Soft X-ray Scanning Research Articles

3-d chemical imaging using angle-scan nanotomography in a soft X-ray scanning transmission X-ray microscope

Three-dimensional chemical mapping using angle scan nanotomography in a soft X-ray scanning transmission X-ray microscope (STXM) has been used to investigate the spatial distributions of a low density polyacrylate polyelectrolyte ionomer inside submicron sized polystyrene microspheres. Acquisition of tomograms at multiple photon energies provides true, quantifiable 3-d chemical sensitivity. Both pre-O 1s and C 1s results are shown. The study reveals aspects of the 3-d distribution of the polyelectrolyte that were inferred indirectly or had not been known prior to this study. The potential and challenges for extension of the technique to studies of other polymeric and to biological systems is discussed.

Comparative Observations of Bone Formation in Peri-implant Tissue using Soft X-ray, Micro-computed Tomography and Confocal Laser Scanning Microscopy

Comparative Observations of Bone Formation in Peri-implant Tissue using Soft X-ray, Micro-computed Tomography and Confocal Laser Scanning Microscopy

Spectromicroscopy Mapping of Colloidal/Particulate Organic Matter in Lake Brienz, Switzerland

Transmission electron microscopy (TEM), soft X-ray scanning transmission X-ray microscopy (STXM), and mu-FTIR spectromicroscopy were used to map colloidal/ particulate material in an ultra-oligotrophic lake, Lake Brienz, Switzerland, with a special focus on organic functionality. Within the statistical margin of error and the uncertainties arising from the representativeness of the results, the research reveals that organic material was associated with potassium-rich inorganic colloids present in surface and deep water (depths of 1 and 100 m, respectively), which indicates a vertical transfer of aggregates by sedimentation. Pure organic colloids could only be detected in surface waters. In addition, correlation map analysis of synchrotron-based mu-FTIR and carbon K-edge STXM spectromicroscopic data using spectra from the Lütschine and Aare Rivers as target spectra revealed spectral similarities with organic components from both tributary rivers in deeper regions (100 m) of the lake. The results prove that STXM and mu-FTIR can characterize colloidal and particulate organic material in low organic carbon systems.

Chemical Imaging by Soft X-ray Scanning Transmission X-ray Microscopy

Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2005

Chemically Sensitive Tomography at 50 nm Spatial Resolution using a Soft X-ray Scanning Transmission X-Ray Microscope

Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2005

Quantitative mapping of chlorhexidine in natural river biofilms

Soft X-ray scanning transmission X-ray microscopy has been applied to map chlorhexidine, a ubiquitous antimicrobial agent, relative to major biochemical components (proteins, lipids, polysaccharides, Ca2+, K+, CO32−) in natural river biofilms. For the first time, bio-accumulation of chlorhexidine in diatoms has been observed unambiguously. The quantitative results show that chlorhexidine bioaccumulated extensively in lipid-rich regions of diatoms and bacteria. Confocal laser scanning microscopy was used to document changes in the biofilm community. The bioaccumulation provides a significant entry point for chlorhexidine into the aquatic food chain. It results in modification of the biofilm community and it impacts the photosynthetic and protozoan species in particular. X-ray microscopy mapping at high spatial resolution is shown to be a powerful tool for studies of antimicrobial agents in the environment.

Soft X-ray scanning transmission X-ray microscopy (STXM) of actinide particles

A descriptive account is given of our most recent research on the actinide dioxides with the Advanced Light Source Molecular Environmental Science (ALS-MES) Beamline 11.0.2 soft X-ray scanning transmission X-ray microscope (STXM) at the Lawrence Berkeley National Laboratory (LBNL). The ALS-MES STXM permits near-edge X-ray absorption fine structure (NEXAFS) and imaging with 30-nm spatial resolution. The first STXM spectromicroscopy NEXAFS spectra at the actinide 4d5/2 edges of the imaged transuranic particles, NpO2 and PuO2, have been obtained. Radiation damage induced by the STXM was observed in the investigation of a mixed oxidation state particle (Np(V,VI)) and was minimized during collection of the actual spectra at the 4d5/2 edge of the Np(V,VI) solid. A plutonium elemental map was obtained from an irregular PuO2 particle with the dimensions of 650 x 650 nm. The Pu 4d5/2 NEXAFS spectra were collected at several different locations from the PuO2 particle and were identical. A representative oxygen K-edge spectrum from UO2 was collected and resembles the oxygen K-edge from the bulk material. The unique and current performance of the ALS-MES STXM at extremely low energies (ca. 100 eV) that may permit the successful measurement of the actinide 5d edge is documented. Finally, the potential of STXM as a tool for actinide investigations is briefly discussed.

Scanning Soft X-ray Microscopy and Diffraction Imaging

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

Imaging and Patterning of Monomolecular Resists by Zone-Plate-Focused X-ray Microprobe

Soft X-ray scanning photoelectron microscopy (SPEM) was applied to image and characterize molecular patterns produced by electron irradiation of various aliphatic and aromatic thiol-derived self-assembled monolayers (SAMs). The observed chemical contrasts allowed us to monitor complex phenomena which occurred as a result of electron-beam patterning, the exposure of the patterned films to ambient, and the irradiation of the films by the X-ray microprobe during image acquisition. The latter effect has been analyzed in detail and utilized for direct lithographic writing in the SAM resists by the zone-plate-focused X-ray beam. The results demonstrate the capabilities of the SPEM technique both for chemical imaging and as a fabrication tool for micro- and nanolithography.

Scanning transmission X-ray, laser scanning, and transmission electron microscopy mapping of the exopolymeric matrix of microbial biofilms.

Confocal laser scanning microscopy (CLSM), transmission electron microscopy (TEM), and soft X-ray scanning transmission X-ray microscopy (STXM) were used to map the distribution of macromolecular subcomponents (e.g., polysaccharides, proteins, lipids, and nucleic acids) of biofilm cells and matrix. The biofilms were developed from river water supplemented with methanol, and although they comprised a complex microbial community, the biofilms were dominated by heterotrophic bacteria. TEM provided the highest-resolution structural imaging, CLSM provided detailed compositional information when used in conjunction with molecular probes, and STXM provided compositional mapping of macromolecule distributions without the addition of probes. By examining exactly the same region of a sample with combinations of these techniques (STXM with CLSM and STXM with TEM), we demonstrate that this combination of multimicroscopy analysis can be used to create a detailed correlative map of biofilm structure and composition. We are using these correlative techniques to improve our understanding of the biochemical basis for biofilm organization and to assist studies intended to investigate and optimize biofilms for environmental remediation applications.

Imaging of patterned self-assembled monolayers by scanning photoelectron microscopy

We have applied soft X-ray scanning photoelectron microscopy (SPEM) to image and characterize molecular patterns produced by electron irradiation of various aliphatic and aromatic thiol-derived self-assembled monolayers (SAMs) through masks. The fabricated patterns can be clearly distinguished and the inverse contrasts for the Au 4f and C 1s images suggest that the goal of chemical imaging has been achieved. The thickness of the films in the irradiated areas appeared to be higher than that in the non-irradiated ones. This can be explained by the adsorption of airborne carbon-containing molecules on the irradiated areas. In addition, the N 1s images were acquired from the structured films of NO 2 (C 6 H 4 ) 2 SH on gold to monitor the electron irradiation-induced transformation of the nitro tail groups into amino moieties. However, no chemical contrast related to the nitro-amino transformation was observed. This can be explained by the small intensity of the nitrogen photoelectron emission with respect to the inelastic background originated from the substrate and by the X-ray induced modification of the lithographic pattern during the image acquisition. The modification of aromatic SAMs caused by the zone-plate-focused X-ray beam has been utilized for direct lithographic writing by the microprobe.

Scanning transmission X-ray microscopy with a segmented detector

A segmented silicon detector has been developed for the Stony Brook soft x-ray scanning transmission x-ray microscope. The detector combines good detective quantum efficiency (90% at 520 e' and low noise (5 photons/ channel/ integration at 520 eV) with the ability of having up to 10 independent sensitive regions that are matched to the microscope geometry. In addition to the usual bright field images, differential phase contrast images and dark field images are recorded simultaneously in one scan. A Fourier filtering method has been employed to recover an estimate of the sample absorption and phase shift from the partially coherent images collected on the detector segments. 'A reconstruction of a Germanium test pattern exhibits good agreement between the predictions from the tabulated x-ray optical constants and the experiment.

Interferometer-controlled scanning transmission X-ray microscopes at the Advanced Light Source.

Two new soft X-ray scanning transmission microscopes located at the Advanced Light Source (ALS) have been designed, built and commissioned. Interferometer control implemented in both microscopes allows the precise measurement of the transverse position of the zone plate relative to the sample. Long-term positional stability and compensation for transverse displacement during translations of the zone plate have been achieved. The interferometer also provides low-distortion orthogonal x, y imaging. Two different control systems have been developed: a digital control system using standard VXI components at beamline 7.0, and a custom feedback system based on PC AT boards at beamline 5.3.2. Both microscopes are diffraction limited with the resolution set by the quality of the zone plates. Periodic features with 30 nm half period can be resolved with a zone plate that has a 40 nm outermost zone width. One microscope is operating at an undulator beamline (7.0), while the other is operating at a novel dedicated bending-magnet beamline (5.3.2), which is designed specifically to illuminate the microscope. The undulator beamline provides count rates of the order of tens of MHz at high-energy resolution with photon energies of up to about 1000 eV. Although the brightness of a bending-magnet source is about four orders of magnitude smaller than that of an undulator source, photon statistics limited operation with intensities in excess of 3 MHz has been achieved at high energy resolution and high spatial resolution. The design and performance of these microscopes are described.

Scanning soft X-ray spectromicroscopy at the Pohang Light Source: commissioning results

A scanning spectromicroscopy facility has been installed at the undulator radiation beamline at the Pohang Light Source. The spectromicroscopy is operational in both the scanning transmission X-ray microscopy (STXM) and the scanning photoelectron microscopy (SPEM) modes. Currently, the measured X-ray spot size on the sample is about 0.4 μm. The effective photon energy range of the STXM is 250–1000 eV and that of the SPEM is 400–1000 eV. The performance of the facility is presented in this report.

Atomic structure and composition of the P-rich InP(001) surfaces

The microscopic structure of the P-rich (2×1)-like surfaces of InP(001) is investigated by soft X-ray photoemission spectroscopy (SXPS) and scanning tunneling microscopy (STM). The samples were grown by metal organic vapor phase epitaxy (MOVPE) and then transferred under ultra high vacuum (UHV) conditions to UHV analysis chambers. STM images show a P-rich as-grown surface after transfer and another less P-rich surface after prolonged annealing at 350°C. The In4d emission line is not affected by the change in surface reconstruction and shows a small surface component shifted by 0.48 eV towards higher binding energies. The line shape of the P2p core level, on the other hand, changes: On the as-grown surface, one surface component which is shifted by 0.98 eV towards higher binding energies is found after transfer, whereas two surface components shifted to higher and lower binding energies, respectively, appear after annealing at 350°C. These results are consistent with the structure models derived from STM for the different P-rich (2×1)-like surfaces.

Effect of intermittent administration of human parathyroid hormone (1-34) on the mandibular condyle of ovariectomized rats

Intermittent administration of human parathyroid hormone (1-34) (PTH) increases bone mass in lumbar vertebrae and long bones of osteoporotic experimental animals. However, whether PTH has the same effect on jaw bones remains unclear. This study determined the effect of intermittent administration of PTH on rat mandibular condyle affected by estrogen deficiency. Fifty 6-month-old rats were either sham operated or ovariectomized, then divided into five groups depending on surgical procedure and hormone administration: sham + vehicle (SV), OVX + vehicle (OV), OVX + PTH 6 micrograms/kg once per week (OP6-1), OVX + PTH 60 micrograms/kg once per week (OP60-1), and OVX + PTH 20 micrograms/kg three times per week (OP20-3). PTH or vehicle was injected intermittently for 6 months in 5 rats of each group either immediately after surgery in a preventive administration experiment, or injected starting 6 months after surgery in a therapeutic administration experiment. The mandibles were excised, and bone morphometry was performed using confocal laser scanning microscopy and soft X-ray images. In both experiments, the bone volume of the OV groups was significantly lower than that of the SV group (P < 0.01); also, depending on dose and frequency, the bone volume of the OP group was higher than that of the OV group, particularly in the OP20-3 group. The value of mineralized surface of the OP groups was significantly higher than that of the OV group (P < 0.01), whereas the value of eroded surface of the OP groups was not significantly higher than that of the OV group. This study indicates that preventive and therapeutic intermittent administration of PTH in ovariectomized rats increase the bone formation in rat mandibular condyle without accelerating bone resorptive activity. This anabolic effect was best induced by the injection mode of 20 micrograms/kg three times per week.

Atomic Surface Structure of MOVPE-Grown InP(001)

In this study soft X-ray photoemission spectroscopy (SXPS) and scanning tunneling microscopy (STM) were used to investigate the microscopic structure of the P-rich so-called (2×1) reconstruction of InP(001). The samples were homoepitaxially grown in a commercial MOVPE reactor, transferred to ultra high vacuum (UHV), and then transported to separate UHV analysis chambers. Electron diffraction patterns of the samples taken after transfer show a (2×1)/(2×2) periodicity with streaks in the [1-10] direction. STM images display rows along the [110] direction showing a twofold periodicity. Consistent with SXPS spectra of the P2p and In4d core levels the structure can be explained by a fractional monolayer of P-dimers adsorbed on a complete second layer of P. The P-dimers are arranged in local (2×2)/c(2×2)/c(4×2) structures showing a lack of long-range ordering.

The Soft X-ray Scanning Photoemission Microscopy Project at SRRC.

The Synchrotron Radiation Research Center (SRRC) and the Institute of Atomic and Molecular Sciences (IAMS) have initiated a project to construct a scanning photoelectron spectromicroscopy end station at SRRC (SRRC-SPEM). High-brightness soft X-rays will be provided by the U5 undulator beamline. Zone-plate-based soft X-ray optics will be used to focus the beam to form the microprobe. A hemispherical sector analyser with multichannel detection capability will collect the photoelectrons. A total of up to 32 images can be acquired concurrently. The apparatus is also equipped with a sample distribution system for in situ sample preparation and characterization in conjunction with other surface spectroscopic techniques.

Scanning soft X-ray imaging at 10 nm resolution

The potential imaging and selected-area near-edge X-ray absorption fine structure spectroscopic (NEXAFS) performance of a new scanning probe X-ray microscope (SPXM) for soft X-rays from synchrotron radiation is examined by computer modelling; an optical design for the microscope is also given. Acceptable dwell times per pixel in image collection are predicted. The microscope is expected to have a spatial resolution for “water-window” X-ray wavelengths (2.3–4.4 nm) of about 10 nm for specimens up to 200 nm thick. The central component of the optical system is a tube collimator forming a probe a few wavelengths in diameter above a scanned specimen. The collimator is illuminated at near-normal incidence by a Fresnel zoneplate condenser, and its exit aperture is positioned a few wavelengths above the specimen. Physical understanding is gained by a two-dimensional (2D) waveguide approach, and by calculations using the full-vector theory of Maxwell's equations. The calculations, because of computational limitations, are carried out mainly in 2D. The vector results agree well with a multislice scalar calculation in 2D which is then applied to 3D to describe the 3D probe imaging and to estimate the energy throughput.

The scanning soft X-ray microscope at Hasylab: imaging and spectroscopy of photoelectrons, photoluminescence, desorbed ions, reflected, scattered and transmitted light

Abstract The scanning soft X-ray microscope operating at Hasylab/Desy has been developed to combine lateral and temporal resolution, tunability and various conventional spectroscopy techniques. Different mirror optics are used to form a microprobe in the energy range 15–1500 eV. A grazing incidence ellipsoidal mirror provides a resolution of 1 μm over the entire energy range, and in the vacuum ultraviolet region below 30 eV, 0.15 μm can be achieved with a Pt-coated Schwarzschild objective. Due to the large working distance of the optics used, the detection and analysis of several surface signals are comparatively simple. Detectors and spectrometers for photoelectrons, luminescence, fluorescence, desorbed ions, reflected, scattered and transmitted light are built in permanently into the microscope. Furthermore, some combinations of the different methods can be used for simultaneous measurements. In this paper the technical developments of recent years are described. A short representation of some exemplary applications will give an insight into the work of our group and illustrate the characteristics of the microscope. The following topics are discussed: cross-luminescence of barium fluoride, visible luminescence and degradation of porous silicon, photoluminescence of ceramics, chemical contrast in photoemission spectroscopy, and Bragg reflection as a contrast mechanism in X-ray microscopy.