An ultra-thin Schottky diode as a transmission particle detector for biological microbeams

Abstract

We fabricated ultrathin metal-semiconductor Schottky diodes for use as transmission particle detectors in the biological microbeam at Columbia University’s Radiological Research Accelerator Facility (RARAF). The RARAF microbeam can deliver a precise dose of ionizing radiation in cell nuclei with sub-micron precision. To ensure an accurate delivery of charged particles, the facility currently uses a commercial charged-particle detector placed after the sample. We present here a transmission detector that will be placed between the particle accelerator and the biological specimen, allowing the irradiation of samples that would otherwise block radiation from reaching a detector behind the sample. Four detectors were fabricated with co-planar gold and aluminum electrodes thermally evaporated onto etched n-type crystalline silicon substrates, with device thicknesses ranging from 8.5 μm – 13.5 μm. We show coincident detections and pulse-height distributions of charged particles in both the transmission detector and the commercial detector above it. Detections are demonstrated at a range of operating conditions, including incoming particle type, count rate, and beam location on the detectors. The 13.5 μm detector is shown to work best to detect 2.7 MeV protons (H+), and the 8.5 μm detector is shown to work best to detect 5.4 MeV alpha particles (4He++). The development of a transmission detector enables a range of new experiments to take place at RARAF on radiation-stopping samples such as thick tissues, targets that need immersion microscopy, and integrated microfluidic devices for handling larger quantities of cells and small organisms.

The cytoplasm as a radiation target: an in silico study of microbeam cell irradiation

“…An alternative method being developed is to select the incident particle energy so it fully penetrates the target and can be detected downstream of the cell by an array of micrometer sized detectors (Niklas et al 2013). Like the ion gas counter of the CENBG microbeam line, other transmission detectors are being developed that can be used upstream of the target (Grad et al 2012) allowing the use of thicker targets and less restriction on the energy of the incident particles. These results may also have some implications for the bystander effect, where unirradiated cells exhibit a biological response to signals from neighbouring irradiated cells.…”

Optofluidic cell manipulation for a biological microbeam

“…Recently, our group has been working on the development of ultra-thin silicon substrates (5-10 μm) that do not significantly scatter alpha particles. 28 Fabrication of an OET device on this etched silicon substrate is necessary for integration into the RARAF charged particle microbeams.…”

Focused ion beam irradiation platform with a 3-D fluorescence imaging system: a flexible tool for cancer research

“…Columbia University's RARAF facility has been designing, developing, and using focused ion beams for biological irradiation for more than 30 years 17, [23][24][25][26][27][28][29][30][31][32][33][34][35] . The focusing systems have used quadrupole focusing elements in electrostatic triplets and quadruplets 24,33 and permanent magnets 26 .…”