Zeiss ?IGMA VP-FE-SEM User manual

EPA/600/R-14/211 | October 2014 | www.epa.gov/research

Zeiss ΣIGMA VP-FE-SEM

User Guide

R E S E A R C H A N D D E V E L O P M E N T

Zeiss ΣIGMA VP-FE-SEM

User Guide

Prepared for

Jeremy Hilgar, Darlene Usi and Katrina Varner

U.S. Environmental Protection Agency

Office of Research and Development

National Exposure Research Laboratory

Environmental Sciences Division

Las Vegas, NV 89119

Although this work was reviewed by EPA and approved for publication, it may not necessarily reflect

official Agency policy. Mention of trade names and commercial products does not constitute

endorsement or recommendation for use.

U.S. Environmental Protection Agency

Office of Research and Development

Washington, DC 20460

SEM Quick Start

Revision No.2

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Zeiss ΣIGMA VP-FE-SEM

User Guide

May 2014

By:

Jeremy Hilgar, Darlene Usi

SEM Quick Start

Revision No.2

May 2014

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TABLE OF CONTENTS

Section Page

1.0 Procedural Section............................................................................................................................................3

1.1 Sample Preparation and Loading .............................................................................................................3

1.1.1 Support Selection................................................................................................................3

1.1.2 Sample Deposition..............................................................................................................3

1.1.2.1 Liquid Samples.....................................................................................................3

1.1.2.2 Solid Samples.......................................................................................................4

1.1.3 Loading the Carousel..........................................................................................................4

1.2 Instrument Startup....................................................................................................................................5

1.2.1 Software Startup .................................................................................................................5

1.2.2 Gas Pressure and Vacuum Control .....................................................................................5

1.2.3 Accelerating Voltage ..........................................................................................................6

1.3 Producing an Image..................................................................................................................................7

1.3.1 Detectors.............................................................................................................................7

1.3.2 Stage Control and Working Distance using Analog Controls.............................................8

1.3.3 Stage Control Using SmartSEM’s Stage Navigation..........................................................9

1.3.4 Scan Speed and Noise Reduction .....................................................................................10

1.3.5 Reduced Raster.................................................................................................................10

1.3.6 Brightness and Contrast....................................................................................................11

1.3.7 Magnification and Focus ..................................................................................................11

1.3.8 Stigmation and Focus Wobbles ........................................................................................11

1.3.9 Saving an Image ...............................................................................................................12

1.4 STEM Mode...........................................................................................................................................13

1.4.1 Stage Navigation and the STEM Detector........................................................................13

1.4.2 Imaging Modes.................................................................................................................14

1.5 Logging Off............................................................................................................................................15

1.5.1 Stage Positioning and STEM Detector .............................................................................15

1.5.2 Accelerating Voltage ........................................................................................................15

1.5.3 Vacuum Control and Gas Pressure ...................................................................................16

1.5.4 Closing the Software.........................................................................................................16

2.0 References ......................................................................................................................................................16

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Zeiss VP-FE-SEM Quick Start Guide

1.0 Procedural Section

1.1 Sample Preparation and Loading

Note: The cleanliness of the vacuum chamber is very important. It is encouraged

that the investigator wear gloves while handling objects that will enter the

vacuum chamber, specifically the sample carousels. It is also good practice to

keep the chamber door closed as often as possible. This practice reduces the

contamination rate of the chamber.

Sample preparation consists of two basics steps and will vary depending

on both the nature of the analyte and the information required from the analyte

1.1.1 Support Selection

Sample supports and films are most broadly categorized by

whether or not they are STEM-compatible. STEM-compatible films and

grids are always slotted to allow the passage (transmission) of electrons to

a detector. The most commonly used STEM-compatible support film is

the lacey carbon copper grid. These grids can come equipped with a

Formvar resin to enhance the stability of the lacey carbon network. The

usage of STEM-compatible support films often proves convenient given

that these sample mounts can also be used in normal SEM mode. The

selection of an appropriate support medium for a given task is often a

process of trial and error.

1.1.2 Sample Deposition

1.1.2.1 Liquid Samples

Liquid samples are deposited onto the appropriate support

in a drop-by-drop fashion using a variety of tools. Given that

sample supports are often large enough to house several different

analytes, it is often desirable to control both the location and size

of the spots deposited. The tools used to reach this end vary, but

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are all fairly simple. Perhaps the most convenient instrument used

to deposit spots on the support is the mechanical micropipette. The

exact volume of the spot will naturally vary depending on the

situation. It is advisable to test different sample volumes on a

separate surface prior to deposition on a support film.

Occasionally the use of a micropipette proves to be rather

unwieldy and the task requires different methodology. It has been

found that simply using the disposable plastic tips of the

micropipette as a spotter is a viable alternative. Glass spotters can

be used to some degree of success, but have found to be a rather

poor alternative to the aforementioned methods.

1.1.2.2 Solid Samples

Samples that are solid are most commonly dissolved or

suspended in an appropriate solvent and mounted the same as

liquid samples (Section 1.1.2.1). Samples that cannot be dissolved

or suspended practically are attached to their support using either a

conductive tape or a conductive paste as adhesives. It is advisable

to refer to the instructions specific to the adhesive being used

before utilizing them. Note that pastes and adhesives are not used

when operating in STEM modes.

1.1.3 Loading the Carousel

Once prepared, sample supports are fixed to an appropriate grid

carousel capable of holding several films simultaneously. These sample

carousels come in many different styles and are what ultimately interface

with the microscope’s stage platform. All carousels are fixed to the stage

via a dovetail joint. One end of the joint on the stage platform has a flat

docking bar that articulates with the flat end of the grooves found on the

bottom of the sample carousel. It is important to ensure that the carousel is

seated correctly before continuing. This precaution will both reduce the

likelihood of collision happening within the vacuum chamber and increase

the ease in which samples can be located on the support carousel using the

STEM Navigation tool (Section 1.3.3).

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1.2 Instrument Startup

This section chronologically outlines the steps required to properly start up

the instrument safely.

1.2.1 Software Startup

The microscope is controlled entirely by the SmartSEM software

suite developed by Zeiss. The software requires users to login to an

account before use. User accounts are important for both logging operator

actions as well as saving personalized user interface preferences. Once

opened and logged in, the software will automatically show a view of the

vacuum chamber as well as the status of the instrument. The operator is

encouraged to become familiar with the layout of the user interface prior

to preforming any work with the instrument. The help system built into the

SmartSEM software suite has been found to be an effective resource in this

arena.

1.2.2 Gas Pressure and Vacuum Control

This microscope uses pressurized gases for both vacuum chamber

valve actuation and variable pressure viewing modes. Prior to pulling a

vacuum, the operator must ensure that the instrument is being supplied

with compressed air at a pressure of 87 psi (116 psi, maximum). If the

operator intends to view samples under variable pressure mode (which

will not be discussed in this guide), the instrument must also be supplied

with nitrogen gas at a pressure of 2.9 psi (4.4 psi, maximum).

Assuming the sample has been properly prepared and loaded

(Section 1.1), the operator must ensure that both the vacuum chamber door

is completely closed, and that the instrument is being supplied with

pressurized gas before pumping down the chamber. Find the Vac status

box at the bottom right section of the SmartSEM interface and select

Pump. At this point the roughing pump will switch on and begin pulling a

vacuum. Shortly thereafter, the turbo molecular pump can be heard

spinning up once the roughing pump has pulled the chamber to an

appropriate pressure.

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The pressure of the sample chamber can be viewed under the

Vacuum tab on the right sidebar. Pressure units can be cycled through to

the user’s preference by left-clicking the vacuum pressure status boxes.

The microscope requires a vacuum below 0.009 Pa before extra high

tension (EHT) can be enabled, which is required to produce an image.

Although the software allows enabling EHT at this pressure, better images

are usually produced at lower pressures (~ 10-4 Pa).

1.2.3 Accelerating Voltage

The voltage used to accelerate electrons toward the sample has an

important impact on the produced image. Before turning on EHT, the

operator is advised to ensure that the accelerating voltage is set to a

reasonably-low value (~ 2.0 kV, ± 1.0 kV). The accelerating voltage can

be changed most easily by double-clicking the EHT textbox at the bottom

of the main camera window. When EHT is off, this textbox will show

EHT = 0.00 kV. After checking that both the vacuum chamber pressure

and accelerating voltages are at reasonable values, EHT can safely be

enabled by clicking the EHT status box at the bottom-right of the

SmartSEM window. If successfully enabled, the status box will change

accordingly. Note that it is common practice to change EHT values in

small increments (no more than ± 5 kV) in hopes of prolonging the

lifetime of the filament responsible for emitting electrons.

As a general rule, lower EHT values gives greater information

about the surface of a sample with cost to resolution. Conversely, higher

accelerating voltages yield higher resolutions while obfuscating details

about the surface. It is also important to use lower voltages (in the absence

of variable-pressure modes) on samples that conduct electrons poorly to

decrease the effects of charging.

It is important to be aware of the effects accelerating voltage has

on the final image. The beginner is encouraged to experiment with

different EHT values while attempting to produce an image (Section 1.3).

The more experienced user will also find this practice to be beneficial

when working with new sample types. Once familiar with the basic

process of producing an image (focusing, stigmating, etc.), practice saving

images (Section 1.3.9) of the same scene at different accelerating voltage

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