An atom in an excited state gives off energy by emitting a photon, a quantum of electromagnetic radiation, according to Bohr’s second postulate. Although Bohr’s specific model of the atom has been vastly extended and incorporated into models based on a different approach , this postulate is still valid. Atoms can acquire internal energy, that […]
The success of Bohr’s model of the atom in accounting for the spectrum of hydrogen left this question: Could experiments show directly that atoms do have only certain, separate energy states? In other words, are there really gaps between the energies that an atom can have? A famous experiment in 1914, by the German physicists […]
Al13 − is one of the most attractive of the so-called magic clusters. It has a perfect icosahedral symmetry with an aluminum atom at the center, a closed-shell electronic configuration (40 electrons), and a large highest occupied molecular orbital−lowest unoccupied molecular orbital (HOMO− LUMO) gap. These features result in an unusual stability and chemical inertness […]
The idea that the solution of Schrödinger’s equation is a wave that represents, not a physical wave, but the probability of finding the associated particle in some specific condition of motion has had great success. In fact, every experiment devised so far to test this interpretation has confirmed these results. Yet many scientists still find […]
In ordinary life it is assumed that any physical property of an object can be measured as accurately as necessary. To reach any desired degree of accuracy would require only a sufficiently precise instrument. Wave mechanics showed, however, that even in thought experiments with ideal instruments there are limits to the accuracy of measurements that […]
By the mid-1920s it was clear that “things” (electrons, atoms, molecules) long regarded as particles also show wave properties. This fact is the basis for the currently accepted theory of atomic structure. This theory, quantum mechanics, was introduced in 1925. Its foundations were developed very rapidly during the next few years, primarily by Born, Heisenberg […]
Condensed matter • Materials • Nanotechnology • Physics • Quantum physics
Silicon surfaces of crystalline solids are part of conventional electronics, but their exploitation in novel materials combining two-dimensional electron states (2DESs) and magnetism, which play an important role in the development of next-generation electronics, still remains elusive. The appearance of 2DESs at surfaces or interfaces and their interplay with magnetic degrees of freedom may open […]
Amplifying Voltage If we place a large resistor in a circuit containing a transistor we can amplify the incoming voltage, since according to Ohm’s law voltage is equal to current times resistance. So a current crossing a small resistance corresponds to a small voltage. But if the same current is made to cross a much […]
Nanoparticles of certain metals, like gold or silver, have attracted substantial interest in recent years owing to their ability to support localized surface plasmon resonances (collective oscillations of conduction electrons). These plasmonic excitations allow manipulation of light at the nanoscale and have enabled technological advances ranging from improved catalytic and photovoltaic cell efficiencies to sensitive […]
The properties of n-type and p-type semiconductors were well known by the end of World War II, during which considerable research was devoted to electronics and the invention of radar. In 1947 three researchers at Bell Laboratories in New Jersey took the idea of the n-p junction diode a step further. William Shockley, Walter Brattain […]