Nanowires are extremely small. Nanowires can be made from a variety of conducting and semiconducting materials like copper, silver, zinc oxide and germanium. Nanowires can also be made from carbon nanotubes. Nanowires can be defined as structures that have a thickness or diameter constrained to tens of nanometers or less and an unconstrained length. Nanorods is a nanosized rod which having a size measured in nanometers. Their dimensions range from 1–100 nm. They may be synthesized from metals or semiconducting materials
1 d structure materials
Supervisor: prof. Nguyen Huu Lam
Group : Hoàng Văn Tiến
Nguyễn Đình Trung
Phạm Đức Thịnh
Class: MSE –K54
-D structure materials
HA NOI UNIVERSITY OF SCIENCE AND TECHNOLOGY
**** ADVANCED TRAINING PROGRAM ****
• Materials with nano structure
has attracted a great
attention of the scientific
commune in over the world
because of their promise
properties with quantum
• Three kinds of nano
structure: 0D (quantum
dots), 2D (thin films), 1D (
• Many ways to fabricate the
nanostructure: CVD, PVD,
SOME 1-D NANOSTRUCTURES
• Spontaneous growth
• Evaporation (dissolation) condensation
• Vapor –liquid –solid (VLS) growth
• Stress- induced recrystallization
• Templated – based synthesis
• Electroplating and electrophoretic deposition
• Colloid dispersion , melt or solution filling
• Conversion with chemical reaction
• A growth driven by reduction of Gibbs free energy or
chemical potential. This can be from either
recrystallization or a decrease in supersaturation.
• Growth along a certain orientation faster than other
direction – anisotropic growth.
• For nanowire, growth occurs only along one direction,
but no growth along other directions.
DISADVANTAGES OF EVAPORATION –
• Nanowire grown by EC most likely have faceted
morphology and are generally short in length with
relatively small aspect ratios, particular when grown in
• Anisotropic growth induced by axial imperfections, such
as screw dislocation, microtwins and stacking faults, or by
impurity poisoning, can result in the growth of nanowires
with large aspect ratios.
- VLS is basically a Chemical Vapor Deposition (CVD) method driven in the
presence of a Catalyst that can accelerate the rate of a reaction, without
itself taking any part in the reaction. Most semiconductor nanomaterials of the
group III-Nitrides class are synthesized by this technique.
- Basic principle : heat a foil or powder of the group III metal such as
Ga, In, or Al (source) in the presence of Nitrogen (N2) or NH3 at temperatures
suitable for vaporization of the source and dissociation of the nitriding gas .
-Catalysts : Transition metal and their oxides
- The easiest form of catalyst used is a thin ﬁlm of the transition metal
(Fe, Ni, Co) or Noble metals like Gold (Au).
STEPS OF VLS GROWTH
• A thin (~1-10 nm) ﬁlm of catalyst(Au in our case) is deposited onto a wafer
substrate(Si) by sputter deposition or thermal evaporation or any other
• Then the precursor (group III material :Ga) is heated to evaporate to take
part in the reaction. The vapour is absorbed by the molten catalytic droplet
which becomes supersatured and Ga gets precipitated to the bottom
where it take part in reactionto form GaN.
• As the melting point of GaN is >2500◦C which is much higher than the
reaction temp (around 900◦C ) so it grows on the Si substrate in a
Hexagonal crystal structure.
Wagner summarized the requirements for VLS growth
1. The catalyst or impurity must form a liquid solution with the crystalline
material to be growth at the deposition temperature
2. The distribution coefficient of the catalyst or impurity must be less than unity
at the deposition temperature
3. The equilibrium vapor pressure of the catalyst or impurity over the liquid
droplet must be very small because it can reduce the total volume of the
4. The catalyst or impurity must be inert chemically ( not react with the
chemical species )
5. The interfacial energy plays a very important role
6. For a compound nanowire growth , one of the constituents can serve as the
7. For controlled unidirectional growth, the solid –liquid interface must be well
defined crystallographycally .
ADVANTAGES OF THE VLS METHOD
• Greatly lowered reaction energy compared to normal vapor-solid
• Wires grow only in the areas activated by the metal catalysts
and the size and position of the wires are determined by that of
the metal catalysts.
• This growth mechanism can also produce highly anisotropic
nanowire arrays from a variety of materials