Volume 14, Issue 3, 01 February 1969
Index of content:
14(1969); http://dx.doi.org/10.1063/1.1652732View Description Hide Description
A maximum in the differential resistance versus applied bias relationship of metal‐semiconductor contacts is predicted to occur when current flow is predominantly by thermionic‐field (thermally excited tunnel) emission. The predicted resistance peaks are generally asymmetrical with respect to voltage and may occur on either side of zero bias. The peak location has only an indirect correlation with the Fermi kinetic energy in the semiconductor. The theoretical approach is generally applicable to any metal‐semiconductor system when the dominant carrier flux is associated with the tail of a Fermi‐Dirac distribution. The theory is in reasonable agreement with recent experimental resistance measurements on Cr–Si Schottky barrierdiodes at 77°K.
14(1969); http://dx.doi.org/10.1063/1.1652733View Description Hide Description
Anomalous electrical conductivity phenomena have been observed in thin tetracene films sandwiched between metalelectrodes. The resistivity of the tetracene layer is observed to change from a high value (``off state'') to a low value (``on state'') upon the application of voltage. In the ``on state'' the resistivity is both temperature insensitive and photoinsensitive. A preliminary interpretation of this behavior is presented.
14(1969); http://dx.doi.org/10.1063/1.1652734View Description Hide Description
In this experiment 2.8‐MeV protons have been implanted into single‐crystal 〈111〉‐oriented silicon at room temperature. Measurements of the damage created as a function of proton fluence show a linear dependence for fluences from 8.2 × 1011 to 4 × 1013 protons/cm2. The resulting lattice defects are found to be positively charged in the presence of a high electric field. The defect introduction rate is found to be 9.1 × 10−3 net (+) defects/2.8‐MeV proton. Carrier trapping effects of the damage in low to medium electric fields are negligible to within the sensitivity of the experiment. The technique for making the above measurements is explained in detail.
14(1969); http://dx.doi.org/10.1063/1.1652735View Description Hide Description
Photoreversible absorption changes have been found in additively colored La‐, Ce‐, Gd‐, or Tb‐ doped CaF2. Results are shown for one of these, Ce:CaF2, in which both the trivalent and divalent rare‐earth absorptions are identifiable. These results suggest a charge transfer between the rare earth and a defect center produced by additive coloration.
14(1969); http://dx.doi.org/10.1063/1.1652736View Description Hide Description
Deflection of laser light has been used to measure room‐temperature acoustic surface wave propagation losses in LiNbO3 at both 1 and 2 GHz. In addition, surface wave delay lines operating at 1 GHz using fundamental frequency interdigital transducers and at 2 and 3 GHz using 3rd and 5th harmonic frequencies are described.
14(1969); http://dx.doi.org/10.1063/1.1652737View Description Hide Description
We have directly measuredacoustic wave amplification of shear waves in high mobility InSb in the frequency range 0.5–2.0 GHz. At 1 GHz we have observed 10 dB net terminal gain. We find good agreement with the modified theory of White in the high magnetic field region where the acoustic wavelength λ is much larger than the Larmor radius of the electrons. In the low magnetic field limit it is necessary to use the Boltzmann transport equation approach of Spector; in this case, good agreement with the observed behavior is obtained. This effect is shown to be responsible for the two‐mode threshold behavior for acoustoelectric domain oscillations in InSb.
14(1969); http://dx.doi.org/10.1063/1.1652738View Description Hide Description
Ultrathin (∼ 1 μm) Cd(SeS) platelets are excited with a mode‐locked He–Ne laser and are shown to lase with a measured time delay of ∼ 10−9 sec. The measured delay agrees with the time required to redistribute optically generated electron‐hole pairs uniformly through the sample thickness and to the proper density (1018/cm3) to form excitons.
14(1969); http://dx.doi.org/10.1063/1.1652725View Description Hide Description
Experiments are described in which the energy spectra of 1‐MeV He+ ions backscattered 150° from a silicon surface have been used to identify and measure the contamination on the surface. Contamination from hydrofluoric acid solutions containing gold and copper in concentrations ranging from 0.1 to 100 parts per million was studied. Less than one half a monolayer of contaminant was easily resolved and identified. Coverages of this order were obtained from solutions containing 0.1 ppm of the contaminant.
14(1969); http://dx.doi.org/10.1063/1.1652726View Description Hide Description
Alternating currentconductance and capacitancemeasurements are made on aqueous solution‐silver chloride‐aqueous solution couples as a function of frequency. The frequency dependence of the measuredconductance and capacitance is found to agree with the calculated results based on a space‐charge‐limited ac conduction model.
14(1969); http://dx.doi.org/10.1063/1.1652727View Description Hide Description
Electromagneticsurface waves on magnetized single crystalline YIG and polycrystallineferrite rods were studied. In particular, the dynamic mode surface waves, which do not exist in the magnetostatic analysis, were measured by the disturbing body technique in a surface waveresonator. The measured results agree very well with the exact analysis. We believe this is the first report in which the existence of dynamic mode surface waves is experimentally demonstrated.
UNEXPECTED EFFECTS OF FORCED HIGH NUCLEATION DENSITIES BY FLASH EVAPORATION OF GOLD ON NaCl and KCl SUBSTRATES14(1969); http://dx.doi.org/10.1063/1.1652728View Description Hide Description
Gold was deposited slowly and simultaneously on air‐cleaved NaCl and vacuum‐cleaved NaCl and KCl crystals, portions of which had been covered with about 20 Å of gold by simultaneous flash deposition prior to the commencement of slow deposition 320°C substrate temperature. The epitaxy of gold on vacuum‐cleaved NaCl substrates is enhanced by the higher nucleation density resulting from the flash deposition while the latter causes a deterioration of the epitaxy on both vacuum‐cleaved KCl and air‐cleaved NaCl substrates. It is proved that no effective substrate contamination results from the flash evaporation. It is suggested that a critical or epitaxialnucleation density exists for each deposit‐substrate system.
14(1969); http://dx.doi.org/10.1063/1.1652729View Description Hide Description
A grating pair, which is capable of detecting the quadratic phase term (linear frequency sweep) and compressing the ultrashort pulses from a mode‐locked Nd‐glass laser has been used in conjunction with second harmonic generation techniques to reveal a periodic wobble of the consecutive pulse envelopes. An asymmetry in the picosecond pulse envelope has been detected by scanning the pulses with their compressed counterparts in a fluorescing dye cell excited by two‐photon absorption.
14(1969); http://dx.doi.org/10.1063/1.1652730View Description Hide Description