The formation of ripples on Si(100) by O+2 sputtering at an angle of incidence of 40° and energies from 1 to 9 keV has been studied using secondary ion mass spectrometry and scanning electron microscopy. At 1 keV no ripples are observed. Between 1.5 and 9 keV ripples are observed oriented perpendicular to the ion direction with average wavelengths that increase, from ∼100 to 400 nm, approximately linearly with O+2 energy. Two-dimensional fast Fourier transforms of secondary electron images are used to investigate the frequency distribution of the ripples. For the conditions studied, the distributions of frequencies appear approximately Gaussian. At 1.5 keV, the wavelength and growth rate with sputtered depth are independent of flux for fluxes from 15 to 150 μA/cm2. Accompanying ripple formation are changes in secondary ion yields. The changes occur abruptly at depths that increase, from ∼0.2 to 5.6 μm, with O+2 energy. In contrast, sputtering with Ar+ at 1.5 and 7 keV to depths 5–10 times those that produce ripples with O+2 produce no observable topography. These results are discussed using several existing theories for ripple formation and growth. Ripple growth and the variations in secondary ion yield are modeled by accounting for the change in local angles of incidence as the ripples grow. This model describes well the variation in secondary ion yield assuming an exponential growth rate. Ripple formation is discussed in terms of a balance between roughening (by sputtering-induced surface stress and by the dependence of the sputtering yield on surface curvature) and smoothing (by both diffusion and ion mixing). Variation in ripple wavelength with energy is not simply explained by these theories. Surface smoothing by cascade ion mixing can, however, make the wavelength, as observed, independent of ion flux. Finally, the possibility of formation of ripples by phase separation within the SiOx surface layer is discussed.

Reconfigurable and morphing structures may provide a range of new functionalities such as optimization over broad operational conditions and multi-mission capability. This article introduces a new generic approach to achieving large strains in materials with high elastic moduli (5-30 GPa). The work centers on creating variable stiffness composite materials which exhibit a controllable change in elastic modulus (bending or axial) and large reversible strains (5-15%). We have performed a simulation study to better understand the implication of various geometric design parameters on the elastic and deformation behavior. Using this information, a series of prototype materials were prepared using a commercial shape memory polymer, and measurements on these materials indicate a controllable change in stiffness as a function of temperature with large reversible strain accommodation. We have fabricated and tested several design variations of laminar morphing materials which exhibit structural stiffness values of 8-12 GPa, changes in modulus of 15-77x and large reversible axial of 2-10%. Results indicate that significant controllable changes in stiffness are possible. Further, agreement between simulations and prototype material properties indicate that simulations may be used an effective screening tool to specify micromechanical design variations for specific application requirements.

Quantitative depth profiling resonance ionization mass spectrometry of GaAs/AlGaAs heterojunction bipolar transistors J. Vac. Sci. Technol. B 10, 385 (1992); 10.1116/1.586363High resolution secondary ion mass spectrometry depth profiling using continuous sample rotation and its application to superlattice and deltadoped sample analysis Effects of sample rotation and sputtering conditions on the depth resolution and ion yield during secondary ion mass spectrometry (SIMS) sputter depth profiles have been studied on bulk GaAs and a GaAs( 5 nm)/ Alo 3 GIlo. 7 As(5 nm) superiattice. Profiles without sample rotation with 1.0-7.0 keY O 2 + show a rapid degradation of the depth resolution with increasing sputter depth. Profiles with Ar + show only slight degradation. Scanning electron microscope (SEM) studies indicate that degradation is associated with development of periodic surface ripples. The wavelength of the ripples is energy dependent and increases with increasing ion impact energy. With sample rotation, no degradation of the depth resolution is observed and SEM micrographs indicate that surfaces sputtered with rotation are smooth. In addition, with 3.0 keY at significant changes in the secondary ion yield of AsO + from bulk GaAs are observed at a depth of -200 nm. No changes are observed with sample rotation. Our results demonstrate that sample rotation during SIMS depth profiling prevents and can reverse the development of surface topography that both degrades depth resolution and changes secondary ion yield. Thus, interpretation and quantitation of SIMS analysis is facilitated.

In this paper, we describe a rapid method for fabricating a low density polymer microlattice with structural organization on two length scales. The topology of this hierarchical cellular structure is achieved through the in situ formation of a microlattice with small‐scale lattice members (≈100 µm diameter) within a microlattice with approximately 12 times larger feature sizes. Compression experiments suggest that an increase in the specific plateau stress is realized by the introduction of hierarchy.