Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session T27: Focus Session: Pulsed Laser Deposition of Electronic and Photonic Thin Films and Nanostructures |
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Sponsoring Units: FIAP Chair: R. D. Vispute, University of Maryland, College Park Room: 329 |
Wednesday, March 18, 2009 2:30PM - 3:06PM |
T27.00001: Plasma Energetic in Pulsed Laser Deposition and Pulsed Electron Deposition Invited Speaker: Surface bombardment by energetic particles strongly affects thin film growth and allows surface processing under non-thermal equilibrium conditions. Deposition techniques enabling energy control can effectively manipulate the microstructure of the film and tune the resulting mechanical, electrical and optical properties. At the high power densities used for depositing stoichiometric films in the case pulsed ablation techniques such as Pulsed Laser Deposition (PLD) and Pulsed Electron Deposition (PED), the initial energetic s of the material flux are typically in the range of 100s of eV, much higher than the optimal values ($\leq$ 10 eV) required for high quality film growth. To overcome this problem and to facilitate particle energy transformation from the original as-ablated to the one optimal for film growth, one needs to carefully select the ablation conditions, conditions for material flux propagation through a process gas (or vacuum)and location of the growth surface (substrate) within this flux. In this talk, I will discuss the energetics of the propagating materials flux in the case of PLD and PED, and identify parameters that require critical control for realizing optimum thin film growth. As an example, growth optimization of epitaxial GaN films is provided. PED is complementary to PLD and exhibits an important ability to ablate materials that are transparent to laser wavelengths typically used in PLD. Some examples include wide band gap materials such as SiO2, Al2O3, MgO etc. Both PLD and PED features can be integrated within a single deposition module. PLD-PED systems enable in-situ deposition of a wide range of materials required for exploring the next generation of complex structures that incorporate metals, complex dielectrics, ferroelectrics, semiconductors and glasses. [Preview Abstract] |
Wednesday, March 18, 2009 3:06PM - 3:18PM |
T27.00002: Interface-controlled thin film growth of conjugated polymers via pulsed laser deposition R.K. Gupta, K. Ghosh, Suchi Guha Matrix-assisted pulsed laser evaporation, a derivative of pulsed laser deposition (PLD), is an alternative method of depositing polymer and biomaterial films that allows homogenous film coverage of high molecular weight organic materials for a layer-by-layer growth without any laser induced damage. Polyfluorene (PF) -based conjugated polymers have attracted considerable attention in blue-emitting displays. Di-octyl substituted polyfluorene (PF8), its copolymers, and thiophene- based polymers were deposited as thin films using matrix- assisted PLD by employing a KrF excimer laser. The optical and structural properties of these films are compared with spincoated films via Raman spectroscopy, absorption and photoluminescence. The Raman spectra of both PLD and spincoated films are similar indicating that the polymer films deposited via PLD maintain their molecular structure. We further discuss the application of interface-controlled PLD grown films in metal-insulator-semiconductor diodes and field-effect transistors. [Preview Abstract] |
Wednesday, March 18, 2009 3:18PM - 3:30PM |
T27.00003: Bi$_{0.4}$Ca$_{0.6}$MnO$_{3 }$Epitaxial Thin Films on Silicon for Electronic and Photonic Applications Vera Smolyaninova, Grace Yong, Benjamin Hofmann, Rajeswari Kolagani, Yong Liang Thin films of rare-earth manganese oxides (manganites) are usually grown on oxide substrates. It is more challenging to grow thin films of these materials on technologically versatile silicon. Upon illumination with visible light, the resistivity of Bi$_{0.4}$Ca$_{0.6}$MnO$_{3 }$epitaxial thin films fabricated via PLD on oxide substrates decreases significantly in a wide temperature range due to the destruction of charge ordering. This makes Bi$_{0.4}$Ca$_{0.6}$MnO$_{3 }$thin films attractive for potential photonic and opto-electronic device applications. Having in mind device applications, we have extended our studies to Bi$_{0.4}$Ca$_{0.6}$MnO$_{3 }$epitaxial thin films grown on Si (001) with different buffer layers. The advantages of different buffer layer schemes on Si (001) will be discussed. Influence of deposition and annealing conditions on film photoresponse will be reported. Photoinduced and current induced effects in films grown on oxide substrates and on buffered Si substrates will be compared. [Preview Abstract] |
Wednesday, March 18, 2009 3:30PM - 3:42PM |
T27.00004: Photoinduced effects in Bi$_{1-x}$Ca$_{x}$MnO$_{3}$ thin films with different oxygen content Grace Yong, Rajeswari Kolagani, Khim Karki, Benjamin Hofmann, Vera Smolyaninova Doped rare-earth manganese oxides (manganites) attract interest due to a variety of electronic, magnetic, and orbital states and their drastic response to application of modest external fields. A photoinduced insulator to conductor transition in thin films of Bi$_{0.4}$Ca$_{0.6}$MnO$_{3 }$ associated with melting of the charge ordering [1] is especially interesting for potential photonic and opto-electronic device applications. From this point of view it is important to know what factors influence the photoinduced effects. We have found that oxygen content of Bi$_{0.4}$Ca$_{0.6}$MnO$_{3}$ thin films significantly modify conductive, structural and photoinduced properties. The role of growing and annealing conditions will be discussed. The change in magnitude and lifetime of photoinduced changes in films with different oxygen content will be reported. The possible origin of these changes will be discussed. [1] V. N. Smolyaninova at al., Phys. Rev. B 76, 104423 (2007) [Preview Abstract] |
Wednesday, March 18, 2009 3:42PM - 3:54PM |
T27.00005: Strain-modulated Self-Assembly of Nanostructures within Epitaxial Thin-films via Pulsed Laser Ablation Amit Goyal, Sung-Hun Wee, Yanfei Gao, Claudia Cantoni, Karren More, Yuri Zuev, Junsoo Shin Nanocomposites comprising three-dimensionally (3D) ordered arrays of nanodots of one type of complex ceramic material embedded in another complex ceramic material are expected to exhibit novel physical properties, tunable by adjusting the overall composition, concentration, feature size and spatial ordering of the nanodots. Applications of such nanocomposites in the areas of multiferroics, photovoltaics, solid state lighting, ultra-high density storage and high temperature (high-Tc) superconductivity are of interest. A joint experimental, theoretical and computational study on achieving ordering via 3D self-assembly of nanodots of one complex ceramic material within another complex ceramic material, such as 3D self-assembly of insulating BaZrO3 (BZO) nanodots within high-Tc superconducting YBCO films, was performed. Vertically or horizontally ordered arrays (or simultaneous ordering in both directions) of BZO nanodots within superconducting films have been made possible via strain modulation between nanodots. Experimental results obtained for novel nanocomposites for other applications involving perovskite-spinel mixtures such as CoFe2O4-BaTiO3, CoFe2O4-BiFeO3, etc. will also be presented. Such materials with ``controlled self-assembly'' of nanostructures should find application in many areas. [Preview Abstract] |
Wednesday, March 18, 2009 3:54PM - 4:06PM |
T27.00006: Efficiency and Plume Dynamics for Mid-IR Laser Ablation of Cornea Aroshan Jayasinghe, Borislav Ivanov, M. Shane Hutson This paper reports ablation experiments on porcine corneal tissue using the Vanderbilt Mark III Free Electron Laser (FEL) and a tabletop Raman-shifted Alexandrite laser. These experiments were designed to test previous models that suggested wavelength and intensity dependent ablation mechanisms. In one test, we compare ablation efficiency and plume dynamics for two FEL wavelengths ($\lambda $=2.77, 6.45 $\mu $m) chosen such that different components of the tissue matrix act as the primary chromophore (water or protein respectively), while keeping the total absorption constant. We find small differences in ablation efficiency (with slightly more efficient ablation at 2.77 $\mu $m); no difference in shockwave propagation; and slightly more particulate matter in the plume at 6.45 $\mu $m. In a second test, we find that the Raman-shifted Alexandrite laser has similar ablation efficiency to the FEL in the 6-7 $\mu $m range -- despite a $\sim $500-fold higher intensity. Although these results do not confirm the previous model predictions, the findings do suggest that the Raman-shifted laser can be a viable alternative to the FEL for surgical applications. [Preview Abstract] |
Wednesday, March 18, 2009 4:06PM - 4:42PM |
T27.00007: Pulsed-Laser Deposition of ZnO Thin Films and Heterostructures for Device Applications Invited Speaker: ZnO is a wide bandgap semiconductor being explored for transparent electronics, UV light emitting diodes, spin-based devices and chemical sensors. In this talk, we will discuss recent progress and understanding for carrier doping and interface formation in epitaxial ZnO thin films grown by pulsed-laser deposition. One of the critical issues for device applications is the formation of low resistivity, high carrier density p-type ZnO material for minority carrier injection. The behavior of acceptor dopants within the ZnO and ZnMgO matrices will be described. Discussion will include stability of transport properties, stabilization of surfaces, and device characteristics. [Preview Abstract] |
Wednesday, March 18, 2009 4:42PM - 4:54PM |
T27.00008: Role of the top electrodes and their interfaces on the resistive switching behavior of epitaxial NiO thin films S.R. Lee, J.H. Bak, Y.D. Park, K. Char, D.C. Kim, S. Seo, X.S. Li, G.S. Park, R. Jung Initial I-V characteristics of resistive switching behavior have been investigated with epitaxial NiO films grown on (100) SrRuO$_3$ by using Al, Pt, and CaRuO$_3$ as the top electrodes. SRO/NiO/Al and SRO/NiO/Pt require an electroforming process for the initialization of the resistive switching, while SrRuO$_3 $/NiO/CaRuO$_3$ is initially in a low-resistance state. The temperature dependence of the initial I-V characteristics indicates that insulating layers exist at the NiO/Al and NiO/Pt interface, presumably broken by the electroforming process. On the other hand, SRO/NiO/Al does not show the resistive memory switching behavior despite the electroforming behavior. The resistive switching endurance is also distinct depending on the top electrodes. Our results suggest that the oxygen defects and their bonding energy with the top electrode metal play a critical role on the resistive switching behavior. [Preview Abstract] |
Wednesday, March 18, 2009 4:54PM - 5:06PM |
T27.00009: Effect of cation substitution on the resistive switching behavior in epitaxial NiO H.M. Kim, S.R. Lee, J.H. Bak, M.L. Jo, Y.D. Park, K. Char The resistive switching behavior of NiO has been extensively investigated due to the nonvolatile ReRAM device applications. In contrast to unipolar resistive switching of NiO grown on Pt, bipolar resistive switching is observed in NiO grown on SrRuO$_{3}$ (SRO). The unipolar switching has been explained by the formation and rupture of filamentary conduction with the Joule heating, while the bipolar switching is still controversial. Our previous study with epitaxial (epi) NiO, prepared under various growth conditions and electrodes, suggested that the oxygen defects at the NiO/top electrode (TE) interface may be responsible for the bipolar switching and TE may compensate the oxygen defects. In order to understand the role of the defect states at the interface on the resistive switching, 1-nm-thick epi-AlO$_{x}$ interlayer has been deposited on and under epi-NiO. The I-V characteristics have been investigated with an epi-CaRuO$_{3}$ (CRO) as TE, resulting in a clean interface with NiO. SRO/NiO/AlO$_{x}$/CRO shows poorer switching endurance in the less than 25{\%} of measured cells. However, SRO/AlO$_{x}$/NiO/CRO exhibits bipolar switching in the most of measured cells with better endurance. This may imply the different oxygen defect states of each interface of NiO. As an effort to investigate the defect states in bulk and their effect on the unipolar switching, the I-V characteristics of Al substitution in epi-NiO will be presented. [Preview Abstract] |
Wednesday, March 18, 2009 5:06PM - 5:18PM |
T27.00010: Ge Quantum Dot Formation on Si (100)-2x1 with Surface Electronic Excitation Ali Oguzer The effect of laser-induced electronic excitations on the self-assembly of Ge quantum dots on Si (100)-2x1 grown by pulsed laser deposition is studied. The samples were first cleaned by using modified Shiraki method and then transferred into the deposition chamber. The vacuum system was then pumped down, baked for at least 12 hours, and the sample was then flashed to 1100 \r{ }C in order for the 2$\times $1 reconstruction to form. The experiment was conducted under a pressure $\sim $1x10$^{-10}$ Torr. A Q-switched Nd:YAG laser (wavelength $\lambda $ = 1064 nm, 10 Hz repetition rate) was used to ablate a Ge target. In-situ RHEED and STM and ex-situ AFM were used to study the morphology of the grown QD. The dependence of the QD morphology on substrate temperature and ablation and excitation laser energy density was studied. Electronic excitation is shown to affect the surface morphology. Laser irradiation of the Si substrate is shown to decrease the roughness of films grown at a substrate temperature of $\sim $450 $^{o}$C. Electronic excitation also affected surface coverage ratio and cluster density and decreased the temperature required to form 3-dimensional quantum dots. Possible mechanisms involved will be discussed. [Preview Abstract] |
Wednesday, March 18, 2009 5:18PM - 5:30PM |
T27.00011: Computer simulations of photochemistry controlled with subwavelength resolution Triet Nguyen, Alex Small A technique called Stimulated Emission Depletion (STED) has recently been developed to beat the diffraction limit in imaging. We propose to adapt this technique to control chemical reactions with nanoscale resolution. We simulated a process in which a series of laser pulses is applied at each site on a surface. The first pulse excites the molecules and the second pulse (with a TEM10 ``doughnut'' profile) then causes the excited molecules away from the node at the center to undergo stimulated emission and return to the ground state. The result is that the molecules at the center of the pulses (in a region of size $<<$lambda) remain in the excited state and can undergo chemical reactions. In this presentation, we will show results of computer simulations of this technique. We will show that even if the reaction rate constants are small, the application of several sequential pulses leads to a fractionation effect that compensates for low reaction rates. We will also show how the resolution of this technique depends on the intensities of the laser pulses used, and propose a few candidate molecules for experimental tests of this concept. [Preview Abstract] |
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