September 23, 2011

Background

 What is nanoscience?  What is considered nanoscale?  What is the significance?

Fullerene (C 60, D<5nm)  Nobel Prize in Chemistry 1996  Harold Kroto, Robert Curl & Richard Smalley (Rice University)

Graphene  Nobel Prize in Physics 2010  Andre Geim & Konstantin Novoselov (University of Manchester)

Carbon Nanotubes (D ~ 4 nm)

Quantum Dots (5 to 50 nm)

Gold Nanoparticles  HeLa cells with fluorescent gold nanoparticles  (Dr. Mengxiao Yu and Dr. Jie Zheng – UT Dallas).

Background

Properties of Light  Light is a wave (Electromagnetic (EM) radiation)  Waves have 3 features  Wavelength ( λ)  Amplitude  Frequency ( ν )  EM radiation = continuous spectrum of all wavelengths (no gaps).

Electromagnetic Spectrum

Equations of Light  c = λν,  c is the speed of light (m/s),  λ is the wavelength (m),  ν is the frequency (s -1 )  ∆E = hν  h is Planck’s constant (J s)  ν is the frequency (s -1 )  ∆E = (hc)/λ

When light hits an object…  Different wavelengths can be…  Absorbed  Transmitted (allowed to pass through)  Reflected  …depending on the wavelengths of light, object’s chemical composition, and its size.

Color Wheel  Object absorbs orange = blue color observed.  No light absorbed = all are reflected or transmitted (white light).  All wavelengths are absorbed = black color observed.

How to separate light  Prism  Diffraction

Figure 5: Diffraction of light (pg 25)  w(sin θ n ) = n λ  tan(θ n ) = y n /L

Purpose  Measure the width of a single hair using a laser pointer and diffraction.  Synthesize Ag NPs, and investigate how color is related to particle size.

Materials  Laser pointer  Measuring tape  Scotch tape  Hair  Stock solutions (Sodium citrate, silver nitrate, hydrogen peroxide, potassium bromide, sodium borohydride)  Large test tubes  Stoppers or parafilm to seal test tubes  Spectrophotometer  Cuvettes (2 to 5)

Safety  Wear goggles and gloves!  AgNO 3 is corrosive  NaBH 4 is flammable and toxic (inhalation, absorption and ingestion)  Sodium Citrate may irritate skin, etc.  Hydrogen peroxide is corrosive and causes burns to eyes, skin etc.  Don’t play with the laser pointers!