David Jurbergs

Silicon nanocrystals with ensemble quantum yields exceeding 60

Silicon nanocrystals with diameters of less than 5nm show efficient photoluminescence at room temperature. For ensembles of silicon quantum dots, previous reports of photoluminescence quantum yields have usually been in the few percent range, and generally less than 30%. Here we report the plasma synthesis of silicon quantum dots and their subsequent wet-chemical surface passivation with organic ligands under strict exclusion of oxygen. Photoluminescence quantum yields exceeding 60% have been achieved at peak wavelengths of about 789nm.

Environmental reactivity characteristics of K3C60 and YBa2Cu3O7-x high-temperature superconductor thin films

Abstract Recently the environmental reactivity behavior of the copper-oxide superconductors has been studied and the following reactivity trends have been established: YBa 2 Cu 3 O 7 > Tl 2 Ba 2 Ca 2 Cu 3 O 10 > Bi 2 Sr 2 CaCu 2 O 8 ≥ La 1.85 Sr 0.15 CuO 4 > Nd 1.85 Ce 0.15 CuO 4 > Nd 1.85 Th 0.15 CuO 4 In this paper, the degradation characteristics of the most reactive cuprate material, YBa 2 Cu 3 O 7 , are compared with those of the fulleride superconductor, K 3 C 60 . Conductivity vs. exposure time measurements acquired for thin film samples in eight different environments are utilized to estimate the degradation rates for the superconductor materials. The cuprate superconductor remains relatively stable in the presence of dry nitrogen, dry oxygen, vacuum, air and acetonitrile environments, but degrades rapidly upon exposure to water solutions. Samples of K 3 C 60 are also unreactive in dry nitrogen and under vacuum, but decompose extremely rapidly upon exposure to dry oxygen, air, acetonitrile or water solutions resulting in the complete loss of the superconducting properties.

Antenna‐coupled high‐Tc bolometers for visible and near‐infrared detection using organic dyes as light‐harvesting layers

Antenna‐coupled high‐Tc bolometers fabricated from YBa2Cu3O7−δ thin films have been prepared using molecular organic dyes. Light‐harvesting layers derived from these visible and near‐infrared absorbers have been utilized to produce detectors which exhibit wavelength‐selective response characteristics in the visible and near‐infrared spectral regions. Using such hybrid structures, initial studies documenting efficient energy transfer between molecular dye layers and superconductor surfaces have been completed.

Electrochemical and optical devices based on molecule/high-Tc superconductor structures

Through the use of electrochemical and vacuum deposition techniques, molecular materials are combined with high-T c superconductors in order to fabricate two new classes of hybrid devices. In the first class of devices, electrochemical methods are utilized to deposit polypyrrole onto YBa 2 Cu 3 O 7-δ structures. With such systems, experiments are conducted which explore electron transfer events which occur between the conductive polymer and the high-T c superconductor at temperatures both above and below T c . Here it is found that the transition temperature (T c ) of the superconductor is depressed dramatically when polypyrrole is oxidized to its conductive form and that it returns to a value which is close to the original value upon reduction of the polypyrrole layer to the neutral, nonconductive form. In the second class of devices, the ability of molecular dye layers to affect the optical properties of YBa 2 Cu 3 O 7-δ photodetectors is demonstrated. By examining changes in the optical and electronic properties of these systems, energy transfer processes which occur between molecules and high-T c superconductors are explored. Here it is found that dye layers are able to act as antenna for optical radiation at those wavelengths which the dye layer absorbs light most strongly.

Dye-coated superconductor structures as optical sensors

The preparation and characterization of a new generation of hybrid optical sensors fabricated from high-temperature superconductor thin films coated with organic dye overlayers is described herein. These dye-coated superconductor structures respond selectively to those wavelengths of light which are absorbed strongly by the molecular dye. Methods for preparing such optical sensors are details. Scanning electron microscopy, resistivity vs. temperature and optical measurements are exploited to characterize the hybrid devices.

Fabrication of organic dye-coated high-Tc superconductor optical devices: Interface chemistry and properties

The preparation and characterization of a new generation of optical sensors fabricated from high-temperature superconductor (HTSC) thin films is reported herein. These new hybrid devices are prepared using HTSC thin films which are coated with organic dye overlayers. These systems have been shown to respond selectively to those wavelengths which are absorbed strongly by the molecular dye. Methods for fabricating the superconductor element and depositing the dye layer are discussed. Moreover, scanning electron microscopy and resistivity versus temperature measurements are utilized to characterize these hybrid structures.

Color selective optical sensors based on dye/superconductor assemblies

This paper describes the design, construction and operation of hybrid dye/superconductor optical sensors. A reflective mirror layer positioned between the dye and superconductor components is used as a means to reject light signals that are not absorbed strongly by the dye. On resonance signals are shown to couple effectively with the underlying superconductor where they evoke measurable responses. These structures form the basis for color selective optical sensors.

Optical studies of dye-coated superconductor junctions

The preparation and characterization of a new generation of optical sensors fabricated from high-temperature superconductor (HTSC) thin films is reported herein. These new hybrid devices are fashioned using HTSC thin films which are coated with organic dye overlayers. These systems are shown to respond selectively to those wavelengths which are absorbed strongly by the molecular dye. Methods for fabricating the superconductor element and depositing the dye layer are discussed. Moreover, resistivity versus temperature measurements before and after dye deposition are utilized to characterize these hybrid structures. The unique optical response properties of these hybrid sensors are also detailed.

Molecule/High-Tc Superconductor Structures as Optical Sensors

Abstract By combining patterned high-temperature superconductor thin films with overlayers of molecular materials, a new generation of hybrid optical sensors is obtained. Here, the ability of molecular dye layers to influence the light sensing properties of a high-Tc superconducting bolometer is described. These dye-coated devices are shown to display selective optical responses which are dependent on the properties of the molecular layer. Two different types of molecular absorbing layers prepared from molecular dyes and conductive polymers are examined in this paper Furthermore, the prospects for producing wavelength tunable detectors from hybrid conducting polymer/superconductor structures are addressed.