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We have investigated the band alignment at the interface of amorphous aluminum oxide (am-${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$) grown by atomic layer deposition on p-Ge(100) and the effects of postgrowth annealing using hard x-ray photoelectron spectroscopy and density function theory (DFT). Accurate determination of the valence-band offsets was obtained by comparing the experimentally measured valence bands with DFT-calculated densities of states. The am-${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ density of states calculated from a weighted ensemble of crystalline ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ structures gives excellent agreement with experiment, sufficiently capturing the nonlinear shape of the valence-band edge. We report a valence-band offset of $2.60\ifmmode\pm\else\textpm\fi{}0.1$ eV for am-${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$/p-Ge, which is reduced by 0.20 eV upon annealing as interfacial ${\mathrm{GeO}}_{x}$ is formed.

We present a low-power, low-noise prototype pixel readout application specific integrated circuit (ASIC) for hyperspectral enegy-resolving X-ray imaging detectors. The ASIC provides 16-by-16 channels to read out positive and negative charges from 16-by-16 heagonal silicon or CZT detector arrays, at a pitch size of $250 \mu \mathrm{m}$, to achieve good spatial resolution and the ability to record the energy of a detected photon as well as its position. The readout is done by bumpbonding the anodes to the inputs of the ASIC. Each channel of the ASIC provides low-noise charge amplification, high-order shaping with baseline stabilization, discrimination, extraction of amplitude (with neighbour channels), multiplexing, and dissipates $\sim0.6$ mW. A smart readout of the triggered pixel and its adjacent six pixels in the hexagonal configuration allows reconstruction of events with charge sharing correction, and can be used to estimate the depth of the photon interaction and to suppress background events. The target equivalent noise charge (ENC) is $\sim10$ electrons for silicon detector pixel and $\sim15$ electrons for CZT detector pixel.

Coahuilite, a new variety of amber is described from the Late Cretaceous Olmos Formation (ca. 73 Ma.), Coahuila, north of México. This amber is totally distinct chemically and stratigraphically from the Miocene Chiapas amber (ca. 23-13 Ma.), Southern México, which according to mineral nomenclature is currently known as Simojovelite var. nov. Additionally, an emended description of Bacalite is proposed, based on the physicochemical analysis and geological record of a fossil resin recently recovery from the Late Cretaceous El Gallo Formation (ca. 73 Ma.), Baja California, northwestern México. The results are supported by characterization of such ambers using synchrotron-based Infrared (FTIR) microspectroscopy.

Chiapas amber is a natural occurring fossil resin structurally composed of long macromolecule chains with semicrystalline phases associated with both fossil and polymerization process. The most conspicuous characteristic of this fossil polymer is that it preserves ancient organic inclusions. In the present work, PIXE/RBS spectrometry (particle-induced X-ray emission/Rutherford backscattering) were combined with complementary K-edge XANES spectroscopy (X-ray absorption near-edge structure) to identify the amount of sulfur in Chiapas amber. Initially, the amber samples were examined using infrared reflected photomicrography. Amber is transparent to infrared light and so embedded plants and animals are easily visible, showing them in extraordinary detail, as if they were immersed in a water-like solution. The PIXE/RBS data show that the proportion of sulfur in amber is significantly higher than that found in recently formed resins, consistent with the biogeochemical process that transforms the resin into amber during long-term burial in geological deposits. The sulfur K-edge XANES spectra from amber confirm the sulfur abundance and reveal sulfur species in the reduced and intermediate oxidation states in amber. Almost no oxidized sulfur was found, whereas the recent resins show mostly oxidized sulfur fractions. This indicates that labile oxidized sulfur decays during fossilization and resin maturation must occur under conditions of oxygen depletion. The implications of the presence of sulfur in amber for organic preservation is also discussed here. Sulfur compounds work as a polymer additive that promotes intense resin solidification. This restricts the early oxidant-specific biodegradation of the embedded biomatter and, over geological time, provides greater stability against chemical changes.

Arrays of Silicon Drift Detectors (SDD) were designed, produced and tested. These arrays are the central part of an X-Ray Spectrometer (XRS) for measuring the abundances of light surface elements (C–Fe) fluoresced by ambient radiation on the investigated celestial object. The basic building element (or cell) of the arrays consists of a single hexagonal SDD. Signal electrons drift toward the center of the hexagon where a very low capacitance anode is located. The hexagonal shape of an individual SDD allows for a continuous covering of large detection areas of various shapes. To match the number of SDD cells with the external Application Specific Integrated Circuit (ASIC), two arrays, one with 16 and another with 64 cells were developed. One side of SDDs, called the window side, is a continuous thin rectifying junction through which the X-ray radiation enters the detector. The opposite side, called the device side contains electron collecting anodes as well as all other electrodes needed to generate the drift field and to sink leakage current produced on Si–SiO 2 interface. On both sides of the detector array there is a system of guard rings, which smoothly adjusts the voltage of the boundary cells to the ground potential of the silicon outside the sensitive volume. The drift voltage inside the detector is generated by an implanted rectifying contact, which forms a hexagonal spiral. This spiral produces the main valley where signal electrons drift as well as the voltage divider to produce the drift field. System performance is shown by a spectrum of Mn X-rays produced by the decay of 55 Fe.

Preliminary X-ray correlation spectroscopy results from the novel three-dimensional vertically integrated photon imaging chip (VIPIC) detector are presented., The Vertically Integrated Photon Imaging Chip (VIPIC) was custom-designed for X-ray photon correlation spectroscopy, an application in which occupancy per pixel is low but high time resolution is needed. VIPIC operates in a sparsified streaming mode in which each detected photon is immediately read out as a time- and position-stamped event. This event stream can be fed directly to an autocorrelation engine or accumulated to form a conventional image. The detector only delivers non-zero data (sparsified readout), greatly reducing the communications overhead typical of conventional frame-oriented detectors such as charge-coupled devices or conventional hybrid pixel detectors. This feature allows continuous acquisition of data with timescales from microseconds to hours. In this work VIPIC has been used to measure X-ray photon correlation spectroscopy data on polystyrene latex nano-colliodal suspensions in glycerol and on colloidal suspensions of silica spheres in water. Relaxation times of the nano-colloids have been measured for different temperatures. These results demonstrate that VIPIC can operate continuously in the microsecond time frame, while at the same time probing longer timescales.

Silicon crystals at room temperature employed as x-ray monochromators on synchrotron radiation beamlines, when subjected to high-power-density loading, suffer thermal distortions which compromise their x-ray diffraction efficiency and result in a reduction of the inherent brilliance of the synchrotron beam. At cryogenic temperatures however (below 150 K), silicon crystals suffer little or no thermal distortions under high-power-density loading. The design and implementation of a channel-cut silicon crystal monochromator which is cooled to as low as 50 K, using a commercial helium refrigerator and circulation system and a custom-designed heat exchanger for the monochromator crystal, are described. Test results have been obtained on the National Synchrotron Light Source X13B in-vacuum undulator beamline as well as the higher power X25 wiggler beamline.

A detector for the X-ray Correlation Spectroscopy (XCS) instrument at the Linac Coherent Light Source (LCLS) in Stanford (CA) is being developed at Brookhaven National Laboratory (BNL). The LCLS is the first operational X-ray free electron laser. It provides extremely bright coherent laser-like X-ray pulses with energy up to 8 keV, shorter than 100 fs and with a repetition rate that will go up to 120 Hz. An ideal detector for XCS experiments should cover a large angular range with high efficiency and provide a proper resolution to resolve the speckle. The requirement for dynamic range is not particularly stringent while a fast readout is needed. In particular, the Charge Pump Detector has to be highly efficient at the energy of 8 keV, provide a dynamic range of 100 photons and a readout noise much better than one photon. The 1024×1024 pixels have to be read within the repetition rate of the laser pulses, that is faster than 8 ms. The pixel size of 56 μm×56 μm is a compromise between charge sharing and small pixel. Working principle and details of the detector will be discussed.

The growth of protein crystals suitable for x-ray crystal structure analysis is an important topic. The quality (perfection) of protein crystals is now being evaluated by mosaicity analysis (rocking curves) and x-ray topographic images as well as the diffraction resolution limit and overall data quality. In yet another study, use of hanging drop vapour diffusion geometry on the IML-2 shuttle mission showed, again via CCD video monitoring, growing apocrustacyanin C(sub 1) protein crystal executing near cyclic movement, reminiscent of Marangoni convection flow of fluid, the crystals serving as "markers" of the fluid flow. A review is given here of existing results and experience over several microgravity missions. Some comment is given on gel protein crystal growth in attempts to 'mimic' the benefits of microgravity on Earth. Finally, the recent new results from our experiments on the shuttle mission LMS are described. These results include CCD video as well as interferometry during the mission, followed, on return to Earth, by reciprocal space mapping at the NSLS, Brookhaven, and full X-ray data collection on LMS and Earth control lysozyme crystals. Diffraction data recorded from LMS and ground control apocrustacyanin C(sub 1) crystals are also described.

In 17th century Old Master Paintings, the underpainting generally refers to the first sketch of a composition. The underpainting is applied to a prepared ground using a monochrome, brown oil paint to roughly indicate light, shade and contours. So far, methods to visualize the underpainting-other than in localized cross-sections-have been very limited. Neither infrared reflectography nor neutron induced autoradiography have proven to be practical, adequate visualization tools. Thus, although of fundamental interest in the understanding of a painting's genesis, the underpainting has virtually escaped all imaging efforts. In this contribution we will show that 17th century underpainting may consist of a highly heterogeneous mixture of pigments, including copper pigments. We suggest that this brown pigment mixture is actually the recycled left-over of a palette scraping. With copper as the heaviest exclusive elemental component, we will hence show in a case study on a Portrait of an Old Man attributed to Rembrandt van Rijn how scanning macro-XRF can be used to efficiently visualize the underpainting below the surface painting and how this information can contribute to the discussion of the painting's authenticity.

A versatile computer environment to manage instrumentation alignment and experimental control at the National Synchrotron Light Source beam lines has been developed. The system is based on a 386 486 personal computer running under a UNIX operating system with X11 Windows. It offers an ideal combination of capability, flexibility, compatibility, and cost. With a single personal computer, the beam line user can run a wide range of scattering and spectroscopy experiments using a multi-tasking data-collection program which can interact with CAMAC, GPIB and AT-Bus interfaces, and simultaneously examine and analyze data and communicate with remote network nodes.

In this work we have demonstrated a 256-channel(element) correlator array design based on a Virtex 6 FPGA for X-ray Photon Correlation Spectroscopy that uses Dynamic Light Scattering to probe nanometer scale structures, where the channel here means one correlator element which could provide auto correlation functions for 36 lags. This design is incorporated along with a design consisting of a 64×64 pixel silicon detector array and a custom 3D integrated circuit called vertically integrated pixel imaging chip (VIPIC). The challenge was how to handle the large amounts of data from VIPIC while performing correlation analysis in a real time. Our design introduces an autocorrelator per pixel to address the per pixel momentum transfer. Initially the VIPIC collects the X-ray photon arrival events from the 64×64 pixels and transfers it over 16 serial buses to the data acquisition system. Timing information is provided by reading the detector contents every 10µs. Readout can be in one of two modes, a sparsified readout mode for low intensity applications where many pixels acquire no events, and an imaging mode in which all pixels are read out sequentially. The correlator design described here can handle either operating mode. This design provides many advantages over the existing commercial correlators as they are not able to meet the requirements of VIPIC. The commercial ones are limited to low intensity light correlation and a few simultaneous inputs. Besides, the large physical size of the commercial correlators makes the implementation of a system with several channels impractical. A multi-τ correlator design based on virtex 2 was addressed earlier but the practical realization was only ended up for one element of such muti-τ correlator. The correlator design discussed in this paper will provide a correlation dynamic range from 10us to 10.24ms for each of its 256 correlator elements. Our target for the design is to reach the minimum physical size, resource and power consumption costs based on the approach of using an 8 stage multi-τ design for each element and barrel shift DSPs and pipelined RAM block for the elements. We are planning to implement this design as the basis for a custom integrated circuit which implements 4×256 element correlator elements.

Man-made perfect single crystal isotopically-enriched diamond is demonstrated to be an excellent X-ray monochromator even when subjected to the highest incident power density expected at third-generation synchrotron source undulator beam lines. Double-crystal rocking curve tests of a diamond (400) wafer exposed to an X-ray power density of 207 W/mm2 (75 W total power) revealed just 1 arc sec of induced thermal distortion integrated across the beam footprint.

Over the past three years NASA Marshall Space Flight Center has been collaborating with Brookhaven National Laboratory and with colleagues at Bear Fight Center to develop a modular Silicon Drift Detector (SDD) X-Ray Spectrometer (XRS) intended for fine surface mapping of light elements of planetary bodies. The SDD is ideally suited to this task, having modest power and cooling requirements and high radiation hardness. The modular form permits tailoring to multiple platforms, from orbiters to surface landers. In the former, possible targets include any airless bodies with sufficient ambient radiation to excite surface fluorescence. These include our moon, Mercury, the moons of Mars and Jupiter, asteroids and comets. Our SDD-XRS instrument can operate with a low energy threshold (i.e. is capable of detecting carbon), has comparable energy resolution to current CCDs (

Flux is a simple yet key indicator of overall beamline alignment. For many synchrotron measurements, the energy resolution and reproducibility are important characteristics as well. However, many beamlines do not have diffractometers capable of measuring the energy resolution in the experimental hutches. For absolute flux measurements, we have found that thickness calibrated Si photodiodes make very convenient, robust detectors capable of handling a wide flux range. For measuring the energy resolution, we have developed a simple, portable instrument analyzer applicable to any beamline with a scanning monochromator. This same instrument is capable of measuring the energy stability and reproducibility as well. We have used these to characterize many of the beamlines on the NSLS X‐ray ring, and will present the methods and our experience to date to demonstrate their usefulness.

We developed a fluorescence‐type monochromatic X‐ray beam‐position monitor (X‐BPM) with high‐spatial resolution for end‐station experiments at the initial project beamlines of the NSLS‐II. We designed a ring array of multi‐segmented Si PIN‐junction photodiodes to use as a position sensor. Further, we integrated a low‐noise charge‐preamplification HERMES4 ASIC chip into an electronic readout system for photon‐counting application. A series of precision measurements to characterize electronically the Si‐photodiode sensor and the ASIC chip demonstrated that the inherent noise from the detector system is sufficiently low to meet our stringent requirements. Using a Gaussian beam, we parametrically modeled the optimum working distance to ensure the detector’s best performance. Based upon the results from the parametric modeling, prototypes of the next versions of the X‐BPM are being developed. In this paper, we describe the methodology for developing the new compact monochromatic X‐ray BPM, including its instrumentation, detector modeling, and future plan.

We describe pump‐probe experiments in the x‐ray region using synchrotron radiation to supply both the pump and probe beams. The time between pump and probe is adjustable on the nanosecond time scale by means of an optical delay line operating in the x‐ray region. With the ‘‘third generation’’ sources presently under construction around the world it should be practicable to study optical excitations using similar techniques to those described here. The initial studies we describe were carried out at the National Synchrotron Light Source. A 30‐μm‐thick silicon [110] crystal was irradiated by white light from a bending magnet. The radiation passing through this sample was monochromated by two silicon [660] reflections in such a way that the monochromatic beam was directed onto the first surface of the thin crystal sample. The surface of this thin crystal was probed by recording the symmetric (220) reflexion 2.78 ns after illumination by the white beam. Techniques for overcoming the background problem resulti...

We have developed a new method to produce thin-entrance-window Silicon Drift Detectors. To produce the desired thin-entrance-window a double implantation was used. This implantation consists of Boron ions (dose of 1×1014/cm2 at 10 keV) plus a second implant of Phosphorus ions (with a dose of 4×1012/cm2 at 50 keV or dose of 9×1011/cm2 at 80 keV) through 500 A of silicon dioxide. The second Phosphorus implantation compensates for the tail portion of the Boron ion implantation, so that the net Boron ion distribution will result in a thinner “dead” silicon layer and an elevated electric field near the silicon surface. We will compare test results from this newly developed thin-window with those from our previous development, where the thin junction was created using a single implantation of Boron ions (dose of 1×1014/cm2 at 10 keV) through a 500 A thick silicon dioxide. All testing was done in the U3C beam line at the National Synchrotron Light Source at Brookhaven National Laboratory.

An integrating fast readout detector is being developed for the X-ray Pump Probe (XPP) instrument at the Linac Coherent Light Source (LCLS). The detector is based on X-ray Active Matrix Pixel Sensors (XAMPS) with their dedicated readout ASICs. It covers a dynamic range of more than 10,000 photons of 8 keV energy with a resolution better than half photon FWHM. The frame of 1024 × 1024 pixels will be read out within the repetition rate of the X-ray laser pulses which will be as fast as 120 Hz. The structure of the sensor allows full fill factor and -100% efficiency at the energy of interest.

Over the past three years NASA Marshall Space Flight Center has been collaborating with Brookhaven National Laboratory to develop a modular Silicon Drift Detector (SDD) X-Ray Spectrometer (XRS) intended for fine surface mapping of the light elements of the moon. The value of fluorescence spectrometry for surface element mapping is underlined by the fact that the technique has recently been employed by three lunar orbiter missions; Kaguya, Chandrayaan-1, and Chang e. The SDD-XRS instrument we have been developing can operate at a low energy threshold (i.e. is capable of detecting Carbon), comparable energy resolution to Kaguya (

A versatile system for controlling beamlines or complex experimental setups is described. The system as currently configured can control up to 32 motors, with all motors capable of full speed operation concurrently. There are 2 limit switch inputs for each motor, and a further input to accept a reference position marker. The motors can be controlled via a front panel keyboard with display, or by a host computer over an IEEE-488 interface. Both methods can be used together if required. There is an emergency stop'' key on the front panel keyboard to stop the motion of all motors without losing track of the motors' position. 3 refs., 4 figs., 1 tab.

A study of ripple formation on sapphire surfaces by 300-2000 eV Ar+ ion bombardment is presented. Surface characterization by in-situ synchrotron grazing incidence small angle x-ray scattering and ex-situ atomic force microscopy is performed in order to study the wavelength of ripples formed on sapphire (0001) surfaces. We find that the wavelength can be varied over a remarkably wide range-nearly two orders of magnitude-by changing the ion incidence angle. Within the linear theory regime, the ion induced viscous flow smoothing mechanism explains the general trends of the ripple wavelength at low temperature and incidence angles larger than 30. In this model, relaxation is confined to a few-nm thick damaged surface layer. The behavior at high temperature suggests relaxation by surface diffusion. However, strong smoothing is inferred from the observed ripple wavelength near normal incidence, which is not consistent with either surface diffusion or viscous flow relaxation., Comment: Revtex4, 19 pages, 10 figures with JPEG format

The paper describes two detectors designed specifically for the SPPS ultrafast x‐ray source, one of which provides 2‐D position and intensity information, and the other acts as a low‐noise point detector for diffraction experiments. The beam position monitor (BPM) was used as a reference detector for most of the experiments performed there, and the point detector was used for pump‐probe experiments involving phonons in bismuth and on photosensitive metal‐organic crystals. The schedule for development of these detectors was extremely tight, so as much as possible we used available designs for amplifiers etc.

The plasma nitridation kinetics of $c$-plane sapphire at both low $(200--300\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C})$ and high $(750\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C})$ substrate temperatures was examined using grazing-incidence real-time x-ray diffraction, in situ x-ray reflection and in situ reflection high-energy electron diffraction (RHEED). These monitored the evolution of the nitride thickness, strain, and surface structure during nitridation. The evolution of the $\mathrm{AlN}(10\overline{1}0)$ peak showed that the heteroepitaxial strain in the first layer of nitride is already significantly relaxed relative to the substrate. Subsequent layers grow with increasing relaxation. In both the high- and low-temperature nitridation cases, the results suggest that the early stage nitridation is governed by a complex nucleation and growth process. Nitridation at both temperatures apparently proceeds in a two-dimensional growth mode with the initial nucleating islands consisting of several monolayers which grow laterally. At low temperature the growth slows or even stops after impingement of the nucleating islands covering the surface, possibly due to low diffusivities through the existing layer. Initial formation and growth rates of nucleating islands at high temperatures are comparable to those at low temperatures, but subsequent growth into the substrate is significantly enhanced over the low temperature case, consistent with activation energies of $0.1--0.25\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$.

We present some measurements of nuclear fluorescence which were made while exploring the potential of a unique source of very hard x‐rays which was installed at ESRF until recently. It produced radiation of energies up to 1MeV. In this range there are many nuclear resonances, and so we made a small survey of some plausible candidates to see if they could indeed be excited using this source. Along with short‐lived resonances, we were also able to indirectly populate long‐lived isomeric states in several nuclei. Thus, simply exposing the samples to the white beam for a period of time caused them to be activated. The samples could them be removed from the beam and their emissions observed using an energy‐resolving detector. Isomeric states in isotopes of indium, cadmium and silver were excited and their subsequent decay observed.

The SPPS and LCLS are next‐generation light sources which will produce ultra‐short x‐ray pulses a few 10’s of femtoseconds long, with large numbers of photons per pulse. These sources will enable new types of x‐ray experiments, but will require new approaches to optical instruments. We present here a spectrograph tailored for use with such sources, allowing the small beam cross‐section to be spatially dispersed by means of a curved asymmetric Brag reflecting crystal. The design allows for an adjustable energy range by changing the radius of curvature within certain limits. Although inspired by these new sources, the device is also well adapted to conventional synchrotron radiation beamlines. It is significantly more compact than conventional wavelength‐dispersive devices, and has resolution advantages.

The SPPS and LCLS are next‐generation light sources which will produce ultra‐short x‐ray pulses a few 10’s of femtoseconds long, with large numbers of photons per pulse. The development of instruments to characterize the temporal properties of these beams is of significant interest. We present in this paper a concept and initial experiments towards the fabrication of an x‐ray interferometer suitable for this purpose. It makes use of the temporal focusing properties of the T‐2T‐T Bonse‐Hart interferometer to minimize the influence of the time‐dispersion of the instrument on the overall response function. Separate path‐length shifters based on an elastically deforming perfect crystal device are used to scan the time delay. Path‐length differences of up to 0.1mm should be possible using this shifter design. An advantage of this design compared to others is that there is in principle no limit to the possible path length shift.

As diffraction experiments in materials science move towards using harder x‐rays, the need for efficient multi‐detectors in the form of 1‐ and 2‐D arrays is felt. Silicon technology is not suitable for this, and germanium has the complexity of requiring cryogenics. Cadmium Zinc Telluride has emerged as the most promising compound for such applications. We describe our efforts towards providing a 1‐D strip detector suitable for high‐energy diffraction.

In order to meet the challenges of EXAFS and XANES spectroscopy of dilute systems, a custom integrated circuit has been fabricated which integrates 32 complete energy resolving photon counting chains onto a 6mm × 4mm chip. This paper reports on initial tests of a 96‐element detector implementation using low‐leakage diodes fabricated at BNL, and on our plans for a 384‐channel version. This large array will initially also use the same diodes but eventually will use a hexagonal drift‐detector array. The ASIC is read out through an embedded microcontroller device, and a software package has been written to allow highly automated setup of the entire system and straightforward integration into standard data acquisition packages.

A flow cell has been commissioned to monitor in situ precipitation reactions under non-ambient conditions. The majority of high-pressure systems use anvils and presses to obtain high pressures around a small reaction area; however, this prototype is unique in that solutions may be examined as they flow through the cell under pressure. The cell is made of single-crystal silicon, which is capable of withstanding the high pressures created by liquid flow within the cell. With the capability of reaching pressures of up to 4 x 10(7) Pa, the cell is ideal for work on geological and oilfield systems. Here it is used to examine the formation of barium sulfate scale in situ under non-ambient conditions using angle-dispersive XRD on beamline X17b1 at the NSLS.

Last year, the X27A beamline at the National Synchrotron Light Source (NSLS) became dedicated solely to X-Ray Computed Microtomography (XCMT). This is a third-generation instrument capable of producing tomographic volumes of 1 - 2 micron resolution over a 2 - 3 mm field of view. Recent enhancements will be discussed. These have focused on two issues: the desire for real-time data acquisition and processing and the need for highly monochromatic beam (.1% energy bandpass). The latter will permit k-edge subtraction studies and will provide improved image contrast from below the Cr (6 keV) up to the Cs (36 keV) k-edge. A range of applications that benefit from these improvements will be discussed as well. These two goals are somewhat counterproductive, however; higher monochromaticity yields a lower flux forcing longer data acquisition times. To balance the two, a more efficient scintillator for X-ray conversion is being developed. Some testing of a prototype scintillator has been performed; preliminary results will be presented here. In the meantime, data reconstruction times have been reduced, and the entire tomographic acquisition, reconstruction and volume rendering process streamlined to make efficient use of synchrotron beam time. A Fast Filtered Back Transform (FFBT) reconstruction program recently developed helped to reduce the time to reconstruct a volume of 150 X 150 X 250 pixels3 (over 5 million voxels) from the raw camera data to 1.5 minutes on a dual R10,000 CPU. With these improvements, one can now obtain a 'quick look' of a small tomographic volume (approximately 106 voxels) in just over 15 minutes from the start of data acquisition.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

For several years we have explored the use of hard x-rays for a broad range of lithographic applications. The high energy available from the NSLS x-ray ring (E>15 keV) allows the exposure of resist up to several cm thick, while maintaining micron level precision. The high flux and close proximity to the source at this machine make it possible to achieve workable exposures on realistic time scales, enabling production work. In addition to the conventional two-dimensional exposure schemes, we have demonstrated methods for achieving fully figured three dimensional objects with internal re-entrant geometry. Users from outside BNL have been sufficiently successful with their work at our prototype beamline (X-27B) that we have initiated the construction of a dedicated exposure station (X-14B) for High Aspect Ratio Precision Manufacture. An overview of our previous work as well as the current status of the new beamline will be described.

The facility has been developed for producing high quality tomographs of order one micrometer resolution. Three dimensional volumes derived from groups of adjacent tomographic slices are then viewed and navigated in a stereographic viewing facility. This facility is being applied to problems in geological evaluation of oil reservoir rock, medical imaging, protein chemistry, and CADCAM.

Real-time grazing-incidence small-angle x-ray scattering has been employed to study the adsorption and desorption of Ga on c-plane sapphire and Ga-polar GaN surfaces. Formation of self-organized liquid Ga nanodroplets has been observed on sapphire during Ga exposure from an effusion cell at high flux. Subsequent to the Ga deposition, the nanodroplets were nitridated in situ by a nitrogen plasma source, which converted the droplets into GaN nanodots. In addition to the droplet studies, at lower Ga flux, the adsorption and desorption of Ga have been studied in the predroplet regime. For identical processing conditions, significantly different Ga adsorption∕desorption rates were observed on sapphire and GaN surfaces.

The formation of self-organized Si nanostructures induced by Mo seeding during normal incidence Ar+ ion bombardment at room temperature is reported. Silicon surfaces without Mo seeding develop only power-law roughness during 1000eV ion bombardment at normal incidence, in agreement with scaling theory expectations of surface roughening. However, supplying Mo atoms to the surface during ion bombardment seeds the development of highly correlated, nanoscale structures (“dots”) that are typically 3nm high with a spatial wavelength of approximately 30nm. With time, these saturate and further surface roughening is dominated by the growth of long-wavelength corrugations.

A new technique to overcome the core-hole lifetime broadening in x-ray absorption spectroscopy is presented. It utilizes a high resolution fluorescence spectrometer which can be used to analyze the fluorescence photon energy with better resolution than the natural lifetime width. Furthermore, the high resolution spectrometer can also be used to select the final state in the fluorescence process which can offer spin selectivity even without long range magnetic order in the sample.