an introduction to microelectromechanical...

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An Introduction to Microelectromechanical Systems(MEMS)

Bing-Feng Ju, ProfessorInstitute of Mechatronic Control Engineering,

College of Mechanical and Energy Engineering,Zhejiang UniversityP.R.China, 310027

Email: [email protected]: 86-571-8795-1730Fax: 86-571-8795-1941

Presented toGraduate students at

College of Mechanical and Energy EngineeringZhejiang University

February to May 2010

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CONTENTSelf-introduction1. Overview of MEMS and Microsystems

Working Principles of Microsystems2. The Scaling Laws

Electromechanical Design of MEMS and Microsystems3. Material for MEMS and Microsystems

Part 1: Silicon and silicon compoundsPart 2: Piezoelectric and polymers

4. Microfabrication ProcessesPart 1: Photolithography, doping with ion implantation and diffusionPart 2: EtchingPart 3: Depositions: physical, chemical and epitaxy

5. MicromanufacturingAssembly, Packaging and Testing to Nanoscale Engineering

Part 1: MicroassemblyPart 2: Packaging with surface and wire bondingPart 3: Reliability and testing

6. Introduction to Nanoscale EngineeringPart 1: Overview of nanoscale engineeringPart 2: Material characterization and measurements

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Lecture 6Introduction to Nanoscale Engineering

“If I were asked for an area of science and engineering that will most likely produce the breakthroughs of tomorrow, I would point to nanoscale science and engineering.”-Neal LaneFormer Assistant to President Clinton for Science and TechnologyA Futuristic Nanoscale Engineering Product:

an artistic view of a step-shaft built with atoms

“Nanotechnology has given us the tools…to play with the ultimate toy box of nature– atoms and molecules. Everything is made from it…..The possibilities to create newthings appear limitless.” by Horst Stormer, a Nobel Laureate in physics

“the way of ingeniously controlling the building of small and large structures, with intricate properties; it is the way of the future, a way of precise, controlled building, with incidentally, environmental benignness built in by design.” by Ronald Hoffmann, a Nobel Laureate in chemistry.

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Lecture 6(Part 1)Overview of Nanoscle Engineering

● Nanotechnology-What is it and why?● Evolution of nanotechnology

● Nanotechnology and nanoscale engineering● Fundamentals of nanomanufacturing

● Applications of nanotechnology● Future outlook

Lecture 6(Part II)Nanoscale Engineering Analysis and

Measurements of Selected Material Properties

Because both nanotechnology and nanoscale engineering are rapidly expandingemerging technologies of the New Century, it is necessary to split this lecture intothe following two parts just to barely cover the current state of the development:

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Nanotechnology is the creation of:

USEFUL/FUNCTIONAL materials, devices and systems through control of matter on the nanometer length (nm)scale, and exploitation of novel phenomena and properties(physical, chemical, biological) at that length scale to satisfy human needs.

What is Nanotechnology?

Lecture 9AOverview of Nanoscle Engineering

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milliMicro*Nano**picofemtoatto

Length (m)0 10-18 10-15 10-12 10-9

(nm)10-6

(µm)10-3

Humanhair:10-4 m

Virus: 10-7 m

DNA < 3 nmProtein: 2-5 nm

Hydrogen atom: 0.1 nm, or one angstrom

Typical electron radius: 2.8x10-15 m

The Perception of Length Scale- The nanometer (nm)

** 1 nm = 10-9 m ≈ span of 10 H2 atoms*1 μm = 10-6 m ≈ one-tenth of human hair

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Why nanotechnology?

Specifically, two factors can determine properties of matter:● The atomic structures (e.g., No. of electrons, as in the periodic table)

Example: Change electric resistivity of silicon by doping.● The arrangement of atoms (e.g., molecular structures)

If only we can manipulate the atomic structures and control the arrangement of the atoms in matter, can we then create materials with desirable properties– e.g., super strength, super electric and thermal conductivities, healthy genomes

and biochemical substances, etc.

All matter that exist in universe are made of atoms and molecules.

The way molecules of various shapes and surface features organize into patterns on nanoscales determines important material properties (e.g. electrical conductivity, optical properties, mechanical strength, etc.)

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Active R&D in Nanotechnology:inspired by Richard Feynman’s speech in 1959

Feynman, R., “There’s Plenty of Room at the Bottom: An invitation to enter a new field of physics,” (miniaturization) first presented at the American Physical Society at California Institute of Technology on December 29, 1959. Subsequent publication in ‘Engineering and Science’, Caltech, February 1960.

(1918 - 1988)A visionary and a Nobel Laureate in Physics, 1965

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Quotations from of Richard Feynman’s Speech:

“ A field, in which little has been done, but in which an enormous amount can be done in principle.”

“This field is Miniaturization.”

“In the tiniest cell, all information for the organization of a complex creature such as ourselves can be stored.

All this information - whether we have brown eyes, or whether we think at all, or that in the embryo the jawbone should first develop with a little hole in the side so that later a nerve can grow through it -- all this information is contained in a very tiny fraction of the cell in the form of

long-chain DNA molecules in which approximately 50 atoms are used for one bit of information about the cell ”

Feynman’s view on “The marvelous biological systems”:

Feynman’s vision on a new field of research:

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Feynman’s view on “The marvelous biological systems”- Cont’d:

“Biology is not simply writing information; it is doing something about it.”

“ Many of the cells are very tiny, but they are active; they manufacturevarious substances; they walk around; they wiggle; and they do all kinds of marvelous things - all on a very small scale. Also they store information.

Consider the possibility that we too can make a thing very small which does what we want - that we can manufacture an object that maneuvers at that level! ”

Feynman’s vision on “Nanotechnology”:

“ So, ultimately, when our computer get faster and faster and more and more elaborate, we will have to make them smaller and smaller.

But there is plenty of room to make them smaller.

There is nothing that I can see in the physical laws that say the computer elements cannot be made enormously smaller than they are now ”

Quotations from Richard Feynman’s Speech (Cont’d):

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The Very First Man-Made Nanostructure -The “Buckyball”

Made from the Buckminsterfullerene - a third form of pure carbon molecule. (after the name of a futurist, R. Buckminster Fuller)

It contained 60 carbon atoms in the shape of a soccer ball with a diameter of 0.7 nanometer.

Created in 1985 by a chemistry professor, Richard Smalley from Rice University -a Nobel Laureate in 1996.

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• Electronics, Computing and Data Storage

• Materials and Manufacturing

• Health and Medicine

• Energy and Environment

• Transportation

• National Security

• Space exploration••

Nanotechnology is anenabling technology

Major Impacts of Nanotechnology(source: Meyya Meyyappan, NASA Ames)

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• Processors using molecular electronics with declining energy use and cost per gate, thus increasing efficiency of computer by 106.

Nanotechnology Benefits in Electronics and Computing(source: Meyya Meyyappan, NASA Ames)

Heat = Horrendous challenge!!

• Small mass storage devices: multi-tera (1012) bit levels.

• Integrated nanosensors: collecting, processing and communicating massive amounts of data with minimal size, weight, and power consumption.

• Higher transmission frequencies and more efficient utilization ofoptical spectrum to provide at least 10 times the bandwidth now.

• Display technologies, e.g., TFT.

• Quantum computing, e.g., spinning single electron transistor. 14

Nanotechnology Benefits inElectronics and Computing-Cont’d

The Nanochip

Nano transistors

Gates

SiO2 film

Silicon substrate(thin pure silicon film)

Advantages: (1) Low unit cost. (2) Narrow gates for faster on-off

boost speed limit of the integrated circuits

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Nanotechnology Benefits inElectronics and Computing-Cont’d

Intel roadmap on nano transistorsusing micro technology:

90 nm

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3222

2003 2005 2007 2009 2011 Year

Tran

sist

or S

ize

Increase Leakage-Another major challenge!

Single-ElectronTransistor

?

Silicon-basedμ-technology

Possible materials?Nanotechnology?(Likely technology)

Length: 50 nm

L = 30

L = 20

L = 15

L = 10

Gate oxide: 1.2 nm

Gate oxide: 0.3 nm

Equivalent to2000 wires in a human hair!

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Nanotechnology Benefits in Data Storage-1 The ever-increasing demand for high density information storage:

2007

10,000 Mbits/in2

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Nanotechnology Benefits in Data Storage-2

Data Storage Requirements:

● Density ● Data rate

● Error rate ● Overall reliability

● Re-writability ● Data retention

● Tracking ● Cost

Source: “Scanning Probes Microscope & Their Potential for Data Storage,” John Mamin, IBM Almaden Research Center, San Jose, CA. (Private communication)

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Nanotechnology Benefits in Data Storage-3● The continuous demands for high density data storage has passed the

limit of traditional electromagnetic means.● A new concept of “Read-Write” is being developed – the “Millepede” project

by IBM, San Jose and Zurich, Switzerland. ● Working principle involving indenting the surface of polymer film using AFM.

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Nanotechnology Benefits in Data Storage-4

● Encouraging initial results of the Millipede development:

40 nm bit size

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• Expanding ability to characterize genetic makeup willrevolutionize the specificity of diagnostics and therapeutics

- Nanodevices can make gene sequencing more efficient.

• Effective and less expensive health care using remote and in-vivo devices.

• New formulations and routes for drug delivery, optimal drug usage.

• More durable, rejection-resistant artificial tissues and organs.

• Sensors for early detection and prevention.

Nanotube-basedbiosensor forcancer diagnostics

Health and MedicineMedical testing, diagnosis; Drug discovery and delivery

(Source: Meyya Meyya[[an, NASA Ames)

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• Ability to synthesize nanoscale building blocks with control on size, composition etc. further assembling into larger structures with designed properties will revolutionize materialsmanufacturing:- Manufacturing metals, ceramics, polymers,

etc. at exact shapes without machining.- Lighter, stronger and programmable

materials.- Lower failure rates and reduced

life-cycle costs.- Bio-inspired materials.- Multifunctional, adaptive materials.- Self-healing materials.


Materials and Manufacturing

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• Energy Production- Clean, less expensive sources enabled by

novel nanomaterials and processes.


Energy and Environment

• Energy Utilization- High efficiency and durable home and

industrial lighting.- Solid state lighting can reduce total

electricity consumption by 10% and cut carbon emission by the equivalent of 28 million tons/year. (Source: Al Romig, Sandia Lab)

• Materials of construction, such as paints, sensing changing conditions, e.g., ambient air temperature, and in response, altering their inner structure for optimal property in thermal conductivity.

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• Thermal barrier and wear resistant coatings.

• High strength, light weight composites for increasing fuelefficiency.

• High temperature sensors for ‘under the hood’.

• Improved displays.

• Battery technology.

• Wear-resistant tires.*

• Automated highways. (Source: Meyya Meyyappan, NASA Ames)

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Major Paradigm Shift in Nanomanufacturing- an overview of molecular manufacturing

Step 1 Isolation of atoms or molecules:Laser source Light detector

Scanning of AFM probe

Repulsive Force

Narrow gap, dFine metal needle tip

Scanning probe

V2. Electromechanical Means –e.g. by using scanning tunneling microscope:

1. Mechanical Means- e.g. by Atomic Force Microscope (AFM):

3. High energy physical chemical means: - plasma sputtering or CVD.

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Step 2 Assembly of loose atoms or molecules:

● Mechanical means by using special equipment, e.g. AFM-guided nanomachining system (AGN), or by special controlled environment.

Major Paradigm Shift in Manufacturing-Overview of molecular manufacturing-Cont’d

● Biochemical means for self assembler and replication.

● Assembled loose gold atoms using STM at IBM:

Final assembledatoms in ”IBM”

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Step 3 Re-bonding free atoms and molecules (Synthesis):

● Mechanical synthesis, e.g. vaporizing free atoms at high temperature in high vacuum, followed by condensations.

● There are other methods for producing nanoscale products, e.g. “epitaxial” growth for nanoparticles and nanowires.

Major Paradigm Shift in Manufacturing-Overview of molecular manufacturing-Cont’d

● Chemical synthesis by diffusion + chemical reactions, e.g. special CVD.

(Synthesized Chinese words of “atom”made by atoms)

● Bio-chemical synthesis, such as the “natural molecular machines” for “growing” proteins, enzymes and antibodies.

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Shaft:

Bearing:

Shaft(axial view):

Bearing(axial view):

(Nano machine components.Nanotechnology-3)HSU.4/14/01

Prospective Nano-scale Device Components

- Building solid structures atom by atom, or molecule by molecule:

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Prospective Nano-scale Device Components – Cont’d

A step-shaft

A pair of matching gears

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● Prevalent nano scale products are limited to the basic rudimentary types of:● Nanodots (Quantum dots or Nanoparticles)

For smart coatings and paints, cosmetic products, etc.

● NanowiresFor gates and switches in molecular electronics, sensors, smart composites, fabrics, etc.

● NanotubesFor structure supports, nano switches, nanofluidics, etc.

Nanotechnology Products and Market Prospects

● Markets and Projected Revenues for Nanotechnology:$50 million in Year 2001$26.5 billion in Year 2003(if include products involving parts produced by nanotechnology)

$1 trillion by Year 2015 (US National Science Foundation)An enormous opportunity for manufacturing industry!!

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)

CNT is a tubular form of carbon with diameter as small as 1 nm. Length: few nm to microns.

CNT is configurationally equivalent to a two dimensional graphene sheet rolled into a tube.

CNT exhibits extraordinary mechanical properties: Young’s modulus over 1 Tera Pascal, as stiff as diamond, and tensile strength ~ 200 GPa.

CNT can be metallic or semiconducting, depending on chirality.

Carbon Nano Tubes (CNT)(Source: Meyya Meyyappan, NASA Ames)

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• The strongest and most flexible molecular material because of C-C covalent bonding and seamless hexagonal network architecture

• Young’s modulus of over 1 TPa vs 70 GPa for Aluminum, 700 GPA for C-fiber

- strength to weight ratio 500 time > for Al; similar improvements over steel and titanium; one order of magnitude improvement over graphite/epoxy

• Maximum strain ~10% much higher than any material

• Thermal conductivity ~ 3000 W/mK in the axial direction with small values in the radial direction

(source: Meyya Meyyappan, NASA Ames)

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• High strength composites.

• Cables, tethers, beams.

• Multifunctional materials.

• Functionalize and use as polymer back bone- plastics with enhanced properties like “blow

molded steel”.

• Heat exchangers, radiators, thermal barriers, cryotanks.

• Radiation shielding.

• Filter membranes, supports.

• Body armor, space suits.Challenges

- Control of properties, characterization- Dispersion of CNT homogeneously in host materials- Large scale production- Application development

(Source: Meyya Meyyappan, NASA Ames)

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• CNT based microscopy: AFM, STM…

• Nanotube sensors: force, pressure, chemical…

• Biosensors

• Molecular gears, motors, actuators

• Batteries, Fuel Cells: H2, Li storage

• Nanoscale reactors, ion channels

• Biomedical- in vivo real time crew health monitoring- Lab on a chip - Drug delivery- DNA sequencing- Artificial muscles, bone replacement,

bionic eye, ear...

Challenges

• Controlled growth• Functionalization with

probe molecules, robustness• Integration, signal processing• Fabrication techniques

(Source: Meyya Meyyappan, NASA Ames)

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Nanotechnology is NOT a natural outgrowth of MEMS technology!!

Microsystems (MST) Technology Nanotechnology Top-down approach Bottom-up approach Miniaturization with micrometer and sub-micrometer tolerances

Miniaturization with atomic accuracy

Builds on solid-state physics Builds on quantum physics and quantum mechanics, e.g. molecular solid and gas dynamics, heat transfer

Evolved from IC fabrication technology Undefined Established techniques for producing electromechanical functions

Far from being developed

Established fabrication techniques Fabrication techniques are in experimental stage

Established manufacturing techniques Limited to manipulation of atoms only Proven devices and engineering systems in marketplace

Only a few staionary machine components of simple geometry are produced

Success in commercialization of a few products A long way to go

Comparison of Micro- and NanosScale Technologies

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There are several issues in transforming NT from scientific discoveries in the laboratory to commercial production by industry:

Nanoscale Engineering-Production and Manufacturing

● Facility for volume production:

- Self-assembly technology.- Reel-to-reel fabrication facility.- Robust tools and processes.- Low capital and operating costs.

● Production systems e.g. “Flexible process-oriented manufacturingsystems” for nanoscale products of: high volume-low variety; medium volume-medium variety, or low volume-high variety of high value.

● Reliability and testing techniques and standards.

● Integration of nanoscale structures and devices into micro-, meso-and macroscale products – packaging and interconnect.

● Production management.36

Future Outlook

Before we look forward to what the ultimate benefits nanotechnology can bring to humankind, let us look back what are great technological breakthroughs in the past Century of human civilization:

Greatest Engineering Achievements of the 20th CenturyAs selected by the US Academy of Engineering

1. Electrification* 11. Highways2. Automobile* 12. Spacecraft*3. Airplane* 13. Internet4. Water supply and distribution 14. Imaging5. Electronics 15. Household appliances*6. Radio and television 16. Health technologies7. Agriculture mechanization* 17. Petroleum and petrochemical

technologies8. Computers 18. Laser and fiber optics9. Telephone 19. Nuclear technology*10. Air conditioning and refrigeration* 20. High performance materials

* with significant mechanical engineering involvement

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• “Dust” sized super-intelligent computers.• “Needle-tip” sized robots for biomedical

applications and for search and rescue.• Spacecraft weighing less than today’s family

cars.

• Biomedicine, e.g. in-vivo systems and surgery that can sustain human lives to 150 years and longer.

• Robots with artificial human intelligence becoming the mainstream workforce in our Society.

• Unlimited supply of clean renewable energies that replace all fossil fuel produced energies on the Earth.

• Tele-transportation systems that can transport human anywhere on Earth in seconds.

• Spacecraft for human/cargo inter-planet traveling.

• New vaccines and medicines that cure many incurable diseases.• Synthetic antibody-like nanoscale drugs and devices seeking out to destroy malignant cells in human or animal bodies.• In-vivo medical diagnostic and drug delivery systems.

• Smart surface coating materials with self-adjusting thermal conductance for buildings and refrigeration systems.• Smart fabrics for self-cleaning clothe.• Super-strong materials for light weight airplanes, vehicles and structures.

• Clean energy conversion systems and super-long life batteries.

• New breed of crops and domestic animals that can feed entire world population.

“Dream” ProductsNear-term Products

Futuristic Industrial Products in the 21st Century by Nanotechnology

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Lecture 6

Nanoscale Engineering Analysis and Measurements of Selected Material Properties

Part INanoscale Engineering Analysis

Part IIMeasurements of Selected Material Properties

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Nanoscale Engineering Analysis

● Any device or engineering system, regardless of its size, is an assembly of components. Nanoscale engineering systems are no exception.

● Each component is expected to perform a specific function, e.g. structural support, or as connecting components, or as signal sensing, or as actuating mechanisms.

● Each component must have proper configuration and sufficient physical strength to carry out the intended function(s).

● Components should sustain externally applied forces, heat, chemical and biological attacks.

● Reliable techniques must be available to ensure components’ ability to perform the intended functions and survive in hostile environmental conditions.

● Techniques in design, plus reliable fabrication, packaging and assemblytechniques for quality and volume production are called nanoscaleengineering.

● Computational nanoscale engineering analysis that ensure the properdesign of these components is thus an essential part of nanoscaleengineering. 40

Engineering Analyses in Micro- and Macroscale

● For structural components in micro- and macroscale(i.e., with linear size > 1 μm):

● The laws of physics based on the behavior of “continuum”apply in these scales .

● A continuum = Aggregations of a great many atoms or molecules.

● Behavior of a “continuum” = Behavior of aggregation of atoms or molecules

● There are differences in behavior of individual atoms or molecules, but the aggregation of large number of these atoms and molecules “average” these differences to give “phenomenological” properties .

● Hence, behavior of individual atoms does not affect the overall behavior of the continuum.

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● Linear theory of elasticity for stress analysis;

● Newton’s 2nd law for rigid-body dynamic analysis;

● Fourier law for heat conduction analysis;

● Newton’s cooling law for heat convection analysis;

● Fick’s law for diffusion analysis;

● Navier-Stokes’s equations for fluid dynamics analysis

Engineering Analyses in Micro- and Macroscale – Cont’d

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● For structural components in nanoscale (i.e., with linear size < 1 μm):

Engineering Analyses in Nanoscale

● The minute size of the component contains many fewer atoms or molecules than a continuum.

(a) A solid plane

≈

(b) Aggregated atoms

(c) Elastic bonds of atoms

::Elastic bonds

Atoms

● Consequently, individual atomic behavior plays dominant role in the overall behavior of the structure.

● Theories derived for continua cannot be used to model nanoscaled substance.

● Phenomenological models based on quantum physics and quantum mechanics are used as bases for engineering analyses of components of nanoscale.

● These few atoms or molecules in a nanoscale substance are interconnectedchemical bonds (simulated by elastic springs):

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● Because the way molecules of various shapes and surface featuresorganize into patterns on nanoscales determines important material properties

● Size-dependent material properties must be incorporated in nanoscaleengineering analysis.

● Inter-molecular physical-chemical actions are another unique elementof nanoscale engineering analyses.

Engineering Analyses in Nanoscale – Cont’d

Inter-molecular distance,d

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Repu

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do

Typical inter-molecular forces:

(c) Elastic bonds of atoms

::Elastic bonds

Atoms

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□ Mechanical strength, e.g., in maximum tensile strength and Young’s modulus.

□ Electrical properties, e.g., electrical resistivity.

□ Chemical properties, e.g., reactivity to chemical reactions.

□ Optical properties, e.g., reactivity to light – same material with different colorsdepending on its size – a value to drug delivery and medical diagnosis.

□ Thermophysical properties, e.g., thermal conductivity, thermal diffusivity, and coefficient of thermal expansion.

□ Melting points and solubility.

□ Magnetic properties.

□ Catalytic properties, e.g., ability to enhance chemical reactions - a vital value to drug discovery processes.

□ Viscosity for liquid and surface tension.

Size-dependent Properties of Nanoscale Materials

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Computational nano-engineering technology aims at the development of nanometer scale modeling and simulation methods to enable the design and construction of realistic nanometer scale devices and systems.

Computational Nanoscale Engineering Analysis

Computational nanoscale engineering design encompasses:

● Stress Analysis

● Molecular Dynamics

● Molecular Heat Transmission

● Molecular Gas Dynamics

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Young’s Modulus of Silicon:

30.3130186.5<111>

34.5110168.0<110>

42.175129.5 <100>

% ChangeYoung’s modulus of nanocantilever at 3 nm thick

Young’s modulus of bulk material

Miller index for orientation

Unit: GPa

Significant size-dependent Young’s modulus of nanoscale materials hasinvalidated the linear generalized Hooke’s law:

Significant modifications of the constitutive relations of materials at this scale b/c the values of both E and vary with the size of the structure.

{ } ( ) { }ευσ ],[ EC=

in which {σ} = stress tensor, {ε} = strain tensor, = the elasticity matrixwith E = Young’s modulus and = Poisson’s ratio.

( )],[ υECν

ν

Stress Analysis of Solids in Nanoscale

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Modifications for finite element analysis of nanoscale solids:The constitutive equations for incremental stress and strain components for a conventional elastoplastic stress analysis of solids with temperature and strain rate-dependent properties:(“The Finite Element Method for Thermomechanics,” T.R. Hsu, 1986)

{ } [ ]{ } [ ]{ } { } { }( ) [ ] ⎟⎠⎞

⎜⎝⎛

∂∂

+∂∂

−++−=−

εε

εαεσ σε &&

&& dFdTTFC

SdDdTDdTCdCd e

Tepep }{1 *

where ( ) [ ]⎭⎬⎫

⎩⎨⎧

⎭⎬⎫

⎩⎨⎧

+⎭⎬⎫

⎩⎨⎧

⎭⎬⎫

⎩⎨⎧

=−−−−

**6,**6 σσσσ ε eCTCS &

[Ce] = elasticity matrix; [Cep] = elastic-plasticity matrix; {DT} and

{ }ε&D

[Ce} = respective temperature-dependent and strain rate-dependent elasticity matrix. α = coefficient of thermal expansion; F = plastic yield function; T = temperature

*σ−

Significant modifications on the above constitutive equations are requiredto accommodate size-dependant material properties and the inter- molecularmechanistic behavior.

and {DT} = respective coefficient matrices relating to the strain rate and temperature T= translated deviatoric stress following von-Mises plastic potential function

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Overview ofMolecular Dynamics

● Deformation of any matter, whether it is solid or fluid, result in movement of atoms or molecules within the matter.

● At molecular level, i.e. nanoscale, such movement of atoms or moleculesmay contribute significantly to the overall physical consequences.

Displacement vector

(a) Initial equilibrium position (b) Position at time t1 (c) Position at time t2

Oscillatory motions of an atom subject to external disturbance

Atoms with elastic bonds:

● One thus needs to treat EVERY problem in nanoscale as a TRANSIENTproblem. The name “static mechanics” does not exist in nano-mechanics.

● Every mechanics analysis is thus related to Molecular Dynamics.

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Principle of Molecular Dynamic Simulation

• It computes the MOTION of individual molecules in solids, liquids and gases.

• Motion of molecules includes: position, velocities and orientations with time(trajectories)

• All molecules are subject to inter-molecular force field and thus the potential energythat includes: static force, kinetic energy, electromagnetic, thermal, etc.

Stochastic Deterministic

Browniandynamics

MetropolisMonte Carlo

Molecular dynamics

Force-biasedMonte Carlo

GeneralLangevindynamics

Simulation methods covers the spectrum of:

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Molecular Dynamics inEngineering Design of Nanoscale Structures

It determines:(1) The required forces (or energy) to move single atoms (or molecules) in a

molecular force field.

Principle-molecular dynamics.Nanotechnology-3)HSU.4/14/01

(2) The motion of individual atoms (or molecules):Trajectories (Positions, Velocities and Orientations) when subject to external force field.

(3) The Schrodinger’s equation (1926) is used as the basic governing equation for the ”deterministic” molecular dynamics.

Displacement vector

(a) Initial equilibrium position (b) Position at time t1 (c) Position at time t2

Atoms with elastic bonds:

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The Schrodinger Equationfor Nonrelativistic Quantum Mechanics (1926)

The position of a charged particle, ),( trrφ in a force fieldof N-charged particles with masses, m0, m1, m2,…, mN-1 can be obtained from the following equation:

ttrihtrtrUtr

rmh

jj j ∂∂

=+∂

∂− ∑

),(),(),(),(12 2

22 rrr

r φφφ

where rr = position vector, or the coordinates),( trU r

= potential energy functionh = the Planck constant

The inter-molecular force on molecule i caused by N-1 other molecules is:

( )r

trFi r

rr

∂∂

−=,φ

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In ter -m o le cu lar dis tan ce ,d

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d o

Inter-Molecular Forces with Separation:

F

d

Molecular DynamicsMolecular Dynamics

(Inter-molecular forces.NEMS-1)HSU.4/5/01

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Potential Energy Function in Schrodinger Equation

∑<

=ji ij

ji

dqq

rUεπ 04

)( r

whereqi, qj = respective charge intensities of Particle i and j

dij = distance between Particle i and jεo = permittivity of the free space.

Molecule i

Molecule jInter-molecular forces

(Potential energy function.Nanotechnology-3)HSU.4/14/01

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Elements of Molecular Dynamic SimulationPrincipal Modules:• Equation of Motion• Environmental Interactions• Molecular Interactions

Sub-modules:• Dynamic equilibrium with applied forces

and energies• Dynamic and static properties• Molecular trajectories

(soft or hard sphere collision)• Phase-space trajectories for vibrating molecules• Distribution functions of sample molecules in

2-D and 3-D (velocities, properties, etc.)• Periodic boundary conditions

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Overview ofMolecular Heat Transmission

in nanoscale

Input thermal energy

(a) Initial state (b) Lattice movement at time t1 (c) Lattice movement at time t2

Any input of thermal energy to a substance from an external source can cause a disturbance to the energy equilibrium in its natural state.

This input energy can cause the LATTICES that connect atoms to deform(extend or contract) depending on the form of the input energy.

Because lattices are considered as elastic bonds, any extension or contractionof any lattice will result in a series of vibrations of lattices.

Vibration of lattices are always associated with energy.

The energy associated with local lattice vibration is called “ENERGY CARRIER” 56

Molecular Heat Transmission

Heat conduction in solids requires carriers.

P1

P2

P3

P4

(t1)(t2)

(t3)(t4)

d 1 d2

d 3

x

y

z

Plane B

Plane A

Thin filmthickness, H

The average “mean free path” (MFP):

The average “mean free time” (MFT):3

321 ddd ++=λ

( ) ( ) ( )33

14342312 tttttttt −=

−+−+−=τ

A. Energy Carrier:

Heat transportation in solids of in sub-micrometeer and nanoscalesis predominantly done by the “flow” of phonons.

There are collisions and scattering of free-phonons take place at all times during heat transmission:

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Molecular Heat Transmission – Cont’d

(For solid size, H < 7λ)

The thermal conductivity, λCVk31

=

Param eters for Therm al Conductivity of Thin Films [Flik et.al. 1992 and Tien and Chen 1994]

M aterials Dielectric andsemiconductors

Specific heats, C Specific heat of electrons, Ce Specific heat of phonons, Cs

M olecular velocity, V Electron Ferm i velocity,V e ≅ 1.4x106 m/sec

Velocity of phonons (soundvelocity), V s ≅ 103 m /sec

Average m ean freepath, λ

Electron mean free path, λe ≅ 10-8 m Phonon m ean free path,λ s ≅ from 10-7 m and up

Example: With an average value of λ = 10-7 m for phonons, the k for 200 nm thick silicon film is only 83% of the same property of silicon in macroscale.

B. Size-dependent Thermophysical Properties

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The heat conduction equation carries additional term for energy carrier’s movement:

t

trTt

trTkQtrT

2

22 ),(),(1),(

∂+

∂∂

=+ ∂∇

rrr

ατ

α

Vλτ =

The value of τ ≈ 10-10 seconds is used for semiconducting materials.

Molecular Heat Transmission –Cont’d

C. Modified Heat Conduction Equation

where the “relaxation time, τ is:

in which V is the average velocity of the heat carrier.

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● Gas dynamics derived from continuum theory breaks down at scale less than 1 µm (or < 1000 nm).

Overview of Molecular Gas Dynamics

• Molecular physics governs.

• Gas flow in this scale is “rarefied”.

“Mean free path” (MFP) and “Mean free time” (MFT) dominate in energy transportation.

Knudson number (Kn) and Mach number (Ma) characterize the flow.

• Kn = MFP (λ)/Characteristic length ( L); λ ≈ 65 nmMa = Speed of sound in the rarefied gas/

Speed of sound at standard conditions (Ma < 0.3)

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Modeling of Molecular Gas Dynamics

Kn0 0.01 0.1 1.0 10

Navier-Stoke Equation

Non-slipboundaries

Slipboundaries

Continuumtheories

Continuumtheories with

slip boundaries

Transition Freemolecular flow

• Kn = MFP (λ)/Characteristic length ( L); λ ≈ 65 nm for most gasesMa = Speed of sound in the rarefied gas/Speed of sound at standard

conditions

LGas Flow

● Modified Navier-Stokes equation can be used for 0.01 < Kn < 0.13. ● New gas dynamics theory and formulations need to be developed for nano scale

gas flow with Kn > 0.13.

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Summary on Nanoscale Engineering Analysis

● R&D on computational nanoscale engineering so far has beensporadic and has not received support as it deserves.

ComputerSimulation

Theory Experiment

● It is a matter of time that industry (and thus the government funding agencies) will recognize its essential value in the design of nano-scale devices and nano-microscale systems.

● Computational nanoscale engineering presents enormous challenge to researchers due to the extreme complexity in thebridging the quantum and continuum mechanics.

● Because of this extreme complexity, the following inter-play relationshipwill play a major role in the overall development of nanoscaleengineering design.

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Typical Instruments

1. SEM/TEM2. AFM/STM/Stylus Profiler3. Nano-indenter

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Typical Instruments


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电子显微镜的发展史

Max Knoll(1897-1969) Ernst Ruska(1906-1988)

电子显微镜的分辨率可以达到纳米级(10-9m)。可以用来观察很多在可见光下看不见的物体,例如病毒。

1938年，德国工程师Max Knoll和Ernst Ruska制造出了世界上第一台透射电子显微镜(TEM)。

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电子显微镜下的蚊子

Charles Oatley

1952年，英国工程师Charles Oatley制造出了第一台扫描电子显微镜(SEM)。

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一、电子显微镜及电子显微术概况

（一）电子显微镜近年来，电镜的研究和制造有了很大的发展。一方面，电

镜的分辨率不断提高，透射电镜的点分辨率达到了0.2-0.3nm，晶格分辨率已经达到0.1nm左右，通过电镜，人们已经能直接观察到原子像；另一方面，除透射电镜外，还发展了多种电镜，如扫描电镜、分析电镜等。

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1．透射电镜（TEM）透射电镜即透射电子显微镜（Transmission Electron

Microscope，简称TEM），通常称作电子显微镜或电镜（EM），是使用最为广泛的一类电镜。

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根据加速电压的大小分为以下3种：（1）一般TEM。最常用的是100KV电镜。这种电镜分辨率高

（点0.3nm，晶格0.14nm），但穿透本领小，观察样品必须很薄，约为30～100nm，如细胞和组织的超薄切片、复型膜和负染样品等。相当普及。

（2）高压TEM。目前常用的是200KV电镜。这种电镜对样品的穿透本领约为100KV电镜的1.6倍，可以在观察较厚样品时获得很好的分辨本领，从而可以对细胞结构进行三维观察。

（3）超高压TEM。目前已有500KV、1000KV和3000KV的超高压TEM。这类电镜具有穿透本领强、辐射损伤小、可以配备环境样品室及进行各种动态观察等优点，分辨率也已达到或超过100KV电镜的水平。在超高压电镜上附加充气样品室，使人们可以观察活细胞内的超微结构动态变化。

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2．扫描电镜（SEM）扫描电镜即扫描电子显微镜（Scanning Electron

Microscope，简称SEM）。主要用于观察样品的表面形貌、割裂面结构、管腔内表面的结构等。

70扫描电镜原理

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工作原理：利用电子射线轰击样品表面，引起二次电子等信号的发射，经检测装置接收后成像的一类电镜。

主要优点：景深长，所获得的图像立体感强，可用来观察生物样品的各种形貌特征。

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一些电镜图片

染色体染色体被精子包围的卵子

骨髓细胞 SARS AIDS

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依据性能不同主要分为：（1）一般SEM。目前一般扫描电镜采用热发射电子枪，分辨

率为6nm左右，若采用六硼化镧电子枪，分辨率可提高到4～5nm。我校有这样的设备。

（2）场发射电子枪SEM。由于场发射电子枪具有亮度高、能量分散少，阴极源尺寸小等优点，这种电镜的分辨率已达到3nm。场发射电子枪SEM的另一个优点是可以在低加速电压下进行高分辨率观察，因此可以直接观察绝缘体而不发生充、放电现象。

（3）生物用SEM。这种SEM备有冰冻冷热样品台，可把含水生物样品迅速冷冻并对冰冻样品进行观察，可以减少化学处理引起的人为变化，使观察样品更接近于自然状态。如要观察内部结构，还可用冷刀把样品进行切开，加温使冰升华，并在其上喷镀一层金属再进行观察，所有这些过程都在SEM中不破坏真空的状态下进行。

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4．分析电镜分析电镜是利用电子射线轰击样品所产生的X射线或俄歇电

子对样品元素进行分析的一类电镜。其特点是能在观察超微结构的同时，对样品中一个极微小的区域进行化学分析，从而在超微结构水平上测定各种细胞结构的化学成分及其变化规律。

（1）分析TEM。在TEM上配备X射线能谱仪后即成为分析TEM，目前很多100KV和 200KV TEM都可以装上X射线检测附件，进行样品的元素分析。

（2）分析SEM。在SEM上配备X射线能谱仪后，便可兼有电子探针分析样品化学成分的功能。

（3）扫描俄歇电镜。把SEM与俄歇电子能量分析仪相结合，即成为扫描俄歇电镜，它能对样品表面进行微区元素分析，是一种表面微观分析电镜。

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5．扫描透射电镜SEM中电子射线作用于样品后，其中一部分电子可透过样品

成为透射电子，将透过样品的透射电子和散射电子用检测器接收成像，即成为扫描透射电镜。这种电镜一般用场发射电子枪，兼有TEM、SEM和分析电镜的特点，能观察较厚的样品，分辨本领和成像质量都很好，是近年来电镜技术的最大改进之一。

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（二）电子显微术电镜具有很高的分辨本领，能观察极微小的结构。但是电

镜不能直接观察天然状态下的生物标本，必须通过各种技术将生物标本制成特殊的电镜生物样品，才能放入电镜进行观察，这些电镜样品制备技术称为电子显微术。

电子显微术：将生物标本制成特殊的电镜观察用生物样品的制备技术。

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1．与TEM有关的电子显微术（1）超薄切片技术。超薄切片技术就是通过固定、脱水、

包埋、切片和染色等步骤，将生物标本切成薄于0.1μm的超薄切片的样品制备技术，用于生物组织的内部超微结构研究。

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上图超薄切片机局部

下图玻璃刀制作仪

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2．与SEM有关的电子显微术（1）SEM常规制样技术。SEM适合于研究生物样品的表面特征

，样品制备包括样品观察面的暴露、固定、干燥和导电等步骤，使表面特征充分暴露而不变形。这一技术是 SEM样品制备的常规技术，主要用于组织、细胞、寄生虫等表面形貌的研究。下图为SEM标本处理设备。

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Typical Instruments


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The Measuring Mechanism of AFM(I)

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The Measuring Mechanism of AFM(II)

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89 90

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X Y

Z

Laser

Cantilever

Laser signalPhotodiode

Specifications of the DI 3100:X-Y Scanning Area: Less than100μm×100μmZ Scanning Distance: About 6μm

Scanning method: Raster

The Configuration of a Typical AFM System (DI 3100 Series)

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The applications of AFM

Part of these images are downloaded from website of www.vecoo.com

I. Life science application

II. Nanoscience application

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Typical Instruments


95 96

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97 98

99 100

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101

Sa

Er 2π

=a

FH max=

2

22

1

21 )1()1(1

EEEr

υυ −+

−=

102

103 104

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105 106

107 108

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Summary

● There has been unprecedented interests (and expectations) expressed by the scientific community, and colossal amount of investments in R&D by governments of leading industrialized nations in the world.

● Current state of nanotechnology appears focused on “scientific discovery”with rudimentary products at laboratory scale.

● Near term breakthroughs in significant commercial applications of nanotechnology appear in the new superior materials and disruptive biomedical applications.

● R&D on creative and novel micro/nano scale products that have identifiedglobal market potentials is a sensible direction to follow.

● Nanoscale engineering is a necessary vehicle to reach this goal.

● Related “soft nanotechnology”, e.g. commercialization and global marketing for nano scale products, and volume production technologies should be encouraged and supported.

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课件下载地址：

http://sklofp.zju.edu.cn/jpkc/index.htm

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