Materials Science and Engineering Aspects of Nanostructures and Nanomaterials

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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_at_glue.umd.edu

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Nanoscience and Nanomaterials
Research Topics
Materials

• 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

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Nanoscience and Nanomaterial Activities

• 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)

• 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

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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

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Scanning Tunneling Microscopy and
SpectroscopyCharacterization of Electronic
Devices - Phaneuf
Topography and Conductance Images of pn devices
on Si under variable reverse bias
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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 (x0.07)
  6.467Å
• High elastic anisotropy

L
PbSe
PbSe
Pb1-xEuxTe Spacer
N periods
PbSe
Pb1-xEuxTe Spacer
D

• 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
PbTe buffer layer (2µm)
wetting layer
BaF2 (111)
L in-plane dot-to-dot distance D Spacer layer
thickness
x 0.05 0.1
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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
35nmltDlt69nm
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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
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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
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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.

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SPONTANEOUS ASSEMBLY of PdO2 TIPS FOR
FIELDEMISSION APPLICATIONS - Ramesh
AFM
Formed by oxidation of metal film
50x50mm
PEEM
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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)
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Block Copolymer NanotemplatesKofinas

• 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

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Metal Oxide Nanoclusters Kofinas
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

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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 (450C) 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.

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Nanoporous Dielectrics by Polymer
TemplatingBriber, R.L. Miller, E. Huang, P. Rice
(IBM Almaden Research Center)
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Plasma-Based Pattern Transfer into Nanoporous
Silica Oehrlein, Standaert (IBM), Gill, Plawsky
(RPI)

• 50 sccm,
• 10 mTorr,
• 1400 W

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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
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Plasma-Based Pattern Transfer into Nanoporous
Silica Oehrlein, Standaert (IBM), Gill, Plawsky
(RPI)

• 50 sccm,
• 10 mTorr,
• 1400 W

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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
RcSiO2/nanoporous silica etch rate ratio
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Fabrication of Ferroelectric Nano-capacitorsRames
h, 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.

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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