Diameter of nanowire is around 10 nm. It is considered to have length to width ratio greater than 1000. In nanometer scale electronic properties becomes different due to quantum confinement effect. Electronic properties of ZnO wires are also found to depend on the shape of nanowires, haxagonal or triangular. You go through the recent papers published on electronic properties of semiconductor nanowires in general and ZnO in particular for further detail.

Diameter of nanowire is around 10 nm. It is considered to have length to width ratio greater than 1000. In nanometer scale electronic properties becomes different due to quantum confinement effect. Electronic properties of ZnO wires are also found to depend on the shape of nanowires, haxagonal or triangular. You go through the recent papers published on electronic properties of semiconductor nanowires in general and ZnO in particular for further detail.

The electronic properties will change as the electrons are being confined to the surface. 

Electronic property will change surely but depends upon the length to width ratio.

The geometry of the semiconductor has effect on its conduction parameters such as the mobility and lifetime. Especially the ratio of the surface to volume of the specimen greatly affect the the mobility and lifetime.  It  is found for specimen with macroscopic dimensions that the lifetime and mobility will decrease by increasing the surface to volume ration because of the presence of the surface states as a consequence of  the interruption of the crystallographic periodicity at the surface.

Scaling down the semiconductor dimension to nanometer bring changes in the transport of charge carriers. The most important effect is quantum mechanical confinement of charge carriers inside the small dimension as the motion of electrons in a potential box with infinite walls. For an ideal well, the electrons can not exist at the wall of the well. This means the surface effects are mitigated. In case of nanowire the electrons are more or less confined in the core of the wire and move along the axes of the wire ideally speaking as if they move in the volume  free of scattering at the surface. Research work showed that reducing the wire size to very  small values increases the phonon scattering and the mobility is degraded. The remedy is to coat the wire with a very thin layer of more rigid material to suppress phonon formation and enhance the mobility.  

At nanoscale the properties will change and governed by quantim behavior 

Aldelhalim Zekry...I read your answer, and part of it you mention the phonon scattering, which I am interested to know how could this happened?

The bulk and single dimensional properties of any semiconductor material diffrent  to each other. Semiconducting properties of any semiconductor widely depends on the on the crystal structure, the crystal structure grain size, and state density change at nanolevel structure like nanowire, nanobelt, nanoneedle, nanorod etc.

As mentioned above surface to volume ratio increases at nanoscale. And nanostructures have too many dangling bonds which will result in recombination and reduced mobilility. This can be resolved by coating nanostructures with thin film of passivation layer on top of nano structures.  Phonon formation can also be thought as generation of heat. 

Dear Mohd,

You can find more information in the site:http://ndl.ee.ucr.edu/Balandin-NL-SiNW-06.pdf

Dear Milea

Thanks for your answer

 I am intrested tp know  how the arrangement of grains affect the electronic properties of nanomaterial ?

Dear Milea,

How did you get that your compound became semiconducting as the grain size decreased to nanometers? Did you find an energy gap in optoelectronic conduction properties of the material. The decrease of the conductivity to the range of semiconducting material is not an evidence of semiconductor because the mobility can dramatically decreased because of  the grain boundaries.

The second note is how [ grains of these nanomaterials are a lot closer one to each other compared to bulk.]. Grain boundaries are less dense than the bulk, how would be gets closer than the bulk.

wish you the best

Obviously the electrical properties will change of the material, if you go for nano wires rather than simple uniform thin films.

considering that the tip of your nano wire is exhibiting quantum size effect r not.

There are too many factors affecting better for more knowledge you go for Electrical properties of ZnO research articles published for simple uniform ZnO thin films and Nanowires.

Size (especially diameter) affects the electronic and as well as photonic properties of the nanostructures.

In the Semiconductors like ZnO you mentioned, which has a wide band gap offers band gap tuning (by decreasing its diameter its bandgap gets decreased).

Please refer to the attached article to understand further its physics. 

There is usually a very high dependency of both electrical and optical properties of nanostructures on substrate material. So, yes expect the electrical properties to vary with substrate type. Also the geometry on your nanowires is another factor that will definitely affect their electrical properties.

Anodic photocurrent generation was observed when an ITO electrode functionalized with ZnTe/ZnS nanocrystals was irradiated in the visible region in a photoelectrochemical cell, indicating that the quantum dots perform spectral sensitization of the electron injection into the ITO electrode. Conversely, cathodic photocurrent generation was not observed; hence, the QD-modified electrode performs electrical rectification under a photon energy input.

I am not sure I understand your second question on the effect on grain arrangement. However, I do know that grain size has a huge effect on electrical properties of materials. If you have small grain size, it means you have a huge number of grain boundaries and these always act as scattering points for charge carriers resulting in reduced carrier mobilities. Carrier mobility and the number of carriers are among the most dominant factors affecting resistivity of materials. For this reason, a material with perfect large crystal is more conductive than the same in amorphous nature (effects of annealing).

Grain arrangement can also result in material defects,(vacancies,  voids, hillocks etc). All these will impact the mobility of holes and electrons (carriers) and hence the electrical properties of the material.