Browsing by Subject "Laser ablation"

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Open Access
2-nm laser-synthesized Si nanoparticles for low-power charge trapping memory devices
(IEEE, 2014-08) El-Atab, N.; Özcan, Ayşe; Alkış, Sabri; Okyay, Ali Kemal; Nayfeh, A.
In this work, the effect of embedding Silicon Nanoparticles (Si-NPs) in ZnO based charge trapping memory devices is studied. Si-NPs are fabricated by laser ablation of a silicon wafer in deionized water followed by sonication and filtration. The active layer of the memory was deposited by Atomic Layer Deposition (ALD) and spin coating technique was used to deliver the Si-NPs across the sample. The nanoparticles provided a good retention of charges (>10 years) in the memory cells and allowed for a large threshold voltage (Vt) shift (3.4 V) at reduced programming voltages (1 V). The addition of ZnO to the charge trapping media enhanced the electric field across the tunnel oxide and allowed for larger memory window at lower operating voltages. © 2014 IEEE.
Open Access
Compact 1.5-GHz intra-burst repetition rate Yb-doped all-PM-fiber laser system for ablation-cooled material removal
(OSA, 2017) Akçaalan, Önder; Kalaycıoğlu, Hamit; Elahi, Parviz; Deminskyi, Petro; İlday, Fatih Ömer
Summary form only given. Femtosecond (fs) laser pulse sources have become increasingly popular in the last decade as a result of their practical features, such as insensitivity to environmental variations, versatile designs, high power outputs. However, much of the progress is with non-integrated specialty fibers, which involve some compromise on these practical features. Monolithic fiber chirped pulse amplification (CPA) systems are very attractive for industrial and scientific applications due to the features such as compactness, reliability and robustness. Although fs fiber laser systems are powerful technologies for material and tissue processing, limited ablation rates and high energy are drawbacks. Recently, we identified a new regime of laser-material interaction, ablation cooled material removal [1], where the repetition rate has to be high enough so that the targeted spot size cannot cool down substantially by heat conduction which scales down ablation threshold by several orders of magnitude and reduces thermal effects to the bulk of the target. Here, we demonstrate a compact all-PM-fiber laser amplifier system with an intra-burst repetition rate of 1.5 GHz able to produce bursts ranging from 20-ns to 65-ns duration with 20 μJ to 80 μJ total energy, respectively, and pulses with up to 1 μJ individual energy at burst repetition rates ranging from 25 kHz to 200 kHz (Fig. 1(a)). The seed signal is generated by a home-built all-normal dispersion oscillator with a spectrum centered at 1035 nm and 20-nm (FWHM), 100 mW output and 385 MHz repetition rate (Fig. 1(b)). After the oscillator, rest of the system is built of polarization maintaining (PM) components and a single-mode pre-amplifier controls both dispersion and nonlinearity in the amplifier system. The pulses are stretched with a 110 m-long fiber after this pre-amplifier and raised to a repetition rate of 1.5 GHz by a multiplier. The signal is amplified again by a second single-mode pre-amplifier before converted into burst-mode via an acousto-optic modulator (AOM). Finally, a forward-pumped double-clad power amplifier, built of PM 10/125 Yb 1200 DC (nLight) fiber and pumped by a 18-W wavelength stabilized diode, boosts the optical power. To compress the pulses, a pair of 1200 line/mm transmission gratings is preferred to denser gratings to limit third order dispersion (TOD). Further, fiber lengths are shortened as much as possible to minimize nonlinear effects including Raman scattering and thus the power conversion efficiency is relatively low, around 20% for the power amplifier. The autocorrelation measurement for the compressed pulses indicates a width of ~250 fs (Fig. 1(d)). The amplified output spectrum of FWHM of 14 nm is shown in (Fig. 1(c)).
Open Access
Double ring firing single optical fiber deflector
(Institute of Electrical and Electronics Engineers Inc., 2019) Seymen, A. A.; Uzcengiz-Şimşek, Elif; Ӧzgür, E.; Ortaç, Bülend
We report a novel fabrication method of double ring firing single optical fiber deflector. The fiber deflector is fabricated as a convergent cone having two different cone angles, by conventional mechanical polishing. The two-angled conical fiber deflector geometry is formed in a single fiber tip, deflecting incoming laser light into two distinct circular rings. Two cone angles provide two deflection angles due to total internal reflection and refraction of the incoming laser light. We achieved two deflected circular beams at 60° and 85° with the cone angles of 56° and 72° at one single fiber deflector. The laser power is evenly split between two conical areas. The fabrication process of the fiber deflector does not involve any splicing or arc discharge process; thus, it is convenient, effective, and high-throughput.
Open Access
Generation of InN nanocrystals in organic solution through laser ablation of high pressure chemical vapor deposition-grown InN thin film
(Springer, 2012-07-27) Alkis, S.; Alevli, M.; Burzhuev, S.; Vural, H. A.; Okyay, Ali Kemal; Ortaç, B.
We report the synthesis of colloidal InN nanocrystals (InN-NCs) in organic solution through nanosecond pulsed laser ablation of high pressure chemical vapor deposition-grown InN thin film on GaN/sapphire template substrate. The size, the structural, the optical, and the chemical characteristics of InN-NCs demonstrate that the colloidal InN crystalline nanostructures in ethanol are synthesized with spherical shape within 5.9-25.3, 5.45-34.8, 3.24-36 nm particle-size distributions, increasing the pulse energy value. The colloidal InN-NCs solutions present strong absorption edge tailoring from NIR region to UV region.
Open Access
Generation of ultra-small InN nanocrystals by pulsed laser ablation of suspension in organic solution
(Springer Verlag, 2017-03) Kurşungöz, C.; U. Şimşek, E.; Tuzaklı, R.; Ortaç, B.
Nanostructures of InN have been extensively investigated since nano-size provides a number of advantages allowing applications in nanoscale electronic and optoelectronic devices. It is quite important to obtain pure InN nanocrystals (InN-NCs) to reveal the characteristic features, which gain interest in the literature. Here, we proposed a new approach for the synthesis of ultra-small hexagonal InN-NCs by using suspension of micron-sized InN powder in ethanol with pulsed laser ablation method. The liquid environment, laser energy and ablation time were optimized and a post-synthesis treatment, centrifugation, was performed to achieve InN-NCs with the smallest size. Besides, the micron-sized InN powder suspension, as a starting material, enabled us to obtain InN-NCs having diameters smaller than 5 nm. We also presented a detailed characterization of InN-NCs and demonstrated that the formation mechanism mainly depends on the fragmentation due to laser irradiation of the suspension.
Open Access
Gold nanoparticle / polymer nanofibrous composites by laser ablation and electrospinning
(Elsevier BV, 2011) Deniz, A. E.; Vural, H. A.; Ortaç, B.; Uyar, Tamer
Poly(vinylpyrolidone) (PVP) nanofibers incorporating gold nanoparticles (Au-NPs) were produced in combination with laser ablation and electrospinning techniques. The Au-NPs were directly synthesized in PVP solution by laser ablation and then, the electrospinning of PVP/Au-NPs solution was carried out for obtaining nanofibrous composites. The presence of Au-NPs in the PVP nanofibers was confirmed by SEM, TEM and EDX analyses. The SEM imaging elucidated that the electrospun PVP/Au-NPs nanofibers were bead-free having average fiber diameter of 810 ± 480 nm. The TEM imaging indicated that the Au-NPs were in spherical shape having diameters in the range of 5 to 20 nm and the Au-NPs were more or less dispersed homogeneously in the PVP nanofiber matrix. The FTIR study suggested the presence of molecular interactions between PVP matrix and the Au-NPs in the nanofibrous composites. The UV-Vis measurement confirmed the enhancement of the optical properties of the PVP/Au-NPs nanofibers in the solid state due to the surface plasma resonance effect of Au-NPs. © 2011 Elsevier B.V. All Rights Reserved.
Open Access
Laser synthesized gold nanoparticles for high sensitive strain gauges
(2013) Burzhuev, Salamat
Recently, the conduction properties of nanoparticle films have received great deal of attention due to their unique properties attributed to quantum tunneling effect. Quantum tunneling effect, highly dependent on quantum barrier height and width, is very attractive for sensor applications. Resistive strain gauges based on gold nanoparticle (Au-NP) films show high strain sensitivity. These strain gauges are applicable for miniature applications because of its size. In addition, this nanoparticle films could be also used for various applications such as pressure and vapor sensors. Clean surfaces of laser generated Au-NPs provide high tunneling decay constant. Therefore, these films are promising for high sensitive sensor applications. In our study, the Au-NPs were directly synthesized in deionized water by nanosecond laser ablation method. The clean surface, size and aggregate clusters of Au-NPs offer advantages for high sensitivity strain sensor. We prepared Au-NPs films on flexible PDMS substrate by using hands-on drop-cast method. To obtain high gauge factor, we also investigated the nanoparticle concentration on the thin films. Laser-generated AuNPs films demonstrated gauge factor of ∼300 for higher than 0.22% strain and ∼80 for the strain lower than 0.22%, which is favorably comparable to reported sensitivities for strain sensors based on Au-NPs. Mechanical characterizations for the prolonged working durations suggest long term stability of these strain sensors. We discuss several models describing conductance of Au-NP films in low and high strain regimes. To the best of our knowledge, the conduction of laser generated Au-NP films has not been studied up to date, and it is the first study that shows high strain sensitivity of these films. Au-NP films may be promising for sensor applications.
Open Access
Laser synthesized gold nanoparticles for high sensitive strain gauges
(Elsevier, 2013-12-01) Burzhuev, S.; Dana, A.; Ortac, B.
We demonstrate high strain sensitivity property of gold nanoparticle (Au-NP) thin films fabricated on flexible polydimethylsiloxane (PDMS) substrates. This behavior is attributed to quantum tunneling effect that is highly dependent on nanoparticle separation. Au-NPs were synthesized in water by nanosecond laser ablation method. The clean surface providing high tunneling decay constant, size of the Au-NPs and Au-NPs aggregate clusters offer advantages for high sensitivity strain sensor. We prepared Au-NPs films on flexible PDMS substrate by using hands-on drop-cast method. To obtain high gauge factor (g factor), we investigated the nanoparticles concentration on the substrate. Laser-generated Au-NPs films demonstrated g factor of ∼300 for higher than 0.22% strain and ∼80 for the strain lower than 0.22% strain, which is favorably comparable to reported sensitivities for strain sensors based on Au-NPs. Mechanical characterizations for the prolonged working durations suggest long term stability of the strain sensors. We discuss several models describing conductance of films in low and high strain regimes.
Open Access
Nanofibrous nanocomposites via electrospinning
(2011) Deniz, Ali Ekrem
In recent years, numerous studies have been reported for fabrication of composite nanofibers from polymeric and inorganic materials by using electrospinning method. In the first part of this study, TiO2 and ZnO inorganic nanofibers were produced by electrospinning from their precursors by using polymeric carrier matrix and their photocatalytic activity of these metal oxide nanofibers were studied. Moreover, electrospun TiO2 nanofibers were crushed into short nanofibers (TiO2-SNF) and embedded in electrospun polymeric nanofiber matrixes such as poly(methyl methacrylate) (PMMA), polyacrylonitrile (PAN), polyethylene terephthalate (PET), polycarbonate (PC) and polyvinylidene fluoride (PVDF). Different weight loading of TiO2-SNF ranging from 2% to 8% (w/w, respect to polymer) incorporated into PVDF nanofibrous matrix was applied and the structural and morphological changes along with their photocatalytic activities were also examined. In the second part, metallic nanoparticles produced by laser ablation method were incorporated into nanofibrous polymeric matrix by using electrospinning technique. For example, gold (Au) and silver (Ag) nanoparticles (NPs) were produced from their metallic sources by laser ablation method directly in the polymer solutions. The NPs/polymer mixtures were electrospun and surface plasmon resonance effect of Au-NPs and Ag-NPs on optical properties of the nanofibers was studied. In addition, germanium nanocrystals produced by means of laser ablation were mixed with PVDF polymer solution and consequently electrospun into composite polymeric nanofiber matrix.
Open Access
Nanosecond pulsed laser ablated sub-10 nm silicon nanoparticles for improving photovoltaic conversion efficiency of commercial solar cells
(Institute of Physics Publishing Ltd., 2017) Rasouli, H. R.; Ghobadi, A.; Ghobadi, T. G. U.; Ates, H.; Topalli, K.; Okyay, Ali Kemal
In this paper, we demonstrate the enhancement of photovoltaic (PV) solar cell efficiency using luminescent silicon nanoparticles (Si-NPs). Sub-10 nm Si-NPs are synthesized via pulsed laser ablation technique. These ultra-small Si nanoparticles exhibit photoluminescence (PL) character tics at 425 and 517 nm upon excitation by ultra-violet (UV) light. Therefore, they can act as secondary light sources that convert high energetic photons to ones at visible range. This down-shifting property can be a promising approach to enhance PV performance of the solar cell, regardless of its type. As proof-of-concept, polycrystalline commercial solar cells with an efficiency of ca 10% are coated with these luminescent Si-NPs. The nanoparticle-decorated solar cells exhibit up to 1.64% increase in the external quantum efficiency with respect to the uncoated reference cells. According to spectral photo-responsivity characterizations, the efficiency enhancement is stronger in wavelengths below 550 nm. As expected, this is attributed to down-shifting via Si-NPs, which is verified by their PL characteristics. The results presented here can serve as a beacon for future performance enhanced devices in a wide range of applications based on Si-NPs including PVs and LED applications.
Open Access
A near-infrared range photodetector based on indium nitride nanocrystals obtained through laser ablation
(IEEE, 2014) Tekcan, B.; Alkis, S.; Alevli, M.; Dietz, N.; Ortac, B.; Bıyıklı, Necmi; Okyay, Ali Kemal
We present a proof-of-concept photodetector that is sensitive in the near-infrared (NIR) range based on InN nanocrystals. Indium nitride nanocrystals (InN-NCs) are obtained through laser ablation of a high pressure chemical vapor deposition grown indium nitride thin film and are used as optically active absorption region. InN-NCs are sandwiched between thin insulating films to reduce the electrical leakage current. Under-1 V applied bias, the recorded photoresponsivity values within 600-1100-nm wavelength range are as high as (3.05 × 10-2) mA/W. An ultrathin layer of nanocrystalline InN thin film is, therefore, a promising candidate for NIR detection in large area schemes. © 2014 IEEE.
Open Access
Novel one-step synthesis of silica nanoparticles from sugarbeet bagasse by laser ablation and their effects on the growth of freshwater algae culture
(Elsevier, 2014) San, N. O.; Kurşungöz, C.; Tümtaş, Y.; Yaşa, Ö.; Ortac, B.; Tekinay, T.
Scientific research involving nanotechnology has grown exponentially and has led to the development of engineered nanoparticles (NPs). Silica NPs have been used in numerous scientific and technological applications over the past decade, necessitating the development of efficient methods for their synthesis. Recent studies have explored the potential of laser ablation as a convenient way to prepare metal and oxide NPs. Due to its high silica content, low cost, and widespread availability, sugarbeet bagasse is highly suitable as a raw material for producing silica NPs via laser ablation. In this study, two different NP production methods were investigated: laser ablation and NaOH treatment. We developed a novel, one-step method to produce silica NPs from sugarbeet bagasse using laser ablation, and we characterized the silica NPs using environmental scanning electron microscopy (ESEM), energy dispersive spectrometry (EDS), dynamic light scattering (DLS), transmission electron microscopy (TEM), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. EDS analysis and XPS confirmed the presence of silica NPs. The NPs produced by laser ablation were smaller (38-190 nm) than those produced by NaOH treatment (531-825 nm). Finally, we demonstrated positive effects of silica NPs produced from laser ablation on the growth of microalgae, and thus, our novel method may be beneficial as an environmentally friendly procedure to produce NPs.
Open Access
A plasmonic enhanced photodetector based on silicon nanocrystals obtained through laser ablation
(Institute of Physics Publishing, 2012-10-18) Alkis, S.; Oruç, F. B.; Ortaç, B.; Koşger, A. C.; Okyay, Ali Kemal
We present a proof-of-concept photodetector which is sensitive in the visible spectrum. Silicon nanocrystals (Si-NCs) obtained by laser ablation are used as the active absorption region. Si-NC films are formed from a polymeric dispersion. The films are sandwiched between thin insulating films to reduce the electrical leakage current. Furthermore, Ag nanoparticles are integrated with the photodetector to enhance the visible response using plasmonic effects. The measured photocurrent is resonantly enhanced, which is explained in terms of enhanced local fields caused by localized plasmons. The UV-vis spectrum of Ag nanoparticles is also measured to verify the resonance.
Open Access
Rapid fabrication of microfluidic PDMS devices from reusable PDMS molds using laser ablation
(Institute of Physics Publishing, 2016) Isiksacan, Z.; Guler, M. T.; Aydogdu, B.; Bilican, I.; Elbuken, C.
The conventional fabrication methods for microfluidic devices require cleanroom processes that are costly and time-consuming. We present a novel, facile, and low-cost method for rapid fabrication of polydimethylsiloxane (PDMS) molds and devices. The method consists of three main fabrication steps: female mold (FM), male mold (MM), and chip fabrication. We use a CO2 laser cutter to pattern a thin, spin-coated PDMS layer for FM fabrication. We then obtain reusable PDMS MM from the FM using PDMS/PDMS casting. Finally, a second casting step is used to replicate PDMS devices from the MM. Demolding of one PDMS layer from another is carried out without any potentially hazardous chemical surface treatment. We have successfully demonstrated that this novel method allows fabrication of microfluidic molds and devices with precise dimensions (thickness, width, length) using a single material, PDMS, which is very common across microfluidic laboratories. The whole process, from idea to device testing, can be completed in 1.5 h in a standard laboratory.
Open Access
Response of porcine articular cartilage to irradiation by an ultrafast, burst-mode laser
(Optical Society of America (OSA), 2019) Dzelzainis, T.; Hammouti, S.; Prickaerts, M.; Cassidy, K.; İlday, F. Ömer; Kalaycıoğlu, Hamit; Yavaş, S.; Karamuk, Ş.; Golaraei, A.; Barzda, V.; Akens, M.; Lilge, L.; Marjoribanks, R.
Plasma-mediated ablation by ultrafast pulses is generally considered to be a material-independent process. We show that, in certain circumstances, this assumption may be invalid. Physical processes involved and the impact on applications are discussed.
Open Access
Synthesis of blue-shifted luminescent colloidal GaN nanocrystals through femtosecond pulsed laser ablation in organic solution
(Springer Netherlands, 2016-05) Demirel, A.; Öztaş T.; Kurşungöz, C.; Yılmaz, İ.; Ortaç, B.
We demonstrate the synthesis of GaN nanocrystals (NCs) with the sizes of less than the doubled exciton Bohr radius leading quantum confinement effects via a single-step technique. The generation of colloidal GaN nanoparticles (NPs) in organic solution through nanosecond (ns) and femtosecond (fs) pulsed laser ablation (PLA) of GaN powder was carried out. Ns PLA in ethanol and polymer matrix resulted in amorphous GaN-NPs with the size distribution of 12.4 ± 7.0 and 6.4 ± 2.3 nm, respectively, whereas fs PLA in ethanol produced colloidal GaN-NCs with spherical shape within 4.2 ± 1.9 nm particle size distribution. XRD and selected area electron diffraction analysis of the product via fs PLA revealed that GaN-NCs are in wurtzite structure. Moreover, X-ray photoelectron spectroscopy measurements also confirm the presence of GaN nanomaterials. The colloidal GaN-NCs solution exhibits strong blue shift in the absorption spectrum compared to that of the GaN-NPs via ns PLA in ethanol. Furthermore, the photoluminescence emission behavior of fs PLA-generated GaN-NCs in the 295–400 nm wavelength range is observed with a peak position located at 305 nm showing a strong blue shift with respect to the bulk GaN.
Open Access
Terahertz time-domain study of silver nanoparticles synthesized by laser ablation in organic liquid
(IEEE Microwave Theory and Techniques Society, 2016-07) Koral, C.; Ortaç, B.; Altan, H.
We report the investigation of laser-synthesized Ag nanoparticles (Ag-NPs) in an organic liquid environment by using terahertz time-domain spectroscopy (THz-TDS) technique. Colloidal Ag-NPs with an average diameter of 10 nm in two-propanol solution through nanosecond pulsed laser ablation were synthesized. THz-TDS measurements were performed on different volumetric concentration of Ag-NPs suspensions placed in 2-mm path length quartz cuvette. Due to the dispersive and highly absorptive nature of the nano liquids, an approach based on extracting the optical properties through the changes in amplitude and phase solely around the main peak of THz waveform is developed. This approach allowed for an accurate estimation of the complex refractive index of the Metallic-NPs suspension for the different prepared volumetric concentrations. In addition, using Maxwell-Garnett theory, the NP concentration is also extracted. This method shows that the time-domain nature of the THz pulse measurement technique is extremely useful in instances where slight variations in highly dispersive samples need to be investigated.
Open Access
Toxicity of internalized laser generated pure silver nanoparticles to the isolated rat hippocampus cells
(SAGE, 2017-02) Kursungoz, C.; Taş, S. T.; Sargon, M. F.; Sara, Y.; Ortaç, B.
Silver nanoparticles (AgNPs) are the most commonly used nanoparticles (NPs) in medicine, industry and cosmetics. They are generally considered as biocompatible. However, contradictory reports on their biosafety render them difficult to accept as 'safe'. In this study, we evaluated the neurotoxicity of direct AgNP treatment in rat hippocampal slices. We produced pure uncoated AgNPs by a pulsed laser ablation method. NP characterization was performed by Ultraviolet (UV) visible spectrophotometer, scanning electron microscope, transmission electron microscope (TEM) and energy-dispersive X-ray spectroscopy. Rat hippocampal slices were treated with AgNPs for an hour. AgNP exposure of hippocampal tissue resulted in a significant decrease in cell survival in a dose-dependent manner. Our TEM results showed that AgNPs were distributed in the extracellular matrix and were taken into the cytoplasm of the neurons. Moreover, we found that only larger AgNPs were taken into the neurons via phagocytosis. This study showed that the pure AgNPs produced by laser ablation are toxic to the neural tissue. We also found that neurons internalized only the large NPs by phagocytosis which seems to be the major mechanism in AgNP neurotoxicity.