After a nearly twenty-year long game of cosmic hide-and-seek, astronomers using ESA’s XMM-Newton space observatory have finally found evidence of hot, diffuse gas permeating the cosmos, closing a puzzling gap in the overall budget of ‘normal’ matter in the Universe.
The market for magnetic field sensors is an expanding one, with size estimates up to USD 4.16 billion in 2022. The multiple purposes of magnetic field sensors such as position detection, current monitoring, speed detection, and angular sensing allow access to a wide range of industries such as automotive, consumer electronics, healthcare and defense. A most common magnetic sensor type utilizes the Hall effect, the production of a potential difference across an electrical conductor when a magnetic field is applied. Hall effect-based sensors constitute 55% of the market share for magnetic sensors.
The key factor for determining sensitivity of Hall effect sensors is high electron mobility. As such, graphene is a highly interesting material for this application, with measured carrier mobility in excess of 200,000 cm2 V-1 s-1. Graphene Hall sensors with current-related sensitivity up to 5700 V/AT and voltage-related sensitivity up to 3 V/VT were demonstrated in graphene encapsulated in boron nitride. Such performance outpaces state-of-the-art silicon and III/V Halls sensors, with a magnetic resolution as low as 50 nT/√Hz. The current practical limit for sensitivity of graphene Halls devices on industry standard wafers is around ~3000 V/AT. For comparison, state of the art Hall sensors from traditional CMOS-compatible materials have sensitivity on the order of ~100 V/AT. Even flexible graphene Hall sensors, produced on Kapton tape, reach sensitivities similar to rigid silicon Hall sensors.
Image: GFET S-10 chip with graphene FETs.
Graphene Hall sensors consist of a graphene sheet on a substrate. The sheet is patterned into a “Hall bar” geometry, with two electrodes on each side providing the source and drain for the charge carriers, and four electrodes on the lateral sides to measure the potential difference. Graphenea provides a chip that houses thirty graphene Hall-bar devices and an additional six with a standard 2-probe geometry. The standard chip offer varying channel length and width, with constant high quality evidenced by field effect mobilities in excess of 1000 cm2/Vs, residual charge carrier densities lower than 2x1012 cm-2, and quality control inspection with Raman spectroscopy and optical microscopy.
European hadron therapy facilities in operation or under construction in 2016 (Image: CERN Courier)
From 19 to 21 June, sixty experts from all over the world are meeting at the European Scientific Institute (ESI) in Archamps, France, to explore future medical accelerators for treating cancer with ions. Ion therapy, also known as hadron therapy, is an advanced form of radiotherapy that uses protons and other ions to precisely target tumour cells while sparing the surrounding healthy tissues. While commercial solutions for proton therapy are now available, there are only a few bespoke facilities providing heavier ions such as carbon. The cost, complexity and size of these facilities are hampering the widespread adoption of this treatment (read more in the CERN Courier features “Therapeutic Particles” and “The changing landscape of cancer therapy”).
The workshop, jointly organised by CERN and GSI, allows scientists to exchange ideas, share current experiences and explore future possibilities towards the design for a next-generation medical research and therapy facility with ions in Europe. It is the second workshop in the series “Ions for cancer therapy, space research and material science”, initiated by GSI to highlight the increasingly important interface between physics and its applications.
CERN’s Maurizio Vretenar, one of the workshop co-organisers, presented “Accelerators for Medicine” last week at CERN. He reviewed the different applications of particle accelerators to the medical field, from cancer treatment with beams of accelerator-produced particles (photons, electrons, protons, ions and neutrons) to the generation of radioactive isotopes used in medical diagnostics, cancer therapy and the new domain of theragnostics. He outlined the status, the potential, and the challenges of meeting the increasing demand for therapeutic procedures based on accelerators.
Watch the recording of the “Accelerators for Medicine” Academic Training Lecture here.
