Transferred electron oscillator

Fig. 4. Schematic representation of binary oscillation involving electron transfer from QAto Qg in the absence of the quinone pool, as monitored by changes in light-induced, EPR signals, EPR data adapted from Butler, Calvo, Fredkin, Isaacson, Okamura and Feher (1984) The electronic structure ofFe in reaction centers from Rhodospseudomonas sphaeroides. III. EPR measurements of the reduced acceptor complex. Biophysical J. 45 955.

Gunn devices belong to a group called transferred electron oscillators and are the ones most often encountered in MMW spectrometry, as they offer the lowest noise figure. They rely on a bulk property of gallium arsenide and indium phosphide when a DC voltage is applied across the end contacts of the n-type material. As the voltage is increased, the current initially increases linearly and then starts to oscillate, with a period closely related to the transit time of the carriers between the contacts across the bulk material. The device is housed in a cavity coupled to a transmission line and is used as a source of MMW radiation, the frequency of which can be tuned mechanically and electronically. 

In another example of energy transfer, an individual electron can transfer energy to several electrons. Such an example is the excitation of a plasmon, a collective oscillation of electrons in the conduction band, known as a plasmon-loss. The shape of the plasmon-loss feature is directly related to the electron structure of the solid. Examples of plasmon-loss structures for silicon with a native oxide and SiOa are shown in Fig. 3.11. Silicon, being semi-metallic exhibits very sharp plasmon-loss features with a smaller separation (hcai) as compared to the broader features of SiOa, which is a wide bandgap insulator. 

Lubzens, D., Photoetching of InP mesas for production of mm wave transferred electron oscillators. Electron. Lett. 13 171-172(1977)... 

The electron-transport system is a series of coupled oxidation-reduction (also called redox) reactions which transfer electrons to molecular oxygen. Carrier 1 (Figure 13.2) in its oxidized form may accept electrons which reduce it. In the reduced state, it may donate the electrons to the oxidized form of carrier 2. In the process of the transfer, carrier 1 becomes reoxidized as carrier 2 becomes reduced. Similarly, reduced carrier 2 may donate electrons to carrier 3 and so on. In each reaction, the electron donor can only release the electrons if there is a suitable acceptor. The electron donor is termed the reductant since it reduces the acceptor and the electron acceptor is termed the oxidant since it oxidizes the donor. In the electron-transport system, each electron carrier oscillates between oxidized and reduced forms which constitute a redox couple. 

Calculations within tire framework of a reaction coordinate degrees of freedom coupled to a batli of oscillators (solvent) suggest tliat coherent oscillations in the electronic-state populations of an electron-transfer reaction in a polar solvent can be induced by subjecting tire system to a sequence of monocliromatic laser pulses on tire picosecond time scale. The ability to tailor electron transfer by such light fields is an ongoing area of interest [511 (figure C3.2.14). 

Evans D G, Coalson R D, Kim H J and Dakhnovskii Y 1995 Inducing coherent oscillations in an electron transfer dynamics of a strongly dissipative system with pulsed monochromatic light Phys. Rev. Lett. 75 3649... 

With tlie development of femtosecond laser teclmology it has become possible to observe in resonance energy transfer some apparent manifestations of tire coupling between nuclear and electronic motions. For example in photosyntlietic preparations such as light-harvesting antennae and reaction centres [32, 46, 47 and 49] such observations are believed to result eitlier from oscillations between tire coupled excitonic levels of dimers (generally multimers), or tire nuclear motions of tire cliromophores. This is a subject tliat is still very much open to debate, and for extensive discussion we refer tire reader for example to [46, 47, 50, 51 and 55]. A simplified view of tire subject can nonetlieless be obtained from tire following semiclassical picture. 

The nature of the light emissions is influenced by the way in which the absorbed energy is transferred through the polymer matrix. In crystalline polymers, exciton migration is possible as all molecules lose their energetic individuality and all electronic and oscillation levels are coupled [20]. Thus, new exciton absorption and emission bands are formed and the excitation energy can move along the chain ... 

Ozawa M, Akagawa K, Sakaguchi T, Tsukahara T, Fuji T (1979) Oscillatory flow instabilities in air-water two-phase flow systems. Report. Pressure drop oscillation. Bull JSME 22 1763-1770 Qu W, Yoon S-M, Mudawar 1 (2004) Two-phase flow and heat transfer in rectangular microchannels. J Electron Packag 126 288-300... 

Inelastic collisions of swift, charged particles with matter are completely described by the distribution of generalized oscillator strengths (GOS s) characterizing the collision. These quantities, characteristic of excitation in the N-electron target (or, in fact, of a dressed projectile as well [1]) from some initial state 0) to a final state n) and concomitant momentum transfer, can be written... 

In systems such as [A... A ]+ where an electron (or a hole) hesitates or oscillates between two equivalent positions on subsystems A or A, symme breakings may occur when the effective transfer integral between the two sites is weak. Hiis will be the case when A and A are far apart, when they are bridged by an "insulating" ligand, or when the two localized MOs concerned by the electron transfer have a very we spatial overlap. 

The left (solid) parabolic curve represents the oxidized state, the right one, the reduced state. Let us assume that the system is initially at the oxidized state (left curve). When the interaction metal-reaction species is small, the electronic coupling between is small and the system may oscillate many times on the left parabolic curve (ox) before it is transferred to the curve on the right (red). On the other hand, if the interaction is strong, the free energy should no longer be represented by the two solid curves in the intermediate region of the reaction coordinate, but rather, by the dashed... 

---