Sapoti: X-ray microscopy’s new frontier at Sirius

Designed to achieve resolutions on the order of 1 nanometer, the Sapoti station of the Carnaúba beamline combines cryogenics, ultra-high vacuum, and cutting-edge mechatronics engineering to reveal structures at the atomic scale

 

Sapoti (Scanning Analysis by PtychO for Tomographic Imaging) is one of the two experimental stations of the Carnaúba beamline at Sirius. The facility is one of the most sophisticated and challenging stations ever developed at the Brazilian accelerator. Its goal is to achieve resolutions on the order of 1 nanometer in coherent X-ray imaging and tomography, a performance that places it among the world’s most precise instruments in synchrotron light-based microscopy.  

The experimental stations of the Carnaúba beamline

The Carnaúba beamline operates in the 2.05 to 15 keV energy range, and was designed to perform simultaneous measurements with multiple X-ray analytical techniques, including diffraction, spectroscopy, fluorescence, and luminescence, as well as two- and three-dimensional imaging. It is the longest line at Sirius and uses a highly bright beam from an undulator, exploring the full potential for coherence and intensity that a fourth-generation synchrotron light source can provide.

Its infrastructure houses two complementary experimental stations. The Tarumã station was designed for in situ, in vivo (with plants), and cryogenic experiments, operating in an open environment with high flexibility for different types of samples. Sapoti operates in ultra-high vacuum and cryogenic conditions, which ensures even greater thermal and mechanical stability, leading to better spatial resolutions, as well as better conditions for experiments at the lower energy limit.

Since its inception in 2018, the Sapoti station has been designed to surpass traditional resolution limits in nanoprobes — systems that focus X-rays onto nanometric points to map material properties with extremely high precision — of synchrotron light sources. To achieve this, advanced solutions in optics and highly complex mechatronics were combined. The X-ray beam, with energies from 2.05 to 15 keV, is focused by an array of Kirkpatrick–Baez (KB) mirrors capable of producing fully coherent X-ray beams with sizes between 30 and 140 nanometers.  

Unlike other systems that use refractive elements, KB mirrors offer greater efficiency and insensitivity to changes in beam energy, which is critical for spectroscopy experiments. However, they also have higher mechanical requirements — a challenge overcome through solutions developed at LNLS itself, applying advanced principles of precision engineering. 

According to Renan Geraldes, physical engineer and leader of the Mechatronics and Precision Engineering group at LNLS/CNPEM, the development of Sapoti was also an exercise in innovation and continuous learning. “From the beginning, it was expected that Sapoti would be one of the stations with the greatest technical challenges that we would have to develop”, he says. “It was a project that extracted the maximum potential from our precision mechatronics, systems engineering, and predictive design tools. Vacuum, cryogenics, optics, sample transfer and positioning — it was necessary to make it all compatible.” 

The technical challenges overcome by the Sapoti station

The Sapoti experimental station features an advanced sample positioning stage, an innovative mechatronic system developed in collaboration with the Dutch company MI-Partners. Inspired by technologies used in the semiconductor industry, the stage utilizes Lorentz actuators instead of conventional piezoelectric ones, allowing it to combine nanometer resolution with a millimeter-level range of motion. This approach makes it possible to navigate with 1 nm precision along three-dimensional trajectories with a range of up to 3 mm, something unprecedented in X-ray nanoprobes.  

Sapoti is a fully vacuum-operated station in which the KB mirrors, the sample, and some of the detectors share the same chamber. This configuration ensures improved component stability, guaranteeing greater rigidity and alignment precision while reducing absorption losses at lower energy levels.  

The station is also capable of operating under controlled cryogenic temperatures, between 100 and 300 K, conditions that not only help mitigate radiation damage but also allow for the study of frozen biological samples and sensitive materials. To achieve this, Sapoti uses a cryogenics system integrated into the stage, equipped with a cryogenic loading module with a vacuum transfer system, which allows for the insertion and manipulation of samples without exposure to air, preserving their physical and chemical properties from preparation to data acquisition.

To ensure versatility in handling different types of samples, Sapoti uses a standard sample holder developed especially for the Carnaúba beamline called CARPIN (CARnaúba PIN). Inspired by the OMNY PIN system, used at the Swiss Light Source (SLS) cSAXS beamline, CARPIN was designed as a universal interface capable of accommodating samples with dimensions ranging from micrometers to a few millimeters, including solid samples, liquids, pastes, powders, electron microscopy grids, and thin membranes. This flexibility facilitates the exchange of samples between different beamlines at Sirius or even other synchrotrons, expanding the possibilities for complementary or collaborative experiments. 

The Sapoti assembly involved a series of complex integration steps. Initial tests with the system in the first half of 2025 showed promising results. “Even in the initial commissioning phase, Sapoti achieved positional stability of approximately 3 nanometers, already allowing the acquisition of images with an estimated resolution of 5.5 nanometers, a performance superior to that achieved by Tarumã, even after several years of operation. As the system progresses through calibration and fine-tuning, it is expected to reach the projected limit of 1 nanometer, consolidating Sapoti among the most advanced experimental stations in the world in coherent X-ray microscopy”, Renan highlights.  

Integration with the new vertical polarization undulator

In 2025, Carnaúba began operating with a new vertical polarization undulator (VPU), a structural advancement that significantly expands the range of experiments supported by the beamline. The new device allows access to energies below 6 keV, paving the way for obtaining spectra of light elements — such as V, Ti, Ca, S, and P — and strengthening applications in areas such as semiconductors, soil science, agriculture, biomaterials, geosciences, and environmental studies. With greater brightness at low energies and excellent coherence, VPU also increases contrast in coherent imaging of biological tissues, revealing subcellular structures that are poorly explored at higher energies.  

According to the beamline coordinator, Rodrigo Szostak, “The installation of the new undulator allows us to investigate samples with lighter elements, which are of broad interest in various fields of knowledge”. “Combining this broadened spectral range with the intrinsic characteristics of the Carnaúba beamline makes this infrastructure a powerful and unprecedented tool for studies in agriculture and geosciences, soil science, environment, and materials”, he says. Initial tests have already validated measurements of chemical elements in standard samples, and full experiments in this new energy range are planned for next year.  

There is also an important strategic aspect: very few micro and nanoscopy beamlines in 3rd and 4th generation synchrotrons operate with high performance below 6 keV, which puts Carnaúba in a unique position on the international stage. “This will be a window of opportunity for researchers to design and carry out new experiments that take full advantage of the potential of Sirius’ beamlines,” says Szostak.  

With its combination of high stability, cryogenics, vacuum, and state-of-the-art mechatronic control, Sapoti represents a technological and scientific leap for Sirius and for Brazil, paving the way for new frontiers in nanoscience, structural biology, and materials science.