A study of Ag/Ag(100) thin film growth with scanning tunneling microscopy

We used STM to study metal thin film growth processes. The following are main conclusions: (1) Large metal cluster diffuse on Ag(100) surface. The metal-metal system large adatom cluster diffusion is reported for the first time. The evaporation-condensation of adatoms dominating the vacancy cluster diffusion process is suggested. The diffusion coefficients is on the order of 10[superscript]-18 cm[superscript]2s[superscript]-1. (2) Metal film evolution behaviors at different coverage regime are examined. At low coverage, cluster diffusion dominates the coarsening process. At high submonolayer coverage, vacancy cluster repining dominates the process. At moderate coverage, edge-running dominates the process. (3) The vacancy cluster diffusion is also observed. The vacancy were formed by controlling the deposition flux and film coverage. The method is simple and offers similar advantages of the sputtering method. The diffusion coefficients is on the order of 10[superscript]-18 cm[superscript]2s[superscript]-1, is smaller than that of adatom clusters, and has a scaling factor [alpha] roughly close to 0.5 in D ∝ N[superscript]-[alpha]. The evaporation-condensation of vacancy monomers dominating the vacancy cluster diffusion process is suggested. (4) We have presented a number of observations of dynamical phenomena of Ag cluster on Ag (100) with UHV-STM. Ag cluster on Ag (100) at room temperature are mobile. The interaction between clusters and between clusters and surface steps are mediated via 2D dilute adatom gas on the terrace and different adatom concentrations around clusters and steps. Background gases and impurities on cluster edges can strongly affect film coarsening process. The former can enhance clusters dissolution, but the latter can stabilize the local structure and geometry of the Ag film

Engineering Biphoton Wave Packets with an Electromagnetically Induced Grating

We propose to shape biphoton wave packets with an electromagnetically induced grating in a four-level double-$\Lambda$ cold atomic system. We show that the induced hybrid grating plays an essential role in directing the new fields into different angular positions, especially to the zeroth-order diffraction. A number of interesting features appear in the shaped two-photon waveforms. For example, broadening or narrowing the spectrum would be possible in the proposed scheme even without the use of a cavity.Comment: Published in Physical Review A 82, 043814 (2010

Effects of mismatched transmissions on two-mode squeezing and EPR correlations with a slow light medium

We theoretically discuss the preservation of squeezing and continuous variable entanglement of two mode squeezed light when the two modes are subjected to unequal transmission. One of the modes is transmitted through a slow light medium while the other is sent through an optical fiber of unit transmission. Balanced homodyne detection is used to check the presence of squeezing. It is found that loss of squeezing occurs when the mismatch in the transmission of the two modes is greater than 40% while near ideal squeezing is preserved when the transmissions are equal. We also discuss the effect of this loss on continuous variable entanglement using strong and weak EPR criteria and possible applications for this experimental scheme.Comment: 7 pages, 4 figure

Coherence assisted resonance with sub-lifetime-limited linewidth

We demonstrate a novel approach to obtain resonance linewidth below that limited by coherence lifetime. Cross correlation between induced intensity modulation of two lasers coupling the target resonance exhibits a narrow spectrum. 1/30 of the lifetime-limited width was achieved in a proof-of-principle experiment where two ground states are the target resonance levels. Attainable linewidth is only limited by laser shot noise in principle. Experimental results agree with an intuitive analytical model and numerical calculations qualitatively. This technique can be easily implemented and should be applicable to many atomic, molecular and solid state spin systems for spectroscopy, metrology and resonance based sensing and imaging.Comment: 5 pages 5 figure