The Impact of The Initial Surface Reconstruction on Heteroepitaxial Film Growth and Defect Formation

While it is well known that growth conditions such as temperature greatly affect defect incorporation in thin films, less is known about the direct effects of the surface reconstruction. In this work, we examine the effect of the initial surface reconstruction on defect incorporation in GaSb/GaAs(001) lattice mismatched films. The stress built up in GaSb films grown on As-terminated and Sb-terminated GaAs was monitored during film growth and shows that the total relaxation is similar in both films along the [110], but lower on the Sb-terminated surface along the . These differences can be understood by examining the ability for the two surface terminations to accommodate strain. The resulting films show that the density of 3D islands is lower for the Sb-terminated surfaces, and that lattice mismatch strain is further accommodated by a 5° tilt. In contrast, the As-terminated surface contains both stacking faults and misfit dislocations. These results demonstrate the possibility to engineer specific defects into films by controlling the starting surface of film growth

Examining the Temperature Dependence of Louche Formation in Absinthe

Absinthe is an anise-flavored alcohol that is typically served by adding cold water to form a cloudy green louche, similar to the cloudy white louche of ouzo. This microemulsion formation, due to the competing interactions within the oil-alcohol-water system, has been termed the ouzo effect. Previous work has examined the ternary oil-alcohol-water phase diagram in ouzo and limoncello. Additional work has also characterized the droplet size and stability of microemulsions in ouzo, limoncello, and pastis. However, less work has been done to examine the effect of temperature on louche formation despite the fact that the louche is traditionally formed by adding ice cold water. This work demonstrates that both the maximum turbidity and the fraction of alcohol at maximum turbidity are temperature-dependent. The louche formation can be fit with a logistic curve, and the resulting fit parameters are linear with temperature. Optical images show that the increased turbidity correlates with an increase in the number of droplets in the microemulsion

The Role of Strain in the Surface Structures of III-V Alloyed Semiconductor Films.

As length scales continue to decrease, it is vital to understand the fundamental physical parameters governing surfaces and surface interactions. In semiconductors particularly, surface reconstructions are known to impact film growth, bulk atomic ordering and the development of interfacial structure, all of which can drastically impact device growth. While the parameters that determine surface reconstructions in homoepitaxially grown films are well known and understood, those that impact alloy film growth are less studied. This work examines the impact of strain on alloy surface reconstructions, using the III-V semiconductors as a model system for any covalently bonded crystal structure. The presence of surface reconstruction coexistence in both mixed cation and mixed anion systems suggests that localized strain fields on alloy surfaces stabilize elastic relaxation at boundaries, resulting in more complex surface structures than those seen on binary, unstrained films. Atomic size mismatch strain is shown to induce an ordering in alloyed surface reconstructions that is not seen in the non-alloyed constituent surfaces. Lattice mismatch strain is shown to both stabilize new reconstructions not common to the homoepitaxial system and to induce surface reconstruction coexistence on alloy surfaces. The supplied flux of material is shown to affect the kinetics of transformation between the two coexisting surface reconstructions and an incorporation model for material on the alloy surface is developed. The effects of strained surface reconstructions on subsequent film growth is explored and it is shown that identical films grown on two different surfaces have very different strain relaxation profiles, surface topographies and defect structures. The strain fields of surface reconstructions and defects are also shown to interact which may have an impact on the insertion of dislocations in these films. Combined together, this deep understanding of the role that alloy induced strain plays in surface reconstructions will lead to a more complete understanding of the properties which govern reconstructions in general, and also create the possibility of engineering specific reconstructions which will form more abrupt interfaces, inject specific types of defects, or act as surfaces for subsequent self-assembly.Ph.D.Materials Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/75875/1/jebickel_1.pd

Elastically Induced Coexistence of Surface Reconstructions

Scanning tunneling microscopy of Sb-capped GaAs shows the coexistence of different surface reconstructions. The majority of the surface consists of an α2(2×4) reconstruction typically observed for GaAs(001) surfaces. At step edges, an α(4×3) reconstruction, common for GaSb(001), is observed. We argue that strain couples the surface reconstruction to the film morphology. Density functional theory calculations show that the (2×4) reconstruction is stabilized in GaSb films when the lattice parameter is constrained to that of GaAs, as happens in the middle of a terrace, while the (4×3) reconstruction is stabilized when the lattice parameter is allowed to relax toward that of GaSb at step edges. This result confirms the importance of elastic relaxation in the coexistence of surface reconstructions

Information transfer by vector spin chirality in finite magnetic chains

Vector spin chirality is one of the fundamental characteristics of complex magnets. For a one-dimensional spin-spiral state it can be interpreted as the handedness, or rotational sense of the spiral. Here, using spin-polarized scanning tunneling microscopy, we demonstrate the occurrence of an atomic-scale spin-spiral in finite individual bi-atomic Fe chains on the (5x1)-Ir(001) surface. We show that the broken inversion symmetry at the surface promotes one direction of the vector spin chirality, leading to a unique rotational sense of the spiral in all chains. Correspondingly, changes in the spin direction of one chain end can be probed tens of nanometers away, suggesting a new way of transmitting information about the state of magnetic objects on the nanoscale.Comment: accepted by Physical Review Letter

Atomic Size Mismatch Strain Induced Surface Reconstructions

The effects of lattice mismatch strain and atomic size mismatch strain on surface reconstructions are analyzed using density functional theory. These calculations demonstrate the importance of an explicit treatment of alloying when calculating the energies of alloyed surface reconstructions. Lattice mismatch strain has little impact on surface dimer ordering for the α2(2×4) reconstruction of GaAs alloyed with In. However, atomic size mismatch strain induces the surface In atoms to preferentially alternate position, which, in turn, induces an alternating configuration of the surface anion dimers. These results agree well with experimental data for α2(2×4) domains in InGaAs∕GaAs surfaces

The Probability of Spotted Lanternfly, Lycorma delicatula (Hemiptera: Fulgoridae), Escape Differs Among Life Stages and Between Two Trapping Techniques Commonly Used By Landowners, Sticky Bands and Duct Tape.

The invasive Lycorma delicatula (White) was first identified in Pennsylvania, U.S.A. in 2014, and has since increased its range to several Eastern states. Lycorma delicatula pose a serious threat to many native species, including hardwoods and grapes, and land owners are continually seeking effective traps to control populations. Both commercially-produced Web-Cote brand sticky bands and less expensive duct tape are often used by land owners to trap L. delicatula. However, the probability of escape from these adhesives has not been formally assessed, and almost certainly differs as a function of life stage and type of adhesive used. The purpose of this work was to determine if the effect of adhesive type (Web-Cote sticky bands vs. duct tape) on the probability of escape differs based on life stage. Additionally, we wanted to know how escape probability differs among life stages when individuals were exposed to each adhesive type, separately. In all life stages, the probability of escape from duct tape was greater than from Web-Cote sticky bands, indicating that sticky bands are a more effective tool in L. delicatula population control. In trials using only Web-Cote sticky bands, the probability of escape was low in second (21.1%), third (32.6%), and fourth (38.5%) instars relative to adults (84.1%). In trials using only duct tape, the probability of escape remained high among all life stages, with approximately 72% of second instars and 100% of adults escaping. Recent studies indicate that alternate trapping techniques, including circle trunk traps, are even more effective at capturing L. delicatula than sticky bands, though they are costlier. We propose a hybrid approach to L. delicatula trapping which utilizes relatively inexpensive sticky bands early in the season, and fewer, more effective circle trunk traps later in the season

Correction to The Probability of Spotted Lanternfly, Lycorma delicatula (Hemiptera: Fulgoridae), Escape Differs Among Life Stages and Between Two Trapping Techniques Commonly Used by Landowners, Sticky Bands and Duct Tape. The Great Lakes Entomologist 53(3-4): 170-177.

This is a manuscript correction in reference to: Desko M, Schiebel C, Silverman S, Bickel J, Felton K, and Chandler JL. (2020) The Probability of spotted lanternfly, Lycorma delicatula (Hemiptera: Fulgoridae), escape differs among life stages and between two trapping techniques commonly used by landowners, sticky bands and duct tape. The Great Lakes Entomologist 53(3-4): 170-177