Suchergebnisse

The fabrication of a novel optofluidic chip using nanochannels optimized for DNA-stretched molecules and optical detection by enhanced fluorescence is reported. The chips are composed of a series of microchannels that allow the transport of molecules in the femto-liter per second inside a fluid or gas. The nanochannels are surrounded by a photonic crystal structure to enhance the emission of fluorescent light from the molecules, which can travel along the nanochannel, allowing for enhanced optical detection of the molecules in motion. The photonic crystal structure provides an enhancement up to 2.5 times in the light emitted from fluorescent molecules inside the nanochannels which increases to around 250 when normalized to the area of the nanochannels emitting fluorescence. The results may help to the detection of fluorescent molecules (like marked-DNA) in series by speeding it and allowing the use of less sophisticated equipment. ; This work was partially supported by Basque Government by Etortek 2013 Grant No. IE13–360 and by Spanish MINECO by Grants TEC2014-54449-C3-3-R and PCIN-2013-179. ; Peer reviewed

Silicon nanowires are key elements to fabricate very sensitive mechanical and electronic devices. We provide a method to fabricate sub-12 nm silicon nanowires in thickness by combining oxidation scanning probe lithography and anisotropic dry etching. Extremely thin oxide masks (0.3-1.1 nm) are transferred into nanowires of 2-12 nm in thickness. The width ratio between the mask and the silicon nanowire is close to one which implies that the nanowire width is controlled by the feature size of the nanolithography. This method enables the fabrication of very small single silicon nanowires with cross-sections below 100 nm2. Those values are the smallest obtained with a top-down lithography method. © 2014 AIP Publishing LLC. ; This work was funded by the European Union FP7/2007-2013 under Grant Agreement No. 318804 (SNM). ; Peer Reviewed

The optical characterization of the surface anisotropy of three Ga-based semiconductor compounds using an in situ technique based on the chemical modulation of the surface is described. In this technique, the anisotropic optical reflectivity is modulated by a periodic variation of the surface stoichiometry using valved pulsed cells for group-V elements (As, P, Sb). The substrate is maintained at sufficiently high temperature in order to obtain rapid desorption of group-V molecules from the surface during flux interruptions. Linearly polarized light, reflected at near normal incidence by the sample, is collected separately along one of the two principal axes of the crystal, [110] and [11¯0]. The change in the surface coverage induces a change in the intensity of the reflected light, and the normalized variation ΔR/R is recorded as a function of wavelength. Spectra for (001) surfaces in the 1–3 eV range have been obtained with this method for a set of Ga-based binary III-V compounds GaP, GaAs, and GaSb, showing well-defined features for light polarized along the [110] direction, parallel to Ga dimers. These observed maxima are attributed to transitions between the occupied Ga dimer and the unoccupied dangling bond bands, at characteristic energies in each material. ; One of the authors (P. A.) acknowledges the support received from the Basque Government. This work was partially supported by a MAT95-0966 Research Action. ; Peer reviewed

The photoluminescence properties of InSb submonolayers and dots are presented. When the amount of InSb deposit on InP is less than 1 ML the growth mode remains two dimensional, while for greater amounts three-dimensional quantum dots are formed. Within the two-dimensional growth mode range the energy of the InSb-related transition decreases as we increase the amount of InSb deposited within the limits of said range. No InSb absorption features have been detected. The observed photoluminescence is interpreted as a recombination of electrons in the InP layers with holes in the InSb layers. We estimate a valence-band offset of 1.525 eV, similar to the predictions of the solid-model theory (1.600 eV). In the samples with InSb dots an InSb related transition has been observed, which is attributed to the wetting layer. ; The authors would like to gratefully acknowledge support by the European Union ~HCM, network CT930349! and by CICYT under Project No. MAT95-0966 ; Peer reviewed

Ultrahigh sensitivity temperature measurement is becoming increasingly relevant for different scientific and technological fields from fundamental physics to high-precision engineering applications. Here, we demonstrate the use of a nanomechanical resonator - free standing silicon nitride membranes with thicknesses in the nanoscale - for room temperature thermometry reaching an unprecedented resolution of 15 μK. These devices were characterized by using an interferometric system at high vacuum, where there are only two possible mechanisms for heat transfer: thermal conductivity and radiation. While the expected behavior should be to decrease the frequency of the mechanical resonance due to the thermoelastic effect, we observe that the nanomechanical response can be both positive and negative depending on the thermal flux: a heat point source always shifts the mechanical resonance to lower frequencies, while a distributed heat source shifts the resonance to higher frequencies. ; This research is funded by the Spanish Ministry of Science under project MOMPs reference TEC2017-89765-R and the European Association of National Metrology Institutes (JRP f14 PhotOQuanT17FUN05). E.G.-S acknowledges financial support by the Spanish Ministry of Science under the project MicroBIOMS, reference PID2019-109765RA-I00. This project has received funding from the EMPIR program co-financed by the Participating States and from the European Union's Horizon 2020 research and innovation program. The service from the Micro and Nanofabrication Laboratory (MiNa) and X-SEM Laboratory is funded by MCIU (CSIC13-4E-1794) and EU (FEDER, FSE).

Beryllium-doped InP layers have been grown by solid source atomic layer molecular beam epitaxy at low substrate temperature. The residual n-type doping was reduced by controlling both the amplitude and the length of the phosphorus pulse. We have shown a well controlled p-type doping and obtained a hole concentration in the range 4×1017–3×1019 cm−3 at room temperature. The electrical and optical properties of InP layers grown at low temperatures were investigated by Hall effect and photoluminescence (PL) measurements. PL spectra for lightly doped samples have a near band emission at 1.41 eV and Be-related emissions around 1.38 eV. ; This work was supported by Project No. TIC95-0563-C05-05 of the Spanish Government. ; Peer reviewed

3 pages, 4 figures. ; We have grown self-organized InSb quantum dots on semi-insulating InP (001) substrates by molecular beam epitaxy. We studied the size dependency of the uncapped InSb quantum dots on the nominal thickness of the deposited InSb by atomic force microscopy. The dot sizes have a pronounced minimum at about 2.2 monolayers of InSb. After a nominal thickness of 3.2 monolayers we observe a drastic change of the dot shape, from quantum dots to quantum dashes. From there on the dots grow in a quasicylindric shape aligned in the (110) direction. ; The authors would like to acknowledge gratefully financial support from the European Union (HCM, Network CT930349). ; Peer reviewed