Institute of Materials Science and Nanotechnology (UNAM)

Permanent URI for this communityhttps://hdl.handle.net/11693/115649

Browse

Now showing 1 - 20 of 2448

Open Access
1018 nm Yb-doped high-power fiber laser pumped by broadband pump sources around 915 nm with output power above 100 W
(OSA - The Optical Society, 2017) Midilli, Y.; Efunbajo, O. B.; Şimşek, B.; Ortaç, B.
We demonstrate a 1018 nm ytterbium-doped all-fiber laser pumped by tunable pump sources operating in the broad absorption spectrum around 915 nm. In the experiment, two different pump diodes were tested to pump over a wide spectrum ranging from 904 to 924 nm by altering the cooling temperature of the pump diodes. Across this so-called pump wavelength regime having a 20 nm wavelength span, the amplified stimulated emission (ASE) suppression of the resulting laser was generally around 35 dB, showing good suppression ratio. Comparisons to the conventional 976 nm-pumped 1018 nm ytterbium-doped fiber laser were also addressed in this study. Finally, we have tested this system for high power experimentation and obtained 67% maximum optical-to-optical efficiency at an approximately 110 W output power level. To the best of our knowledge, this is the first 1018 nm ytterbium-doped all-fiber laser pumped by tunable pump sources around 915 nm reported in detail.
Open Access
130 nJ 77 fs dissipative soliton fiber laser
(OSA, 2010) Baumgartl, M.; Ortaç, Bülend; Lecaplain, C.; Hideur, A.; Limpert J.; Tünnermann, A.
We report on ultrashort high-energy pulse generation from an all-normal-dispersion fiber oscillator. The watt-level laser directly emits chirped pulses with a duration of 1ps and 163nJ of pulse energy. These can be compressed to 77fs. © 2010 Optical Society of America.
Open Access
[2+2] cycloadditions of sorbyl tosylate with imines/1-azadienes: a one-pot domino approach for α-alkylidene-β-lactams and their computational studies and antimicrobial evaluation
(Wiley-Blackwell, 2018) Kumar, Y.; Bedi, P. M. S.; Singh, P.; Adeniyi, A. A.; Singh-Pillay, A.; Singh, P.; Bhargava, G.
The manuscript describes a straightforward and atom-efficient method for the synthesis of α-alkylidene-β-lactams using sorbyl tosylate and imines/1-azadienes at high temperature (80 °C). The Density functional theory calculations have shown the prevalence of the first order kinetics in these [2+2] cycloadditions to produce mixture of 3-butadienyl-azetidin-2ones and 3-but-2-enylidene-azetidin-2-ones in good yields. The 3-but-2-enylidene-azetidin-2-ones have also shown antimicrobial activity against the E. coli, S. aureus, P. aeruginosa, B. cereus and B. subtilis.
Open Access
2D Network overtakes 3D for photocatalytic hydrogen evolution
(Royal Society of Chemistry, 2022-07-18) Ahmad, Aliyu Aremu; Türkan Gamze Ulusoy, Ghobadi; Özbay, Ekmel; Karadaş, Ferdi
3-Dimensional (3D) cyanide coordination polymers, typically known as Prussian blue Analogues (PBAs), have received great attention in catalysis due to their stability, easily tuned metal sites, and porosity. However, their high crystallinities and relatively low number of surface-active sites significantly hamper their intrinsic catalytic activities. Herein, we report the utilization of a 2-dimensional (2D) layered cobalt tetracyanonickelate, [Co–Ni], for the reduction of protons to H2. Relying on its exposed facets, layered morphology, and abundant surface-active sites, [Co–Ni] can efficiently convert water and sunlight to H2 in the presence of a ruthenium photosensitizer (Ru PS) with an optimal evolution rate of 30 029 ± 590 μmol g−1 h−1, greatly exceeding that of 3D Co–Fe PBA [Co–Fe] and Co–Co PBA [Co–Co]. Furthermore, [Co–Ni] retains its structural integrity throughout a 6 hour photocatalytic cycle, which is confirmed by XPS, PXRD, and Infrared analysis. This recent work reveals the excellent morphologic properties that promote [Co–Ni] as an attractive catalyst for the hydrogen evolution reaction (HER).
Open Access
2D vibrational properties of epitaxial silicene on Ag(111)
(IOP Publishing, 2016-10) Solonenko, D.; Gordan, O. D.; Lay, G. L.; Sahin, H.; Cahangirov, S.; Zahn, D. R. T.; Vogt, P.
The two-dimensional silicon allotrope, silicene, could spur the development of new and original concepts in Si-based nanotechnology. Up to now silicene can only be epitaxially synthesized on a supporting substrate such as Ag(111). Even though the structural and electronic properties of these epitaxial silicene layers have been intensively studied, very little is known about its vibrational characteristics. Here, we present a detailed study of epitaxial silicene on Ag(111) using in situ Raman spectroscopy, which is one of the most extensively employed experimental techniques to characterize 2D materials, such as graphene, transition metal dichalcogenides, and black phosphorous. The vibrational fingerprint of epitaxial silicene, in contrast to all previous interpretations, is characterized by three distinct phonon modes with A and E symmetries. Both, energies and symmetries of theses modes are confirmed by ab initio theory calculations. The temperature dependent spectral evolution of these modes demonstrates unique thermal properties of epitaxial silicene and a significant electron-phonon coupling. These results unambiguously support the purely two-dimensional character of epitaxial silicene up to about 300°C, whereupon a 2D-to-3D phase transition takes place. The detailed fingerprint of epitaxial silicene will allow us to identify it in different environments or to study its modifications.
Open Access
∼3-nm ZnO nanoislands deposition and application in charge trapping memory grown by single ALD step
(Nature Publishing Group, 2016) El-Atab, N.; Chowdhury F.; Ulusoy, T. G.; Ghobadi, A.; Nazirzadeh A.; Okyay, Ali Kemal; Nayfeh, A.
Low-dimensional semiconductor nanostructures are of great interest in high performance electronic and photonic devices. ZnO is considered to be a multifunctional material due to its unique properties with potential in various applications. In this work, 3-nm ZnO nanoislands are deposited by Atomic Layer Deposition (ALD) and the electronic properties are characterized by UV-Vis-NIR Spectrophotometer and X-ray Photoelectron Spectroscopy. The results show that the nanostructures show quantum confinement effects in 1D. Moreover, Metal-Oxide-Semiconductor Capacitor (MOSCAP) charge trapping memory devices with ZnO nanoislands charge storage layer are fabricated by a single ALD step and their performances are analyzed. The devices showed a large memory window at low operating voltages with excellent retention and endurance characteristics due to the additional oxygen vacancies in the nanoislands and the deep barrier for the trapped holes due to the reduction in ZnO electron affinity. The results show that the ZnO nanoislands are promising in future low power memory applications. © The Author(s) 2016.
Open Access
3D-printed, implantable alginate/CuS nanoparticle scaffolds for local tumor treatment via synergistic photothermal, photodynamic, and chemodynamic therapy
(American Chemical Society, 2023-09-08) Çolak, B.; Cihan, M. C.; Ertaş, Yavuz Nuri
A promising method for treating cancer is localized therapy, which mainly employs hydrogel-based delivery systems. Recently, the capability of 3D printing techniques has been revealed as a promising tool to tackle cancer. In this work, alginate (Alg)-based 3D-printed implantable scaffolds containing bovine serum albumin (BSA)-coated copper sulfide (CuS) nanoparticles, Alg-CuS/BSA, were fabricated for local breast cancer therapy and applied to inhibit tumor development through utilizing synergistic photothermal, photodynamic, and chemodynamic effects. The Alg-CuS/BSA scaffolds were flexible; however, their modulus was significantly lower than that of human breast tissues. Under 808 nm irradiation, the scaffolds demonstrated efficient photothermal, photodynamic, and chemodynamic effects both in vitro and in vivo via improving photothermal transduction and singlet-oxygen formation, and also as Fenton catalysts, the scaffolds produced hydroxyl radicals in the presence of H2O2 within the tumor microenvironment. Without the use of conventional anticancer drugs, the promising tumor treatment of implanted scaffolds can offer potential applications in local cancer treatment and prevent metastasis after surgical removal of tumors.
Open Access
4,5-dianilinophtalimide protects neuroendocrine cells against serum deprivation-induced stress and apoptosis
(2013) Ergin V.; Erdogan, M.; Karasu Ç.; Menevşe, A.
OBJECTIVE: The aim of this study was to reveal the effects of 4,5-dianilinophthalimide (DAPH), which inhibits amyloid β fibrillization, against serum deprivation (SD)-induced apoptosis and the possible mechanisms in differentiated PC12 neuron cells. METHODS: Firstly, we evaluated whether DAPH protects cell viability exposed to SD by MTT assay. Next, we examined the changes of phospho-p38 MAPK (Thr180/Tyr182), phospho-HSP27 (Ser82), phospho-c-JUN (Ser73) and cleaved-CASP3 (Asp175) profiles by immunoblotting, in PC12 cells exposed to SD. Intracellular reactive oxygen species (ROS) level was also measured. RESULTS: SD induced apoptosis accompanied by up-regulation of phospho-p38 MAPK (Thr180/Tyr182), phospho-HSP27 (Ser82), phospho-c-JUN (Ser73), cleaved-CASP3 (Asp175) and intracellular ROS content. Co-treatment with nontoxic doses of DAPH prevented apoptosis by the attenuation of activated proteins and reduction of ROS level. These results suggest that serum deprivation-induced apoptosis inhibited by DAPH administration. CONCLUSION: We have provided for the first evidence that DAPH has a neuroprotective effect on SD-caused stress, probably via contributing the reestablishment of redox homeostasis. © 2013 Neuroendocrinology Letters.
Open Access
48 W continuous-wave output from a high- efficiency single emitter laser diode at 915 nm
(Institute of Electrical and Electronics Engineers, 2022-09-19) Liu, Y.; Yang, G.; Zhao, Y.; Tang, S.; Lan, Y.; Zhao, Y.; Demir, Abdullah
Improving the power and efficiency of 9xx-nm broad-area laser diodes has a great help in reducing the cost of laser systems and expanding applications. This letter presents an optimized epitaxial structure with high power and conversion efficiency. Laser diodes with 230 μm emitter width and 5 mm cavity length deliver continuous-wave output power up to 48.5 W at 48 A, 30 °C, the highest power reported for 9xx-nm single emitter lasers so far. The slope efficiency is as high as 1.23 W/A due to a low internal optical loss of 0.31 cm−1 and a high internal efficiency of 96%. The maximum power conversion efficiency reaches 72.6% at 15.3 W and 67.3% at the operating power of 30 W under a heatsink temperature of 25 °C. Life test results show no failure in 1000 hours for 55 laser diodes.
Open Access
48 W continuous-wave output power with high efficiency from a single emitter laser diode at 915 nm
(SPIE - International Society for Optical Engineering, 2023-03-14) Yang, G.; Liu, Y.; Zhao, Yongming; Tang, S.; Zhao, Yuliang; Lan, Y.; Bai, L.; Li, Y.; Wang, X.; Demir, Abdullah; Zediker, Mark S.; Zucker, Erik P.
Improving the power and efficiency of 9xx-nm broad-area laser diodes reduces the cost of laser systems and expands applications. LDs with more than 25 W output power combined with power conversion efficiency (PCE) above 65% can provide a cost-effective high-power laser module. We report a high output power and high conversion efficiency laser diode operating at 915 nm by investigating the influence of the laser internal parameters on its output. The asymmetric epitaxial structure is optimized to achieve low optical loss while considering high internal efficiency, low series resistance, and modest optical confinement factor. Experimental results show an internal optical loss of 0.31 cm-1 and internal efficiency of 96%, in agreement with our simulation results. Laser diodes with 230 μm emitter width and 5 mm cavity length have T0 and T1 characteristic temperatures of 152 and 567 K, respectively. The maximum power conversion efficiency reaches 74.2% at 5 °C and 72.6% at 25 °C, and the maximum output power is 48.5 W at 48 A (at 30 ℃), the highest reported for a 9xx-nm single emitter laser diode. At 25 oC, a high PCE of 67.5% is achieved for the operating power of 30 W at 27.5 A, and the lateral far-field angle with 95% power content is around 8°. Life test results show no failure in 1200 hours for 55 laser diodes. In addition, 55.5 W output was achieved at 55 A from a laser diode with 400 μm emitter width and 5.5 mm cavity length. A high PCE of 64.3% is obtained at 50 W with 47 A. © 2023 SPIE.
Open Access
A [5]Rotaxane-Based photosensitizer for photodynamic therapy
(WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim, 2019) Özkan, Melis; Keser, Yağmur; Hadi, Seyed Ehsan; Tuncel, Dönüş
A [5]rotaxane was synthesized through a catalytically self‐threading reaction in which CB6 serves as a macrocycle and acts as a catalyst for the 1,3‐dipolar cycloaddition reaction between the alkyne substituted porphyrin core and azide functionalized stopper groups by forming triazole. Application of this rotaxane as a photosensitizer in photodynamic therapy against cancer cells and in bacteria inactivation have also been demonstrated. This photosensitizer has an excellent water solubility and remains stable in biological media at physiological pH (7.4) for prolonged times. It has the ability to generate singlet oxygen efficiently; while it shows no dark cytotoxicity up to 300 µm to the MCF7 cancer cell line, it is photocytotoxic even at 2 µm and reduces the cell viability to around 70 % when exposed to white light. It also displays light‐triggered biocidal activity both against gram‐negative bacteria (Escherichia coli, E. coli) and gram‐positive bacteria (Bacillus subtilis). Upon white light irradiation for 1 min with a flux of 22 mW/cm2 of E. coli suspension incubated with [5]rotaxane (3.5 µm), a killing efficiency of 96 % is achieved, whereas in the dark the effect is recorded as only around 9 %.
Open Access
808 nm broad-area laser diodes designed for high efficiency at high-temperature operation
(Institute of Physics Publishing Ltd., 2021-09-21) Lan, Y.; Yang, G.; Liu, Y.; Zhao, Y.; Wang, Z.; Li, T.; Demir, Abdullah
Semiconductor lasers with high power conversion efficiency (PCE) and output power are heavily investigated driven by more energy-efficient commercial applications. In this paper, an asymmetric broad area laser (A-BAL) design is studied and compared with a conventional symmetric broad area laser (S-BAL) design for 808 nm single emitter laser diodes. We present a comparative theoretical and experimental investigation by studying the thermal effects on the laser parameters. The output characteristics and efficiency loss paths for the designs were analyzed. The leakage of carriers was identified as the primary source of the PCE reduction with temperature. Suppressing this leakage by optimization of the A-BAL design, a record continuous-wave PCE of 68% at 25 °C and 60.4% at 75 °C were achieved for a single emitter laser with 10 W output power. These devices deliver high efficiency at high temperatures with reliable operation achieving 2000 h of an accelerated aging lifetime without failures.
Open Access
83 W, 1 ns, 3.1 MHz all-fiber laser for micromachining
(IEEE, 2011) Özgören, Kıvanç; Öktem, Bülent; Yılmaz, Sinem; İlday, F. Ömer; Pasin, E.; Eken, K.
Fiber lasers are commonly used for various material processing applications. The advantages (such as simplicity of the system, high material removal rate) and disadvantages (larger heat-affected zone, reduced precision) of nanosecond pulses over sub-picosecond pulses are well known. © 2011 IEEE.
Open Access
83 W, 3.1 MHz, square-shaped, 1 ns-pulsed all-fiber-integrated laser for micromachining
(Optical Society of America, 2011-08-29) Özgören, Kıvanç; Öktem, Bülent; Yılmaz, Sinem; İlday, F. Ömer; Eken, K.
We demonstrate an all-fiber-integrated laser based on off-the-shelf components producing square-shaped, 1 ns-long pulses at 1.03 mu m wavelength with 3.1 MHz repetition rate and 83 W of average power. The master-oscillator power-amplifier system is seeded by a fiber oscillator utilizing a nonlinear optical loop mirror and producing incompressible pulses. A simple technique is employed to demonstrate that the pulses indeed have a random chirp. We propose that the long pulse duration should result in more efficient material removal relative to picosecond pulses, while being short enough to minimize heat effects, relative to nanosecond pulses commonly used in micromachining. Micromachining of Ti surfaces using 0.1 ns, 1 ns and 100 ns pulses supports these expectations. (C) 2011 Optical Society of America
Open Access
915 nm pumped 1018 nm Yb-doped all-fiber high power fiber laser system
(Institute of Electrical and Electronics Engineers Inc., 2019) Midilli, Yakup; Efunbajo, O. Benjamin; Şimşek, Bartu; Ortaç, Bülend
Fibers lasers have attracted great attention in the last decades and the power scaling has reached tens of kW levels. Especially with the tandem pump configuration, pumping the active medium with a pump laser light instead of a diode laser, has made a breakthrough and so many research has been conducted about 1018 nm fiber laser systems [1]. Decreasing the quantum defect, the slope efficiency could be increased up to 90 % levels; on the other hand, due to the emission cross section of the Ytterbium (Yb), to operate the laser in the 1018 nm wavelength region is very challenging because of the presence of the ASE about the 1030 nm region. However, in the literature by using 976 nm pump diodes multi-hundred watts level 1018 nm fiber lasers could be demonstrated [2, 3].
Open Access
94.8 km-range direct detection fiber optic distributed acoustic sensor
(Optical Society of America(OSA), 2019) Uyar, Faruk; Uyar, Talha; Ünal, Canberk; Kartaloğlu, Tolga; Özdur, İbrahim; Özbay, Ekmel
This work demonstrates an ultra-long range direct detection fiber optic distributed acoustic sensor which can detect vibrations at a distance of 94.8 km with 10 m resolution along the sensing fiber.
Open Access
97 percent light absorption in an ultrabroadband frequency range utilizing an ultrathin metal layer: randomly oriented, densely packed dielectric nanowires as an excellent light trapping scaffold
(Royal Society of Chemistry, 2017) Ghobadi, A.; Dereshgi, S. A.; Hajian, H.; Birant, G.; Butun, B.; Bek, A.; Özbay, Ekmel
In this paper, we propose a facile and large scale compatible design to obtain perfect ultrabroadband light absorption using metal-dielectric core-shell nanowires. The design consists of atomic layer deposited (ALD) Pt metal uniformly wrapped around hydrothermally grown titanium dioxide (TiO2) nanowires. It is found that the randomly oriented dense TiO2 nanowires can impose excellent light trapping properties where the existence of an ultrathin Pt layer (with a thickness of 10 nm) can absorb the light in an ultrabroadband frequency range with an amount near unity. Throughout this study, we first investigate the formation of resonant modes in the metallic nanowires. Our findings prove that a nanowire structure can support multiple longitudinal localized surface plasmons (LSPs) along its axis together with transverse resonance modes. Our investigations showed that the spectral position of these resonance peaks can be tuned with the length, radius, and orientation of the nanowire. Therefore, TiO2 random nanowires can contain all of these features simultaneously in which the superposition of responses for these different geometries leads to a flat perfect light absorption. The obtained results demonstrate that taking unique advantages of the ALD method, together with excellent light trapping of chemically synthesized nanowires, a perfect, bifacial, wide angle, and large scale compatible absorber can be made where an excellent performance is achieved while using less materials.
Open Access
A dormant reagent reaction-diffusion method for the generation of Co-Fe Prussian Blue analogue periodic precipitate particle libraries
(Wiley-VCH GmbH, 2023-08-25) Tootoonchian, Pedram; Kwiczak-Yiğitbaşı, Joanna; Turab Ali Khan, Muhammad; Chalil Oglou, Ramadan; Holló, G.; Karadaş, Ferdi; Lagzi, I.; Baytekin, Bilge
Liesegang patterns that develop as a result of reaction-diffusion can simultaneously form products with slightly different sizes spatially separated in a single medium. We show here a reaction-diffusion method using a dormant reagent (citrate) for developing Liesegang patterns of cobalt hexacyanoferrate Prussian Blue analog (PBA) particle libraries. This method slows the precipitation reaction and produces different-sized particles in a gel medium at different locations. The gel-embedded particles are still catalytically active. Finally, the applicability of the new method to other PBAs and 2D systems is presented. The method proves promising for obtaining similar inorganic framework libraries with catalytic abilities. © 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.
Open Access
A high-power and broadband gan spdt mmic switch using gate-optimized hemts
(Institute of Electrical and Electronics Engineers, 2022-05-22) Erturk, V.; Gurdal, A.; Özbay, Ekmel
A high-power, broadband monolithic microwave integrated circuit (MMIC) single-pole double-throw (SPDT) switch is designed with gate-optimized high-electron-mobility transistors (HEMTs) using AlGaN/Gallium nitride (GaN) technology. The foot length of the gate is varied from 200 to 250 nm, and the head length is varied from 500 to 750 nm in the T-gate structure to optimize the radio frequency (RF) performance. The SPDT switch is designed in a series-shunt-shunt topology using gate topology as a design parameter. The switch has achieved an insertion loss better than 0.75 dB throughout the 3.5-13.5-GHz bandwidth. It can transmit 30-W output power at 0.1-dB compression point and handle 47.5-dBm input power at P-1dB. The isolation is above 25 dB, and the return loss is better than 11 dB. With its low insertion and high power-handling capacity in broadband, the SPDT switch shows state-of-the-art performance for high-power communication systems and radar applications.
Embargo
A machine learning approach for the estimation of photocatalytic activity of ALD ZnO thin films on fabric substrates
(Elsevier, 2024-02-01) Akyıldız, Halil I.; Yiğit, E.; Arat, A. B.; Islam, S.
Research in the field of photocatalytic wastewater treatment is striving to enhance catalyst materials to achieve high-performance systems. A promising approach to this goal has been immobilizing photocatalytic materials on fibrous substrates via atomic layer deposition (ALD). Nevertheless, both the ALD process and the assessment of photocatalytic performance involve a multitude of parameters necessitating thorough investigation. In this study, we employ popular machine-learning algorithms, including Support Vector Regression (SVR) and Artificial Neural Networks (ANN), to predict the photocatalytic activity of ALD-coated textiles. The photocatalytic activity is evaluated through methylene blue and methyl orange degradation tests. Machine learning algorithms are tested and trained using the k-fold cross-validation technique. The findings demonstrate that the ANN and SVR methods utilized in this research can predict catalytic activity with mean absolute percentage errors (MAPE) of 2.35 and 3.25, respectively. This study illuminates that, within the defined range of process parameters, the photocatalytic activity of ALD-coated textiles can be precisely estimated with suitable machine-learning algorithms.