You may follow the AAO template assisted method.

First make NiO NWs  by means of electro-deposition on the template in a potentiostat. Then coat the NiO NW arrays with ZnO by means of simple wet chemical route. Doing these you may get core/shell type NiO/ ZnO nano-heterostructure. 

These papers may be really helpful.

1. A. K. Singh, D. Sarkar, G. G. Khan, and K. Mandal, J. Mater. Chem. A, 2013,1,12759.

2. Appl. Phys. Lett. 2014, 104, 133904.

3. RSC Adv. 2014, 4, 55629-55634.

You can simply spin cast ZnO then NiO in the form of thin film. Plesse see the standard process to deposit ZnO and NiO. (Note the precursor and the sintering temperature).

Otherway, you can deposit ZnO first and then NiO nanowire as suggested in first comment.

Or you can deposit NiO thin film by solgel spin casting and then a seed layer of ZnO and grow ZnO nanowire by simple hydrothermal or aqueous chemical growth technique.

Thanks for your answers, however, I need to sythesize nanostructures of NiO and then nanostructures of ZnO to form p-n junctions. Both should be prepared by preferable Hydrothermal or chemical bath approach. So, if you can suggest something relared to this. 

 After making the NiO NWs in an AAO template,(back side of the template should be coated with gold or platinum) you may apply dip-coat method. In this process, you have to first prepare an ethanolic Zn(CH3COO)2 solution (0.1M) then you may follow any of the following processes,

dip the NiO NW sample into the solution,

you may drop the Zinc acetate solution on the NiO sample,

 you may also apply spin-coating method.

After this, you dry the sample and anneal it in air at  say 400oC. 

You may check the following paper for ZnO nano-shell preparation.

RSC Adv. 2014, 4, 55629-55634.

http://pubs.rsc.org/en/Content/ArticleLanding/2014/RA/c4ra09456e#!divAbstract

Hello  Sayan 

All the answers seems are very appropriates but remember the morphology of ZnO from the reaction of Zn(NO3)2 and NH4OH by CBD methods depends drastically on the initial substrates as well as the concentration of the chemcials, temperatures and time.

( “A versatile cost-effective and one step process to engineer ZnO superhydrophobic surfaces on Al substrate", Ashoka Siddaramanna, N. Saleema and D. K. Sarkar, Appl. Surf. Sci. 311 (2014) 182)  

On the other hand, Ni(NO3)3 might produce Ni(OH)2 than NiO, an observation we had  few years back (Not published)

The spin coating is a good option, as you need to anneal them above 500 C after the coating. The hydroxide will change to oxides.

AAO is very good option but you will etch out ZnO with AAO in the alkaline solution

Your best option would be make the nanoparticles in sol-gel process and spin coat and anneal them to be sure that they are oxides not hydroxides particularly NiO. You can follow the following recepie  as we used to make SiO2 and published (“Synthesis of monodisperse fluorinated silica nanoparticles and their superhydrophobic thin films”, J. D. Brassard, D. K. Sarkar, J. Perron, ACS-Appl. Mater. Interfaces 3 (2011) 3583–3588). Remember, chemistry of metal precursor and Si are not the same.

To make a p-n junction, you can use Pt-coated Si substrates and spin coat the ZnO/NiO annaled them 500 C. Use a top coating of Pt (by sputtering) or simply silver paste to make your p-n junction. I assume, Sayan, you are interested to develop a thermoelectric device.

Either thermoelectric or supercapacitor using similar materials, if you are interested to pursue PhD at my lab, I have an immediate opening. If you know someone else please pass this message.

Good luck

Dilip

Dear Sir,

Many thanks for your answer. I have replied to you in your mail id.

Thanks & Regards,

Sayan

Sir,

I have also forwarded your offer to a few of my friends and juniors and they will certainly mail you soon. Once again, thank you very much for your offer and your valuable suggestions.

Thanks & Regards,

Sayan