Showing papers by "Christopher B. Murray published in 2004"
TL;DR: In this article, structural and magnetic properties of 3-layer polyethylenimine (PEI) and 4-nanometre Fe58Pt42 nanoparticles were studied using x-ray diffraction, small angle neutron scattering and magnetometry.
Abstract: Chemically ordered, self-assembled FePt nanoparticle arrays with high magnetic anisotropy are considered as a candidate medium for data storage beyond 1 Tbit/in2. We report comprehensive structural and magnetic studies on thin (three-layer) assemblies of polyethylenimine (PEI) and 4 nm Fe58Pt42 nanoparticles using x-ray diffraction, small angle neutron scattering, and magnetometry. We show that prior to annealing FePt nanoparticles in the PEI-FePt assembly consist of a metallic magnetic core surrounded by a weakly magnetic or nonmagnetic shell. High temperature annealing creates the desired L10 chemical ordering and results in high coercivity FePt nanoparticles. However, we find that the high temperatures necessary to establish full chemical ordering leads to particle sintering and agglomeration. Understanding the magnetic and physical properties of these assemblies allows future research directions to be clarified for nanoparticle arrays as data storage media.
42 citations
TL;DR: In this paper, the authors measured the charge and polarizability of 12-nm PbSe nanocrystals on n- and p-type silicon with a 2-nm thermal oxide layer.
Abstract: By use of electrostatic force microscopy, we measure the charge and polarizability of 12-nm PbSe nanocrystals on n- and p-type silicon with a 2-nm thermal oxide layer. Individual nanocrystals show a dielectric constant of >100. In ambient light, the nanocrystals generate static electric fields of magnitudes too weak to be caused by a full elementary charge. These nanocrystals are statically polarized by surface electric fields generated by fixed charges in the oxide substrate. We model this effect quantitatively and assign charge locations in the oxide. Upon 442-nm photoexcitation, we observe some of the nanocrystals (∼35%) photoionize and slowly relax overnight back to their initial states. Just above a charge in the oxide, the surface electric field can approach 108 V/cm.
37 citations
Patent•
22 Nov 2004TL;DR: In this article, a high temperature non-aqueous synthetic procedure for the preparation of substantially monodisperse IV-VI semiconductor nanoparticles is provided, which includes introducing a first precursor selected from the group consisting of a molecular precursor of a Group IV element and a molecular pre-group VI element into a reaction vessel that comprises at least an organic solvent to form a mixture.
Abstract: A high temperature non-aqueous synthetic procedure for the preparation of substantially monodisperse IV-VI semiconductor nanoparticles is provided. The procedure includes introducing a first precursor selected from the group consisting of a molecular precursor of a Group IV element and a molecular precursor of a Group VI element into a reaction vessel that comprises at least an organic solvent to form a mixture. Next, the mixture is heated and thereafter a second precursor of a molecular precursor of a Group IV element or a molecular precursor of a Group VI element that is different from the first is added. The reaction mixture is then mixed to initiate nucleation of IV-VI nanocrystals and the temperature of the reaction mixture is controlled to provide nanoparticles having a diameter of about 20 nm or less.
28 citations