Materials and methods

3.1 Introduction

The specific details of the different analytical techniques applied in this research will be presented in this chapter. This includes the experimental parameters and settings of various instruments as well as ionic concentrations of solutions used and details of sample cleaning and preparation. Table 3.1 lists all materials and equipment used.

3.2 Sample preparation

A mirror finish was essential to obtain on the Ti samples as smooth surfaces are prerequisite for the surface analysis techniques applied in the current work. The presence of prominent surface features such as peaks will create shadows thus hindering the detection from the other surface areas (valleys). In addition to surface characterization problems, a rough surface will also interfere with the ion implantation process itself resulting in preferential ion implantation and inhomogeneous doping of the Ti substrate.

It should be noted that the CP Ti samples used in the present work were from two different batches, however the surface characterization of these samples revealed no significant compositional variations between these as demonstrated in chapter 4.

Material Remarks Manufacturer

Ti disc CP Ti 99.6% Grade 1 Goodfellow Cambridge Ltd England

SiC paper 1200 Struers A/S Denmark

SiC paper 2400

OP Chem cloth

OPS Colloidal silica

suspension

Polishing machine Struers Rotopol II

Hydrogen peroxide 5% BDH laboratory supplies Poole England

W ax Modelling wax Associated Dental Products Ltd. England

Toluene 99.8% HPLC grade Sigm a-A ldrich, Steinheim Germany

Acetone HPLC grade BDH laboratory supplies Poole England

HBSS Without phenol red Invitrogen Corporation England

Mounting jig Made for fixing Ti

discs during polishing

Biomaterials EDI 256 Grays Inn Rd London WC1X0L8

Ultrasonic bath Sonorex Transistor Bandelin Electronics, Berlin, Germany

Tissue culture wells 24 well plates Beckton Dickinson Labware. France

Ion implanter Wickham 200 Whickham Ion Beam Services Ltd in

Darlington, at Imperial College London

XPS ESCALAB 2201-XL Vacuum generators, East Grinstead, UK

SIMS Atomika 6500 ion

microprobe

Perkin Elmer. Atomika at Imperial College London

SEM Stereoscan S90B Cambridge Instruments at EDI

WLI Zygo - New View 200 Imperial College London

XRD Siemens D5000 Siemens, Germany at QMUL

SigmaPlot software Computer Programme SPSS Inc. Chicago, Illinois

Eclipse software Computer Programme Thermo VG Scientific, East Grinstead, UK

CasaXPS software Computer Programme Microsoft Corporation, U S A

SRIM 2000 Computer Programme (Ziegler 2000)

Profile Code Computer Programme (Profile Code 2003)

Table 3.1 M aterials a n d Instrum ents used in sam ple cleaning, preparation and analysis.

3.2.1 Polishing

Samples used were circular CP Ti discs Grade 1 (99.6%) the dimensions of which were 8 mm diameter x 1 mm thick or 14 mm diameter x 1 mm thick. These were polished using silicon carbide paper discs of grit 1200 and 2400 respectively followed by a colloidal silica suspension (OPS) of 0.1 pm particle dimension containing 5% H2O2 Full details are given in Table 3.2.

The samples were mounted on to methyl methacrylate resin (MMA) jigs to allow for their positioning on the polishing stage. Three different methods of mounting the samples were used in an attempt to achieve a mirror surface finish which was very difficult due to the inherently soft Ti, which tends to facet during polishing as a result of its multiplanar crystalline structure. In the first batch of samples circular discs with a central recess to precisely house the sample were cast in a cobalt chromium alloy (Co-Cr) and then embedded into the MMA jigs. However because samples were not fixed to the jigs and were moved during cleaning in between various polishing stages, faceting and doming of the surface of a large percent of the samples was unavoidable. Alternatively the second batch of samples was embedded in resin jigs which were then mounted onto the polishing machine. These were found to have slanted surfaces, which is not ideal for the surface modification and analysis techniques applied in this work. Finally the samples were fixed onto the resin jigs using molten wax that was left to set for a minimum of 2 h prior to polishing. This method of fixation resulted in an optimised surface finish on most samples.

Samples used in the present work were polished using either jigs with Co-Cr cast discs (PR.1) or by embedding in wax (PR.2). These are shown in figure 3.1. The polishing protocol is detailed in table 3.2.

m m - - :

Figure 3.1 The two jig s used to mount the samples for polishing. The one on the left was the PR.1 Jig while the one on the right was for the PR.2 polishing regime.

S tage Force (N ) Tim e Speed (R P M ) Polishing disc Lubricant 1 30 4 5 s 300 1 200 grit SiC W a te r 2 30 4 5 s 300 2 4 0 0 grit SiC W a te r

3 2 5 6 min 150 O P chem. cloth O P S + 5% H2O2 ratio 4:1

Table 3.2 Protocol for polishing Ti discs

3.2.2 Cleaning

Samples were manually removed from the jigs and remaining traces of wax (PR.2) were dissolved by ultrasonication in toluene using successive baths of fresh solvent until no traces of wax were detected. The samples were then ultrasonicated in HPLC grade acetone and HPLC grade water. Each solution was used for no more than five minutes and was then replaced with fresh solvent as needed. HPLC grade water rinsing was carried out in between solvents. Finally, following a last rinse in ultra pure water to remove any trace elements, samples were placed on paper towels to draw the liquid off the surface and left to air dry. The samples were then stored in tissue culture wells 84

and were either left in the ambient environment or placed in a dry environment (desiccator). Gloves were worn throughout the sample cleaning and preparation process to avoid excessive contamination of the discs.

3.2.3 Implantation

3.2.3.1 System used

Ion implantation was carried out at Imperial College, London by Dr. T.J. Tate using a Wickham 200 ion implanter. This implanter is equipped with a Freeman ion source, a graphite arch chamber and tungsten filament and is maintained at a background pressure of 2 x 10'^ mbar. The beam was set at energy of 40 keV and the ion beam passes through a mass analysing magnet to achieve 1 a.m.u. resolution.

Main Chamber Movable Target Stage Primary Ion Beam Final (beam defining) aperture

Figure 3.2 The Wickham 200 ion implanter (courtesy o f D r T.J. Tate).