Henrik Björkman

Diamond replicas from microstructured silicon masters

Abstract We are developing a microstructure technology for thick film diamond replicas, using deposition by hot filament chemical vapour deposition (CVD) on microstructured silicon. This technology is primarily intended to make micromechanical structures for microstructured carriers, fluidic cooling systems, systems for biochemical analyses and processes, and moulds for thermoplastic and metal microstructures. With thick film deposition ridges, trenches, and capillary channels with high resolution coverage and low roughness, rms

Diamond microstructures for optical micro electromechanical systems

We have used hot filament chemical vapour deposition (HFCVD) to fabricate diamond microstructure components for optical micro electromechanical systems (MEMS). In order to demonstrate the wide application range for diamond technology we have made componen

Split Renal Function in Patients with Suspected Renal Artery Stenosis: a Comparison between Gamma Camera Renography and Two Methods of Measurement with Computed Tomography

Purpose: To validate a method for calculating split renal function from computed tomography (CT) compared with gamma camera renography, and to test a new method for the measurement based on a volume-rendering technique. Material and Methods: Thirty-eight patients, aged 65.7±11.6 (range 37.8–82.1) years, who had undergone both CT angiography and gamma camera renography for a suspected renal artery stenosis were included in this study. Split renal function was calculated from the CT examinations by measuring area and mean attenuation in the image slices of the kidneys, and also by measuring volume and mean attenuation from a 3D reconstruction of the kidneys. Gamma camera renography with 99mTc-MAG3 with or without captopril enhancement was used as a reference. Results: The 2D CT method had good correlation with renography (r = 0.93). Mean difference was 4.7±3.6 (0–12) percentage points per kidney. There was also excellent correlation between the two CT methods (r = 1.00). Conclusion: CT is equivalent to renography in determining split renal function, and the measurement from the CT examination can be made more quickly and equally accurately with a 3D technique.

Designed abrasive diamond surfaces

With the aim to explore their abrasive and grinding properties, flat diamond surfaces with protruding pyramidal abrasive tips have been designed and manufactured. The manufacturing process is a replica technique based on hot filament chemical vapour deposition of diamond onto a silicon wafer, in which the shape, size and packing pattern of the pyramids have been defined by photolithography and etching. After the diamond deposition, the silicon master is removed by etching and the thin diamond film is cemented to a supporting steel disk. Three different pyramid sizes, each with two different packing densities, were fabricated on the same silicon wafer. One of these structures was selected for further evaluation. The resulting shape and quality of the diamond surface was evaluated by scanning electron microscopy (SEM) and Raman spectroscopy. The abrasive properties and durability were evaluated in a pin-on-disc test followed by SEM studies of the abrasive structures and the abraded surfaces. The manufacturing process proved successful in producing well-defined abrasive diamond structures, showing practically constant tip shape and size. The diamond structures suffered negligible damage when abrading brass and tin, exhibited limited fracture when abrading steel, and rather extensive fracture when abrading aluminium oxide. The fracture was mainly due to an unintentional limited diamond thickness in the outermost parts of the pyramids. The combination of extreme mechanical properties of diamond and possibilities to design exceptionally well-defined abrasive structures promise very interesting possibilities for development of novel grinding tools and standardised abrasive wear tests.

Diamond microstructure replicas from silicon masters

We are developing a microstructure technology for thick film diamond replicas, using deposition by hot filament CVD on microstructured silicon. This technology is primarily intended to make micromechanical structures for building-sets, fluidic cooling systems, systems for biochemical analyses and processes, and moulds for thermoplastic microstructures. In the thick film deposition on trenches in silicon, complete filling was possible with an aspect ratio up to 1.6. At higher aspect ratios, voids or channels are formed within the diamond replica. Ridges, trenches and capillary channels with high resolution coverage and low roughness, rms<2 nm, were created. Demonstrator structures for microfluidic, building-sets and polymer moulding applications are presented.

Microstructured diamond dies for transfer moulding

The wear of Ni dies, used for transfer moulding of abrasive polymer compounds, was investigated and found to be too severe for high precision moulding of micromechanical structures. A diamond die was manufactured as an alternative. It consisted of a thin replicated diamond film on an electroplated Ni carrier. The wear of the diamond die was investigated and found to be negligible. Initially, with normal hydrogen-terminated diamond surfaces, the polymer stuck to the die. The reason for this was that a hydrogen-terminated diamond surface is hydrophobic, which makes it difficult for the release spray to stay on the diamond surface. To solve the problem, the diamond surface was made hydrophilic (polar) by wet oxidation, which enabled the release spray to stay on the surface during plastic moulding. Consequently, no sticking of the polymer to the polar diamond surface was observed. Thus, diamond proved to be a very good die material, with enormous wear resistance compared to Ni, for transfer moulding of abrasive polymers.

Diamond microstructures for optical MEMS

Diamond is difficult to micromachine due to its hardness and chemical inertness. Therefore it is preferable to make use of diamond replication. The well developed area of silicon micromachining makes it possible to fabricate complicated structures that can be used as moulds for diamond. A microstructure technology for diamond replicas following the authors process flow scheme below is given. Different silicon microstructures have been manufactured by standard bulk micromachining processes i.e. lithography, wet etching, and dry etching, to evaluate diamond replication.