Free-electron lasers (FELs) have an electron problem: a “dark” current that can propagate with the electron beam, limiting the performance of the system. Now Guan Shu of Zhangjiang Laboratory in China and colleagues have developed a method that can reduce the strength of this unwanted dark current by 3 orders of magnitude [1]. Because their method requires no structural changes to existing equipment, Shu says it could be easily implemented in existing FELs. Their bright beams of x rays—generated by electrons—are increasingly popular for structural studies.

Most high-repetition-rate free-electron lasers are fed by very-high-frequency (VHF) electron guns. A VHF electron gun contains a photocathode that releases electrons when hit with a laser. These electrons are accelerated by a strong electric field and exit the photocathode as a beam through a port at the front. But the same field generates other electrons by pulling them off the photocathode’s surface and from nearby copper surfaces via the field effect. These so-called dark electrons—they don’t need light to free them—can cause unwanted heating that degrades the main electron beam and damages the beam line.

To weaken the dark current, researchers have typically lowered the gun voltage. But that route reduces the brightness of the main electron beam. Shu and colleagues found an alternative solution: modifying the plug upon which the photocathode material is deposited and grown. The team showed that by pushing the plug around 0.5–1 mm deeper than a standard plug, they were able to reduce the intensity of the dark current by nearly 2 orders of magnitude. The over-inserted plug also had another benefit—it defocused the dark current. Rather than propagating downstream to join the main beam, the dark current struck the VHF gun cavity walls before it could leave the photocathode.

A new method called vdW squeezing enables the creation of stable, atomically thin 2D metals, opening doors to advanced devices and fundamental discoveries in materials science. Since the discovery of graphene in 2004, research into two-dimensional (2D) materials has advanced rapidly, opening new

Study found that magnetic order of chromium sulfide bromide can be turned on or off—like a switch—by changing the temperature.

Two-dimensional (2D) semiconductor materials could enable the development of smaller yet highly performing electronic components, thus contributing to the advancement of a variety of devices. While significant strides have been made in the synthesis of 2D semiconductors with advanced electronic properties, their clean transfer onto substrates and reliable integration in real devices has so far proved challenging.

Researchers at Peking University, the Beijing Graphene Institute and other institutes in China have recently developed a new method to integrate 2D semiconductors with dielectric materials, which are insulating materials that help control the flow of electric charge in devices. Their approach, outlined in a paper published in Nature Electronics, entails the epitaxial growth of an ultra-thin dielectric film on a graphene-covered copper surface, which subsequently enables its transfer onto various substrates with minimal defects.

“The paper emerged from recognizing persistent challenges in integrating two-dimensional materials—such as graphene—into microelectronic devices,” Zhongfan Liu, Li Lin, and Yanfeng Zhang, corresponding authors of the paper, told Tech Xplore.