Specimen Selection Mechanical Polishing Cooling Ion Milling

Fig. 4. The specimen used is a mounted barnacle mechanically cut in half to allow for observation along the baseplate in cross-section view as shown in Figure 4. This sample is selected to demonstrate the practicality of low temperature broad ion milling as a viable method for preparing calcite based biomaterials or other calcium carbonate rich specimens for EBSD analysis.

Fig. 5. The base plate surface, top of sample was resurfaced using 1200 grit SiC paper to make it planar for mating with the mask. There after, the cross-section face of the base plate was mechanically polished using 600 and 1200 grit SiC paper with a water solution. The Maruto hand polisher set was used for mechanical preparation as shown which utilizes the same sample mount for ion milling or EM observation, therefore reducing time and increasing accuracy.

Fig. 6. Sample, cross-section stage and mask are aligned then the cold block is placed onto the entire assembly. The assembly is then placed in a protective bag to freeze for ~3 hours.

Fig. 7. The entire assembly is removed from the freezer and inserted into the IM4000. Ion milling conditions : Mask Position: 25µm from edge Vacc: 3kV Stage: C3 [± 30° / 3rpm] Time: 2hrs

Fig 1. IM4000 Broad Ion Milling System

Fig 2. Diagram of broad ion milling principle in cross-section mode.

Fig 3. Diagram of cold block and detachable stage for IM4000 cross-section ion milling.

EBSP Data

(1) The results show that combining techniques of broad ion milling and low temperature cooling by a cold block allows for improved high quality results with no thermal deformation.

(2) EBSP analysis shows the variation of orientation of small calcite grains along the inner layer of the base plate and the progression of size and symmetry towards the external wall of the base plate.

(3) The Hitachi IM4000 broad ion milling machine is useful as a damage-less technique for cross-section preparation .

Acknowledgments: Alexis C. Lewis, Ph.D., Naval Research Laboratory, DC, USA for the barnacles used in this study. http://www.nrl.navy.mil/content_images/10_FA1.pdf http://www.ncbi.nlm.nih.gov/pubmed/18247205

Comparison

Fig 8. The base plate cross-section face are shown above before and after ion milling. Calcite grain contrast is observable along the base plate region indicating a high quality cross-section surface that can be used for EBSP analysis.

Application of Low Temperature Broad Ion Milling for Crystallographic Orientation Analysis of Biocalcite Sample Preparation Technique by Cold Block Ion Milling with the IM4000

Jamil J. Clarke* * Hitachi High Technologies America, 944 Clopper Road, Gaithersburg MD 20878, USA

M&M 2013 Indianapolis, IN August 5, 2013

Poster ID: A17.P1 Vendor Symposium: Latest Developments in Tools for Life and Materials Sciences Poster #: 54

1. Abstract A sample preparation technique for sectioning soft materials such as calcite is presented. Conventional sample preparation techniques often require several polishing steps to produce a smooth surface prior to Electron Backscatter Pattern (EBSP) analysis. Broad ion milling can aid to reduce steps required for preparing soft materials mechanically. The IM4000 makes it possible to create a cross-section without mechanical artifacts. Temperature sensitive materials are subject to thermal damage during the ion milling process, therefore with the advent of low temperature cooling, thermally sensitive materials such as biocalcite can be performed and subsequently allow for surface sensitive structural analysis.

2. Instrumentation

4. Results

EM Parameter Selection: After loading into the microscope, SEM observation was conducted on the base plate portion exposed to cross-section ion milling. By utilizing high current and very low acceleration voltage, grain size variation along the baseplate from the inner layer to the outer layer near the cement producing ducts are visualized. The table below describes the SEM and EPBSP Detector conditions used for attaining crystallographic patterning along the base plate region.

Cold Block Method: A thermocouple for monitoring sample temperature was placed under the mask plate in the same region that is exposed to the ion beam. Chart 1 shows the temperature trend during ion milling with and without the cold block. The cold block and stage assembly were placed in a freezer and cooled for a period of 3hours at a temperature below 0 ° C. Results indicate that temperature retention below ambient temperature conditions are retained for a period of up to 2.5 – 3 hours.

The Hitachi IM4000 is used for material processing and the resulting cross-section face observed by a variable pressure SEM. Figure one shows the IM4000 broad ion milling system capable of different modes such as cross-section milling, flatmilling©, low temperature milling and LN2-cryo milling. The basic principle of cross-section milling illustrated in Figure 2. is performed by irradiating the sample cross-section face by argon ions which sputters away material exposed beyond the mask plate edge. A smooth cross-section face is formed by the placement of a protective mask plate that is attached to the topmost surface of the sample. In order to maximize a large surface that is exposed to the argon ion beam the stage oscillates in order to sweep the beam across the cross-section face at a user settable angle. Figure 3. shows a detachable cold block that was used to suppress the temperature of the barnacle sample from increasing above room temperature during ion milling.

Fig 9: Cross-section view of the base plate area analyzed for EBSP.

3. Method Overview

SU6600 SEM Conditions Oxford Aztec EBSP Conditions Vacc 19kV Phase Calcite Emission Current 32µA Image Capture 512/35µs dwell Time Probe Current Medium Reflectors 59 Cond1 13 Binning 4x4(336x256) Probe Current (meas) 2.80nA Gain High Working Distance 18.2mm Exposure Time 43.23 Magnification 1000X Static Bkgnd Enabled:32frames HFW 127µm Auto Bkgnd Enabled:8frames avg Tilt 70° Map Size 100µmX30µm Signal BSE@25Pa Step Size 0.271µm

5. Results

Table 1: SEM and EBSD Settings Chart 1 : Cool Block Temp Vs. Time

C°

(Hrs.)

Band Contrast(IQ)

Euler Angle Map(All)

IPF(X)

IPF(Y)

IPF(Z)