Acknowledgments

Financial support by the Beilstein-Institute,

within the research collaboration NanoBiC.

Generous allotment of computer time by CSC

and Loewe - CSC in Frankfurt.

Aim of the study

EBID with W(CO)6 has been extensively used in

recent years

– Many unanswered preliminary questions.

1) The nature of chemical interaction between

W(CO)6 with the surface of SiO2?

2) Structure – (Deposit) Composition

Relationship?

3) Growth Mechanism of Nanoparticles during

EBID?

Introduction

Conventional Fabrication Techniques:

Novel Method

Electron Beam Induced Deposition (EBID)

Method

Periodic Density Functional Theory (DFT),

PAW Pseudo potential – GGA,

Vienna Ab-Initio Simulation Package (VASP),

Amorphous SiO2 (a-SiO2) used in experiments

– Difficult to model amorphous SiO2

β- Cristobalite has many similarities in physical

properties as a-SiO2 and hence used as a

representative structure.

The Bravais-Donnay-Friedel- Harker (BDFH)

predicts (111) face of β- Cristobalite are

dominant.

1 to 5 Layers of (111) surface cluster models

were considered – Structural and electronic

properties converge for 4L.

Two different surfaces: Fully and Partially

hydroxylated surfaces corresponding to surfaces

before and after irradiation of electron beam were

considered.

W(CO)6 Molecule – Geometry optimized – Oh

geometry.

Dispersion corrections by Grimme et al

implemented in VASP 5.2 have been considered.

Results

Interaction of W(CO)6 with the fully

hydroxylated SiO2 substrate.

Corresponds to the substrate prepared under

wet chemical conditions in the absence of an

electron or ion beam.

Three different orientations - Prefers bonding

through its multiple CO ligands

a) b)

FIG. 2: a) Schematic view of three different

configurations of W(CO)6 (Config.(1-3)) are shown.

b) Variation of Adsorption energy (ΔE) for different

orientation on the fully and partially hydroxylated

surfaces with and without inclusion of dispersion

corrections are shown.

Interaction of W(CO)6 with the

partially hydroxylated SiO2 substrate.

1. Chemical Vapor Decomposition

2. Arc Discharge Method

3. Hydrothermal Techniques etc.,

Fabrication of self-standing nanostructures at

selected position on selected substrate and

position controllability is still a challenge

Due to the controllability of the electron beam

nanometer sized structures such as nanodots,

nanowires, and deposits with desired patterns

have been successfully fabricated.

Substrate-precursor interaction,

Electron-substrate interaction,

Electron-precursor interaction

This study focus on understanding

Substrate (SiO2) – Precursor (W(CO)6)

interaction

Three main interactions have to be understood

Theoretical Investigation on the Interaction

between the precursor molecule illustrates

- Tendency of a precursor molecule to role

on the fully hydroxylated surface

- Activation and spontaneous dissociation on

the partial hydroxylated surface.

Studies are being extended to explain the growth

mechanism of W nanoparticles from W(CO)6 on

the surface during EBID.

Institut fϋr Theoretische Physik, Goethe-Universität, Frankfurt am Main, Germany,

Email: muthukumar@itp.uni-frankfurt.de

Theoretical Investigation of W(CO)6 Adsorption on SiO2 Surfaces – Insights to Electron Beam Induced Deposition

K. Muthukumar, I. Opahle, J. Shen, H. O. Jeschke, R. Valentí

Weak adsorption (Physisorption) on fully

hydroxylated Surfaces Fig. 2b - Minor structural

changes observed both in the surface and the

precursor molecules.

FIG. 3 (a-f) Figure illustrating the role of vdW correction

in determining the bonding of W(CO)6 to the fully and

partially hydroxylated surfaces.

Dispersion corrections play a crucial role in

stabilizing precursor molecules (cf. 3 c & e) on the

fully hydroxylated surfaces.

Partial de-hydroxylation of the surface of SiO2

substrate - expected to occur under irradiation

with an electron or ion beam or at elevated

temperatures – Direct bonding of substrate Si

atoms with the precursor.

Chemisorption - As seen from Fig 3. d & f,

spontaneous dissociation of CO ligands were

observed.

Minor structural changes - upon incorporating

dispersion corrections in the calculations.

Conclusion:

References:

1) J. Wnuk et al, Surf. Sci., 2011, 605, 257.

2) I. Utke et al, J. Vac. Sci. Tech. B, 2008, 26, 1197.

FIG. 1: (a) Structure of bulk -cristobalite SiO2 and

(b) side view of the slab geometry with a (111)

surface used for this study.(c) Comparison of

bulk DOS with Slab

(c)