Infrared (IR) #spectroscopy is a powerful technique that allows to obtain information about the chemical structure of a variety of substances by utilizing infrared electromagnetic radiation. In this science video we will discuss the basics of this technique with the help of 3D animations and also perform a practical demonstration, where we study a Teflon substrate with ATR technique. The video was made by Captain Corrosion OÜ in collaboration with Uno Mäeorg (Associate Professor in Organic Chemistry, Institute of Chemistry, University of Tartu).
Educators can download some of the animations used in the video from our online library to enhance their courses.
What Does a fly look like under the scanning electron microscope? In this video we will explain how biological samples are prepared for scanning electron microscopy (SEM) studies. We will also take some images of the eye, leg, mouth and wing of the fly.
We have started making a new science video about X-Ray fluorescence spectroscopy (XRF). In this 6 minute video we will explain with 3D animations the basics of this materials characterization technique and do a demonstrations where we use XRF to measure the elemental composition of an ancient coin.
This video will be published in October 2016.
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In collaboration with the University of Tartu we can study your material with state of the art techniques in unprecedented detail and provide you with the needed information.
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Here is a list of some common techniques used in our daily research and their possible applications:
Scanning electron microscopy (SEM)– Used to obtain high resolution images of a materials surface with a magnification far greater than in the case of optical microscopes. SEM can also be used to study the distribution of different elements in a microscopic scale or even locally (few microns area) measure the elemental composition of a material. SEM is also a valuable tool to visualize microscopic cracks and defects in a material that affect its mechanical properties. Another useful application of SEM is to study the individual grain size of powders and also evaluate the size distribution. Learn more by watching our educational video and visiting our gallery.
X-ray fluorescence spectroscopy (XRF)– Quick and easy way to precisely study the average elemental composition of various materials such as a metal alloys, ceramics and polymers. For instance, we can use XRF to verify if your supplier provides you with the metal alloy that you requested and also see if it contains any unwanted impurities. Learn more by watching our educational video.
Atomic force microscopy (AFM) – Allows to measure the roughness and surface details of extremely smooth surfaces such as glass or various fine polished materials. For example, the nano scaled roughness plays a significant role in the performance of self-cleaning windows. Learn more by watching our educational video.
X-ray diffraction (XRD)– Gives information about the crystal structure of bulk materials, powders and thin films. For instance, XRD allows to verify if a titanium dioxide powder is amorphous, anatase, rutile or a mixture. It can also give information about the effect of different thermal treatments on a metal.
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Low-energy ion scattering spectroscopy (LEIS) is an exciting technique that allows to study the structure and chemical composition of a materials surface.
In this materials characterization method the sample is bombarded with a stream of ions and the positions, velocities and energies of the scattered ions are observed. The energy of scattered ions depends on the mass of the target, so there are distinct peaks in the energy spectrum of the scattered ions. These peaks give information about the samples elemental composition. The uniqueness of this technique lies in its sensitivity to the very first atomic layer on a sample and with forward scattering setup it is even capable of directly observing hydrogen atoms.
One of the main components of the system is the ion gun, that shoots ions at the studied substrate. The most widely used ions for that purpose are ionized noble gas or alkali atoms. Noble gas such as helium, neon or argon is ionized with electrons, giving them a positive charge. Alkali ion beams can be created by heating alkali wafers. In low-energy ion scattering spectroscopy the ions usually have an energy from 500 eV to 10 000 eV. The precise desired energy of the ions is obtained by applying a suitable accelerating voltage.
Before interacting with the substrate, the ions first need to pass through the ion beam manipulator, that narrows the beam and also filters the ions based on mass and velocity. For some experiments the ion beam is also chopped with an unipolar electrical chopper – a pulsed-wave generator, that lets through ions only when no voltage is applied. As a result the ion beam leaves the ion beam manipulator in pulses. By using short ion pulses, one can separate backscattered primary ions, for example He, from sputtered ions of different masses by time gating. This makes it possible to detect signals that would otherwise be buried in the background that is caused by ions sputtered from the sample surface.
The sample itself is attached to a special holder that allows the operator to adjust the position and angle of the sample for different experiments. When the ions hit the substrate, different interactions take place. Some ions are scattered at a certain angle and also their energy will be different after the impact. Some ions however become neutral as they pick up electrons from the substrate. The ions may also be implanted into the material or deposited on the substrate surface. The primary beam ions may also kick out electrons or atoms from the substrate and the atoms may even be ionized in the process. Radiation may also be emitted from the substrate as the excited atoms undergo a relaxation process.
The electrostatic analyzer is commonly used to detect the velocities and energies of the scattered ions. In this hemispheric device an electrical potential is applied between the inner and outer wall. The outer wall with positive potential repels the positive ions and the inner wall with negative potential attracts the positive ions. Neutral particles are unaffected by the field and hit the wall and thus never reach the detector. Positive ions with too low energy are pulled to the inner wall and also don’t reach the detector. If the cations energy is too high however then it simply hits the outer wall. Only if the ions energy is just right, it can pass through the analyzer and create a signal by interacting with the detector. By changing the potential between the walls, the operator can scan through a wide energy range in order to find out the energy of the emitted particles. In newer systems however a double toroidal analyzer is preferred as it integrates the signal over the scattering azimuth, so the intensity is some orders of magnitude higher compared to a hemispherical analyzer. The drift tube is used in TOF experiments in order to detect the energies and velocities of the scattered ionic and also neutral particles. Neutrals can easily be seperated from ions with the accelerator. There are two types of detectors that are commonly used – channel electron multipliers and microchannel plates. If the ion or a neutral particle with sufficient energy hits the detector then a cascade of secondary electrons is created and the signal significantly amplified. Microchannel plates also give information about the particles position but that comes at the cost of sensitivity.
Measurements with low-energy ion scattering spectroscopy are performed in ultra-high vacuum in order to avoid interactions with the surrounding gas. Having a good vacuum also ensures that the studied substrate and system parts are clean. Ultra-high vacuum is achieved with turbomolecular and ion pumps with the help of rough vacuum pumps.
Samples that have been exposed to open air are always contaminated for this type of surface sensitive characterization method and therefore they need to be cleaned inside the system in vacuum with appropriate equipment. Common ways to remove the contaminated top layer are sputtering, annealing or exposing to atomic oxygen.
There are of course few other surface sensitive materials characterization techniques such as XPS, AFM and SEM but each of them has distinct advantages and disadvantages. Therefore they are often used together when studying novel nanomaterials as they compensate each others weaknesses and allow to get a better overview.
Nuclear radiation is emitted from a material when the nucleus of an unstable atom loses energy by emitting ionizing radiation. The emitted radiation consists of gamma rays, alpha particles (He2+), beta particles (high energy electrons or positrons) and conversion electrons. From these components gamma rays are most dangerous for humans as they can easily penetrate the skin and cause severe damage to internal organs. Although gamma radiation is often an unwanted byproduct when producing nuclear power, it also has found use in medicine and food industry. In medicine gamma radiation is used for cancer treatment as it kills the cancer cells. In food industry the radiation is used to sterilize food as it kills bacteria and leaves the food unharmed. Gamma radiation can easily penetrate different materials and this makes radiation protection difficult. The penetration depends on the atomic number and therefore heavy metals such as Pb (lead) are used for shielding. In this experiment we use a geiger counter to measure the radiation emitted from a cobalt-60 isotobe and see how well we can block the radiation by using different materials such as wood, aluminum, steel, tungsten, pork cutlets and led casing.
The Auger electron is generated during an excited atoms relaxation process, where excess energy is transfered to an outer shell electron, which leaves the atom and becomes the Auger electron. The energy of this electron depends on the binding energies of the participating electrons and is unique to the element where it occurs. As the Auger electrons energy is very low, it can escape the material from only near the surface (few nanometers). This means that this signal is highly surface sensitive and can be used to obtain information from only the surface, not from the bulk material as it is common with other material characterization methods.
Characteristic X-Rays are generated when excited sample atoms undergo a relaxation process. For that the atoms need to be excited first and this can be done with high energy electromagnetic radiation (in XRF) or accelerated particles such as electrons (in SEM). The primary beam kicks out an inner shell electron and a vacant spot is left behind. As this state is unstable, a higher shell electron will soon move into this vacant spot and during this process energy is emitted in the form of X-Rays. This emitted radiation has a specific energy which depends on the binding energies of the two electrons that participated in this process. If this emitted ( characteristic ) x-ray radiation is detected then the composition of the material can be measured.
Photoelectric effect, photoelectron spectroscopy (XPS) and scanning photoelectron microscopy (SPEM) are explained in this short lecture. The photoelectric effect occurs when the inner shell electrons of the sample atoms are kicked out by high energy electromagnetic radiation. These electrons, that were kicked out, are called photoelectrons and their energy depends on the energy of the exciting radiation, the electrons initial binding energy and on the work function. When having a radiation source with well defined energy and measuring the energy of the emitted electrons, it is possible to get information about the samples composition and chemical state. In the case of photoelectron microscopy the exciting beam is focused into a narrow spot on the sample surface. The sample is then moved in such a way that the spot moves row by row across the sample surface and as a result photoelectrons are emitted from each irradiated spot. By collecting these photoelectrons, it is possible to map the composition or chemical state across the selected sample area (for example 100 x 100 microns area on a 2 x 2 cm sample). Photoelectrons can escape the material only from near the surface and this means that these methods are very surface sensitive, which makes them extremely useful for surface studies. This also means that the surfaces need to be very clean (cleaned with ion bombardment before measurements) and therefore ultra-high vacuum is needed.