1.
Atom
–
An atom is the smallest constituent unit of ordinary matter that has the properties of a chemical element. Every solid, liquid, gas, and plasma is composed of neutral or ionized atoms, Atoms are very small, typical sizes are around 100 picometers. Atoms are small enough that attempting to predict their behavior using classical physics - as if they were billiard balls, through the development of physics, atomic models have incorporated quantum principles to better explain and predict the behavior. Every atom is composed of a nucleus and one or more bound to the nucleus. The nucleus is made of one or more protons and typically a number of neutrons. Protons and neutrons are called nucleons, more than 99. 94% of an atoms mass is in the nucleus. The protons have an electric charge, the electrons have a negative electric charge. If the number of protons and electrons are equal, that atom is electrically neutral, if an atom has more or fewer electrons than protons, then it has an overall negative or positive charge, respectively, and it is called an ion. The electrons of an atom are attracted to the protons in a nucleus by this electromagnetic force. The number of protons in the nucleus defines to what chemical element the atom belongs, for example, the number of neutrons defines the isotope of the element. The number of influences the magnetic properties of an atom. Atoms can attach to one or more other atoms by chemical bonds to form compounds such as molecules. The ability of atoms to associate and dissociate is responsible for most of the changes observed in nature. The idea that matter is made up of units is a very old idea, appearing in many ancient cultures such as Greece. The word atom was coined by ancient Greek philosophers, however, these ideas were founded in philosophical and theological reasoning rather than evidence and experimentation. As a result, their views on what look like. They also could not convince everybody, so atomism was but one of a number of competing theories on the nature of matter. It was not until the 19th century that the idea was embraced and refined by scientists, in the early 1800s, John Dalton used the concept of atoms to explain why elements always react in ratios of small whole numbers
Atom
–
Scanning tunneling microscope image showing the individual atoms making up this
gold (
100) surface. The surface atoms deviate from the bulk
crystal structure and arrange in columns several atoms wide with pits between them (See
surface reconstruction).
Atom
–
Helium atom
2.
Crystal
–
A crystal or crystalline solid is a solid material whose constituents are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macroscopic single crystals are usually identifiable by their geometrical shape, the scientific study of crystals and crystal formation is known as crystallography. The process of crystal formation via mechanisms of crystal growth is called crystallization or solidification, the word crystal derives from the Ancient Greek word κρύσταλλος, meaning both ice and rock crystal, from κρύος, icy cold, frost. Examples of large crystals include snowflakes, diamonds, and table salt, most inorganic solids are not crystals but polycrystals, i. e. many microscopic crystals fused together into a single solid. Examples of polycrystals include most metals, rocks, ceramics, a third category of solids is amorphous solids, where the atoms have no periodic structure whatsoever. Examples of amorphous solids include glass, wax, and many plastics, Crystals are often used in pseudoscientific practices such as crystal therapy, and, along with gemstones, are sometimes associated with spellwork in Wiccan beliefs and related religious movements. The scientific definition of a crystal is based on the arrangement of atoms inside it. A crystal is a solid where the form a periodic arrangement. For example, when liquid water starts freezing, the change begins with small ice crystals that grow until they fuse. Most macroscopic inorganic solids are polycrystalline, including almost all metals, ceramics, ice, rocks, solids that are neither crystalline nor polycrystalline, such as glass, are called amorphous solids, also called glassy, vitreous, or noncrystalline. These have no periodic order, even microscopically, there are distinct differences between crystalline solids and amorphous solids, most notably, the process of forming a glass does not release the latent heat of fusion, but forming a crystal does. A crystal structure is characterized by its cell, a small imaginary box containing one or more atoms in a specific spatial arrangement. The unit cells are stacked in three-dimensional space to form the crystal, the symmetry of a crystal is constrained by the requirement that the unit cells stack perfectly with no gaps. There are 219 possible crystal symmetries, called space groups. These are grouped into 7 crystal systems, such as cubic crystal system or hexagonal crystal system, Crystals are commonly recognized by their shape, consisting of flat faces with sharp angles. Euhedral crystals are those with obvious, well-formed flat faces, anhedral crystals do not, usually because the crystal is one grain in a polycrystalline solid. The flat faces of a crystal are oriented in a specific way relative to the underlying atomic arrangement of the crystal. This occurs because some surface orientations are more stable than others, as a crystal grows, new atoms attach easily to the rougher and less stable parts of the surface, but less easily to the flat, stable surfaces
Crystal
–
A crystal of
amethyst quartz
Crystal
–
Macroscopic (~16cm) halite crystal. The right-angles between crystal faces are due to the cubic symmetry of the atoms' arrangement.
Crystal
–
Ice crystals.
Crystal
–
Fossil shell with
calcite crystals.
3.
Surface chemistry
–
It includes the fields of surface chemistry and surface physics. Some related practical applications are classed as surface engineering, the science encompasses concepts such as heterogeneous catalysis, semiconductor device fabrication, fuel cells, self-assembled monolayers, and adhesives. Surface science is related to interface and colloid science. Interfacial chemistry and physics are common subjects for both, in addition, interface and colloid science studies macroscopic phenomena that occur in heterogeneous systems due to peculiarities of interfaces. The field of surface chemistry started with heterogeneous catalysis pioneered by Paul Sabatier on hydrogenation, irving Langmuir was also one of the founders of this field, and the scientific journal on surface science, Langmuir, bears his name. The Langmuir adsorption equation is used to model monolayer adsorption where all surface adsorption sites have the affinity for the adsorbing species. Gerhard Ertl in 1974 described for the first time the adsorption of hydrogen on a surface using a novel technique called LEED. Similar studies with platinum, nickel, and iron followed, Surface chemistry can be roughly defined as the study of chemical reactions at interfaces. Surface science is of importance to the fields of heterogeneous catalysis, electrochemistry. The adhesion of gas or liquid molecules to the surface is known as adsorption and this can be due to either chemisorption or physisorption, and the strength of molecular adsorption to a catalyst surface is critically important to the catalysts performance. However, it is difficult to study these phenomena in real catalyst particles, instead, well-defined single crystal surfaces of catalytically active materials such as platinum are often used as model catalysts. Results can be fed into chemical models or used toward the design of new catalysts. Reaction mechanisms can also be clarified due to the precision of surface science measurements. The behavior of an interface is affected by the distribution of ions within the electrical double layer. These studies link traditional electrochemical techniques such as cyclic voltammetry to direct observations of interfacial processes, geologic phenomena such as iron cycling and soil contamination are controlled by the interfaces between minerals and their environment. Surface physics can be defined as the study of physical changes that occur at interfaces. The study and analysis of surfaces involves both physical and chemical analysis techniques, several modern methods probe the topmost 1–10 nm of surfaces exposed to vacuum. Many of these techniques require vacuum as they rely on the detection of electrons or ions emitted from the surface under study, at 0.1 mPa, it only takes 1 second to cover a surface with a contaminant, so much lower pressures are needed for measurements
Surface chemistry
–
STM image of a
quinacridone adsorbate. The
self-assembled supramolecular chains of the
organic semiconductor are adsorbed on a
graphite surface.
4.
Platinum
–
Platinum is a chemical element with symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious and its name is derived from the Spanish term platina, translated into little silver. Platinum is a member of the group of elements and group 10 of the periodic table of elements. It has six naturally occurring isotopes and it is one of the rarer elements in Earths crust with an average abundance of approximately 5 μg/kg. It occurs in some nickel and copper ores along with some deposits, mostly in South Africa. Because of its scarcity in Earths crust, only a few hundred tonnes are produced annually, Platinum is one of the least reactive metals. It has remarkable resistance to corrosion, even at high temperatures, consequently, platinum is often found chemically uncombined as native platinum. Because it occurs naturally in the sands of various rivers. Platinum is used in catalytic converters, laboratory equipment, electrical contacts and electrodes, platinum resistance thermometers, dentistry equipment, and jewelry. Being a heavy metal, it leads to health issues upon exposure to its salts, compounds containing platinum, such as cisplatin, oxaliplatin and carboplatin, are applied in chemotherapy against certain types of cancer. Pure platinum is a lustrous, ductile, and malleable, silver-white metal, Platinum is more ductile than gold, silver or copper, thus being the most ductile of pure metals, but it is less malleable than gold. The metal has excellent resistance to corrosion, is stable at temperatures and has stable electrical properties. Platinum reacts with oxygen slowly at high temperatures. It reacts vigorously with fluorine at 500 °C to form platinum tetrafluoride and it is also attacked by chlorine, bromine, iodine, and sulfur. Platinum is insoluble in hydrochloric and nitric acid, but dissolves in hot aqua regia to form chloroplatinic acid and its physical characteristics and chemical stability make it useful for industrial applications. Its resistance to wear and tarnish is well suited to use in fine jewelry, the most common oxidation states of platinum are +2 and +4. The +1 and +3 oxidation states are common, and are often stabilized by metal bonding in bimetallic species. As is expected, tetracoordinate platinum compounds tend to adopt 16-electron square planar geometries, Platinum has six naturally occurring isotopes, 190Pt, 192Pt, 194Pt, 195Pt, 196Pt, and 198Pt
Platinum
–
Platinum, 78 Pt
Platinum
–
Platinum being dissolved in hot
aqua regia
Platinum
–
A native platinum nugget,
Kondyor mine,
Khabarovsk Krai
Platinum
–
Antonio de Ulloa is credited with the discovery of platinum.
5.
Miller index
–
Miller indices form a notation system in crystallography for planes in crystal lattices. In particular, a family of planes is determined by three integers h, k, and ℓ, the Miller indices. They are written, and denote the family of planes orthogonal to h b 1 + k b 2 + ℓ b 3, by convention, negative integers are written with a bar, as in 3 for −3. The integers are written in lowest terms, i. e. their greatest common divisor should be 1. There are also several related notations, the notation denotes the set of all planes that are equivalent to by the symmetry of the lattice, Miller indices were introduced in 1839 by the British mineralogist William Hallowes Miller. The method was also known as the Millerian system. The Miller indices are defined with respect to any choice of cell and not only with respect to primitive basis vectors. There are two equivalent ways to define the meaning of the Miller indices, via a point in the reciprocal lattice, in either case, one needs to choose the three lattice vectors a1, a2, and a3 that define the unit cell. Given these, the three primitive lattice vectors are also determined. Then, given the three Miller indices h, k, ℓ, denotes planes orthogonal to the lattice vector. That is, simply indicates a normal to the planes in the basis of the reciprocal lattice vectors. Because the coordinates are integers, this normal is itself always a lattice vector. The requirement of lowest terms means that it is the shortest reciprocal lattice vector in the given direction, equivalently, denotes a plane that intercepts the three points a1/h, a2/k, and a3/ℓ, or some multiple thereof. That is, the Miller indices are proportional to the inverses of the intercepts of the plane, if one of the indices is zero, it means that the planes do not intersect that axis. The related notation denotes the direction, h a 1 + k a 2 + ℓ a 3 and that is, it uses the direct lattice basis instead of the reciprocal lattice. Note that is not generally normal to the planes, except in a lattice as described below. For the special case of cubic crystals, the lattice vectors are orthogonal and of equal length. Thus, in this case, the Miller indices and both simply denote normals/directions in Cartesian coordinates
Miller index
6.
Van der Waals force
–
It can be shown that van der Waals forces are of the same origin as the Casimir effect, arising from quantum interactions with the zero-point field. The resulting van der Waals forces can be attractive or repulsive, the term includes, force between permanent dipoles force between a permanent dipole and a corresponding induced dipole force between instantaneously induced dipoles. It is also used loosely as a synonym for the totality of intermolecular forces. Van der Waals forces define many properties of compounds and molecular solids. In low molecular weight alcohols, the properties of their polar hydroxyl group dominate other weaker van der Waals interactions. In higher molecular weight alcohols, the properties of the hydrocarbon chain dominate. Van der Waals forces quickly vanish at longer distances between interacting molecules, Van der Waals forces include attraction and repulsions between atoms, molecules, and surfaces, as well as other intermolecular forces. They differ from covalent and ionic bonding in that they are caused by correlations in the fluctuating polarizations of nearby particles, Intermolecular forces have four major contributions, A repulsive component resulting from the Pauli exclusion principle that prevents the collapse of molecules. Attractive or repulsive electrostatic interactions between permanent charges, dipoles, quadrupoles, and in general between permanent multipoles, the electrostatic interaction is sometimes called the Keesom interaction or Keesom force after Willem Hendrik Keesom. Induction, which is the interaction between a permanent multipole on one molecule with an induced multipole on another. This interaction is sometimes called Debye force after Peter J. W. Debye, dispersion, which is the attractive interaction between any pair of molecules, including non-polar atoms, arising from the interactions of instantaneous multipoles. Returning to nomenclature, different texts refer to different things using the van der Waals force. Some texts describe the van der Waals force as the totality of forces, all intermolecular/van der Waals forces are anisotropic, which means that they depend on the relative orientation of the molecules. The induction and dispersion interactions are attractive, irrespective of orientation. That is, the force can be attractive or repulsive. Sometimes this effect is expressed by the statement that random thermal motion around room temperature can usually overcome or disrupt them, clearly, the thermal averaging effect is much less pronounced for the attractive induction and dispersion forces. The Lennard-Jones potential is used as an approximate model for the isotropic part of a total van der Waals force as a function of distance. Van der Waals forces are responsible for cases of pressure broadening of spectral lines
Van der Waals force
–
Geckos can stick to walls and ceilings because of Van der Waals forces; see the section below.
Van der Waals force
–
Gecko climbing a glass surface
7.
Miller indices
–
Miller indices form a notation system in crystallography for planes in crystal lattices. In particular, a family of planes is determined by three integers h, k, and ℓ, the Miller indices. They are written, and denote the family of planes orthogonal to h b 1 + k b 2 + ℓ b 3, by convention, negative integers are written with a bar, as in 3 for −3. The integers are written in lowest terms, i. e. their greatest common divisor should be 1. There are also several related notations, the notation denotes the set of all planes that are equivalent to by the symmetry of the lattice, Miller indices were introduced in 1839 by the British mineralogist William Hallowes Miller. The method was also known as the Millerian system. The Miller indices are defined with respect to any choice of cell and not only with respect to primitive basis vectors. There are two equivalent ways to define the meaning of the Miller indices, via a point in the reciprocal lattice, in either case, one needs to choose the three lattice vectors a1, a2, and a3 that define the unit cell. Given these, the three primitive lattice vectors are also determined. Then, given the three Miller indices h, k, ℓ, denotes planes orthogonal to the lattice vector. That is, simply indicates a normal to the planes in the basis of the reciprocal lattice vectors. Because the coordinates are integers, this normal is itself always a lattice vector. The requirement of lowest terms means that it is the shortest reciprocal lattice vector in the given direction, equivalently, denotes a plane that intercepts the three points a1/h, a2/k, and a3/ℓ, or some multiple thereof. That is, the Miller indices are proportional to the inverses of the intercepts of the plane, if one of the indices is zero, it means that the planes do not intersect that axis. The related notation denotes the direction, h a 1 + k a 2 + ℓ a 3 and that is, it uses the direct lattice basis instead of the reciprocal lattice. Note that is not generally normal to the planes, except in a lattice as described below. For the special case of cubic crystals, the lattice vectors are orthogonal and of equal length. Thus, in this case, the Miller indices and both simply denote normals/directions in Cartesian coordinates
Miller indices
–
Planes with different Miller indices in cubic crystals
8.
Bragg diffraction
–
In physics, Braggs law, or Wulff–Braggs condition in post-Soviet countries, a special case of Laue diffraction, gives the angles for coherent and incoherent scattering from a crystal lattice. When X-rays are incident on an atom, they make the electronic cloud move as does any electromagnetic wave, the movement of these charges re-radiates waves with the same frequency, blurred slightly due to a variety of effects, this phenomenon is known as Rayleigh scattering. The scattered waves can themselves be scattered but this secondary scattering is assumed to be negligible, a similar process occurs upon scattering neutron waves from the nuclei or by a coherent spin interaction with an unpaired electron. These re-emitted wave fields interfere with each other either constructively or destructively, the resulting wave interference pattern is the basis of diffraction analysis. This analysis is called Bragg diffraction and they found that these crystals, at certain specific wavelengths and incident angles, produced intense peaks of reflected radiation. The concept of Bragg diffraction applies equally to neutron diffraction and electron diffraction processes, both neutron and X-ray wavelengths are comparable with inter-atomic distances and thus are an excellent probe for this length scale. Sir William Lawrence Bragg explained this result by modeling the crystal as a set of parallel planes separated by a constant parameter d. It was proposed that the incident X-ray radiation would produce a Bragg peak if their reflections off the various planes interfered constructively. Although simple, Braggs law confirmed the existence of particles at the atomic scale, as well as providing a powerful new tool for studying crystals in the form of X-ray. William Lawrence Bragg and his father, Sir William Henry Bragg, were awarded the Nobel Prize in physics in 1915 for their work in determining crystal structures beginning with NaCl, ZnS and they are the only father-son team to jointly win. William Lawrence Bragg was 25 years old, making him then, for a crystalline solid, the waves are scattered from lattice planes separated by the interplanar distance d. When the scattered waves interfere constructively, they remain in phase since the difference between the lengths of the two waves is equal to an integer multiple of the wavelength. The path difference between two waves undergoing interference is given by 2dsinθ, where θ is the scattering angle, the effect of the constructive or destructive interference intensifies because of the cumulative effect of reflection in successive crystallographic planes of the crystalline lattice. Note that moving particles, including electrons, protons and neutrons, have an associated wavelength called de Broglie wavelength, a diffraction pattern is obtained by measuring the intensity of scattered waves as a function of scattering angle. Very strong intensities known as Bragg peaks are obtained in the pattern at the points where the scattering angles satisfy Bragg condition. Suppose that a single wave is incident on aligned planes of lattice points, with separation d. Points A and C are on one plane, and B is on the plane below, there will be a path difference between the ray that gets reflected along AC and the ray that gets transmitted, then reflected, along AB and BC respectively. Putting everything together, n λ =2 d sin θ =2 d sin θ sin 2 θ, which simplifies to n λ =2 d sin θ, which is Braggs law
Bragg diffraction
–
X-rays interact with the atoms in a
crystal.
9.
Low-energy electron diffraction
–
LEED may be used in one of two ways, Qualitatively, where the diffraction pattern is recorded and analysis of the spot positions gives information on the symmetry of the surface structure. In the presence of an adsorbate the qualitative analysis may reveal information about the size, quantitatively, where the intensities of diffracted beams are recorded as a function of incident electron beam energy to generate the so-called I-V curves. By comparison with theoretical curves, these may provide information on atomic positions on the surface at hand. The theoretical possibility of the occurrence of electron diffraction first emerged in 1924 when Louis de Broglie introduced wave mechanics, in his Nobel laureated work de Broglie postulated that the wavelength of a particle with linear momentum p is given by h/p, where h is Plancks constant. These observations were consistent with the theory for X-rays developed by Bragg. Before the acceptance of the de Broglie hypothesis diffraction was believed to be a property of waves. Davisson and Germer published notes of their electron diffraction experiment result in Nature, One month after Davisson and Germers work appeared, Thompson and Reid published their electron diffraction work with higher kinetic energy in the same journal. Those experiments revealed the wave property of electrons and opened up an era of electron diffraction study, though discovered in 1927, low energy electron diffraction did not become a popular tool for surface analysis until the early 1960s. Also, since LEED is a sensitive method, it required well-ordered surface structures. Techniques for the reconstruction of clean metal surfaces first became available much later, in the early 1960s LEED experienced a renaissance as ultra high vacuum became widely available and the post acceleration detection method was introduced. Using this technique diffracted electrons were accelerated to high energies to produce clear, at this stage a detailed determination of surface structures, including adsorption sites, bond angles and bond lengths was not possible. A dynamical electron diffraction theory which took into account the possibility of multiple scattering was established in the late 1960s, with this theory it later became possible to reproduce experimental data with high precision. In order to keep the studied sample clean and free from unwanted adsorbates, a simplified sketch of an LEED setup is shown in figure 2. The sample is usually prepared outside the chamber by cutting a slice of around 1 mm in thickness and 1 cm in diameter along the desired crystallographic axis. The correct alignment of the crystal can be achieved with the help of x-ray methods, after being mounted in the UHV chamber the sample is chemically cleaned and flattened. Unwanted surface contaminants are removed by ion sputtering or by processes such as oxidation and reduction cycles. The surface is flattened by annealing at high temperatures, once a clean and well-defined surface is prepared, monolayers can be adsorbed on the surface by exposing it to a gas consisting of the desired adsorbate atoms or molecules. Often the annealing process will let bulk impurities diffuse to the surface, the problem is that impurities which adsorb without changing the basic symmetry of the surface, cannot easily be identified in the diffraction pattern
Low-energy electron diffraction
–
Figure 2 Diagram of a LEED optics apparatus.
Low-energy electron diffraction
Low-energy electron diffraction
–
Image 1: LEED pattern of a clean platinum-rhodium (100) (Miller-index) single crystal. Taken in high vacuum using an electron gun with an energy of 85 eV.
Low-energy electron diffraction
–
Image 2: LEED pattern of CO on platinum-rhodium (100) (Miller-index) surface of a single crystal. Taken in high vacuum using an electron gun with an energy of 94 eV.
10.
Rutherford backscattering spectroscopy
–
Rutherford backscattering spectrometry is an analytical technique used in materials science. Rutherford backscattering spectrometry is named after Lord Ernest Rutherford, a physicist sometimes referred to as the father of nuclear physics, Rutherford supervised a series of experiments carried out by Hans Geiger and Ernest Marsden between 1909 and 1914 studying the scattering of alpha particles through metal foils. At most small deflections should occur as the alpha particles passed almost unhindered through the foil, instead, when Marsden positioned the detector on the same side of the foil as the alpha particle source, he immediately detected a noticeable backscattered signal. According to Rutherford, It was quite the most incredible event that has happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of paper and it came back. Rutherford interpreted the result of the Geiger–Marsden experiment as an indication of a Coulomb collision with a massive positive particle. This led him to the conclusion that the positive charge could not be diffuse but instead must be concentrated in a single massive core. Calculations indicated that the necessary to accomplish this deflection was approximately 100 times the charge of the electron. This model was superseded by the Bohr atom, incorporating some early results from quantum mechanics. If the energy of the incident particle is increased sufficiently, the Coulomb barrier is exceeded and this may result in nuclear reactions in certain cases, but frequently the interaction remains elastic, although the scattering cross-sections may fluctuate wildly as a function of energy. This case is known as Elastic Backscattering Spectrometry, there has recently been great progress in determining EBS scattering cross-sections, by solving Schrödingers equation for each interaction. We describe Rutherford backscattering as an elastic, hard-sphere collision between a kinetic energy particle from the incident beam and a stationary particle located in the sample. Elastic in this means that no energy is transferred between the incident particle and the stationary particle during the collision, and the state of the stationary particle is not changed. Note that nuclear interactions are not elastic, since a collision may result in a nuclear reaction. Nuclear reaction analysis is useful for detecting light elements, however, this is not Rutherford scattering. The plus sign is taken when the mass of the projectile is less than that of the target, while this equation correctly determines the energy of the scattered projectile for any particular scattering angle, it does not describe the probability of observing such an event. For that we need the differential cross-section of the event, d ω d Ω =214. This equation is written in the centre of mass frame of reference and is not a function of the mass of either the projectile or the target nucleus
Rutherford backscattering spectroscopy
–
A single stage 2 MeV linear Van de Graaff particle accelerator, here opened for maintenance
Rutherford backscattering spectroscopy
–
Left: Expected results: alpha particles passing through the plum pudding model of the atom undisturbed. Right: Observed results: a small portion of the particles were deflected, indicating a small, concentrated positive charge.
11.
Scanning tunneling microscopy
–
A scanning tunneling microscope is an instrument for imaging surfaces at the atomic level. Its development in 1981 earned its inventors, Gerd Binnig and Heinrich Rohrer, for a STM, good resolution is considered to be 0.1 nm lateral resolution and 0.01 nm depth resolution. With this resolution, individual atoms within materials are routinely imaged and manipulated, the STM can be used not only in ultra-high vacuum but also in air, water, and various other liquid or gas ambients, and at temperatures ranging from near zero kelvin to over 1000°C. STM is based on the concept of quantum tunneling, when a conducting tip is brought very near to the surface to be examined, a bias applied between the two can allow electrons to tunnel through the vacuum between them. The resulting tunneling current is a function of tip position, applied voltage, information is acquired by monitoring the current as the tips position scans across the surface, and is usually displayed in image form. First, a bias is applied and the tip is brought close to the sample by coarse sample-to-tip control. In this situation, the bias will cause electrons to tunnel between the tip and sample, creating a current that can be measured. Once tunneling is established, the bias and position with respect to the sample can be varied. If the tip is moved across the sample in the x-y plane and these changes are mapped in images. This change in current with respect to position can be measured itself, or the height, z and these two modes are called constant height mode and constant current mode, respectively. In constant current mode, feedback electronics adjust the height by a voltage to the piezoelectric height control mechanism, all images produced by STM are grayscale, with color optionally added in post-processing in order to visually emphasize important features. In addition to scanning across the sample, information on the structure at a given location in the sample can be obtained by sweeping voltage. This type of measurement is called scanning tunneling spectroscopy and typically results in a plot of the density of states as a function of energy within the sample. Framerates of at least 25 Hz enable so called video-rate STM, framerates up to 80 Hz are possible with fully working feedback that adjusts the height of the tip. Video-rate STM can be used to surface diffusion. The components of an STM include scanning tip, piezoelectric controlled height and x, y scanner, coarse sample-to-tip control, vibration isolation system, the resolution of an image is limited by the radius of curvature of the scanning tip of the STM. Additionally, image artifacts can occur if the tip has two tips at the end rather than an atom, this leads to “double-tip imaging. Therefore, it has been essential to develop processes for consistently obtaining sharp, recently, carbon nanotubes have been used in this instance
Scanning tunneling microscopy
–
Image of reconstruction on a clean
Gold (100) surface
Scanning tunneling microscopy
–
A close-up of a simple scanning tunneling microscope head using a platinum–iridium tip.
Scanning tunneling microscopy
–
Nanomanipulation via STM of a
self-assembled organic semiconductor monolayer (here: PTCDA molecules) on
graphite, in which the logo of the
Center for NanoScience (CeNS),
LMU has been written.
Scanning tunneling microscopy
–
Image of a
graphite surface at an atomic level obtained by an STM.
12.
Atomic force microscopy
–
The information is gathered by feeling or touching the surface with a mechanical probe. Piezoelectric elements that facilitate tiny but accurate and precise movements on command enable very precise scanning, the AFM has three major abilities, force measurement, imaging, and manipulation. In force measurement, AFMs can be used to measure the forces between the probe and the sample as a function of their mutual separation and this can be applied to perform force spectroscopy. For imaging, the reaction of the probe to the forces that the sample imposes on it can be used to form an image of the shape of a sample surface at a high resolution. This is achieved by scanning the position of the sample with respect to the tip. The surface topography is commonly displayed as a pseudocolor plot, in manipulation, the forces between tip and sample can also be used to change the properties of the sample in a controlled way. Examples of this include atomic manipulation, scanning probe lithography and local stimulation of cells, simultaneous with the acquisition of topographical images, other properties of the sample can be measured locally and displayed as an image, often with similarly high resolution. Examples of such properties are mechanical properties like stiffness or adhesion strength, in fact, the majority of SPM techniques are extensions of AFM that use this modality. Therefore, it does not suffer from a limitation of space due to diffraction limit and aberration. There are several types of scanning microscopy including scanning probe microscopy, although SNOM and STED use visible light to illuminate the sample, their resolution is not constrained by the diffraction limit. Fig.3 shows an AFM typically consisting of the following features, optionally, a piezoelectric element oscillates the cantilever. The sharp tip is fixed to the end of the cantilever. The detector records the deflection and motion of the cantilever, the sample is mounted on the sample stage. An xyz drive permits to displace the sample and the stage in x, y. Although Fig. Controllers and plotter are not shown in Fig.3, numbers in parentheses correspond to numbered features in Fig.3. Coordinate directions are defined by the coordinate system, the detector of AFM measures the deflection of the cantilever and converts it into an electrical signal. The intensity of signal will be proportional to the displacement of the cantilever. Various methods of detection can be used, e. g. interferometry, optical levers, the method, the piezoelectric method
Atomic force microscopy
Atomic force microscopy
Atomic force microscopy
–
Fig.4: X-Y scan of AFM. Here, (1):Tip, (2):Sample, (3):Cantilever, and (4):X-Y Orbit of tip apex.
Atomic force microscopy
–
Fig.5: Schematics of Topographic image forming by AFM. Here, (1):Tip apex, (2):Sample surface, (3):Z-Orbit of Tip apex, and (4):Cantilever.
13.
Silicon
–
Silicon is a chemical element with symbol Si and atomic number 14. A hard and brittle crystalline solid with a metallic luster. It is a member of group 14 in the table, along with carbon above it and germanium, tin, lead. It is not very reactive, although more reactive than germanium, Silicon is the eighth most common element in the universe by mass, but very rarely occurs as the pure element in the Earths crust. It is most widely distributed in dusts, sands, planetoids, over 90% of the Earths crust is composed of silicate minerals, making silicon the second most abundant element in the Earths crust after oxygen. Most silicon is used commercially without being separated, and often with little processing of the natural minerals, such use includes industrial construction with clays, silica sand, and stone. Silicate is used in Portland cement for mortar and stucco, and mixed with sand and gravel to make concrete for walkways, foundations. Silicates are used in whiteware ceramics such as porcelain, and in traditional quartz-based soda-lime glass, Silicon compounds such as silicon carbide are used as abrasives and components of high-strength ceramics. Elemental silicon also has an impact on the modern world economy. Most free silicon is used in the refining, aluminium-casting. Silicon is the basis of the widely used synthetic polymers called silicones, Silicon is an essential element in biology, although only tiny traces are required by animals. However, various sea sponges and microorganisms, such as diatoms and radiolaria, silica is deposited in many plant tissues, such as in the bark and wood of Chrysobalanaceae and the silica cells and silicified trichomes of Cannabis sativa, horsetails and many grasses. Silicon is a solid at room temperature, with a point of 1,414 °C. Like water, it has a density in a liquid state than in a solid state and it expands when it freezes. With a relatively high conductivity of 149 W·m−1·K−1, silicon conducts heat well. In its crystalline form, pure silicon has a gray color, like germanium, silicon is rather strong, very brittle, and prone to chipping. Silicon, like carbon and germanium, crystallizes in a cubic crystal structure with a lattice spacing of 0.5430710 nm. The outer electron orbital of silicon, like that of carbon, has four valence electrons, the 1s, 2s, 2p and 3s subshells are completely filled while the 3p subshell contains two electrons out of a possible six
Silicon
–
Silicon, 14 Si
Silicon
–
Spectral lines of silicon
Silicon
–
Silicon powder
Silicon
–
Quartz crystal cluster from
Tibet. The naturally occurring mineral is a network solid with the formula SiO 2.
14.
Diamond cubic
–
The diamond cubic crystal structure is a repeating pattern of 8 atoms that certain materials may adopt as they solidify. Diamond cubic is in the Fd3m space group, which follows the face-centered cubic Bravais lattice, the diamond lattice can be viewed as a pair of intersecting face-centered cubic lattices, with each separated by 1/4 of the width of the unit cell in each dimension. Many compound semiconductors such as gallium arsenide, β-silicon carbide, and indium antimonide adopt the analogous zincblende structure, zincblendes space group is F43m, but many of its structural properties are quite similar to the diamond structure. The atomic packing factor of the cubic structure is π√3/16 ≈0.34. Zincblende structures have higher packing factors than 0.34 depending on the sizes of their two component atoms. The first-, second-, third-, fourth- and fifth-nearest-neighbor distances in units of the lattice constant are √3/4, √2/2, √11/4,1 and √19/4. Mathematically, the points of the cubic structure can be given coordinates as a subset of a three-dimensional integer lattice by using a cubic unit cell four units across. With these coordinates, the points of the structure have coordinates satisfying the equations x = y = z, and x + y + z =0 or 1. There are eight points that satisfy these conditions, All of the points in the structure may be obtained by adding multiples of four to the x, y. Adjacent points in this structure are at distance √3 apart in the integer lattice and this structure may be scaled to a cubical unit cell that is some number a of units across by multiplying all coordinates by a/4. Alternatively, each point of the cubic structure may be given by four-dimensional integer coordinates whose sum is either zero or one. Two points are adjacent in the structure if and only if their four-dimensional coordinates differ by one in a single coordinate. The total difference in values between any two points gives the number of edges in the shortest path between them in the diamond structure. These four-dimensional coordinates may be transformed into three-dimensional coordinates by the formula →, because the diamond structure forms a distance-preserving subset of the four-dimensional integer lattice, it is a partial cube. Yet another coordinatization of the diamond cubic involves the removal of some of the edges from a grid graph. The diamond cubic is sometimes called the lattice but it is not, mathematically. However, it is still a highly symmetric structure, any incident pair of a vertex, moreover the diamond crystal as a network in space has a strong isotropic property. Another crystal with this property is the Laves graph, the compressive strength and hardness of diamond and various other materials, such as boron nitride, is attributed to the diamond cubic structure
Diamond cubic
–
Example of a diamond cubic
truss system for resisting
compression
Diamond cubic
–
Pole figure in
stereographic projection of the diamond lattice showing the 3-fold symmetry along the
[111] direction.
15.
Reflection high energy electron diffraction
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Reflection high-energy electron diffraction is a technique used to characterize the surface of crystalline materials. Transmission electron microscopy, another common electron diffraction method samples the bulk of the due to the geometry of the system. Low-energy electron diffraction is also sensitive, but LEED achieves surface sensitivity through the use of low energy electrons. A RHEED system requires a source, photoluminescent detector screen. The electron gun generates a beam of electrons which strike the sample at a small angle relative to the sample surface. The electrons interfere according to the position of atoms on the sample surface, Figure 1 shows the most basic setup of a RHEED system. In the RHEED setup, only atoms at the sample surface contribute to the RHEED pattern, the glancing angle of incident electrons allows them to escape the bulk of the sample and to reach the detector. Atoms at the sample surface diffract the incident electrons due to the properties of electrons. The diffracted electrons interfere constructively at specific angles according to the structure and spacing of the atoms at the sample surface. Some of the waves created by constructive interference collide with the detector. Users characterize the crystallography of the surface through analysis of the diffraction patterns. Figure 2 shows a RHEED pattern, two types of diffraction contribute to RHEED patterns. Some incident electrons undergo a single, elastic scattering event at the crystal surface, dynamic scattering occurs when electrons undergo multiple diffraction events in the crystal and lose some of their energy due to interactions with the sample. Users extract non-qualitative data from the diffracted electrons. These electrons account for the high intensity spots or rings common to RHEED patterns, RHEED users also analyze dynamically scattered electrons with complex techniques and models to gather quantitative information from RHEED patterns. RHEED users construct Ewalds spheres to find the properties of the sample surface. Ewalds spheres show the diffraction conditions for kinematically scattered electrons in a given RHEED setup. The user must relate the geometry and spacing of the spots of a pattern to the Ewalds sphere in order to determine the reciprocal lattice of the sample surface
Reflection high energy electron diffraction
–
Figure 1. Systematic setup of the electron gun, sample and detector /CCD components of a RHEED system. Electrons follow the path indicated by the arrow and approach the sample at angle θ. The sample surface diffracts electrons, and some of these diffracted electrons reach the detector and form the RHEED pattern. The reflected (specular) beam follows the path from the sample to the detector.
16.
Gerd Binnig
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Gerd Binnig is a German physicist, who won the Nobel Prize in Physics in 1986 for the invention of the scanning tunneling microscope. He was born in Frankfurt am Main and played in the ruins of the city during his childhood and his family lived partly in Frankfurt and partly in Offenbach am Main, and he attended school in both cities. At the age of 10, he decided to become a physicist and he concentrated more on music, playing in a band. He also started playing the violin at 15 and played in his school orchestra, Binnig studied physics at the J. W. Goethe University in Frankfurt, gaining a degree in 1973 and remaining there do a PhD with in Werner Martienssens group. In 1969, he married Lore Wagler, a psychologist, and they have a daughter born in Switzerland and his hobbies are reading, swimming and golf. In 1978, he accepted an offer from IBM to join their Zürich research group, there they developed the scanning tunneling microscope, an instrument for imaging surfaces at the atomic level. The Nobel committee described the effect that the invention of the STM had on science, the IBM Zürich team were soon recognized with a number of prizes, the German Physics Prize, the Otto Klung Prize, the Hewlett Packard Prize and the King Faisal Prize. In 1986, Binnig and Rohrer shared half of the Nobel Prize in Physics, in 1985, Binnig invented the atomic force microscope and Binnig, Christoph Gerber and Calvin Quate went on to develop a working version of this new microscope for insulating surfaces. In 1987 Binnig was appointed IBM Fellow, the company developed Cognition Network Technology to analyze images just like the human eye and brain are capable of doing. In 2016, Binnig won the Kavli Prize in Nanoscience, the Binnig and Rohrer Nanotechnology Center, an IBM-owned research facility in Rüschlikon, Zurich is named after Gerd Binnig and Heinrich Rohrer. Pioneers in Electricity and Magnetism - Gerd Binnig National High Magnetic Field Laboratory Autobiography of Gerd Binnig Astra Zeneca acquires Definiens
Gerd Binnig
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Gerd Binnig
17.
Heinrich Rohrer
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Heinrich Rohrer was a Swiss physicist who shared half of the 1986 Nobel Prize in Physics with Gerd Binnig for the design of the scanning tunneling microscope. The other half of the Prize was awarded to Ernst Ruska, Rohrer was born in Buchs, St. Gallen half an hour after his twin sister. He enjoyed a carefree country childhood until the family moved to Zürich in 1949 and he enrolled in the Swiss Federal Institute of Technology in 1951, where he was student of Wolfgang Pauli and Paul Scherrer. His PhD thesis was supervised by Prof P. Grassmann who worked on cryogenic engineering, Rohrer measured the length changes of superconductors at the magnetic-field-induced superconducting transition, a project begun by Jörgen Lykke Olsen. In the course of his research, he found that he had to do most of his research at night after the city was asleep because his measurements were so sensitive to vibration and his studies were interrupted by his military service in the Swiss mountain infantry. In 1961, he married Rose-Marie Egger and their honeymoon trip to the United States included a stint doing research on thermal conductivity of type-II superconductors and metals with Bernie Serin at Rutgers University in New Jersey. In 1963, he joined the IBM Research Laboratory in Rüschlikon under the direction of Ambros Speiser, the first couple of years at IBM, he studied Kondo systems with magnetoresistance in pulsed magnetic fields. He then began studying magnetic phase diagrams, which brought him into the field of critical phenomena. In 1974, he spent a year at the University of California in Santa Barbara, California studying nuclear magnetic resonance with Vince Jaccarino. Until 1982 he worked on the scanning tunneling microscope and he was appointed IBM Fellow in 1986, and led the physics department of the research lab from 1986 until 1988. Rohrer died of natural causes on 16 May 2013 at his home in Wollerau and he was aged 79 and is survived by his wife, daughters Doris and Ellen, and two grandchildren
Heinrich Rohrer
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Heinrich Rohrer
18.
Gold
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Gold is a chemical element with symbol Au and atomic number 79. In its purest form, it is a bright, slightly yellow, dense, soft, malleable. Chemically, gold is a metal and a group 11 element. It is one of the least reactive chemical elements and is solid under standard conditions, Gold often occurs in free elemental form, as nuggets or grains, in rocks, in veins, and in alluvial deposits. It occurs in a solid solution series with the element silver and also naturally alloyed with copper. Less commonly, it occurs in minerals as gold compounds, often with tellurium, golds atomic number of 79 makes it one of the higher numbered, naturally occurring elements. It is thought to have produced in supernova nucleosynthesis, from the collision of neutron stars. Because the Earth was molten when it was formed, almost all of the present in the early Earth probably sank into the planetary core. Gold is resistant to most acids, though it does dissolve in aqua regia, a mixture of acid and hydrochloric acid. Gold also dissolves in solutions of cyanide, which are used in mining and electroplating. Gold dissolves in mercury, forming amalgam alloys, but this is not a chemical reaction, as a precious metal, gold has been used for coinage, jewelry, and other arts throughout recorded history. A total of 186,700 tonnes of gold is in existence above ground, the world consumption of new gold produced is about 50% in jewelry, 40% in investments, and 10% in industry. Gold is also used in infrared shielding, colored-glass production, gold leafing, certain gold salts are still used as anti-inflammatories in medicine. As of 2014, the worlds largest gold producer by far was China with 450 tonnes, Gold is cognate with similar words in many Germanic languages, deriving via Proto-Germanic *gulþą from Proto-Indo-European *ǵʰelh₃-. The symbol Au is from the Latin, aurum, the Latin word for gold, the Proto-Indo-European ancestor of aurum was *h₂é-h₂us-o-, meaning glow. This word is derived from the root as *h₂éu̯sōs, the ancestor of the Latin word Aurora. This etymological relationship is presumably behind the frequent claim in scientific publications that aurum meant shining dawn, Gold is the most malleable of all metals, a single gram can be beaten into a sheet of 1 square meter, and an avoirdupois ounce into 300 square feet. Gold leaf can be thin enough to become semi-transparent
Gold
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Gold, 79 Au
Gold
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Moche gold necklace depicting feline heads.
Larco Museum Collection. Lima-Peru
Gold
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Mirror for the future
James Webb Space Telescope coated in gold to reflect infrared light
Gold
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The
world's largest gold bar has a mass of 250 kg.
Toi museum,
Japan.
19.
Crystal structure
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In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystalline material. Ordered structures occur from the nature of the constituent particles to form symmetric patterns that repeat along the principal directions of three-dimensional space in matter. The smallest group of particles in the material that constitutes the pattern is the unit cell of the structure. The unit cell completely defines the symmetry and structure of the crystal lattice. The repeating patterns are said to be located at the points of the Bravais lattice, the lengths of the principal axes, or edges, of the unit cell and the angles between them are the lattice constants, also called lattice parameters. The symmetry properties of the crystal are described by the concept of space groups, all possible symmetric arrangements of particles in three-dimensional space may be described by the 230 space groups. The crystal structure and symmetry play a role in determining many physical properties, such as cleavage, electronic band structure. The crystal structure of a material can be described in terms of its unit cell, the unit cell is a box containing one or more atoms arranged in three dimensions. The unit cells stacked in three-dimensional space describe the arrangement of atoms of the crystal. Commonly, atomic positions are represented in terms of fractional coordinates, the atom positions within the unit cell can be calculated through application of symmetry operations to the asymmetric unit. The asymmetric unit refers to the smallest possible occupation of space within the unit cell and this does not, however imply that the entirety of the asymmetric unit must lie within the boundaries of the unit cell. Symmetric transformations of atom positions are calculated from the group of the crystal structure. Vectors and planes in a lattice are described by the three-value Miller index notation. It uses the indices ℓ, m, and n as directional parameters, which are separated by 90°, by definition, the syntax denotes a plane that intercepts the three points a1/ℓ, a2/m, and a3/n, or some multiple thereof. That is, the Miller indices are proportional to the inverses of the intercepts of the plane with the unit cell, if one or more of the indices is zero, it means that the planes do not intersect that axis. A plane containing a coordinate axis is translated so that it no longer contains that axis before its Miller indices are determined, the Miller indices for a plane are integers with no common factors. Negative indices are indicated with horizontal bars, as in, in an orthogonal coordinate system for a cubic cell, the Miller indices of a plane are the Cartesian components of a vector normal to the plane. Likewise, the planes are geometric planes linking nodes
Crystal structure
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Quartz is one of the several thermodynamically stable
crystalline forms of
silica, SiO 2. The most important forms of silica include:
α-quartz,
β-quartz,
tridymite,
cristobalite,
coesite, and
stishovite.
Crystal structure
