Spin-on spintronics: ultrafast electron spin dynamics in ZnO and Zn₁-xCoxO sol-gel films.

We use time-resolved Faraday rotation spectroscopy to probe the electron spin dynamics in ZnO and magnetically doped Zn(1-x)Co(x)O sol-gel thin films. In undoped ZnO, we observe an anomalous temperature dependence of the ensemble spin dephasing time T(2), i.e.

Electron transfer between colloidal ZnO nanocrystals.

Colloidal ZnO nanocrystals capped with dodecylamine and dissolved in toluene can be charged photochemically to give stable solutions in which electrons are present in the conduction bands of the nanocrystals. These conduction-band electrons are readily monitored by EPR spectroscopy, with g* values that correlate with the nanocrystal sizes. Mixing a solution of charged small nanocrystals (e(-)(CB):ZnO-S) with a solution of uncharged large nanocrystals (ZnO-L) caused changes in the EPR spectrum indicative of quantitative electron transfer from small to large nanocrystals.

Charge-controlled magnetism in colloidal doped semiconductor nanocrystals.

Electrical control over the magnetic states of doped semiconductor nanostructures could enable new spin-based information processing technologies. To this end, extensive research has recently been devoted to examination of carrier-mediated magnetic ordering effects in substrate-supported quantum dots at cryogenic temperatures, with carriers introduced transiently by photon absorption. The relatively weak interactions found between dopants and charge carriers have suggested that gated magnetism in quantum dots will be limited to cryogenic temperatures.

Colloidal ZnO quantum dots in ultraviolet pillar microcavities.

Three dimensional light confinement and distinct pillar microcavity modes in the ultraviolet have been observed in pillar resonators with embedded colloidal ZnO quantum dots fabricated by focused ion beam milling. Results from a waveguide model for the mode patterns and their spectral positions are in excellent agreement with the experimental data.

Ultrafast spin dynamics in colloidal ZnO quantum dots.

Time-resolved Faraday rotation measurements in the ultraviolet have been performed to reveal the ultrafast spin dynamics of electrons in colloidal ZnO quantum dots. Oscillating Faraday rotation signals are detected at frequencies corresponding to an effective g factor of g = 1.96.

Room-temperature electron spin dynamics in free-standing ZnO quantum dots.

Conduction band electrons in colloidal ZnO quantum dots have been prepared photochemically and examined by electron paramagnetic resonance spectroscopy. Nanocrystals of 4.6 nm diameter containing single S-shell conduction band electrons have g(*)=1.

Stable photogenerated carriers in magnetic semiconductor nanocrystals.

We report the preparation and investigation of charged colloidal Co2+:ZnO and Mn2+:ZnO nanocrystals. Although both charged and magnetically doped colloidal semiconductor nanocrystals have been reported previously, colloidal charged and magnetically doped semiconductor nanocrystals as described herein have not. Conduction band electrons were introduced into colloidal ZnO diluted magnetic semiconductor (DMS) nanocrystals photochemically, and the resulting TM2+-e-CB interactions were observed by electron paramagnetic resonance spectroscopy (TM2+ = Co2+ or Mn2+).