Uber Laser Data Memory: "Transient Structures and Possible Limits of Data Recording in Phase-Change Materials"

""DVDs and Blu-ray disks contain so-called phase-change materials that morph from one atomic state to another after being struck with pulses of laser light, with data "recorded" in those two atomic states. Using ultrafast laser pulses that speed up the data recording process, Caltech researchers adopted a novel technique, ultrafast electron crystallography (UEC), to visualize directly in four dimensions the changing atomic configurations of the materials undergoing the phase changes. In doing so, they discovered a previously unknown intermediate atomic state--one that may represent an unavoidable limit to data recording speeds.

By shedding light on the fundamental physical processes involved in data storage, the work may lead to better, faster computer memory systems with larger storage capacity. The research was done in the laboratory of Ahmed Zewail, Linus Pauling Professor of Chemistry and professor of physics.

When the laser light interacts with a phase-change material, its atomic structure changes from an ordered crystalline arrangement to a more disordered, or amorphous, configuration. These two states represent 0s and 1s of digital data.

Using ultrafast 4-D imaging, the new UEC technique allows researchers to "film " the atomic mechanism behind the recording process in memories based on phase change materials. Credit: Jianbo Hu, Giovanni M. Vanacore, and Ahmed H. Zewail

"Today, nanosecond lasers--lasers that pulse light at one-billionth of a second--are used to record information on DVDs and Blu-ray disks, by driving the material from one state to another," explains Giovanni Vanacore, a postdoctoral scholar and an author on the study. The speed with which data can be recorded is determined both by the speed of the laser--that is, by the duration of each "pulse" of light--and by how fast the material itself can shift from one state to the other.

Thus, with a nanosecond laser, "the fastest you can record information is one information unit, one 0 or 1, every nanosecond," says Jianbo Hu, a postdoctoral scholar and the first author of the paper. "To go even faster, people have started to use femtosecond lasers, which can potentially record one unit every one millionth of a billionth of a second. We wanted to know what actually happens to the material at this speed and if there is a limit to how fast you can go from one structural phase to another."

To study this, the researchers used their technique, ultrafast electron crystallography. The technique, a new development--different from Zewail's Nobel Prize-winning work in femtochemistry, the visual study of chemical processes occurring at femtosecond scales--allowed researchers to observe directly the transitioning atomic configuration of a prototypical phase-change material, germanium telluride (GeTe), when it is hit by a femtosecond laser pulse.

In UEC, a sample of crystalline GeTe is bombarded with a femtosecond laser pulse, followed by a pulse of electrons. The laser pulse causes the atomic structure to change from the crystalline to other structures, and then ultimately to the amorphous state. Then, when the electron pulse hits the sample, its electrons scatter in a pattern that provides a picture of the sample's atomic configuration as a function of the time.

With this technique, the researchers could see directly, for the first time, the structural shift in GeTe caused by the laser pulses. However, they also saw something more: a previously unknown intermediate phase that appears during the transition from the crystalline to the amorphous configuration. Because moving through the intermediate phase takes additional time, the researchers believe that it represents a physical limit to how quickly the overall transition can occur--and to how fast data can be recorded, regardless of the laser speeds used.

"Even if there is a laser faster than a femtosecond laser, there will be a limit as to how fast this transition can occur and information can be recorded, just because of the physics of these phase-change materials," Vanacore says. "It's something that cannot be solved technologically--it's fundamental."

Despite revealing such limits, the research could one day aid the development of better data storage for computers, the researchers say. Right now, computers generally store information in several ways, among them the well-known random-access memory (RAM) and read-only memory (ROM). RAM, which is used to run the programs on your computer, can record and rewrite information very quickly via an electrical current. However, the information is lost whenever the computer is powered down. ROM storage, including CDs and DVDs, uses phase-change materials and lasers to store information. Although ROM records and reads data more slowly, the information can be stored for decades.

Finding ways to speed up the recording process of phase-change materials and understanding the limits to this speed could lead to a new type of memory that harnesses the best of both worlds.""

http://www.sciencecodex.com/better_memory_with_faster_lasers-161276

3D Printer Hype for Multitudes of Libraries in the States

""At hundreds of libraries across the U.S., 3-D printers can sometimes be heard whirring in the background, part of an effort to encourage interest in the new technology and foster DIY "maker spaces."

In some libraries, officials have begun to set restrictions on the 3-D printers amid concerns about how they'll be used.

At the University City Public Library in St. Louis, Patrick Wall recently printed a green plastic sword from the game Minecraft.

He runs this library and was demonstrating its new 3-D printer for a group of kids and adults. The play sword took close to 1 1/2 hours to print, Wall says.

The printer is roughly the size of a microwave with an open space in the middle. A coil of filament feeds an extruder that moves back and forth inside, dabbing molten plastic into layers that harden.

The 3-D printer, a 3-D scanner and filament cost about $4,500, Wall says.

University City was the first of two public libraries in the St. Louis area to set up 3-D printers for public use. But, according to the American Library Association, more than 250 libraries across the country that have one.

"It's actually part of a larger trend," says the ALA's Sari Feldman. 3-D printers are just the newest example of the interactive spaces that libraries are becoming for their communities, she says.

"So, where once we thought of libraries as places where we had things for people, now we really do things for people — or do things with people," Feldman says.

She says libraries large and small across the U.S. are setting up so-called "maker spaces," offering increasingly sophisticated hardware and software, including studio production equipment, design software and in some cases, even laser cutters.

But Feldman says the possibilities that come with cheap, user-friendly 3-D printers have also created a new gray area in setting library policy.

"There are many legal and intellectual freedom issues that need to be addressed when you make 3-D printers freely available for public use," she says.

For instance, the same technology that can print a plastic Minecraft sword is also capable of printing plastic gun parts or other items.

The ALA has recommended guidelines for libraries to address concerns about safety, access and liability. But some local libraries have established rules on their own.

At the Pope County Library System in central Arkansas, new restrictions have been placed on its two printers. They include printing objects that are prohibited by law, or deemed obscene or otherwise inappropriate.

Adult and Teen Services Librarian Sherry Simpson says there were just too many unknowns.

"We want to inspire their interest in design and we want them to bring their creations to life. However, some creations probably don't need to see life through the library," she says.

Like most other libraries, University City's currently has no specific limits on using its 3-D printer. Director Patrick Wall says it falls under the library's general policy that applies to 2-D printers and other services and materials.""

http://www.npr.org/blogs/alltechconsidered/2015/04/29/401236656/libraries-make-space-for-3-d-printers-rules-are-sure-to-follow