Overcoming Environmental Challenges in Electron Microscopy

AZoMaterials spoke to Reid Whitney, Vice President of Herzan, about the challenges of electron microscopy, including understanding and removing environmental noise, and how Herzan's solutions overcome these.

Could you give our readers some background on how Herzan partners with electron microscope (i.e. SEMs/TEMs) manufacturers and users to understand and remove environmental noise?

For over 27 years, Herzan has worked with instrument manufacturers and end users to remove difficult environmental noise from their research. The origin of this partnership usually begins with a site survey, where a Herzan engineer will provide a tailored measurement based on the specifications of the instrument being installed.

Once the environment has been fully characterized, recommendations can be made to address the noise in the lab, including: recommending a new and quieter lab location, removing noise sources, damping noise sources, or providing cancellation solutions for the SEM or TEM (which Herzan specializes in).

If a cancellation solution is required for the SEM or TEM, Herzan’s range of active vibration control platforms, custom modular/paneled acoustic enclosures, and magnetic field cancellations systems ensure the quietest operating environment for the SEM or TEM. When providing a cancellation solution to a researcher, Herzan’s team focuses on delivering three things: top quality performance, complete and reliable solutions, and attentive customer service.

Figure 1: Modular and Scalable Design allows the AVI Platform to Suport a Variety of SEMs and TEMs.

Why is environmental noise such an issue for SEMs and TEMs?

Environmental noise limits the capability of SEMs and TEMs to inform researchers about the sample they are analyzing. It slows down research, minimizes the detail one can gain from a sample, and causes downtime if the noise local to the SEM or TEM is severe. Noise can also be difficult to discern as some vibration noise issues appear to be magnetic field issues, and vice versa. In total, unmitigated environmental noise costs researchers time and money that are better spent focusing on their research or the advancement of their research project.

Why do SEM/TEM manufacturers set environmental specifications for their microscopes? 

Manufacturers set environmental specifications to guarantee their customers receive an optimal user experience. They have extensively tested threshold levels for all forms of environmental noise, testing the conditions and capability of their microscopes to ensure an optimal image quality is achieved. Having this information is valuable as every research lab is unique, with various characteristics affecting the overall noise profile (i.e. local noise sources within the building, noise sources close to the building itself, position within the building, and more).

Consulting firms who specialize in environmental analysis often assist instrument manufacturers in defining specifications for their instrument based on their various expertise in analysing structural vibrations and acoustics, as well as assessing impacts of magnetic fields on an image.

Herzan’s team of engineers help instrument manufacturers characterize their instruments, leading to a more nuanced understanding of their instruments and allowing them to achieve their ultimate goal: an optimal user experience. This expertise is often why instrument manufacturers partner with Herzan based on its extensive experience understanding and addressing environmental noise for research instruments. 

What are the most common environmental noise issues affecting SEMs and TEMs?

The two most common reasons why a SEM or TEM lab will not meet environmental specification are magnetic fields and vibration noise. Specifications for vibrations and magnetic fields are also very stringent as manufacturers cannot fully address these noise sources through the structural design of the instrument alone, often requiring mitigation solutions. These noise sources are pervasive and immediately apparent in the imaging of the SEM or TEM.

The impact of vibrations is frequency dependent, but often causes a blurring or edging effecting on the SEM or TEM image (Left). Magnetic fields are often presented in a wavy distortion to the image (DC Fields) or a jagged distortion (AC Fields) (Right).

Figure 2: Vibration Noise Affecting An Image (Left) and AC Field Noise Affecting An Image (Right)

What solutions are available to address these issues?

There are many solutions for each type of environmental noise, with a variance in terms of cost, complexity, and time required to implement. Fortunately, there are some shared strategies researchers can use when approaching how to get rid of unwanted environmental noise:

• Choosing A Different Location: while not always an option, this solution can be the least expensive and time intensive approach to addressing noise issues. When this option is considered, a site survey will be needed to perform measurements in all labs that may be available and convenient for the researcher. Comparing this data and selecting the location with the lowest noise-profile achieves the goal of the researcher for the sole cost of a site survey.
• Removing the Noise Source: decoupling the noise source from the lab is common when scroll pumps or chillers are creating noise in the room as researchers plan to locate these items in a nearby room or storage closet. This approach provides a simple and free solution to addressing the noise issue, but the limiting factor is having the ability to not limit functionality of the SEM or TEM when decoupling the noise source from the room, as well as having the space to house the noise source nearby.
• Isolating the Noise Source: this option varies widely by the type of noise affecting the area, with some examples including placing sorbathane under vibration generating equipment or dedicated acoustic enclosures for pumps and chillers. These solutions can help limit the impact it has on the instrument in question and potentially other instruments in the lab, but it does not impact the instrument if a new noise source is introduced to the lab.

If the above options are not feasible, dedicated cancellation solutions are available for each respective type of noise (Figure 3):

Figure 3: Vibration, Acoustic, and EMI Isolation Solutions for SEMs/TEMs

What makes low-frequency vibration noise so difficult to address?

Low-frequency vibration noise is difficult to address because the sources are often inherent to the location itself and cannot be decoupled from the lab. Isolating the source is rarely a solution as low-frequency vibration noise sources (noted in the table below), aren’t uniform in their distribution and attempting to isolate these noise sources is either not possible or more expensive then dedicated microscope vibration control platforms.

Additionally, the most common solution to address vibration noise is a passive, air-based isolation system, which has a natural resonant frequency that will exacerbate the issue, leading to worse image resolution and further delays towards a user’s research.

Active vibration control systems are often considered when low-frequency vibrations are affecting a location, but it is important researchers know that not all active isolation systems are made equally, and vary widely due to their control loop method (feedback vs. feedforward), sensor arrangement design (series vs. parallel), and core internal technology (piezoelectric sensors/actuators vs. voice coil). These distinct differences play an important into the long-term reliability and capability of a vibration control platform and can affect the lifetime cost and time required addressing vibration noise for researchers.

What solutions does Herzan have available to address low-frequency vibration problems and how do they compare to other solutions?

Herzan’s low-frequency vibration isolation products stem from the originating technology created by John Sandercock of Table Stable (previously RCA Technologies). Herzan’s AVI and TS Series offer unique benefits for researchers as these solutions have been upgraded and refined for over 40 years, with John Sandercock continuing to lead a team of engineers to advance the field of active vibration control.

The AVI and TS Series incorporate a feedback loop control system that dynamically responds to incoming vibrations and provides an out-of-phase, inverse force to the top plate, delivering a near vibration-free support surface. Both platforms incorporate a series of piezoelectric sensors (parallel arrangement), actuators, and control electronics, producing reliable low-frequency isolation tested across 1,000s of labs throughout the world.

SEM and TEM users are supported by the AVI Series as it is a modular and scalable solution capable of supporting even the heaviest TEMs on the market. The low-profile nature and maintenance free operation make the AVI Series a popular choice among SEM and TEM users around the world needing an effective and not overly cumbersome solution to address their vibration problems. 

Figure 4: Internal Technology of an AVI Series Platform

Why is understanding the uniformity of magnetic fields in a lab important for TEMs?

Magnetic field uniformity tells us how a field may change over a set distance. This is important for TEMs as they often include multiple components sensitive to magnetic fields (i.e. GIF, Source, Stage) that are far away from one another, which is why understanding how fields in a room change will impact the overall effectiveness and design of the magnetic field cancellation system. Magnetic field cancellation systems have a volume of cancellation, which is impacted by the number of loops created (single or dual loop) and the size of the loops (affected by room or frame size). The number of loops and size can be optimized given the measured fields in the room and their respective uniformity.

How does Herzan help users understand the uniformity of magnetic fields and what solutions are available to cancel them?

Herzan can quickly assess uniformity of magnetic fields in a room using the WaveCatcher site survey tool, where multiple EMI sensors are placed at approximate locations of the three sensitive components. Once the measurements have been taken, a Herzan engineer compares the fields measured at the three locations to assess how they change.

With this information in hand, Herzan uses a proprietary software supplied by its partner Spicer Consulting, to optimize the field cancellation system to meet instrument specification and account for non-uniform fields in the room. 

The SC22 System addresses AC fields, while the SC24 System addresses AC and DC Fields in a room. Either solution is relevant to SEMs and TEMs, with TEMs requiring dual-loop cable solutions to ensure optimal uniformity of magnetic field cancellation.

Figure 5: Unique Software Utilized to Optimize Magnetic Field Uniformity and Cancellation

With the technological advancement of SEMs/TEMs, what new challenges are manufacturers and users facing? What solutions does Herzan have available for these new challenges? 

SEMs and TEMs continue to charter new territory in seeing the unseen, making absolute precision and a quiet noise floor critical. While previously not considered a pervasive issue, acoustic noise has recently presented problems for SEMs and TEMs, disrupting imaging and being more difficult to address than vibration noise or magnetic fields as you also need to address an ancillary problem: heat management.

SEMs and TEMs can generate a lot of heat, which is an issue made worse when enclosing them in an acoustic enclosure as they will overheat and become inoperable (unless preventative measures are taken). SEMs generate less heat and are more compact than TEMs, which enables them to be supported by an acoustic enclosure, but it is critical temperature control is properly designed and incorporated into the enclosure. Herzan’s EM Acoustic Enclosure utilizes a passive heat dissipation system, which automates fan speeds based on the heat generated internally, as well as provides a real-time display of internal temperature and humidity information next to the SEM column. Each enclosure is built around the SEM through its modular design that allows users to specifically remove panels and open access windows uniquely designed for their SEM. All EM acoustic enclosures are custom designed to meet the needs of each end user.

TEMs are more difficult to enclose as the generate an enormous amount of heat and have stringent heat variation requirements. TEM acoustic enclosures that can effectively isolate acoustic noise, while managing temperature changes, are a few years away. The most common solution is to treat the lab room with acoustic panels to help reduce the acoustic energy as it encounters the multi-layered, variable density panels. Herzan consults on TEMs affected by acoustic noise and can recommend architectural firms who are best suited to modify existing rooms to be acoustically treated.

Figure 6: Easily Customizable designs meeting the unique requirements of SEMs.

Outside of the environmental solutions being offered, what else has benefited the customer process in your experience?

In general, researchers do not want to spend time focusing on the environmental solution they receive. Their main goal is to get the instrument operating at maximum capability so their research can advance. What Herzan does to ensure the user experience is focused on the researcher’s needs is to be attentive, informed, and resolute in what we offer so that the researcher is confident in our capability to solve their problem and that we are able to do so quickly without taking up too much of their time.

Not being beholden to the infrastructure of a larger company and the complexity/cost that comes with that, Herzan’s team of engineers, technicians, and support staff are available and eager to support the needs of future customers. We pride ourselves on our responsiveness and ability to offer distinct features based on unique research requirements, so every researcher does not have to compromise on their vision.

About Reid Whitney

Reid Whitney is the Vice President of Herzan in charge of improving the customer experience and leading business operations. Reid charters Herzan’s mission to discover new ways to advance the research of existing customers, while also identifying new industries where Herzan can help researchers understand and control noise.

Reid is located at Herzan’s Headquarters in Southern California and enjoys spending time with his friends, family, and young daughter at home.