Femtosecond laser ablation studies of silicon with and without the native oxide on the surface were conducted in an ultrahigh vacuum environment. SEM results show a clear difference in the laser intensity threshold fo...
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We outline key design features for a versatile imaging and hard X-ray beamline for operation at the Australian Synchrotron. Special attention is paid to the implementation of in-line phase-contrast imaging using both ...
The room temperature crystal structures of Er5SixGe4−x alloys change systematically with the concentration of Ge from the orthorhombic Gd5Si4-type when x=4, to the monoclinic Gd5Si2Ge2 type when 3.5⩽x⩽3.9 and to the o...
The room temperature crystal structures of Er5SixGe4−x alloys change systematically with the concentration of Ge from the orthorhombic Gd5Si4-type when x=4, to the monoclinic Gd5Si2Ge2 type when 3.5⩽x⩽3.9 and to the orthorhombic Sm5Ge4 type for x⩽3. The Curie-Weiss behavior of Er5SixGe4−x materials is consistent with the Er3+ state. The compounds order magnetically below 30K, apparently adopting complex noncollinear magnetic structures with magnetization not reaching saturation in 50kOe magnetic fields. In Er5Si4, the structural-only transformation from the monoclinic Gd5Si2Ge2-type to the orthorhombic Gd5Si4-type phase occurs around 218K on heating. Intriguingly, the temperature of this polymorphic transformation is weakly dependent on magnetic fields as low as 40kOe (dT∕dH=−0.058K∕kOe) when the material is in the paramagnetic state nearly 200K above its spontaneous magnetic ordering temperature. It appears that a magnetostructural transition may be induced in the 5:4 erbium silicide at ∼18K and above by 75kOe and higher magnetic fields. Only Er5Si4 but none of the other studied Er5SixGe4−x alloys exhibit magnetic field induced transformations, which are quite common in the closely related Gd5SixGe4−x system. The magnetocaloric effects of the Er5SixGe4−x alloys are moderate.
Temperature and magnetic field dependencies of the magnetization of single crystal Gd5Ge4 indicate antiferromagnetic coupling along the c direction below 130 K. Both a reversible spin-flop transition when a magnetic f...
Temperature and magnetic field dependencies of the magnetization of single crystal Gd5Ge4 indicate antiferromagnetic coupling along the c direction below 130 K. Both a reversible spin-flop transition when a magnetic field of ∼8.4kOe is applied along the c direction, and irreversible metamagneticlike transitions when a 20 kOe or greater magnetic field is applied at 4.3 K along any of the three crystallographic axes are observed. Although Gd3+ ions have negligible single ion anisotropy, the metamagnetic transitions and magnetization of Gd5Ge4 in the ferromagnetic state depend on the crystallographic direction reflecting the anisotropy of the exchange interactions due to the distinctly layered Sm5Ge4-type crystal structure.
We present the first direct observations of tile-based DNA self-assembly in solution using fluorescent nanotubes composed of a single tile. The nanotubes reach tens of microns in length by end-to-end joining rather th...
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We present the first direct observations of tile-based DNA self-assembly in solution using fluorescent nanotubes composed of a single tile. The nanotubes reach tens of microns in length by end-to-end joining rather than by sequential addition of single tiles. Their exponential length distributions withstand dilution but decay via scission upon heating, with an energy barrier Esc∼180kBT. DNA nanotubes are thus uniquely accessible equilibrium polymers that enable new approaches to optimizing DNA-based programming and understanding the biologically programmed self-assembly of protein polymers.
Nanomorphing with ultrafast lasers may have a significant role in direct write stamp production. Surface conditions play a critical role in the ablative properties of materials. We have conducted femtosecond laser (pu...
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We demonstrate the growth of self-assembled nanowires of cobalt silicide on Si(111), (100), and (110) substrates during deposition of Co onto a heated Si substrate. Silicide islands form via an endotaxial mechanism, g...
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We demonstrate the growth of self-assembled nanowires of cobalt silicide on Si(111), (100), and (110) substrates during deposition of Co onto a heated Si substrate. Silicide islands form via an endotaxial mechanism, growing into the substrate along inclined Si{1¯11} planes, which breaks the symmetry of the surface and leads to a long, thin nanowire shape. During growth, both the length and width of the islands increase with time in a fixed proportion that varies strongly with growth temperature, which shows that the nanowire shape is kinetically determined. It is expected that nanowires could form in many other overlayer/substrate systems via this mechanism.
We proposed an approach to precisely control the density of tethered chains on solid substrates using PEO-b-PS and PLLA-b-PS. As the crystallization temperature Tx increased, the PEO or PLLA lamellar crystal thickness...
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We proposed an approach to precisely control the density of tethered chains on solid substrates using PEO-b-PS and PLLA-b-PS. As the crystallization temperature Tx increased, the PEO or PLLA lamellar crystal thickness dL increased as well as the reduced tethering density σ˜ of the PS chains. The onset of tethered PS chains overcrowding in solution occurs at σ˜*∼3.7–3.8 as evidenced by an abrupt change in the slope between (dL)−1 and Tx. This results from the extra surface free energy created by the tethered chain that starts to affect the growth barrier of the crystalline blocks.
Results of isothermal magnetization and magnetic relaxation measurements are presented probing the nature of the magnetic-field-induced magnetostructural transition in the intermetallic compound Gd5Ge4. This transitio...
Results of isothermal magnetization and magnetic relaxation measurements are presented probing the nature of the magnetic-field-induced magnetostructural transition in the intermetallic compound Gd5Ge4. This transition shows the characteristics of a disorder-influenced first order transition including distinct metastable behavior. Below approximately 21K, the transition from the magnetic-field-induced ferromagnetic state back to the antiferromagnetic state shows additional interesting features. Similarities with other classes of magnetic systems exhibiting magnetostructural transitions are pointed out.
We outline key design features for a versatile imaging and hard X‐ray beamline for operation at the Australian Synchrotron. Special attention is paid to the implementation of in‐line phase‐contrast imaging using bo...
We outline key design features for a versatile imaging and hard X‐ray beamline for operation at the Australian Synchrotron. Special attention is paid to the implementation of in‐line phase‐contrast imaging using both the plane‐wave and spherical‐wave cases.
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