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1.
In a series of recent experiments, research groups have made absolute frequency measurements with laser beams in the infrared region of the spectrum (λ ? 10 μm) using a metal point contact diode for generation, frequency mixing and detection. It has been postulated that the mechanism for the nonlinear current-voltage characteristic of the diode is tunnelling of electrons through an intermediate oxide film from the whisker into the metal base, i.e., the configuration is considered to be a metal-oxide-metal (MOM) tunnelling junction. Several features of the diode's operation create considerable doubt concerning the applicability of the MOM tunnelling mechanism. Analysis of the available experimental data led us to postulate an alternate solid state mechanism, namely a thermally enhanced field emission process. Such emission would be a consequence of the immersion of the whisker tip in the laser radiation resulting in (1) conduction heating which induces thermionic emission and (2) generation of an electric field at the tip necessary for electron tunnelling by field emission. In this paper we calculate rigorously the power absorbed in the metal whisker from the incident radiation. From the power absorbed, the heat conduction equation is solved for model geometries to obtain the laser induced temperature distribution at the whisker surface. Estimates of the electric field are obtained and combined with temperature calculations to obtain the nonlinear I–V characteristics of the thermally enhanced field emission model. Finally some simple experiments are proposed to test the thermal field emission hypothesis as a possible mechanism to explain the nonlinear characteristics of the metal whisker point contact diode. 相似文献
2.
T. E. Sullivan A. A. Lucas P. H. Cutler 《Applied Physics A: Materials Science & Processing》1977,14(3):289-294
In a series of recent experiments, research groups have made absolute frequency measurements with laser beams in the infrared
region (μm) using a metal-metal point contact diode for the generation, frequency mixing and detection. At present there are
two models which attempt to explain the rectification mechanism of the diode: 1) Tunneling of electrons through an intermediate
oxide film from whisker to the metal base, i.e., configuration is considered to be a metal-oxide-metal (MOM) tunneling junction.
2) Rectification and nonlinear processes are the result of a thermal enchanced field emission. Such emission is a consequence
of the immersion of the whisker in the laser radiation which results in conduction induced thermionic emission and/or generation
of an electric field at the tip necessary for electron tunneling by field emission. The purpose of this comment is: a) to
discuss qualitatively the basic difference between MOM and TFE theories as regards the origin of the nonlinearity and rectification
properties of the metal point contact junction; b) to review the analyses describing the ultimate frequency response of the
device; and 3) to provide a possible explanation for polarity reversal consistent with the TFE mechanism describing the operation
of the whisker diode.
This research was supported in part by the NATO Research Grants Program, Scientific Affairs, Brussels, Belgium, and under
the auspices of the joint projects ESIS (electronic structure in solids) and IRIS (Institute for Research in Interface Sciences)
of the Belgian Ministry for Science Policy 相似文献
3.
It is shown that in thin-film MOM diodes of contact area ~ 2.5 × 10-9 m2 the basic mechanism of infrared and visible laser radiation detection is the tunneling current dependence on contact temperature (thermally enhanced tunneling). Experiments were run on Al—Al2O3—Al MOM diodes. 相似文献
4.
Nano-structured phosphorus-doped diamonds were fabricated for field emitters and their field emission properties were characterized. Two kinds of nano-structures were prepared; tip array structures and whiskers on tip structures. The tips, which have 100 nm radius and 10 μm height, are used in tip array structures; whiskers have tip radii of 5 nm and height of 500 nm. Following nano-structure formation, a reduction of threshold fields is observed compared to non-patterned flat surfaces. This is ascribed to field concentration at the tips. However, at higher electric fields, a saturation of the emission current is observed due to non-negligible bulk resistances in tips and whiskers. 相似文献
5.
N. M. Miskovsky P. H. Cutler T. E. Feuchtwang A. A. Lucas 《International Journal of Infrared and Millimeter Waves》1981,2(4):739-772
Using the Mehler-Fock transformation to solve Poisson's equation in prolate spheroidal coordinates, we have obtained an exact Green's function solution for all multiple image corrections to the vacuum tunneling barrier for a hyperboloidal tip-planar-anode model of a point-contact junction consisting of identical or dissimilar metals.These calculations show that the image corrections significantly modify both the form and area of the barrier, producing an enhancement in the rectification and tunneling currents at low bias.I–V characteristics have also been obtained for the hyperboloidal tip model using estimates of the emission and collection regions based on field emission experiments for whisker tips of comparable dimensions. These results are compared with earlier calculations whichThis research was supported in part by the NATO Research Grants Program, Grant No. 1902, Scientific Affairs Division, Brussels, BELGIUM. 相似文献
6.
The non-linear current-voltage characteristic of thermally enhanced field emission is proposed to explain the operation of a metal-metal point contact diode used for laser harmonic frequency generation and frequency mixing in the infrared region. This mechanism can explain several experimental observations which appear inconsistent with the previous analysis based on a planar metal-oxide-metal tunneling geometry. 相似文献
7.
The well-known defects of the surface of a solid, microscopic projections and spikes, play a decisive role in electron emission
induced by an electric field. If there are mobile electrons of holes in the solid, then the electric field is enhanced by
a factor of 10–100 at the tip of a microscopic projection. This effect was discovered in electrostatics more than a century
ago. In turn, the probability of tunnel emission of an electron from a metal into a vacuum is an exponential function of the
electric field strength. Correspondingly the electron emission current density at the tip of a microscopic spike can be larger
than that on a smooth surface by an astronomical factor. This effect is particularly strikingly manifested when picosecond
pulses of infrared laser radiation of moderate power are used to initiate autoelectronic emission. Relative to a smooth surface,
the emission current density is enhanced by hundreds of orders of magnitude. These experimental conditions can be used to
scan the surface of a conducting material with a laser beam and to detect all the microscopic projections, in order to male
detailed observations with subpicosecond time resolution of the phase transition from autoelectronic emission to explosive
emission.
Polytechnic University, Tomsk. Institute of Electrophysics, Ural Branch of the Russian Academy of Sciences. French National
Scientific Center, Saclay, France. Translated from Izvestiya Vysshikh Uchenbnykh Zavedenii, Fizika, No. 11, pp. 42–44, November,
1997. 相似文献
8.
We report on electron emission from tungsten tips with the help of 800 nm-8 fs laser pulses from a Ti:sapphire laser oscillator. We have measured autocorrelation traces of the exciting laser pulse in the photoelectron current, which allows a measurement of the non-linearity as a function of DC voltage applied to the tip. These data are well described by a numerical integration of the one-dimensional Schrödinger equation. The simulation shows us that electron emission resolves the electric field structure of the driving laser pulse, a regime which is currently an extremely fruitful area of research with atoms in the gas phase. For an 8 fs laser pulse with the correct carrier-envelope phase setting the emission duration is as short as 800 nm. 相似文献
9.
H. Gobrecht H. -E. Gumlich H. Nelkowski K. Lacmann 《Zeitschrift für Physik A Hadrons and Nuclei》1962,168(3):273-282
The x-ray excited luminescence of a zinc-cadmium sulfide phosphor activated by manganese and cobalt can be enhanced by infrared or red light, by alternating electric fields, and by both together. The infrared light as well as the electric field enhance the same emission band caused by manganese. The dependence of the enhancement on the strength and on the frequency of the electric field, and on the intensity and on the wavelength of the stimulating radiation has been investigated. Maximum enhancements are observed at frequencies of about 20 cps and at wavelengths of 0.77 and 1.35 μ of the stimulating light. When both the electric field and the stimulating light are applied together, the enhancement is lower than the sum of both effects. While at small intensities of the infrared the emission is increased by an additional electric field, it is diminished at high intensities. If the non-excited phosphor is exposed to the infrared a memory effect is found quite similar to that produced by electric fields reported byDestriau. The results are discussed using a model published earlier. 相似文献
10.
《Revue Generale de Thermique》1998,37(8):725-739
The heat-photon conversion phenomenon can be used to obtain a thermal image of an electromagnetic field. The electromagnetic field is partially absorbed by a sensitive paint or by a coating deposited on structures or on thin films. A map of the temperature increase of this absorbing medium is an image of the electric or magnetic intensity field distribution, depending on the electric and magnetic properties of the medium. A brief history of the various techniques used to obtain thermal images of electromagnetic fields is first presented. Emphasis is then put on infrared thermography which has been preferentially used in the past 20 years. An analysis of the thermal problems involved is presented. It appears that the solution to these problems is the key for the enhancement of the technique and for really quantitative work. Original solutions have been developed at ONERA, based on the combined use of optimised thin films with controlled electric conductivity, very sensitive infrared cameras, lock-in infrared thermography, and microwave interferometry. In these conditions, quantitative images of both amplitude and phase are obtained. Such an electromagnetic field imaging technique is a powerful tool which has no equivalent and which can be used for several types of applications such as: i) antenna radiation pattern characterization; ii) mode propagation characterization in waveguides; iii) study of absorption phenomena in complex materials; iv) nondestructive evaluation of dielectric structures (electromagnetic windows) or radar absorbing materials; v) knowledge of surface currents distribution on metallic structures. 相似文献
11.
E. C. Niculescu A. Radu 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,80(1):73-82
Tunneling effect on the intersubband optical absorption in a
GaAs/Al
x
Ga1-
x
As quantum well under simultaneous presence of
intense non-resonant laser and static electric fields is theoretically
investigated. Based on the shooting method the quasi-stationary energy
levels and their corresponding linewidths are obtained. By considering the
joint action of the two external fields the linear absorption coefficient is
calculated by means of Fermi’s golden rule and taking into account the
intersubband relaxation. We found that: (i) the linewidth broadening due to
the electron tunneling has an appreciable effect on the absorption spectrum;
(ii) a constant relaxation time adopted in the previous studies could not be
justified even for moderate electric fields, especially in the laser dressed
wells. Our model predicts that the number of absorption peaks can be
controlled by the external applied fields. While in the high-electric fields
the excited states become unbounded due to a significant tunneling of the
electrons, for high laser intensities and low/moderate electric
fields the absorption spectrum has a richer structure due to the
laser-generated resonant states. The possibility of tuning the
resonant absorption energies by using the combined effects of the static
electric field and the THz coherent radiation field can be useful in
designing new optoelectronic devices. 相似文献
12.
J. Jersch F. Demming I. Fedotov K. Dickmann 《Applied Physics A: Materials Science & Processing》1999,68(6):637-641
Time-resolved dependence of the transient current through a ns laser pulse illuminated scanning tunneling microscope (STM)
tip/sample gap in tunneling mode and out of tunneling range is presented. A self-designed fast STM-preamplifier (bandwidth
35 MHz) allows one to resolve the fine structure of the transient signal as well as the observation of some effects that are
undetectable by using conventional low-band preamplifiers. The dependence of the threshold laser pulse intensity, which corresponds
to the beginning of electron emission from tip (in non-tunneling mode), as a function of the tip/sample distance was investigated.
At tip/sample distances from tunnel contact up to approximately 1 μm a linear dependence is found. This behavior is in good
agreement with the theory for field enhancement in a STM tip/sample system. In tunneling mode a ns (fast component) as well
as a μs (slow component) current response was found as a result of the laser pulse illumination. These data suggest the tip
bending to be an important factor in clarifying the thermal/mechanical mechanism of laser-assisted surface nanomodification.
Received: 4 May 1998 / Accepted: 29 January 1999 / Published online: 28 April 1999 相似文献
13.
C. M. Mann T. Nozokido J. J. Chang T. Suzuki K. Mizuno 《International Journal of Infrared and Millimeter Waves》1994,15(11):1867-1881
A 250× scale model of a Schottky diode corner cube mixer designed for operation in the terahertz region has been built and tested. It has been successfully used to measure the embedding impedance presented to the diode at the whisker tip and also determine the impedance of the whisker antenna itself. The results have been input into a computer analysis to determine as to how the performance may be improved. With regards to improving the physical ruggedness of such mixers, a simple equivalent whisker structure has been determined and a new technique that may be used to fabricate a space qualifiable corner cube mixer intended for terahertz operation is disclosed. 相似文献
14.
Calculation of the temperature and thermal expansion of a STM tip heated by a short laser pulse 总被引:1,自引:0,他引:1
A mathematical model for the calculation of the temperature field in a scanning tunneling microscope (STM) tip under laser
illumination is developed. The duration of the laser pulse is a few nanoseconds or shorter. A Gaussian distribution of the
laser light intensity in time and space is assumed. Two different mechanisms of tip heating are taken into account: 1. due
to an enhanced electric field on the tip; 2. due to heating of the side surface of the tip by the focused spot of laser light.
An average tip temperature is calculated using the heat conductivity equation. The enhanced electric field on the tip is calculated
by the method of boundary integral equations.
Received: 20 August 2002 / Revised version: 4 December 2002 / Published online: 19 March 2003
RID="*"
ID="*"Corresponding author. Fax: +49-2551/962-490, E-mail: sklein@fh-muenster.de 相似文献
15.
K. Huber G. Rehm N. Richt 《International Journal of Infrared and Millimeter Waves》1999,20(2):265-278
With increasing frequencies the whisker structures used to contact honeycomb Schottky diodes remain no longer thin compared to wavelength. Whereas the finite thickness and the detailed tip shape do not influence the antenna pattern very much the antenna base impedance depends on these parameters to a great extent. A good impedance matching between Schottky diode and whisker antenna is necessary to optimise mixer or detector performance and can only be achieved if the antenna impedance is known.Antenna base impedances have been simulated numerically and checked by means of scaled model measurements for several whisker shapes. The influence of further parts of the antenna environment, as for example reflectors, has also been investigated. Simulation results have been discussed and compared to theory. Simulation has been found out to be a reliable tool for the determination of base impedances of almost arbitrarily shaped whisker antennas. 相似文献
16.
An analysis is made of the ionization of deep impurity centers by high-intensity far-infrared and submillimeter-wavelength
radiation, with photon energies tens of times lower than the impurity ionization energy. Within a broad range of intensities
and wavelengths, terahertz electric fields of the exciting radiation act as a dc field. Under these conditions, deep-center
ionization can be described as multiphonon-assisted tunneling, in which carrier emission is accompanied by defect tunneling
in configuration space and electron tunneling in the electric field. The field dependence of the ionization probability permits
one to determine the defect tunneling times and the character of the defect adiabatic potentials. The ionization probability
deviates from the field dependence e(E) ∝ exp(E
2/E
c
2
) (where E is the wave field, and E
c is a characteristic field) corresponding to multiphonon-assisted tunneling ionization in relatively low fields, where the
defects are ionized through the Poole-Frenkel effect, and in very strong fields, where the ionization is produced by direct
tunneling without thermal activation. The effects resulting from the high radiation frequency are considered and it is shown
that, at low temperatures, they become dominant.
Fiz. Tverd. Tela (St. Petersburg) 39, 1905–1932 (November 1997) 相似文献
17.
18.
Femtosecond laser pulse shaping techniques have been restricted to propagating transverse electromagnetic waves. We present a scheme for pulse shaping of optical near fields based on the excitation of longitudinal electromagnetic fields with polarization-shaped light pulses. By solving Maxwell's equations for a model nanostructure, i.e., a scanning tunneling microscope tip, with help from the boundary-element method, we demonstrate that the electric field vector oscillates in a complex yet controllable fashion in three dimensions. Many applications are envisioned because literally another dimension in the optimal control of light-matter interaction is accessible. 相似文献
19.
C. Fumeaux W. Herrmann H. Rothuizen P. De Natale F. K. Kneubühl 《Applied physics. B, Lasers and optics》1996,63(2):135-140
Mixing experiments with 30 THz CO2-laser radiation as well as the detection of 35 ps 30 THz pulses of an optical-free-induction-decay CO2-laser system have been performed with the first nanometer thin-film Ni-NiO-Ni diodes with a minimum contact area of 0.012 µm2. Difference frequencies up to 85 MHz were detected by mixing two different CO2-laser beams coupled to the diode with an integrated bow-tie antenna. The dependence of the beat signal on bias voltage, laser power and polarization of the infrared laser radiation was determined. 相似文献
20.
Schwirzke F. Hallal M.P. Jr. Maruyama X.K. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1993,21(5):410-415
When an increasing diode voltage is applied, enhanced field emission of electrons begins from a growing number of small spots or whiskers on the cathode surface. This stimulates desorption of weakly bound adsorbates from the surface of a whisker. As the diode voltage increases, the 100-V equipotential surface moving toward the cathode is met by the desorbed neutrals moving away from the cathode, resulting in sharp risetime for the onset of ionization of desorbed neutrals by field-emitted electrons. Positive ions produced in the ionization region a few microns from the electron emitting spot are accelerated back to it. This bombardment leads to surface heating of the spot. The onset of breakdown by this mechanism requires much less current than the Joule heating mechanism. The localized buildup of plasma above the electron emitting spot leads to pressure and electric field distributions that ignite unipolar arcs. The high current density of the unipolar arc and the associated surface heating by ions result in the explosive formation of cathode spot plasma 相似文献