temsil etmiş olan Mustafa Köksal'ın tecrübelerinden yararlanılmıştır.