By Bill Mollon and Ming Pan, Gatan

Introduction

We have all heard the quote “A picture is worth a thousand words” when describing how much information can really be represented by a single image. Many of you may have written and published pages of results all based sometimes on a single piece of important data such as an electron micrograph. Of course, if one image is worth a thousand words, as the saying goes, how much would 30 or more be worth? With the advent of better performing electronics and development of newer CCD technology Gatan is able to extend the famous saying and complete it with “but a movie tells the whole story”. By extending the single acquired image into a series of fast acquired frames, movie creation is possible. This capability allows us to record dynamic events in many different applications, all leading towards sharing the sequence of images and telling a more complete story that cannot be done with one image alone. A brief background on how this technique is used in electron microscopy follows.

In-Situ Experiments in TEM

Observing dynamic events in the TEM is not a recent or new technique. Doing an internet search just on “in-situ transmission electron microscopy” will give you over 269,000 results alone. Some of the in-situ topics range from: heating thin metals, stress-relief experiments, nano-indentation of metals, melting and freezing of crystalline materials, growing of nanotubes, to biological cryo imaging or using environmental cells for biological events. These types of electron microscopy techniques are on an upswing trend as can be seen by their popularity in the many recent symposiums and conferences held at key scientific meetings in the U.S (ASU Jan 2006, FEMMS meeting Sept 2007, AVS meeting in Seattle Oct.2007).

Historically speaking, one of the major requirements to record time-based events such as heating, deformation and straining required appropriate specimen holders and also TV cameras interfaced to the TEM. Gatan was the 1st commercial company to supply these type of tools to the scientific community. The cameras were analog based systems that produced a RS-170 standard output. For the complicated experiments there also was required sophisticated recording equipment to store the video data onto some type of semi-permanent media such as magnetic recording tape or the early forms of laser disk media. Character generators for data overlays and time tracking equipment also were employed. The analog TV-cameras that entered the market were not exactly perfect and without some technical drawbacks that plagued most equipment developers due to the technology at hand for the time. When using TV-cameras for in-situ experiments many of these drawbacks had to be considered. Some of them are still in existence today:

1. Small field of view
2. Analog signal source
3. Un-even intensities across the camera active area
4. Uncorrectable cosmetic defects
5. Non-universal recording format
6. Expensive computing equipment for movie creation

Additionally, conventional CCD camera solutions suffered from very slow frame rates which was primarily due to the trade-off between sensitivity and resolution. The camera could not collect high resolution images without having considerable noise due to in-sensitive detection design. This later leads to the intensified detector systems to help improve the signal to noise ratio and “raise the bar” a bit higher to obtain better resolution. Sometimes the camera would also be slowed down to increase the signal but this created a major risk in missing events that occurred faster than the frame rate selected. Because of the post image processing that some investigators needed there was even a higher demand on computer power needed to put the data in a form that showed a more complete story.

New Solutions in Digital CCD TV Imaging

Referring back to the question that brought you here, “Can your digital CCD camera record in-situ movies at true TV-rates (30fps – frames per second) under low electron beam conditions?” It can if it is the new ORIUS™ family member, the Model 830 SC200. Gatan has taken careful consideration of all the points mentioned above to come up with an answer for those seeking new digital CCD imaging at true TV-rate speeds.

Take a look at an example movie created with this new CCD camera (Movie 1), once it has downloaded just click the play button.

Click here to download in full resolution AVI Format (490 meg)
Click here to download in WMV format (7 Meg)

The movie shows the structural change of a nano Au particle in a 400kV TEM under normal HREM imaging condition. As you can see from the movie this camera has a very fast response and is able to capture high resolution lattice imaging at TV-rate speed of over 30fps. Such high speed allows user to observe the rapid structural change (single and multiple twinning, moving of the twinning plane, creation and disappearance of multiple twinning, etc.) of this nano Au particle under the electron beam.
The user can at any time acquire a single frame image using the camera’s high quality mode of operation (Fig.1).

Figure 1 showing a high quality mode image (L) as compared to a single frame in the fast TV imaging mode (R)

Other key performance – High Sensitivity

The Model 830 SC200 CCD camera is a new member to the ORIUS™ family of high performance CCD cameras. It is a 2k x 2k CCD (4M pixels) camera designed to deliver extraordinary resolution at TV readout speed for imaging applications in both life and materials science. The combination of HCR™ (high-contrast resolution) optical technology (Fig. 2) and advanced CCD readout electronics has given the SC200 camera the best price-performance value.

Gatan first developed HCR™ optical stack technology for the UltraScan™ camera family which has quickly become the industry standard. This same technology used in the ORIUS family of CCD cameras assures maximum signal transfer at critical points in the optical path. It also minimizes "point spread effects" at all accelerating voltages. When conditions require higher or lower accelerating voltage operation, HCR optics guarantee that image quality is not compromised.

When your application requires the use of a higher kV range TEM (up to 400kV) the SC200 has a specific model configuration that uses a phosphor sensor which has been optimized for the accelerating voltage. This unique design feature allows for an increase of 4x the sensitivity (Fig. 2) compared to a non-optimized sensor. This is accomplished without the worry of significant loss of resolution.

Figure 2 showing the optimization of the sensor for higher accelerating voltages. Both images were acquired on a 400kV TEM at 200kX magnification at the same exposure time (0.1s). Right image shows optimized sensor showing 2520 counts as compared to the left image from a non-optimized sensor producing only 640 counts.

When looking at Biological applications the SC200 has proven to be very capable as a fast TV rate surveying camera when used with cryo samples at lower magnifications. Ease of use, judging ice quality, particle distribution, maintaining low electron beam dosage and even capturing of single high quality image frames (Fig. 3) also makes it a good companion camera with our Ultrascan series of CCD cameras.


Figure 3 showing high quality mode image (L) and fast TV rate mode image (R) under low electron beam dosage. Exposure times for the left and right images were 1sec. and 0.05sec respectively.

In cryo-biological applications the amount of electrons, or beam dosage, hitting the sample is critical and needs to be very closely maintained so as not to introduce specimen damage that could alter the morphology or 3D model being investigated. These cryo sample images shown in Figure 3 were obtained under controlled electron beam conditions with minimal dosage using a 200kV FETEM at 2500x magnification. At such a low magnification the low dose beam is spread over a very large area which helps minimize the specimen to beam interaction effects, ie., radiation/sample damage. This type of surveying at lower magnifications is very common so as to judge the ice condition and distribution of the sample that will be viewed and later captured at the higher magnifications. The use of the SC200 camera with its fast 30fps TV rate made the surveying very easy and quick even in the lowest of beam conditions. The calculated dosage for the images in Figure 3 were approximately 0.03601 (binx1) and 0.06152 (binx4) electrons/Å2/second respectively.

– Electron diffraction patterns

The exceptional anti-blooming performance also makes the SC200 an ideal camera for recording electron diffraction patterns with ease. Figure 4 shows a selected area electron diffraction (SAED) pattern from a thin silicon crystal in [110] orientation. This is evidenced by the weak (200) and (-2,00) diffraction spots. The pattern was recorded at 400kV with spot size #1 and camera length 0.3n*m. The excellent anti-blooming design of SC200 camera eliminates the “streaking” phenomenon that is frequently observed in electron diffraction patterns as recorded by CCD cameras. The intensity line scan of the diffraction pattern shows excellent resolution and dynamic range (14-bit).


Figure 4 SAED Diffraction pattern of Si with adjoining line plot.

ORIUS™ Family of CCD Cameras

ORIUS™ implements a new, revolutionary imaging platform. Its design houses critical cutting edge technologies in CCD electronics, mechanical engineering, scintillator design and fiber-optical coupling. Specifically, ORIUS™ combines Gatan’s successful HCR™ optical technology with the latest generation of large format CCD sensors. The result: ORIUS™ CCD cameras deliver superior price/performance value. The family now comprises the very successful SC1000 (4008x2672), the SC600 (2672x2672) and now the new SC200 (2048x2048). Each of the ORIUS cameras have as part of their design the capability of fast frame acquisition ranging from 14fps of the SC1000 and SC600 models to the 30fps of the new SC200.

ORIUS™ cameras all have a camera retraction mechanism which ensures complete compatibility with a broad range of TEM detectors, including the Gatan GIF Tridiem™ energy filter and ENFINA™ spectrometer systems. This powerful configuration gives the user high-resolution digital imaging and analytical capabilities on the same TEM.

To meet the needs of rapidly growing TEM digital imaging applications, ORIUS™ CCD cameras deliver exactly what you need: MORE in pixels, resolution, speed, stability, and now capabilities such as in-situ movie creation and low electron dose imaging. Delivering optimal imaging systems with the best price-performance value for your applications is our goal.

ORIUS Family CCD Cameras

Model	Mounting	Pixel Resolution	Frame Rate
830 SC200	Bottom	2048x2048	>30fps
831 SC600	Bottom	2672x2672	>14fps
832 SC1000	Bottom and 35mm port	4008x2672	>14fps

For more information on the SC200, click here.

For the ORIUS™ product page, click here.

For product and ordering information please contact your local Gatan Sales Office.