In today s lecture, we will cover:

Transcription

1 In today s lecture, we will cover: Chemical Vapour Deposition Atomic Layer Deposition Layer-by-Layer Polyelectrolyte Depositions 1

2 Nanofilms Goals for this section: Understand the chemistry of deposition for ALD and CVD, as well as the requirements for the precursor Examine the versatility of reagents and molecular level control in Layer-by-Layer film deposition

3 Thin Film Deposition Nanoscale thin films can be prepared using a variety of bottom-up different techniques Physical Deposition Evaporation Sputtering Thin Film Deposition Chemical Deposition Chemical Vapour Deposition Atomic Layer Deposition Dip/Spin coating

4 Chemical Vapour Deposition Chemical Vapour Deposition (CVD) is a common thin film growth technique. It relies on a precursor compound reacting at a surface (called the substrate) to produce a material. The reaction can be with a secondary reaction gas or it can be thermolysis (thermal breakdown) of the precursor itself. In this second instance, the precursor supplies all components of the target film, and is called a single source precursor.

5 Many Examples of CVD

6 Reactors N 2 NH 3 + N 2 Furnace Heater Vapourizer substrate Ga 2 (NMe 2 ) 6 The reactor setup is relatively simple for CVD: two independent precursors are introduced simultaneously, one typically carrying the metal, and one typically carrying the other atom to make a thin film. The example above was drawn for gallium nitride, a widebandgap semiconductor: Ga 2 (NMe 2 ) NH 3 2 GaN + 6 HNMe 2

7 Basic Process Steps

8 Atomic Layer Deposition A more precise approach is to deposit the film one atom layer at a time. This is the principle of ALD. It is common to run 1,000 cycles, which can take ~1,000 minutes.

9 ALD The Principle A vapour is introduced over a surface where it reacts chemically, anchoring itself. Due to specific chemical design, only one layer forms. This is the key to ALD. After removing excess chemical from the gas phase, a second vapour is introduced It reacts with the monolayer to produce a one molecule thick layer of target material.

10 ALD The Process

11 Conformality is the hallmark of ALD

12 List of materials deposited by ALD Materials Today Volume 17, Issue 5, June 2014, Pages doi: /j.mattod

13 ALD applications: Li ion batteries High performance cathodes and anodes tend to lose effectiveness over time, especially under high temperatures or charging conditions. A thin protective coating can help but too thick of a coating inhibits electron and ion transfer. ALD can create sub-nm thin coatings that can improve cycle life, rate capability, and even safety. Image:

14 ALD applications: Flexible coatings Flexible ultrabarriers for applications including OLEDs, photovoltaics and packaging. Nanothin films offer glass-like water and oxygen protection, with excellent adhesion Image:

15 Layer-by-Layer Polyelectrolyte Deposition Sequential deposition of a monolayer of charged material on a charged substrate

16 Layer-by-Layer Polyelectrolyte Deposition Advantages: deposition on surfaces of almost any kind and any shape many control parameters: concentration, adsorption time, ionic strength, solvent, composition, temperature

17 Nanomaterials can be incorporated with great control Adv. Mater. 1997, 9, 61-65

18 Can scale up using spray coating

19 Can deposit on almost any charged Hollow capsules can be prepared using a sacrificial charged spherical template Deposition, centrifugation (for rinsing, and dissolution of the template) surface

20 Applications of polyelectrolyte multilayers Multicomponent coatings can be put together with nanoscale control, using an environmentally friendly low cost technique The first commercial products have already been introduced to the market (early as 2001) Coatings for contact lenses

21 Applications: Bone regeneration

22 Applications: Flexible metal films Metal rubber