摘要:

Germanium surface behavior has become of great interest recently, chiefly for its importance in the understanding of diode and transistor technology. In general, the surface may be treated as an assemblage of allowed electron states occurring in the normally forbidden energy range. A review of the measurements of the electrical properties suggests that there are two distinct types of state. The ``fast'' state has a hole or electron capture time not greater than a microsecond and is chiefly involved in the recombination process. The ``slow'' state has capture times from a millisecond to several minutes and determines the density and type of carrier at the surface. ``Fast'' states are believed to occur at the interface between the germanium and the oxide layer, and their density of about 1011cm−2is determined by the initial surface treatment. ``Slow'' states are associated with the structure of the oxide layer and the gaseous ambient, and have a density greater than 1013cm−2. Since these states determine the conductivity type at the surface, they contribute to surface ``leakage'' in diodes and transistors and, because of their long equilibrium times, to low‐frequency noise. The adsorption of gases such as water vapor, not only controls the density and energy of the ``slow'' states but also leads to possible electrolytic conduction along the surface, in addition to the normal electron flow in the bulk semiconductor.

ISSN:0021-8979    

DOI:10.1063/1.1722317

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

The phase contrast principle has been applied to a telescopic system to produce a simple instrument of high sensitivity for studying inhomogeneities in fluid media. As an example of the power of the method, the phase contrast telescope has been used to study the regions in and around premixed propane gas flames.

ISSN:0021-8979    

DOI:10.1063/1.1722318

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

A method is described for making estimates of the total emissivity of hydrogen in the temperature and pressure ranges where hydrogen atoms predominate under equilibrium conditions. For a typical geometrical depth of 50 cm, and temperatures of the order of 12 500°K and higher, with pressures of the order of 100 atmos and higher, the emissivity approaches unity(&egr;[similar or greater-than]0.95), while for temperatures of the order of 9500°K and lower, with pressures of the order of 10 atmos and lower, the emissivity approaches zero(&egr;[similar or less-than]0.05). The variations of the emissivity between these approximate limits are shown graphically as functions of temperature and pressure with the geometrical depth set at 50 cm. The variation of the emissivity with geometrical depth is also shown graphically at 12 600°K and 20 atmos.

ISSN:0021-8979    

DOI:10.1063/1.1722319

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

An attempt has been made to explain the properties of the ``plasma'' of fluorescent lamps in considerable detail, using the ambipolar diffusion theory of Schottky, modified to include ionization by multiple electron impacts. Ionization is assumed to occur by electron collisions with excited and metastable atoms. The cross section for this process is one of two inaccurately known parameters, which we treat as adjustable constants, occurring in the calculations. The other is the effective diffusion constant for quanta of the resonance line, in the presence of a high‐temperature electron gas.Qualitative agreement of the foregoing theory with experiment is demonstrated for all the derived quantities as functions of the several parameters of the discharge. The magnitudes of the calculated electron temperature, electric field, total light output, and efficiency are also in sufficiently good agreement with experimental values for the lamps of greatest commercial interest to permit extrapolations to be made with reasonable confidence. Optimum agreement of theory with experiment for T‐12 lamps is obtained using a mean life time of ultraviolet photons in the discharge 3.6 times that employed by Kenty for diffusion in un‐ionized vapor, and with a value 3.3 for the ratio of cross section for ionization of excited state to that of the ground state.

ISSN:0021-8979    

DOI:10.1063/1.1722320

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

A simple model of the sliding process is developed in which the junctions are of the same size, but have different shear strengths, and, using an artificially obtained friction trace, it is shown that the size of the junctions may be deduced through a simple autocorrelation analysis. Applied to real friction traces obtained at slow sliding speeds, the technique gives an average junction diameter of 9.10−4cm, in good agreement with previous estimates, while a different statistical method gives a value of 5.10−4cm.

ISSN:0021-8979    

DOI:10.1063/1.1722321

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

A fundamental study of graphite sliding contacts shows that atmospheric concentrations of only a few parts per million of the larger organic molecules are sufficient to prevent the severe wear of graphite which occurs in a dry atmosphere. The experimental results suggest roughly the empirical rule that the minimum relative ``humidity'' of a vapor for effective lubrication decreases logarithmically with chain length in the region 5 to 15 A.

ISSN:0021-8979    

DOI:10.1063/1.1722322

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

Theories of rough surface reflection by Rayleigh, Eckart, and Brekhovskikh are utilized to calculate the dependence, on surface and radiation parameters, of the amplitudes of reflected radiation when an acoustic beam is incident on a pressure‐release surface with sinusoidal corrugations. The results of these theories are compared, with emphasis on the assumptions used. Experimental results for the reflection of an underwater acoustic beam from this type of surface are presented and compared with each of the theories. The best agreement between theory and experiment is obtained for surfaces of small slope, indicating that this criterion is basic to the validity of the theories. However, surprisingly similar results are obtained for surfaces of large slope. The theories seem to predict the behavior of the lower orders of reflection more closely than that of the higher orders. Good agreement between theory and experiment is obtained for directions of reflection and for cut‐off frequencies.

ISSN:0021-8979    

DOI:10.1063/1.1722323

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

A simple and inexpensive vacuum procedure has been employed to grow copper single crystals by the Bridgman method. Crystals grown at a lowering rate of 2 inches per hour have a high degree of perfection as indicated by the presence of Kikuchi lines on electron diffraction patterns. The perfection varies along the length of the crystal, that portion freezing last being the most perfect. It is suggested that this variation in perfection along the length will occur to some degree in all unseeded crystals made by the Bridgman method because of the greater supercooling that occurs when the first metal freezes.

ISSN:0021-8979    

DOI:10.1063/1.1722324

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

The expansion coefficients of specimens under tensile stress and after the stress has been removed have been measured for three steels (0.20, 0.40, 0.80% carbon) and for two types of Invar. If the applied stress is below the elastic limit the change in expansion coefficient &agr;, with stress &sgr; is shown to be given by(∂&agr;/∂&sgr;)T=−1/E2(∂E/∂T)&sgr;, whereEis Young's modulus andTthe temperature; if the stress is removed the expansivity returns to its original value. When the applied stress exceeds the elastic limit, there is a discontinuous change in expansion coefficient, and the expansivity on unloading differs from the original value. The lattice distortion associated with the onset of even a slight plastic strain (2×10−6) appears sufficient to change the expansion coefficient both under load and after the load is removed.

ISSN:0021-8979    

DOI:10.1063/1.1722325

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

Recent investigations of the time dependence of electrical breakdown in liquid hydrocarbons have led to a disagreement regarding the influence of molecular structure upon the formative time lag. This paper represents an attempt to resolve the discrepancy, and to determine if possible the significance of the time lag in the breakdown process. The experiments involve the application of rectangular pulses of voltage of variable duration and amplitude to the liquids between hemispherical electrodes.The results of the investigation show definitely that the formative time lag is insensitive to changes in the molecular weight of the hydrocarbon liquid. Consequently, it cannot be associated with the time required for positive ions to cross the spark gap, as has been suggested by recent investigators. Its characteristic dependence upon the electrode separation, however, suggests that it may be mainly a measure of the transit time of an electron or an electron avalanche.

ISSN:0021-8979    

DOI:10.1063/1.1722326

出版商:AIP    

年代:1956

数据来源: AIP