High yield of self-catalyzed GaAs nanowire growth on silicon (111) substrate templated by focused ion beam patterning.

We report and detail a lithography-free method to pattern Si substrates. In particular, a focused Ga ion beam is used to create regular patterns of holes which serve as a template for the growth of vertically aligned GaAs nanowires (NW)s on Si(111) substrates using self-catalyzed molecular beam epitaxy. We show that the hole diameter plays a crucial role in the growth of the NWs at the drilled holes. The critical parameters defining the width of the holes are: ion dose quantities, wet etching procedures, and high-temperature steps at the process of growth. As a result, we obtained a yield of more than 80% for vertically aligned NW. Compared to other methods of patterning our approach provides the following advantages: (i) it is a lithography-free procedure, (ii) allows for quick patterning process and hole diameter optimization within a small window of trial and error, (iii) and provides potential applicability for different material systems.

Spatially-resolved luminescence and crystal structure of single core-shell nanowires measured in the as-grown geometry.

We report on the direct correlation between the structural and optical properties of single, as-grown core-multi-shell GaAs/In0.15Ga0.85As/GaAs/AlAs/GaAs nanowires. Fabricated by molecular beam epitaxy on a pre-patterned Si(111) substrate, on a row of well separated nucleation sites, it was possible to access individual nanowires in the as-grown geometry. The polytype distribution along the growth axis of the nanowires was revealed by synchrotron-based nanoprobe x-ray diffraction techniques monitoring the axial 111 Bragg reflection. For the same nanowires, the spatially-resolved emission properties were obtained by cathodoluminescence hyperspectral linescans in a scanning electron microscope. Correlating both measurements, we reveal a blueshift of the shell quantum well emission energy combined with an increased emission intensity for segments exhibiting a mixed structure of alternating wurtzite and zincblende stacking compared with the pure crystal polytypes. The presence of this mixed structure was independently confirmed by cross-sectional transmission electron microscopy.

Fibrillary glomerulopathy in a 10-year-old female.

A 10-year-old African-American female was evaluated for asymptomatic proteinuria. Initial investigation did not reveal the etiology of her renal disease. She subsequently underwent a percutaneous renal biopsy, which was consistent with fibrillary glomerulopathy. This condition is rare in children and is identified histologically by a solid, randomly arranged, amyloid-like fibrillar structure with a diameter of about 18-22 nm. It is a diagnosis of exclusion, the clinical presentation of which can be quite varied. Children usually present with nephrotic syndrome. There is no effective therapy for this condition. Therapy with steroids, cytotoxic agents, and plasmapheresis does not confer any real benefit in stabilizing or improving renal function. However, angiotensin converting enzyme inhibitors can decrease the proteinuria. End-stage renal disease is known to occur in 50% of patients within 4 years of diagnosis. The nephrotic-range proteinuria in our patient significantly decreased during a 4-year follow-up without any therapy, while maintaining normal renal function.