Pulsed Laser Ablation (PLA) method

The emerging nanoscience results in the production of nanoparticles having the potential to be used in a number of different applications including medical, biological, electronic, and industrial fields. Nanometer scale provides materials unique physicochemical properties that are completely different than their bulk counterparts. Most NP synthesis techniques, such as physical vapor deposition, precipitation, solvothermal/hydrothermal methods, and sol–gel methods (e.g., sol–gel combustion), are expensive and complex and offer only limited control over particle size and size uniformity. One of the top-down nanoparticle production methods, pulsed-laser ablation (PLA) of solids in solution offers a prominent way for the nanoparticle production due to its versatility and low cost. Moreover, synthesis of NPs by laser ablation shown the potential feasibility of laser ablation for large-scale synthesis applications.

  • There has been a lot of attention on group III-nitride nanostructures for the nanoscale applications. Among those nanostructures, due to their outstanding electronic and optoelectronic properties such as high electron mobility, high saturation velocity because of their low effective mass, small band gap, terahertz/near-infrared emission, and high surface electron accumulation, indium nitride nanoparticles (InN NPs) have an increasing interest. There are a number of nanoparticle production methods to obtain the nanoscale InN crystal. However, all these methods include complex chemical procedures and the use of various precursor chemicals that are critical for the purity of the system. Pulsed laser ablation (PLA) method is a promising method for nanoparticle production. A number of novel semiconductor, nitride, and metal and metal oxide nanoparticles can be successfully produced by the PLA method. Compared to other methods, PLA, offers a versatile way of producing colloidal, highly pure, and agent-free nanocrystals.

    S. Alkis, M. Alevli, S. Burzhuev, H. A. Vural, Ali K. Okyay and B. Ortaç Journal of Nanoparticle Research, vol. 14, pp. 1048 (2012)

    Blue luminescent colloidal silicon nanocrystals (Si-NCs) were produced in a two-stage process. In the first step, synthesis of Si-NCs was achieved by femtosecond pulsed laser ablation of a silicon wafer, which was immersed in deionized water. The size and the structural and the chemical characteristics of colloidal Si-NCs were investigated by TEM and EDAX analyses, and it is found out that the Si-NCs are in spherical shape and the particle diameters are in the range of 5−100 nm. In the second step, ultrasonic waves and filtering chemical-free post-treatment of colloidal Si-NCs solution was performed to reduce the particle size. High-resolution TEM (HRTEM) studies on post-treated colloidal solution clearly show that small (1−5.5 nm in diameter) Si-NCs were successfully produced. Raman spectroscopy results clearly confirms the generation of Si nanoparticles in the crystalline nature, and the Raman scattering study of post-treated Si-NCs confirms the reduction of the particle size. The UV−vis absorption and photoluminescence (PL) spectroscopy studies elucidate the quantum confinement effect of Si-NCs on the optical properties. The colloidal Si-NCs and post-treated Si-NCs solutions present strong absorption edge shifts toward UV region. Broadband PL emission behavior is observed for the initial colloidal Si-NCs, and the PL spectrum of post-treated Si-NCs presents a blue-shifted broadband PL emission behavior due to the particle size reduction effect.

    S. Alkis, Ali K. Okyay and B. Ortaç Journal of Physical Chemistry C, vol. 116, pp. 3432-3436 (2012)

    Two-dimensional MoS2 nanosheets (2D MoS2 NS) and fullerene-like MoS2 nanostructures (3D MoS2 NS) with varying sizes are synthesized by nanosecond laser ablation of hexagonal crystalline 2H-MoS2 powder in organic solution (methanol). Structural, chemical, and optical properties of MoS2 NS are characterized by optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman and UV−vis−near infrared absorption spectroscopy techniques. Results of the structural analysis show that the obtained MoS2 NS mainly present a layered morphology from micrometer to nanometer sized surface area. Detailed analysis of the product also proves the existence of inorganic polyhedral fullerene-like 3D MoS2 NS generated by pulsed laser ablation in methanol. The possible factors which may lead to formation of both 2D and 3D MoS2 NS in methanol are examined by ab initio calculations and shown to correlate with vacancy formation. The hexagonal crystalline structure of MoS2 NS was determined by XRD analysis. In Raman spectroscopy, the peaks at 380.33 and 405.79 cm−1 corresponding to the E1 2g and A1g phonon modes of MoS2 were clearly observed. The colloidal MoS2 NS solution presents broadband absorption edge tailoring from the UV region to the NIR region. Investigations of MoS2 NS show that the one-step physical process of pulsed laser ablation−bulk MoS2 powder interaction in organic solution opens doors to the formation of “two scaled” micrometer- and nanometer-sized layered and fullerene-like morphology MoS2 structures.

    T. Oztas, H. S. Sen, E. Durgun and B. Ortaç Journal of Physical Chemistry C, vol. 118, pp. 30120–30126 (2014)

    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.

    N. O. San, C. Kurşungöz, Y. Tümtaş, Ö. Yaşa, B. Ortaç and T. Tekinay Particuology, vol. 17, pp. 29-35 (2014)

  • 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.

    A. E. Deniz, H. A. Vural, B. Ortaç and T. Uyar Materials Letters, vol. 65, pp. 2941-2943 (2011)

    The photoluminescent germanium nanocrystals (Ge-NCs) were successfully incorporated into electrospun polymeric nanofiber matrix in order to develop photoluminescent nanofibrous composite web. In the first step, the synthesis of Ge-NCs was achieved by nanosecond pulsed laser ablation of bulk germanium wafer immersed in organic liquid. The size, the structural and the chemical characteristics of Ge-NCs investigated by TEM, XPS, XRD and Raman spectroscopy revealed that the Ge-NCs were highly pure and highly crystalline having spherical shape within 3–20 nm particle size distribution. In the second step, Ge-NCs were mixed with polyvinyl alcohol (PVA) polymer solution, and then, Ge-NC/PVA nanofibers were obtained via electrospinning technique. The electrospinning of Ge-NCs/PVA nanoweb composite structure was successful and bead-free Ge-NCs/PVA nanofibers having average fiber diameter of 185 ± 40 nm were obtained. The STEM analysis of the electrospun Ge-NCs/PVA nanofibers elucidated that the Ge-NCs were distributed homogeneously in the polymeric nanofiber matrix. The UV–Vis absorption and photoluminescence spectroscopy studies indicated the quantum confinement effect of Ge-NCs on the optical properties of the electrospun Ge-NCs/PVA nanoweb.

    B. Ortaç F. Kayacı, H. A. Vural, A. E. Deniz and T. Uyar Reactive and Functional Polymers, vol. 73, pp. 1262-1267 (2013)

  • 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.

    S. Burzhuev, A. Dana and B. Ortaç Sensors & Actuators: A. Physical, vol. 203, pp. 131-136 (2013)

    In this work, the fabrication of charge trapping memory cells with laser-synthesized indium-nitride nanoparticles (InN-NPs) embedded in ZnO charge trapping layer is demonstrated. Atomic layer deposited Al2O3 layers are used as tunnel and blocking oxides. The gate contacts are sputtered using a shadow mask which eliminates the need for any lithography steps. High frequency C-Vgate measurements show that a memory effect is observed, due to the charging of the InN-NPs. With a low operating voltage of 4 V, the memory shows a noticeable threshold voltage (Vt) shift of 2 V, which indicates that InN-NPs act as charge trapping centers. Without InN-NPs, the observed memory hysteresis is negligible. At higher programming voltages of 10 V, a memory window of 5 V is achieved and the Vt shift direction indicates that electrons tunnel from channel to charge storage layer.

    N. El-Atab, F. Cimen, S. Alkis, B. Ortaç, M. Alevli, N. Dietz, A. K. Okyay and A. Nayfeh Applied Physics Letters, vol. 104, , pp. 253106-261105-4 (2014)

    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.
    B. Tekcan, S. Alkis, M. Alevli, N. Dietz, B. Ortaç, N. Biyikli and A. K. Okyay IEEE Electron Device Letters, vol. 35, pp. 936-938 (2014)

    We report on the development of UV range photodetector based on molybdenum disulfide nanocrystals (MoS2-NCs). The inorganic MoS2- NCs are produced by pulsed laser ablation technique in deionized water and the colloidal MoS2-NCs are characterized by transmission electron microscopy, Raman spectroscopy, X-ray diffraction and UV/VIS absorption measurements. The photoresponse studies indicate that the fabricated MoS2- NCs photodetector (MoS2-NCs PD) operates well within 300-400 nm UV range, with diminishing response at visible wavelengths, due to the MoS2- NCs absorption characteristics. The structural and the optical properties of laser generated MoS2-NCs suggest promising applications in the field of photonics and optoelectronics.
    S. Alkis, T. Öztaş, L. E. Aygün, F. Bozkurt, A. K. Okyay and B. Ortaç Optics Express, vol. 20, pp. 21815-21820 (2012)

    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.
    S. Alkis, F. B. Oruç, B. Ortaç, A. C. Koşger and A. K. Okyay Journal of Optics, vol. 14, pp. 125001 (2012)

  • The present study investigates and models the effect of laser ablated silver nanoparticles (AgNPs) on the development of the aquatic macrophyte Lemna minor. Toxic effects of five different AgNP concentrations (8, 16, 32, 96 and 128 lg L1 ) on L. minor were recorded over seven days under simulated natural conditions. Biosorption of AgNPs by L. minor was modeled using four sorption isotherms, and the sorption behavior was found to agree most closely with the Langmuir–Freundlich model (R2 = 0.997). While toxic effects of AgNPs could be observed in all models and concentrations, the greatest increase in toxicity was in the 8–32 lg L1 range. Dry weight- and frond number-based inhibition experiments suggest that growth inhibition does not necessarily scale with AgNP concentration, and that slight fluctuations in inhibition rates exist over certain concentration ranges. Very close fits (R2 = 0.999) were obtained for all removal models, suggesting that the fluctuations are not caused by experimental variation. In addition, L. minor was found to be a successful bioremediation agent for AgNPs, and displayed higher removal rates for increasing AgNP doses. FT-IR spectroscopy suggests that carbonyl groups are involved in AgNP remediation.
    E. Üçüncü, A. D. Özkan, C. Kurşungöz, Z. E. Ülger, T. Tekinay, B. Ortaç and E. Tunca Chemosphere, vol. 108, pp. 251-257 (2014)