Siemens Research laboratories
What was the name of the employer Walter H. Schottky work for from 1927 to 1958?
Walter H . Schottky Walter Hans Schottky ( 23 July 1886 – 4 March 1976 ) was a German physicist who played a major early role in developing the theory of electron and ion emission phenomena , invented the screen-grid vacuum tube in 1915 while working at Siemens , co-invented the ribbon microphone and ribbon loudspeaker along with Dr . Erwin Gerlach in 1924 and later made many significant contributions in the areas of semiconductor devices , technical physics and technology . Early life . Schottkys father was mathematician Friedrich Hermann Schottky ( 1851–1935 ) . Schottky had one sister and one brother . His father was appointed professor of mathematics at the University of Zurich in 1882 , and Schottky was born four years later . The family then moved back to Germany in 1892 , where his father took up an appointment at the University of Marburg . Schottky graduated from the Steglitz Gymnasium in Berlin in 1904 . He completed his B.S . degree in physics , at the University of Berlin in 1908 , and he completed his PhD in physics at the Humboldt University of Berlin in 1912 , studying under Max Planck and Heinrich Rubens , with a thesis entitled : Zur relativtheoretischen Energetik und Dynamik ( translates as About Relative-Theoretical Energetics and Dynamics ) . Career . Schottkys postdoctoral period was spent at University of Jena ( 1912–14 ) . He then lectured at the University of Würzburg ( 1919–23 ) . He became a professor of theoretical physics at the University of Rostock ( 1923–27 ) . For two considerable periods of time , Schottky worked at the Siemens Research laboratories ( 1914–19 and 1927–58 ) . Inventions . In 1924 , Schottky co-invented the ribbon microphone along with Erwin Gerlach . The idea was that a very fine ribbon suspended in a magnetic field could generate electric signals . This led to the invention of the ribbon loudspeaker by using it in the reverse order , but it was not practical until high flux permanent magnets became available in the late 1930s . Major scientific achievements . Possibly , in retrospect , Schottkys most important scientific achievement was to develop ( in 1914 ) the well-known classical formula , now written This computes the interaction energy between a point charge q and a flat metal surface , when the charge is at a distance x from the surface . Owing to the method of its derivation , this interaction is called the image potential energy ( image PE ) . Schottky based his work on earlier work by Lord Kelvin relating to the image PE for a sphere . Schottkys image PE has become a standard component in simple models of the barrier to motion , M ( x ) , experienced by an electron on approaching a metal surface or a metal–semiconductor interface from the inside . ( This M ( x ) is the quantity that appears when the one-dimensional , one-particle , Schrödinger equation is written in the form Here , formula_3 is Plancks constant divided by 2π , and m is the electron mass. ) The image PE is usually combined with terms relating to an applied electric field F and to the height h ( in the absence of any field ) of the barrier . This leads to the following expression for the dependence of the barrier energy on distance x , measured from the electrical surface of the metal , into the vacuum or into the semiconductor : Here , e is the elementary positive charge , ε is the electric constant and ε is the relative permittivity of the second medium for vacuum ) . In the case of a metal–semiconductor junction , this is called a Schottky barrier ; in the case of the metal-vacuum interface , this is sometimes called a Schottky–Nordheim barrier . In many contexts , h has to be taken equal to the local work function φ . This Schottky–Nordheim barrier ( SN barrier ) has played an important role in the theories of thermionic emission and of field electron emission . Applying the field causes lowering of the barrier , and thus enhances the emission current in thermionic emission . This is called the Schottky effect , and the resulting emission regime is called Schottky emission . In 1923 Schottky suggested ( incorrectly ) that the experimental phenomenon then called autoelectronic emission and now called field electron emission resulted when the barrier was pulled down to zero . In fact , the effect is due to wave-mechanical tunneling , as shown by Fowler and Nordheim in 1928 . But the SN barrier has now become the standard model for the tunneling barrier . Later , in the context of semiconductor devices , it was suggested that a similar barrier should exist at the junction of a metal and a semiconductor . Such barriers are now widely known as Schottky barriers , and considerations apply to the transfer of electrons across them that are analogous to the older considerations of how electrons are emitted from a metal into vacuum . ( Basically , several emission regimes exist , for different combinations of field and temperature . The different regimes are governed by different approximate formulae. ) When the whole behaviour of such interfaces is examined , it is found that they can act ( asymmetrically ) as a special form of electronic diode , now called a Schottky diode . In this context , the metal–semiconductor junction is known as a Schottky ( rectifying ) contact . Schottkys contributions in surface science/emission electronics and in semiconductor-device theory now form a significant and pervasive part of the background to these subjects . It could possibly be argued that – perhaps because they are in the area of technical physics – they are not as generally well recognized as they ought to be . Awards . He was awarded the Royal Societys Hughes medal in 1936 for his discovery of the Schrot effect ( spontaneous current variations in high-vacuum discharge tubes , called by him the Schrot effect : literally , the small shot effect ) in thermionic emission and his invention of the screen-grid tetrode and a superheterodyne method of receiving wireless signals . In 1964 he received the Werner von Siemens Ring honoring his ground-breaking work on the physical understanding of many phenomena that led to many important technical appliances , among them tube amplifiers and semiconductors . Controversy . The invention of superheterodyne is usually attributed to Edwin Armstrong . However , Schottky published an article in the Proceedings of the IEEE that may indicate he had invented and patented something similar in Germany in 1918 . The Frenchman Lucien Lévy had filed a claim earlier than either Armstrong or Schottky , and eventually his patent was recognized in the US and Germany . - 1939 : first p–n junction Legacy . The Walter Schottky Institute for semiconductor research and the Walter Schottky Prize are named after him . Books written by Schottky . - Thermodynamik , Julius Springer , Berlin , Germany , 1929 . - Physik der Glühelektroden , Akademische Verlagsgesellschaft , Leipzig , 1928 .