Low Temperature Chemical Growth of Composite

Nanostructures

Omer Salih Mohamed Nour

(O. Nur)

Department of science and Technology, Campus Norrköping,

Linköping University, Norrköping, Sweden

Introduction:

There are different approaches to grow composite ‘’hybrid’’ nano-materials. Usually the

growth using the wet ‘’aqueous’’ chemical route is a very easy and popular approach. Before

this growth usually a seed layer can be used to control the growth f the first nanomaterial.

This nanomaterial will work as a support to grow the other secondary nanomaterial.

Hence the wet-chemically seed-mediated growth provides an effective method for the

synthesis of the hybrid nanoparticles with well controlled structures, where the secondary

species attach and sequentially grow on the preformed seeds [1]. To ensure the deposited

species well-dispersed on the supports, heterogeneous nucleation and growth through atomic

addition must be achieved and homogeneous nucleation should be avoided. Significant

progress has been achieved in the synthesis of the core shell and dumbbell nanoparticles

combining two different components. When the individual components involved have similar

crystal structures and lattice parameters, each component fuses together giving the dumbbell

shape [1]. In a dumbbell structure consisted of one particle bounded another, charged transfer

across nanoscale junction could significantly change local electronic configuration that give

the remarkable properties. While large lattice space difference of the individual components

results in core–shell-shaped structure obtained by growing a uniform layer of a shell material

around colloidal particles [1].

Hybrid materials are becoming very popular due to the multi-functions possible to

gain by employing them ino devices. An example is in nano-medicine. A major goal in nano-

medicine is the coherent implementation of multifunctional platforms within a single targeted

nano-delivery system that would simultaneously perform diagnosis, targeted delivery and

efficient therapy. The hybrid nanomaterials are becoming a hot research area as they enable

the tracking of cells to simultaneous medical therapy and diagnosis [1].

The Zinc oxide is a (II-VI) material and possesses a variety of excellent properties.

These properties are of interest for technological as well as medical applications (devices).

Beside of interest for photonic applications, it is a bio-safe and biocompatible and has the

strongest electromechanical coupling. The relatively large electro-mechanical coupling makes

ZnO an excellent piezoelectric material. Moreover, ZnO possesses self-organized growth

property. His makes it possible to grow good crystal ZnO material on any surface being

amorphous or crystalline. This property combined with the excellent other properties makes

ZnO interesting for many applications, among it, light emitting didoes, laser diodes, energy

harvesting components. Since the waste ambient mechanical energy is the most abundant

source of energy, ZnO is of potential for developing such energy providing materials.

On the other hand, low temperature chemical growth can be used to grow ZnO

nanostructures of good quality. The temperature can be as low as room temperature (but

longer duration of growth is needed). This enables the use of soft and foldable material, like

e.g. plastic as a substrate, and hence develops plastic electronics. This will lead to reduce the

cost of electronic components considerably. The chemical growth can be combined with first

apply a seed layer to lead to nucleation cites and hence achieve a uniform growth.

In this activity we will use the wet chemical growth at low temperature (less than 100 oC). Here we will use zinc oxide (ZnO) as the first nanomaterial, then a secondary

nanomaterial will be grown on top. The secondary materials to be grown are copper oxide

(CuO) and nikel oxide (NiO), both are p type material by intrinsic doping. Hence we will get

two systems CuO/ZnO and NiO/ZnO hetero-nano-junctions. Usually the growth starts with

the deposition of a seed layer (ZnO nanoparticles) on the surface and then this is followed by

the growth of ZnO nanowires. After this we use same way to grow the other material, first a

seed layer and then we put our sample with grown ZnO nanowires on the new growth solution

to grow the secondary nano-material. Below is the seed solution preparation and the

preparation of the growth solution for the ZnO, CuO, and NiO.

Seed solution for ZnO nanostructures growth:

In order to prepare a seed solution containing ZnO nanoparticles ~ 5-10 nm the

following two procedures can be adapted. Depending on the substrate to be used, one of them

can be chosen.

Procedure1:

This procedure needs post-deposition annealing:

Dilute 5 mM (110 mg) of Zinc Acetate dihydrate in a very pure 100 ml ethanol

(99%) and then shake very well the solution (stirring is better) until the ZnAce is completely

dissolved in the solution and the solution has become transparent. The solution is now ready

for use by spin coating (3000 rpm) or put some drops of the solution to cover the cleaned

substrate then wait for 10s and then repeat this step for 3-5 times followed by cleaning the

substrate in ethanol after each dropping step, another way to do this is by dip coat the

substrate number of times and then clean it by the ethanol. Finally, anneal the substrate at 350

oC for 20 minutes to decompose the acetate. After that the substrate is ready for the growth

procedure.

Procedure 2

Mix the Zinc Acetate dehydrates in absolute methanol (99%). Then use 0.01M

concentration of ZnAce (274 mg) in 125 ml of methanol under stirring. The solution must be

transparent, heat this solution to 60 oC under continuous stirring. Dissolve 109 mg of KOH in

65 ml of methanol (0.03M concentration), shake this solution well until it becomes

transparent. Add drop-wise the KOH solution to the heated ZnAce solution under continuous

stirring. The

resulting solution should be kept under stirring and heating (60 oC) for 2 hours before it is

ready for use. Then you can put some drops of the solution on the substrate and coat follow by

spinng, or just apply drops and leave it to dry. Then clean the sample by ethanol or better with

methanol. No annealing of the substrate is required for this solution you can just load your

samples for the ZnO nanorods growth.

Figure 1: typical ZnO nanowires (NWs) grown by the low temperature wet chemical

approach.

The aqueous chemical growth solution for the ZnO nanowires:

Add any Zinc source salt (nitrate, acetate, phosphate, sulfate, ZnCl2) the most used one are

the first two. Add this zinc source material in 100 ml of deionized water you can change your

concentration from (25 mM up to 400 mM) depending on the final ZnO nanorods diameter

you desire (50 – 500 nm). Add Hexamethylenetetramine (HMTA) in 100 ml of DI-water, the

final ratio between the Zn concentration and the HMTA can be 1:1 or 1.5:1. In case if the

HMTA is not available NaOH can work fine to produce the ZnO nanostructures and that by

adding few drops of NaOH to the Zn solution. The seeded substrates must be loaded having

its face down in the aqueous solution and then load the solution inside an oven heated at

temperature 50-96 oC for 3-6 hours. Then clean carefully the unloaded substrate in deionized

water and dry them. Now your samples are ready for characterization and application. Prior to

the coating of the substrate by the ZnO seed solution the substrate MUST be very clean since

the dirty substrate results in quite poor growth of ZnO nanostructures. The standard cleaning

procedures are mentioned below: Pour some acetone on the substrate and shake it very well

for at least 1 minute, then clean it with DI water, then again pour some isopropanol and repeat

the same steps mentioned above. Dry your substrate and then put your seed solution as

mentioned previously.

Solution for the growth of CuO growth on ZnO nanowires:

Below is the description of the growth preparation to grow CuO on ZnO nanowires.

For the growth process of CuO nanostructures, the freshly grown NR substrate was

submerged having face up in a 5mMaqueous solution of [Cu(NO3)23H2O], and then heated to

60 oC for 1.5–4 h.

OR:

Dip the freshly prepared ZnO nanorods verticall into equimolar solution of 0.025 M copper

nitrate penthydrate and hexamethylenetetramine. Afterwards the samples were kept in

preheated oven at 80oC for 3-6 hours

If you want to grow only CuO nanostructures then the growth can be obtained using

the following solution and procedure:

The CuO (NFs) were grown on the glass substrate. For the synthe- sis of CuO NFs, 5 mM

of copper nitrate and 1 mM of hexamethylene tetramine (HMT) were mixed in de-ionized

(DI) water in a glass vessel. The solution was magnetically stirred for 5 min. Then the

reaction vessel containing the substrate was loaded in a laboratory oven at 90 C for 4–5 h. To

check the role of the pH on the growthof CuO, the pH of the solution was adjusted from 2 to

11 pH by adding HNO3or NH3H2O [3].

Figure 2: Typical grown of CuO/ZnO nano-corals.

Solution for the growth of NiO growth on ZnO nanowires:

For the growth of NiO on ZnO nanomaterial an equimolar concentration of

nickel acetate and hexamethylenetetramine was prepared and left in oven at 90oC for 4 hours.

Finally, the p-NiO/n-ZnO heterostructures were annealed at 400-500oC in order to ensure

complete transformation of the nickel hydroxide phase into NiO nanocrystalline phase.

Figure 3: Show the SEM image of ZnO nanorods, (b, c) NiO/ZnO heterojunction at low and

high magnification respectively, (d) XRD spectrum of NiO/ZnO heterojunction

References:

[1] Thanh-Dinh Nguyen , ‘’Portraits of colloidal hybrid nanostructures: Controlled synthesis

and potential applications’’, Colloids and Surfaces B: Biointerfaces 103 (2013) 326– 344.

[2] A. Zainelabdin, G. Amin, S. Zaman, O. Nur, and M. Willander, Journal of Materials

Chemistry 22, 2012, 11583

[3] S. Zaman, M.H. Asif, A. Zainelabdin, G. Amin, O. Nur, M. Willander, ‘’ CuO nano-

flowers as an electrochemical pH sensor and the effect of pH on the growth‘’, Journal of

Electroanalytical Chemistry 662 (2011) 421–425.

[4] Mazhar Ali Abbasi, Zafar Hussain Ibupoto, Azam Khan, Omer Nur and Magnus

Willander, ‘’ Fabrication of UV photo detector based on coral reef like p-NiO/n-ZnO nano-

composite structures’’, in press Materials Letters (2013.