Departamento de Fsica Curso Electivo INTRODUCCIN A PELCULAS DELGADAS

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Departamento de Física - Curso ElectivoINTRODUCCI
ÓN A PELÍCULAS DELGADAS

• Física de películas delgadas
• Técnicas de Crecimiento de películas
• Técnicas de Caracterización de películas
• Propiedades de películas

Segundo Período 2003 Profesora María Elena Gómez
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Departamento de Física - Curso ElectivoINTRODUCCI
ÓN A PELÍCULAS DELGADAS

• II Técnicas de Crecimiento de películas
• Vacuum and kinetic theory of gases
• Evaporation
• Sputtern deposition
• Cathodic arc deposition
• Molecular beam epitaxy
• Chemical vapor deposition

Segundo Período 2003 Profesora María Elena Gómez
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5. Molecular beam epitaxy
Departamento de Física Curso Electivo INTRODUCCIÓN
A PELÍCULAS DELGADAS

• Epitaxy
• Structure
• Surface and Interface Crystallography
• Parameters

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Molecular Beam Epitaxy

• evaporation at very low deposition rates
• typically in ultra-high vacuum
• very well controlled
• grow films with good crystal structure
• expensive
• often use multiple sources to grow alloy films
• deposition rate is so low that substrate
  temperature does not need to be as high

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Epitaxy

• growth of film with a crystallographic
  relationship between film and substrate
• homoepitaxy (autoepitaxy, isoepitaxy) film and
  substrate are same material
• Heteroepitaxy film and substrate are different
  materials
• Structures
• 1. matched
• 2. strained (pseudomorphy)
• 3. relaxed

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Structures

• Matched common in homoepitaxy, sometimes in
  heteroepitaxy

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Structures (2)

• strained (pseudomorphy) film grows with
  structure different from bulk
• not stable
• at some thickness film will convert to bulk
  structure
• example Co is hcp
• can deposit as fcc up to one micron thick
• example strained layer superlattices
• can make materials with unusual properties

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Structures (3)

• relaxed
• form edge dislocations
• strained vs. relaxed depends on minimizing energy
  of system
• strain energy vs. dislocation energy

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Surface and Interface Crystallography

• Surfaces
• - not always the same as the bulk
• - vertical changes outer layers may move in or
  out from
• bulk positions
• - lateral changes surface may reconstruct
• atoms move laterally on surface
• Interfaces
• use Miller indices to specify planes and or
  directions example NiO on Ni NiO(100)Ni(111)
• lattice misfit f nao(substrate) - mao(film) /
  ao(film) ao bulk lattice constant (function
  of temperature !!) n, m integers
• f gt 0 film in tension
• f lt 0 film in compression

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Parameters

• substrate temperature
• critical epitaxial temperature TC
• depends on deposition rate and materials
• typical values 100 - 500 C
• T gt TC perfect epitaxial growth
• T lt TC polycrytalline growth
• deposition rate
• lower rate improves epitaxy
• if system is clean
• for good epitaxy, typically want
• Example Ge on Ge

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Modification of ThinFilms by EnergeticParticles

• Fast Particle Modification of Films
• Residual Stress
• Inert Gas Trapping
• Reduction of Crystal Defects
• Microstructure Modification
• Adhesion Promotion
• Modification of Nucleation
• Metastable Phases and Structures

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Fast Particle Modification of Films

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Fast Particle Modification of Films (2)

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Fast Particle Modification of Films (3)

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Fast Particle Modification of Films (4)

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Sources of Energetic Particles

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Reflected particle energy and flux changewith
incident ion mass and energy.

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