M. Ramanathan

Thickness dependent hierarchical meso/nano scale morphologies of a metal-containing block copolymer thin film induced by hybrid annealing and their pattern transfer abilities

In this paper we describe dewetting phenomena in organic (polystyrene, PS)/inorganic (polyferrocenyldimethylsilane, PFS) block copolymer thin films. Mesoscale dendritic structures are induced when the spin-cast thin film of this polymer is subjected to so-called hybrid annealing, which involves both thermal and solvent annealing. We show that the development and arrangement of these mesoscale dendritic structures depends on the initial film thickness in addition to the annealing time. Importantly, there are two criteria that must be fulfilled to achieve these mesoscale morphologies: (i) the film has to be subjected to hybrid annealing, i.e. either only thermal or only solvent annealing does not produce any notable mesostructures and (ii) both PS and PFS blocks must be present during the thermal and solvent annealing procedures; if one of the blocks, for instance PS, is removed before annealing then there is no mesostructure. Various possible mechanisms for the formation of these structures are discussed and results indicate that the PFS block dominates the structure formation. We also observe a ring- or worm-like nanostructure which develops only when the film is subjected to hybrid annealing at a particular film thickness. Apart from these results, here we demonstrate that mesoscale structures can be successfully transferred onto underlying substrates.

A new approach to determining the charge distribution in copper compounds

An analysis of the energy moments of X-ray absorption spectra at the copper K edge has been used to assign characteristic energies for a series of copper compounds with formal valences of +1, +2, and +3. The results indicate that there is a good correlation between the characteristic energies defined in this way for near-edge X-ray absorption spectra and the charge distribution in these copper compounds.

Nanopatterning of ultrananocrystalline diamond thin films via block copolymer lithography

Nanopatterning of diamond surfaces is critical for the development of diamond-based microelectromechanical system/nanoelectromechanical system (MEMS/NEMS), such as resonators or switches. Micro-/nanopatterning of diamond materials is typically done using photolithography or electron beam lithography combined with reactive ion etching (RIE). In this work, we demonstrate a simple process, block copolymer (BCP) lithography, for nanopatterning of ultrananocrystalline diamond (UNCD) films to produce nanostructures suitable for the fabrication of NEMS based on UNCD. In BCP lithography, nanoscale self-assembled polymeric domains serve as an etch mask for pattern transfer. The authors used thin films of a cylinder-forming organic-inorganic BCP, poly(styrene-block-ferrocenyldimethylsilane), PS-b-PFS, as an etch mask on the surface of UNCD films. Orientational control of the etch masking cylindrical PFS blocks is achieved by manipulating the polymer film thickness in concert with the annealing treatment. We have observed that the surface roughness of UNCD layers plays an important role in transferring the pattern. Oxygen RIE was used to etch the exposed areas of the UNCD film underneath the BCP. Arrays of both UNCD posts and wirelike structures have been created using the same starting polymeric materials as the etch mask.Nanopatterning of diamond surfaces is critical for the development of diamond-based microelectromechanical system/nanoelectromechanical system (MEMS/NEMS), such as resonators or switches. Micro-/nanopatterning of diamond materials is typically done using photolithography or electron beam lithography combined with reactive ion etching (RIE). In this work, we demonstrate a simple process, block copolymer (BCP) lithography, for nanopatterning of ultrananocrystalline diamond (UNCD) films to produce nanostructures suitable for the fabrication of NEMS based on UNCD. In BCP lithography, nanoscale self-assembled polymeric domains serve as an etch mask for pattern transfer. The authors used thin films of a cylinder-forming organic-inorganic BCP, poly(styrene-block-ferrocenyldimethylsilane), PS-b-PFS, as an etch mask on the surface of UNCD films. Orientational control of the etch masking cylindrical PFS blocks is achieved by manipulating the polymer film thickness in concert with the annealing treatment. We have ob...

Multipurpose monochromator for the Basic Energy Science Synchrotron Radiation Center Collaborative Access Team beamlines at the Advanced Photon Source x‐ray facility

The Basic Energy Science Synchrotron Radiation Center (BESSRC) Collaborative Access Team (CAT) will construct x‐ray beamlines at two sectors of the Advanced Photon Source facility. In most of the beamlines the first optical element will be a monochromator, so that a standard design for this critical component is advantageous. The monochromator is a double‐crystal, fixed exit scheme with a constant offset designed for ultrahigh vacuum windowless operation. In this design, the crystals are mounted on a turntable with the first crystal at the center of rotation. Mechanical linkages are used to correctly position the second crystal and maintain a constant offset. The main drive for the rotary motion is provided by a vacuum compatible Huber goniometer isolated from the main vacuum chamber. The design of the monochromator is such that it can accommodate water, gallium, or liquid‐nitrogen cooling for the crystal optics.

An overview of the information distribution system at the Advanced Photon Source

The Advanced Photon Source (APS) has been in operational mode for more than 5 yr. Currently there are over 40 beamlines in various phases of operation. The control system of choice at the APS is the Experimental Physics and Industrial Control System (EPICS). We have provided various interfaces to the beamlines from the APS control system. An overview of the various systems will be discussed. The General Control System Information (GCSI) uses dedicated computers as EPICS process variable gateways to provide data from the APS control system to each beamline. The GCSI architecture makes the APS control system secure, yet has the flexibility of providing access control to any data available on the APS control system. In addition, the gateway reduces the load on the APS control system equipment by making only one connection for each process variable accessed by multiple users. Each sector, consisting of a bending magnet and insertion device beamlines, is provided its own gateway, which resides on the local sector network. This scheme has the advantage of providing network security and more reliable operation. To provide real-time accelerator data to beamlines, each sector has been provided a chassis to display the storage ring current and other relevant information. These data are transmitted via a direct fiber link from the APS control system hardware to the beamlines. The beamlines are also provided VME-based hardware and associated EPICS software to retrieve key information provided via this fiber link. Some of the information on this link is beam current, lifetime, injection status, and sector specific information such as shutter status, insertion device gap, and energy, and storage ring and front-end beam position monitor signals. The data rates on this link are typically 10 Hz but can be as high as 272 kHz. This scheme allows the beamlines using EPICS-based software to seamlessly use the data from the APS control system without excessively impacting the system. For high-precision x-ray timing experiments, a new scheme has been designed to distribute the radio-frequency timing signals to the beamlines. Using VME-based hardware and EPICS software, the bunch clock signal is generated at the beamline for use in timing experiments. Data are provided at the radio frequency of 352 MHz. Beamlines have also been provided with hardware and software to generate the bunch clock signal for timing experiments.

A Four‐Motor Insertion Device Control System at the Advanced Photon Source

The Advanced Photon Source (APS) is a third‐generation synchrotron with major emphasis on insertion device (ID) sources. In the storage ring there are 35 straight sections, each about five meters in length, for possible insertion devices. Most of the insertion devices at the APS are 2.4 meters long. Currently there are 27 undulators installed in 25 straight sections. Twenty‐two of the undulators are the original design fabricated by STI Optronics, which used two motors, one for each end of the device. A synchronizing mechanism between the upper and lower magnetic arrays was also used at each end. Recently, the APS has designed a new gap‐separation mechanism for all new undulators. The new design is based on four independent motors, one driving each end of each magnetic array of the device. The control system of choice at the APS is EPICS. The control system is designed to be transparent to the user of the beamline who routinely operates the device. The differences between the two‐motor and the four‐motor ...

VME insertion device control at the Advanced Photon Source

The Advanced Photon Source (APS) currently has 29 insertion devices (IDs) installed and operating. The need to remotely diagnose and correct problems has become increasingly important. This has been accomplished through the development of a new control system with greatly enhanced input/output (I/O) capabilities specifically targeted to this control task. The system features a custom VME control card and three rack-mounted interface chassis for ID control, encoder interface, and motor drive shutdown. The card provides device interlocks, limit switch logic, motor axis selection, digital I/O, and status feedback. This VME insertion device control was designed to operate with an eight-axis intelligent motor controller and a stepper-motor drive that accepts step and direction inputs. The front panel of the card has two connectors for all of the control signals for the stepper-motor drives. There is a third connector for the ID limit switch inputs and the emergency stop circuit, and a fourth connector provides 23 bits of digital outputs and 16 bits of digital inputs. Light-emitting diodes indicate which motions are inhibited by the limit switch logic. An experimental physics industrial control system (EPICS) (http://www.APS.ANL-GOV/EPICS) device driver was developed to access all the registers on the VME control card. Using standard EPICS records, the insertion device status can be viewed remotely. This minimizes downtime for APS ID beamline users by allowing faster resolution of any problems preventing a user from operating the insertion device. This new insertion device control has been in use at the APS since July of 1999. The design features of the control system and rationale for them will be presented, along with our experience in building, testing, installing, and operating the control system.

New Techniques for Synchrotron Powder Diffraction Studies

This manuscript discusses two different powder diffraction methods which possess high resolution, low background and very high counting rates. Both methods utilize analyzer crystals in combination with position sensitive detectors. The first method uses a curved perfect crystal analyzer diffracting in the scattering plane to diffract a range of angles into the position sensitive detector. The second method is somewhat simpler, it uses a graphite analyzer crystal diffracting out of the scattering plane. Applications of these methods to anomalous scattering from both powder and amorphous materials are also discussed. One of the techniques should also be very useful for small angle scattering.

Importance of components cleaning in the ultrahigh vacuum performance of beamline front ends

The Advanced Photon Source (APS) has 40 beamline front ends in its initial phase of operations; eventually a total of 69 beamline front ends will be connected to the storage ring. The ultrahigh vacuum performance of these front ends will have a significant impact on the storage ring vacuum and on the lifetime of the positron beam. In this paper we emphasize the importance of proper component cleaning to the ultrahigh vacuum performance of beamline front ends. Critical issues in the cleaning process include using environmentally friendly cleaning agents and applications of ultrasonic agitation, thorough deionized water rinsing, and vacuum furnace baking. A simple and cost‐effective cleaning facility consisting of ultrasonic cleaning tanks, a drying tank, and a vacuum furnace has been set up. The effectiveness of component cleaning is evaluated by the base pressure achievable in comparison to what is expected according to vacuum calculations using available outgassing rates for the components. Each major co...

Alignment and commissioning of the APS beamline front ends

Fifteen out of forty phase-one beamline front ends have been installed in the storage-ring tunnel at the 7-GeV Advanced Photon Source (APS). For the front-end installation, a four-step alignment process was designed and consists of (1) prealigning the front-end components with support tables in the preassembly area, (2) installing the components with tables in the storage-ring tunnel and aligning relative to the APS global telescope survey network, (3) confirming the alignment using a tooling laser alignment system, and (4) performing adjustments with the synchrotron-radiation beam during commissioning. The laser alignment system and the prealignment data- base have been of great importance for the expedient maintenance of front-end components. These tools are very important to a large synchrotron radiation facility such as the APS, since they make a quick alignment setup possible and minimize alignment time inside the tunnel. This paper will present the four-step alignment process, the laser alignment system, and discuss the alignment confirmation results. 6 refs., 5 figs.