Widely and continuously tuneable liquid crystal lasers

Liquid crystal lasers offer wide, continuous tuneability across the visible and near-infrared (450-850 nm). Compared to conventional tuneable laser technology, liquid crystal lasers are highly compact and have simple and scalable manufacturability. Their ability to emit multiple simultaneous emissions of arbitrarily selectable wavelength also gives them functional advantages over competing technologies. This paper describes Förster transfer techniques that have enabled this extended continuously tunable emission range, whilst maintaining a common pump source. © 2012 OSA.

2 μm solid-state laser mode-locked by single-layer graphene

We report a 2 μm ultrafast solid-state Tm: Lu2O3 laser, mode-locked by single-layer graphene, generating transform-limited ∼ 410 fs pulses, with a spectral width ∼ 11.1 nm at 2067 nm. The maximum average output power is 270 mW, at a pulse repetition frequency of 110 MHz. This is a convenient high-power transform-limited ultrafast laser at 2 μm for various applications, such as laser surgery and material processing. © 2013 American Institute of Physics.

Investigation of fluorine three-dimensional redistribution during solid-phase-epitaxial-regrowth of amorphous Si

The fluorine redistribution during partial solid-phase-epitaxial-regrowth at 650°C of a preamorphized Si substrate implanted by F was investigated by atom probe tomography (APT), transmission electron microscopy, and secondary ions mass spectrometry. Three-dimensional spatial distribution of F obtained by APT provides a direct observation of F-rich clusters with a diameter of less than 1.5 nm. Density variation compatible with cavities and F-rich molecular ions in correspondence of clusters are in accordance with cavities filled by SiF 4 molecules. Their presence only in crystalline Si while they are not revealed by statistical analysis in amorphous suggests that they form at the amorphous/crystal interface. © 2012 American Institute of Physics.

Fluorine redistribution and incorporation during solid phase epitaxy of preamorphized Si

The redistribution of fluorine during solid phase epitaxial regrowth (SPER) of preamorphized Si has been experimentally investigated, explained, and simulated, for different F concentrations and temperatures. We demonstrate, by a detailed analysis and modeling of F secondary ion mass spectrometry chemical-concentration profiles, that F segregates in amorphous Si during SPER by splitting in three possible states: (i) a diffusive one that migrates in amorphous Si; (ii) an interface segregated state evidenced by the presence of a F accumulation peak at the amorphous-crystal interface; (iii) a clustered F state. The interplay among these states and their roles in the F incorporation into crystalline Si are fully described. It is shown that diffusive F migrates by a trap limited diffusion mechanism and also interacts with the advancing interface by a sticking-release dynamics that regulates the amount of F segregated at the interface. We demonstrate that this last quantity determines the regrowth rate through an exponential law. On the other hand we show that neither the diffusive F nor the one segregated at the interface can directly incorporate into the crystal but F has to cluster in the amorphous phase before being incorporated in the crystal, in agreement with recent experimental observations. The trends of the model parameters as a function of the temperature are shown and discussed obtaining a clear energetic scheme of the F redistribution and incorporation in preamorphized Si. The above physical understanding and the model could have a strong impact on the use of F as a tool for optimizing the doping profiles in the fabrication of ultrashallow junctions. © 2010 The American Physical Society.

Failure and formation of axial nanowire heterostructures in vapor-liquid-solid growth

To observe the axial growth behavior of InAs on GaAs nanowires, InAs was grown for different growth durations on GaAs nanowires using Au nanoparticles. Through transmission electron microscopy, we have observed the following evolution steps for the InAs growth. (1) In the initial stages of the InAs growth, InAs clusters into a wedge shape preferentially at an edge of the Au/GaAs interface by minimizing Au/InAs interfacial area; (2) with further growth of InAs, the Au particle moves sidewards and then downwards by preserving an interface with GaAs nanowire sidewalls. The lower interfacial energy of Au/GaAs than that of Au/In As is attributed to be the reason for such Au movement. This downward movement of the Au nanoparticle later terminates when the nanoparticle encounters InAs growing radially on the GaAs nanowire sidewalls, and with further supply of In and As vapor reactants, the Au nanoparticle assists the formation of InAs branches. These observations give some insights into vapor-liquid-solid growth and the formation of kinks in nanowire heterostructures. © 2008 Materials Research Society.