Fernando Rey García

Bimodal atomic force microscopy imaging of isolated antibodies in air and liquids

We have developed a dynamic atomic force microscopy (AFM) method based on the simultaneous excitation of the first two flexural modes of the cantilever. The instrument, called a bimodal atomic force microscope, allows us to resolve the structural components of antibodies in both monomer and pentameric forms. The instrument operates in both high and low quality factor environments, i.e., air and liquids. We show that under the same experimental conditions, bimodal AFM is more sensitive to compositional changes than amplitude modulation AFM. By using theoretical and numerical methods, we study the material contrast sensitivity as well as the forces applied on the sample during bimodal AFM operation.

Fabrication of gold nanowires on insulating substrates by field-induced mass transport

A method for the fabrication of nanometer size gold wires on insulating surfaces is presented. An oscillating gold-coated atomic force microscope tip is brought into close proximity of a silicon dioxide surface. The application of a negative sample voltage produces the transport of gold atoms from the tip to the surface. The voltage is applied when there is a tip–surface separation of ∼3 nm. The finite tip–surface separation enhances the tip lifetime. It also allows the application of sequences of multiple voltage pulses. Those sequences allow the fabrication of continuous nanowires. The atomic force microscope gold deposition is performed at room temperature and in ambient conditions which makes the method fully compatible with standard lithographic techniques. Electron transport measurements of the wires show a clear metallic behavior. Electrical resistivities of ∼3×10−7 Ω m and current densities of up to 5×1011 A m−2 are reported.

High magneto-optical activity and low optical losses in metal-dielectric Au/Co/Au-SiO2 magnetoplasmonic nanodisks

Metal-dielectric Au-Co-SiO(2) magnetoplasmonic nanodisks are found to exhibit large magneto-optical activity and low optical losses. The internal architecture of the nanodisks is such that, in resonant conditions, the electromagnetic field undertakes a particular spatial distribution. This makes it possible to maximize the electromagnetic field at the magneto-optically active layers and minimize it in the other, optically lossy ones.

Detection of the Early Stage of Recombinational DNA Repair by Silicon Nanowire Transistors

A silicon nanowire-based biosensor has been designed and applied for label-free and ultrasensitive detection of the early stage of recombinational DNA repair by RecA protein. Silicon nanowires transistors were fabricated by atomic force microscopy nanolithography and integrated into a microfluidic environment. The sensor operates by measuring the changes in the resistance of the nanowire as the biomolecular reactions proceed. We show that the nanoelectronic sensor can detect and differentiate several steps in the binding of RecA to a single-stranded DNA filament taking place on the nanowire-aqueous interface. We report relative changes in the resistance of 3.5% which are related to the interaction of 250 RecA·single-stranded DNA complexes. Spectroscopy data confirm the presence of the protein-DNA complexes on the functionalized silicon surfaces.

Linewidth determination in local oxidation nanolithography of silicon surfaces

We measure the linewidth of structures fabricated by local oxidation lithography on silicon surfaces. Two different structures, isolated and arrays of parallel lines have been generated. The oxide structures have been fabricated in the proximity of sexithiophene islands whose size is comparable to the oxide motives. The comparison between local oxides and sexithiophene islands reveals that atomic force microscopy (AFM) images faithfully reproduce the size and shape of local silicon oxides. The oxide lines have a trapezoidal shape with a flat section at the top. AFM images of the oxide structures show rather small slopes ∼0.05–0.15 which imply angles with the horizontal between 3° and 8°. The shallow angles imply a minimum feature size of 14 nm at the base for an oxide thickness of 1 nm. Linewidths of 7 nm and 20 nm at the top and base, respectively, have been fabricated. We have also demonstrated the ability to pack structures with a periodicity of 13 nm.

Mimicking electromagnetically induced transparency in the magneto-optical activity of magnetoplasmonic nanoresonators

We show that the interaction between a plasmonic and a magnetoplasmonic metallic nanodisk leads to the appearance of magneto-optical activity in the purely plasmonic disk induced by the magnetoplasmonic one. Moreover, at specific wavelengths the interaction cancels the net electromagnetic field at the magnetoplasmonic component, strongly reducing the magneto-optical activity of the whole system. The MO activity has a characteristic Fano spectral shape, and the resulting MO inhibition constitutes the magneto-optical counterpart of the electromagnetic induced transparency.

New materials by agglomeration of petroleum coke fines

The agglomeration process is of broad potential use in revaluing fine-sized petroleum coke wastes and waste products known as impalpable fines. These materials were agglomerated in a disc pelletizer with binding agents to obtain pellets with high carbon content, good reactivity and good consolidation in hot and cold environments. Pellets formed with the addition of carboxymethylcellulose and oven-dried at 100°C possess adequate compressive strength and may be used as carburizers, e.g. in steel manufacturing. In steel melting tests the pellets had a high resistance to thermal shock. High levels of steel carburization were obtained, to a carbon content of ∼6.1 wt%.

Fabrication of sub-12 nm thick silicon nanowires by processing scanning probe lithography masks

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.

Electrical and optical properties of Be-doped InP grown at low temperature by solid source atomic layer molecular beam epitaxy

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.

Optimizing magneto-optical activity and optical losses in metal-dielectric magnetoplasmonic nanodisks

In this work we show that the insertion of a dielectric layer in Au/Co/Au magnetoplasmonic nanodisks fabricated by hole mask colloidal lithography makes it possible to obtain systems that simultaneously exhibit large magneto-optical (MO) activity and low optical extinction. The physical mechanism underlying this effect is the internal EM field redistribution, in such a way to concentrate it in the MO active layer (Co) and, at the same time, reduce it in the non MO active elements. We have performed a systematic study of the optical and MO response upon the variation of the Co layer thickness within the nanodisk, finding an increase of the MO response with the increment of thickness, accompanied with a blue shift and broadening of the peaks associated with the plasmon excitations.