Browsing by Subject "Gold"
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Item Open Access Broadband optical transparency in plasmonic nanocomposite polymer films via exciton-plasmon energy transfer(OSA - The Optical Society, 2016) Dhama R.; Rashed, A. R.; Caligiuri V.; El Kabbash M.; Strangi, G.; De Luca A.Inherent absorptive losses affect the performance of all plasmonic devices, limiting their fascinating applications in the visible range. Here, we report on the enhanced optical transparency obtained as a result of the broadband mitigation of optical losses in nanocomposite polymeric films, embedding core-shell quantum dots (CdSe@ZnS QDs) and gold nanoparticles (Au-NPs). Exciton-plasmon coupling enables non-radiative energy transfer processes from QDs to metal NPs, resulting in gain induced transparency of the hybrid flexible systems. Experimental evidences, such as fluorescence quenching and modifications of fluorescence lifetimes confirm the presence of this strong coupling between plexcitonic elements. Measures performed by means of an ultra-fast broadband pump-probe setup demonstrate loss compensation of gold NPs dispersed in plastic network in presence of gain. Furthermore, we compare two films containing different concentrations of gold NPs and same amount of QDs, to investigate the role of acceptor concentration (Au-NPs) in order to promote an effective and efficient energy transfer mechanism. Gain induced transparency in bulk systems represents a promising path towards the realization of loss compensated plasmonic devices. © 2016 Optical Society of America.Item Open Access Capacitance-conductance-current-voltage characteristics of atomic layer deposited Au/Ti/Al2O3/n-GaAs MIS structures(Elsevier Ltd, 2015) Turut, A.; Karabulut, A.; Ejderha, K.; Bıyıklı, NecmiWe have studied the admittance and current–voltage characteristics of the Au/Ti/Al2O3/nGaAs structure. The Al2O3 layer of about 5 nm was formed on the n-GaAs by atomic layer deposition. The barrier height (BH) and ideality factor values of 1.18 eV and 2.45 were obtained from the forward-bias ln I vs V plot at 300 K. The BH value of 1.18 eV is larger than the values reported for conventional Ti/n-GaAs or Au/Ti/n-GaAs diodes. The barrier modification is very important in metal semiconductor devices. The use of an increased barrier diode as the gate can provide an adequate barrier height for FET operation while the decreased barrier diodes also show promise as small signal zero-bias rectifiers and microwave. The experimental capacitance and conductance characteristics were corrected by taking into account the device series resistance Rs. It has been seen that the noncorrection characteristics cause a serious error in the extraction of the interfacial properties. Furthermore, the device behaved more capacitive at the reverse bias voltage range rather than the forward bias voltage range because the phase angle in the reverse bias has remained unchanged as 901 independent of the measurement frequency.Item Open Access Charging/discharging of Au (core)/silica (shell) nanoparticles as revealed by XPS(American Chemical Society, 2005) Tunc, I.; Demirok, U. K.; Süzer, Şefik; Correa-Duatre, M. A.; Liz-Marzan, L. M.By recording XPS spectra while applying external voltage stress to the sample rod, we can control the extent of charging developed on core-shell-type gold nanoparticles deposited on a copper substrate, in both steady-state and time-resolved fashions. The charging manifests itself as a shift in the measured binding energy of the corresponding XPS peak. Whereas the bare gold nanoparticles exhibit no measurable binding energy shift in the Au 4f peaks, both the Au 4f and the Si 2p peaks exhibit significant and highly correlated (in time and magnitude) shifts in the case of gold (core)/silica (shell) nanoparticles. Using the shift in the Au 4f peaks, the capacitance of the 15-nm gold (core)/6-nm silica (shell) nanoparticle/nanocapacitor is estimated as 60 aF. It is further estimated that, in the fully charged situation, only 1 in 1000 silicon dioxide units in the shell carries a positive charge during our XPS analysis. Our simple method of controlling the charging, by application of an external voltage stress during XPS analysis, enables us to detect, locate, and quantify the charges developed on surface structures in a completely noncontact fashion. © 2005 American Chemical Society.Item Open Access Chiral single-wall gold nanotubes(American Physical Society, 2004) Senger, R. T.; Dag, S.; Çıracı, SalimThe formation of freestanding and tip-suspended chiral-wall (n,m) nanotubes, which were composed of helical atomic strands, from gold atoms was investigated using first-principles calculations, where (n,m) notation defines the structure of the tube. The tubes with 3≤n≤5 were found to be stable and exhibited electronic and transport properties investigated. The (5,3) gold tube was energetically the most favourable. It was observed from the quantum ballistic conductance, band structure and charge density analysis that the current on these wires was less chiral, and no direct correlation between the numbers of conduction channels and helical strands was found.Item Open Access Comparative study of thin film n-i-p a-Si: H solar cells to investigate the effect of absorber layer thickness on the plasmonic enhancement using gold nanoparticles(Elsevier Ltd, 2015) Islam, K.; Chowdhury F.I.; Okyay, Ali Kemal; Nayfeh, A.In this paper, the effect of gold nanoparticles on n-i-p a-Si:H solar cells with different intrinsic layer (i-layer) thicknesses has been studied. 100nm and 500nm i-layer based n-i-p a-Si:H solar cells were fabricated and colloidal gold (Au) nanoparticles dispersed in water-based solution were spin-coated on the top surface of the solar cells. The Au nanoparticles are of spherical shape and have 100nm diameter. Electrical and quantum efficiency measurements were carried out and the results show an increase in short-circuit current density (Jsc), efficiency and external quantum efficiency (EQE) with the incorporation of the nanoparticles on both cells. Jsc increases from 5.91mA/cm2 to 6.5mA/cm2 (~10% relative increase) and efficiency increases from 3.38% to 3.97% (~17.5% relative increase) for the 100nm i-layer solar cell after plasmonic enhancement whereas Jsc increases from 9.34mA/cm2 to 10.1mA/cm2 (~7.5% relative increase) and efficiency increases from 4.27% to 4.99% (~16.9% relative increase) for the 500nm i-layer cell. The results show that plasmonic enhancement is more effective in 100nm than 500nm i-layer thickness for a-Si:H solar cells. Moreover, the results are discussed in terms of light absorption and electron hole pair generation. © 2015 Elsevier Ltd.Item Open Access Comparison of Au(III) and Ga(III) ions' binding to calf thymus DNA: Spectroscopic characterization and thermal analysis(Humana Press Inc., 2014) Sarioglu O.F.; Tekiner-Gursacli, R.; Ozdemir, A.; Tekinay, T.Metals have been studied as potential chemotherapeutic agents for cancer therapies due to their high reactivity toward a wide variety of substances. The characterization of metal ion-binding capacities is essential to understand the possible effects of metals on target biomolecules. In the present study, biochemical effects of Au(III) and Ga(III) ions on calf thymus DNA (ctDNA) were studied comparatively via bioanalytical, spectroscopic, and thermal methods. Briefly, UV-Vis absorbance spectroscopy, fluorescence spectroscopy, circular dichroism (CD) spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy were utilized for spectroscopic characterization, and isothermal titration calorimetry (ITC) measurements were performed for thermal analysis. Our results reveal that both Au(III) and Ga(III) ions are capable of interacting with ctDNA, and Au(III) ions display a more favorable interaction and a higher binding affinity. ITC analyses indicate that the Au(III)-DNA interaction displays a binding affinity (Ka) around 1.43×106 M -1, while a Ka around 1.17×105 M -1 was observed for the Ga(III)-DNA binding. It was suggested that both metal ions are unlikely to change the structural B-conformation while interacting with ctDNA. © 2014 Springer Science+Business Media.Item Open Access Concentric ring structures as efficient SERS substrates(Institute of Electrical and Electronics Engineers, 2013) Cinel, N. A.; Cakmakyapan, S.; Ertas, G.; Özbay, EkmelPlasmonic nanopatterned structures that can work as highly efficient surface-enhanced Raman scattering (SERS) substrates are presented in this study. A 'coupled' concentric ring structure has been designed, fabricated, tuned, and compared to an 'etched' concentric ring structure and plain gold film via SERS experiments. The proposed design gives Raman signal intensity 630 times larger than plain gold film and 8 times larger than an 'etched' concentric ring structure. The surface plasmons were imaged with the fluorescence imaging technique and supporting numerical simulations were done.Item Open Access Cyclodextrin functionalized nanofibers via electrospinning(Bilkent University, 2014) Çelebioğlu, AslıElectrospinning is a commonly studied and widely applied technique for generating nanofibers, with a diameter ranging from several tens of nanometers to a few micrometers. The low-cost, simple set-up, relatively high production rate and reproducibility increase the interests on this method in both academia and industry. Electrospun nanofibers are produced from a broad range of materials with extremely high surface area, very light-weight, nano-porous features and distinct physical/mechanical properties. The general talk in this technique focuses on the production of nanofibers from polymer base materials. However, very recent studies demonstrated that, it is also possible to obtain nanofibers from non-polymeric systems. For this novel development in electrospinning researches, we have achieved to generate nanofibers from cyclodextrins (CD) without using a polymeric template. CD are cyclic oligosaccharides consisting of α-(1,4)-linked glucopyranose units. The truncated cone shape structure of CD provides a favorable place for various kinds of organic molecules to form non-covalent host-guest inclusion complexes (IC). The enhancements and progressing at the guest molecules property and situation, creating with the inclusion complexation, make CD applicable in variety of areas including filtration, pharmaceuticals, cosmetics, functional foods, textiles, analytic chemistry etc. In this thesis, we report on the electrospinning of CD nanofibers, represent their functionalization and potential applications. Firstly, we produced CD nanofibers from three different chemically modified CD types (hydroxypropyl-β-cyclodextrin (HPβCD), hydroxypropyl-γ-cyclodextrin (HPγCD) and methyl-β-cyclodextrin (MβCD)). Afterwards, the electrospinning of native CD (α-CD, β-CD and γ-CD) nanofibers was achieved. The molecular entrapment capability of CD nanofibers was shown by capturing toxic volatile organic compounds (VOCs) from the surrounding. As the next step, the polymer-free nanofibers were obtained from the cyclodextrin inclusion complexes (CD-IC) with antibacterial agent, vanillin and essential oils. Here, we have also indicated applicability of CD-IC nanofibers as a result of antibacterial test. The functionalization of the CD nanofibers was continued with the green and one-step synthesis of metal nanoparticles (Ag-NP, Au-NP and Pd-NP) incorporated nanofibers, in which CD were used as reducing, stabilizing agent and fiber template. Even, the antibacterial, SERS and catalyst potential of these CD based nanofibers were demonstrated for the related nanoparticles. Our research is expanded to a new stage by the production of insoluble poly-CD nanofibers. We have worked on different crosslinking agents to attain insoluble poly-CD nanofibers with uniform morphology. After the optimization of poly-CD nanofibers, the most durable polyCD nanowebs were selected for further analysis and evaluation of the filtration performance in liquid environment. Within poly-CD nanofibers, we have eliminated the solubility challenge of CD nanofibers that restrict their usage. So, we assume that, poly-CD nanofibers will lead-up to generation of new advances for practices of CD nanofibers. All studies showed that, the self-assembly and self-aggregation property of CD are the prior requirements for the electrospinnability of these small molecules. To conclude, very intriguing materials were obtained by integrating large surface area of nanofibers with specific host-guest inclusion complexation capability and non-toxic, biocompatible nature of the CD. Moreover, CD molecules, which are generally used in the powder form, were rendered into more applicable nanofibers form that will represent ease during their usage.Item Open Access Dynamic relationship between precious metals(2013) Sensoy, A.We use a relatively new approach to endogenously detect the volatility shifts in the returns of four major precious metals (gold, silver, platinum and palladium) from 1999 to 2013. We reveal that the turbulent year of 2008 has no significant effect on volatility levels of gold and silver however causes an upward shift in the volatility levels of palladium and platinum. Using the consistent dynamic conditional correlations, we show that precious metals get strongly correlated with each other in the last decade which reduces the diversification benefits across them and indicates a convergence to a single asset class. We endogenously detect the shifts in these dynamic correlation levels and reveal uni-directional volatility shift contagions among precious metals. The results show that gold has a uni-directional volatility shift contagion effect on all other precious metals and silver has a similar effect on platinum and palladium. However, the latter two do not matter in terms of volatility shift contagion. Thus, investors that hedge with precious metals should, in particular, monitor the volatility levels of gold and silver. © 2013 Elsevier Ltd.Item Open Access Dynamic risk spillovers between gold, oil prices and conventional, sustainability and Islamic equity aggregates and sectors with portfolio implications(Elsevier B.V., 2017) Mensi, W.; Hammoudeh, S.; Al-Jarrah, I. M. W.; Sensoy A.; Kang, S. H.This paper investigates the time-varying equicorrelations and risk spillovers between crude oil, gold and the Dow Jones conventional, sustainability and Islamic stock index aggregates and 10 associated disaggregated Islamic sector stock indexes (basic materials, consumer services, consumer goods, energy, financials, health care, technology, industrials, telecommunications and utilities), using the multivariate DECO-FIAPARCH model and the spillover index of Diebold and Yilmaz (2012). We also conduct a risk management analysis at the sector level for commodity-Islamic stock sector index portfolios, using different risk exposure measures. For comparison purposes, we add the aggregate conventional Dow Jones global index and the Dow Jones sustainability world index. The results show evidence of time-varying risk spillovers between these markets. Moreover, there are increases in the correlations among the markets in the aftermath of the 2008–2009 GFC. Further, the oil, gold, energy, financial, technology and telecommunications sectors are net receivers of risk spillovers, while the sustainability and conventional aggregate DJIM indexes as well as the remaining Islamic stock sectors are net contributors of risk spillovers. Finally, we provide evidence that gold offers better portfolio diversification benefits and downside risk reductions than oil. © 2017 Elsevier B.V.Item Open Access Effect of solvent refractive index on the surface plasmon resonance nanoparticle optical absorption(2007) Ertas, G.; Süzer, ŞefikOptical properties of plasmon coupled silver and gold nanoparticles were studied as a function of the refractive index of the surrounding medium. Our studies confirmed that the effect of changes in the refractive index of the surrounding medium was more difficult to demonstrate from an experimental point of view, because of the very high susceptibility of nanoparticles to aggregate in aqueous and organic solvents. Whereas the position of the absorption bands of triiodide in these solvents shows a clear dependence on medium's refractive index, the surface plasmon band position of silver and gold nanoparticles do not exhibit the same dependence. This is attributed to a non-negligible interaction of these solvents with nanoparticle surfaces. Copyright © 2007 American Scientific Publishers All rights reserved.Item Open Access Electronic properties of polypyrrole/polyindene composite/metal junctions(Elsevier, 1997) Bozkurt, A.; Ercelebi, C.; Toppare, L.Junction properties between conducting polymer composites of polypyrrole/polyindene (PPy/PIn) with different conductivities and metals like Pt, Au, Al and In have been investigated. Rectifying junctions were observed for low work function metals, In and Al; however, high work function metals, Pt and Au, were observed to form ohmic contacts to PPy/PIn composite in the sandwich geometry. The rectifying behavior of the metal/composite/Pt junctions improved when the conductivity of the composite was decreased from 1 to 0.01 S/cm. Using the ideal Schottky theory various junction parameters have been determined. All planar junctions were ohmic regardless of the conductivities of the samples.Item Open Access Enhanced in vivo radiotherapy of breast cancer using gadolinium oxide and gold hybrid nanoparticles(American Chemical Society, 2023-01-24) Nosrati, H.; Salehiabar, M.; Charmi, J.; Yaray, K.; Ghaffarlou, M.; Balcıoğlu, E.; Ertaş, Yavuz NuriRadiation therapy has demonstrated promising effectiveness against several types of cancers. X-ray radiation therapy can be made further effective by utilizing nanoparticles of high-atomic-number (high-Z) materials that act as radiosensitizers. Here, in purpose of maximizing the radiation therapy within tumors, bovine serum albumin capped gadolinium oxide and gold nanoparticles (Gd2O3@BSA-Au NPs) are developed as a bimetallic radiosensitizer. In this study, we incorporate two high-Z-based nanoparticles, Au and Gd, in a single nanoplatform. The radiosensitizing ability of the nanoparticles was assessed with a series of in vitro tests, following evaluation in vivo in a breast cancer murine model. Enhanced tumor suppression is observed in the group that received radiation after administration of Gd2O3@BSA-Au NPs. As a result, cancer therapy efficacy is significantly improved by applying Gd2O3@BSA-Au NPs under X-ray irradiation, as evidenced by studies evaluating cell viability, proliferation, reactive oxygen species production, and in vivo anti-tumor effect.Item Open Access Enhanced interactions of amino acids and nucleic acid bases with bare black phosphorene monolayer mediated by coadsorbed species(American Chemical Society, 2019) Kadıoğlu, Y.; Görkan, T.; Üzengi-Aktürk, O.; Aktürk, E.; Çıracı, SalimIn this paper, we characterize amino acids and nucleic acid bases (nucleobases), such as glutamine, histidine, tyrosine, adenine, guanine, cytosine, and thymine, and examine their interaction with bare, as well as with gold cluster and Ti adatom covered, black phosphorene (α-P) monolayers using density functional theory. The binding of these amino acids and nucleobases to the bare α-P monolayer is realized generally through weak van der Waals interaction and comprises only a small amount of charge exchange. Accordingly, the electronic energy structures of adsorbates and underlying substrate are not affected significantly. However, the electronic structure of bare α-P is significantly affected upon adsorption of a gold cluster and a single Ti adatom; depending on the size of the adsorbate and the symmetry of their coverage, the energy band gap can be tuned and permanent magnetic moments can be attained. Additionally, the adsorption of amino acids or nucleobases to these adsorbates on an α-P monolayer results in enhanced binding and hence makes their sustainable fixation on α-P monolayer possible. In particular, a semiconducting Au decorated α-P monolayer undergoes a metal–insulator transition upon the adsorption of tyrosine. This and similar effects favor the α-P monolayer in biosensor applications. In contrast to the situation with adsorbates, the binding of amino acid is not enhanced when it adsorb to patterned vacancy or divacancy sites of the α-P monolayer. Our study shows that the absorbance of the bare α-P monolayer can be enhanced by coating with amino acid and nucleobases. The absorbance spectrum can be further modified by the adsorption of these molecules to gold atoms on the α-P monolayer.Item Open Access Femtosecond pulse generation from a Ti3+: Sapphire laser near 800 nm with voltage reconfigurable graphene saturable absorbers(OSA - The Optical Society, 2017) Baylam, Işınsu; Özharar, Sarper; Kakenov, Nurbek; Kocabaş, Coşkun; Sennaroglu, AlphanWe experimentally show that a voltage-controlled graphene-gold supercapacitor saturable absorber (VCG-gold-SA) can be operated as a fast saturable absorber with adjustable linear absorption at wavelengths as low as 795 nm. This was made possible by the use of a novel supercapacitor architecture, consisting of a high-dielectric electrolyte sandwiched between a graphene and a gold electrode. The high-dielectric electrolyte allowed continuous, reversible adjustment of the Fermi level and, hence, the optical loss of the VCG-gold-SA up to the visible wavelengths at low bias voltages of the order of a few volts (0-2 V). The fast saturable absorber action of the VCG-gold-SA and the bias-dependent reduction of its loss were successfully demonstrated inside a femtosecond Ti3+:sapphire laser operating near 800 nm. Dispersion compensation was employed by using dispersion control mirrors and a prism pair. At a bias voltage of 1.2 V, the laser operated with improved power performance in comparison with that at zero bias, and the VCG-gold-SA initiated the generation of nearly transform-limited pulses as short as 48 fs at a pulse repetition rate of 131.7 MHz near 830 nm. To the best of our knowledge, this represents the shortest wavelength where a VCG-gold-SA has been employed as a mode locker with adjustable loss. © 2017 Optical Society of America.Item Open Access Formation of alkylsilane-based monolayers on gold(American Chemical Society, 2002) Owens, T. M.; Nicholson, K. T.; Banaszak Holl, M. M.; Süzer, S.The formation of monolayers of alkylsilanes on a gold surface is characterized by X-ray photoelectron and reflection-absorption infrared spectroscopies. The reaction occurs through the activation of multiple Si-H bonds. Reactivity of the newly synthesized systems to oxygen and water is reported. Copyright © 2002 American Chemical Society.Item Open Access Gold and gold jewelry : exploration of consumer practices(Bilkent University, 2003) Ertimur, BurçakThis thesis explores consumers’ practices and experiences in relation to consumption of gold and gold jewelry. It focuses on the underlying motivations of consumers, the uses of gold and gold jewelry, and examines the practices and meanings that emerge as a result of these uses. Data were collected through qualitative research methods. The participants include twenty-four female consumers and four industry representatives. Age, income, and use of gold jewelry/coin constitute the main criteria in selection of the consumers. The findings indicate three main uses for gold and gold jewelry: Gift-giving, ornamentation, and investment. Both utilitarian and symbolic motives are identified in giving gold jewelry/coins as a gift. Whereas previous research focuses on the symbolic aspects of the gift, the findings suggest that there are utilitarian aspects as well. The practices and experiences related to the use as ornamentation illustrate the relation of gold jewelry to fashion, highlight the item’s significance for sense of self, and reveal patterns of complementarity with the product category of clothing. The exploration of the use of investment uncovers the dual function of gold jewelry, and indicates the interaction between ornamentation and investment. The study concludes with a discussion of the contributions, limitations, and implications for future research on the topic.Item Open Access Gold catalysts supported on ceria doped by rare earth metals for water gas shift reaction: influence of the preparation method(2009) Andreeva, D.; Ivanov, I.; Ilieva, L.; Abrashev, M. V.; Zanella, R.; Sobczak, J. W.; Lisowski, W.; Kantcheva, M.; Avdeev, G.; Petrov, K.Gold catalysts based on ceria, doped by various RE metals (La, Sm, Gd, Yb, Y) were studied. The influence of the preparation methods on structure, properties and catalytic activity in the WGS reaction was investigated. The catalysts' supports were prepared using two different methods: co-precipitation (CP) and mechanochemical activation (MA). The catalysts were tested in a wide temperature interval without and after reactivation. All samples were characterized using a combination of X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), Raman spectroscopy (RS) and X-ray photoelectron spectroscopy (XPS) and TPR. It was found that the catalytic activity of MA catalysts is higher than CP ones. The gold catalysts based on ceria doped by Yb and Sm exhibited the highest activity. After reactivation in air the MA samples almost kept the WGS activity same, while the CP catalysts increased it. The catalysts of a single- and double-phase structure are formed as a result of CP and MA preparation, respectively. There are no big differences in the gold particles size (2-3 nm) depending on dopants and on the preparation techniques. The RS spectra analysis indicates that most probably the oxygen vacancies are adjacent to Me3+ dopant and the ceria structure seems to be better ordered than in the case of alumina as a dopant. There is no distinct correlation between reducibility and WGS activity. The XPS analysis disclose positively charged gold particles in addition to metallic gold within a surface region of fresh samples and only metallic gold on the samples after catalytic processing. There is no simple correlation between the concentration of Ce3+ in the samples and their WGS activity.Item Open Access Gold supported on ceria doped by Me3+ (Me = Al and Sm) for water gas shift reaction: Influence of dopant and preparation method(2010) Andreeva, D.; Kantcheva, M.; Ivanov, I.; Ilieva, L.; Sobczak, J. W.; Lisowski, W.Gold catalysts supported on ceria doped by Sm and Al were studied. The influence of the preparation method, as well as the nature of dopants on the structure, properties and WGS activity are investigated. The applied methods of preparation cause the modification of ceria in a different extent. In the sample prepared by co-precipitation (CP) and doped by Al, the vacancies are located within the bulk of ceria structure, whereas in the corresponding AuCeSmCP sample the vacancies are located most likely around Sm and the ceria structure seems to be better ordered than the Al doped ceria. There is no distinct correlation between the reducibility and WGS activity of the studied catalysts. The Au 4f XPS spectra of fresh samples reveal higher contribution of dispersed form of Au for Sm doped catalysts than for the corresponding Al doped samples. The Ce 3d XPS spectra disclose also a higher concentration of Ce3+ evaluated before the catalytic operation for Sm doped catalysts as compared with the Al doped fresh samples. The observations by "in situ" FT-IR spectroscopy agree well with the model of active sites and the, mechanism of the WGS reaction proposed recently by some of us. The amount of formate species observed on the AuCeSmCP is higher than that on the AuCeAlCP catalyst and parallels the catalytic activity. The higher concentration of active sites on the surface of the AuCeSmCP catalyst facilitates the dissociation of water.Item Open Access Graphene-gold supercapacitor as a voltage controlled saturable absorber for femtosecond pulse generation(Optical Society of America, 2016-02) Baylam, I.; Balci, O.; Kakenov, N.; Kocabas, C.; Sennaroglu, A.We report, for the first time to the best of our knowledge, use of a graphene-gold supercapacitor as a voltage controlled fast saturable absorber for femtosecond pulse generation. The unique design involving only one graphene electrode lowers the insertion loss of the device, in comparison with capacitor designs with two graphene electrodes. Furthermore, use of the high-dielectric electrolyte allows reversible, adjustable control of the absorption level up to the visible region with low bias voltages of only a few volts (0-2 V). The fast saturable absorber action of the graphene-gold supercapacitor was demonstrated inside a multipass-cavity Cr:forsterite laser to generate nearly transform-limited, sub-100 fs pulses at a pulse repetition rate of 4.51 MHz at 1.24 μm.
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