摘要:

Self‐alignment of InGaAs quantum dots was achieved by growing the quantum dots on the multiatomic steps in metalorganic chemical vapor deposition. In this technique, first GaAs epilayer with multiatomic step structures along straight lines was grown on a vicinal GaAs substrate under appropriate growth conditions. Then, the InGaAs quantum dots were grown selectively on the multiatomic step edges using strain effects. This growth technique results in spontaneously aligned InGaAs quantum dots without any preprocessing technique prior to the growth. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114133

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We demonstrate single electron charging in fully controllable nanoscale quantum devices at temperatures above 4 K. Hitherto, single electron devices operating at ‘‘high’’ temperatures have been two‐terminal, having no control electrode, whereas fully tunable structures such as quantum dots have only shown charging effects at temperatures of 4 K or less. We have fabricated ultrasmall quantum dots on modulation doped heterostructures where the two‐dimensional electron gas is less than 30 nm from the surface. Dots with lithographic diameter 150 nm show Coulomb oscillations up to temperatures of 7 K. Higher temperature operation allows potential applications to be considered without the need, for example, of a dilution fridge. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114134

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The effects of liquid methanol on the photoluminescence intensity and FTIR spectra of red and blue emitting porous silicon were investigated. Hydrogen passivated red emitting samples exhibit quenching and recovery of photoluminescence intensity and broadening of the Si‐Hxstretch bands upon exposure to liquid methanol. Oxygen passivated red emitting samples exhibitnophotoluminescence quenching. The sensitivity of the red emitting sample is due to the microstructure of porous silicon at the surface and the ability of methanol to penetrate the pores. The blue photoluminescence of thermally oxidized samples is quenched upon exposure to methanol. This is attributed to the solvent’s ability to change the surface passivation which modifies existing traps and introduces competitive recombination channels for electrons. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114135

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have designed and prepared a T‐shaped GaAs edge quantum wire (T‐QWR) structure with AlAs barriers by cleaved edge overgrowth method. Three photoluminescence (PL) peaks have been observed and their origins are identified using the spatially resolved PL technique. The effective binding energy of carriers in this T‐QWR is precisely determined as the energy spacing between T‐QWRs and the adjacent QWs. When the well width of constituent QWs was 5 nm, the effective binding energy is found to be as large as 35 meV, which is far beyond the thermal energykTat room temperature. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114136

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have prepared electrically tunable microwave resonators incorporating superconducting YBa2Cu3O7−x(YBCO) and paraelectric SrTiO3(STO) layers on LaAlO3substrates. The top YBCO layer for each sample was patterned into a 8 mm long coplanar transmission line with a 40 &mgr;m gap and a 20 &mgr;m center line width. The microwave transmission through the coplanar transmission line exhibits resonances corresponding to standing microwaves along the coplanar transmission line. These resonances are modulated by applying a bias voltage between the center line and the ground planes. Samples with a 0.5 &mgr;m thick (2 &mgr;m thick) bottom STO layer show, for a resonance at around 8 GHz (5 GHz), a frequency modulation of about 4% (24%) and a quality factorQof about 200 (50) under 100 V bias at 80 K. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114137

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We describe an effective method for discovery of new superconductors, which combines phase‐spread alloy thin film preparation with a magnetic field modulated (MFM) microwave absorption technique. The MFM technique can detect superconductivity in YBa2Cu3O7−&dgr;volumes as small as 5×10−11cm3. As an illustration, PrxGd1−xBa2Cu3O7−&dgr;thin films with varyingxwere simultaneously grown on the same substrate using a phase‐spread alloy technique. The onset temperature determined from the microwave absorption agrees with resistivity, Auger spectroscopy, and energy‐dispersive x‐ray microanalysis data. When phase‐spread Lax(NiB)1−xNyfilms (0<x<1) were grown at several different N partial pressures and temperatures, no superconductivity was detected except that of pure La. In contrast, superconductivity was detected in Yx(NiB)1−xCyfilms grown on MgO. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114138

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have studied the flux pinning behavior ofBi2Sr2CaCu2Oxmulticrystalline samples using a magneto‐optical flux observation method. When a magnetic field is applied parallel to theabplane, we find low flux density regions at the intersections of small angle grain boundaries. The flux density distribution can be explained by considering both flux pinning at the small angle grain boundaries and the intrinsic pinning effect at the BiO layers. High resolution electron microscopy observations show that amorphous patches with columnar structure exist at the small angle grain boundaries (<20°), while other defects such as misfit dislocations and distorted microstructures appear at general grain boundaries. The fact that flux pinning only occurs at small angle grain boundaries (<20°) indicates that the columnar amorphous structures could act as flux pinning centers. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114139

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Fine grain BaTiO3thin films with a grain size ranging between 100 and 1000 A˚ were deposited using the reactive partially ionized beam deposition technique at 550–600 °C. A metal/insulator/metal structure of these materials was fabricated and the dielectric response was measured up to 40 GHz using a network analyzer. It is shown that these films are not ferroelectric. However, these films show a dielectric relaxation in the frequency interval between several MHz and 1 GHz. We propose that this indicates a relaxation mechanism not related to the ferroelectric domain walls. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114140

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

An organosilane monolayer was formed from a precursor vapor (trimethylchlorosilane, TMCS) onto the surface of silicon oxide (SiOx) nanopatterns surrounded by hydrogen‐terminated silicon (Si–H). The nanopattern was fabricated with a resolution of 20 nm by scanning probe anodization, that is, localized anodization induced beneath the tip of a scanning probe microscope. The area‐selectivity arises from the difference in the chemical reactivity of the vapor between the SiOxand Si–H surfaces. The TMCS‐coated SiOxpatterns showed a resistivity to chemical etching with an aqueous solution of ammonium fluoride and hydrogen peroxide. Lateral force microscopy with an organosilane‐coated probe also indicated the presence of the monolayer on SiOxthrough a friction force contrast between the monolayer‐coated and uncoated regions. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114141

出版商:AIP    

年代:1995

数据来源: AIP