Single cell microstructure characterization

Scanning electron microscopy (SEM) is a widely used technique for the characterization of solid materials, and it has a lot of advantages over traditional optical microscope, for example, high resolution image, a larger depth of field, and wider range of magnifications. Besides, SEM can provide lots of information on sample’s microstructure, morphology, and chemical composition/elemental identification that are inaccessible by light microscope. SEM also has modest restrictions on sample preparation and is user friendly. Because of these traits, SEM has actually become a valuable tool in research today.

Chapter

A diagram of the key components of a SEM is presented in Fig. 2. utilises electron beam instead of light

image of the specimen. A microscope by electron gun

beam travels through electromagnetic towards the specimen sitting in

the highly focused electron beam strikes the surface of specimen, a variety of signals, as shown in Fig. 2.16, will be generated as a result of interaction between the incident electrons and sample. The signals

properties, including morphology, microstructure and composition

by various detectors and converted into a signal that is sent to a screen to produce the final image. Noticeably, it is necessary

interference from air particles in the atmosphere which would block the path of electron beam and distort the surface of the specimen.

Fig. 2.16Different signals

specimen under observation (the highlighted signal is the one most familiar in SEM)

Of all the signals ejected from

with the specimen under examination,

of information in SEM are the secondary electrons

Chapter 2: Methods and techniques

A diagram of the key components of a SEM is presented in Fig. 2.15. In principle, SEM instead of light as probe to scan and produce a largely

A steady stream of incident electrons is created at the top of gun. Following a vertical path in the microscope, the electron electromagnetic lenses, which focus the electron beam down sitting in the sample chamber at the base of a microscope. the highly focused electron beam strikes the surface of specimen, a variety of signals, as

, will be generated as a result of interaction between the incident The signals carry a wealth of information about a sample's properties, including morphology, microstructure and composition and will be detected and converted into a signal that is sent to a screen to produce the Noticeably, it is necessary for a SEM working in a vacuum column to avoid interference from air particles in the atmosphere which would block the path of electron beam and distort the surface of the specimen.

Different signals emitted as a result of incident electrons interaction with specimen under observation (the highlighted signal is the one most familiar in SEM)

ejected from the specimen due to the interaction of incident electrons with the specimen under examination, the three signals that provide the greatest amount of information in SEM are the secondary electrons (SE), backscattered electrons

. In principle, SEM largely magnified created at the top of Following a vertical path in the microscope, the electron , which focus the electron beam down microscope. When the highly focused electron beam strikes the surface of specimen, a variety of signals, as , will be generated as a result of interaction between the incident a wealth of information about a sample's and will be detected and converted into a signal that is sent to a screen to produce the for a SEM working in a vacuum column to avoid interference from air particles in the atmosphere which would block the path of electron

interaction with the specimen under observation (the highlighted signal is the one most familiar in SEM)[20]

the interaction of incident electrons provide the greatest amount , backscattered electrons (BE),

Chapter 2: Methods and techniques

electrons and the electrons of atoms presented in the surface of sample, thus SE provide information on the sample’s surface topography and the images SE produced are most familiar. The BE are primary incident electrons that are scattered by sample atoms and reflected from the sample surface. BE provide information on the topographic and contrast of the specimen with the contrast determined by the atomic number of the sample atoms, therefore, the image produced will show chemical composition information of the sample. X-rays are produced by the incident electrons interaction with the inner shell electrons of atoms in the sample. Characteristic X-rays are emitted from the specimen atom after a secondary electron is produced and allow qualitative identification of elements in sample. SEM coupled with energy-dispersive X-rays detector (EDX) offers information not only on topographic microstructure, but also on the chemical composition/element composition maps of materials.

The field-emission gun (FEG) SEM employs a field-emission gun, rather the traditional tungsten-filament, as a source of electrons. The secondary electron image resolution for an ideal sample is about 3.5 nm for a tungsten-filament electron source SEM and 1.5 nm for field emission SEM[21].

Although SEM requires little restrictions on sample preparation as long as the sample stands stable in vacuum environment, it is essential for the sample that is to be observed to be conductive. Otherwise, sputter coating should be carried out to cover a very thin layer of metal or carbon, to make it conductive. Further, the sample should have a clean surface before going into SEM.

In our experiment, SEM measurements were performed to study the microstructure and morphology of SOEC cathode and cathode/electrolyte interfaces. In some cases, EDX was incorporated with SEM to inspect the distribution of elements in cathode materials. The SEM equipments used were JEOL JSM-5600 (with tungsten filament as electron gun) and JEOL JSM-6700F (with field emission gun). An Oxford INCA Energy 200 device was coupled with JSM-5600 instrument for EDX examination. All the samples examined were coated with a thin layer of gold on its surface, in order to obtain clear and informative images.

Chapter 2: Methods and techniques