Fachgebiet 3D-Nanostrukturierung, Institut für Physik

Contact: yong.lei@tu-ilmenau.de

fabian.grote@tu-ilmenau.de

yan.mi@tu-ilmenau.de

Office: Heliosbau 1102, Prof. Schmidt-Straße 26 (tel: 3748)

www.tu-ilmenau.de/nanostruk

Vorlesung: Mittwochs (U), 9 – 10:30, C 108

Übung: Mittwochs (G), 9 – 10:30, C 108

Yong Lei, Fabian Grote, Yan Mi

Techniken der Oberflächenphysik (Technique of Surface Physics)

Main contents of this course (Nano)

Surfaces become more important for smaller objects

All the aspects of surface physics of different

nanostructures:

Optical properties (band-gap, defect emissions)

Sensing properties (gas, chemical and bio-sensors)

Field-emission properties

Devices (super-capacitors, sensors, optical …)

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)

‘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 unique nature of nanomaterials, has achieved exciting

technological advancement for the benefit of mankind.

Nobel Prize Winners 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: development of

methods for 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

Two most important structural aspects of nanostructures:

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

Quantum confinement effect

6

G. Binnig, H. Rohrer

Nobel Prize 1986 – Physics

Development STM

7

Konstantin Novoselov & Andre Geim

Nobel Prize 2010 – Physics

Graphene

The electronic, chemical, and optical processes on metal oxides concerning the sensing, which

is benefit from reduction in size to the nano range (Kolmakov, Annu Rev Mater Res 2004)

Surface charge properties of nanostructures is the major

point of functions of metal oxide nanowire-based devices.

The main reason of the high interest in the use of 1D

nanostructures is the large surface-to-volume ratio, so that

more surface atoms to participate in the surface reactions.

Surface plasmon resonance: plasmons propagate in x- and y-directions along

metal-dielectric interface. The interaction between surface-confined EM wave

and surface layer leads to shifts in the plasmon resonance condition.

Localized surface plasmons: light interacts with particles much smaller

than the incident wavelength. This leads to a plasmon that oscillates

locally around the nanoparticle with a LSPR frequency. Enhanced - SERS

Schematic of (a) a surface plasmon resonance and (b) a localized surface plasmon

resonance. (Katherine A., Annu. Rev. Phys. Chem. 2007. 58, 267.)

Surface patterns in nature

Structural color – function of surface patterns

1 µm

butterfly

peacock

packing of melanin cylinders

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

1996 – 2001: PhD study in Chinese Academy of Science

(CAS):

Anodic Alumina Oxide (AAO) Nano-Porous Template

AAO nano-porous template

(size controllable 10 – 400 nm & large area cm2)

(a) (b)

Regular arrays nanowires after removing templates

2001 - 2003

National University of Singapore (Singapore-MIT Alliance)

Idea of the UTAM surface nano-patterning

• Surface nano-patterning - key to device miniaturization to

nano-size level - large-scale ordered surface nanostructures.

• An exciting idea and new concept:

Transfer advantages of templates to surface nano-patterning

- prepare an ultra-thin alumina membrane (UTAM) on a

substrate

The idea is attractive - high challenging (crazy): many

technical points.

From Intel Homepage, Public

Relations

Dual-core CPU

feature-size 45 nm

Si substrate

Ultra-thin AAO template

Normal AAO

template

2003 – 2006

Institute of Nanotechnology (INT) in FZK at Karlsruhe, Germany

Realize the idea of the UTAM surface nano-patterning

• 2004 solved all the technical points

• 2004 - 2006, published the results, gave a name ‘UTAM

surface nano-patterning’ - received wide international

scientific recognition

• Invited to publish a review (75 pages) in ‘Progress in

Materials Science’ of UTAM nano-patterning technique

• I like to work on high-impact and risky ideas to challenge my

imagination

UTAMs

Regular nanodots on a Si

wafer

Tuning of the shapes and sizes of UTAM-prepared nanostructures

To control the structural parameters (shape, size and spacing) is

very important

Controllable sizes and shapes:

The pore diameters of the UTAMs can be adjusted from about 10 to

400 nm to yield nanoparticles of corresponding size.

Nanometer-sized discs, hemispheres, hemi-ellipsoids, and

conics (by changing the aspect ratio of the pores of the UTAMs,

and the amount of material deposited through the UTAMs).

Highly ordered nano-disc arrays. Pore diameter, cell size and thickness of the

UTAM are about 80, 105, and 160 nm, respectively. The aspect ratio of the

apertures of the UTAM is about 1:2. The average height and size of the nano-discs

are approximately 1.5 and 80 nm, respectively.

Highly ordered nano-disc arrays

AFM Section Analysis of the nano-discs, the average height and size of

the nano-discs are approximately 1.5 and 80 nm, respectively.

Highly ordered nano-hemisphere arrays. Pore diameter, cell size and thickness of

the UTAM are about 80, 105, and 240 nm, respectively. The aspect ratio of the

apertures of the UTAM is about 1:3. The average height and base diameter of the

nano-hemispheres are approximately 35-40 and 75 nm, respectively.

Highly ordered nano-hemisphere arrays

AFM Section Analysis of the nano-hemisphere. To accurately reflect the shape

of the nanoparticles, we used the same dimension scale for the horizontal and

vertical coordinates. The average height and base diameter of the nano-

hemispheres are approximately 35-40 and 75 nm, respectively.

Ordered nano-hemiellipsoid arrays. Pore diameter, cell size and thickness of the

UTAM are about 80, 105, and 310 nm, respectively. The aspect ratio of the

apertures of the UTAM is about 1:4. The average height and base diameter of the

nano-hemiellipsoids are approximately 50-55 and 65 nm, respectively.

Highly ordered nano-hemiellipsoid arrays

AFM Section Analysis of the nano-hemiellipsoids. To accurately reflect the shape

of the nanoparticles, we used the same dimension scale for the horizontal and

vertical coordinates. The average height and base diameter of the nano-

hemiellipsoids are approximately 50-55 and 65 nm, respectively.

Ordered nano-conic arrays. Pore diameter, cell size and thickness of the UTAM

used in the fabrication process are about 80, 105, and 650 nm, respectively. The

aspect ratio of the apertures of the UTAM is about 1:8. The average height and

base diameter of the nano-conics are approximately 55-60 and 60 nm, respectively.

Highly ordered nano-conic arrays

AFM Section Analysis of the nano-conics. To accurately reflect the shape of the

nanoparticles, we used the same dimension scale for the horizontal and vertical

coordinates. The average height and base diameter of the nano-conics are

approximately 55-60 and 60 nm, respectively.

Be awarded the first prize of

the best posters in the 6th

Conference of the NanoMat

Network (held in Karlsruhe,

Germany on Apr 7-8, 2005) for

the research work entitled

“Surface nanostructuring with

ordered arrayed nanoparticles

of tunable size and shape”.

A challenging technical point for UTAM technique to realize quantum-sized surface structures (below 10 nm)

Well-controlled wet etching process to the barrier layer of UTAMs

realizing pore-opening and surface nanostructures within the quantum-sized range

UTAM surface nano-patterning

～ 17 nm

～ 10 nm

20 min

～5 nm

Small 2010, 6 (5), 695-699.

UTAM surface nano-patterning

Barrier layer 5 nm

10 nm 17 nm

Quantum dot array

Small 2010, 6 (5), 695-699.

UTAM surface nano-patterning

Attractive features of the UTAM surface nano-patterning

Large pattern area (> 1cm2) and high throughput;

high density of the surface nanostructures (1010 - 1012 cm-2);

a general process to prepare different patterns (semiconductors, metals);

well-defined nanostructures;

low equipment costs.

Y. Lei, et al., Progress in Materials Science, 52, 465, 2007.

Y. Lei, et al., Chem. Soc. Rev. 40, 1247, 2011

UTAM surface nano-patterning

2006: University of Muenster

Started my junior research group

Three-Dimensional Surface Nano-Patterning: Concepts, Challenges and

Applications

From Intel Homepage, Public Relations

Dual-core CPU

feature-size 45 nm

Three-Dimensional Surface Nano-Patterning: Concepts, Challenges and

Applications

Multifunctional surface nano-structures

An efficient evolution from 2-D to 3-D surface nano-patterning:

Change from nanodots or nanorings to nanowires or nanotubes

One of the most attractive advantages of nano-

materials (extremely large surface area) is missing in

the existing 2-D surface nano-patterns

Large contacting influence from the substrate → very

large signal noises → degrades device performance

Only way to increase the device density is to

decrease the pattern size

nanodots

nanorings

nanowires

nanotubes

Where is the money?

A complicated new concept of surface nano-

structuring

ERC Starting Grant (2009)

1.4 million Euro – independent group

My ERC Experiences in Uni-Muenster

The react of university when I got the ERC funding:

Junior group leader) → W1 Professor

Got some labs and offices for my group

In 2011, obtained W2 university professorship

(Fachgebietsleiter) in TU-Ilmenau

with good support to my Fachgebiet:

1.About one million Euro equipments;

2.Large lab and office space;

3.A large BMBF project (2.6 Million Euros).

Better conditions to realize 3D nanostructuring and

nano-devices

Eight fabrication strategies are proposed:

Three basic strategies I, II, and III

Strategy I: free-standing nanotubes (c2)

Strategy II: free-standing nanowires (d2)

Strategy III: connected nanotubes (e)

(a) (b) (e)

(c1) (c2) (d2) (d1)

I

I

II

II

III Tubes are connected on the

top and the pore bottom

From 2D to 3D surface patterns using templates

Large-scale free-standing metallic nanowires for 3D surface patterns: (Left): top view of

nanowire array of an area of about 775 μm2. (Right): high regularity of nanowire arrays.

Schematic of the addressing system (only shows an array of 3 × 3)

Addressing System for 3-D surface nano-patterns

with nano-scale resolution

3D Surface Nano-Patterning: Addressing

nanowire ‘1A’

Addressing System for 3-D surface nano-patterns

large-scale (mm2 – cm2) with nano-scale resolution

Device applications (BMBF-ZIK funding)

A device based on 3-D surface nano-structures with addressing system

(for a 1 mm2 area of 3-D surface nano-patterns with pattern spacing of

100 nm, the addressing system has 10000 lines for each set of electrodes)

1. The short-range pore regularity of UTAMs or AAO templates

→ Template with large-scale perfect pore arrays (to mm2 or even to cm2)

3D Surface Nano-Patterning: nano-templates with large-scale

(up to 1 mm2) perfect pore arrays without defects

2. Hexagonal pore arrangement

→ Rectangle pore arrangement

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

defects

(Pre-patterned process on Al layer before anodization)

ZnO nanotubes array for gas sensor

Template-prepared surface nano-patterns:

Device application

UTAM + ALD (atomic layer deposition) Process

ZnO nanotubes array for gas sensor

Schematic of ZnO nantubes array gas sensor device

Template-prepared surface nano-patterns:

Device application

The sensitivity of the sensor to NO2 gas could reach to 25 ppb

Thank you for your attention!