BU Advanced Technologies R&D Center
Electron Microscopy and Microanalysis Unit

 Bogaziçi University R&D Center Electron Microscopy and Microanalysis Unit
34342 Bebek, Istanbul, TURKEY

Tel: +90 212 359 72 30

                                            Email :gedikb@boun.edu.tr
                                            Web: www.arge.boun.edu.tr

We always welcome feedback and invite you to contact us
 
 
 

[About EM Unit]   

[ESEM]   

[EDX/Image Processing System]   

[Environmental Secondary Detector]   

[Vacuum System]   

[Image Gallery]




The Philips XL30 ESEM-FEG/EDAX system: Microscopy & Microanalysis Lab

XL30 ESEM-FEG/EDAX system is a new type of high resolution environmental scanning electron microscopy & microanalysis, which allows the examination of specimens in the presence of gases. As a result, wet or dry, insulating or conducting and, generally, all specimens can now be viewed with no or minimal preparation.

The aim of this Laboratory is to promote R&D in the field of ESEM

XL30 ESEM-FEG/EDAX system is designed to satisfy the needs of the industry and the scientific community following up on new technology and materials development, especially in Ceramics, Polymers, Metals, Thin Films, Composites, Coatings, Biological, Electronic Materials & Products.

For further details, you may contact Bilge Gedik Uluocak.

Extraordinary performing and recording capabilities:

    Highly stable imaging of hydrated and wet samples

    Pure SE imaging of nonconducting uncoated materials at any kV

    SE imaging in both gaseous and high vacuum conditions

    Controlled gas ionization (to suppress charging artifacts)

    High-resolution (as good as 2.00nm) of SE imaging, outgassing heated or light emitting samples.

[Prices of ESEM Analysis]

Notable advancements with ESEM-FEG

    Dynamic experiments can be carried out and recorded under ambient levels of light. This is because, unlike the Everhart-Thornley secondary electron detector of conventional SEMs, the gaseous secondary electron detector (GSED) is neither light nor heat sensitive.

   Optional heating/cooling stage: Samples can be heated/cooled, crystallized or melted while they are in the microscope chamber. The entire process can also be reversed without having to remove the sample from the chamber. This permits continuous observation and recording of in-situ experiments with a resolution never before seen. The ESEM-FEG vacuum automatically stabilizes the chamber pressure even if the sample outgasses during experimentation.

   XL30 ESEM-FEG offers high resolution secondary electron imaging at pressures as high as 10 torr and sample temperatures as high as 1,000 oC; The wet, oily, dirty, outgassing and non-conductive samples can be examined in their natural state without significant sample modification or preparation.

  Benefits of the ESEM-FEG are realized by eliminating the high vacuum requirements of SEMs in the microscope chamber.

In the ESEM, multiple Pressure Limiting Apertures (PLA’s) separate the sample
chamber from the column. The column remains at high vacuum while the chamber may sustain pressures as high as 50 Torr.
 
 

General & Special Techniques for ESEM-FEG Imaging/Image Analysis and Quantitative Techniques

    Secondary/Backscattered Electron Imaging
            Conventional (High vac.Mode)
            Gaseous (Wet/Dry and Low/High vac Mode)

    Image Processing

    Image analysis of X-ray Maps

    Image Reconstruction

    Stereology 


Go to Image Gallery

 
 
 
 

      ESEM-FEG/EDAX Application Guide

Samples/Surfaces Preparation , as follows:

    Fractures:
            metals(by mechanical machinery or others)
            non-metals(plastics, ceramics, and organics)

    Sections:
            hard materials/cross section (composite,i.e.commercial products or dedicated materials such as metals, rocks, ceramics and glass)
            soft materials/cross/thin sections (plastics, paints,rubbers,woods, and paper, some polimer)

    Dispersions:
            wet dispersions (in suspension: polimer, paint pigment, biological culture)
            dry dispersions (powders, fibers)

    Live material observation :
            Insalt samples, if fresh (removed fats)
            Plant, if fresh (after cryo treatment)

    Replica: (for bulk of the object, or bad materials of the vacuum system)
            Geological materials
            Peroleum-Based materials
 
 

Some Techniques:

    Initial Preparation of Biological and Materials Specimens

    Special Specimen Preparation Methods( casting, drying, molding, replicating, i.e.)

    Specimen Coating (Vacuum evaporation, Sputter coating)

    Mounting and Storing Spec.(polylysine and lacting adhesives, mounting powder)

    Specimen Etching

    Ion-Beam Etching

    Plasma Ashing Preparation

Return to top

 
 
 

Electron Microscopy and Microanalysis (EM&M):

Electron Microscopy: Some of the more common techniques which are associated with this field include the following: scanning electron microscopy (SEM), environmental scanning electron microscope (ESEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), scanning tunneling microscopy (STM), scanning ion microscopy (SIM), analytical electron microscopy (AEM), high resolution electron microscopy (HR EM), high voltage electron microscopy (HvEM), etc. (the list can continue).......

Microanalysis should be considered to include a technique which employ a probe such as: electrons, ions, mechanical and/or electromagnetic radiation to form a representation or characterization of the microstructure (internal or external) of any material in either physical sciences applications: electron microprobe analyzers (EMPA), X-ray energy dispersive spectroscopy (EDX), (the list can continue).......
 
 

 ESEM /EDAX System in Description of Some ESEM Related Terms

ESEM - Environmental SEM: is a special type of electron microscope that works under controlled environmental conditions;
In three major functions:

    Pure SE detection

    Compatibility with water through Environmental Secondary Dedector (ESD) and Gaseous Secondary Electron Detector (GSED) provides better discrimination against parasitic electron signals. Highly efficient backscattered electron (BSE) detectors have allowed ESEM examination of truly wet specimens at room temperature using low beam accelerating voltage and current. No beam damage is detected during examination. Surface properties can be studied by observing the reaction with various liquids.

    High chamber pressure (max.20 Torr),
With a question, “What does it look like in its natural state?"
It was exactly this question that led to the development of the Environmental Scanning
Electron Microscope. Researchers in Australia wanted to look at wool in its natural state
— wet, oily and dirty — definitely vacuum intolerant, very vacuum unfriendly and
highly non-conductive. They realized that the solution lay in eliminating the high
vacuum requirement in the sample chamber. To do this they had to cross two technical
hurdles. First they had to separate the vacuum environment of the electron column from
the environment of the sample chamber. Second, they needed a secondary electron
detector that could function in this non-vacuum sample environment. Their solutions to these problems are the keys to the development of the Environmental SEM. The environment in an ESEM can be selected among water vapor, air, N2, Ar, O2, etc. Dynamic characterization of wetting, drying, absorption, melting, corrosion, and crystallization can be performed using ESEM in situ Testing Stage:

    Peltier cooling stage permits examination of samples over a temperature range of 5oC to +70oC.

With key benefits (as listed by Philips Electron Optics (now FEI-Philips), all kinds of samples( non-conductive, wet, dirty, outgassing, dynamic samples without cleaning or coating) can be observed & investigated in a variety of environments by manipulating pressure, temperature, humidity, and composition of ambient gas or liquid:

    True secondary electron imaging at 10 torr chamber pressure

    No charging of non-conductive samples

    Low-Z materials

    Observation of contaminating samples

    Porous material observation

    BC stability < 1%/hour, Schottky emitter

    Hydrated samples remain fully stable

    No coating interference

    Phase transitions

    Hydration processes

    Oxidation/corrosion

    Stress testing

 Return to top

 
 
 
 
 
 
 

Energy Dispersive X-ray Analysis (EDX):

Energy Dispersive Spectrometry EDS: In general, this type of spectroscope identifies and counts the impinging X-rays based upon their characteristic energy levels. EDS is useful in obtaining rapid qualitative analysis of an unknown sample. Quantitative analysis is available using the appropriate standards.
The X-ray spectrum, used in quantitative analysis, is generated by the sample in response to a finely focused electron beam striking the sample at a right angle. The intensity of the X-rays are measured by EDS.

In general view, EDX is a nondestructive analysis method for which minimal sample preparation is required. A well polished surface is sufficient for quantitative analysis. The electron microanalyzer serves two purposes:

    it provides a complete qualitative/quantitative analysis of microscopic volumes of solid materials through X-ray emission spectrometry, and
    it provides high-resolution scanning electron and elemental X-ray images (also known as concentration maps).

Some capabilities of EDX are as follows:

    analysis of elements with atomic number >4 (B to U)
    minimum detection limit: 50 ppm (under favorable conditions)
    quantitative light element (F,O,N,C,B) analysis
    high resolution compositional imaging with backscattered electrons
    surface imaging using secondary electrons
    X-ray mapping, including large area mosaic maps and stage-rastered images
particle size and modal analysis of digital images

EDX: X-RAY Analysis in ESEM  has new dimensions with key benefits:

    The lack of charging artifacts in the ESEM has direct benefits for X-ray analysis. It eliminates the interference of sample coatings and it permits analyes at higher accelerating voltages on non-conductive samples. However, there are additional variables to be considered in optimizing the ESEM for X-ray analysis. Any coating applied to a sample contributes to the characteristic X-ray spectrum. X-rays from the coating can interfere with the detection and counting of X-rays from sample elements having lines of the same energy. The absence of conductive coatings on ESEM samples eliminates the potential for absorption and interference.

    Pure Element Intensity Factors (PEIF's) were made more accurate and actually eliminate the measured PEIF's. This eliminated the need for different sets of PEIF's at different kV's in our system.

    Other significant benefit of our system’s new algorithms is that it's finally possible to do accurate and reliable light element quantitative analysis. The taken data was acquired over a wide range, if excitation conditions illustrate the quality of the used standardless quantitative method. The results show a very small deviation from the given results.
 

 Return to top

 
 

EDX- Image Processing & Analysis in ESEM-FEG is a special image processing and analysis system to detect, characterize, and classify closed features from ESEM images under low(water, air, or N2) and high vacuum conditions with no limitation. This system can be utilized for hundreds of applications where you need to acquire and analyze images in options for EDX Multi Element Mapping/Line Scanning/Particle & Phase Analysis. The system has following functions:

    Image acquisition from video, CCD cameras, scanners, Photo CD, scientific image databases
    Treatment of color, gray scale, and black and white imaging
    Geometric measurements and structure-function relationships.
    Customized applications and automate functions.
    Test, comparison, and visualization of data for some statistical results.
 
 
 

Enviromental Secondary Detector (ESD/GSED)

Secondary electrons provide the highest resolution images. The ESEM uses a proprietary Environmental Secondary Detector (ESD). In its simplest form the ESD is a conical electrode, a positive potential of a few hundred volts, applied to the detector, attracts secondary electrons emitted by the sample. As the electrons accelerate in the detector field they collide with gas molecules. The resulting ionizations create additional electrons, called
environmental secondary electrons, and positive ions. This process of acceleration and ionization repeats many times resulting in a proportional cascade amplification of the original secondary electron signal. The detector collects this signal and passes it directly to an electronic amplifier.
The ionization characteristics of the gas in the sample chamber affect the imaging
process directly. The more easily the gas ionizes, the higher the amplification gain will
be. Varying the detector bias modulates the gain and permits the use of a variety of
different gases. The most commonly used environmental gas is water vapor. It ionizes
easily to provide excellent imaging performance. It is convenient and non-toxic. Last but
not least, it is an abundant component of our own environment and, thus, frequently of
interest as part of the experimental system under observation.

The Gaseous Secondary Electron Detector (GSED) is a refinement of hte original ESD. It improves image quality by discriminating against spurious signals from backscattered electrons and type III secondary electrons.
The primary function of the GSED is to discriminate the noise forming electrons so that image quality and resolution are comparable to that of conventional high vacuum FEG-SEMs.

Return to top

 
 
 

ESEM Vacuum System

In the ESEM, the pressure gradient between the specimen chamber and the electron optics is achieved by creating a series of differentially pumped vacuum zones, separated by pressure limiting apertures. These apertures are sufficiently large to allow the electron beam to pass through, but still small enough to severely limit gas flow from one compartment to the next. The system was the integration of two closely spaced pressure limiting apertures into the final lense of the electron column. The regions below, between, and above the PLA’s are separately pumped to provide a graduated vacuum from as low as 50 Torr, in the sample chamber, to 10 -5 Torr, or better, in the column and gun. The gun chamber is connected to an ion pump sufficient to achieve pressures of 10-6 and 10-9 torr, respectively.

What is  the Multiple Pressure/ Limiting Apertures?

    If resolution in an SEM depends on its ability to focus the beam electrons into the smallest possible spot on the sample surface.

Can the ESEM maintain its performance in a gaseous environment?

    Yes, this is an achievement of Environmental Secondary Detector (ESD).
Note: In order to understand the effects of the gas on the beam, you may look more closely at electron scattering (discussed in detail by using physics parameters and graphics on the FEI-Philips pages).

Does the gas scatter the primary electrons and does it degrade resolution?

Yes, the gas scatters the electrons, but it does not necessarily impact resolution.

Return to top

 
 

Image Gallery

Examples of Recent Research

High-resolution images taken on ESEM-FEG/Mix Det(GSED & BSED):


Uncoated Powders
 

ESEM-FEG/GSED gives all the information about both the particle shape and particle size distribution

a):tilted plane view


 
 

b):cross section


Uncoated Polymer
 

Chemical/shape distribution maps taken on ESEM-FEG/EDAX System:


Uncoated Ceramic Powders
 
 

[About EM Unit]

[ESEM]    

[EDAX]

[Environmental Secondary Detector]

[Vacuum System]

[Image Gallery]



 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Return to top]