Nanostructure Growth on Surfaces

Group Members:

M. C. Tringides

Goals:

This project focuses on low dimensional surface structures (ultrathin metallic films, islands, wires, etc.), especially in systems exhibiting Quantum Size Effects (QSE). Since such structures are metastable and are grown far from equilibrium, it is important to identify the optimal kinetic pathways. This requires a better understanding of many atomistic processes (surface diffusion, nucleation, coarsening etc.) that define the kinetic pathway. In addition the properties of the grown structures (band structure, density of states, etc.) depend on the structure dimensions, so this also opens the possibility to control their potential uses in chemical reactivity and energy storage.

Publications:

"Anomalous Mass Transport in the Pb Wetting Layer on the Si(111) Surface" K.L. Man, M. C. Tringides, M. M. T. Loy, and M.S. Altman Phys. Rev. Let. 101, 226102 (2008)

"Quantum Size Effects in Metallic Nanostructures" M. C. Tringides, M. Jalochowski, and E. Bauer Invited feature article for the April Issue of Physics Today

"Strongly driven Coarsenting of Height Selected Islands on Si(111)" M. Li, J. W. Evans, C. Z. Wang, M. Hupalo, M. C. Tringides, T. L. Chan, and K. M. Ho Surf. Sci. Lett. 601 140 (2007)

"Low temperature ultra fast mobility in systems with long range repulsive interactions: Pb/Si(111)" M.Hupalo, M. Yakes, M. Zaluska-Kotur, Z. Gortel and M. C. Tringides Phys. Rev. Let. 98 135504 (2007)

"Ultrafast kinetics in Pb/Si(111) from the collective spreading of the wetting layer" M. Hupalo and M. C. Tringides Phys. Rev. B 75 235443 (2007)

"Quantum size effect on the diffusion barrier and growth morphology on Pb/Si(111)" TL.Chan, C. Z. Wang, M.Hupalo, MC.Tringides, and K. M. Ho Phys. Rev. Let. 96 226102 (2006)

"Novel nucleation mechanisms driven by Quantum Size Effects" R. Feng, E. H. Conrad, M. C. Tringides, M Hupalo, P. Ryan, C. Kim, and P. F. Miceli Phys. Rev. Let. 96 106105 (2006)

"Non-classical kinetics processes and morphologies in QSE driven growth in Pb/Si(111)" Z. Kuntova, M. Hupalo, Z. Chvoj, and M. C. Tringides Surf. Sci. 600 4765 (2006)

"Wetting layer transformation for Pb nano-crystals grown in Si(111)" R. Feng, E. H. Conrad, M. C. Tringides, C. Kim, and P. Miceli Appl. Phys. Lett. 85 17 3866 (2004)

"Devil's staircase in Pb/Si((111) ordered phases" M.Hupalo, J. Schmalian, and M.C.Tringides Phys. Rev. Lett. 90 216106 (2003)

Press coverage: Physicist observes novel liquid-like motion and nucleation in metallic nanostructures

Experimental Techniques:

High resolution LEED (SPA-LEED)

In Low Energy Electron Diffraction (LEED) electrons with low energy (that energy is usually between 30 and 200 eV) are directed on a surface. In conventional LEED the electrons diffract of the surface, excite a phosphor coating on a glass window and fluoresce. The pattern can be used to determine the surface structure. In SPA-LEED a channeltron is used to detect the electrons diffracting of the surface. The great resolution in SPA-LEED comes from specially designed electron optics that minimize the beam divergence. To get the whole pattern there is an octopole electric field that sweeps the entire pattern past the channeltron.

Variable Temperature Omicron STM

Source: Universe Review

In Scanning Tunneling Microscopy (STM) a very sharp tip is moved close to the sample and a small voltage is applied across the two. This causes electrons to tunnel through the vacuum between the two objects. The tunneling current depends exponentially upon the height of the tip above the sample giving the STM atomic resolution.

Collaborators:

K.M. Ho ( Iowa State) C. Z. Wang (Ames Lab) J. W. Evans ( Ames Lab) E. Bauer (Arizona) M. Jalochowski ( Lublin Poland) M. Altman( Hong Kong) M. Loy(Hong Kong) P.Miceli (Missouri) E. Conrad ( Georgia Tech) Z. Chvoj ( Czech Republic) Z. Gortel ( Alberta) M. Zaluska -Kotur( Warsaw) M. Horn von Hoegen (Essen),V. Chab (Prague)

Uniform Height Metal Islands due to QSE

(Both Pb/Si(111) and In/Si(111) show preferred height islands)

Controlling Nucleation with QSE

Split Islands

Experiment in Ames
Simulation by Chvoj and Kuntova (Academy of Sciences, Czech Republic)

Figure showing the experimental results of growing on top of 200x200 nm^2 single island Pb that shows different morphology ( left part show few fractal islands and right part many small islands. The left part is 5-layers and the right part is 4-layers). The figure to the right shows the simulation carried out by Czech collaborators. It shows that the nanoscale process depends on the height of the island.

Unusually Mobile Wetting Layer

Diffraction Intensity Oscillations

$Diffraction Intensity Oscillations$

Pb/Si(111) T = 180K

7-layer islands

Using SPA-LEED to measure the island height is similar to the way light produces fringes in a thin film.


Experiment in Ames	Simulation by Chvoj and Kuntova (Academy of Sciences, Czech Republic)
Figure showing the experimental results of growing on top of 200x200 nm^2 single island Pb that shows different morphology ( left part show few fractal islands and right part many small islands. The left part is 5-layers and the right part is 4-layers). The figure to the right shows the simulation carried out by Czech collaborators. It shows that the nanoscale process depends on the height of the island.