Fachgebiet 3D-Nanostrukturierung, Institut für Physik

Contact: yong.lei@tu-ilmenau.de; yang.xu@tu-ilmenau.de

Office: Unterpoerlitzer Straße 38 (Heisenbergbau) (tel: 3748) http://www.tu-ilmenau.de/3dnanostrukturierung/

Vorlesung: Wedsnesday 9:00 – 10:30, C 108

Übung: Friday (G), 9:00 – 10:30, C 110

Prof. Yong Lei & Dr. Yang Xu

(a) (b2) (b1)

UTAM-prepared free-standing one-dimensional surface nanostructures on Si

substrates: Ni nanowire arrays (a) and carbon nanotube arrays (b).

Nanostrukturphysik (Nanostructure Physics)

Contents of Class 1

A general introduction of fundamentals of nano-

structured materials

Definition of nanostructures or nano-structured

materials

Significance of nano-structured materials

Structural aspects

An outline of all the 10 classes

Characterization of nano-strcutures

One-dimensional nanostructures

Surface Nanostructures realized using UTAM

‘There’s plenty of room at the bottom,

the principles of physics, as far as I can see, do not

speak against the possibility of manoeuvring things atom

by atom...’

By the legendary physicist Richard Feynman in 1959

(Feynman R., Eng Sci, 1960)

Progress made in past two decades has proven this

statement by the amazing nature of nanomaterials, has

achieved exciting technological advancement for the

benefit of mankind.

Definition of nanostructures or nano-materials

The word ‘nanometer’ has been assigned to indicate the size of 10-9

meter

Structures with at least one dimension within 1-100 nanometer (nm)

called ‘nanostructures’ (Prof. H. Gleiter 1986-1988)

The word ‘nano’ derived from a Greek word ‘nanos’, means ‘dwarf’

(small)

Nanostructures have received high research interest because of their

peculiar and fascinating properties, as well as their unique applications

superior to their counterparts - bulk materials.

Nowadays, nanomaterials and nanostructures are not only one of the

hottest fundamental research topics, but also gradually intrude into our

daily life.

From: J. Henk Introduction to the Theory of Nanostructures (Lecture Notes 2006)

Nobel Prizes with research related to nanotechnology:

1986 Physics: G. Binnig, H. Rohrer: design of the scanning

tunneling microscope (STM) → SPM systems;

1996 Chemistry: R. Curl, H. Kroto, R. Smalley: discovery of

fullerenes (C60, bucky balls);

2002 Chemistry: J. Fenn, K. Tanaka, K. Wüthrich: identification

and structure analyses of biological macromolecules;

2003 Chemistry: P. Agre, R. MacKinnon: discoveries of

channels in cell membranes.

2010 Physics: A. Geim, K. Novoselov: for groundbreaking

experiments regarding the two-dimensional graphene

G. Binnig (German) & H. Rohrer (Swiss) Nobel Prize 1986 Physics Designing of the scanning tunneling microscope (STM) → SPM systems

Nobel Prizes with research related to nanostructures:

G. Binnig also designed AFM with other 2 scientists, and started the company ‚Definiens‘ in 1994. He worked as honorary professors in some universities, e.g., Uni-Muenchen.

8

Konstantin Novoselov & Andre Geim (Russian) Nobel Prize 2010 Physics for groundbreaking experiments regarding the two-dimensional graphene

Prof. Andre Geim (from: en.wikipedia.org/wiki/Andre_Geim)

obtained first tenured position in 1994, associate professor at

Uni-Nijmegen, one doctoral student at Nijmegen was Novoselov.

Geim said that he had an unpleasant time during his career in

Netherlands. He was offered professorships at Nijmegen and

Eindhoven, but turned them down as he found the Dutch

academic system too hierarchical and full of politicking. "This can

be pretty unpleasant at times," he says. "It's not like the British

system where every staff member is an equal quantity.“

Geim writes in his Nobel lecture that "the situation was a bit

surreal because outside the university walls I received a warm-

hearted welcome from everyone around……

In 2001 he became a professor at the University of Manchester,

and was appointed director of the Manchester Centre for

Mesoscience and Nanotechnology in 2002.

For carbon nanotubes –

CNT (by Ijima in 1991)

and the equally important

discovery of inorganic

fullerene structures (by

Tenne)

1996: Curl, Kroto, Smalley

1985 or1986: fullerenes

(C60, bucky balls);

2010: Geim, Novoselov

2005-2007: 2D graphene

The allotropes of

carbon:

hardest natural

substance, diamond

one of the softest known

substances, graphite.

Allotropes of carbon: a) diamond; b) graphite;

c) lonsdaleite; d–f) fullerenes (C60, C540, C70); g)

amorphous carbon; h) carbon nanotube.

from http://en.wikipedia.org/wiki/Carbon.

Graphene is a 1-atom thick sheet of sp2-bonded carbon atoms that are

densely packed in a honeycomb crystal lattice. Graphene is easily

visualized as an atomic-scale wire made of carbon atoms and their bonds.

Graphite consists of many graphene sheets stacked together.

(http://en.wikipedia.org/wiki/Graphene)

Zigzag carbon nanotube

Armchair carbon nanotube

Why are nanostructures interesting?

• small is different: new properties of materials

at nanometer scale

• look at quantum mechanics

• nanostructure + functions or properties:

revolution in information technology, medicine,

media ......

Many opportunities might be realized by making new types

of nanostructures (fabrication ways):

1. simply by down-sizing existing microstructures into 1-100

nm range:

most successful example is microelectronics, where

‘smaller‘ means greater performance (since the invention of

integrated circuits): more components per chip, faster

operation, lower cost, and less power consumption;

Structural aspects of nano-structured materials:

Extremely large surface area (very large surface/volume ratio):

when the dimensions decrease from micron level to nano level, the

surface area increases by 3 orders in magnitude. This will lead to much

improved and enhanced physical properties (sensing, optical,

catalysis ...):

Cube – Cubic structures – divided into 8 pieces – surface area 2

times(doubled)

Cube – Cubic structures – divided into 1000 pieces – surface area 10

times

Many opportunities might be realized by making new types

of nanostructures (fabrication ways):

2. Miniaturization also represent the trend in a range of

other technologies:

Information storage, e.g., many efforts to fabricate magnetic

and optical storage components with critical dimensions

(feature size) as small as tens of nanometer – device

miniaturization

From Intel Homepage, Public Relations

Dual-core CPU

feature-size 45 nm

Electronic properties:

Dimensions of a system - comparable with Bohr (exciton) radius (which is

comparable to nanowire diameter):

energy bands cease to overlap – discrete

The typical electronic properties of the nanostructures are a result of

tunneling currents and coulomb blockade effects.

However, owing to their wavelike nature, electrons can tunnel through

between two closely adjacent nanostructures

If a voltage is applied between two nanostructures, which aligns discrete

energy levels, resonant tunneling occurs – largely increases tunneling

current

The physical properties of functional nanostructure are different from

those of the bulk materials, especially for optical properties:

Quantum confinement effect (size-reduction down to the nm-sized

range) → a band-gap shift → adjust the optical properties of

nanostructures.

Quantum confinement effect:

It is widely accepted that quantum confinement of electrons by the

potential wells of nanometer-sized structures provides the most

powerful (and versatile) means to control the electrical, optical,

magnetic, and thermoelectric properties of a solid-state materials.

Metallic nanostructures (especially Au and Ag) have unique optical

properties → surface-enhanced plasmon resonance light-scattering

and Raman scattering (SERS or SRR).

Quantum confinement effect

When the feature size of a structure (e.g., particle) is comparable

with the size of Bohr (exciton) radius (about 2–50nm, usually below

10-15 nm), electron becomes more confined in particle, quantum

confinement effect lead to an increasing of energy band-gap.

Furthermore, the valence and conductive bands break into

quantized discrete energy levels.

Many exceptional physical properties of nano-materials are attributed to

the changes in the total energy and structure of the system.

Band-gap shift due to the Quantum confinement effect:

ΔEg = h2/8R2μ – 1.8e2 /4πεoεR

Quantum confinement in semiconductor nanoparticles

Optical fluorescence of CdSe nanoparticles

of various sizes.

The band gap emission is observed to shift

through the entire visible range, from red emission for the largest particles, to blue

emission for the smallest clusters.

(B. O. Dabbousi, J. Phys. Chem. B, 1997, 101, 9463)

Global funding status in nanotechnology

This course is try to overview this 21st century’s leading science and

technology based on fundamental and applied research during the

last 2 decades → Nano - World

Zentralbau des Deutschen Museums

https://de.wikipedia.org/wiki/Deutsches_Museum

Deutsches Museum

• Class 1: a general introduction of fundamentals of nano-structured materials, and definition

• Class 2: research at 3D-Nanostructuring

• Class 3: optical properties of 1D nanostructures

• Class 4: carbon nanotubes

• Class 5: graphene

• Class 6: 2D atomically thin nanosheets

• Class 7: lithium-ion batteries: Si nanostructures

• Class 8: solar water splitting I: fundamentals

• Class 9: solar water splitting II: nanostructures for water splitting

• Class 10: solar cells

Class 2: research at 3D-Nanostructuring

From template to energy: • Sodium-ion

batteries • Solar water

splitting • Supercapacitors

Class 3: optical properties of 1D nanostructures

• Features

• Quantum confinement

• Nanowire lasing

• Field emission display

Class 4: carbon nanotubes

• History

• Fabrication

• Applications

Class 5: graphene

• Introduction

• Brief history

• Characterizing graphene flakes

• Devices with peeled graphene

• Alternatives to mechanical exfoliation

Class 6: atomically thin nanosheets

• Characterization of structure

• Electronic structure regulation

• Energy device construction

Class 7: nanostructured Si anodes for lithium-ion batteries

• Principle of lithium-ion batteries

• Opportunities and challenges of Si anodes

• Nanostructured Si anodes

Class 8: fundamentals of solar water splitting

• Related semiconductor physics

• Thermodynamic and kinetics of semiconductor-liquid interface

Class 9: nanostructures for solar water splitting

• Pros and cons

• Material designs and nanostrcutured architectures

Anode Cathode Electrolyte

Class 10: nanostructures for enhancing light absorption in solar cells

• Semiconductor nanostructures

• Metal nanostructures: surface plasmons

Characterization of nano-strcutures

An appropriate characterization will play a crucial role in determining

various structures and properties of nanostructures.

Three broadly approved aspects of characterization are

1. Morphology

2. Crystalline structure

3. Chemical analysis

SEM: Scanning Electron Microscopy; STM/AFM: Scanning Tunneling

Microscopy/Atomic Force Microscopy; ATEM: Analytical Transmission

Electron Microscopy

X-Ray: X-ray Morphology; IP: Image Processing; LM: Lightweight

Morphology; RBS: Rutherford Backscattering Spectrometry (Kelsall et al., Nanoscale science and technology. 2005)

ATEM: Analytical Transmission Electron Microscopy; AES: Auger

Electron Spectrometer; XRD: X-ray Diffraction; RBS: Rutherford

Backscattering Spectrometry; XPS: X-ray Photoelectron Spectrometer;

(Kelsall et al., Nanoscale science and technology. 2005)

SEM: Scanning Electron Microscopy; ATEM: Analytical Transmission

Electron Microscopy;

AEM: Auger Electron Microscopy. XRD: X-ray Diffraction; LEED: Low-

energy electron diffraction; RBS: Rutherford Backscattering

Spectrometry (Kelsall et al., Nanoscale science and technology. 2005)

Types of Nanostructure: Two-dimensional nanostructure: nanowalls, quantum wells... One-dimensional nanostructure: nanowires, nanotubes, nanorods, nanobelts... Zero-dimensional nanostructure: quantum dots or nanoparticles

Graphene is a 1-atom thick sheets of sp2-bonded carbon atoms that are densely

packed in a honeycomb crystal lattice. Graphene is easily visualized as an atomic-

scale wire made of carbon atoms and their bonds. Graphite consists of many

graphene sheets stacked together.

(http://en.wikipedia.org/wiki/Graphene)

Templates with large-scale (1 mm2) perfect rectangular pore arrays without defect

Templates with large-scale (1 mm2) perfect rectangular pore arrays without defect

Perfect regular 3D nanostructure arrays with different wire configuration

One dimensional nanostructures

One dimensional (1D) nanostructure: nanowires,

nanotubes, nanorods, nanobelts...

One dimensional nanostructure refers to the systems with

the lateral dimension in the range of 1-100 nm.

In comparison with 0D nanostructures, 1D nanostructures

provides a better model system to investigate the

dependence of properties (electronic transport, optical,

and mechanical) on size confinement and dimension.

Nanowires, in particular, plays an important role as both

interconnects and active components in preparing

nanoscale devices (Nano-devices).

One-Dimensional Nanostructures

(a) (b2) (b1)

UTAM-prepared free-standing one-dimensional surface nanostructures on Si substrates: Ni

nanowire arrays (a) and carbon nanotube arrays (b). (Y. Lei et al., Chemistry of Materials, 2004)

A schematic summary of the kinds of

one dimensional nanostructures already

reported:

(A) nanowires and nanorods;

(B) core–shell structures;

(C) nanotubes/hollow nanorods;

(D) heterostructures;

(E) nanobelts/nanoribbons;

(F) nanotapes;

(G) dendrites;

(H) hierarchical nanostructures;

(I) nanosphere assembly;

(J) nanosprings.

(Kolmakov et al., Annu Rev Mater Res 2004)

Highly ordered CdS nanodot arrays, UTAMs and CdS top layer on

the surface of the UTAM.

CdS replicated mask

Alumina

CdS nanodots

Surface patterns in nature

Structural color – function of surface patterns

1 µm

butterfly

peacock

packing of melanin cylinders (provided by L Chi)

Surface patterns and structures (artificial)

and their applications in diverse (micro-electronic) devices

From Intel Homepage, Public Relations

Dual-core CPU

feature-size 45 nm

Surface Nano-Patterning

Fabrication of surface nanostructures

Memory devices with high integration density;

Field emission devices;

Sensors with high sensitivity;

Optical devices with tunable properties

What is an excellent surface nano-patterning technique?

1. Ability to prepare surface patterns within the nanosized range;

2. Well-defined surface nano-patterns;

3. Large pattern area – high throughput;

4. A general process – applicable;

5. Low cost. Perfect ?

Electron-beam lithography

Excellent structural controlling Low throughput

High equipment costs

Imprint technologies

High throughput Wear

Structures with low

aspect ratio

Self assembly Low costs

High throughput

Limited class of materials

Low structural controlling

Some surface nano-patterning techniques

in fabricating ordered surface nanostructures

Alternative method that combines these advantages and is applicable

for a broad range of surface nanostructures ?

UTAM (ultra-thin alumina mask) surface nano-patterning:

Template-based surface nano-fabrications

Porous Alumina Membranes (PAMs)

Interesting and useful features:

• highly ordered pore arrays +

large area

• Nanometer-sized pores

• High aspect ratio

• size controllable (10 – 400 nm)

Configuration diagram of the PAMs

Porous Alumina Membranes (PAMs)

(a) (b)

Regular arrays of short (a) and long Ni nanowires (b) after the removal of PAM, the

diameter is about 90 nm, the length is about 800-1000 nm (a) and 3-4 μm (b), respectively.

thus the aspect ratio of the nanowires are about 10 (a) and 40 (b), respectively.

Motivation

Use ultra-thin ordered porous alumina as evaporation or etching masks, and

transfer the regularity of the pore arrays to the nanostructure arrays on

substrates.

UTAM surface nano-patterning technique

Fabrication of Highly Ordered Nanoparticle Arrays Using Ultra-thin

Alumina Mask (UTAM)

Fabricating ultra-thin alumina masks (UTAM) on Al foils and then

mounting them onto the surface of silicon wafers

Al foil

First alumina layer

Al foil Al foil

Second alumina layer

Al foil

Ultra-thin alumina mask

Si wafer

Ultra-thin alumina mask

Fabrication process

Fabrication of the nanodot arrays

Ultra-thin alumina mask

Si wafer

Ultra-thin alumina mask

Si wafer

Ultra-thin alumina mask Nanoparticle array

Si wafer Si wafer

Highly ordered CdS nanodot arrays, UTAMs and CdS top layer on

the surface of the UTAM.

CdS replicated mask

Alumina

CdS nanodots

• Class 1: a general introduction of fundamentals of nano-structured materials, and definition

• Class 2: research at 3D-Nanostructuring

• Class 3: optical properties of 1D nanostructures

• Class 4: carbon nanotubes

• Class 5: graphene

• Class 6: 2D atomically thin nanosheets

• Class 7: lithium-ion batteries: Si nanostructures

• Class 8: solar water splitting I: fundamentals

• Class 9: solar water splitting II: nanostructures for water splitting

• Class 10: solar cells

Thanks for your attention