Nano-structure deposition techniques
Sol-Gel Hydrothermal ALD Thermal Evaporation
Sol-Gel
Sol–gel chemistry is the preparation of inorganic polymers or ceramics from solution through a
transformation from liquid precursors to a sol and finally to a network structure called a ‘gel’. Traditionally,
the formation of a sol occurs through hydrolysis and condensation of metal alkoxide precursors but a sol can
be more generally defined as a colloidal suspension, which encompasses a wider range of systems.
Hydrothermal
The synthesis method uses the solubility in water of almost all inorganic substances at elevated temperatures
and pressures, and subsequent crystallization of the dissolved material from the fluid. As implemented in the
name, water at elevated temperatures plays an essential role in the precursor material transformation. By
hydrothermal route we can fabricate numerous varieties of nanostructures like, nanorods, nanowires,
nanosheets, nanoflakes, nanotrees, nanourchins, nanoparticles, nanospheres, nanodiamonds and so on.
Controlling of nanostructures by Hydrothermal
Different parameters for controlling nanostructures by Hydrothermal
1) Seed Layer (For vertically aligned nanostructure and increased adhesion)
2) Concentration of Precursors (Density of a particular nanostructure for both seed layer and growth sol.)
3) Role of pH, growth time, growth temperature (To initiate a particular chemical reaction)
4) Surfactants (attack on surface cleavage energies of nuclei to modify nanostructure growth)
5) Growth Modifiers/Additives (increase or decrease growth time of nanostructures)
6) Substrate Angle (avoid ppt. and effect on morphology)
7) UV-Ozone and plasma treatment (To improve electronic properties)
Atomic Layer Deposition
1) Exposure to Precursor 1: The first precursor is exposed to the surface and is chemically adsorbed on the surface until
the surface is saturated. Further chemical adsorption ceases. The adsorbed precursors and precursor in the gas phase do not
react with other precursor molecules. The chemically adsorbed precursor does not desorb under the ALD conditions.
2) Purge: Unreacted precursor (both in the gas phase and physically adsorbed on the surface) is removed from the entire
deposition zone. The substrate surface is left chemically to reach with the second precursor.
3) Exposure to Precursor 2: The second precursor is exposed to the surface and chemically adsorbed on the surface
modified by the first precursor until the surface is saturated. Further chemical adsorption ceases. The chemically adsorbed
precursor does not desorb under the ALD conditions.
4) Purge: Unreacted precursor (both in the gas phase and physically adsorbed on the surface) is removed from the entire
deposition zone.
Atomic Layer Deposition
Unique Properties of ALD:
• ALD attributes self-limited growth.
• Good reproducibility.
• Excellent uniformity and conformity over the large substrate areas.
• Uniform step coverage.
• Accurate control of film thickness and composition.
• ALD is mostly preferred for angstrom to nm film thickness.
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Thermal Evaporation (PVD)
(PVD) process in which material from a thermal vaporization source reaches the substrate with little or no
collision with gas molecules in the space between the source and substrate. The trajectory of the vaporized
material is “line-of-sight”. The vacuum environment also provides the ability to reduce gaseous
contamination in the deposition system to a low level. Typically, vacuum deposition takes place in the gas
pressure range of 10-5 Torr to 10-9 Torr depending on the level of gaseous contamination that can be tolerated
in the deposition system.
Deposition Techniques Step coverage
Solar Cell Device
• Method.
by Ban et al. Material & Design (2016)
Requirements:
1. Low temperature of deposition (120°C).
2. Ideal geometry.
3. Uniform coating.
Basic Characterizations Techniques for IPSC
• SEM is used to study the morphology of the samples up to the range of < 300 nm
• HR-TEM is used to study the atomic lattice structure and morphology up to <1 A*
• AFM is used to check the surface roughness of the thin films
• UVS is used to determine the transmittance and band gap of the thin films
• XPS is used to determine %age composition and oxidation bonding states of material
• EIS is used to determine the election life times and Rshunt and Rseries of circuit
• Hall measurements provides us data on the electrical properties of the thin films
• EQE provides us information on the tendency of the material to absorb photons and
generate excitons.
• Solar Simulator provides us information on the performance indicators related to the
solar cell.
Generalized IOSC Fabrication Steps
Motivation and Experimental
Experimental
Experimental
A. Substrate/Cathode:
- ITO/FTO/Silicon
- IPA, Acetone, IPA 20min sonication
B. Electron transport layer:
Fabrication steps for low density ZnO nanorods:
Seed layer:
- 0.05 M ZAD + 0.05 M EA sol. in ethanol stirred @80*C for 23 hours.
Hydrothermal growth sol:
- 0.05 M ZNH + 0.05 M HMTA (In Water).
- Heating reactor in furnace at 90*C for different time intervals.
- Cleaning and drying of substrate in oven.
Steps for ALD surface treatment:
-ALD Regime (0.2, 10, 0.5, 20) DEZ PurgeWaterPurge
-1000 mtorr operating pressure @ 150*C
-Growth Rate = 0.14 nm/cycle and Film Thickness = 1, 3, 5, 30 nm.
C. Active layer:
- P3HT : PCBM (1 : 0.8 wt%) / Chlorobenzene
- Spin-coating for 35s @ 1000rpm
- Solvent annealing for 10min
D. Hole transfer layer:
Fabrication steps for V2O5 as HTL:
- Vanadium(V) oxitriisopropoxide (133ul) : IPA (20ml) mixing at 40*C for 1 h
- Spin-coating for 45s @ 8000 rpm
- Annealing on hot plate at 165*C for 5mins
E. Cathode:
- Ag electrode 100nm deposition (thermal evaporated)
F. Measurement:
- All devices to be measured on solar simulator AM 1.5.
Results and Discussion
(a, b) Low areal density ZnO NRs (top and side view) and (c, d) High-resolution TEM images of ZnO NRs (a) with 5 nm thickness
high areal density ZnO NRs (top and side view). and (b) without ALD-ZnO.
Reaction Mechanism
For Seed Solution:
4Zn(CH3COO)2.2H2O → Zn4O + 7H2O+ 2HCH3COO (Sol. in Ethanol)
Zn(CH3COO)2.2H2O Zn2+ + 2OH- + 2CH3COOH (Sol. in Water)
Zn2+ + 2OH- Zn(OH)2
Zn(OH)2 ZnO + H2O (Heating)
For Growth Medium Solution:
Zn(NO3)2 Zn2+ + 2NO3-
(CH2)6N4 + 6H2O 4NH3 + 6HCHO
NH3 + H2O NH3.H2O
NH3.H2O NH4+ + OH-
Zn2+ + 2OH- Zn(OH)2
Zn(OH)2 ZnO + H2O (Heating)
• Z.L. Wang, ZnO nanowire and nanobelt platform for nanotechnology. Mat. Sci. & Engg R 64 (2009) 33–71.
• Preparation and characterization of hydrothermally grown zinc oxide nanorods for photocatalytic applications, Gowthaman (PhD Thesis)
• D. Polsongkram, P. Chamninok, S. Pukird, L. Chow, O. Lupan,G. Chai, H. Khallaf, S. Park, A. Schulte, Effect of synthesis conditions on
the growth of ZnO nanorods via hydrothermal method. Physica B 403 (2008) 3713– 3717
• Fraunhofer, Germany
Reaction Mechanism
TDMAT chemistry for ALD
Me2N NMe2 Me2N NMe2
Ti H H
Me2N NMe2
Me2N NMe2
H H Ti
O O O O
<TDMAT>
@ Low Temperature
Ti[N(CH3)2]4 + 2H2O → TiO2 + 4HN(CH3)2
Ti[N(CH3)2]4 + 4/3NH3 → TiN + 4HN(CH3)2 + 1/6 N2
TiN + O2 → TiO2 + 1/2 N2, ∆G = -139 Kcal/mol
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