Research

More information on our research projects:

  1. Metal nanowire films
  2. Nano-chirallity and chiroptical effects
  3. Magneto-transport in magnetic nanoparticle films

 

1. Metal nanowire films:

We have developed a wet-chemical technique for the deposition of high aspect ratio gold/silver nanowire mesh films by depositing the growth solution on a substrate and letting the nanowire grow while the film is drying. This forms a new type of transparent conductor films which we hope to exploit for various applications.

Currently, there are several alternatives to conducting oxides, such as indium tin oxide or zinc oxide, being explored: carbon nanotube/conducting polymer composite films, graphene, and various types of metal nanoparticle or metal nanowire meshes. All these techniques require to first synthesize the nanomaterial then do some isolation or purification steps, sometimes also re-dispersion in solvents and then transfer to the desired substrate. Our method is unique, it is a single step, self-assembly process, forming the nanowire mesh directly on the desired substrate.

 

Nanowires1 Nanowires2

The mechanism of the nanowire formation involves formation of a tubular surfactant template which is induced by the metal seeds that initiate the nanowire growth reaction. This reaction proceeds trough catalytic reduction of gold and silver ions by ascorbate on the pre-fromed metal seed particles, until all the seed particles become connected into ultrathin nanowires within the tubular surfactant structures.

Nanowires4    Nanowires3   Nanowire SEM

TEM images of the nanowire bundles      Dark fiedl optical micrograph              SEM image of the nanowires
                                                          showing the nanowire bundles  

2. Nano-chirallity and chiroptical effects

Our work in nano-chirality is about connecting chiral molecules and inorganic nanostructures in various ways. We are primarily interested in chiroptical properties of such hybrid structures. The main spectroscopy technique that we use is circular dichroism (CD).

 Nanochirality1         

A typical system that we study is a colloidal noble metal (gold, silver) nanoparticle with strong surface plasmon excitations or a semiconductor quantum dot with discrete electron-hole excitations coated with chiral (bio)molecules, such as amino acids. In many cases we observe circular dichroism peaks at wavelengths corresponding to electronic transitions of the inorganic core (plasmons, excitons). Our aim is to study and understand the mechanisms leading to the induction of the chiroptical effects in the nanocrystal cores. We believe that circular dichroism spectroscopy of such systems may reveal new information on the interaction of molecules with metal and semiconductor surfaces and about the molecular conformation at these surfaces.

An interesting case is when the nanocrystals are made of material which crystallizes in a chiral symmetry group, as in the famous case of quartz. In this case interesting chiroptical effects are expected. We have recently demonstrated that intrinsically chiral mercury sulfide (Cinnabar) nanocrystals can be prepared with high enantiomeric excess using chiral thiolated molecules such as cysteine or penicilamine. Later we showed that also intrinsically chiral Tellurium and Selenium nanocrystal can be prepared at high enantiomeric excess using similar methods.

     HgS          Chiral Te

 Unit cell of α-HgS showing           Electron tomography reconstructed images of a 
  the chiral nature of the               Tellurium nanocrystal, exhibiting a chiral shape
  crystal structure                        They were grown in the presence of chiral glutathione molecules
 

3. Magneto-transport in individual magnetic nanoparticle and in films

In another set of projects we have studied magnetite (Fe3O4) nanocrystals. Magnetite has very interesting electronic properties – it is ferrimagnetic and was claimed to be half-metallic. Hence, it is supposed to be a strongly spin-polarized conductor. The bulk material shows a metal-insulator phase transition around 120K and we were able to observe this phenomenon around 100K in 5 nm nanocrystals. In one recent work we have prepared magneto-resistive double tunnel junctions from a spin-filtering substrate on which we scattered isoltaed colloidal magnetite nanocrystals and a scanning tunneling micriscope's (STM) tip above the particle. By tuning the temperature in a variable temperature STM we were able to slow down the magnetization switching of small magnetite nanocrystals (~10 nm) and observe current fluctuations due tot he magnetization switching of the nanocrystal.

MR STM   Telegraph noise

                                                 STM current fluctuation measured over an isolated magnetite nanocrystal
                                                               in the configuration shown on the left, measured at ~110K.
          

We have recently prepared films of colloidal nickel nanoparticles which were conducting and exhibited substantial Extraordinary Hall Effect signals (in collaboaration with the group of Alexander Gerber (TAU School of Physics). Such films may be printed using inkjet printing techniques and thus be integrated in 3D printed electronic systems.

 

Contact Details

Location: Multidisciplinary Research Building, room 207
Phone: 972-3-640-6985
Fax: 972-3-640-5911
E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.">This email address is being protected from spambots. You need JavaScript enabled to view it.
Mailing Adress: School of Chemistry, Tel-Aviv University, Tel-Aviv,
69978 Israel

Laboratory:
Phone: 972-3-640-9018, 5165
Fax: 972-3-640-5911

Prof. Gil Markovich, Location: Multidisciplinary Research Building, room 207. Phone: 972-3-640-6985. Fax: 972-3-640-5911. E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.