Materials Science and Engineering Aspects of Nanostructures and Nanomaterials

1. Materials Science and Engineering Aspects of Nanostructures and Nanomaterials Gottlieb S. Oehrlein Department of Materials & Nuclear Engineering & Institute for Research in Electronics and Applied Physics University of Maryland, College Park, MD 20742‑2115 *oehrlein@glue.umd.edu

2. Semiconducting (electronic, optoelectronic, etc.) Magnetic Dielectric Metallic Organic Biological Synthesis of nanoscale clusters, nanocrystalline materials Self-assembly Nanoscale materials characterization Functional materials Combinatorial synthesis Biomimetic approaches Top-down nanostructure fabrication, sensing, control Nanoscience and Nanomaterials Research Topics Materials

3. Mohamad Al-Sheikhly (DNA selfassembly on semiconductors and insulators) Sreeramamurthy Ankem (Ti alloys, biocompatibility, nanoscale surface modifications) Robert Briber* (organic nanomaterials + characterization) Aris Christou* (inorganic selfassembly) John Kidder* (chemical vapor deposition, nanoscale particles) Peter Kofinas* (selfassembly of organic, templating) Isabel Lloyd (sintering of nano particles) Luz Martinez-Miranda (liquid crystals, nanoscale characterization) Gottlieb Oehrlein* (plasma processing of nanomaterials and nanostructures) Nanoscience and Nanomaterial Activities • Ray Phaneuf* (nanoscale characterization) • Ramamoorthy Ramesh* (magnetic oxides, nanoscale selfassembly, functional materials) • Gary Rubloff (nanoscale fabrication, sensing and control) • Alexander Roytburd (strain modeling of nanomaterials) • Ichiro Takeuchi (combinatorial synthesis) • Lourdes Salamanca-Riba* (characterization of nanoscale structures and materials) • Otto Wilson, Jr. (biomimetic approaches to novel materials) • Manfred Wuttig (functional materials, phase transformations in nanocrystals) • Examples of research will • be discussed in this talk

4. Nanotechnology and Nanomaterials • Nanoscale Characterization • Selfassembly • Organic nanomaterials & templating • Processing of nanomaterials & novel effects • Top-down nano-lithograpy - formation of nano-scale structures and devices

5. Preamp x y z actuator STM ADC/DAC interface Vp Summing # 1 p Lock-in amp n Mod’n voltage Depletion zone Summing # 2 Vn 0V -10V Vr Scanning Tunneling Microscopy and SpectroscopyCharacterization of Electronic Devices - Phaneuf Topography and Conductance Images of pn devices on Si under variable reverse bias

6. Tunable PbSe QD Superlattices with PbEuTe Spacer Layers Obtained by MBE - TEM Characterization Salamanca-Riba, Springholz, Bauer (Linz, Austria) • PbSe (IV-VI) Q.D. / Pb1-xEuxTe* superlattice on PbTe (111) for mid-IR lasers and detectors, thermoelectric materials • Exploit: Tensile strain for PbSe Q.D. • (5.5% mismatch between PbSe & PbTe) • PbSe; 6.124Å PbTe; 6.443Å Pb1-xEuxTe (x=0.07); 6.467Å • High elastic anisotropy L • MBE growth • S-K growth mode • Deposit 5 PbSe ML / dot • Variables; • - Spacer thickness (32-312nm) • - Growth temperature • (335oC, 380ºC) • Analysis • - TEM: Shape and size of buried dots • Dot stacking • - AFM: Shape and size of surface dots PbSe PbSe Pb1-xEuxTe Spacer* N periods PbSe Pb1-xEuxTe Spacer* D PbSe PbSe PbTe buffer layer (2µm) wetting layer BaF2 (111) L: in-plane dot-to-dot distance D: Spacer layer thickness * x = 0.05 ~ 0.1

7. (b) Pyramid shape Q.D.s (base=30nm, height=12nm) for 35nm<D Tunable PbSe QD Superlattices with PbEuTe Spacer Layers Obtained by MBE - TEM Characterization Salamanca-Riba, Springholz, Bauer (Linz, Austria) 1st. Q.D. layer 60th Period Q.D. (a) In plane dot distributions for 35nm<D<69nm

8. Tunable PbSe QD Superlattices with PbEuTe Spacer Layers Obtained by MBE - TEM Characterization Salamanca-Riba, Springholz, Bauer (Linz, Austria) 43 nm spacer layer thickness electron beam Dots are placed at the minimum elastic energy density position with respect to the dots of previous layer

9. 3-D Schematic of Pseudo fcc Unit Cell Tunable PbSe QD Superlattices with PbEuTe Spacer Layers Obtained by MBE - TEM Characterization Salamanca-Riba, Springholz, Bauer (Linz, Austria) where L : closest dot-dot distance D : the spacer thickness  : the trigonal angle (39º) 14% compressed along the trigonal direction

10. InAs Self Assembled Quantum Dots (QD) for Nano-LasersChristou • InAs/InAlAs/InGaAs on (110) InP • Quantum Dots via Self Assembly • Cathodoluminescence spectra at 10-13 meV FWHM • Excitonic Transitions via PL.

11. AFM SPONTANEOUS ASSEMBLY of PdO2 TIPS FOR FIELDEMISSION APPLICATIONS - Ramesh Formed by oxidation of metal film 50x50mm PEEM

12. Nucleation and Morphology Evolution in Chemical Vapor Deposition -Praertchoung, Kidder In ULSI devices, Nano-Scale Morphology and Surface Features are Critical Atomic force microscopy images of Ta2O5 thin films grown on Si(100) by chemical vapor deposition. Early stage of nuclei formation detected after 5 min, followed by coalescence and roughening. NEXT STEP Atomic Layer Deposition technique will be studied for control of nucleation and surface morphology. 1 min 5 min 5 nm islands 10 min 15 min Work supported by University of Maryland - NSF - MRSEC  (NSF-DMR-00-80008)

13. Blocks of sequences of repeat units of one homopolymer chemically linked to blocks of another homopolymer sequence. Microphase separation due to block incompatibility Templates for synthesis of metal and metal oxide nanoclusters A-Block B-Block Chemical Link 0 - 21 % 21 - 34 % 34 - 38 % 38 - 50 % Increasing Volume Fraction of Minority component Block Copolymer NanotemplatesKofinas

14. Metal Oxide NanoclustersKofinas Mixed Metal Oxide Magnetic Nanoclusters Piezoelectric Nanoclusters • CoFe2O4 • Hard magnetic material • High coercivity • Moderate saturation magnetization • Can be used for high density memory devices • ZnO • Wide band gap semiconductor (3.3eV) • Electro-acoustic devices (Piezoelectric) • Conductive layer in solar cells • UV emitter • pressure sensors for tires

15. Nanoporous PMSSQ Synthesis Schematic Dielectric constant vs. porogen content Nanoporous Dielectrics by Polymer TemplatingBriber, R.L. Miller, E. Huang, P. Rice (IBM Almaden Research Center) • Objective: • Characterize nanoporous low k dielectrics for next • generation interlayer materials • Nanoporous dielectrics are synthesized from poly(methylsilsesquioxane) (PMSSQ) by templating the pore structure with polymers (termed porogens). A mixture of MSSQ and porogen is spin cast, cured and heat treated (450°C) to degrade the porogen and form the pores. • A nanoporous structure will lower the dielectric constant (of PMSSQ). • The morphology of the pores (size, shape, connectivity) will control many properties of the materials. • Approach: • Use TEM, neutron scattering and neutron reflectivity to determine the pore structure. • Small angle neutron scattering to follow the evolution of pore structure in-situ using deuterated porogen polymer.

16. TEM Results (FIB sample preparation): Nanoporous films are formed by degradation of the porogen. A percolation transition from isolated to interconnected pores is observed at ~30% porogen content. Pore size/spacing is 6-25nm (depending on synthesis details). SANS Results: Structural evolution is observed during cure from low temperature (green curve) to high temperature (blue curve). Upon degradation of the porogen and formation of the pores the scattering intensity is lost (open black triangles) because of the small neutron scattering contrast between the pores and the matrix. Nanoporous Dielectrics by Polymer TemplatingBriber, R.L. Miller, E. Huang, P. Rice (IBM Almaden Research Center)

17. Plasma-Based Pattern Transfer into Nanoporous Silica – Oehrlein, Standaert (IBM), Gill, Plawsky (RPI) 50 sccm, 10 mTorr, 1400 W

18. Plasma-Based Pattern Transfer into Nanoporous Silica – Oehrlein, Standaert (IBM), Gill, Plawsky (RPI) CHF3(50 sccm, 10 mTorr, 1400 W, -125V, 40 sec) • Fairly satisfactory pattern transfer • Low etch selectivity relative to SiN etch stop layer Photoresist Xerogel Si3N4 Etch Stop Layer

19. Plasma-Based Pattern Transfer into Nanoporous Silica – Oehrlein, Standaert (IBM), Gill, Plawsky (RPI) 50 sccm, 10 mTorr, 1400 W

20. Plasma-Based Pattern Transfer into Nanoporous Silica – Oehrlein, Standaert (IBM), Gill, Plawsky (RPI) • More CFx material on porous silica than on SiO2 • Porous silica etch rate is suppressed as CFx material builds up Schematic Picture of Surface Rc=SiO2/nanoporous silica etch rate ratio

21. Fabrication of Ferroelectric Nano-capacitorsRamesh, Melngailis (ECE/IREAP) Ferroelectric materials exhibit a broad range of valuable physical properties they exhibit, with potential applications in information storage technologies. To be competitive, ferroelectric memories have to be implemented at densities of the order of 1Gbit on a 1cm x 1cm chip. This necessitates the reduction in the lateral dimensions of the storage element into the sub-micron range. For example, it is expected that a Gbit chip will have storage capacitor areas of the order of 100nm x 100nm, in a planar arrangement.

22. Fabrication and Characterization of Nanoscale WiresOehrlein, Kuan (SUNY), Rossnagel (IBM) • Electron-beam lithography of PMMA resist • High-density plasma etching of 20-50 nm wide trenches in SiO2 • High-density plasma deposition of Cu • Removal of excess Cu by chemical mechanical planarization