Publications

2004
Miri Kazes, David Y Lewis, and Uri Banin. 2004. “Method for Preparation of Semiconductor Quantum‐Rod Lasers in a Cylindrical Microcavity.” Advanced Functional Materials, 14, 10, Pp. 957-962. Publisher's Version Abstract

An efficient method for preparation of semiconductor quantum rod films for robust lasing in a cylindrical microcavity is reported. A capillary tube, serving as the laser cavity, is filled with a solution of nanocrystals and irradiated with a series of intense nanosecond laser pulses to produce a nanocrystal film on the capillary surface. The films exhibit intense room‐temperature lasing in whispering‐gallery modes that develop at the film–capillary interface as corroborated from the spacing detected for the lasing modes. Good lasing stability is observed at moderate pump powers. The method was applied successfully to several quantum‐rod samples of various sizes.

Eyal Nahum, Yuval Ebenstein, Assaf Aharoni, Taleb Mokari, Uri Banin, Nira Shimoni, and Oded Millo. 2004. “Transport and charging in single semiconductor nanocrystals studied by conductance atomic force microscopy.” Nano Letters, 4, 1, Pp. 103-108. Publisher's Version Abstract

Electrical transport measurements through single InAs and CdSe semiconductor nanocrystals embedded in a thin polymer film were performed using conductance atomic force microscopy. The current and topography images showed excellent correlation, where current was detected only over the nanocrystals. A rapid current decay in consecutive scans was observed for positive sample bias, while remaining intact at negative bias. This current decay was accompanied by bias-dependent changes in the height of the nanocrystals. These phenomena, which were not observed for gold nanocrystals, are attributed to long-sustained charging of the nanocrystals.

Eli Rothenberg, Yuval Ebenstein, Miri Kazes, and Uri Banin. 2004. “Two-photon fluorescence microscopy of single semiconductor quantum rods: Direct observation of highly polarized nonlinear absorption dipole.” The Journal of Physical Chemistry B, 108, 9, Pp. 2797-2800. Publisher's Version Abstract

Two-photon polarization fluorescence microscopy is used to study the nature of the emission and nonlinear absorption dipole of single CdSe/ZnS quantum rods. Rods showed strongly polarized nonlinear excitation with sharp angular dependence, following a cos4(φ) functional form, in agreement with the predicted two-photon absorption process. The two-photon absorption is parallel to the emission polarization and allows high orientation selectivity in excitation to be achieved. This further demonstrates the role of single molecule measurements in unraveling basic principles of light−matter interactions otherwise masked by ensemble averaging.

Dov Steiner, David Katz, Oded Millo, Assaf Aharoni, ShiHai Kan, Taleb Mokari, and Uri Banin. 2004. “Zero-dimensional and quasi one-dimensional effects in semiconductor nanorods.” Nano Letters, 4, 6, Pp. 1073-1077. Publisher's Version Abstract

Abstract Image

Scanning tunneling microscopy (STM) and optical spectroscopy measurements were performed on InAs nanorods 7 to 25 nm long. Both methods reveal a clear dependence of the band-gap on length, with a red shift for longer rods. This (zero-dimension like) behavior is different than that of CdSe rods, where the band-gap is nearly insensitive to length, a signature of quasi one-dimensionality. The transition between these two regimes is governed by the ratio between the Bohr radius and the nanorod length. The gaps measured by tunneling spectroscopy are larger than the optical gaps by a factor that depends on the tunneling configuration. This is attributed to a combination of the Coulomb interaction and the voltage division between the two tunnel junctions in the STM experiment.

The present invention provides a new method for the production of inorganic semiconductor nanocrystals having a rod-like shape. More specifically the present invention provides a method of synthesizing rod shaped Group III-V semiconductor nanocrystals. The method comprises: reacting, in a high-boiling point organic solvent, a two-source precursor solution comprising at least one metal source and at least one nonmetal source, or a single-source precursor solution, with a metal catalyst or an agent capable of producing said metal catalyst, said high-boiling point organic solvent having a temperature above 200° C., thereby forming a reaction product comprising semiconductor nanocrystals of various shape; cooling the reaction product, and subsequently exposing said cooled reaction product to at least one centrifugal step so as to obtain semiconductor nanocrystals having substantially rod-like shape.

The rod-shaped nanocrystals obtained by the method of the invention usually have organic ligands as a coating on their outer surfaces. Such organic ligands affect the solubility of the particles and may be substituted or removed, according to the application intended for said particles after the reaction is completed.

Taleb Mokari, Eli Rothenberg, Inna Popov, Ronny Costi, and Uri Banin. 2004. “Selective growth of metal tips onto semiconductor quantum rods and tetrapods.” Science, 304, 5678, Pp. 1787-1790. Publisher's Version Abstract

We show the anisotropic selective growth of gold tips onto semiconductor (cadmium selenide) nanorods and tetrapods by a simple reaction. The size of the gold tips can be controlled by the concentration of the starting materials. The new nanostructures display modified optical properties caused by the strong coupling between the gold and semiconductor parts. The gold tips show increased conductivity as well as selective chemical affinity for forming self-assembled chains of rods. Such gold-tipped nanostructures provide natural contact points for self-assembly and for electrical devices and can solve the difficult problem of contacting colloidal nanorods and tetrapods to the external world.