L. Nilsson

Bio: L. Nilsson is an academic researcher from University of Fribourg. The author has contributed to research in topics: Field electron emission & Carbon nanotube. The author has an hindex of 9, co-authored 11 publications receiving 1512 citations.

Scanning field emission from patterned carbon nanotube films

Abstract: The investigation of the field emission (FE) properties of carbon nanotube (CNT) films by a scanning anode FE apparatus, reveals a strong dependence on the density and morphology of the CNT deposit. Large differences between the microscopic and macroscopic current and emission site densities are observed, and explained in terms of a variation of the field enhancement factor β. As a consequence, the emitted current density can be optimized by tuning the density of CNTs. Films with medium densities (on the order of 107 emitters/cm2, according to electrostatic calculations) show the highest emitted current densities.

Patterned Films of Nanotubes Using Microcontact Printing of Catalysts

Abstract: change in the vibrational structure of the PL spectrum were effected by MWNTs. The reduction of the PL efficiency can be a result of energy transfer and partial hole transfer from PPV chains to MWNTs, together with scattering and absorption by MWNTs. Using the composite, photovoltaic devices have been fabricated by employing MWNT as a hole-collecting electrode. We obtained good quantum efficiency (1.8 % at 2.9±3.2 eV), about twice that of the standard ITO device. It is considered that the high efficiency arises from a complex interpenetrating network of PPV chains with MWNTs and the relatively high work function of the MWNT film. The present results suggest the possible application of carbon nanotubes as a new interesting electrode material in macroscale devices.

Characterization of thin film electron emitters by scanning anode field emission microscopy

Abstract: Scanning anode field emission microscopy is used to map the electron emission current I(x,y) under constant anode voltage and the electron extraction voltage V(x,y) under constant emission current as a function of tip position on carbon based thin film emitters. The spatially resolved field enhancement factor β(x,y) is derived from V(x,y) maps. It is shown that large variations in the emission site density (ESD) and current density can be explained in terms of the spatial variation of the field enhancement β(x,y). Comparison of β(x,y) and I(x,y) shows that electron emission currents are correlated to the presence of high aspect ratio field enhancing structures. We introduce the concept of field enhancement distribution f(β), which is derived from β(x,y) maps to characterize the field emission properties of thin films. In this context f(β)dβ gives the number of emitters on a unit surface with field enhancement factors in the interval (β,β+dβ). It is shown experimentally for the carbon thin film emitters investigated that f(β) has an exponential dependence with regard to the field enhancement factor β. The field enhancement distribution function f(β) can be said to give a complete characterization of the thin film field emission properties. As a consequence, the emitted current density and ESD can be optimized by tuning f(β) of the emitting thin film.

Printing Gel-like Catalysts for the Directed Growth of Multiwall Carbon Nanotubes

Abstract: Microcontact printing is used to transfer an Fe(III)-containing gel-like catalyst precursor from a hydrophilized elastomeric stamp to a substrate. The catalytic pattern activates the growth of multiwall carbon nanotubes using chemical vapor deposition of acetylene. Our results show that the choice of the catalyst is of extreme importance. Most of the aqueous and ethanolic Fe(III) inks used give rise to drying effects on the stamp surface, which lead to the formation of islands of the catalyst within the pattern. To avoid these shortcomings, we developed a catalyst precursor, which has better performance on the stamp and as a catalyst on the substrate. Simple aging of the ethanolic Fe(III) ink results in a polymerized gel-like catalyst, which can be printed homogeneously on the substrate with excellent contrast. Changing the concentration of the catalyst in the ink allows the density of the carbon nanotubes in the film to be tuned. A scanning anode field emission microscope was used to investigate the micr...

Collective emission degradation behavior of carbon nanotube thin-film electron emitters

Abstract: The current-induced emission degradation of a carbon nanotube (CNT) thin-film electron emitter is studied under constant emission current for different current levels, using a scanning anode field emission microscope. A permanent emission degradation is observed for emission currents higher than 300 nA per CNT and is associated with resistive heating at the CNT–substrate interface for the sample under investigation. A second field-induced emission degradation mechanism, associated with the removal of CNTs from the substrate, is also reported.

Diamond-like amorphous carbon

Abstract: Diamond-like carbon (DLC) is a metastable form of amorphous carbon with significant sp3 bonding. DLC is a semiconductor with a high mechanical hardness, chemical inertness, and optical transparency. This review will describe the deposition methods, deposition mechanisms, characterisation methods, electronic structure, gap states, defects, doping, luminescence, field emission, mechanical properties and some applications of DLCs. The films have widespread applications as protective coatings in areas, such as magnetic storage disks, optical windows and micro-electromechanical devices (MEMs).

Engineering atomic and molecular nanostructures at surfaces

Abstract: The fabrication methods of the microelectronics industry have been refined to produce ever smaller devices, but will soon reach their fundamental limits. A promising alternative route to even smaller functional systems with nanometre dimensions is the autonomous ordering and assembly of atoms and molecules on atomically well-defined surfaces. This approach combines ease of fabrication with exquisite control over the shape, composition and mesoscale organization of the surface structures formed. Once the mechanisms controlling the self-ordering phenomena are fully understood, the self-assembly and growth processes can be steered to create a wide range of surface nanostructures from metallic, semiconducting and molecular materials.

Electronic and transport properties of nanotubes

Abstract: This article reviews the electronic and transport properties of carbon nanotubes. The focus is mainly theoretical, but when appropriate the relation with experimental results is mentioned. While simple band-folding arguments will be invoked to rationalize how the metallic or semiconducting character of nanotubes is inferred from their topological structure, more sophisticated tight-binding and ab initio treatments will be introduced to discuss more subtle physical effects, such as those induced by curvature, tube-tube interactions, or topological defects. The same approach will be followed for transport properties. The fundamental aspects of conduction regimes and transport length scales will be presented using simple models of disorder, with the derivation of a few analytic results concerning specific situations of shortand long-range static perturbations. Further, the latest developments in semiempirical or ab initio simulations aimed at exploring the effect of realistic static scatterers chemical impurities, adsorbed molecules, etc. or inelastic electron-phonon interactions will be emphasized. Finally, specific issues, going beyond the noninteracting electron model, will be addressed, including excitonic effects in optical experiments, the Coulomb-blockade regime, and the Luttinger liquid, charge density waves, or superconducting transition.

Scanning field emission from patterned carbon nanotube films

Abstract: The investigation of the field emission (FE) properties of carbon nanotube (CNT) films by a scanning anode FE apparatus, reveals a strong dependence on the density and morphology of the CNT deposit. Large differences between the microscopic and macroscopic current and emission site densities are observed, and explained in terms of a variation of the field enhancement factor β. As a consequence, the emitted current density can be optimized by tuning the density of CNTs. Films with medium densities (on the order of 107 emitters/cm2, according to electrostatic calculations) show the highest emitted current densities.