Road Trip 2019 In 1995, I visited the Russian nuclear weapons city of Sarov. Here, I’m showing a copy of the newspaper where I worked at the time, the Los Alamos Monitor, to physicist Viktor Adamsky, who helped design the Tsar Bomba — the most powerful nuclear weapon ever exploded. Stephen Shankland/CNET Military I spent more than five years as a reporter in Los Alamos, New Mexico, birthplace of the atomic bomb, home to a major national laboratory, and the 18,000-person town where I grew up. I covered everything from President Bill Clinton visiting the lab to mostly harmless radioactive cat poop triggering radiation alarms at the county landfill. But the story that made the biggest impression on me took place thousands of miles away, in Russia.In May 1995, I was part of a seven-person civilian delegation that traveled to Los Alamos sister city Sarov, about 230 miles east of Moscow. It’s the home of the institute where Russia developed its first atomic bomb. Our visit was timed to coincide with a 50th anniversary celebration of the end of the Great Patriotic War, aka World War II, which for the Russians ended when the Germans capitulated in May 1945.It was a sobering visit — the economic devastation; the Soviet-era microphones bugging away in our hotel; the angry and impoverished veterans; and the daunting quantities of vodka, champagne and cognac that accompanied us during a weeklong series of banquets. I spoke with Viktor Adamsky, one of the designers of the biggest nuclear bomb of all time, the 50-megaton Tsar Bomba, which was more powerful than all the bombs dropped in World War II.I’m remembering it now because I’ve recently interviewed Siegfried Hecker, former director of Los Alamos National Laboratory and a key leader of the US-Russian lab collaboration that led to my trip. Back when US-Russian relations were thawingDuring the time of my trip, relations between Russia and the US were warming, but now they’re cooling once again. That troubles Hecker — even though he spent much of his career designing the nuclear weapons the US aimed at the then-USSR.It troubles me, as well. I grew up during the Cold War, and I’m not eager to introduce my children to concepts like nuclear winter and megadeath. And even as treaties between the US and Russia fizzle out and the two countries rev up another arms race, worries are piling up about the nuclear weapons capabilities of Iran and North Korea, too.But Hecker stresses the similarities between the US and Russia — “They’re so much like us,” he says — and what was most interesting on my 1995 trip was the cultural connection between Los Alamos and Sarov. There was a clear kinship between the cities’ researchers — a curious camaraderie given that those very researchers designed the warheads perched atop ICBMs aimed at each other.A Russian in the nuclear weapons design city of Sarov in 1995 gave me this medal — the Order of the Badge of Honor — as a token of goodwill after the Cold War ended. The Soviet Union awarded the medal for achievements in labor, culture and science. Stephen Shankland/CNET Each city benefited from its government’s largesse during the Cold War. “When I first came here, I thought it was a paradise. Such food!” one Sarov man told me. Meanwhile, Los Alamos received a federal funding boost for its schools and its police and fire departments. Each city suffered when government funding dropped with the end of the Cold War. Both cities teem with elite researchers who play important military roles and are curious about what makes the universe tick. Both cities have nuclear weapons museums showing off the hulking casings of early bombs.Even the names of the cities had a parallel. When I visited, Sarov still went by its Cold War name of Arzamas-16 — a bit of geographic misdirection to make it look like it was part of a nothing-special city that actually is 30 miles northeast. During World War II, mail for Manhattan Project researchers in Los Alamos was addressed to P.O. Box 1663 in Santa Fe, about the same distance away from Los Alamos as Arzamas is from Sarov.Lab-to-lab collaborationMy trip was an outgrowth of the US-Russia nuclear collaboration undertaken by Hecker and his colleagues after the collapse of the Soviet Union. The effort, funded by the Nunn-Lugar Cooperative Threat Reduction Program, saw US and Russian scientists working on joint research and helping to get a grip on the vast quantities of Soviet-era nuclear weapons materials.I understood the political appeal of the program. For would-be terrorists or countries aspiring to join the nuclear weapons club, the hardest step is obtaining potent plutonium or weapons-grade uranium. Paying Russians to better control those materials — and to discourage scientists from looking for new jobs elsewhere — made sense for US foreign policy.Sarov, called Arzamas-16 during the Cold War, is home to a museum showing several historic Russian nuclear bombs. I’m second from left. Stephen Shankland/CNET But seeing Sarov firsthand showed me the human side of the program’s benefits.After the economic crisis that accompanied the demise of the USSR, Sarov residents had to grow potatoes in their window flower boxes and turn their countryside dachas into small farms. A typical scientist’s salary at the time was about $80 per month, as the ruble collapsed in value. Hardest hit by the end of the Cold War were elderly World War II veterans thrust back onto the job market after their pensions became worthless. The security fence around Sarov came to be enjoyed as a way to keep away the outsiders who’d had it even worse.Like Hecker, I visited Russians in their homes. After attending the World War II memorial around which our visit centered, I slipped off with some journalists from Sarov’s City Courier newspaper. They introduced me to their children, spoke of using surreptitious “samizdat” publications to disseminate information in the Soviet years, taught me how to spell my name in Cyrillic (Стѳфѳн Шѳнкланд), and told me how they cobbled together rafts for weeks-long descents of Siberian rivers. One gave me a present symbolic of US-Russian cooperation: a massive hand-cranked drill, made in Massachusetts but given to Russians in World War II and used during the German siege of Leningrad.In short, they showed me they were human.Personal connectionsI feel a more personal connection to Russia myself, too. In 1995, I met Boris Nemtsov, a reform-minded politician who then led the nearby Nizhny Novgorod (named Gorky in the Soviet era) region and earned a Ph.D. in physics. Among his policies was a “meter by meter” privatization push that let people gradually buy their apartments from the state. The discussion felt a lot more forward-looking than seeing Lenin’s waxy corpse in Moscow’s Red Square.Enlarge ImageSarov’s City Courier newspaper from 1995 chronicled the visit I and others from Los Alamos, New Mexico, paid to the Russian nuclear weapons design city. I’m in the center photo, showing the newspaper to some students. Stephen Shankland/CNET Nemtsov rose to become a national reform leader, willing to speak out against President Vladimir Putin. But in 2015, Nemtsov was assassinated on a bridge in Moscow. I felt it more closely than an “ordinary” episode of political violence.And I felt the same tie when five Sarov scientists were killed in a Russian missile test explosion this month.Hecker has a lot more of those connections. He’s friends with plenty of Russians and sees their cultural values as very similar to ours. And he’s keeping his communication links alive even though the US-Russia lab-to-lab collaboration project he helped begin is now all but dead. He’ll take his 57th trip to Russia in November.The two countries can move past sticking points like NATO’s eastward expansion and Russia’s military action in the Crimea and eastern Ukraine, Hecker says. Today’s nationalistic fervor might make it hard to defrost the relationship, but seeing the world from the other side’s perspective will help, he says.”There is absolutely no need for Russia and the US to be adversaries and enemies,” Hecker tells me. “Absolutely none.” 5 Sci-Tech Tags This story is part of Road Trip 2019, profiles of the troublemakers and trailblazers who are designing our future. Share your voice Comments
Paris mayor Anne Hidalgo. Photo: CollectedParis mayor Anne Hidalgo on Sunday praised the heroism of a Malian immigrant who scaled the facade of a four-storey building in the north of capital to save a child hanging from a ledge, saying the city will support his effort to settle in France.The video of Mamoudou Gassama’s quick climbing to reach the child, cheered on by terrified onlookers, went viral on social media, with people calling the 22-year-old a real spider man.Gassama has even been invited to the Elysee presidential palace to meet with President Emmanuel Macron on Monday morning, an official at Macron’s office said.”Congratulations to Mamoudou Gassama for his act of bravery that saved the life of a child,” Hidalgo said on her official Twitter account, adding that she spoke with him by phone to thank him.Hidalgo said Gassama told her that he arrived from Mali a few months ago and wished to stay in France.”I replied that his heroic gesture was an example for all citizens and that the City of Paris will obviously be keen to support him in his efforts to settle in France,” Hidalgo said.French minister and former government spokesman Christophe Castaner also took to Twitter to say how admirable it was that Gassama stepped forward to save a life without giving any thought for his own.Le Parisien newspaper reported that Gassama was walking by when he saw a gathering in front of the building and leapt into action.”I did it because it was a child,” the paper quoted him saying. “I climbed… Thank God I saved him.”
, Advanced Materials This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. The work demonstrated the atomic geometry of metallic quantum contacts that could be modulated with light and the ability to reverse switch (on/off, vice versa) their conductance using plasmonic heating. While the atom-by-atom separation of electrodes were clearly observed, they could also adjust the gap size, between the electrodes at sub-angstrom resolution by controlling the intensity of light. Zhang et al. showed that the plasmon can potentially breakthrough the diffraction limit of light to realize nanofocusing, to transfer the plasmon-controlled atomic switch to realize highly integrated nanodevices; opening a new path to engineer nanoelectronic devices. Explore further While generating a nanogap was crucial to fabricate single molecule-based devices, engineering an adjustable atomic-scale gap has remained a significant challenge. Although fixed gap sizes could not be adjusted post-fabrication, the gap-size could be readily and continuously adjusted through plasmonic heating at sub-angstrom resolution, as shown by Zhang and the research team. For this, they used a commercial light-emitting diode (LED) lamp as a light source in the experiments with an AC adaptor to continuously control the intensity of light. The experimental setup did not require special optical hardware or high power laser sources. They used a commercially available gold wire with a constriction in the middle on a spring steel substrate to construct the nano contacts. Then using a ‘mechanically controllable break junction’ (MCBJ), the scientists stretched the constriction by bending the substrate, and observed it with scanning electron microscopy (SEM) images. Thereafter, the scientists reduced the cross-section of the constriction to form two separate electrodes. When they turned the light on, the conductance increased and decreased when the light was turned off; the large conductance resulting from light illumination strongly reconnected the two separated electrodes.The scientists analyzed the phenomenon at the level of atomic arrangement, upon light illumination. They showed that the nanogaps had strong absorption of light in the visible and near infrared regions due to localized surface plasmon resonances (LSPR). When the frequency of the LED light matched the oscillation frequency of the free electrons and the electromagnetic field at the tip of the electrodes, the LSPR around the gap was excited. The absorbed light then converted to thermal energy causing nanoelectrode expansion and their reconnection. The conductance reached its maximum value when the system was at thermal equilibrium. When the light was shut off, the electrons separated once more. Characterization of MCBJ devices and simulation of expansion distribution of the electrodes upon light illumination. a) System for the measurement of optical spectroscopy. b) Measured dark field scattering spectra from the gap area that employs three different samples. The gap size is ~2 nm in sample A and ~0.2 nm in sample B. The electrodes were strongly reconnected, and no nanogap is observed in sample C. Plasmonic resonances are indicated by the arrows. c) Model used in the simulation. Parts of the large metal wire close to the nanotips were considered. The gap size between two nanotips is initially set to 2 nm. The polarization of the incident light is parallel to the x-axis. d) Expansion distribution (in X component) when equilibrium temperature was established. Credit: Light: Science & Applications, doi: 10.1038/s41377-019-0144-z. , Light: Science & Applications Zhang et al. also observed how the nanogap size could be precisely modulated by light by showing that the conductance could be modified in the tunneling region, between the gap of the two electrodes, by controlling the LED light. When the light intensity was fixed, they could keep the tunneling current constant for longer. The scientists estimated the distance between the two electrodes using the Simmons equation; used to describe the relationship between the tunneling current and the tunneling gap size. They could thereby precisely control the distance between the two separated electrodes at sub-angstrom accuracy using the light intensity.To confirm that the origin of switching behavior was plasmon-induced heating in the nanoscale plasmonic systems, the scientists investigated the scattering spectrum of the MCBJ samples to reveal the frequency of plasmonic resonance. The results indicated that the conductance change related to the expansion of the electrodes due to plasmonic heating. Zhang et al. also performed finite element method simulations to estimate the expansion of the electrodes and solved the electric field distribution, temperature distribution and thermal expansion on light illumination, using the COMSOL Multiphysics program package. The simulation calculated the maximum displacement of the electrodes as approximating 0.4 nm. Zhang et al. were able to further optimize the switching frequency by optimizing the characteristic dimensions for heat transfer. In this way, the scientists experimentally proved that atomic switches could be rapidly operated via plasmonic heating. Illumination system with different frequencies. Credit: Light: Science & Applications, doi: 10.1038/s41377-019-0144-z Dependence of conductance on the incident light. a) Real-time measurement of the conductance upon the LED light illuminations in the tunneling regime. Vbias = 1 mV. b) Schematic of the gap size variation upon light illumination. The dashed lines indicate the new position of the nanoelectrodes upon LED illumination. c) The conductance of the tunneling gap dependent on the laser polarization. When a p-polarized laser (pink) is employed, the conductance is approximately two times larger than the conductance when an s-polarized laser (orange) is employed. The laser central wavelength is 640 nm with a bandwidth of 5.7 nm, and the maximum laser power density is 0.5 mW/mm2. Credit: Light: Science & Applications, doi: 10.1038/s41377-019-0144-z. , Nature Nanotechnology © 2019 Science X Network Current modulated by the light illumination. Credit: Light: Science & Applications, doi: 10.1038/s41377-019-0144-z. LEFT: a) A metal wire with a notch in the middle is fixed on the substrate. The notch can be stretched until it finally breaks due to the bending of the substrate, which produces two separated electrodes. b SEM images of the notched microwire during the stretching process. Scale bar: 50 μm. c Real-time measurement of the current with the light switched on/off every 50 s–60 s. Zoomed image: conductance decreases in quantum steps at multiples of G0 (=2e2/h) as the light intensity decreases. d Schematic of the atomic arrangement, which corresponds to four conductance states upon light illumination. State 1: the two electrodes are separated by a few angstroms (G ≪ 1 G0). State 2: the two electrodes are reconnected upon light illumination (G ~ 80 G0). State 3: the two electrodes are stretched, and a gold atom chain is formed before the nanocontact breaks when the light intensity is reduced (G ~ 1 G0). State 4: the two electrodes are separated again due to the heat dissipation as the light is completely turned off (G ≪ 1 G0). RIGHT: Fabricating a nanocontact. a) Setup to roundly cut the metal wire. The metal wire was sandwiched between a knife blade and a supporting platform. The platform can move in the vertical (Z) and parallel (X) directions with a resolution of ~5 μm. b) SEM image of the nanogap after breakage of nanocontact. Scale bar: 5 μm. c) Optical micrograph of the metal wire with a notch in the middle. Scale bar: 50 μm (d) SEM image of the metal wire. Scale bar: 20 μm. Credit: Light: Science & Applications, doi: 10.1038/s41377-019-0144-z. In the method developed by Zhang et al. light can be used to control electrical conductance at the junction between gold nano-electrodes by heating electrons at the electrode surface, in a technique known as ‘plasmonic heating.’ They validated the experimental mechanisms using simulations. The research team expanded electrodes via plasmonic heating to close the gap and turn the switch on, paving the way to build single-molecule transistors and nanopore-based biosensors at the nanoscale. Molecular junctions were previously investigated as an approach to build nanoswitches by employing photochromic (light sensitive) molecules that switched between two distinct isoforms. The present work by Zhang et al. contrastingly demonstrated conductance switch behavior only with a bare metallic contact, under light illumination, without any molecules. They demonstrated the conductance of bare metallic quantum contacts as reversible switches across eight orders of magnitude to substantially exceed the performance of the previous molecular switches. The scientists were able to adjust the gap size between the two electrodes after the switch process with sub-angstrom accuracy, by controlling the light intensity or polarization. Illumination system with different frequencies. Credit: Light: Science & Applications, doi: 10.1038/s41377-019-0144-z More information: Weiqiang Zhang et al. Atomic switches of metallic point contacts by plasmonic heating, Light: Science & Applications (2019). DOI: 10.1038/s41377-019-0144-z K. Terabe et al. Quantized conductance atomic switch, Nature (2005). DOI: 10.1038/nature03190 Kasper Moth-Poulsen et al. Molecular electronics with single molecules in solid-state devices, Nature Nanotechnology (2009). DOI: 10.1038/nnano.2009.176 Tsuyoshi Hasegawa et al. Atomic Switch: Atom/Ion Movement Controlled Devices for Beyond Von-Neumann Computers, Advanced Materials (2011). DOI: 10.1002/adma.201102597 Scientists have recently developed a light controlled nano-switch to lay groundwork for atomic device development in nanotechnology. They engineered the switches at the nanoscale in a first step toward fully integrated electronic device miniaturization. The multidisciplinary research was conducted by Weiqiang Zhang and co-workers, and an international team of collaborators. Results of the study are now published in Light: Science & Applications. Journal information: Nature To understand how conductance depended on the light intensity, the scientists performed experiments where the maximum light intensity within each illuminated circle gradually increased. Zhang et al. showed that the maximum conductance in each circle increased approximately linearly with the intensity of light. They obtained repeatable data of the current as a function of the light intensity and showed how the conductance of quantum contact, could be regulated by the intensity of light. In the present study, Zhang et al. used this principle to show how a metallic, atomic scale contact could be operated reliably as a conductance switch through controlled illumination of light. To engineer the metallic atomic-scale contact they precisely stretched a metal nanowire using the mechanically controllable break junction. When they reduced the cross-section of the metal wire to a few nanometers or a few atoms, the diameter became comparable to the Fermi wavelength of the electrons, allowing quantum-mechanical effects to strongly influence the properties of electron transport. Using these principles, Zhang et al. showed how the conductance of an atomic gold contact could be switched from a few quanta of conductance to hundreds of quanta, and vice versa with light illumination. The scientists were able to reversibly switch the metallic quantum contacts between the open and closed state by controlling the light intensity. They created a nanogap between the quantum contacts within which coherent tunneling governed electron transport. In-plane coherent control of plasmon resonances for plasmonic switching and encoding Citation: Atomic switches by plasmonic heating of metallic contact points (2019, April 3) retrieved 18 August 2019 from https://phys.org/news/2019-04-atomic-plasmonic-metallic-contact.html Engineering electronic devices using functional building blocks at the atomic scale is a major driving force in nanotechnology to form key elements in electronic circuits, which were previously miniaturized using mechanical tunneling, bias voltage/current operation and electrochemistry. Previous studies did not, however, address the concept of atomic switches controlled by plasmonic heating. Surface plasmons are coherent delocalized electron oscillations at the interface between two materials that form metallic nanostructures, which can be concentrated into the subwavelength gaps between the materials. In principle, when the resonance frequency of surface plasmons match the frequency of the incident light, the plasmon resonance is excited to produce strong light absorption and substantial plasmonic heating.