Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session H25: Focus Session: Probing and Modifying Materials with Lasers I |
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Sponsoring Units: DMP Chair: Michael Kelley, College of William and Mary Room: 327 |
Tuesday, March 17, 2009 8:00AM - 8:36AM |
H25.00001: Advances in micro/nano scale materials processing by ultrafast lasers Invited Speaker: Materials processing by ultrafast lasers offers several attractive possibilities for micro/nano scale applications based on surface and in bulk laser induced modifications. The origin of these applications lies in the reduction of undesirable thermal effects, the non-equilibrium surface and volume structural modifications which may give rise to complex and unusual structures, the supression of photochemical effects in molecular substrates, the possibility of optimization of energy dissipation by temporal pulse shaping and the exploitation of filamentation effects. Diverse applications will be discussed, including the development and functionalization of laser engineered surfaces, the laser transfer of biomolecules and the functionalization of 3D structures constructed by multiphoton stereolithography. Two examples will be presented in this context: A new approach for the development of superhydrophobic, self-cleaning surfaces [1,2] and the fabrication of functional scaffolds for tissue engineering applications [3-5]. \\[4pt] References: \\[0pt] [1] V. Zorba et al., ``Biomimetic artificial surfaces quantitatively reproduce the water repellency of a Lotus leaf'', Advanced Materials 20, 4049 (2008).\\[0pt] [2] V. Zorba et al., ``Tailoring the wetting response of silicon surfaces via fs laser structuring'', Applied Physics A 93, 819 (2008).\\[0pt] [3] V. Dinca et al., ``Quantification of the activity of biomolecules in microarrays obtained by direct laser transfer'', Biomedical Microdevices 10, 719 (2008).\\[0pt] [4] B. Hopp et al., ``Laser-based techniques for living cell pattern formation'', Applied Physics A 93, 45 (2008).\\[0pt] [5] V. Dinca et al., ``Directed three-dimensional patterning of self-assembled peptide fibrils'', Nano Letters 8, 538 (2008). [Preview Abstract] |
Tuesday, March 17, 2009 8:36AM - 8:48AM |
H25.00002: Positional Accuracy in Optical Trap-Assisted Nanolithography Craig B. Arnold, Euan McLeod The ability to directly print patterns on size scales below 100 nm is important for many applications where the production or repair of high resolution and density features are important. Laser-based direct-write methods have the benefit of quickly and easily being able to modify and create structures on existing devices, but feature sizes are conventionally limited by diffraction. In this presentation, we show how to overcome this limit with a new method of probe-based near-field nanopatterning in which we employ a CW laser to optically trap and manipulate dispersed microspheres against a substrate using a 2-d Bessel beam optical trap. A secondary, pulsed nanosecond laser at 355 nm is directed through the bead and used to modify the surface below the microsphere, taking advantage of the near-field enhancement in order to produce materials modification with feature sizes under 100 nm. Here, we analyze the 3-d positioning accuracy of the microsphere through analytic modeling as a function of experimental parameters. The model is verified in all directions for our experimental conditions and is used to predict the conditions required for improved positional accuracy. [Preview Abstract] |
Tuesday, March 17, 2009 8:48AM - 9:00AM |
H25.00003: 3D photofabrication by femtosecond laser pulses and its applications in biomedicine. Aleksandr Ovsianikov, Xiao Shizhou, Mangirdas Malinauskas, Boris Chichkov Two-photon polymerization (2PP) is a novel laser-based microstructuring technique. In this approach, the multiphoton absorption of femtosecond laser pulses is used to induce a highly localised chemical reaction leading to a photopolymerization of the material. By moving the laser focus in 3D the trace of modified material is created. In the next step, the unmodified material is removed by an appropriate developer, and the fabricated structure is revealed. Therefore, fabrication of any computer generated 3D structure by ''direct laser recording'' into the volume of photosensitive material is possible. Nonlinear nature of the interaction allows true 3D microfabrication and realisation of structures with submicrometer resolution. Recently, we studied possible applications of 2PP technique in biomedicine. It is a very attractive technology for the fabrication of drug delivery systems and medical implants. Application of 2PP in tissue engineering provides possibility to fabricate series of exactly identical scaffolds. Therefore, it is possible to conduct systematic studies of cell interactions in 3D environment. In this contribution, our recent advances in two-photon activated laser processing, properties of applied materials, and applications of this technology are discussed. [Preview Abstract] |
Tuesday, March 17, 2009 9:00AM - 9:12AM |
H25.00004: Single-pulse fabrication of deep vertical nano-holes with a microjoule~femtosecond laser. Lloyd M. Davis, Yelena V. White, Xiaoxuan Li, Zbigniew Sikorski, William H. Hofmeister When a single energetic 200-femtosecond laser pulse is tightly focused onto the surface of a dielectric material, Zener (tunnelling) ionization and Zener-seeded saturation avalanche ionization cause a plasma to be formed at the surface. The tail of the pulse reflects from the plasma so that the resultant damage is typically shallow. However, we have found that when the laser pulse is focused with negative spherical aberration, holes exceeding 11 microns in depth and with diameters at the surface of only 200---500 nm may be created. A simple acetate sample replication technique is used to estimate the dimensions of the holes. The validity of the replication technique for characterizing such high-aspect-ratio features is confirmed by focused ion-beam sectioning of holes followed by visualization with a scanning electron microscope. We discuss physical processes that may be responsible for the creation of such deep nano-holes, including the role of self-focusing of the laser beam, and the possibility of acceleration of electrons along the direction of the laser beam into the hole. Applications, including direct laser writing of vertical channels for nanofluidic devices, are discussed. Related research on femtosecond laser machining of diamond is also presented. [Preview Abstract] |
Tuesday, March 17, 2009 9:12AM - 9:48AM |
H25.00005: Optical Bulk Metamaterials Invited Speaker: Metamaterials are artificially designed subwavelength composites that possess extraordinary properties not existing in naturally occurring materials. In particular, they can alter the propagation of electromagnetic waves resulting in negative refraction, sub-wavelength focusing, and transmission of sub-wavelength information over a finite distance. Such unusual properties can be obtained by a careful design of the metal-dielectric composites on a deep sub-wavelength scale. The metamaterials may have profound impact in wide range of applications such as nano-scale imaging, nanolithography, and integrated nano photonics. I will discuss a few recent experiments demonstrating intriguing phenomena associated with Metamaterials. These include sub-diffraction limit imaging and focusing, low loss negative refraction and imaging in bulk optical metamaterials, and Negative-index Metamaterials (NIM) exhibiting negative phase propagation that can be accessed from free-space. I'll also discuss nano plasmonics for imaging and bio-sensing. [Preview Abstract] |
Tuesday, March 17, 2009 9:48AM - 10:00AM |
H25.00006: Coloration of single crystal ZnO with ultraviolet laser irradiation Enamul Khan, S.C. Langford, J.T. Dickinson Many dielectric crystals color in the visible region of the spectrum when exposed to intense ultraviolet light such as excimer laser irradiation. In the alkali and alkaline earth halides, the decay of self-trapped excitons produces strongly absorbing defects. We were recently surprised to see single crystal ZnO darken dramatically during exposure to 193-nm ArF excimer laser radiation. ZnO is a wide bandgap (3.44 eV) semiconductor of significant technological interest. The increase in absorption is very broadband, extending from the bandgap into the infrared, and appears nearly black or grey. We present convincing evidence that this color is due to metallic zinc nanoparticles residing on the surface of the irradiated region. As expected, the laser fluence has considerable impact on the size, number, and spatial distribution of these nanoparticles. We propose a model for production of metallic nanoparticles on the surface. [Preview Abstract] |
Tuesday, March 17, 2009 10:00AM - 10:12AM |
H25.00007: Generation of point defects in femtosecond laser interactions with Cr targets Eaman Tahir, Zhibin Lin, Leonid Zhigilei The mechanisms and driving forces responsible for the generation of point defects (vacancies and interstitials) in femtosecond laser interactions with Cr target are investigated in atomic-scale simulations. Two series of simulations are performed. In the first set of simulations, the processes induced by 200 fs laser pulse irradiation of a bulk Cr target are studied with a computational model that combines the classical molecular dynamic method with a continuum description of the laser excitation of conduction band electrons, electron-phonon coupling, and electron heat conduction. The distribution of point defects in the surface regions of irradiated targets is analyzed for a broad range of laser fluences, covering the regimes of surface melting, photomechanical spallation, and ablation. To investigate the relative contributions of the thermally-activated generation of vacancy-interstitial pairs and the production of the vacancies during the solidification process, the second series of simulations of solidification at fixed temperatures below the melting point is performed. The densities of vacancies generated under different undercooling conditions are related to the distributions observed in laser-irradiated targets. The implications of the computational predictions for atomic mixing and damage accumulation in multi-pulse irradiation regime are discussed. [Preview Abstract] |
Tuesday, March 17, 2009 10:12AM - 10:24AM |
H25.00008: Nanostructuring of thin gold films by femtosecond laser-induced melt dynamics Arseniy Kuznetsov, Jurgen Koch, Boris Chichkov Femtosecond laser irradiation of thin gold films with fluences close to the ablation threshold induces formation of various nanostructures on the film surface [1-3]. These structures are formed due to laser-induced melting of gold and redistribution of the melted material from the edges into the center of the irradiated region. Shape of the created structures can be controlled by varying the laser intensity distribution on the gold film surface. It is shown that the sizes of the produced structures can be below than 100 nm. In this paper, a study of laser-induced molten material dynamics is presented. Analysis of the structural shapes produced with different laser intensity distributions and dynamical reflection measurements allow clarifying mechanisms of the structure formation. Possible applications of this nanostructuring method are discussed. \\[3pt] [1] F. Korte, J. Koch, B.N. Chichkov, Appl. Phys. A 79 (2004), pp. 879-881. \\[0pt] [2] J.Koch, F. Korte, T. Bauer, C. Fallnich, A. Ostendorf, B.N. Chichkov, Appl. Phys. A 81 (2005), pp. 325-328. \\[0pt] [3] A.I. Kuznetsov, J. Koch, B.N. Chichkov, Appl. Phys. A (2008), DOI 10.1007/s00339-008-4859-6. [Preview Abstract] |
Tuesday, March 17, 2009 10:24AM - 10:36AM |
H25.00009: Laser-diffraction-assisted ordering effects in nano-quasipercolated silver thin films. E. Haro-Poniatowski, J. C. Alonso-Huitron, C. Acosta-Zepeda, M. C. Acosta-Garcia, N. Batina Nanostructured silver thin films in a quasipercolated state are used as the starting morphology for inducing changes in shape and ordering effects by pulsed laser irradiation with a Nd:YAG laser (355 nm) [1,2]. The complex nanostructures are transformed into nanospheres which in turn are ordered in regular patterns when irradiated through a diffractive element such as a slit or a pinhole. The samples are deposited onto TEM grids by the pulsed laser deposition technique. These transformations are subsequently characterized by transmission electron microscopy and by atomic force microscopy. The observed effects are explained using Fresnel diffraction theory. Excellent agreement with the experimental results are obtained. [1] E. Haro-Poniatowski et al. Appl. Phys. Lett. 87, 143103, 2005 [2] E. Haro-Poniatowski et al. Radiation Effects {\&} Defects in Solids 162, 491-499 (2007) [Preview Abstract] |
Tuesday, March 17, 2009 10:36AM - 10:48AM |
H25.00010: Examining Femtosecond Laser Induced Plasma Dynamics via Ultrafast Electron Shadow Imaging Junjie Li, Richard Clinite, Xuan Wang, Jim Cao, Zhaoyang Chen, Samuel Mao We report a study of the dynamics of plasma creation and evolution in real time using a pulsed electron beam to create two-dimensional shadow images of the plasma plume. Due to the electron beam's sensitivity to charge, the dynamics of electric fields and charge motion during the earliest stage of laser ablation of Copper plate were directly measured by taking snapshots of the plasma shadow images. Based on a dipole field assumption, a multiplying magnitude of Q(total charge), d(average electrons' distance from surface), and t(duration time of field) is obtained, Q*d*t $\sim $ 12*10$^{-8}$ e*m*s under 6.8*10$^{12}$W/cm$^{2}$ laser power on 0.3mm diameter area, moreover, most electrons which are initially emitted retract back in 1 to 2 ps after laser pulse. The results provide new information about multi-photon emission and charge motion during intense laser material interaction. [Preview Abstract] |
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