Lisa Karlsson

Nanometre-scale evidence for interfacial dissolution–reprecipitation control of silicate glass corrosion

Silicate glasses are durable solids, and yet they are chemically unstable in contact with aqueous fluids-this has important implications for numerous industrial applications related to the corrosion resistance of glasses, or the biogeochemical weathering of volcanic glasses in seawater. The aqueous dissolution of synthetic and natural glasses results in the formation of a hydrated, cation-depleted near-surface alteration zone and, depending on alteration conditions, secondary crystalline phases on the surface. The long-standing accepted model of glass corrosion is based on diffusion-coupled hydration and selective cation release, producing a surface-altered zone. However, using a combination of advanced atomic-resolution analytical techniques, our data for the first time reveal that the structural and chemical interface between the pristine glass and altered zone is always extremely sharp, with gradients in the nanometre to sub-nanometre range. These findings support a new corrosion mechanism, interfacial dissolution-reprecipitation. Moreover, they also highlight the importance of using analytical methods with very high spatial and mass resolution for deciphering the nanometre-scale processes controlling corrosion. Our findings provide evidence that interfacial dissolution-reprecipitation may be a universal reaction mechanism that controls both silicate glass corrosion and mineral weathering.

Electrical properties of self-assembled branched InAs nanowire junctions

We investigate electrical properties of self-assembled branched InAs nanowires. The branched nanowires are catalytically grown using chemical beam epitaxy, and three-terminal nanoelectronic devices are fabricated from the branched nanowires using electron-beam lithography. We demonstrate that, in difference from conventional macroscopic junctions, the fabricated self-assembled nanowire junction devices exhibit tunable nonlinear electrical characteristics and a signature of ballistic electron transport. As an example of applications, we demonstrate that the self-assembled three-terminal nanowire junctions can be used to implement the functions of frequency mixing, multiplication, and phase-difference detection of input electrical signals at room temperature. Our results suggest a wide range of potential applications of branched semiconductor nanostructures in nanoelectronics.

Electrospraying of colloidal nanoparticles for seeding of nanostructure growth

Nanometre-sized particles (1-100 nm) have unique properties receiving growing attention in wide areas of research. Here, a convenient method to deposit size-selected nanoparticles on surfaces by means of electrospraying colloidal suspensions in the aerosol phase is presented. We demonstrate the deposition of individual nanoparticles and the feasibility of this method in seeding gold particles for nanostructure growth. An advantage of the present method is the easy set-up and operation, using only commercially available machinery and substances. Problems regarding low deposition rates and colloidal remnants are approached, e. g. the aerosol flow is examined in a differential mobility analyser. This method is not material dependent and could be extended to deposit any colloidal particle.

Improving InAs nanotree growth with composition-controlled Au–In nanoparticles

Au nanoparticles are commonly used as seeds for epitaxial growth of III-V semiconductor nanowires. However, the interaction between Au and In-containing III-V materials makes it difficult to control the growth of more complex nanowire structures in materials such as InAs. Here we report the growth of InAs nanowires and branched nanotrees using Au and Au-In nanoparticles. We show that the initial composition of the particle does not affect the morphology of the first-generation nanowires, nor does it affect the final composition of the particle after growth. However, when the Au-In particles were used to seed a second generation of nanowires, producing nanotrees, the branches exhibited a 2-3 times higher growth rate and more regular shape than those seeded by pure Au particles. This result is attributed to the decreased interaction between the seed particle and the trunk nanowires when Au-In particles are used. Thus the incorporation of In into the seed particle during particle production allows for modification of the particle-wire interaction.

Understanding the 3D structure of \mathrm {GaAs\langle 111\rangle B} nanowires

The effects of lamellar twinning in epitaxial particle-assisted nanowires are investigated in an extensive high resolution electron microscopy (HRTEM) study of the low index zones , , and . As these directions are non-parallel to the () twin planes we find that the twin segments exhibit two different zone axes as a consequence of twinning. In the first three cases the alternative zones were found to be , and . These findings are supported by a comparison of experimental HRTEM images and multi-slice simulations along with fast Fourier transform mapping. From the appearance of non-overlapping regions we conclude that the nanowires are bound by {111} facets only. The twin formation and the development of the stable side facets are discussed.The effects of lamellar twinning in epitaxial particle-assisted GaAs B nanowires are investigated in an extensive high resolution electron microscopy (HRTEM) study of the low index zones , , and . As these directions are non-parallel to the (-1-1-1) twin planes we find that the twin segments exhibit two different zone axes as a consequence of twinning. In the first three cases the alternative zones were found to be and . These findings are supported by a comparison of experimental HRTEM images and multi-slice simulations along with fast Fourier transform mapping. From the appearance of non-overlapping regions we conclude that the nanowires are bound by {111} facets only. The twin formation and the development of the stable side facets are discussed (Less)

Size- and compostition-controlled Au-Ga aerosol nanoparticles

A simple gas-phase method has been developed for producing size- and composition-controlled nanoparticles of binary alloys. The process includes the formation and classification of aerosol nanoparticles of one material and the subsequent condensation of a controlled shell of another. The shell thickness is controlled by the evaporation temperature of the second material. Here we study the Au–Ga system with particle compositions ranging from pure Au to 50 atomic percent Ga. Transmission electron microscopy was used to study the morphology, composition, and structure of the generated particles.

Understanding the 3D structure of GaAs⟨111⟩B nanowires

The effects of lamellar twinning in epitaxial particle-assisted nanowires are investigated in an extensive high resolution electron microscopy (HRTEM) study of the low index zones , , and . As these directions are non-parallel to the () twin planes we find that the twin segments exhibit two different zone axes as a consequence of twinning. In the first three cases the alternative zones were found to be , and . These findings are supported by a comparison of experimental HRTEM images and multi-slice simulations along with fast Fourier transform mapping. From the appearance of non-overlapping regions we conclude that the nanowires are bound by {111} facets only. The twin formation and the development of the stable side facets are discussed.The effects of lamellar twinning in epitaxial particle-assisted GaAs B nanowires are investigated in an extensive high resolution electron microscopy (HRTEM) study of the low index zones , , and . As these directions are non-parallel to the (-1-1-1) twin planes we find that the twin segments exhibit two different zone axes as a consequence of twinning. In the first three cases the alternative zones were found to be and . These findings are supported by a comparison of experimental HRTEM images and multi-slice simulations along with fast Fourier transform mapping. From the appearance of non-overlapping regions we conclude that the nanowires are bound by {111} facets only. The twin formation and the development of the stable side facets are discussed (Less)

Crystal structure of branched epitaxial III-V nanotrees

In this review we discuss the morphology and crystal structure of branched epitaxial III–V semiconductor structures, so called nanotrees, based on our own work with GaP, InAs and GaP/InP. These structures are formed by epitaxial growth in a step-wise procedure where each level can be individually controlled in terms of diameter, length and composition. Poly-typism is commonly observed for III–Vs with zinc blende, wurtzite or combinations thereof as the resulting crystal structure. Here we review GaP as an example of zinc blende and InAs of wurtzite type of growth in terms of nanotrees with two to three levels of growth. Included are also previously unpublished results on the growth of GaP/InP nanotrees to demonstrate effects of heteroepitaxial growth with substantial mismatch. For these structures a topotaxial growth behavior was observed with InP wires crawling along or spiraling around the GaP nanowires acting as a free-standing substrates.

Experimental evidence for evaporation/condensation nonuniform flow in a horizontal aerosol generator

The formation of deposition patterns in the cooling zone during operation of a horizontal evaporation/condensation nanoparticle generator was studied to obtain information about flow conditions during particle formation. Quartz reactor tubes were used together with a simple light attenuation measurement to characterize deposition as a function of axial location. Results for the onset and pattern of deposition for four different metals—indium, gallium, silver, and lead—were obtained, and size distributions for indium and gallium particle nanoparticles at different temperatures were measured. Distinct deposition bands could be observed resulting from vapor deposition, nanoparticle deposition, or a combination of both. The location of the bands varied with metal and evaporation temperature. Experimentally observed fluctuations in temperature, bimodal size distributions obtained at the highest furnace temperatures, as well as asymmetric deposition patterns suggested the flow in the cooling portion of the generator is nonuniform, possibly as a result of buoyancy. These results are important for the design of nanoparticle generation systems, in that horizontal evaporation/condensation generators are often chosen on the basis of assumed simplicity with respect to flow, and this may not always be the case.

Understanding the 3D structure of GaAs nanowires

The effects of lamellar twinning in epitaxial particle-assisted nanowires are investigated in an extensive high resolution electron microscopy (HRTEM) study of the low index zones , , and . As these directions are non-parallel to the () twin planes we find that the twin segments exhibit two different zone axes as a consequence of twinning. In the first three cases the alternative zones were found to be , and . These findings are supported by a comparison of experimental HRTEM images and multi-slice simulations along with fast Fourier transform mapping. From the appearance of non-overlapping regions we conclude that the nanowires are bound by {111} facets only. The twin formation and the development of the stable side facets are discussed.The effects of lamellar twinning in epitaxial particle-assisted GaAs B nanowires are investigated in an extensive high resolution electron microscopy (HRTEM) study of the low index zones , , and . As these directions are non-parallel to the (-1-1-1) twin planes we find that the twin segments exhibit two different zone axes as a consequence of twinning. In the first three cases the alternative zones were found to be and . These findings are supported by a comparison of experimental HRTEM images and multi-slice simulations along with fast Fourier transform mapping. From the appearance of non-overlapping regions we conclude that the nanowires are bound by {111} facets only. The twin formation and the development of the stable side facets are discussed (Less)