摘要:

The bulk trap state properties of a naphthyl-substituted benzidine derivative (NPB) and tris-8-(hydroxyquinoline) aluminum(Alq3)have been measured using thermally stimulated luminescence (TSL). The TSL spectra for both organic materials show significant trap distributions over the temperature range from 8 to 300 K. Using a general order TSL expression, the four peaks in NPB were modeled with trap states centered from 0.20 to 0.05 eV.Alq3has three TSL peaks over the temperature range, with the peak at 156 K modeled as a distribution of trap states from 0.25 to 0.13 eV. For both materials, the trapping mechanism involves a combination of first and second order emission. NPB andAlq3have trap states sufficiently deep to influence the carrier transport and recombination process in bilayer organic based light emitting. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122173

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We report emission from individual quantum dots excited by tunneling current injection using a scanning tunneling microscope (STM). By scanning the STM tip above the self-assembled InAs quantum dots, a spatially resolved scanning tunneling luminescence (STL) image was measured, which contained a fluorescent circular region with a diameter of 50 nm originating from a single InAs quantum dot. It was found that the spatial resolution of the STL system was about 40 nm, which is mainly due to lateral diffusion of holes injected into a GaAs capping layer grown at low temperature(480 °C).We also obtained STL spectra with a sharp single luminescent peak from a single InAs quantum dot. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122174

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have demonstrated an excitation method to produceKr2*by using soft x rays emitted from a laser-produced plasma. We have found thatKr2+ions were directly produced by photoionization of Kr atoms by soft x rays. The behavior ofKr2*emission was similar to that ofKr2+,indicating fast relaxation processes to produceKr2*fromKr2+during the plasma producing laser pulse. Numerical results based on a photoionization model of Kr reproduced the experimental results, which verified the production ofKr2*initiated by the photoionization of Kr. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122175

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We proposed and experimentally studied a technique of vibration object monitoring. The technique is based on self-diffraction of the speckle pattern on the adaptive correlation filter recorded in photorefractiveBi12TiO20crystal. This filter is recorded owing to the light-induced scattering known as fanning effect. The proposed technique is as sensitive as interferometric systems and it is very simple for implementation: neither reference nor readout beam is needed for operation. It is shown that the system has a linear response on the lateral displacement of the object surface and its dynamic range can be easily varied depending on experimental conditions. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122216

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

An apertureless near-field optical-imaging method is presented that achieves high spatial resolution as well as a∼4000-fold increase in detection sensitivity, by exploiting the highly localized enhanced near-field interactions between the sample (e.g., Au nanospheres) and a sharp atomic force microscope tip under evanescent laser field illumination. This represents a general method for optical imaging at⩽2 nmspatial resolution, and is applicable to both resonant (i.e., scattering) as well as nonresonant (i.e., fluorescence, Raman, etc.) spectroscopic methods. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122176

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Infrared reflectivity measurements have been carried out on samples with structures of GaN/sapphire andAlxGa1−xN/GaN/sapphireas well as sapphire substrates. Analyses of the reflectance data of sapphire using the Kramers–Kronig technique and fitting of the reflectance spectra of GaN andAlxGa1−xNsamples using analytical expressions have been made. The high-frequency dielectric constant&egr;∞and the transverse phonon frequency&ohgr;TO,are found to vary from 5.15 to 4.2 and from 559.7 to 586.4 cm−1, respectively, when the compositionxis varied from 0 to 0.35 at room temperature. The E2 mode, which arises from the disordered state of the alloys, has been observed in the reflectivity spectrum ofAlxGa1−xN,and the intensity of the peak is enhanced by increasing the Al content. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122177

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

An injection distributed-feedback vertical-cavity surface-emitting laser (VCSEL) with tunnel junctions served as quasi-Ohmic intercontacts (tunnel-junction-connected distributed-feedback VCSEL) is proposed. A periodic structure of vertically stacked double-heterostructure laser diodes connected by low-resistance tunnel junctions forms a vertical distributed-feedback (DFB) laser medium. To minimize the threshold, the DFB structure is placed in a Fabry–Perot cavity designed to match gain layers with the maximums of the optical mode, and the tunnel junctions—with its minimums. The passive regions with tunnel junctions provide effective vertical injection into each active region of this multiple-active-region laser. This DFB VCSEL is expected to have an improved performance, specifically, reduced threshold current and heightened output power. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122217

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We discuss the enhancement effect of the third-order nonlinear response of excitons coupled with cavity modes, on the basis of a self-consistent calculation of response field and induced polarization. It is shown that a single framework is enough to describe the spectral features of nonlinear spectra in both strong and weak coupling regimes, where the splitting of coupled modes (cavity polaritons) in linear response is larger and smaller, respectively, than the widths. In the latter regime, the nonlinear signal is strongest at the bare excitonic resonance, and its enhancement due to the cavity effect is remarkable. In the former regime, on the other hand, the nonlinear signal appears at the energy positions of the coupled modes, whose spectral shape represents the reduction of normal-mode splitting due to the nonlinear effect. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122178

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We report quantitative measurements on the decay of optical absorption at various elevated temperatures in ultraviolet (UV)-irradiatedSiO2glasses doped with Ge. From the Arrhenius plots of decay time constants, the activation energy of theGe E′center in the UV-irradiated glasses has been determined to be2.4±0.3 eV,while the reported activation energy ofGe E′decay in UV-poled glasses is0.4±0.1 eV.The present experimental results strongly suggest that the decay process of theGe E′center induced in UV-irradiated glasses is quite different from that in UV-poled glasses. ©1998 American Institute of Physics.&hthinsp;

ISSN:0003-6951    

DOI:10.1063/1.122179

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

An optical system utilizing the photoinduced dichroism in a bacteriorhodopsin film has been demonstrated for the optical implementation of wavelet transforms. The dichroism, induced by the image of a wavelet filter on a bacteriorhodopsin film leads to polarization rotation of the Fourier components of an image. The polarization-rotated Fourier components of an input scene are analyzed with a polarizer to give the wavelet transform components. The dichroism is induced with beams whose profiles are determined by wavelet filters in order to perform the optical wavelet transform. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122180

出版商:AIP    

年代:1998

数据来源: AIP