Painting with Biomolecules at the Nanoscale: Biofunctionalization with Tunable Surface Densities

We present a generic and flexible method to nanopattern biomolecules on surfaces. Carbon-containing nanofeatures are written at variable diameter and spacing by a focused electron beam on a poly­(ethylene glycol) (PEG)-coated glass substrate. Proteins physisorb to the nanofeatures with remarkably high contrast factors of more than 1000 compared to the surrounding PEG surfaces. The biological activity of model proteins can be retained as shown by decorating avidin spots with biotinylated DNA, thereby underscoring the universality of the nano-biofunctionalized platform for the binding of other biotinylated ligands. In addition, biomolecule densities can be tuned over several orders of magnitude within the same array, as demonstrated by painting a microscale image with nanoscale pixels. We expect that these unique advantages open up entirely new ways to design biophysical experiments, for instance, on cells that respond to the nanoscale densities of activating molecules

Room-Temperature Group-IV LED Based on Defect-Enhanced Ge Quantum Dots

As recently demonstrated, defect-enhanced Ge quantum dots (Ge-DEQDs) in a crystalline Si matrix can be employed as CMOS-compatible gain material in optically pumped lasers. Due to the stability of their optical properties up to temperatures beyond 300 K, the Ge-DEQD system is a highly promising candidate for the realization of an electrically pumped group-IV laser source for integration in a monolithic optoelectronic platform fit for room-temperature operation. We report on the realization of light-emitting diodes based on Ge-DEQDs operating at telecom wavelengths and above room temperature. The DEQD electroluminescence characteristics were studied spectrally resolved as a function of driving current and device temperature. The experimental results show that the excellent optical properties of Ge-DEQDs are maintained under electrical pumping at high current densities and at device temperatures of at least 100 °C. Furthermore, the emission intensity scales with the number of quantum dot layers embedded into the <i>p</i>-<i>i</i>-<i>n</i> diode structures, thus, indicating the scalability of the approach for large gain material volumes. The presented results form an essential step toward the future demonstration of a CMOS-compatible, electrically pumped room-temperature laser based on Ge-DEQDs

Enhanced Telecom Emission from Single Group-IV Quantum Dots by Precise CMOS-Compatible Positioning in Photonic Crystal Cavities

Efficient coupling to integrated high-quality-factor cavities is crucial for the employment of germanium quantum dot (QD) emitters in future monolithic silicon-based optoelectronic platforms. We report on strongly enhanced emission from single Ge QDs into L3 photonic crystal resonator (PCR) modes based on precise positioning of these dots at the maximum of the respective mode field energy density. Perfect site control of Ge QDs grown on prepatterned silicon-on-insulator substrates was exploited to fabricate in one processing run almost 300 PCRs containing single QDs in systematically varying positions within the cavities. Extensive photoluminescence studies on this cavity chip enable a direct evaluation of the position-dependent coupling efficiency between single dots and selected cavity modes. The experimental results demonstrate the great potential of the approach allowing CMOS-compatible parallel fabrication of arrays of spatially matched dot/cavity systems for group-IV-based data transfer or quantum optical systems in the telecom regime