Touch on Nanomaterials

Jin WangDept. Mechanical and Aerospace Engineering

Feb.28,2007

Outline

What is nanomaterial…

Why nano and select methods to fabricate nanomaterials

…

Fabrication of nanocrystals by controlling nucleation and growth process

Fabrication of nanostructured materials via wet chemical route --Sol-gel --Hydrothermal synthesis

Fabrication of nanostructures via top-down lithography strategy

What is nanomaterials…

~100 m

Divide into 1000

equal parts

100 nm

human hair virus Manmadeparticles

~100nm

Natural nanomaterial Artificial nanomaterial

Generally it refers to the materials whose dimensions (either on 1, 2, or 3 dimensions) are on the order of a billionth of a meter.

Why nano…Due to the small size…

Distinct behaviors while interacting with external stimuli(optic, electric, magnetic…)

Promising performance in optical and electrical devices

Extraordinarily large surface to volume ratio

High-efficiency catalysts, high-sensitivity sensors and transducers

Intel’s transistorshttp://snf.stanford.edu

Access to better understand the material world on the order which has never been so small ---- to better control the small world

Fabrication of nanocrystals by controlling nucleation and growth process---- fabrication of nanocrystals in glass matrix

The formation of crystals always comprise two steps:nucleation-- a process in a phase transition in which nuclei of a new phase are first formed; growth-- the propagation of the new phase at a faster rate.

If we provide suitable environment to let the process go on and then cut off to stop theprocess just after the nucleation or at the early stage of growth, it can be imagined thatwe can control the size of the as obtained crystals on small scale.

Example--fabrication of rear earth doped oxyfluoride glass ceramics

Rear earth ions– optical active speciesOxyfluoride glass ceramics:Oxide glass matrix– good mechanical properties and stability under harsh environment,widened spectrum band, ability to be fiberized;Fluoride crystals– provide rear earth ions low-phonon environment thus the optical output efficiency is greatly enhanced. Nanocrystals– avoid refraction loss and keep the material transparent in the UV-VISrange ---- key to insure the performanceAnother bonus: access to investigate the optical properties of rear earth ions innanocrystals

Fabrication of nanocrystals by controlling nucleation and growth process---- fabrication of nanocrystals in glass matrix

Process:Melting the raw materials at high temperature (~1400 0C)rapid quenching to have the oxyfluoride glassesDTA measurement to find glass transition temperature and crystalization temperatureperform nucleation and growth process under appropriate heat treatment scheme (temperature, time, ramp speed).

20 40 60 80

141

115

40222

130

2113

300

111

110

Inte

nsity

2

glass

600oC-4hr

625oC-4hr

650oC-4hr

675oC-4hr

200 400 600 800 1000

0

20

40

60

80

100

Tra

nsm

itta

nce

(%)

Wavelength(nm)

glass

600oC

625oC

650oC

675oC

450 500 550 600 650

4 S3

/2→

4 I 15

/2

2 H1

1/2→

4 I 15

/2

Inte

nsity

Wavelength (nm)

glass

600oC

625oC

650oC

675oC

Fabrication of nanostructured materials via wet chemical route -- sol-gel synthesis of La0.6Sr0.4CoO3 nanostructured materials

Wet and Chemical: the reaction process which is performed in solution

Evaporation

Nanograined film Nanoparticles Nanotubes/Nanowires

Metal alkoxidesolution

Sol

Xerogel film

Sol-filled template

Nanotube/Nanowire-filled template

Dissolve template

Heat

Heat

Gel

Heat

Spincoating

Evaporation

Template filling

Example:Our sol-gel process

When we want large area-to-volume-ratio of nanomaterials to enhance theefficiency of surface reaction, wet chemical route is a good resort. Mass production and low cost!

SEM image of La0.6Sr0.4CoO3 nanograined film AFM image of La0.6Sr0.4CoO3 nanograined film

Fabrication of nanostructured materials via wet chemical route -- sol-gel synthesis of La0.6Sr0.4CoO3 nanostructured materials

500nm

SEM image of La0.6Sr0.4CoO3 nanotubes SEM image of La0.6Sr0.4CoO3 nanowires

Fabrication of nanostructured materials via wet chemical route -- sol-gel synthesis of La0.6Sr0.4CoO3 nanostructured materials

Fabrication of nanostructured materials via wet chemical route -- Hydrothermal synthesis of nanotubes/nanowires

Definition:Techniques of crystallizing substances from high-temperature aqueous solution at high vapor pressure. The term “hydrothermal" is of geologic origin.

Tools:The process is performed in an apparatus consisting of a steel pressure vesselcalled autoclave, in which a nutrient is supplied along with water.

How to fabricate 1D nanomaterial:If the product itself has unique preferential crystal structureor, some additives with preferential structure (always organic polymers like PVP, PEG etc) were incorporated into the system, the growth of the new phase will be along one priority crystal direction,thus 1D structure can be obtained.

SEM images of hydrogen titanate nanotubesvia hydrothermal synthesis at 120ºC

SEM images of hydrogen titanate nanowiresvia hydrothermal synthesis at 200ºC

Fabrication of nanostructured materials via wet chemical route -- Hydrothermal synthesis of nanotubes/nanowires

Fabrication of nanostructures via top-down strategy

Crossover with solid state silicon techniques:Utilize lithgraphy (photo lithography, dip-pen, eBeam, SPM…) to generate template;Combined with molecular self-asembly to functionalize template surface.

--Provide what experimenter appreciates the most: certainty and controllability

Example: Our approach:Combine sol-gel and photo lithography to produce microstructuresspin coating photo resist filmalign mask and UV exposure to do photolithographydevelop exposed photo resist film and check the template under microscopedeposit the material you want (sol-gel spin coating)

Fabrication of nanostructures via top-down strategy

The resolution of photo lithography limited the size of structures on the orderof micrometers. Ebeam lithography can provide smaller and SPM lithography is able to produce thesmallest. The smaller you want, the more difficulties you face.

Ebeam lithgraphy and sol-gel

S.Donthu, Z.X.Pan, B.Myers, et al, Nano lett. 5, 1710 (2005).