After completion of an independent review, a new launch date for the James Webb Space Telescope has been announced: 30 March 2021.
An object from another star system that made a brief appearance in our skies guised as an asteroid turns out to be a tiny interstellar comet.
Data from the international Cassini spacecraft have revealed complex organic molecules originating from Saturn’s icy moon Enceladus, strengthening the idea that this ocean-world hosts conditions suitable for life.
A surprising application of graphene is its use in photodetectors. Light detection capabilities of graphene are inherently limited because a single sheet of the material absorbs only ~2.3% of light across the visible part of the spectrum. Such high transparency is desired for applications such as transparent conductors, however detecting light requires strong absorption. Nevertheless, the frequency-independent absorption of graphene coupled with extremely high carrier mobility peaked the interest of optics researchers, who found that interfacing graphene with strong light-absorbing materials can result in excellent practical photodetectors that surpass the capabilities of competing materials.
First attempts of improving the photoresponse of graphene were in the direction of integration in nanocavities, microcavities, and plasmonic resonators, nano-engineered devices that locally increase the intensity of light, so that more response is obtained from the same graphene. These approached yield high sensitivity, however they restrict the usable bandwidth, cancelling the broadband nature of graphene. Spectrally broader response was obtained from hybrid graphene-quantum dot detectors, which however sacrificed device speed. Finally, a balance was achieved by laying graphene over photonic waveguides, increasing responsivity to 0.1 A/W with 20 GHz operation. The same working principle was since integrated in wafer-scale production and pushed to 75 GHz.
A particularly interesting direction of research is the use of hybrid graphene-quantum dot photodetectors as broadband image sensors for CMOS cameras. These fab-compatible devices have very high responsivity, on the order of 107 A/W and operate in both the visible and short-wave infrared parts of the spectrum (300-2,000 nm). The response times are fast enough (0.1-1 ms) for use in infrared cameras. What is perhaps the most interesting about this device is that it is a CMOS integrated circuit, similar to those used for commercial image sensors in digital cameras, commonly used in smartphones. Thus exploiting the full broadband capability of graphene, such chips will enable applications in safety and security, night vision, smartphone cameras, automotive sensor systems, food and pharmaceutical inspection, and environmental monitoring beyond capabilities offered by state-of-the-art semiconductor chips.
Illustration of photovoltage creation following light absorption in graphene (image copyright 2015 Achim Woessner)
Other approaches employ plasmon resonances to locally enhance intensity in graphene. Plasmons are light waves coupled to electron oscillations on the surface of a metal. Because plasmons are confined to a surface and because they propagate near the speed of light, they are considered by many as good candidates for on-chip optical information processing. Plasmon-enhanced photoresponse in graphene can have applications in nanoscale optoelectronic devices, where precise control of light behavior on dimensions smaller than half a wavelength is desired.
Other than for light detection, graphene can be used in light-emitting devices as well. An archetypal usage of graphene in such devices is as a transparent electrode. Transparent conductor applications are certainly an exciting application of graphene, because of its high transparency and extremely large carrier mobility. For example, graphene has been used as an electrode in organic light emitting diodes (OLEDs) which compose many of today’s screens and monitors. Another use, again enabled by graphene’s unusual electronic properties, is electrical control of light emission from molecules, with potential applications in optoelectronics.
Photodetection is one of many interesting uses of graphene. Some types of graphene-based photodetectors, for example the ones that utilize quantum dots or surface plasmons, can make use of graphene field effect transistors (GFETs). Researchers working in this field can now benefit from ready-made GFETs available from Graphenea, reducing the entry barriers and speeding up device development.
ISOLDE researcher Magdalena Kowalska is leading the study into DNA molecules using isotopes.
Though known for particle physics, CERN’s facilities also dip their toes into other fields. For example, researchers at CERN’s nuclear physics facility, ISOLDE, have been investigating DNA molecules. The researchers have applied an ultrasensitive variant of nuclear magnetic resonance (NMR) spectroscopy, called beta-NMR, to these molecules in both solid and cell-like liquid environments. Beta-NMR has been used widely to study exotic nuclei and solid materials, but this is the first time the technique has been applied to biological matter.
The data, recorded in May, show that the NMR signal produced by a sodium isotope changes and disappears much more slowly in the presence of DNA than without it. This points to the expected interaction between this vital element and DNA. Future work should shed more light on this interaction and uncover the binding site of sodium in the DNA.
NMR spectroscopy is one of the go-to techniques for visualising the structure of biological molecules, such as proteins and DNA, and their interaction with essential metal ions such as sodium and potassium. It does so by placing a few micrograms of a sample of biological molecules in a strong magnetic field and analysing how the magnetic nuclei within the sample absorb radio waves. The magnetic field causes these nuclei, or spins, to line up either parallel or antiparallel to the magnetic field, and the radio waves cause the spins to change between different spin directions. The radio frequency that triggers this change depends on the strength of the magnetic field and the identity and environment of the atoms of the nuclei. The spin flip, or NMR signal, is detected through the electric current it induces in a radiofrequency coil.
However, the technique is relatively insensitive; to produce a useful NMR signal, it requires a large number of magnetic nuclei. By contrast, beta-NMR spectroscopy requires far fewer magnetic nuclei inside the sample. In this variant of NMR, which is up to a billion times more sensitive than conventional NMR, the magnetic nuclei can be neatly oriented using lasers and the NMR signal is detected through the emission of beta particles (electrons or positrons) from magnetic short-lived nuclei that are implanted into the sample.
In their study, the ISOLDE researchers, led by Magdalena Kowalska, took short-livedsodium ions produced at the ISOLDE facility, placed them into samples containing DNA molecules – both solid and cell-like liquid samples – and applied the beta-NMR technique. They studied DNA G-quadruplex structures, which are a variation of the well-known double-helix structure.
The researchers found that the NMR signal emitted by sodium disappears much more slowly, on a timescale of the order of a second, when DNA G-quadruplex structuresare present in the samples. The result is in agreement with classical NMR studies on other DNA structures, which showed that the same can happen when “free” sodium moves towards DNA. Future work involving a detailed comparison between the NMR spectra and chemical calculations is expected to reveal the location of sodium in the DNA samples.
In the long run, the researchers also hope to use other isotopes, such as copper and zinc, which, for reasons that are not yet fully clear, tend to be found in large and small quantities respectively, in the brains of patients with Alzheimer’s or Parkinson’s disease.
All high-resolution images and the underpinning data from Rosetta’s pioneering mission at Comet 67P/Churyumov-Gerasimenko are now available in ESA’s archives, with the last release including the iconic images of finding lander Philae, and Rosetta’s final descent to the comet’s surface.
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.
ESA’s XMM-Newton observatory has discovered the best-ever candidate for a very rare and elusive type of cosmic phenomenon: a medium-weight black hole in the process of tearing apart and feasting on a nearby star.
Artist’s impression of the merger of two neutron stars (Image: University of Warwick/Mark Garlick)
Quark matter – an extremely dense phase of matter made up of subatomic particles called quarks – may exist at the heart of neutron stars. It can also be created for brief moments in particle colliders on Earth, such as CERN’s Large Hadron Collider. But the collective behaviour of quark matter isn’t easy to pin down. In a colloquium this week at CERN, Aleksi Kurkela from CERN’s Theory department and the University of Stavanger, Norway, explained how neutron-star data have allowed him and his colleagues to place tight bounds on the collective behaviour of this extreme form of matter.
Kurkela and colleagues used a neutron-star property deduced from the first observation by the LIGO and Virgo scientific collaborations of gravitational waves – ripples in the fabric of spacetime – emitted by the merger of two neutron stars. This property describes the stiffness of a star in response to stresses caused by the gravitational pull of a companion star, and is known technically as tidal deformability.
To describe the collective behaviour of quark matter, physicists generally employ equations of state, which relate the pressure of a state of matter to other state properties. But they have yet to come up with a unique equation of state for quark matter; they have derived only families of such equations. By plugging tidal-deformability values of the neutron stars observed by LIGO and Virgo into a derivation of a family of equations of state for neutron-star quark matter, Kurkela and colleagues were able to dramatically reduce the size of that equation family. Such a reduced family provides more stringent limits on the collective properties of quark matter, and more generally on nuclear matter at high densities, than were previously available.
Armed with these results, the researchers then flipped the problem around and used the quark-matter limits to deduce neutron-star properties. Using this approach, the team obtained the relationship between the radius and mass of a neutron star, and found that the maximum radius of a neutron star that is 1.4 times more massive than the Sun should be between about 10 and 14 km.
Want to find out more? Read the paper describing the research.
