Bulk metallic glasses (BMGs) are strong, highly elastic, and resistant to wear but still find limited utility due to their macroscopic brittle nature, high costs, and difficulty of processing, particularly when complex shapes are desired. These drawbacks can be mitigated when BMGs are used in miniature parts (< 1 cm), an application which takes advantage of BMGs' enhanced plasticity at small length scales as well the insignificant material cost associated with such parts. As an alternative to traditional metal processing techniques, thermoplastic forming (TPF)-based microfabrication methods have been developed which can process some BMGs like plastics. In this article, we discuss the properties and fabrication of BMGs on minuscule length scales to explore their prospective application in small-scale devices.

A micromachining process is described for fabricating a mass spectrometry electrospray source on a silicon chip. The process utilizes polymer (parylene) layers to form a system of chambers, filters, channels, and hollow needle structures (electrospray emitters) that extend more than a millimeter beyond the edge of the silicon substrate. The use of photoresist as the sacrificial layer facilitates the creation of long channels. Access to the channel structures on the chip is through a port etched through the silicon substrate that also serves as a sample reservoir. A reusable chip holder consisting of two plastic plates and an elastomer gasket provides the means to mount the chip in front of the mass spectrometer inlet and make electrical and gas connections. The electrospray emitters have tapered tips with 5 microns x 10 microns rectangular openings. The shape of the tip can be varied depending on the shape of the mask used to protect the parylene structures during the final plasma etch. The parylene emitters are physically robust and require only a high electric field to achieve stable electrospray operation over a period of a few hours. Direct comparisons with conventional glass or fused silica emitters indicated very similar performance with respect to signal strength and stability, spectral quality, and endurance. The automated MS/MS analysis of a mixture of tryptic peptides was no more difficult and yielded nearly identical results as the analysis of the same sample using a conventional nanospray device. This work demonstrates that an efficient electrospray interface to mass spectrometry can be integrated with other on-chip structures and mass-produced using a batch process.

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