Ionography of nanostructures with the use of a laser plasma of cluster targets

It has been shown that a femtosecond plasma of cluster targets is an almost isotropic source of fast ions and, hence, can be used to obtain ionographic images with a wide field of view. The spatial resolution of the resulting ionographic images is no worse than 600 nm, which corresponds to a uniquely high value of about 105 of the ratio of the field of view to the resolution. The use of 100–300-keV ion fluxes ensures the sensitivity of the method to the sample thickness of no worse than 100 nm even for samples consisting of light chemical elements (C, H). The proposed method can be used to obtain images of low-contrast biological objects, thin films, membranes, and other nanostructured objects.     

Multi-millijoule, nonlinear preamplifier for high intensity femtosecond Yb:YAG chirped-pulse amplification lasers at 1030 nm

We report the highest energy broadband laser pulses at a center wavelength of 1030 nm based on optical parametric chirped-pulse amplification (OPCPA). We have demonstrated amplification of 1030 nm femtosecond laser pulses from a broadband Yb oscillator to over 6.5 mJ with a total gain of greater than 10⁷ achieved in a single pass through only 56 mm of gain material at a 10 Hz repetition rate. The amplified spectral bandwidth of 10.8 nm affords recompression to a 230 fs pulse duration following amplification. As an alternative to the regenerative amplifier (RA) this system is one of the more promising candidates for realizing compact, high intensity, direct diode-pumped, high repetition rate femtosecond Yb:YAG chirped-pulse amplification (CPA) in laser systems.     

How cold is cold dark matter? Small-scales constraints from the flux power spectrum of the high-redshift lyman-alpha forest

We present constraints on the mass of warm dark matter (WDM) particles derived from the Lyman-alpha flux power spectrum of 55 high-resolution HIRES spectra at 2.0 or approximately 1.2 keV (2sigma) if the WDM consists of early decoupled thermal relics and m(WDM) > or approximately 5.6 keV (2sigma) for sterile neutrinos. Adding the Sloan Digital Sky Survey Lyman-alpha flux power spectrum, we get m(WDM) > or approximately 4 keV and m(WDM) > or approximately 28 keV (2sigma) for thermal relics and sterile neutrinos. These results improve previous constraints by a factor of 2.     

The development of a comprehensive toolbox based on multi-level,high-throughput screening of MOFs for CO/N2 separations

The separation of CO/N₂ mixtures is a challenging problem in the petrochemical sector due to the very similar physical properties of these two molecules, such as size, molecular weight and boiling point. To solve this and other challenging gas separations, one requires a holistic approach. The complexity of a screening exercise for adsorption-based separations arises from the multitude of existing porous materials, including metal–organic frameworks. Besides, the multivariate nature of the performance criteria that needs to be considered when designing an optimal adsorbent and a separation process – i.e. an optimal material requires fulfillment of several criteria simultaneously – makes the screening challenging. To address this, we have developed a multi-scale approach combining high-throughput molecular simulation screening, data mining and advanced visualization, as well as process system modelling, backed up by experimental validation. We have applied our recent advances in the engineering of porous materials'' morphology to develop advanced monolithic structures. These conformed, shaped monoliths can be used readily in industrial applications, bringing a valuable strategy for the development of advanced materials. This toolbox is flexible enough to be applied to multiple adsorption-based gas separation applications.

The separation of challenging mixtures through adsorption is a multidimensional problem that requires a holistic approach. Our toolbox combines experiments, molecular and process simulations with data visualization to find optimal, porous materials.     

Thermal physics in carbon nanotube growth kinetics

The growth of single wall carbon nanotubes (SWNTs) mediated by metal nanoparticles is considered within (i) the surface diffusion growth kinetics model coupled with (ii) a thermal model taking into account heat release of carbon adsorption-desorption on nanotube surface and carbon incorporation into the nanotube wall and (iii) carbon nanotube-inert gas collisional heat exchange. Numerical simulations performed together with analytical estimates reveal various temperature regimes occurring during SWNT growth. During the initial stage, which is characterized by SWNT lengths that are shorter than the surface diffusion length of carbon atoms adsorbed on the SWNT wall, the SWNT temperature remains constant and is significantly higher than that of the ambient gas. After this stage the SWNT temperature decreases towards that of gas and becomes nonuniformly distributed over the length of the SWNT. The rate of SWNT cooling depends on the SWNT-gas collisional energy transfer that, from molecular dynamics simulations, is seen to be efficient only in the SWNT radial direction. The decreasing SWNT temperature may lead to solidification of the catalytic metal nanoparticle terminating SWNT growth or triggering nucleation of a new carbon layer and growth of multiwall carbon nanotubes.     

Twisted smectic A phases in side chain liquid crystal polymers

The syntheses of two side chain liquid crystal polymers, a polyacrylate and a polymethacrylate, are reported. In each of the polymers the liquid-crystalline side group carries an asymmetric carbon atom, thereby making some of the liquid crystal phases formed by the polymers optically active and chiral. For the chiral polyacrylate smectic A and chiral ferroelectric smectic C phases are observed, however for the chiral polymethacrylate a cholesteric phase is detected above the smectic A phase. It is found that the smectic A to cholesteric phase transition is mediated by the formation of an intermediary twisted smectic A phase. This intermediary phase is a liquid-crystalline analogue of the Abrikosov flux phase found in Type II superconductors.