Highly conformal fabrication of nanopatterns on non-planar surfaces.

While the number of techniques for patterning materials at the nanoscale exponentially increases, only a handful of methods approach the conformal patterning of strongly non-planar surfaces. Here, using the direct surface self-assembly of colloids by electrostatics, we produce highly conformal bottom-up nanopatterns with a short-range order. We illustrate the potential of this approach by devising functional nanopatterns on highly non-planar substrates such as pyramid-textured silicon substrates and inherently rough polycrystalline films. We further produce functionalized polycrystalline thin-film silicon solar cells with enhanced optical performance. The perspective presented here to pattern essentially any surface at the nanoscale, in particular surfaces with high inherent roughness or with microscale features, opens new possibilities in a wide range of advanced technologies from affordable photovoltaics and optoelectronics to cellular engineering.

Disordered nanostructures by hole-mask colloidal lithography for advanced light trapping in silicon solar cells.

We report on the fabrication of disordered nanostructures by combining colloidal lithography and silicon etching. We show good control of the short-range ordered colloidal pattern for a wide range of bead sizes from 170 to 850 nm. The inter-particle spacing follows a Gaussian distribution with the average distance between two neighboring beads (center to center) being approximately twice their diameter, thus enabling the nanopatterning with dimensions relevant to the light wavelength scale. The disordered nanostructures result in a lower integrated reflectance (8.1%) than state-of-the-art random pyramid texturing (11.7%) when fabricated on 700 µm thick wafers. When integrated in a 1.1 µm thin crystalline silicon slab, the absorption is enhanced from 24.0% up to 64.3%. The broadening of resonant modes present for the disordered nanopattern offers a more broadband light confinement compared to a periodic nanopattern. Owing to its simplicity, versatility and the degrees of freedom it offers, this potentially low-cost bottom-up nanopatterning process opens perspectives towards the integration of advanced light-trapping schemes in thin solar cells.

Design, fabrication and optical characterization of photonic crystal assisted thin film monocrystalline-silicon solar cells.

In this paper, we present the integration of an absorbing photonic crystal within a monocrystalline silicon thin film photovoltaic stack fabricated without epitaxy. Finite difference time domain optical simulations are performed in order to design one- and two-dimensional photonic crystals to assist crystalline silicon solar cells. The simulations show that the 1D and 2D patterned solar cell stacks would have an increased integrated absorption in the crystalline silicon layer would increase of respectively 38% and 50%, when compared to a similar but unpatterned stack, in the whole wavelength range between 300 nm and 1100 nm. In order to fabricate such patterned stacks, we developed an effective set of processes based on laser holographic lithography, reactive ion etching and inductively coupled plasma etching. Optical measurements performed on the patterned stacks highlight the significant absorption increase achieved in the whole wavelength range of interest, as expected by simulation. Moreover, we show that with this design, the angle of incidence has almost no influence on the absorption for angles as high as around 60°.

Cardiac involvement in sickle beta-thalassemia.

Cardiovascular involvement is a leading cause of mortality and morbidity in patients with inherited hemoglobinopathies, but it has not been adequately assessed in sickle beta-thalassemia. We evaluated 115 sickle beta-thalassemia patients, aged 34 +/- 14 years, along with 50 healthy controls, by resting echocardiography. Patients with systolic left ventricular (LV) dysfunction or severe pulmonary hypertension (PHT) also underwent left and right cardiac catheterization and cardiac magnetic resonance imaging (CMR). Left and right chamber dimensions, LV mass, and cardiac index were significantly higher in patients compared to controls (p < 0.001 in most cases). Three patients (2.9%) had reduced LV ejection fraction (<55%); mean LV ejection fraction was significantly lower in patients (p < 0.001). Left and right ventricular systolic tissue Doppler indices and LV diastolic tissue Doppler indices were also impaired in patients. All three patients with systolic LV dysfunction had normal coronary arteries and mild myocardial iron load (CMR T2* values, 18-25 ms). Systolic pulmonary artery pressure was significantly higher in patients compared to controls (p = 0.002); PHT was present in 28 patients (27%), while severe PHT in three (2.9%). In three patients with severe PHT, only one had impaired LV ejection fraction and increased pulmonary wedge pressure. Overall, three patients (2.9%) had a history of heart failure, two with systolic LV dysfunction, and one with severe PHT. Cardiac involvement in sickle beta-thalassemia concerns biventricular dilatation and dysfunction along with PHT, leading to congestive heart failure.