Advanced Nano Deposition Methods E-Book
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- Herausgeber: Wiley-VCH Verlag GmbH & Co. KGaA
- Kategorie: Fachliteratur
- Sprache: Englisch
This concise reference summarizes the latest results in nano-structured thin films, the first to discuss both deposition methods and electronic applications in detail.
Following an introduction to this rapidly developing field, the authors present a variety of organic and inorganic materials along with new deposition techniques, and conclude with an overview of applications and considerations for their technology deployment.
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Seitenzahl: 595
Veröffentlichungsjahr: 2016
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Table of Contents
Cover
Title Page
Copyright
List of Contributors
Chapter 1: Pulsed Laser Deposition for Complex Oxide Thin Film and Nanostructure
1.1 Introduction
1.2 Pulsed Laser Deposition System Setup
1.3 Advantages and Disadvantages of Pulsed Laser Deposition
1.4 The Thermodynamics and Kinetics of Pulsed Laser Deposition
1.5 Monitoring of Growth Kinetics
1.6 Fundamental Parameters in Thin Film Growth
1.7 Pulsed Laser Deposition for Complex Oxide Thin Film Growth
1.8 Pulsed Laser Deposition for Nanostructure Growth
1.9 Variation of Pulsed Laser Deposition
1.10 Conclusion
References
Chapter 2: Electron Beam Evaporation Deposition
2.1 Introduction
2.2 Electron Beam Evaporation System
2.3 Characterization of Thin Film
2.4 Summary
Acknowledgments
References
Chapter 3: Nanostructures and Thin Films Deposited with Sputtering
3.1 Introduction
3.2 Nanostructures with Sputtering
3.3 Thin Films Deposited with Sputtering
3.4 Summary
Acknowledgments
References
Chapter 4: Nanostructures and Quantum Dots Development with Molecular Beam Epitaxy
4.1 Introduction
4.2 Technology of MBE
4.3 Nanoheterostructures Fabricated by Molecular Beam Epitaxy
4.4 Quantum Dots Development with Molecular Beam Epitaxy
4.5 Summary
Acknowledgments
References
Chapter 5: Carbon Nanomaterials and 2D Layered Materials Development with Chemical Vapor Deposition
5.1 Introduction
5.2 Carbon Nanotube Synthesis by Chemical Vapor Deposition
5.3 Graphene Synthesis by Chemical Vapor Deposition
5.4 Metal Dichalcogenide Synthesis by Chemical Vapor Deposition
5.5 Summary
References
Chapter 6: Nanostructures Development with Atomic Layer Deposition
6.1 Introduction
6.2 Reaction Mechanisms
6.3 Nanostructures Based on ALD
6.4 Summary
Acknowledgments
References
Chapter 7: Nanomaterial Development with Liquid-Phase Epitaxy
7.1 Introduction
7.2 Hydrothermal Method
7.3 Nanostructures Fabricated Using LPE
7.4 Summary
Acknowledgments
References
Chapter 8: Nanostructural Thin Film Development with Chemical Solution Deposition
8.1 Introduction
8.2 Precursor Solution Preparation
8.3 Coating
8.4 Thermal Treatment
8.5 Control of the Microstructures in Thin Films Prepared by CSD Techniques
8.6 Examples of Nanostructural Thin Films Prepared by CSD Techniques
8.7 Summary
References
Chapter 9: Nanomaterial Development Using In Situ Liquid Cell Transmission Electron Microscopy
9.1 Introduction
9.2 The Technological Development of
In Situ
Liquid Cell TEM
9.3 Nanomaterial Development Using
In Situ
Liquid Cell TEM Technology
9.4 Summary and Outlook
Acknowledgments
References
Chapter 10: Direct-Writing Nanolithography
10.1 Introduction
10.2 Electron Beam Lithography
10.3 Focused Ion Beam Lithography
10.4 Gas-Assisted Electron and Ion Beam Lithography
10.5 SPM Lithography
10.6 Dip-Pen Lithography
10.7 Summary
Acknowledgments
References
Chapter 11: 3D Printing of Nanostructures
11.1 Introduction
11.2 3D Printing Processes
11.3 Types of 3D Printing
11.4 3D Direct Laser Writing by Multiphoton Polymerization
11.5 3D Printing Applications
11.6 Summary
Acknowledgments
References
Chapter 12: Nanostructured Thin Film Solid Oxide Fuel Cells
12.1 Introduction
12.2 Solid Oxide Fuel Cells
12.3 Summary
Acknowledgments
References
Chapter 13: Nanostructured Magnetic Thin Films and Coatings
13.1 Introduction
13.2 High-Frequency Devices
13.3 Magnetic Information Storage Devices
13.4 Summary
Acknowledgments
References
Chapter 14: Phase Change Materials for Memory Application
14.1 Introduction
14.2 Ge
2
Sb
2
Te
5
and Its Properties' Improvement
14.3 High-Speed and Lower-Power TiSbTe Materials
14.4 Summary
Acknowledgments
References
Chapter 15: Nanomaterials and Devices on Flexible Substrates
15.1 Introduction
15.2 Nanomaterials on Flexible Substrates
15.3 Devices on Flexible Substrates
15.4 Summary
Acknowledgments
References
Index
End User License Agreement
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Guide
Cover
Table of Contents
Begin Reading
List of Illustrations
Chapter 1: Pulsed Laser Deposition for Complex Oxide Thin Film and Nanostructure
Figure 1.1 Schematic diagram of typical pulsed laser deposition.
Figure 1.2 Free energy as a function of cluster size
r
.
r
* is the critical nucleus size and Δ
G
* is the critical free energy barrier for nucleation.
Figure 1.3 Basic modes of thin film growth: (a) island or Volmer–Weber mode, (b) layer-by-layer or Frank–van der Merwe mode, and (c) layer plus island or Stranski–Krastanov mode.
Figure 1.4 The curve is a simple model of the fluctuation of the intensity of a single RHEED point during PLD.
Figure 1.5 Schematic representation: (a) the mismatch between the film and the substrate is negative; (b) the mismatch is positive.
Figure 1.6 (a–d) Transmission electron microscopic images for four different thicknesses of LBCO thin films on the MgO substrate and (e) cross-sectional high-resolution transmission electron microscopy for 34-nm thin film.
Figure 1.7 (a) Temperature dependence of resistivity with different thickness and (b) logarithm of theresistivity versus
T
−1/4
plot. Insets in (b): logarithm of the resistivity versus
T
−1/
n
plots (where
n
= 1, 2) for 82-nm LBCO thin film on MgO substrate.
Figure 1.8 Temperature dependence of the resistivity for LBCO thin filmson various substrates.
Figure 1.9 Temperature dependence of resistivity from 300 to 20 K for the as-grown LBCO thin films on different miscut angle (001) SrTiO
3
substrates. The inset is the MR value of as-grown LBCO at different temperatures under 7 T magnetic field.
Figure 1.10 The thin film/substrate mismatch in the epitaxial LBCO film grown on the vicinal (001) SrTiO
3
substrates with low miscut angle: (a) the generation of the “residual mismatching gap” at the end of the step terrace; (b) the formation of nonconservative antiphase domain boundary; and (c) the formation of locally strained domains induced by the “residual mismatching gap.”
Figure 1.11 A typical XRD pattern of the as-grown LBCO thin films on (001) MgO substrates. The inset (a) shows the (200) diffraction peaks of the as-grown and the oxygen-annealed thin films. The inset (b) shows the φ scans taken around the (101) diffraction of the LBCO thin films and MgO substrates.
Figure 1.12 (a) ZFC and FC magnetization of no annealing and oxygen annealing of LBCO thin film on (001) MgO substrate. (b) Resistivity change for the two samples with temperature. Inset is the applied magnetic field dependence of the MR effects at isothermal magnetoresistance measurements.
Chapter 2: Electron Beam Evaporation Deposition
Figure 2.1 The deposition process of electron-beam-induced evaporation by e-type electron gun.
Figure 2.2 Schematic drawings showing several different sources with different electron paths.
Figure 2.3 AFM images (500 nm × 500 nm) of Cu films with effective thickness values of (a) 4.3 nm, (b) 9.1 nm, and (c) 13.1 nm. Some interspaces between islands are marked by white circles. Copper thin films with nanometer-range thickness are prepared by electron beam evaporation of QUAD-EV-C HP mini e-beam evaporator (Mantis Deposition Ltd).
Figure 2.4 Measurement principle of ellipsometry.
Figure 2.5 The measured angles
Ψ
change with wavelength from 240 to 1000 nm at fixed angles 58° and 68°. Copper thin films with nanometer-range thickness are prepared by electron beam evaporation of QUAD-EV-C HP mini e-beam evaporator (Mantis Deposition Ltd) [24].
Figure 2.6 The measured angles Δ change with wavelength from 240 to 1000 nm at fixed angles 58° and 68°. Copper thin films with nanometer-range thickness are prepared by electron beam evaporation of QUAD-EV-C HP mini e-beam evaporator (Mantis Deposition Ltd) [24].
Figure 2.7 Schematic ellipsometry iterated with transmittance method.
Figure 2.8 Ellipsometric parameter-fitting spectra for 9.6-nm silver film at 58° incident angle.
Figure 2.9 Dependence of the refractive index
n
(a) and extinction coefficient
k
(b) on the wavelength for silver films at different thicknesses. Inset in (b) shows the optical constants
n
and
k
of films with 4.7 and 6.0 nm effective thicknesses.
Chapter 3: Nanostructures and Thin Films Deposited with Sputtering
Figure 3.1 Sketch of sputtering work mechanism.
Figure 3.2 (a) The SEM image of the MoO
3
nanobelts and (b) the crystal structure of MoO
3
nanowires (silver gray lozenge representing MoO
6
octahedra) [17].
Figure 3.3 The XRD pattern of the post-annealing (a) and pre-annealing (b) MoO
3
nanowires/Cu/quartz [17].
Figure 3.4 The proposed growth process (a–d) and post-annealing (e) of needle-shaped MoO
3
nanowires [17].
Figure 3.5 FESEM images of samples deposited on Si(001) with a Bi seeding layer at (a) 400 °C, (b) 450 °C, (c) 500 °C, and (d) 550 °C by rf magnetron sputtering.
Figure 3.6 (a,b) Cross-sectional FESEM images of samples deposited with a Bi seeding layer at 500 °C. (c) Photograph of Bi
2
O
3
nanocones grown on a 4 cm × 4 cm Si (001). (d) EDX spectrum of sample deposited at 500 °C.
Figure 3.7 (a) TEM image of α-Bi
2
O
3
nanocones. Inset shows SAED patterns from a single α-Bi
2
O
3
nanocone grown at 400 °C. (b) TEM image of a β-Bi
2
O
3
nanocone. Inset shows SAED patterns from a single β-Bi
2
O
3
nanocone grown at 500 °C.
Figure 3.8 Model of the growth of Bi
2
O
3
nanocones by magnetron sputtering.
Figure 3.9 FESEM images of the samples prepared on the scratched Si (100) wafers for 45 min, with a Ni catalyst layer of about 100 nm; a discharge current of 180 mA; a voltage of 350 V; and different CH
4
/(N
2
+ H
2
) ratios of (a) 1/10, (b) 1/20, (c) 1/40, (d) 1/100, (e) 1/150, and (f) 0, respectively.
Figure 3.10 TEM images of the nanocones grown at the CH
4
/(N
2
+ H
2
) ratios of (a) 1/10, (b) 1/150, and (c) 0; corresponding SAED patterns taken from (d, f, h) bodies and (e, g, i) tops in (a–c); and (j–o) EDXS spectra and their analytical histograms at the nearby locations corresponding to subgraphs (d–i).
Figure 3.11 Schematic of the growth mechanisms of (a) silicon nanocones, (b) g-CNNCs, and (c) diamond nanocones.
Figure 3.12 (a) Cross-sectional SEM image of the Al
1−
x
In
x
N nanorods grown with a Ti
0.79
Zr
0.21
N seed layer assistance. The inset shows the interface of Al
1−
x
In
x
N nanorods/Ti
1−
y
Zr
y
N seed layer/sapphire. The scale shown in the inset is 60 nm. (b) Corresponding top-view image of the Al
1−
x
In
x
N nanorod arrays.
Figure 3.13 Top-view (a,c) and side-view (b,d) SEM images of the In
x
Al
1−
x
N grown at the various substrate temperatures (a,b) 700 °C and (c,d) 750 °C by DC magnetron sputtering technique [54].
Figure 3.14 Schematic illustration of controlled curved-lattice epitaxial growth (CLEG) and the growth of one period of a nanospiral structure. (a) A curved rod segment of an In
x
Al
1−
x
N nanospiral (one-fourth of a spiral turn in this sample) controlled by CLEG. Dark gray to light gradient along the lateral direction of the curved rod segment indicates the compositional gradient from high to low Al content In
x
Al
1−
x
N. (b,c) One period of a left- and right-handed nanospiral structure, respectively. One turn of a nanospiral is comprised of four curved rod segments, obtained by temporal control of the azimuthal orientation of the deposition fluxes. The arrow diagrams illustrate the sequence and direction of the curvature of each segment, as seen from the top, in the two cases of left- and right-handed nanospiral growth [66].
Figure 3.15 SEM images of In
x
Al
1−
x
N nanorods and nanospirals. (a) Straight nanorods. (b,c) Left- and right-handed nanospirals, respectively, comprising five turns at 200 nm pitch. The nanospiral's growth is homogeneous in both length (∼1 µm) and diameter (60 nm) [66].
Figure 3.16 SEM images of sectional LaNi
5
thin films at (a) low magnification and (b) high magnification.
Figure 3.17 SEM images of LaNi
5
thin films: (a) non-annealed and (b) annealed at 700 °C.
Figure 3.18 FESEM cross-sectional images and atomic force microscope images of samples [74].
Figure 3.19 AFM images captured on 3 µm × 3 µm area of the different bilayer thin films. The thickness of BTO layer was kept fixed at 100 nm while BFO layer was deposited for different thicknesses of 50 nm (a), 100 nm (b), 150 nm (c), and 200 nm (d), respectively.
Figure 3.20 Cross-sectional FESEM image of bilayer thin film of BFO/BTO: (a) top view of film interface; inset (b) BTO layer; inset (c) interdiffusion and BFO layer; and (d) side-view bilayer interface.
Chapter 4: Nanostructures and Quantum Dots Development with Molecular Beam Epitaxy
Figure 4.1 The setup of the laser-MBE (a) and the UH vacuum chamber of the LMBE (b).
Figure 4.2 Schematic diagram of a solid-source MBE growth chamber.
Figure 4.3 A diagram of laser-MBE system equipped with RHEED (including an electron gun and phosphor screen).
Figure 4.4 RHEED patterns during the MBE growth of an epitaxial GaAs layer deposited on a GaAs (100) substrate; the surface reconstruction is the As-stabilized (2 × 4) one. The azimuths are [1 −1 0] and [−1 −1 0] for the panels (a) and (b), respectively.
Figure 4.5 Different stages of layer-by-layer growth by nucleation of 2D islands and the corresponding intensity of the zero-order diffracted RHEED beam. See text.
Figure 4.6 RHEED patterns (a,c,e) during the 2D deposition of GaAs (b), the 2D deposition of InAs (d), and the 3D deposition of InAs (f) on a (100) GaAs buffer layer, respectively.
Figure 4.7 AFM image (250 × 250 nm
2
) of InAs deposited on GaAs (100) with a coverage exceeding
q
c
.
Figure 4.8 Schematic representation of the lattice distortion in a 3D island.
Figure 4.9 RHEED patterns for heteroepitaxial growth of ZnO thin films on GaAs via STO buffer layer with the laser repetition of 2 Hz and 2 J/cm
2
laser energy density at various thicknesses: GaAs substrate (a), 100 Å STO (b), 50 Å ZnO (c), and 2000 Å ZnO (d).
Figure 4.10 XRD pattern of the heteroepitaxial growth of ZnO films on GaAs (001) via STO as buffer layer.
Figure 4.11 The capacitance of the Au/ZnO/STO/GaAs heterostructure as a function of frequency (a) and the inset shows the schematic of the Au/ZnO/STO/GaAs heterostructure and the capacitance–voltage response of the heterostructure under the bias voltage of 6 V at the frequency of 1 MHz (b). The arrows denote the direction of the bias sweeping.
Figure 4.12 Current–voltage properties under the bias voltage of 5 V of the ZnO/STO/GaAs heterostructure at room temperature. The arrows indicate that the bias voltage was swept as −5 → 0 → +5 → 0 → −5 V, and the numbers from 1 to 4 indicate the direction of the sweep. The inset shows the current–voltage properties (in log scale) under the bias voltage of 7 V at various temperatures in the range of 50–250 K.
Figure 4.13 RHEED patterns for heteroepitaxial growth of CoFe
2
O
4
thin films on MgO(100) and STO(100) with the laser repetition of 3Hz and 2J/cm
2
laser energy density at various time: 0 (a), 10s (b), 60s (c), 300s (d), 600s (e), and laser off (f).
Figure 4.14 XRD pattern and rocking curve of heteroepitaxial growth CoFe
2
O
4
films on MgO (100) in which separate peaks from (004) MgO substrate peak (2θ ≈ 93.6°) to CoFe
2
O
4
film peak (2θ ≈ 94.112°) are clearly distinguishable (a) and the XRD pattern and rocking curve of heteroepitaxial growth CoFe
2
O
4
films on STO (100) (b).
Figure 4.15 AFM and MFM images of the CoFe
2
O
4
thin films on MgO (100) (a,b) and STO (100) (c,d), respectively.
Figure 4.16 Parallel and perpendicular hysteresis loops of the CoFe
2
O
4
thin films on MgO (100) (a) and STO (100) (b), respectively.
Figure 4.17 Schematic diagram of conduction band (CB) and valence band (VB) profiles for an InAs/GaAs QD structure (b) along an arbitrary direction shown by the arrow (a). The confined ground levels for electrons and holes are indicated. The fundamental optical transition has an energy
E
. The energy gap of the QD material is indicated by
E
g
, while
E
e
and
E
h
are the confinement energies for electrons and holes, respectively.
DV
e
and
DV
h
are the band discontinuities for CB and VB, respectively.
Figure 4.18 AFM image of InAs dot arrays on InGaAs/GaAs. (Inset) A single InAs quantum dot.
Chapter 5: Carbon Nanomaterials and 2D Layered Materials Development with Chemical Vapor Deposition
Figure 5.1 (a) Illustrations of the structure of MWCNT (left) and SWCNT (right). Schematic of (b) a thermal CVD equipment for CNT growth, (c) the base-growth mechanism, and (d) the tip growth mechanism.
Figure 5.2 (a–c) Transmission electron microscopy (TEM) images of carbon nanotubes grown using iron nanoclusters with average diameters of 3, 9, and 13 nm (from (a) to (c)). Scale bars: 20 nm. (d–f) Histograms of nanotube diameters corresponding to the samples at the left. The solid lines correspond to Gaussian fits. (g) The relation between as-grown CNT average diameter, average wall number, and iron catalyst thin film thickness. (h) The surface atomic force microscopic (AFM) images of iron catalyst thin film with thickness of 1.6, 3, and 5 nm.
Figure 5.3 Schematic of (a) selective growth of metallic SWCNT with electric field and (b) selective growth of semiconducting SWCNT with ultraviolet beam.
Figure 5.4 (a,b) Scanning electron microscope (SEM) images of well-aligned CNT array grown on porous silicon, (c) AFM image, (d) SEM image of aligned CNTs grown on the
a
-plane sapphire substrate, (e) schematic of tip growth mode of the aligned ultralong CNTs, and (f) mosaic SEM images of aligned ultralong CNTs.
Figure 5.5 Schematic of graphene growth mechanisms on (a) single crystal Ni(111), (b) polycrystalline Ni, and (c) Cu.
Figure 5.6 Low-energy electron microscopy (LEEM) images of graphene growing on Cu(111) at 815 °C. (a) After initial nucleation and (b) after secondary nucleation following an increase in the carbon flux. Graphene is bright, while dark stripes are Cu step bunches. The field of view is 20 µm.
Figure 5.7 The graphene flakes grown by methane/hydrogen low-pressure CVD with different total pressure and methane ratio.
Figure 5.8 (a) The highlighted elements, including transition metals and three chalcogen elements, are able to form layered TMDs. Partial highlights for Co, Rh, Ir, and Ni indicate that not all the TMDs formed by these elements are layered structure. (b)
c
-axis and [10, 12–19, 21] sectional view of trigonal prismatic and octahedral phase monolayer TMD. Dark gray and light gray represent metal and chalcogen, respectively. AbA and AbC represent two different stacking sequences.
Figure 5.9 (a) Schematic of one-step MoS
2
growth method with gas reaction of MoO
3
and S. (b) Schematic of two-step MoS
2
growth method by sulfurizing the Mo thin film. (c) Schematic of two-step MoS
2
growth method by (NH
4
)
2
MoS
4
decomposition.
Figure 5.10 (a–c) The dendritic MoS
2
flakes grown on STO under growth temperature, 730, 780, and 880 °C. (d,e) The MoS
2
flakes synthesized by two-step method with sulfurization time, 0.5 and 6 h. (f–k) The MoS
2
flakes grown by two-step route at 0.5–1, 1–4, 4–10, 10–40, 40–80, and 80–120 kPa, respectively.
Chapter 6: Nanostructures Development with Atomic Layer Deposition
Figure 6.1 Schematic representation of ALD using self-limiting surface chemistry and an AB binary reaction sequence. (George
et al.
[2]. Reproduced with permission of American Chemical Society.)
Figure 6.2 Cross-sectional SEM image of an Al
2
O
3
ALD film with a thickness of 300 nm on a Si wafer with a trench structure.
Figure 6.3 Proposed principles for Lewis base catalysis of SiO
2
ALD during (a) the SiCl
4
reaction and (b) the H
2
O reaction.
Figure 6.4 Mass gain monitored by quartz crystal microbalance for 30 cycles during W ALD with WF
6
and Si
2
H
6
as the reactants. (Fabreguette
et al.
[36]. Reproduced with permission of Elsevier.)
Figure 6.5 (a) Cross-sectional TEM, (b–d) HRTEM images of a Ho
2
O
3
–TiO
2
nanolaminate in the as-deposited state, and (e) compositional EDX map from the nanolaminate.
Figure 6.6 FESEM images of ALD TiO
2
films deposited at 350 °C with an increasing number of deposition cycles. The scale bar applies to all images.
Figure 6.7 (a) A STEM image of a TiO
2
nanotube formed by replication of a cellulose nanofiber. (b) A BSE image of an Ir/TiO
2
/cellulose composite formed by ALD of TiO
2
and Ir on filter paper at 250 °C.
Figure 6.8 (a) SEM image and (b) TEM image of as-TiO
2
deposited electrospinning fibers. (c) A close-up SEM image and (d) TEM image of several titania tubes after calcination.
Figure 6.9 A BSE image of a conformal Ru thin film deposited on the pore walls of macroporous Si by ALD.
Chapter 7: Nanomaterial Development with Liquid-Phase Epitaxy
Figure 7.1 Scanning electron micrograph of (a) titania gel spheres and (b) titania gel sphere and flakes from broken spheres.
Figure 7.2 Water molecules in an alternating electrical field under microwave irradiation [25].
Figure 7.3 Typical TEM image of Ag nanoparticles prepared in an aqueous system using AgNO
3
as the silver source, l-lysine as a reducing agent, and soluble starch as a capping agent via microwave irradiation at 150 °C for only 10 s.
Figure 7.4 (a) Photograph of the continuous flow reactor system for the microwave-assisted synthesis of Ag nanoparticles; the TEM image of the as-prepared Ag colloid is also displayed. (b) Schematic illustration of the overall experimental setup.
Figure 7.5 Experimental setup of the microwave-assisted continuous flow reactor system and a photograph of the microwave cavity part.
Figure 7.6 Schematic architectures of core–shell nanoparticles.
Figure 7.7 Different types of core–shell structures. The upper panel illustrates core–shell UCNPs with epitaxial layers: (a) core–shell UCNPs with an “inert” shell layer, (b) core–shell UCNPs with an active shell layer, (c) core–shell UCNPs with multiple shell layers, (c) core–multishell type, (d) UCNPs@silica core–shell nanoparticles, (e) core–shell–shell UCNPs@silica@metal nanoparticles, and (f) UCNPs coated with organic dye molecules.
Figure 7.8 TEM and HRTEM (inset) images of α-NaNdF
4
(a), α-NaEuF
4
(b), α-NaYF
4
(c), and α-NaYbF
4
(d) nanopolyhedra.
Figure 7.9 (a–e) TEM images and size distribution of NaYF
4
:Yb
3+
/Er
3+
(15/2%) core NCs (
t
= 0), NaYF
4
:Yb
3+
/Er
3+
(15/2%) core/NaYF
4
shell NCs after successive layer-by-layer epitaxial growth at
t
= 5, 10, 15, and 20 min, respectively; (f) ICP-MS elemental analysis of the core and core–shell NCs with same number concentration of NCs; and (g) upconversion emission spectra of the hexane dispersions of core and core–shell NCs with same number concentration of NCs under 980 nm excitation.
Figure 7.10 (a) Sketch of NaYF
4
: Yb, Tm-NaGdF4 core–shell nanoparticles via cation exchange and (b,c) TEM images of NaYF
4
:Yb
3+
/NaGdF
4
:Tm
3+
core–shell nanoparticles.
Figure 7.11 Tuning upconversion through energy migration in core–shell nanoparticles. (a) Schematic design of a lanthanide-doped NaGdF
4
@NaGdF
4
core–shell nanoparticle for EMU (X: activator ion). (b) An enlarged view of the selected area indicated by a light gray box, showing lanthanide (Ln) and Na atomic columns. Digitally processed STEM image by imposing projection symmetry to enhance the signal-to-noise ratio.
Figure 7.12 (a) Schematic illustration of the proposed energy-transfer mechanisms in the quenching-shield sandwich-structured UCNPs upon 800 nm excitation. (b) Aberration-corrected high-angular annular dark-field (HAADF) STEM image of a single quenching-shield sandwich nanoparticle projected from the [001] direction. Corresponding enlarged annular bright field (ABF) STEM image reveals the distribution of Na
+
ions and Ln
3+
ions. Simulated HAADF image based on the fast Fourier transformation (FFT) multislice method to enhance the signal-to-noise ratio.
Figure 7.13 Coating of UCNPs with a mesoporous silica shell. (a) Schematic of the calcination method and corresponding TEM images of mesoporous silica-coated NaYF
4
:Yb
3+
/Er
3+
@silica nanoparticles. (b) Schematic of the template method and dark-field STEM image of NaYF
4
:Tm
3+
/Yb
3+
@NaYF
4
@mSiO
2
. (c) Schematic of the etching method and HAADF STEM image of NaYF
4
:Yb/Tm@NaYF4@hmSiO
2
[48–50].
Figure 7.14 (a) Schematic illustration for preparing core–shell–shell structures of metallic@silica@UCNPs, along with (b–d) TEM images of the nanostructures obtained in each step.
Chapter 8: Nanostructural Thin Film Development with Chemical Solution Deposition
Figure 8.1 (a) Schematic illustration of filtration used in the PAD process and (b) photograph of an Amicon ultrafiltration cell used in the experiment.
Figure 8.2 Schematic diagram of the free energies of a CSD-derived amorphous film.
Figure 8.3 X-ray diffraction patterns of converted films on SrTiO
3
substrates. (a) Without and (b) with filtration of the solutions.
Figure 8.4 TEM (a), SAED (b), and the corresponding HRTEM image (c) of the Eu
2
O
3
thin film on the LaAlO
3
substrate.
Figure 8.5 XRD patterns from θ to 2θ scans of vanadium oxide films prepared under the optimal conditions for V
2
O
3
, V
4
O
7
, VO
2
, and V
2
O
5
, respectively.
Figure 8.6 (a,b) Cross-sectional HRTEM images of an SiO
2
–CFO (30 : 70) composite film on an LAO substrate and the corresponding SAED pattern (inset) taken from the interface between the film and the substrate.
Figure 8.7 (a) The AFM image of sample TiO
2
thin films prepared at 900 °C; (b) 3D image of (a); (c) the profile along the OX line in (a); (d) perpendicular strips on the surface of the film; and (e,f) strips with different widths on the same sample.
Chapter 9: Nanomaterial Development Using In Situ Liquid Cell Transmission Electron Microscopy
Figure 9.1 (a) Schematic and (b) photograph of an
in situ
liquid cell. The setup was used for observing electrochemical growth of metal nanoclusters in liquid with TEM.
Figure 9.2 (a) Schematic of an O-ring-sealed
in situ
liquid setup, (b) an
in situ
fluid cell setup with flow channels, and (c) schematic of a graphene liquid cell.
Figure 9.3 (a) Photographs of Poseidon 510 liquid cell with E-chip and accessory produced by Protochips Inc. (Reproduced with kind permission from Protochips) [23], (b) photograph of the Hummingbird Scientific
in situ
liquid spectroscopy holder tip and a liquid sample spectrum obtained with it [24] (Reproduced with kind permission from Hummingbird Scientific), and (c) Hummingbird cross-correlative holder with the tip being able to get removed and transferred to optical microscope and SEM [24]
Figure 9.4 Copper cluster nucleation and growth observed
in situ
. Small regions extracted from a video recorded during deposition at 5 mA/cm
2
. The images were acquired at the times shown (in seconds) after current flow began. Scale bar 500 nm.
Figure 9.5
In situ
TEM observations of nickel electrodeposition under −1 V bias at (a) 66 s, (b) 83 s, and (c) 95 s; and electropolishing under +1 V at (d) 0 s, (e) 2 min 30 s, and (f) 3 min 10 s.
Figure 9.6 The picture shows the growth of the dendrite versus time
in situ
liquid TEM.
Figure 9.7 (a) Trajectories of two particles (P1 and P2) showing pairwise oscillation and (b) a bismuth oxide hollow nanoparticle formed at 190 °C and its collapse by inward mass diffusion.
Figure 9.8 Assembly of gold nanoparticles on the window membrane surface by rapid changing of the electron beam size: (a) trajectories of the selected particles and (b) color maps show the electron beam density variations inside the beam region. The six selected particles in (a) are highlighted as black dots in (b).
Chapter 10: Direct-Writing Nanolithography
Figure 10.1 The basic idea of e-beam lithography.
Figure 10.2 The diagram of an e-beam lithography system.
Figure 10.3 SEM image of sub-10-nm-wide Si patterns fabricated by e-beam lithography after etching in propanol-added KOH solution: (a) original Si patterns and (b) additionally etched Si.
Figure 10.4 The diagram of FIB system.
Figure 10.5 SEM image of an array of FIB-etched lines on a multilayered sample AlF
3
(50 nm thick)/GaAs
4
.
Figure 10.6 The schematic and atomic force microscopy images of fabricating designed Au nanoparticle structures on silica surface.
Figure 10.7 The composition of STM (a) and AFM (b).
Figure 10.8 STM images of the process for making a quantum corral built with 39 Ag atoms on Ag.
Figure 10.9 (a) The STM images for 3-nitrobenzal malononitrile (NBMN) and 1,4-phenylenediamine (pDA) composite film on HOPG. Panels (b–f) show the reversible conductance transitions of these organic compound films by the application of local electric field pulses by scanning tunneling microscope.
Figure 10.10 Schematic diagram of the DPL process.
Figure 10.11 LFM images of (a) ODT and (b) MHA dots patterned onto a gold substrate under tip–substrate contact force of 0.5 nN and holding times of 2, 4, and 8 s; the frictional force profiles of (c) ODT and (d) MHA dot patterns. Thick lines represent Gaussian fits.
Chapter 11: 3D Printing of Nanostructures
Figure 11.1 The principle of stereolithography.
Figure 11.2 The principle of fused deposition modeling.
Figure 11.3 The printing process of selective deposition lamination.
Figure 11.4 The principle of selective laser sintering.
Figure 11.5 The diagram of energy transitions in two-photon absorption.
Figure 11.6 A typical experimental setup consisting of a light source, beam and sample movement components, beam control and focusing optics, and a vision system.
Figure 11.7 The experimental procedure for fabricating a 3D structure by direct laser writing.
Figure 11.8 3D scaffolds made by direct laser writing using PEG as a photopolymer.
Chapter 12: Nanostructured Thin Film Solid Oxide Fuel Cells
Figure 12.1 A schematic diagram of the principle of solid oxide fuel cell operation.
Figure 12.2 (a) SEM micrograph of the YSZ film deposited on the nickel foil substrate indicating a smooth YSZ surface. (b) XRD 2θ scan indicating a YSZ film (100) ordered in the film normal direction.
Figure 12.3 (a) GAADS φ-scan of the roll-textured nickel foil showing strong in-plane atomic ordering of the nickel; (b) GAADS φ-scan of YSZ on the nickel foil showing the 45° rotation of the YSZ lattice with respect to the nickel lattice; and (c) lattice cell diagram of the lattice structure of the nickel and YSZ materials with indication of the 45° rotation of the YSZ lattice to the nickel lattice.
Figure 12.4 SEM micrographs of photolithographically patterned and etched nickel foil substrate; (a) hexagonal array of etched pores; (b) single pore showing a continuous membrane at the bottom of the pore; and (c) the LSCO/YSZ side of the etched sample showing a continuous and intact LSCO/YSZ coating with the shadow of the pore in the nickel layer below.
Figure 12.5 The area-specific resistance (ASR) for LSCO films grown at room temperature and annealed at various temperatures. Note that the 550 °C annealed film has the lowest resistance of the annealed group of samples.
Figure 12.6 SEM micrographs of LSCO films grown at room temperature and annealed at various temperatures: (a) 450 °C, (b) 550 °C, (c) 650 °C, and (d) 750 °C. The film annealed at 550 °C was chosen for application as a cathode for the thin film fuel cell.
Figure 12.7 SEM of (a) the dense bottom LSCO layer and (b) the top of the annealed porous LSCO layer. The particles seen are due to the laser deposition process.
Figure 12.8 (a) Surface exchange coefficient (
k
) for LSCO films pre- and postannealed. Note the more than 1 order of magnitude increased in surface exchange coefficient upon annealing; (b) AFM scan of LSCO film preannealed; and (c) AFM scan of the LSCO film postannealed. Note the increase in surface roughness of the postannealed film.
Figure 12.9 (a) LSCO/YSZ/LSCO sample impedance analysis at 450 °C and (b) its equivalent circuit-fitting model.
Figure 12.10 Electrode area-specific resistance obtained from impedance measurements. Note the lower ASR for the composite LSCO cathode.
Figure 12.11 Thin film fuel cell performance test at different temperatures.
Figure 12.12 SOFC maximum power output at different temperatures from several fuel cells indicated by different shaped data points.
Figure 12.13 Cell output current as a function of YSZ electrolyte thickness at an operating temperature of 550 °C.
Figure 12.14 SEM micrograph of the nickel side of the LSCO/YSZ/Ni cells after controlled electrochemical etching on the nickel anode. Note the nickel islands in the center of the pores (dark region) connected to the pore sides.
Figure 12.15 Thin film cell output for cells having pores with clean bottoms (
S
1
) and cells having pores with nickel islands at the bottom (
S
2
).
Figure 12.16 (a) The ceramic frame of the fuel cell stack with cells stacked in parallel and (b) fuel cell stainless steel interconnect coated with gold.
Figure 12.17 Thin film SOFC performance as a function of operating temperatures. (a) Single-cell current versus produced power and (b) 10-cell stack current versus produced power.
Figure 12.18 (a) SEM micrograph of cracking of the self-support electrolyte membrane after cell testing and (b) calculations of oxide membrane failure as a function of nickel pore diameter.
Chapter 13: Nanostructured Magnetic Thin Films and Coatings
Figure 13.1 Hysteresis curve for a ferromagnetic material.
Figure 13.2 Schematic of NiFe
2
O
4
thin film fabrication procedure.
Figure 13.3 Atomic force microscopy images of (a) CD master, (b) PDMS stamp, and (c,d) patterned NiFe
2
O
4
thin films.
Figure 13.4 X-ray diffraction scans of (a) plain and (b) patterned NiFe
2
O
4
thin films.
Figure 13.5 Magnetic hysteresis of NiFe
2
O
4
thin films measured parallel to the plane of the film. Higher magnification image of the origin is shown in inset.
Figure 13.6 Magnetic force microscopy images of (a) a planar NiFe
2
O
4
thin film and (b) a patterned NiFe
2
O
4
thin film magnetized out-of-plane. The red and blue overlay indicates magnetic field orientation.
Figure 13.7 Schematic drawing of (a) longitudinal magnetic recording and (b) perpendicular magnetic recording.
Figure 13.8 Schematic of line-doubling technique: (a) PS-
b
-PMMA BCP pattern at twice the final period, (b) trimmed BCP stripes, (c) pattern transfer to the carbon layer, (d) spacer deposition, (e) removal of the spacer material and the carbon walls, and (f) pattern transfer into the final silicon layer.
Figure 13.9 Schematic of combining two pattern submasters to create a final master.
Figure 13.10 Scanning electron microscopy images of BPM magnetic dots in (a) 1 Tdot/in.
2
hexagonal array, (b) 1.2 Tdot/in.
2
rectangular array, and (c) 1.6 Tdot/in.
2
rectangular array. (d–f) Higher magnification images of (a–c).
Figure 13.11 2D readback image of shingled magnetic recording on bit patterned media with areal density of 1.6 Tdot/in.
2
: (a) before and (b) after.
Chapter 14: Phase Change Materials for Memory Application
Figure 14.1 Atomic arrangement of the metastable phase of GST.
Figure 14.2 Sheet resistances of the GST film.
Figure 14.3 Dependence of sheet resistances (
R
s
) on the annealing temperature for GSTN film.
Figure 14.4 XRD results of GSTN and GST films: (a) GSTN at different annealing temperature and (b) comparison of GSTN and GST films at the same annealing temperature (400 °C).
Figure 14.5 (a) Temperature dependence of
R
s
for the GSTC films (inset is the activation energy analysis for electrical conduction of the films) and (b) Kissinger plots for
E
a
calculation of the GSTC films with various C contents.
Figure 14.6 Programmed and measured temperature as a function of time (a) GST and (b) GSTC18% films; XRD results for (c) GST and (d) GSTC18% films.
Figure 14.7 TEM and SAED patterns: (a) GST film; (b) GSTC18% film; HRTEM images: (c) GST and (d) GSTC18% film (insets show schematic illustrations of crystalline phases); (e) HEX GST film; and (f) HEX GSTC18% film.
Figure 14.8 (a)
I–V
characteristics of the PCM cell using GSTC18%; (b) reset operations of GSTC18%-based PCRAM cells with various pulse widths; (c)
R–V
curves of the PCRAM cells based on GSTC18%; and (d) endurance performance of a cell using GSTC18%.
Figure 14.9 (a) Sheet resistances (
R
s
) of Sb
2
Te and Ti
10
Sb
60
Te
30
films as a function of the annealing temperature and (b) data retention characteristics for Ti
10
Sb
60
Te
30
films.
Figure 14.10 (a) XRD results for Sb
2
Te and Ti
10
Sb
60
Te
30
films and (b–d) XPS of Ti
10
Sb
60
Te
30
film.
Figure 14.11
R–T
curves of Ti-doped Sb
2
Te
3
film.
Figure 14.12 XRD patterns of (a) pure Sb
2
Te
3
and (b) Ti-doped Sb
2
Te
3
films.
Figure 14.13 (a,b) TEM, (c) HRTEM, and (d) SAED results of crystalline Sb
2
Te
3
. (e,f) TEM, (g) HRTEM, and (h) SAED results of crystalline Ti-doped Sb
2
Te
3
films.
Figure 14.14
R–V
characteristics of PCRAM cell with (a) TST and (b) GST films; (c) set operation as a function of applied pulse widths at different amplitudes; and (d) endurance of TST-based PCRAM cells.
Chapter 15: Nanomaterials and Devices on Flexible Substrates
Figure 15.1 SEM images of blank and TiO
2
-coated polyester fabric: (a) coating time (90 min) and (b) coating time (180 min).
Figure 15.2 Schematic diagram of the Co
3
O
4
NPAs on FCFs and the corresponding photographic images.
Figure 15.3 (a,b) FESEM images and (c) EDX spectrum of the ZnO nanorods grown on ZnO seed layer/PTFE substrates.
Figure 15.4 Schematic illustration of the generic process flow for transfer printing solid objects.
Figure 15.5 Rate dependence of stamp adhesion. (a) The rate-dependent adhesion causes a steel cylinder rolling down an inclined slab of PDMS to assume a constant speed dependent on the angle of inclination, allowing calculation of the energy release rate,
G
, from the loss of gravitational potential energy. (b,c) Slow removal of a PDMS stamp from the silicon beams leaves them intact, but the much higher adhesive force associated with fast stamp removal cleanly breaks the structures from their anchor (c).
Figure 15.6 (a) Photograph of the fabricated sensor attached to a curved surface and the optical microscope image (inset) of the SU-8 bump on the CNT–PDMS composite. (b) The HRSEM image of CNT–PDMS composite. CNTs are dispersed uniformly within the PDMS matrix, and individual CNTs are tangled or curved. (c) The current–voltage (
I–V
) characteristics of the CNT–PDMS composite. (Pyo
et al.
[37]. Reproduced with permission of the Institute of Physics Publishing Group.)
Figure 15.7 (a) Schematic of the main components of the dynamically stretchable supercapacitor. (b) Cyclic voltammogram (CV) curves under static 0% strain and 31.5% strain at a scan rate of 100 mV/s. The device gives approximately 4% larger specific capacitance than that of the cell. (c) With applied dynamic stretching/releasing cycling at a high strain rate of 1.11% strain per second and 4.46% strain per second, the stretchable supercapacitor shows good cycling stability. The current density is 10 A/g. (d) The CV curves of the stretchable supercapacitor at the flat state (light gray), fully bent state, and dynamic bending at a strain rate of 2.1% per second.
Figure 15.8 (a) Top-view SEM image of gold nanotrough networks. (b) SEM image of the cross section of a single gold nanotrough, revealing its concave shape. (c) Gold nanotrough networks transferred onto PET. (d) Sheet resistance optical transmission for copper, gold, silver, and aluminum nanotrough networks, described by percolation theory. The performances of device-grade ITO, carbon nanotubes, graphene, silver nanowires, silver grid, and nickel thin films are shown for comparison. (e,f) Photographs of “conducting paper,” fabricated by transferring Au nanotrough networks onto paper.
Figure 15.9 (a) Schematic illustration of the steps for implanting PI electrode arrays with a dissolvable silk support. (b–d) Photographic images and the corresponding average evoked response from each electrode implanted on a feline brain with (b) 76-µm, (c) 2.5-µm, and (d) 2.5-µm-mesh electrode arrays.
List of Tables
Chapter 2: Electron Beam Evaporation Deposition
Table 2.1 Evaporation characteristics of target materials.
Chapter 10: Direct-Writing Nanolithography
Table 10.1 Precursor names
Chapter 13: Nanostructured Magnetic Thin Films and Coatings
Table 13.1 Results of magnetic measurements taken on multilayered Nife
2
O
4
thin films
Table 13.2 Comparison of BPM at different areal densities
Edited by Yuan Lin and Xin Chen
Advanced Nano Deposition Methods
Editors
Prof. Yuan Lin
University of Electronic Science and Technology of China
State Key Laboratory of Electronic Thin films and Integrated Devices
No. 4, Section 2, North Jianshe Road Chengdu
Sichuan 610054
PR China
Prof. Xin Chen
East China University of Science and Technology
130 Meilong Road
200237 Shanghai
China
Cover
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List of Contributors
Hongliang Cao
East China University of Science and Technology
School of Materials Science and Engineering
Shanghai Key Laboratory of Advanced Polymeric Materials
Key Laboratory for Ultrafine Materials of Ministry of Education
130 Meilong Road
Shanghai 200237
PR China
Chonglin Chen
University of Texas at San Antonio
Department of Physics and Astronomy
One UTSA Circle
San Antonio, TX 78249
USA
Xin Chen
East China University of Science and Technology
School of Materials Science and Engineering
Shanghai Key Laboratory of Advanced Polymeric Materials
Key Laboratory for Ultrafine Materials of Ministry of Education
130 Meilong Road
Shanghai 200237
PR China
and
Chinese Academy of Sciences
Shanghai Institute of Microsystem and Information Technology
State Key Laboratory of Functional Materials for Informatics
865 Changning Road
Shanghai 200050
PR China
Rabi Ebrahim
University of Houston
Center for Advanced Materials
Houston, TX 77204-5504
USA
Daniel Fisher
University of Houston
Center for Advanced Materials
Houston, TX 77204-5504
USA
Min Gao
University of Electronic Science and Technology of China
State Key Laboratory of Electronic Thin Films and Integrated Devices
No. 4, Section 2, North Jianshe Road
Chengdu
Sichuan 610054
PR China
Wen Huang
University of Electronic Science and Technology of China
School of Microelectronics and Solid-State Electronics
No. 4, Section 2, North Jianshe Road
Chengdu
Sichuan 610054
PR China
Alex Ignatiev
University of Houston
Center for Advanced Materials
Houston, TX 77204-5004
USA
Yanda Ji
University of Electronic Science and Technology of China
State Key Laboratory of Electronic Thin films and Integrated Devices
No. 4, Section 2, North Jianshe Road
Chengdu
Sichuan 610054
PR China
Yuan Lin
University of Electronic Science and Technology of China
State Key Laboratory of Electronic Thin films and Integrated Devices
No. 4, Section 2, North Jianshe Road
Chengdu
Sichuan 610054
PR China
Chunrui Ma
Xi'an Jiaotong University
School of Materials Science and Engineering State Key Laboratory for Mechanical Behavior of Materials
No. 28, Xianning West Road Xi'an
Shanxi 710049
PR China
Taisong Pan
University of Electronic Science and Technology of China
State Key Laboratory of Electronic Thin films and Integrated Devices
No. 4, Section 2, North Jianshe Road
Chengdu
Sichuan 610054
PR China
Goran Rasic
North Carolina Central University
Department of Physics
1801 Fayetteville Street
Durham, NC 27707
USA
Zhitang Song
Chinese Academy of Sciences
Shanghai Institute of Microsystem and Information Technology
State Key Laboratory of Functional Materials for Informatics
865 Changning Road
Shanghai
PR China
Serekbol Tokmoldin
Institute of Physics and Technology
11 Ibragimov Street
Almaty 050032
Kazakhstan
Zhongping Wang
University of Science and Technology of China
School of Physical Sciences
Center for Physics Experiments
No. 96 Jinzhai Road
Hefei Anhui 230026
PR China
Liangcai Wu
Chinese Academy of Sciences
Shanghai Institute of Microsystem and Information Technology
State Key Laboratory of Functional Materials for Informatics
865 Changning Road
Shanghai
PR China
Naijuan Wu
University of Houston
Center for Advanced Materials
Houston, TX 77204-5504
USA
Debiao Xie
East China University of Science and Technology
School of Materials Science and Engineering
Shanghai Key Laboratory of Advanced Polymeric Materials
Key Laboratory for Ultrafine Materials of Ministry of Education
130 Meilong Road
Shanghai 200237
PR China
Weiqing Yang
Southwest Jiaotong University
School of Materials Science and Engineering
Key Laboratory of Advanced Technologies of Materials (Ministry of Education)
Ring North of a Section 111
Chengdu
Sichuan 610031
PR China
Mukhtar Yeleuov
University of Houston
Center for Advanced Materials
Houston, TX 77204-5504
USA
Hulin Zhang
University of Electronic Science and Technology of China
School of Microelectronics and Solid-State Electronics
No. 4, Section 2, North Jianshe Road
Chengdu
Sichuan 610054
PR China
Zengming Zhang
University of Science and Technology of China
School of Physical Sciences
Center for Physics Experiments
No. 96 Jinzhai Road
Hefei Anhui 230026
PR China
Wangfan Zhou
East China University of Science and Technology
School of Materials Science and Engineering
Shanghai Key Laboratory of Advanced Polymeric Materials
Key Laboratory for Ultrafine Materials of Ministry of Education
130 Meilong Road
Shanghai 200237
PR China
Chapter 1Pulsed Laser Deposition for Complex Oxide Thin Film and Nanostructure
Chunrui Ma and Chonglin Chen
1.1 Introduction
Complex oxide thin films and nanostructures are at the heart of new “oxide electronic” applications, such as ultraviolet light-emitting diodes [1–3], resistive switching memories [4, 5], chemical sensor [6, 7], and so on. They are often grown by pulsed laser deposition (PLD) because the technique is believed to be material agnostic. PLD is a thin film deposition technique – a type of physical vapor deposition. A high-power pulsed laser beam is focused on and strikes a target of the material that is to be deposited in a vacuum chamber. This material is vaporized from the target in a plasma plume and deposited as a thin film on a substrate. This process can occur in ultrahigh vacuum or in the presence of a background gas, such as oxygen, which is commonly used when depositing complex oxides.
The synthesis of novel thin films and structures is advancing on two fronts: one is the complexity of materials being deposited; and the other is the reduction in the typical dimensions of the features. As a rule of thumb, any structure that has one or more dimension smaller than about 100 nm is considered to be a nanostructured material. PLD is one of the most promising techniques for the formation of complex oxide heterostructures and nanostructures. The basic setup of PLD is simple relative to many other deposition techniques, and it can stoichiometrically transfer a material from a solid source to a substrate to form its thin film. The first use of PLD to deposit the films of semiconductors and dielectrics by ruby laser is reported in the literature as early as 1965 [8]. PLD for the film growth of SrTiO3 and BaTiO3 was achieved in 1969 [9]. Six years later, stoichiometric intermetallic materials (Ni3Mn and ReBe22) were fabricated by using PLD [10]. In 1987, PLD had a real breakthrough in its successful application to the in situ growth of epitaxial high-temperature superconductor films at Bell Communications Research [11]. Since then, PLD has been used extensively in the growth of high-temperature cuprates and numerous other complex oxides, including materials that cannot be obtained by an equilibrium route [12–16].
This chapter details the PLD setup and focuses primarily on the operating principle, growth mechanism, and parameters of PLD for complex oxide thin film and nanostructure.
1.2 Pulsed Laser Deposition System Setup
The technique of PLD is conceptually simple, as illustrated schematically in Figure 1.1. The system consists of a laser, a vacuum chamber equipped with pumps, a target holder and rotator, and a substrate heater and is typically equipped with various pressure gauges, controllers, and other instruments to control the deposition environment of the system [17]. Film growth can be carried out in reactive environments, such as that for oxides where a partial pressure of oxygen, ozone, or atomic oxygen is carefully controlled. The substrate heater controls the substrate temperature. PLD systems are also often equipped with a set of optics including apertures, attenuators, mirrors, and lenses to focus and direct the laser beam into the target with the right energy density. The bulk material target orients at an angle of 45° toward the incident laser beam. The laser beam is focused onto the target surface by a set of optical components. The target locally absorbs the laser pulse energy and ejects a small amount of target material in the form of a plume containing many energetic species including atoms, molecules, electrons, ions, clusters, particulates, and molten globules. The plasma is then deposited onto a substrate facing the target with a separation distance of 3–5 cm. The substrate temperature can be varied from room temperature to 1000 °C, even higher than 1000 °C, depending on the heater type. The film microstructure depends on various parameters such as substrate temperature; laser energy density and pulse repetition rate; pressure and type of gas inside the chamber; and substrate-to-target distance.
Figure 1.1 Schematic diagram of typical pulsed laser deposition.
1.3 Advantages and Disadvantages of Pulsed Laser Deposition
PLD exhibits many fascinating properties and practical advantages. Firstly, it has the ability to faithfully keep the stoichiometry of the target material, which is the first aspect that draws the attention of the thin film growth community [18]. Secondly, the energy source for material transport (i.e., the laser) is outside the chamber, minimizing any impurities caused by in-vacuum power components; it is very flexible, cost effective, and fast. Many different materials can be ablated by using the same apparatus, and the different laser wavelengths are available in principle. The isolated local heating by the laser spot means that several different materials can be sequentially ablated in a single vacuum chamber by using a carousel system or a segmented target rod to fabricate heterostructures with little of cross-contamination of the source target material. This avoids the interconnected vacuum transfer and is an important advantage in research environment: one laser can serve many vacuum systems in order to save the laser cost, and high-quality samples can be grown in 10 or 20 min. Finally, it is easy to control film thickness and multilayer film by controlling the pulse repetition rate, growth time, and the use of multiple target holders; it demands a much lower substrate temperature than other film deposition techniques because the high kinetic energy (10–100 eV) of species in the ablation plume promotes surface mobility during film growth.
In spite of the above-mentioned advantages of PLD, there are some drawbacks in using the PLD technique. One of the major problems is limited uniformity because the plasma plume ejected from the target can only provide a narrow forward angular distribution. Another problem is high defect or particulate concentration due to surface boiling. The size of particulates may be as large as a few micrometers, which will greatly affect the growth of the subsequent layers as well as the electrical properties of the films. Therefore, these features limit the large-scale film growth. New techniques, such as rotating both target and substrate and using a shadow mask to block the particulates in order to fabricate a large and uniform film, have been developed to improve the film quality.
1.4 The Thermodynamics and Kinetics of Pulsed Laser Deposition
PLD is a nonequilibrium growth technique owing to the high electronic excitation, degree of ionization, and kinetic energies of flux. There are many distinct stages to film growth: [19] the ablation process of the target material by the laser irradiation; the creation of a plasma plume with high energetic ions; and the crystalline growth of the film itself on the heated substrate. In this section, we will thoroughly describe these processes.
1.4.1 Laser–Material Interactions
After the laser pulse is extinguished, a very hot cloud of vaporized material, typically of 104 K or more, has been generated, which is commonly referred to as the ablation plasma or plume. This process is called laser ablation. The mechanisms depend on the laser characteristics as well as on the optical, topological, and thermodynamic properties of the target material. Absorption in a material is defined as
where 1/α is the absorption length, which is approximately 100 nm for many oxide materials at laser wavelengths commonly used in PLD (<400 nm). In this process, electrons in the target are excited and thermalized within several picoseconds or nanoseconds depending on the energy density, duration, wavelength, and shape of the laser pulse as well as on the material properties (reflectivity, absorption coefficient, heat capacity, thermal conductivity, density, etc.). The next step includes surface melting of the target and conduction of heat into the target. The thermal diffusion length is described as
where is the thermal diffusivity, is the thermal conductivity, is the mass density, c is the specific heat, and is the pulse duration. During this process, the temperature rises in the surface of the target. The heating rates as high as 1011
