Mats Boman

Self-Supported Three-Dimensional Nanoelectrodes for Microbattery Applications

A nanostructured three-dimensional (3D) microbattery has been produced and cycled in a Li-ion battery. It consists of a current collector of aluminum nanorods, a uniform layer of 17 nm TiO(2) covering the nanorods made using ALD, an electrolyte and metallic lithium counter electrode. The battery is electrochemically cycled more than 50 times. The increase in total capacity is 10 times when using a 3D architecture compared to a 2D system for the same footprint area.

Microfabrication of three‐dimensional boron structures by laser chemical processing

A method for microfabrication of three‐dimensional structures in free space is presented. Laser‐assisted chemical vapor deposition is used to grow a material at a point where a laser beam locally heats the substrate. By moving the substrate relative to the laser beam with a micropositioning system, three‐dimensional shapes can be created. Helical shapes are generated utilizing three linear translational axes as well as an additional rotational axis. Tilting the substrate to align the growth direction with the laser beam direction facilitates improved process control. The smallest structures that can be grown with this technique are about 1 μm. Amorphous boron fibers and crystalline boron springs have been manufactured as two examples of micromechanical elements. The amorphous boron fibers show excellent mechanical properties: A modulus of elasticity of 420–450 GPa, a fracture strain of 2.7%–3.7%, and a fracture stress of 12–17 GPa. The crystalline boron springs produced so far display only moderate mechan...

Carbon growth by thermal laser-assisted chemical vapour deposition

Abstract The heated area in thermal laser-assisted chemical vapour deposition (LCVD) is much smaller than in large area CVD. This affects the growth conditions drastically. One important growth aspect is that CVD processes requiring homogeneous reactions in the vapour are not effective for thermal LCVD. In this work LCVD of carbon from a non-adsorbable precursor (CH 4 ) and an adsorbable precursor (C 2 H 4 ) in combination with cold wall and hot wall reactors was investigated. The combination with the hot wall reactor also means that adsorbable carbon-carrying species can be generated homogeneously in the vapour before deposition. For laser CVD of carbon from CH 4 a high deposition temperature was needed. The threshold laser power density was 9.0 × 10 4 W cm −2 (3500 K) for a hot wall reactor temperature of 1270 K. For carbon LCVD from C 2 H 4 carbon lines could be deposited already under cold wall conditions at the same laser power density as was used in the CH 4 case. The thickness profile perpendicular to the grown lines was close to gaussian for deposition temperatures below 3600 K. Bimodal profiles, which were observed for higher temperatures, indicate evaporation or surface diffusion of carbon. The deposited lines were fine grained with a nodular appearance. Crystalline carbon was found to grow in a layer structure parallel to the substrate surface. The lines deposited from CH 4 were considerably wider than the laser spot diameter. This may be due to the thermal anisotropy of the material. The temperature profile and also the line will be broadened since the heat conduction is much better along the graphitic planes than perpendicular to them. The lateral growth direction of the lines as well as the orientation of the graphite layers indicate that the edge atoms of the graphitic basal planes are very active during the growth.

Deposition of palladium nanoparticles on the pore walls of anodic alumina using sequential electroless deposition

Palladium nanoparticles were deposited using a sequential electroless deposition technique on the pore walls of nanoporous anodic alumina. For the particle deposition a Pd(NH3)42+ solution was soaked in the alumina membrane and a heated air flow was applied in order to reduce the palladium complex to palladium metal nanoparticles. By repeating the deposition process the size of the nanoparticles could be tailored in this investigation between 6 and 11nm. The size of the nanoparticles was also affected by the concentration of the Pd(NH3)42+ solution, i.e., higher concentration yielded larger particle mean diameters. The samples were investigated using high resolution scanning electron microscopy, x-ray diffraction (XRD), inductively coupled plasma with a mass spectrometer, high resolution transmission electron microscopy, and energy dispersive spectroscopy (EDS). Analysis revealed narrow size distributions of the particles as well as uniform particle coverage of the pore walls. No by-products were observed...

Well-ordered nanopore arrays in rutile TiO2 single crystals by swift heavy ion-beam lithography

Ion track lithography has been applied for transferring the self-ordered nanopattern of porous anodic alumina to single-crystalline rutile TiO2 substrates. As a result, nanometre resolved arrays have been fabricated with an aspect ratio ranging from 5 to 16, over areas of several square millimetres. Differences in the expected aspect ratio of the resulting nanopores in rutile TiO2 single crystals are analysed and discussed. Some of these differences may be ascribed to varying densities of the mask material.

Free‐standing silicon microstructures fabricated by laser chemical processing

Laser‐assisted chemical‐vapor deposition (LCVD) is used for growth in ‘‘free space’’ of microscale fibers and helical structures of silicon. The LCVD technique is also used for fabrication of a tungsten coil on a cylindrical silicon substrate, i.e., a microsolenoid is realized. The microstructure of the silicon deposits is investigated by transmission electron microscopy, and their mechanical strength is evaluated by micromechanical testing in situ in a scanning electron microscope. The resistivity of the tungsten coil is measured, and the magnetic properties of the microsolenoid are investigated by means of superconducting quantum interference device equipment.

Selective deposition of tungsten—prediction of selectivity

Preferential or selective chemical vapor deposition to a substrate region is based on a difference in thermochemical stability between different substrate regions. The higher this difference is, the higher selectivity is expected. In this paper a thermodynamic analysis of selective deposition of tungsten from H2 and WF6 on silicon regions in the presence of silicon dioxide is presented. At the initial stages of growth—silicon present in the vapor—the selectivity is favored by a low temperature, a low total pressure and a high WF6 concentration in the vapor. For the continuation—growth on the deposited tungsten—a low total pressure, a low WF6 concentration in the vapor and a higher temperature than that used initially should be chosen for highest selectivity. From the analysis it is also seen that simultaneous etching and tungsten oxide/tungsten deposition may occur on the silicon dioxide. The technique used to analyze the selective tungsten deposition process seems to be a useful tool for optimizing the s...

Helical microstructures grown by laser assisted chemical vapor deposition

It is reported that laser-assisted chemical vapor deposition (LCVD) was used for growth in free space of microscale rods and helical structures of silicon. Using a newly developed rotable goniometer stage, the LCVD technique was also used for fabrication of a tungsten coil on a cylindrical silicon substrate, i.e. a simple microsolenoid was realized. The microstructure of the silicon deposits was investigated by cross-sectional transmission electron microscopy (TEM), and their mechanical strength was evaluated by micromechanical testing in situ in an SEM. The resistivity of the tungsten coil is measured, and the magnetic properties of the microsolenoid are investigated by means of SQUID equipment.<<ETX>>

A comparative study of size-distribution of nanoparticles generated by laser ablation of graphite and tungsten

Abstract Nanoparticles (NPs) were generated by ArF excimer laser ablation of graphite and tungsten targets in N2 ambient at atmospheric pressure. The size distribution of the particles was monitored in situ by a scanning mobility particle sizer (SMPS) system, based on differential mobility analyser. The experimental conditions made possible to record the size distributions in the 7–133-nm diameter range and results are presented for different laser fluences, repetition rates and ablated areas, respectively. Material analysis was performed by photoelectron spectroscopy (XPS), Raman spectroscopy, X ray diffraction and SEM.

Freeform fabrication of functional microsolenoids, electromagnets and helical springs using high-pressure laser chemical vapor deposition

This paper reports recent progress in the use of 3D-LCVD as a viable micromanufacturing tool for helical microstructures. Freestanding fibers of diamond-like carbon were grown from ethylene at linear rates of up to 3.5 mm/s. Helical carbon fiber coils were also grown, yielding highly elastic springs which may be used in low-frequency-response accelerometers, seismometers, and switching devices. Continuous fibers with diameters as small as 5 /spl mu/m were obtained at ethylene pressures of 3 atmospheres. Freestanding conductive coils of polycrystalline tungsten and tungsten carbide were also grown at axial deposition rates of up to 175 /spl mu/m/s using mixtures of WF/sub 6/, H/sub 2/, and C/sub 2/H/sub 4/. Single-crystal tungsten needles of square cross-section and hexagonal tungsten carbide crystals were obtained with specific WF/sub 6/-H/sub 2/-C/sub 2/H/sub 4/-He mixtures. The WF/sub 6/-W/sub 2/-He-Xe system was studied to determine the effects of buffer gas molecular weight on the potential for natural convection and deposition rate enhancement during tungsten growth. In addition, high field-density microsolenoids 100 microns in diameter were written on boron fibers using laser direct writing. Tungsten lines were drawn about silicon-coated Co-Fe-Si-B magnetic cores from a mixture of WF/sub 6/ and hydrogen, yielding prototype microelectromagnets.