Optimized minigaps for negative differential resistance creation in strongly delta-doped (1D) superlattices

The "atomic saw method" uses the passage of dislocations in two-dimensional (2D) quantum-well superlattices to create periodic slipping layers and one-dimensional (1D) quantum wire superlattices. The effects of this space structuring of the samples on the allowed energies are analysed in the case of GaAs d-doped superlattices. If they are sufficiently large, the various minigaps appearing in the 1D band structure could be responsible for the presence of negative differential resistance (NDR) with high critical current in these systems. The purpose is to determine the evolution of the minigaps in terms of the sample parameters and to obtain the means to determine both the 2D and 1D structural characteristics where NDR could appear.Comment: see erratum 10.1006/spmi.1998.070

Study and characterization by magnetophonon resonance of the energy structuring in GaAs/AlAs quantum-wire superlattices

We present the characterization of the band structure of GaAs/AlAs quantum-wire 1D superlattices performed by magnetophonon resonance with pulsed magnetic fields up to 35 T. The samples, generated by the "atomic saw method" from original quantum-well 2D superlattices, underwent substantial modifications of their energy bands built up on the X-states of the bulk. We have calculated the band structure by a finite element method and we have studied the various miniband structures built up of the masses m_t and m_l of GaAs and AlAs at the point X. From an experimental point of view, the main result is that in the 2D case we observe only resonances when the magnetic field B is applied along the growth axis whereas in the 1D case we obtain resonances in all magnetic field configurations. The analysis of the maxima (or minima for B // E) in the resistivity rho_xy as a function of B allows us to account, qualitatively and semi-quantitatively, for the band structure theoretically expected

GaAs delta-doped quantum wire superlattice characterization by quantum Hall effect and Shubnikov de Haas oscillations

Quantum wire superlattices (1D) realized by controlled dislocation slipping in quantum well superlattices (2D) (atomic saw method) have already shown magnetophonon oscillations. This effect has been used to investigate the electronic properties of such systems and prove the quantum character of the physical properties of the wires. By cooling the temperature and using pulsed magnetic field up to 35 T, we have observed both quantum Hall effect (QHE) and Shubnikov de Haas (SdH) oscillations for various configurations of the magnetic field. The effective masses deduced from the values of the fundamental fields are coherent with those obtained with magnetophonon effect. The field rotation induces a change in the resonance frequencies due to the modification of the mass tensor as in a (3D) electron gas. In view the QHE, the plateaus observed in rho_yz are dephased relatively to rho_zz minima which seems to be linked to the dephasing of the minima of the density of states of the broadened Landau levels

Synthesis of localized 2D-layers of silicon nanoparticles embedded in a SiO2 layer by a stencil-masked ultra-low energy ion implantation process

We propose an original approach called “stencil-masked ion implantation process” to perform a spatially localized synthesis of a limited number of Si nanoparticles (nps) within a thin SiO2 layer. This process consists in implanting silicon ions at ultra-low energy through a stencil mask containing a periodic array of opened windows (from 50 nm to 2 um). After the stencil removal, a thermal annealing is used to synthesize small and spherical embedded nps. AFM observations show that the stencil windows are perfectly transferred into the substrate without any clogging or blurring effect. The samples exhibit a 3 nm localized swelling of the regions rich in Si nps. Moreover, photoluminescence (PL) spectroscopy shows that due to the quantum confinement only the implanted regions containing the Si nps are emitting light

Space Charge at Nanoscale: Probing Injection and Dynamic Phenomena Under Dark/Light Configurations by Using KPFM and C-AFM

International audienc

Plasmonic photocapacitance of self-assembled gold colloidal nanoparticle monolayers

International audienceWe report on the plasmo-electronic properties of self-assembled monolayers of gold colloidal nanoparticles (NPs) formed on a polyimide flexible substrate. The dependence of both resistance and capacitance of these NP assemblies on temperature, bias voltage, optical excitation, and strain is investigated both experimentally and theoretically. Resistance and capacitance appear to bring complementary information on the charge transport properties of the NP assemblies as they exhibit opposite behaviors. Based on a nanocircuit junction model combined with numerical simulations, we were able to account for both the resistance and capacitance and their photo-induced modifications. The dependence of the capacitance on laser irradiation intensity and wavelength was measured, and the role of the surface plasmon resonance was pointed out. We show that the plasmonic-induced photocapacitance can reach 43% for a moderate irradiation intensity of 3.5W/cm2. Moreover, the NP assemblies, deposited on flexible substrate, were submitted to a uniaxial strain which allows for controlling the interparticle distances and hence for probing the plasmo-electro-mechanical properties of the assembly. We found that, under plasmonic pumping of charges, the photo-capacitance gauge factor is three times larger than the one measured under dark conditions, in agreement with the calculations. The presented work thus paves the way to the emergence of a new class of plasmonic-enhanced capacitance strain sensors

Stencil assisted reactive ion etching for micro and nano patterning

Stencil-assisted oxygen reactive ion etching is a low-cost and parallel process for the replication of micrometric and nanometric patterns in any organic material. This lithography process allows the patterning of organic material non sensitive to electronic or optical radiations, sensitive to solvents, or already patterned which cannot be patterned by conventional lithography methods. We demonstrate the versatility of stencil-assisted reactive ion etching though 3 examples. First to define 500 nm holes in PMMA. Secondly, the fabrication step has been integrated in a lift-off process of metal or molecular self-assembled monolayers. We finally apply stencil-assisted reactive ion etching to pattern an assembly of 100 nm latex nanoparticles

Electro-mechanical sensing in freestanding monolayered gold nanoparticle membranes

The electro-mechanical sensing properties of freestanding monolayered membranes of dodecanethiol coated 7 nm gold nanoparticles (NPs) are investigated using AFM force spectroscopy and conductive AFM simultaneously. The electrical resistance of the NP membranes increases sensitively with the point-load force applied in the center of the membranes using an AFM tip. Numerical simulations of electronic conduction in a hexagonally close-packed two-dimensional (2D) array of NPs under point load-deformation are carried out on the basis of electronic transport measurements at low temperatures and strain modeling of the NP membranes by finite element analysis. These simulations, supporting AFM-based electro-mechanical measurements, attribute the high strain sensitivity of the monolayered NP membranes to the exponential dependence of the tunnel electron transport in 2D NP arrays on the strain-induced length variation of the interparticle junctions. This work thus evidences a new class of highly sensitive nano-electro-mechanical systems based on freestanding monolayered gold NP membranes

Chemical patterns of Octadecyltrimethoxysilane monolayers for the selective deposition of gold nanoparticles on silicon substrate

Abstract not available

Versatile, rapid and robust nano-positioning of single-photon emitters by AFM-nanoxerography

International audienceAbstract Atomic force microscopy (AFM) nanoxerography was successfully used to direct the assembly of colloidal nanodiamonds (NDs) containing nitrogen-vacancy (NV) centres on electrostatically patterned surfaces. This study reveals that the number of deposited NDs can be controlled by tuning the surface potentials of positively charged dots on a negatively charged background written by AFM in a thin PMMA electret film, yielding assemblies down to a unique single-photon emitter with very good selectivity. The mechanisms of the ND directed assembly are attested by numerical simulations. This robust deterministic nano-positioning of quantum emitters thus offers great opportunities for ultimate applications in nanophotonics for quantum technologies