The hardware and software used to execute fly scans at Sector 16 of the Advanced Photon Source are described. The system design and capabilities address dimensions and time scales relevant to samples in high pressure diamond anvil cells. The time required for routine sample positioning and centering is significantly reduced, and more importantly, the time savings associated with fly scanning make it feasible for users to routinely generate two-dimensional x-ray transmission and x-ray diffraction maps. Consequently, this facilitates an important shift in high pressure research as experimentalists embrace the study of heterogeneous and minute sample volumes in the diamond anvil cell.

For imaging or scattering measurements using electromagnetic radiation, scanning often becomes either useful or necessary when the size of the incident beam is small compared to the relevant sample dimensions. A relatively smaller beam is often desirable, offering a relatively greater spatial resolution, but this comes at the cost of increasing the time required to scan a fixed sample volume. With this in mind, it is clearly desirable to develop optimized scanning methods. One well-known and effective strategy is to scan on the fly, continuously collecting data during the motion of one or more components in the experimental configuration.1 

In the context of synchrotron radiation measurements carried out on samples in a high pressure diamond anvil cell (DAC), scanning is routinely used to locate the sample position with respect to the x-ray beam. A typical DAC sample chamber has a diameter ranging from a few tens of microns to a few hundred microns, and in most cases, it is confined at its circumference by a metallic gasket (see, for example, Fig. 1). To locate the sample chamber with respect to the x-ray beam, the DAC is systematically scanned in the plane normal to the x-ray beam. The variation in sample/gasket density gives rise to a characteristic x-ray transmission profile (see, for example, the scan in Fig. 5) as the sample chamber is scanned across the beam.

FIG. 1.

Micrograph of a typical sample chamber in the diamond anvil cell (looking along the compression axis, through the diamond anvils). The 16-sided culet (flat diamond tip) is 300 µm in diameter and extends to the boundary of the shiny metallic gasket. The sample chamber is 150 µm in diameter and contains a sample approximately 50 µm in diameter, as well as a small ruby microsphere for pressure measurements. The balance of the sample chamber is filled with helium as a pressure transmitting medium.

FIG. 1.

Micrograph of a typical sample chamber in the diamond anvil cell (looking along the compression axis, through the diamond anvils). The 16-sided culet (flat diamond tip) is 300 µm in diameter and extends to the boundary of the shiny metallic gasket. The sample chamber is 150 µm in diameter and contains a sample approximately 50 µm in diameter, as well as a small ruby microsphere for pressure measurements. The balance of the sample chamber is filled with helium as a pressure transmitting medium.

Close modal

To execute a conventional step scan with n data points, a number of tasks—move and settle the sample stage, arm and trigger the x-ray photon counter (scaler), and acquire and store the data—must be carried out n times. In contrast, to execute a fly scan, these tasks are carried out once. By taking advantage of the position- or time-based pulse output from a motion controller for channel advance of a multi-channel scaler, the sample stage is moved once (the full range of the scan), the scaler is armed once (with pulse-based channel advance during the scan), and the data are read out and saved at the end. This significantly reduces the overhead associated with many aspects of a typical step scan, and depending on various scan parameters, a conventional step scan that might take a few tens of seconds can be executed in just a few seconds with an equivalent fly scan.

The High Pressure Collaborative Access Team, HPCAT, is located at Sector 16 of the Advanced Photon Source (APS). The sector consists of four simultaneously operating endstations dedicated to the study of materials at extreme conditions.2 At HPCAT, we have developed and implemented the necessary hardware and software to execute fly scans of DAC samples. Fly scanning offers a substantial improvement in operational efficiency; it greatly reduces the time required for routine sample positioning and centering. More importantly, two-dimensional (2D) x-ray transmission and x-ray diffraction scans—which in the past have been possible but too time consuming to routinely execute—are now regularly carried out during the course of experiments. Below we describe the beamline, hardware, and software which together constitute the fly scan instrument. We present a number of practical examples highlighting the value and importance of exploring the complete DAC sample volume using two-dimensional x-ray transmission scans.

Although fly scanning capabilities have been extended to all endstations at HPCAT, the initial development and the subsequent extension to simultaneous x-ray diffraction imaging were carried out at beamline 16-ID-B. A more detailed description of the beamline’s source and front-end optics can be found elsewhere.3 Here we briefly note that using an undulator with a tunable gap and a Si double-crystal monochromator, users can select a monochromatic beam ranging in energy from ∼18 to 50 keV. At a typical operating energy of 30 keV using the Si(111) crystal pair, the flux on the sample is on the order of 1011 photons/s.

Focusing optics include a choice between two Kirkpatrick-Baez (KB) mirror assemblies;4 the large-mirror assembly can focus the beam to better than 4 µm (vertical) × 6 µm (horizontal), as characterized by the full width at half maximum (FWHM) of the derivative of a knife-edge scan. The small-mirror assembly can focus to better than 1 µm (vertical) × 2.5 µm (horizontal) at FWHM. This improvement in spatial resolution comes at the cost of flux—about 1/5th of that obtained with the large-mirror assembly.

Tungsten clean-up apertures are used to remove the extended tails of the focused beam, helping to maximize spatial resolution and minimize unwanted scattering from the sample’s surrounding gasket material. Diameters range from 10 to 100+ µm and are chosen based on the size of the DAC sample chamber and other surrounding apparatus. Figure 2 shows a schematic of the basic scattering geometry near the sample position.

FIG. 2.

Schematic of the experimental configuration with key components including (a) a small KB mirror assembly, (b) a pinhole assembly, (c) a high precision stage stack for sample motion/scanning, (d) a diamond anvil cell, (e) a beamstop with integrated diode for measuring x-ray transmission, and (f) a high-frequency area detector for collecting x-ray diffraction images.

FIG. 2.

Schematic of the experimental configuration with key components including (a) a small KB mirror assembly, (b) a pinhole assembly, (c) a high precision stage stack for sample motion/scanning, (d) a diamond anvil cell, (e) a beamstop with integrated diode for measuring x-ray transmission, and (f) a high-frequency area detector for collecting x-ray diffraction images.

Close modal

The hardware configuration used for fly scanning at HPCAT includes (1) motion controllers capable of position- and/or time-based pulse output, (2) a multi-channel scaler capable of external channel advance, (3) a digital I/O interface with built-in logical circuits, (4) a beam stop with integrated diode for x-ray transmission measurements, (5) a high-frequency area detector for x-ray diffraction measurements, and (6) ancillary equipment, e.g., line drivers.

1. Motion controller

The basic requirement for a motion controller is the capability to output pulses that are synchronized with the position of the sample stage. Figure 3 schematically depicts the typical motion/pulse concept. To allow for acceleration, the stage motion begins and ends beyond the relevant scan range; thus, the stage traverses the scan range at constant velocity. During motion, the motion controller outputs pulses. Many controllers can output a single, dedicated pulse for each scan point in the scan range (simplest approach), but it is also possible to take many pulses—for example, the step output from open-loop stepper stages or the quadrature encoder output from closed-loop stages—and use additional electronics to generate a single trigger pulse every nth controller or encoder pulse.

FIG. 3.

Schematic plot of the stage velocity and pulse output during a fly scan. The stage starts at an initial position i and reaches constant velocity before entering the scan range from 0 to N, after which it decelerates to a final position f. During the scan, the multichannel scaler is triggered at specific and regular intervals indicated by solid-line pulses. Depending on the pulse output capabilities of the controller, there may be additional (dashed-line) pulses which should be discriminated against using the appropriate filtering.

FIG. 3.

Schematic plot of the stage velocity and pulse output during a fly scan. The stage starts at an initial position i and reaches constant velocity before entering the scan range from 0 to N, after which it decelerates to a final position f. During the scan, the multichannel scaler is triggered at specific and regular intervals indicated by solid-line pulses. Depending on the pulse output capabilities of the controller, there may be additional (dashed-line) pulses which should be discriminated against using the appropriate filtering.

Close modal

For position-based pulse output, the counting time for each step will vary slightly due to mechanical imperfections in the stage and practical limitations of the control loop. Similarly, for time-based pulse output, the actual position of the stage will vary slightly with respect to the ideal position. These imperfections can be mitigated by normalizing the measured transmission intensity to either a clock or a reference intensity. We have used various combinations of pulse output (single and multiple pulses per scan point, position- and time-based pulse output) depending on controller capability and convenience, and we do not necessarily favor one scheme over the other for effective scan generation. We have used motion controllers from manufacturers including Aerotech, Inc., Newport Corp., and OMS Motion, Inc.

2. Multichannel scaler

The requirements for the multichannel scaler are straightforward; it must have a control input for external channel advance from the motion controller, a sufficient number of counting inputs, and a sufficient number of channels per counting input. Additional conveniences could include, for example, a divide-by-n option (to execute channel advance every nth motion controller pulse) and an on-board clock. At HPCAT, we use a typical configuration for photon counting (diode/ion chamber → current preamplifier → voltage-to-frequency converter → multichannel scaler). We have used VME (Versa Module Europa) based multichannel scalers from Struck Innovative Systems.

For a conventional step scan with N + 1 points, counts are measured and plotted at each point 0, 1, 2, …, N of the scan. For an equivalent fly scan described in this work, the first counting bin begins at 0 and ends at 1, the second counting bin begins at 1 and ends at 2, …, and the last counting bin begins at N − 1 and ends at N such that there are N data points collected during the fly scan (one fewer than the equivalent step scan). Our convention is to plot the bin intensity at the corresponding midpoint position of each bin, viz., at 0.5, 1.5, 2.5, …, N − 0.5.

3. Digital I/O

For a given experimental hutch at HPCAT, the user has the option of fly scanning a dozen or more different open- and closed-loop stages controlled by multiple motion controllers from various manufacturers. With several different pulse types and sources, it becomes necessary to have some sort of digital I/O interface. At HPCAT, we use a tool called softGlue developed by the Beamline Controls and Data Acquisition Group at the Advanced Photon Source. softGlue is an field-programmable gate array (FPGA)-based digital I/O module which serves as a convenient I/O interface and also has a number of predefined digital circuits including logical AND, logical OR, up/down counters, and divide-by-n counters. The connections between various I/O channels and logical circuits are established using process variables (PVs) and can be made through a dedicated software user interface. All of the various pulse sources from motion controllers are wired to inputs which can be linked to just a few outputs, viz., the multichannel scaler and x-ray area detector trigger inputs. The incoming pulses can be manipulated as needed (e.g., generating a single pulse out for n pulses in). softGlue is also a convenient diagnostic tool for troubleshooting, verifying hardware synchronization, and other related tasks.

4. Beamstop diode

For x-ray transmission measurements, we use a small PIN diode integrated into a custom beamstop assembly. This compact design, highlighted in Fig. 4, makes it possible to simultaneously collect x-ray transmission and x-ray diffraction. The beamstop is 6 mm in diameter and machined from two pieces of tungsten alloy. The front piece is drilled out to house the diode and a ceramic cylinder which locates the diode and insulates the wire junctions. The rear piece is solid and made long enough to absorb the transmitted beam. The supporting arm is made from a printed circuit board with traces for the signal, eliminating the need for additional wires in the detector’s field-of-view.

FIG. 4.

Schematic of the beamstop/diode assembly with cutaway to show basic internal construction. The beamstop is mounted on a PCB arm and is made from two pieces of machinable tungsten alloy. See the inset for details, where the arrow shows the location of the diode.

FIG. 4.

Schematic of the beamstop/diode assembly with cutaway to show basic internal construction. The beamstop is mounted on a PCB arm and is made from two pieces of machinable tungsten alloy. See the inset for details, where the arrow shows the location of the diode.

Close modal

5. X-ray detector

A high-frequency x-ray detector is needed to optionally collect x-ray diffraction images on the fly. At HPCAT, we use a PILATUS 1MF with an imaging frequency of 125 Hz and a readout time of less than 3 ms. The same pulse output used for channel advance of the multichannel scaler is used for triggering the x-ray detector such that the scan points of the x-ray transmission map correspond to sample positions associated with the images of the x-ray diffraction map. We here note that with this configuration, users can rapidly collect high pressure single crystal x-ray diffraction data by fly scanning the rotation axis of the sample stage stack. A description of the dedicated software and specific technical considerations used to execute these measurements goes beyond the scope of this work.

6. Ancillary equipment

Because of the location of various pieces of hardware relative to one another, it has sometimes been necessary to send pulses over relatively long distances (several meters). This distance, possibly exacerbated by impedance mismatch from one component to the next, can give rise to excessive ringing, leading to errors in pulse counting. We have been able to achieve extremely reliable pulse delivery using commercially available line drivers. In some instances, these drivers also provide the convenience of pulling up open-collector outputs on some of the motion controllers. We have used line drivers from Pulse Research Lab, Inc.

A dedicated graphical user interface (GUI) has been developed for defining, executing, and displaying the data from one- and two-dimensional fly scans. The program is called Diptera after the order of true flies in the insect world. It is written in Python 2.7 using the built-in GUI platform Tkinter. The PyEpics library is used for channel access of EPICS PVs (EPICS—Experimental Physics and Industrial Control System—is the beamline control architecture used at the APS). The Matplotlib library is used for plotting and evaluating the scan data.

Figure 5 shows the Diptera interface. The left side is used for displaying and interacting with the most recent scan data or for displaying a previous scan through conventional file dialog controls. The right side is divided into a number of panels for various tasks as follows:

  1. Scan control—for setting up the basic scan parameters of 1D (and 2D) fly scans including options for selecting the stage(s), scan dimension(s), endpoints, number of steps, step size, and count time (per step) and also for displaying (and allows users to select) the file location and the index of the scan data. With Diptera, 1D scans are always executed on the fly and always in the same direction of increasing position coordinates. For 2D scans, the motion of the second stage (the step axis) proceeds as a conventional step scan with a fly scan executed by the first stage (the fly axis) at each step, always in the same direction of increasing position coordinates.

FIG. 5.

Graphical user interface for Diptera, showing the results of a one-dimensional fly scan of a DAC sample chamber. This is a characteristic transmission profile obtained when scanning the sample and gasket region of a diamond anvil cell in the plane normal to the incident x-ray beam.

FIG. 5.

Graphical user interface for Diptera, showing the results of a one-dimensional fly scan of a DAC sample chamber. This is a characteristic transmission profile obtained when scanning the sample and gasket region of a diamond anvil cell in the plane normal to the incident x-ray beam.

Close modal

A typical fly scan of a DAC sample might range from 100 to 300 µm in one dimension with step sizes from 1 to 10 µm. Count times are typically 20 ms per step for x-ray transmission and 100 ms or longer per step for simultaneous x-ray diffraction measurements. The time required to execute a single, 1D x-ray transmission fly scan ranges from ∼5 to 10 s.

  1. Centering control—for executing a dedicated 2D scan routine associated with accurately positioning the DAC at a unique sample position in the experimental configuration and for displaying the results of semi-automated centering scan analysis for making necessary corrections to the sample position.

  2. Intensity control—for selecting the x-ray counter(s), e.g., diodes and ion chambers, used to display x-ray transmission data. It includes simple arithmetic operations for normalization and scaling, also has an option for displaying a point-by-point derivative of a scan, and includes controls for scaling and color resolution of contour plots.

  3. Position control—for displaying and moving to unique stage positions associated with the scan data. For 1D scans, the plot area includes three vertical bars (see Fig. 5) which can be adjusted on the screen by the user. The sample can be moved to any of these positions by clicking on a corresponding button. For 2D scans, clicking on a point of interest on the data plot loads the associated stage positions in the position control fields, and subsequently clicking those fields will move the stages to those positions.

The lower right portion of the Diptera interface includes buttons for bringing up additional controls for scan overlay, x-ray imaging, and beamline alignment. The x-ray imaging controls allow x-ray diffraction images to be simultaneously collected with x-ray transmission data, with the same dimension, step size, and count time as defined in the Scan Control panel.

Fly scanning significantly reduces the amount of time required to scan the sample. This has been convenient for efficiently executing the typical 1D scans represented in Fig. 5. As the number of points (and hence, potential overhead) in a scan increases, the difference in time required to execute step scans vs. fly scans becomes more pronounced, and thus, it is especially noticeable in 2D scans. Table I provides a comparison of scan times for 1D and 2D applications with and without simultaneous x-ray diffraction imaging. Because of the significant time savings, the real revolution associated with fly scans at HPCAT has been the occasion to routinely execute 2D x-ray transmission scans, which has greatly facilitated the study of the heterogeneous sample volume in the DAC. We primarily focus on this benefit by highlighting the examples of 2D applications.

TABLE I.

A comparison of the total time required to complete various types of scans typically executed at 16-ID-B, including one- and two-dimensional x-ray transmission scans, with and without simultaneous x-ray diffraction, executed using step and fly methods. For step scans, the settling times were 0.100 s at each point. In a single-frame mode (i.e., for step scans), the overhead introduced by the detector at each point varies and can be substantial (sometimes a couple of seconds) due to file transfer over the network. The authors note that the total scan time for both fly scans and step scans can vary significantly depending on several factors, and thus, the differences reported here may be substantially larger or smaller than those observed in other scanning applications.

Count time (s)Total scan time (s)
DimensionDiffractionScan pointsRange (mm)(Per step)StepFly
1D No 51 0.200 0.05 20 
2D No 51 × 51 0.200 × 0.200 0.05 1079 296 
1D Yes 21 0.200 0.05 108 
2D Yes 21 × 21 0.200 × 0.200 0.05 2296 200 
Count time (s)Total scan time (s)
DimensionDiffractionScan pointsRange (mm)(Per step)StepFly
1D No 51 0.200 0.05 20 
2D No 51 × 51 0.200 × 0.200 0.05 1079 296 
1D Yes 21 0.200 0.05 108 
2D Yes 21 × 21 0.200 × 0.200 0.05 2296 200 

The high pressure community is keenly interested in technical advances which allow researchers to routinely reach higher static pressures. Because pressure is inversely proportional to unit area, the basic approach to attaining ultrahigh pressure is to reduce the sample size. For doing so, a number of methods have been used, including conventional anvils with beveled and very small culets5 (the culet is the flat portion of the anvil in contact with the gasket and sample), toroidal culets,6,7 chemical vapor deposited nanocrystalline diamond micro-anvils,8,9 and high-pressure high-temperature grown nanocrystalline diamond spheres or hemispheres.10,11 In each of these instances, there are steep pressure gradients in the region of highest pressure, and the ultimate high pressure for a given sample configuration may be reached only locally on the micron or even submicron scale.12 This makes it crucial to have the highest possible spatial resolution and makes it advantageous to be able to explore the high pressure region systematically and efficiently with fly scanning.

Figure 6 (top) shows an SEM image of the culet of a diamond anvil with a nanocrystalline diamond micro-anvil grown in the central region of a single-crystal diamond anvil and (bottom) a 2D scan from a sample with the same anvil design. The scan in this example is relatively large—over a region 400 × 400 µm2 with 8 µm step sizes in both dimensions—which allows the researcher to get a quick overview of the sample chamber. The area of the highest x-ray transmission reveals the location of the micro-anvil. Following up this large-area scan with a high-resolution scan of the central area—with micron or even submicron step sizes—can reveal the highest pressure in the sample chamber.9 

FIG. 6.

(Top) SEM image of a diamond anvil culet of 300 µm in diameter with a nanocrystalline diamond micro-anvil grown in the center. (Bottom) A 2D x-ray transmission scan of a similar sample assembly. The dashed circle is 300 µm in diameter, corresponding to the approximate boundary of the culet in the scan. The high-transmission portion in the center reveals the precise location of the micro-anvil. SEM image and transmission scan data courtesy Vohra.

FIG. 6.

(Top) SEM image of a diamond anvil culet of 300 µm in diameter with a nanocrystalline diamond micro-anvil grown in the center. (Bottom) A 2D x-ray transmission scan of a similar sample assembly. The dashed circle is 300 µm in diameter, corresponding to the approximate boundary of the culet in the scan. The high-transmission portion in the center reveals the precise location of the micro-anvil. SEM image and transmission scan data courtesy Vohra.

Close modal

While the typical DAC sample chamber is loaded with a single sample material, it is sometimes beneficial or even necessary to load two or more distinct materials in the sample chamber. In many cases, the various samples can be distinguished using x-ray transmission. By quickly fly scanning the entire sample chamber, the location of the various materials within the chamber can be identified. Diptera’s interactive graphical user interface makes it possible to click on the regions of interest to identify and move to specific sample coordinates.

Figure 7 (top) is a micrograph of a sample chamber approximately 50 µm in diameter, with eight distinct sample materials loaded together with helium gas as a pressure transmitting medium. The purpose of such a loading is to compare the unit cell volume of the various materials at the same high pressure conditions. Figure 7 (bottom) shows a 2D scan of the sample chamber. Seven of the eight samples can be immediately located using the transmission map, and the eighth sample can be located by comparing the transmission map with the micrograph. The precise stage positions corresponding to each sample in the chamber can be determined by simply clicking on the sample in the data plot. These positions can then be used to rapidly collect x-ray diffraction images from each sample.

FIG. 7.

(Top) Micrograph of the DAC sample chamber of approximately 50 µm in diameter loaded with eight different samples in a helium pressure transmitting medium. (Bottom) 2D x-ray transmission scan identifying the location of several individual samples within the sample chamber.

FIG. 7.

(Top) Micrograph of the DAC sample chamber of approximately 50 µm in diameter loaded with eight different samples in a helium pressure transmitting medium. (Bottom) 2D x-ray transmission scan identifying the location of several individual samples within the sample chamber.

Close modal

Figure 8 (top) shows a micrograph of a different kind of multiphase assemblage. In this case, four distinct sample chambers have been sectioned off in a single metallic gasket and the same sample material, a pyrochlore, has been loaded into each chamber. Each was then laser-heated with variations in temperature and/or duration. The temperature-quenched sample was later systematically studied using x-ray diffraction. The x-ray transmission scan shown in Fig. 8 (bottom) was used to map out the various sample regions with respect to the stage positions and collect x-ray diffraction from each of the distinct areas. The differences among the corresponding x-ray diffraction patterns were ultimately used to identify an unknown phase synthesized at high pressure/temperature conditions.13 

FIG. 8.

(Top) Micrograph of a DAC sample chamber containing the same starting sample material divided into four distinct regions. (Bottom) 2D x-ray transmission scan used to identify the four spatially distinct regions for subsequent x-ray diffraction measurements. Micrograph courtesy Salamat.

FIG. 8.

(Top) Micrograph of a DAC sample chamber containing the same starting sample material divided into four distinct regions. (Bottom) 2D x-ray transmission scan used to identify the four spatially distinct regions for subsequent x-ray diffraction measurements. Micrograph courtesy Salamat.

Close modal

In many instances, a multiphase assemblage may be present which may not give rise to any x-ray transmission contrast. In these cases, it is often useful to execute fly scans with combined x-ray transmission and x-ray diffraction. The x-ray diffraction images rather than the x-ray transmission contrast are used to identify the local region(s) of interest within the sample volume. HPCAT has developed complementary software XDI to thoroughly explore this type of combined transmission and diffraction measurement. A detailed description of the software and capabilities related to HPCAT’s multimode scanning x-ray diffraction microscopy technique is presented elsewhere.14 

Centering is a good example of a routine experimental procedure that is made more efficient by fly scanning. The motivation for and description of DAC sample centering have been described elsewhere.15–17 Let it suffice here to point out that centering is a special kind of 2D scan where the translation of the sample across the beam serves as the first dimension (the fly axis) and the rotation of the sample about the rotation axis of the sample stages serves as the second dimension (the step axis). When plotting the 2D centering scan using Diptera, the user at once gets a qualitative idea of the sample’s position with respect to the center of rotation. If the sample is off-center, the transmission scan will contain three distinct regions that are misaligned in the vertical direction of the plot (see Fig. 9, top). After making the necessary corrections to locate the sample chamber at the center of rotation, a subsequent scan qualitatively confirms proper centering as the three regions are well-aligned vertically (see Fig. 9, bottom). This particular example relies on the marked difference in transmission intensity between the gasket and the sample region. In cases for which the contrast may be poor (e.g., a low-Z gasket material such as beryllium), centering can still be effectively executed using any distinct absorption feature that can be identified in or near the sample chamber, e.g., a high-Z pressure marker such as gold.

FIG. 9.

2D centering scans (consisting of three steps at −ω, 0, and +ω degrees). (Top) The off-center sample shows a systematic offset in relative scans. (Bottom) After correcting the sample position, the proper location of the sample over the center of rotation is qualitatively indicated by the vertical alignment of the 2D scan.

FIG. 9.

2D centering scans (consisting of three steps at −ω, 0, and +ω degrees). (Top) The off-center sample shows a systematic offset in relative scans. (Bottom) After correcting the sample position, the proper location of the sample over the center of rotation is qualitatively indicated by the vertical alignment of the 2D scan.

Close modal

We have developed and implemented hardware and software for executing fly scans of samples in high pressure diamond anvil cells. This has led to a more efficient use of beamtime in terms of routine scanning for sample positioning and centering. But the most valuable benefit has been the occasion to routinely execute two-dimensional x-ray transmission and x-ray diffraction scans of relatively large sample volumes in a relatively short period of time compared to traditional step scanning. This is an important development in terms of facilitating the study of heterogeneous and minute sample volumes in the diamond anvil cell. We expect the continued and widespread development of these methods in the near future.

We thank Mark Rivers for extensive technical assistance and discussion. We also thank Kurt Goetze and Arun Bommannavar for technical assistance, Yogesh Vohra and Ashkan Salamat for providing sample images, and Ligang Bai for loading the samples shown in Fig. 7. This project was supported by the Department of Energy (DOE)—Office of Science/Division of Materials Science and Engineering under Award No. DE-FG02-99ER45775 (G.S.). This work was performed at HPCAT (Sector 16), Advanced Photon Source (APS), Argonne National Laboratory. HPCAT operations are supported by DOE-NNSA’s Office of Experimental Sciences. The Advanced Photon Source is a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.

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The authors note that the scientific literature is rich with examples of fly scanning in numerous and varied laboratory and synchrotron applications. The authors are not aware of existing fly scan apparatus addressing diamond anvil cell applications.

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