摘要:

Electrooptic spectroscopy of an antiferroelectric liquid crystal is carried out over a range of frequencies from 1 Hz to 100 kHz. In the antiferroelectricSmCAphase two relaxation processes are found, one at the fundamental frequency of a mode and the second at twice the frequency of a different mode. A comparison of the results of the electro-optic spectroscopy with a theoretical study of the motion of the director of an antiferroelectric helix subject to a weak alternating field enables a determination of the origin of the relaxation processes in antiferroelectric phases. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121147

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Controlled spontaneous lifetimes are demonstrated in InGaAlAs/GaAs quantum dots confined in planar microcavities. Due to their independent and spectrally sharp light emission, the quantum dot emitters provide an excellent means for studying the spontaneous lifetime dependence on microcavity tuning, while maintaining experimental parameters such as temperature and pump intensity constant. The measured lifetime changes are compared with calculated results and show good agreement. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121148

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Narrow-band spectrally selective image detection based upon the resonance ionization of mercury atoms in a low pressure cell is described. Image dimensions and intensities were measured versus the wavelength of ionizing laser radiation and the dependence upon the voltage applied to electrodes was studied. The position sensitive image of the electron beam, created by two-step resonance photoionization of mercury, was studied when the detected laser beam was scanned spatially. A distorting influence of space charge due to positive mercury ions on the electron beam image was observed. Means of eliminating these distortions are discussed. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121149

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We present results of transmittance measurements on periodic layers ofAg/MgF2at optical and microwave frequencies. These one-dimensional, photonic band gap materials exhibit transparency bands at optical frequencies and a huge stop band that extends throughout the near-IR to microwave frequencies and beyond. A unique feature of these metal/dielectric photonic band gap (MD–PBG) materials is that the overall transmittance in the pass band may increase as more periods are deposited. The center frequency, width, and sharpness of the pass bands are adjustable and generally depend on the thickness of the layers and the number ofAg/MgF2periods. These simple periodic structures have applications as sensor and eye protection devices, heat reflecting windows, ultraviolet blocking films, and transparent electrodes for light emitting diodes and liquid crystal displays. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121150

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We report on the photorefractive properties of thermally stable polymer composites based on the dye 2,N,N-dihexylamino-7-dicyanomethylidenyl-3,4,5,6,10-pentahydronaphthalene. At an applied field of 50 V/&mgr;m, we have achieved a dynamic range of&Dgr;n=8.5×10−3and a net two-beam coupling gain of202 cm−1.The diffraction efficiency peaks at an applied field of 28 V/&mgr;m, giving an external diffraction efficiency of 71&percent;. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121187

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Using GaAs based quantum well infrared photodetectors (QWIPs) with either GaAs or InGaAs wells, we experimentally investigate the accuracy of the polarization selection rule for conduction band intersubband transitions. We employ a device structure and a light coupling geometry where the parasitic light scattering is negligible. The experiments imply that the selection rule is followed to an accuracy of 0.2&percent; for a 8.1 &mgr;m QWIP with GaAs wells; this degrades to 3&percent; for a 4.6 &mgr;m QWIP withIn0.1Ga0.9Aswells. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121151

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

In the present investigation, we have studied the effect of electric field on the growth of carbon nanotubules. Different electric fields corresponding to 3, 6, 9, 15, and 21 V have been applied during the growth of the tubules. The estimate of the electric field corresponding to these voltages cannot be precisely evaluated in view of only approximately defined electrode dimensions. It has been observed that the application of electric field leads to the agglomerates (bundles) of nanotubules. The size, length, and alignment of these bundles varies with the strength of the applied electric field. The best results have been obtained with electric field corresponding to 6 V where the as-formed tubules are in parallel alignment and exist as bundles. As the electric field is increased, the alignment of tubules in the bundle becomes randomly oriented. The degree of randomness increases with increase of electric field after its optimum value corresponding to 6 V. The parallel alignment of the graphitic tubules is thought to result due to orientation of the tubule axis along the direction of the applied electric field corresponding to an optimum value (which for the present case is 6 V) of the impressed voltage. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121152

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A group of well-defined exciton transitions from the localized states were observed inZnSe-Zn0.75Cd0.25Sedouble-superlattice structure. The photoluminescence and photoreflectance have been employed to study the subband transitions at low temperatures. At 1.4 K, except the two ground states and two higher subbands ofn=1light-hole andn=2heavy-hole excitonic transitions, other four peaks (A, B, C, and D) also were observed in wider-well superlattice. Those peaks were attributed to the excitonic transitions fromn=2heavy-hole subband due to the fluctuation of well-barrier interface. Another localized excitonic transition from narrower-well superlattice appeared as increasing the modulated intensity in photoreflectance spectra. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121153

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The compressibility of wurtzitic boron nitride(wBN)taken in mixture with cubic BN has been measured at room temperature up to 66 GPa, using a diamond anvil cell and powder diffraction of synchrotron radiation. From the obtained pressure-volume relation forwBNthe isothermal bulk modulus ofB0=375±9 GPaand its first pressure derivative ofdB0/dp=4.9±0.7have been calculated indicating that this phase has nearly the same compressibility ascBN(B0=377±4 GPaanddB0/dp=4.1±0.2). Thermodynamic calculations using our findings onwBNequation of state have shown that wurtzitic boron nitride is metastable over the whole ranges of pressures and temperatures. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121186

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We report the results ofin situarsenic doping in HgCdTe layers grown by molecular beam epitaxy (MBE). Arsenic incorporation was carried out by two mechanisms called conventional doping and planar doping. The obtained results indicate that for both mechanisms, after Hg anneal, arsenic was successfully incorporated as an acceptor during the MBE growth. Secondary ion mass spectrometry and Hall-effect measurements before and after Hg annealing were used to characterize arsenic activity in the grown layers. Close to 100&percent; acceptor doping efficiency with arsenic has been obtained on these MBE grown layers up to total arsenic concentrations of approximately2×1018 cm−3,which is more than sufficient for a wide range of infrared devices. At much higher total arsenic concentrations, electrical activity falls off drastically as the doping level saturates. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121154

出版商:AIP    

年代:1998

数据来源: AIP