Following successful sign in, you will be returned to Oxford Academic.Do not use an Oxford Academic personal account. When on the institution site, please use the credentials provided by your institution.Select your institution from the list provided, which will take you to your institution's website to sign in.Click Sign in through your institution.Shibboleth/Open Athens technology is used to provide single sign-on between your institution’s website and Oxford Academic. This authentication occurs automatically, and it is not possible to sign out of an IP authenticated account.Ĭhoose this option to get remote access when outside your institution. Typically, access is provided across an institutional network to a range of IP addresses. If you are a member of an institution with an active account, you may be able to access content in one of the following ways: Get help with access Institutional accessĪccess to content on Oxford Academic is often provided through institutional subscriptions and purchases. The various imaging, diffraction and spectroscopy modes available in a dedicated STEM or a field emission TEM/STEM instrument are reviewed and the application of these techniques to the study of nanoparticles and nanostructured catalysts is used as an example to illustrate the critical role of the various STEM techniques in nanotechnology and nanoscience research. The availability of sub-nanometer or sub-angstrom electron probes in a STEM instrument, due to the use of a field emission gun and aberration correctors, ensures the greatest capabilities for studies of sizes, shapes, defects, crystal and surface structures, and compositions and electronic states of nanometer-size regions of thin films, nanoparticles and nanoparticle systems. High-resolution STEM imaging, when combined with nanodiffraction, atomic resolution electron energy-loss spectroscopy and nanometer resolution X-ray energy dispersive spectroscopy techniques, is critical to the fundamental studies of importance to nanoscience and nanotechnology. However, STM requires extremely clean samples and it can be tricky getting it to work.ĭevelopment of the scanning tunneling microscope earned Gerd Binnig and Heinrich Rohrer the 1986 Nobel Prize in Physics.Scanning transmission electron microscopy (STEM) techniques can provide imaging, diffraction and spectroscopic information, either simultaneously or in a serial manner, of the specimen with an atomic or a sub-nanometer spatial resolution. Unlike other types of electron microscopy, the instrument is affordable and easily made. The change in the current of the tip is measured as it is scanned across the sample to form an image. When a voltage difference is applied, electrons can tunnel between the tip and the specimen. An electrical conducting tip is brought near the surface of the sample. It can be used over a wide temperature range, from near absolute zero to over 1000 degrees C. STM can be used not only in a vacuum, but also in the air, water, and other gases and liquids. Its resolution is about 0.1 nanometers, with a depth of about 0.01 nanometers. It is the only type of electron microscopy that can image individual atoms. Musée d'histoire des sciences de la Ville de Genève / Wikimedia Commons / CC BY 3.0Ī scanning tunneling microscope (STM) images surfaces at the atomic level. These are transmission electron microscopy (TEM), scanning electron microscopy (SEM), and scanning tunneling microscopy (STM). There are three main types of electron microscopy, which differ according to how the image is formed, how the sample is prepared, and the resolution of the image. The image is produced by electrons, so it is viewed either by taking a photograph (an electron micrograph) or by viewing the specimen through a monitor. The electromagnets bend the electron beam in much the same way lenses bend light. Instead of lenses, electromagnetic coils focus the electron beam. The air inside the specimen chamber is pumped out to form a vacuum because electrons don't travel far in a gas. The specimen needs to be specially prepared so the electrons can interact with it. In an electron microscope, a beam of electrons takes the place of the beam of light. The optical microscope setup consists of a specimen, lenses, a light source, and an image that you can see. In an optical microscope, you look through an eyepiece and lens to see a magnified image of a specimen. The easiest way to understand how an electron microscope works is to compare it to an ordinary light microscope. The disadvantages include the cost and size of the equipment, the requirement for special training to prepare samples for microscopy and to use the microscope, and the need to view the samples in a vacuum (although some hydrated samples may be used). The advantages of using an electron microscope over an optical microscope are much higher magnification and resolving power.
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