Tunning galvano-magnetic properties of axial implanted ZnO nanowires

E. Matei1, C. Florica1, A. Costas1,M. Oancea1, D. Pantelica2, P.Ionescu2, D.M. Dracea2, M. Statescu2, I.

Enculescu1 1National Institute for Materials Physics, RO077125, 105 bis Atomistilor Str., Magurele, ROMANIA

2Horia Hulubei National Institute for Physics and Nuclear Engineering (IFIN-HH), P.O.B. MG-6, RO-077125,

30 Reactorului Str., Magurele, ROMANIA

A very important and challenging research area is based on preparation of nanostructures and

their use in various applications. For such nanostructures new methods of fabrication with high control

over the properties of low dimensional objects were developed. The reward consists in the

development of new devices which exploit the small size of nanostructures not only in terms of

miniaturization but also of increased functionality. Nanowires represent an important class of

nanoobjects. Therefore, the research effort was directed towards two critical points: development of

preparation methods which shall lead to complex nanowires with high quality and integration of

nanowires into functional devices. The most preparation methods led to uniform nanowires in terms of

shape and composition. However, in developing devices, nanowires with complex structure such as

multisegment, core-shell or multilayer should be employed. In this case the preparation process

becomes much more complicated.

In the last decade a large number of reports are dedicated to nanowire transistors with

applications ranging from biosensors and gas sensors to logic gates and memory elements.

Predominant are the devices where nanowires with uniform composition were employed. The

limitations of such devices are related to the difficulty in preparing high quality drain and source

elements. As in the case of their planar counterparts (fig.1), a proper charge injection from source to

the channel should be ensured, therefore the doping of the nanowire should be modulated along the

nanowire axis. For a good contact to an n type channel, the source and drain are n+ regions, in classic

planar technology these being formed by ion implantation.

Fig.1. Schematic representation of an n channel field effect transistor.

The nanowires will be prepared by template method. The templates will be obtained by the

irradiation of polymer foils of 30µm thick with swift heavy ions. Subsequently, the ion tracks will be

chemically etched and pores with controlled morphology and dimensions being created. Thus, as a

function of etching time and conditions, pores with diameters ranging from 20 nm to 1 µm and of

cylindrical or conical shape can be obtained. A working electrode will be deposited by sputtering a

porous membrane

(1) deposition of a thin metallic film as working electrode (2) electrodeposition of thicker layer for mechanic resistance purposes

(3) electrodeposition of nanowires inside pores

(4) growth of cap on template’s surface after complete pore filling.

(5) Co ions implantation

Fig.2. The sequence employed for preparing implanted wires in a nanoporous membrane foil.

metallic layer on one face of the membrane and then the pores will be filled with ZnO by

electrochemical deposition resulting wires with pores morphology (fig.3).

(a)

(b)Fig.3.Nanowires prepared by the group: (a) ZnO wires; (b) Ni – ZnO – Ni wires (elemental

analysis mapping – red Ni, green Zn)

Such ZnO nanowires embedded in PC membranes will be implanted with Co ions with energy

of 9 MeV and fluences 10E14-10E17 particles/cm2

We will make use of the larger than usual ion implanters energies provided by the 3 MV accelerator in

order to perform the experiments in a particular geometry namely along the nanowires axis. This will

lead to multisegmented nanostructures in terms of composition.

The nanowires prepared in this way will be extracted from the membrane by removing the

working electrode and dissolving the polymer template in organic solvents. Thus, a suspension

containing the nanowires will be obtained.

For fabricating the devices, a system of interdigitated electrodes will be deposited on Si/SiO2

wafers substrates and the liquid suspension containing the nanowires will be placed on top (fig.4).

The nanowires will be connected to the interdigitated electrode system by electron beam lithography

for carrying out galvano-magnetic characterization measurements.

(a) (b)

Fig4. ZnO nanowire prepared by the group contacted to a interdigitated electrode system. (a) and (b)

secondary electrons and elemental mapping respectively.

The main purpose of these studies corresponds to a complex characterization of the nanowires

and of the devices. In principal there are two main goals: to study the influence of the preparation

conditions on the basic properties of the nanowires and further to determine the galvano-magnetic

properties of the axial implanted ZnO nanowire based device.

Beam request:

3 days(15 shifts) at the 3 MV Tandem