Physics at surfaces An Overview of physical and chemical

properties that change when the materials are of nanometres in Size

Lec. (2)

    Multiplier Prefix Symbol Numerical Exponential

yotta Y 1,000,000,000,000,000,000,000,000 1024

zetta Z 1,000,000,000,000,000,000,000 1021

exa E 1,000,000,000,000,000,000 1018

peta P 1,000,000,000,000,000 1015

tera T 1,000,000,000,000 1012

giga G 1,000,000,000 109

mega M 1,000,000 106 kilo k 1,000 103

hecto h 100 102 deca da 10 101

no prefix means: 1 100 deci d 0.1 10¯1 centi c 0.01 10¯2 milli m 0.001 10¯3 micro m 0.000001 10¯6

nano n 0.000000001 10¯9

pico p 0.000000000001 10¯12

femto f 0.000000000000001 10¯15

atto a 0.000000000000000001 10¯18

zepto z 0.000000000000000000001 10¯21

yocto y 0.000000000000000000000001 10¯24

A List of the Metric Prefixes

NanoScienceNanotechnology

Physics

MaterialScience

Engineering

Chemistry

Biology

Medicine

Working with nanoscale requires the impact combination of all traditional science

The Secret• Molecules are made of atoms• Atoms are made up of electrons, protons and neutrons• Electrons and protons are “charged”• Opposites attract/likes repel• Moving charges can create a magnetic field (and vice versa)• They are moving all of the time• Most atoms are not spherical• The atoms and molecules interact with each other all the time• ALL forces and interactions are present ALL of the time at ALL

size scales• What does change at different size scales is that the PRIORITY

of the forces and interactions will change

Forces and Interactions• Electrostatic• Magnetic• Gravitational• Thermal• Vibration• Adhesion• Surface tension• Friction• Chemical• Quantum

Bohr radius = 0.5292Å ≈ 0.05 nm

C atom (VdW radius)=0.17 nm

In a 1nm line: 3 C atoms

In a 1nm·1nm surface: 9 C atoms

In a 1nm·1nm·1nm cube: 27 C atoms

In a 1m·1m·1m cube: 2.7·1028 C atoms

Typical nanosystems may contain from hundreds to tens of thousands of atoms.

The Nanoscale 1, 2, 3 Dimensions

Number of Nano-Dimensions:

1 – Nanofilms

2 – Nanowires

3 - Nanodots

One can start by creating Nanofilms on a substrate and proceed to Nanowires and Nanodots by lateral lithography

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CarbonDiamond

Graphite: 2.3·103 Kg·m-3 = 1.15·1029 C atoms·m-3

Diamond: 3.5·103 Kg·m-3 = 1.76·1029 C atoms·m-3

Superhydrophobic (SHPB)

Superhydrophobic – having a water contact angle of greater than 150°

Water repellent surfaceAchieved by surface nanotexturing and low surface energy

Laser structuring of water-repellent biometic surfaces

A water-resistant surface inspired by the lotus leaf could enable applications in microfluidics, underwater coatings, and controlled deposition.

Example:

Most MetalsPolycrystalline grains of varying shapes and sizes.Misaligned planes of atoms slip past each other easily, absorbing energy and allowing dislocations to move, making deformation permanent.Grain boundaries represent weak spots of less than optimal atomic packing, where fractures can form and corrosion starts.

Metallic GlassCooled faster than atoms can rearrange into a crystal.Dislocation movement obstructed so absorbs less energy and rebounds elastically to its initial shape.Resistant to corrosion and wear.Slow heat conduction limits casting thickness.

Description: Luminescent CdS (Cadmium Sulfide) nanoparticles immobilized on copolymer microspheres were produced by the chemical precipitation of poly(St-co-GMA-IDA)–Cd2+ (PSG–Cd2+) complexes. PSG latex with GMA-IDA has chelating groups within the copolymer latex with coordination sites for chelating metal ions, at which CdS particles were grown. Using ethanol as a cosolvent improved both the particle monodispersity and the surface charge. The size distribution, morphology and structure of CdS nanoparticles were measured by transmission electron microscope (TEM) and x-ray diffraction (XRD) analysis. The growth kinetics of CdS nanoparticles were studied by TEM and obtaining photoluminescence (PL) spectra. The size and morphology of CdS particles were influenced by the amount of the chelating, iminodiacetic acid group on the surface of the copolymer microsphere, the concentration of Cd2+ ions and the pH. The shown PSG-A3–CdS sample which was formed from ultrafine CdS particles with mean diameters below 5 nm immobilized on the surface of copolymer microspheres, emitted photons with a higher energy than other samples in this investigation.

References:Yuan-Chih Chu, Cheng-Chien Wang, Yao-Hui Huang and Chuh-Yung Chen. "Preparation and characterization of luminescent CdS nanoparticles immobilized on poly(St-co-GMA-IDA) polymer microspheres." Nanotechnology 16 (4), 376, (2005).

CdS Nanoparticles on Polymer Microspheres

Sporting EquipmentAccuFlex® Evolution Golf Shaft

Babolat® NS™ Tour Tennis Racket

BMC Racing Fourstroke FS01

Nanodesu X Bowling Ball

Nanodynamics MX™ Golf Balls

Nitro Hockey Sticks

Orca PFLEX™ Fullsleeve Wetsuit

Stealth CNT® Baseball Bat

XLC Nanotech Crampon

Nanoscale Devices: Electronic devices that are designed with lateral features of 100 nm or less. Designers began searching for a new name for their smaller devices for two main reasons:

Fabrication Difficulties

Physical Operation: Bulk Properties of Physics VS. Quantum Mechanics

(An overview of both will be covered soon!)

To understand the problem, let’s review the operation of the most popular transistor in use today, the MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor)

MOSFETS are built starting with a substrate that is doped, or loaded with impurities that give the substrate a large amount of extra mobile charge (positive in the case of holes, negative in the case of electrons.)

Nanoscale Electronics

Source Drain

SiO2 Insulator (Glass)

Gate

holes

electrons

5 volts

electrons to be transmitted

Figure 2

Image courtesy of me. =o)

MOSFET Operation Animation

Step 1: Apply Gate Voltage

Step 2: Excess electrons surface in channel, holes are

repelled.

Step 3: Channel becomes saturated with electrons.

Electrons in source are able to flow across channel to Drain.

P

N N

MOSFET Fabrication Problems

Present Day Fabrication Method (Lithography): IC Pattern is projected in 1 cm2 increments onto a silicon wafer using UV light and a series of lenses that reduce the pattern to some given required resolution. Each 1 cm2 section contains roughly 109 picture elements (pixels).

Nanoscale Devices: Most features of the typical nanoscale device are too small to be made like present day devices so a sharp focused beam of electrons is used to build the 1 cm2 pattern one device at a time. Of course, this is way too slow for mass fabrication.

Difficulties in CMOS Scaling2 below 0.10 µm

As mentioned earlier, CMOS devices are currently fabricated using some form of lithography. In order to obtain the minute resolution needed for the nanoscale regime, optical lithography (using a 193 nm wavelength laser) with phase-shifting could be used. Unfortunately, this method relies on surface changes in the mask that cause interference patterns that sharpen the image cast on the silicon. Due to this geometric dependence, this method is not very useful for building arbitrary devices. (.10 to .12 µm)

X-Ray Lithography is another possible solution to the fabrication problem. In this method, an x-ray emitting device is passed over (very closely) silicon covered in an x-ray absorbing material (such as Au) to image a circuit. The problem with this mainly is that the absorbing material cannot be pressure-deformed as this will alter the image accuracy. (30 nm features)

Electron Beam (Projection Lithography): Two different methods using similar technology. Main difficulties here are throughput and Coulomb interactions and geometric imperfections. (10 nm and 50 nm respectively)

F

A

B

R

I

C

A

T

I

O

N

Figure 3 - X-RAY Lithography – 80 nm wide lines.2

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Technology: Building Smaller Devices and Chips

Nanolithography to create tiny patterns Lay down “ink” atom by atom

Mona Lisa, 8 microns tall, created by AFM nanolithography

Sources: http://www.ntmdt.ru/SPM-Techniques/Principles/Lithographies/AFM_Oxidation_Lithography_mode37.htmlhttp://www.chem.northwestern.edu/~mkngrp/dpn.htm

Transporting molecules to a surface by dip-pen nanolithography

Nanoscience is where atomic physics converges with the physics and chemistry of complex systems.

Quantum Mechanics Statistical Mechanics

Quantum Mechanics dominates the world of atoms, but typical nanosystems may contain from hundreds to tens of thousands atoms.

Emergent behavior

How much a system is quantum mechanical?

1. Below a certain length scale (that depends on interaction strengths) systems must be described using quantum mechanics.

Ex. quantum dots, nanocatalysts, electronic transport through nanowires amd thin films

2. Many processes depend on the number of available energy states per unit energy. This quantity varies with the dimensionality of the system.

3. The effective concentration of reactants that are confined in nanostructures may be very high.