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Introduction

Low energy electron diffraction (LEED) is a very powerful technique that allows for the characterization of the surface of materials. Its high surface sensitivity is due to the use of electrons with energies between 20-200 eV, which have wavelengths equal to 2.7 – 0.87 Å (comparable to the atomic spacing). Therefore, the electrons can be elastically scattered easily by the atoms in the first few layers of the sample. Its features, such as little penetration of low–energy electrons have positioned it as one of the most common techniques in surface science for the determination of the symmetry of the unit cell (qualitative analysis) and the position of the atoms in the crystal surface (quantitative analysis).

History: Davisson and Germer experiment

In 1924 Louis de Brogile postulated that all forms of matter, such as electrons, have a wave-particle nature. Three years later after this postulate, the American physicists Clinton J. Davisson and Lester H. Germer ( [link] ) proved experimentally the wave nature of electrons at Bell Labs in New York, see Figure 1. At that time, they were investigating the distribution-in-angle of the elastically scattered electrons (electrons that have suffered no loss of kinetic energy) from the (111) face of a polycrystalline nickel, material composed of many randomly oriented crystals.

Davisson and Germer
Clinton Davisson (right) and Lester Germer (left) in their laboratory, where they proved that electrons could act like waves in 1927. Author unknown, public domain.

The experiment consisted of a beam of electrons from a heated tungsten filament directed against the polycrystalline nickel and an electron detector, which was mounted on an arc to observe the electrons at different angles. During the experiment, air entered in the vacuum chamber where the nickel was, producing an oxide layer on its surface. Davisson and Clinton reduced the nickel by heating it at high temperature. They did not realize that the thermal treatment changed the polycrystalline nickel to a nearly monocrystalline nickel, material composed of many oriented crystals. When they repeated the experiment, it was a great surprise that the distribution-in-angle of the scattered electrons manifested sharp peaks at certain angles. They soon realized that these peaks were interference patterns, and, in analogy to X-ray diffraction, the arrangement of atoms and not the structure of the atoms was responsible for the pattern of the scattered electrons.

The results of Davisson and Germer were soon corroborated by George Paget Thomson, J. J. Thomson’s son. In 1937, both Davisson and Thomson were awarded with the Nobel Prize in Physics for their experimental discovery of the electron diffraction by crystals. It is noteworthy that 31 years after J. J. Thomson showed that the electron is a particle, his son showed that it is also a wave.

Although the discovery of low-energy electron diffraction was in 1927, it became popular in the early 1960’s, when the advances in electronics and ultra-high vacuum technology made possible the commercial availability of LEED instruments. At the beginning, this technique was only used for qualitative characterization of surface ordering. Years later, the impact of computational technologies allowed the use of LEED for quantitative analysis of the position of atoms within a surface. This information is hidden in the energetic dependence of the diffraction spot intensities, which can be used to construct a LEED I-V curve.

Questions & Answers

important of enocomic
Adu Reply
what is division of labour
Dennis Reply
division of labour can be defined as the separation of task to individuals in any economic system to specialize on it.
Ahmad
what is demand curve
Victoria Reply
demand curve is a downward sloping economic graph that shows the relationship between the price of product and the quantity of the product demanded.
Ahmad
What is demand
Frank Reply
It refers to the quantity of a commodity purchased in the market at a price and at a point of time.
Basanta
refers to amount of commodities a consumer is willing and able to buy at particular price within a period of time
Clifford
It is the ability and willingness a customer buys a product or service at a particular price, place and time while other things remaining constant or the same
kum
In which case is opportunity cost is zero
Francis Reply
where no alternative is available
Bhartendu
who is the father of economic
Omar Reply
Adam Smith
Suraj
ok
Tony
Adam Smith
Francis
Adam smith
Opana
Adam Smith
Basanta
What is monopoly
Mauthoor Reply
it an economic situation where one individual controls the essential commodities or value product for maximum profit
James
monopoly is a market situation in which there is only one producer of a good or service which has no close substitutes
eliano
is where only one person is solely the price taker
Francis
what is Monopoly
Dauda Reply
The word Monopoly is a Latin word. it is the combination of two words-Mono means single and Poly means seller. thus Monopoly means single seller. but this is not the full meaning of Monopoly. Monopoly must produce a product which does not have close substitute in the market.
Basanta
Monopoly is define as a firm in an industry with very high barriers to entry.
Favour
If close substitute is available, Monopoly will be a king without a crown.
Basanta
what does it array
Cbdishakur Reply
what are the differences between monopoly and.oligopoly
Onome Reply
what are the difference between monopoly and oligopoly
Cbdishakur
The deference between Monopoly and Oligopoly: Monopoly means:A single-firm-Industry producing and selling a product having no close business and Oligopoly means:A market structure where a few sellers compete with each other and each controls a significant portion of market .
Basanta
so that the price-output policy one affects the other.
Basanta
what are difference between physical policy and monotory policy
hon
what is economic
Emakpor Reply
what is economic
Cbdishakur
the word economic was derived from the Greek word oikos (a house)and mein(to manage) which in effect meant managing a household with the limited funds available 🙂.
Basanta
good excample about scarsity
hon
An Enquiry into the nature and causes of wealth Nations, this book clearly defined what economic is🙂🙂🙏🙏 thank you...
Basanta
good example about scarcity: money,time, energy, human or natural resources. Scarcity of resources implies that there supply is very much limited in relation to demand.
Basanta
equilibrium is a situation in which economic forces such as demand and supply are balanced and in the absence of external influences,the value of economic variables will not change
Onome Reply
hmnn
Emakpor
marginal cost and marginal revenue is equilibrium .
Kho
yessss
Basanta
what is equilibrium
Rodrice Reply
policy prescriptions for unemployment
Jeslyne Reply
Am working on it
Blacks
Study
Janelle
study
simeon
what are the factors effecting demand sedule
Kalimu Reply
we should talk about more important topics, you can search it on Google n u will find your answer we should try to focus on how we can improve our society using economics
shubham
so good night
hon
Why do people buy more grapes in December than in July?
lungi
because at time know money
Adu
advantages of NAA
Sai Reply
how I can reaction of mercury?
Sham Reply

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Source:  OpenStax, Physical methods in chemistry and nano science. OpenStax CNX. May 05, 2015 Download for free at http://legacy.cnx.org/content/col10699/1.21
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