Whether creating a contaminant-free environment for depositing material or minimizing unwanted collisions in spectrometers and accelerators, vacuum environments are a crucial element of many scientific endeavours. Creating and maintaining very low pressures requires a holistic approach to system design that includes material selection, preparation, and optimization of the vacuum chamber and connection volumes. Measurement strategies also need to be considered across the full range of vacuum to ensure consistent performance and deliver the expected outcomes from the experiment or process.
Developing a vacuum system that achieves the optimal low-pressure conditions for each application, while also controlling the cost and footprint of the system, is a complex balancing act that benefits from specialized expertise in vacuum science and engineering. A committed technology partner with extensive experience of working with customers to design vacuum systems, including those for physics research, can help to define the optimum technologies that will produce the best solution for each application.
Over many years, the technology experts at Agilent have assisted countless customers with configuring and enhancing their vacuum processes. “Our best successes come from collaborations where we take the time to understand the customer’s needs, offer them guidance, and work together to create innovative solutions,” comments John Screech, senior applications engineer at Agilent. “We strive to be a trusted partner rather than just a commercial vendor, ensuring our customers not only have the right tools for their needs, but also the information they need to achieve their goals.”
In his role Screech works with customers from the initial design phase all the way through to installation and troubleshooting. “Many of our customers know they need vacuum, but they don’t have the time or resources to really understand the individual components and how they should be put together,” he says. “We are available to provide full support to help customers create a complete system that performs reliably and meets the requirements of their application.”
In one instance, Screech was able to assist a customer who had been using an older technology to create an ultrahigh vacuum environment. “Their system was able to produce the vacuum they needed, but it was unreliable and difficult to operate,” he remembers. By identifying the problem and supporting the migration to a modern, simpler technology, Screech helped his customer to achieve the required vacuum conditions improve uptime and increase throughput.
Agilent collaborates with various systems integrators to create custom vacuum solutions for scientific instruments and processes. Such customized designs must be compact enough to be integrated within the system, while also delivering the required vacuum performance at a cost-effective price point. “Customers trust us to find a practical and reliable solution, and realize that we will be a committed partner over the long term,” says Screech.
Expert partnership yields success
The company also partners with leading space agencies and particle physics laboratories to create customized vacuum solutions for the most demanding applications. For many years, Agilent has supplied high-performance vacuum pumps to CERN, which created the world’s largest vacuum system to prevent unwanted collisions between accelerated particles and residual gas molecules in the Large Hadron Collider.
Physics focus: The Large Hadron Collider (Courtesy: Shuttershock Ralf Juergen Kraft)
When engineering a vacuum solution that meets the exact specifications of the facility, one key consideration is the physical footprint of the equipment. Another is ensuring that the required pumping performance is achieved without introducing any unwanted effects – such as stray magnetic fields – into the highly controlled environment. Agilent vacuum experts have the experience and knowledge to engineer innovative solutions that meet such a complex set of criteria. “These large organizations already have highly skilled vacuum engineers who understand the unique parameters of their system, but even they can benefit from our expertise to transform their requirements into a workable solution,” says Screech.
Agilent also shares its knowledge and experience through various educational opportunities in vacuum technologies, including online webinars and dedicated training courses. The practical aspects of vacuum can be challenging to learn online, so in-person classes emphasize a hands-on approach that allows participants to assemble and characterize rough- and high-vacuum systems. “In our live sessions everyone has the opportunity to bolt a system together, test which configuration will pump down faster, and gain insights into leak detection,” says Screech. “We have students from industry and academia in the classes, and they are always able to share tips and techniques with one another.” Additionally, the company maintains a vacuum community as an online resource, where questions can be posed to experts, and collaboration among users is encouraged.
Agilent recognizes that vacuum is an enabler for scientific research and that creating the ideal vacuum system can be challenging. “Customers can trust Agilent as a technology partner,” says Screech. “We can share our experience and help them create the optimal vacuum system for their needs.”
You can learn more about vacuum and leak detection technologies from Agilent through the company’s website. Alternatively, visit the partnership webpage to chat with an expert, find training, and explore the benefits of partnering with Agilent.
UHV suitcases address an important challenge facing people who use ultrahigh vacuum (UHV) systems: it can be extremely difficult to move samples from one UHV system to another without the risk of contamination. While some UHV experiments are self contained, it is often the case that research benefits from using cutting-edge analytical techniques that are only available at large facilities such as synchrotrons, free-electron lasers and neutron sources.
Normally, fabricating a UHV sample in one place and studying it in another involves breaking the vacuum and then removing and transporting the sample. This is unsatisfactory for two reasons. First, no matter how clean a handling system is, exposing a sample to air will change or even destroy its material properties – often irrevocably. The second problem is that an opened UHV chamber must be baked out before it can be used again – and a bakeout can take several days out of a busy research schedule.
These problems can be avoided by connecting a portable UHV system (called a UHV suitcase) to the main vacuum chamber and then transferring the sample between the two. This UHV suitcase can then be used to move the sample across a university campus – or indeed, halfway around the world – where it can be transferred to another UHV system.
Ultralight aluminium UHV suitcases
While commercial designs have improved significantly over the past two decades, today’s UHV suitcases can still be heavy, unwieldy and expensive. To address these shortcomings, US-based VolkVac Instruments has developed the ULSC ultralight aluminium suitcase, which weighs less than 10 kg, and an even lighter version – the ULSC-R – which weighs in at less than 7 kg.
Key to the success of VolkVac’s UHV suitcases is the use of lightweight aluminium to create the portable vacuum chamber. The metal is used instead of stainless steel, a more conventional material for UHV chambers. As well as being lighter, aluminium is also much easier to machine. This means that VolkVac’s UHV suitcases can be efficiently machined from a single piece of aluminium. The lightweight material is also non-magnetic. This is an important feature for VolkVac because it means the suitcases can be used to transport samples with delicate magnetic properties.
Based in Escondido, California, VolkVac was founded in 2020 by the PhD physicist Igor Pinchuk. He says that the idea of a UHV suitcase is not new – pointing out that researchers have been creating their own bespoke solutions for decades. The earliest were simply standard vacuum chambers that were disconnected from one UHV system and then quickly wheeled to another – without being pumped.
This has changed in recent years with the arrival of new materials, vacuum pumps, pump controllers and batteries. It is now possible to create a lightweight, portable UHV chamber with a combination of passive and battery-powered pumps. Pinchuk explains that having an integrated pump is crucial because it is the only way to maintain a true UHV environment during transport.
Including pumps, controllers and batteries means that the material used to create the chamber of a UHV suitcase must be as light as possible to keep the overall weight to a minimum.
Aluminium is the ideal material
While aluminium is the ideal material for making UHV suitcases, it has one shortcoming – it is a relatively soft metal. Access to UHV chambers is provided by conflat flanges which have sharp circular edges that are driven into a copper-ring gasket to create an exceptionally airtight seal. The problem is that aluminium is too soft to provide durable long-lasting sharp knife edges on flanges.
This is why VolkVac has looked to Atlas Technologies for its expertise in bi-metal fabrication. Atlas fabricate aluminium flanges with titanium or stainless steel knife-edges. Because VolkVac requires non-magnetic materials for its UHV suitcases, Atlas developed titanium–aluminium flanges for the company.
Atlas Technologies’ Jimmy Stewart coordinates the company’s collaboration with VolkVac. He says that the first components for Pinchuk’s newest UHV suitcase, a custom iteration of VolkVac’s ULSC, have already been machined. He explains that VolkVac continues to work very closely with Atlas’s lead machinist and lead engineer to bring Pinchuk’s vision to life in aluminium and titanium.
Close relationship between Atlas and VolkVac
Stewart explains that this close relationship is necessary because bi-metal materials have very special requirements when it comes to things like welding and stress relief.
Stewart adds that Atlas often works like this with its customers to produce equipment that is used across a wide range of sectors including semiconductor fabrication, quantum computing and space exploration.
Because of the historical use of stainless steel in UHV systems, Stewart says that some customers have not yet used bi-metal components. “They may have heard about the benefits of bi-metal,” says Stewart, “but they don’t have the expertise. And that’s why they come to us – for our 30 years of experience and in-depth knowledge of bi-metal and aluminium vacuum.” He adds, “Atlas invented the market and pioneered the use of bi-metal components.”
Pinchuk agrees, saying that he knows stainless steel UHV technology forwards and backwards, but now he is benefitting from Atlas’s expertise in aluminium and bi-metal technology for his product development.
Three-plus decades of bi-metal expertise
Atlas Technologies was founded in 1993 by father and son Richard and Jed Bothell. Based in Port Townsend, Washington, the company specializes in creating aluminium vacuum chambers with bi-metal flanges. Atlas also designs and manufactures standard and custom bi-metal fittings for use outside of UHV applications.
Binding metals to aluminium to create vacuum components is a tricky business. The weld must be UHV compatible in terms of maintaining low pressure and not being prone to structural failure during the heating and cooling cycles of bakeout – or when components are cooled to cryogenic temperatures.
Jed Bothell points out that Japanese companies had pioneered the development of aluminium vacuum chambers but had struggled to create good-quality flanges. In the early 1990s, he was selling explosion-welded couplings and had no vacuum experience. His father, however, was familiar with the vacuum industry and realized that there was a business opportunity in creating bi-metal components for vacuum systems and other uses.
Explosion welding is a solid-phase technique whereby two plates of different metals are placed on top of each other. The top plate is then covered with an explosive material that is detonated starting at an edge. The force of the explosion pushes the plates together, plasticizing both metals and causing them to stick together. The interface between the two materials is wavy, which increases the bonded surface area and strengthens the bond.
Strong bi-metal bond
What is more, the air at the interface between the two metals is ionized, creating a plasma that travels along the interface ahead of the weld, driving out impurities before the weld is made – which further strengthens the bond. The resulting bi-metal material is then machined to create UHV flanges and other components.
As well as bonding aluminium to stainless steel, explosive welding can be used to create bi-metal structures of titanium and aluminium – avoiding the poor UHV properties of stainless steel.
“Stainless steel is bad material for vacuum in a lot of ways,” Bothell explains, He describes the hydrogen outgassing problem as “serious headwind” against using stainless steel for UHV (see box “UHV and XHV: science and industry benefit from bi-metal fabrication”). That is why Atlas developed bi-metal technologies that allow aluminium to be used in UHV components – and Bothell adds that it also shows promise for extreme high vacuum (XHV).
UHV and XHV: science and industry benefit from bi-metal fabrication
Lightweight and easy to machine The custom aluminium vacuum chamber with titanium flanges used as part of VolkVac’s latest UHV suitcase. (Courtesy: VolkVac/Atlas Technologies)
Modern experiments in condensed matter physics, materials science and chemistry often involve the fabrication and characterization of atomic-scale structures on surfaces. Usually, such experiments cannot be done at atmospheric pressure because samples would be immediately contaminated by gas molecules. Instead, these studies must be done in either UHV or XHV chambers – which both operate in the near absence of air. UHV and XHV also have important industrial applications including the fabrication of semiconductor chips.
UHV systems operate at pressures in the range 10−6–10−9 pa and XHV systems work at pressures of 10−10 pa and lower. In comparison, atmospheric pressure is about 105 pa.
At UHV pressures, it takes several days for a single layer (monolayer) of contaminant gases to build up on a surface – whereas surfaces in XHV will remain pristine for hundreds of days. These low pressures also allow beams of charged particles such as electrons, protons and ions to travel unperturbed by collisions with gas molecules.
Crucial roles in science and industry
As a result UHV and XHV vacuum technologies play crucial roles in particle accelerators and support powerful analytical techniques including angle resolved photoemission spectroscopy (ARPES), Auger electron spectroscopy (AES), secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS).
UHV and XHV also allow exciting new materials to be created by depositing atoms or molecules on surfaces with atomic-layer precision – using techniques such as molecular beam epitaxy. This is very important in the fabrication of advanced semiconductors and other materials.
Traditionally, UHV components are made from stainless steel, whereas XHV systems are increasingly made from titanium. The latter is expensive and a much more difficult material to machine than stainless steel. As a result, titanium tends to be reserved for more specialized applications such as the X-ray lithography of semiconductor devices, particle-physics experiments and cryogenic systems. Unlike stainless steel, titanium is non-magnetic so it is also used in experiments that must be done in very low magnetic fields.
An important shortcoming of stainless steel is that the process used to create the material leaves it full of hydrogen, which finds its way into UHV chambers via a process called outgassing. Much of this hydrogen can be driven out by heating the stainless steel while the chamber is being pumped down to UHV pressures – a process called bakeout. But some hydrogen will be reabsorbed when the chamber is opened to the atmosphere, and therefore time-consuming bakeouts must be repeated every time a chamber is open.
Less hydrogen and hydrocarbon contamination
Aluminium contains about ten million times less hydrogen than stainless steel and it absorbs much less gas from the atmosphere when a UHV chamber is opened. And because aluminium contains a low amount of carbon, it results in less hydrocarbon-based contamination of the vacuum
Good thermal properties are crucial for UHV materials and aluminium conducts heat ten times better than stainless steel. This means that the chamber can be heated and cooled down much more quickly – without the undesirable hot and cold spots that affect stainless steel. As a bonus, aluminium bakeout can be done at 150 °C, whereas stainless steel must be heated to 250 °C. Furthermore, aluminium vacuum chambers retain most of the gains from previous bakeouts making them ideal for industrial applications where process up-time is highly valued.
Magnetic fields can have detrimental effects on experiments done at UHV, so aluminium’s slow magnetic permeability is ideal. The material also has low residual radioactivity and greater resistance to corrosion than stainless steel – making it favourable for use in high neutron-flux environments. Aluminium is also better at dampening vibrations than stainless steel – making delicate measurements possible.
When it comes to designing and fabricating components, aluminium is much easier to machine than stainless steel. This means that a greater variety of component shapes can be quickly made at a lower cost.
Aluminium is not as strong as stainless steel, which means more material is required. But thanks to its low density, about one third that of stainless steel, aluminium components still weigh less than their stainless steel equivalents.
All of these properties make aluminium an ideal material for vacuum components – and Atlas Technologies’ ability to create bi-metal flanges for aluminium vacuum systems means that both researchers and industrial users can gain from the UHV and XHV benefits of aluminium.
This video examines the unique measurement capabilities of the modular M81-SSM synchronous source measure system from Lake Shore Cryotronics. In this hands-on demonstration, Lake Shore looks at its components, including four types of amplifier modules that are combined with the M81-SSM instrument to enable low-level DC, AC and mixed AC/DC measurements.
The video discusses how all source and measure channels are simultaneously sampled at a very high rate and provide DC to 100 kHz operation – including lock-in operation – on up to three source and three measure channels at the same time to ensure time-correlated synchronous measurements.
Also demonstrated is how quickly and easily the M81-SSM can measure various values of resistance using very low DC and AC currents, illustrating the limitations of DC methods and the advantages of AC lock-in methods as the signal of interest becomes affected by thermal offsets and other parasitic effects.
Unique MeasureSync™ signal synchronization technology
The M81-SSM’s MeasureSync™ technology ensures inherently synchronized measurements from one to three source channels and from one to three measure channels per each half-rack instrument. Amplitude and frequency signals are transmitted to/from the remote amplifier modules using a proprietary real-time analogue method that minimizes noise and ground errors while ensuring tight time and phase synchronization between all modules. Because the M81-SSM sources and measures channels synchronously, multiple devices can be tested under identical conditions so users can easily obtain time-correlated data.
Connect up to three source modules and up to three measure modules at once
The M81-SSM provides DC to 100 kHz precision electrical source and measure capabilities with 375 kHz (2.67 μs) source/measure digitization rates across up to three source and three measurement front-end modules.
Users can choose from differential voltage measure (VM-10) and balanced current source (BCS-10) modules, and single-ended current measure (CM-10) and voltage source (VS-10) modules. All modules use 100% linear amplifiers and are powered by highly isolated linear power supplies for the lowest possible voltage/current noise performance — rivalling the most sensitive lock-in amplifiers and research lab-grade source and measure instruments.
On the VS-10 module, dual AC and DC range sourcing allows for precise full control of DC and AC amplitude signals with a single module and sample/device connection. And on the VM-10 module, seamless range change measuring significantly reduces or eliminates the typical range change-induced measurement offsets/discontinuities in signal sweeping applications that require numerous range changes.
Connexion
