Date of Award

January 2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics & Astrophysics

First Advisor

Nuri Oncel

Abstract

Scanning Tunneling Microscopy and Spectroscopy (STM/STS), Transmission Electron

Microscopy (TEM), and X-Ray Photoelectron Spectroscopy (XPS) studies were performed to

characterize the morphology, electronic properties, and chemical properties of the Iridium

(Ir) induced nano-structures formed on clean Si (110) surface. It was found that the

deposition of Ir in the sub-monolayer and monolayer (ML) regime on clean Si (110) ``16 × 2’’

surface produces Ir-silicide nano-structures, as this surface is suitable for growing

nanostructures because of its inherent structural asymmetry. STM shows that nanowires

with an average length and width of 100 nm and 21 nm, respectively, were grown on clean

Si (110) surface when 0.25 ML of Ir was deposited. Statistical analysis of STM images of Irsilicide

nanowires show that the length and the width of the nanowires are correlated. TEM

results show that there are two different regions across the nanowires, one close to the Si

substrate which is made of IrSi2 and other close to the nanowire surface which is possibly

made of amorphous Ir. STS indicates that the nanowires have different electronic properties.

The smaller nanowires are metallic based on size, but the bigger nanowires are

semiconducting with a band gap of  0.34 eV.

STM images indicate that 2 ML of Ir deposition produces Ir covered flat terraces on

clean Si (110). The interface between the Ir and substrate is Ir-silicide.

xv

In addition, quasi periodic Ir quantum dots (QDs) appear on Ir terraces. Quantum dots

are loosely bound to the terraces as they tend to move around if the STM tip comes close to

them. STS indicates that Ir-QDs exhibit Coulomb blockade and a negative differential

resistance at room temperature. Coulomb blockade and a negative differential resistance in

the dI/dV plot indicates a Coulomb gap of  0.7 eV.

XPS data shows that the binding energy of both Ir modified Si 2p3/2 and Si modified

Ir 4f7/2 peaks shift towards higher energy with respect to pure Si and Ir which indicates that

the interface between Ir terrace and the Si substrate has a Si rich silicide layer.

Download

Share

COinS