What is chaos? Chaos is a concept related to dynamical systems, that are nothing but systems than can be described by amounts that change in time. There are examples of dynamical systems everywhere: the amount of money in your bank account, your weight, your room’s temperature, … all of them evolve in time, and therefore […]
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 […]
A phase may be defined as a homogeneous portion of a system that has uniform physical and chemical characteristics. Every pure material is considered to be a phase; so also is every solid, liquid, and gaseous solution. For example, a sugar–water syrup solution is one phase, and solid sugar is another. Each has different physical […]
We saw that one of the devices based on semiconductors are photocells. A photocell working in reverse is also useful. If a conduction electron in an n-p diode happens to fall into a hole, it will emit the excess energy as a photon, much as an electron would do in an atom as it jumps […]
A new vista in spintronics was opened in 2004 with the observation of the spin Hall effect in GeAs at 20 K by David Awschlom and his group. In the spin Hall effect the electrons of a charge current flow in a nonmagnetic conducting material in the absence of an external magnetic field. An applied […]
Let’s take a p-type semiconductor with a very clean surface and place it right next to the clean surface of a n-type semiconductor. This type of device is called an n-p junction diode , or simply a diode . What happens? Scientists realized that the electrons in the conduction band of the n-type semiconductor are […]
Ionization is a fundamental process in chemistry and physics, lying at the heart of many fascinating phenomena. Ionization is the process of producing ions. Certain molecules ionize in solution, for example. But ions may also be formed when an atom or molecule loses one or more electrons as a result of energy gained in a […]
The most extensive use of semiconductors, such as silicon or germanium, including their use as transistors, arises from their behavior when, after being sufficiently purified of atoms other than the basic element (e.g., silicon or germanium), very small amounts of special impurities are carefully introduced. While the methods for first purifying then adding small amounts […]