Perpendicular Surface Research Articles

Molecular structure of self-assembled bimolecular films on gold and silicon surfaces studied by external reflection infrared spectroscopy

Self-assembled bimolecular films were prepared by coupling homologous n-alkylsiloxane overlayers (CH 3(CH 2) n SiO x , RSiO, n = 10, 13–17) to HO-terminated primer layers of HO(CH 2) 16SH (HHDT) on Au(111) and HO(CH 2) 11SiO x (HUDS) on oxidized Si(100). The structure and surface orientation of the hydrocarbon chains in the RSiO overlayers were investigated by external reflection infrared spectroscopy (ERIRS) and ellipsometry, and were compared to the molecular structure of alkanethiolate monolayers (CH 3(CH 2) n S, RS) on Au(111) and RSiO monolayers on oxidized Si(100). Similar structural properties were found for the RSiO overlayers on gold and silicon, despite the different structure of the primer layers HHDT and HUDS. The long-chain RSiO overlayers ( n > 15) show a highly ordered structure consisting of predominantly all- trans hydrocarbon chains with a uniform, close to perpendicular surface orientation of the chain axes, which is identical to the corresponding RSiO monolayers, but is markedly different to RS monolayers on Au(111), where the hydrocarbon chains are tilted by ∼ 30° with respect to the surface normal. Shorter-chain RSiO overlayers ( n < 15) exhibit increasing disorder with decreasing chain length caused by a gradual increase of the chain tilt angles associated with a destruction of the all- trans chain geometry, which results in an isotropic, liquid-like film structure for the shortest-chain molecules in this series ( n = 10). Similar order-disorder transitions also occur in the monolayer films RS Au and RSiO Si , whereby the transition region is shifted by at least five CH 2 groups toward shorter chains.

Fatigue damage at room temperature in aluminium single crystals—III. Lattice rotation

Lattice rotation was observed in different scales in aluminium single crystals fatigued in push-pull in air at room temperature, a constant shear stress amplitude 4 MPa, zero mean stress and frequency of 20 Hz. Using the channelling contrast technique in SEM, contrast of grey and dark bands consistent in dimensions with those of PSBs was observed on the surface sectioned parallel to the Burgers vector b in an Al single crystal after 1.2 × 106 cycles, suggesting that there was lattice misorientation (rotation or tilt) between PSBs and the matrix in the specimen. It might be caused by local net material movement due to irreversible slip or non-uniform deformation in PSBs. Lattice rotation (about 6°) always appeared between a macroband and the matrix relative to the normals of two perpendicular surfaces of the specimens, as a result of net irreversible slip in one direction of b in PSBs. Often more cracks were found in a positive macroband than a negative one. Deformation bands coarser than PSBs and smaller than macrobands were also found on the surface containing b by the scanning acoustic microscope. They deviated slightly from the direction of the PSBs and were probably formed to release the internal stresses between macrobands and the matrix due to macroband formation. The macroband effect is likely a general metallographic characteristic of unidirectional fatigue in planar-slip metal single crystals. The lattice rotation was probably one of the key factors controlling crack initiation and early propagation in the Al single crystals.

Effect of chirality on liquid crystals in capillary tubes with parallel and perpendicular anchoring.

The director field of a cholesteric liquid crystal confined to cylindrical cavities with parallel and perpendicular surface anchoring was studied by means of optical polarizing microscopy. The chirality of the liquid crystal could be varied continuously due to a temperature-induced twist inversion of the cholesteric structure. The results indicate the occurrence of a twisted escaped radial structure for perpendicular anchoring and an eccentric double twist configuration for parallel anchoring. \textcopyright{} 1996 The American Physical Society.

Transport of submicron particles from a leak to a perpendicular surface in a chamber at reduced pressure

At subatmospheric pressure, thermodynamic conditions of semiconductor manufacturing processes change rapidly during pump down or venting operations. Important insights regarding the behavior of particles in real equipment can be obtained using simplified models and idealized experiments under static conditions. Experimental and theoretical studies were performed in order to understand the particle transport into a chamber and the particle deposition behavior on a free-standing wafer at reduced pressure (down to 10 2 Pa). The transport mechanisms taken into account were convection, diffusion and external forces such as sedimentation and thermophoresis. To model these particle transport processes, the analogy between the governing equations of momentum, energy and mass was applied to the extended diffusion equation. In their nondimensional form, the results of the numerical calculation give detailed information about velocity, temperature and particle concentration boundary layer thickness as well as their distributions. In particular, the influence of external forces on the particle concentration field in the vicinity of the surface was investigated. The experimental study consisted of the generation of a monodisperse, fluorescent latex aerosol, the injection of the aerosol through a tiny capillary at the top of a vertical chamber at subatmospheric pressure and the deposition of the particles on a cooled, free-standing wafer in the chambers center. The deposited particles were detected and counted by an optical microscope connected to an image processing unit. This paper presents the results from particle transport and deposition experiments conducted in a chamber while varying the pressure level and the temperature of test surface.

Transport of submicron particles from a leak to a perpendicular surface in a chamber at reduced pressure

At subatmospheric pressure, thermodynamic conditions of semiconductor manufacturing processes change rapidly during pump down or venting operations. Important insights regarding the behavior of particles in real equipment can be obtained using simplified models and idealized experiments under static conditions. Experimental and theoretical studies were performed in order to understand the particle transport into a chamber and the particle deposition behavior on a free-standing wafer at reduced pressure (down to 10 2 Pa). The transport mechanisms taken into account were convection, diffusion and external forces such as sedimentation and thermophoresis. To model these particle transport processes, the analogy between the governing equations of momentum, energy and mass was applied to the extended diffusion equation. In their nondimensional form, the results of the numerical calculation give detailed information about velocity, temperature and particle concentration boundary layer thickness as well as their distributions. In particular, the influence of external forces on the particle concentration field in the vicinity of the surface was investigated. The experimental study consisted of the generation of a monodisperse, fluorescent latex aerosol, the injection of the aerosol through a tiny capillary at the top of a vertical chamber at subatmospheric pressure and the deposition of the particles on a cooled, free-standing wafer in the chambers center. The deposited particles were detected and counted by an optical microscope connected to an image processing unit. This paper presents the results from particle transport and deposition experiments conducted in a chamber while varying the pressure level and the temperature of test surface.

The particle motion through the fringing field of a toroidal condenser in a third-order approximation

The ion trajectories through the extended fringing field of a toroidal condenser are calculated including the effects of curved field boundaries. The optical fringing-field effects are expressed by analytical formulas including fringing-field integrals using the transfer matrix method. These formulas describe in an effective third-order approximation all effects in the plane of deflection as well as in the perpendicular surface to this plane. The obtained expressions are compared to precise numerical ray-tracing calculations through typical field distributions.

Mean-field theory for spin-reorientation phase transitions in magnetic thin films.

A mean-field theory for spin-reorientation phase transitions in magnetic thin films is worked out, solving analytically the relevant differential equation. The role of the exchange stiffness A in the competition between the in-plane shape anisotropy ${\mathit{K}}_{\mathit{v}}$ and the perpendicular surface anisotropy ${\mathit{K}}_{\mathit{s}}$ is addressed. The spin-reorientation transition from the perpendicular configuration to the in-plane one with increasing thickness is derived. Two different stable spin configurations are presented at large thickness for ${\mathit{K}}_{\mathit{s}}$ \ensuremath{\surd}${\mathit{AK}}_{\mathit{v}}$ and vice versa. The phase transition with temperature is also explored. Asymptotic formulas are given for energy stocked in the film per unit area, which enable one to evaluate the surface anisotropy.

Surface spin waves in a semi-infinite ferromagnet with perpendicular surface anisotropy

The effect of perpendicular surface anisotropy on surface spin-wave excitations in a semi-infinite ferromagnet is studied by solving the coupled equations of motion of spin-wave annihilation and creation operators. The ground-state spin arrangement in our model is either as in-plane ordering or a canted one due to a competition between the perpendicular anisotropy in the surface and the bulk anisotropy parallel to the surface, and surface spin-wave frequencies are calculated in both phases. It is shown that at the transition point between these two distinct phases a low-lying surface spin-wave branch becomes soft, and consequently the ellipticity and the amplitude of spin precessions in the surface layer grow large in the vicinity of the transition point.

Perpendicular magnetic anisotropy in ultrathin fcc iron films and surfaces at finite temperature

The perpendicular magnetic anisotropy in one to six monolayer fcc iron films is studied by the Green-function method based upon the spin pinning model ( S⩾1) with out-of-plane spin orientation of the atoms at the surfaces, in which the strength of surface anisotropy D measures the fact that the spin be perpendicularly pinned to some degree at the surface, and taking into account the Heisenberg exchange interaction and magnetostatic dipole interaction. We calculate the surface anisotropy constant K s( T), the effective volume anisotropy constant K v( T) and the shape anisotropy constant K d( T) as functions of the thickness of ultrathin films and temperatures, and prove that there is a perpendicular remanence ( K v( T)- K d>0) for an intermediate range of thickness of ultrathin films and temperature, and that the transition temperature for the reversible transition between perpendicular and in-plane magnetization is sensitively affected by D. The calculated results for ultrathin fcc iron film with perpendicular surface anisotropy energy ≅o.5 meV/ atom agree with the experiments for the ultrathin films of fcc Fe on Cu(001).

Movements of the Trifoliate Leaf of Bean ( Phaseolus vulgaris L.) during a Simulated Day, and their Consequences for Solar-Tracking Fidelity and Interception of Solar Radiation

Summary Movements of the terminal and lateral leaflets in the trifoliate leaf of pinto bean (Phaseolus vulgaris L.) cv. Bulgarian were studied under simulated daytime conditions (12-h photoperiod), during which a light source directed on the leaflet lamina was moved at the angular velocity of the earth (15 deg h-1) in a vertical arc centered on the pulvinule, either along the plane of the mid-vein, or transversely, at right angles to it. The time-course of change in laminar elevation, azimuth and rotation was recorded. These data were used to evaluate the fidelity of solar-tracking and calculate the changes of laminar orientation to the sun (angle of light incidence, AI) throughout the day. Interception of incident light throughout the day was estimated by the ratio between the PPF incident on the lamina and on a perpendicular surface, and was calculated as cosine of the angle of light incidence on the lamina. Leaflet movements contributed to the interception of solar radiation, but did not exhibit significant, or consistent solar-tracking. Calculated integrated interception by all three leaflets was similar in all directions of solar traverse over the trifoliate leaf.

Magnetostrictive surface anisotropy of epitaxial multilayers.

An additional perpendicular surface anisotropy term resulting from lattice misfit is found for both coherent and incoherent states. From magnetic strain theory it can be concluded that the magnetic surface anisotropy depends not only on the thickness of the magnetic layer but also on the thickness of the nonmagnetic layer. The influence of surface roughness on magnetostrictive anisotropy is also calculated. We find surface roughness usually reduces the magnitude of surface anisotropy irrespective of its sign. Furthermore, a strong 1/${\mathit{t}}^{2}$ dependence of magnetic anisotropy for multilayers with identical elastic constants is found.

Deformation twinning in high-hydrogen-solubility refractory alloy crystals

Abstract Deformation twinning was studied in single crystals of three high-hydrogen-solubility refractory alloys; Ta-10 at.% Nb, Nb-10 at.% Mo, and Nb-10 at.% V. The hydrogen concentration was maintained close to 150 p.p.m. by weight. Four different crystal orientations were tested in uniaxial tension and compression; in each case, at four different temperatures: 77K, 142K, 195K and 300K. Trace analyses of the deformation markings were carried out on pairs of perpendicular surfaces to determine the crystallographic nature of slip, twinning, cleavage and hydride precipitates. The sense of the deformation twin shear strains conforms with their occurrence under tensile or compressive stresses for the different crystal orientations. The activation energy for the nucleation of twins is determined by means of dislocation modelling of the twin lamella. It is shown that a stress concentration, either from planar dislocation arrays formed during microslip or from a cleavage crack tip, enables the activation energy...

Analytic solution to the problem of magnetic films with a perpendicular surface anisotropy.

The one-dimensional magnetization structure in a film with a perpendicular surface anisotropy is solved analytically, with or without an applied in-plane magnetic field.Received 30 September 1992DOI:https://doi.org/10.1103/PhysRevB.47.8296©1993 American Physical Society

Oscillatory Indirect Coupling Between Perpendicularly Magnetized Co Monolayers Through Cu (111)

ABSTRACTCo-Monolayers, prepared by MBE on Cu (111) -surfaces at room temperature and covered by Cu, are ferromagnetic with a Curie-temperature of about 430 K. They are magnetized perpendicularly because of a strong perpendicular magnetic surface anisotropy of the Cu/Co (111) -interface. They provide a remarkably good representation of the 2-dimensional Ising Model. The indirect coupling between these perpendicularly magnetized ferromagnetic monolayers was investigated using samples of type Cu (111) /lCo/DçuCu/lCo/Cu, containing Co/Cu/Co-trilayers composed of Co-Monolayers and a spacer consisting of DCu atomic layers of Cu (111). Torsion oscillation magnetometry of these samples showed clearly a coupling between the monolayers with an oscillatory dependence on DCu. The amplitude of the oscillation is strongly reduced if the coupled Co-films consist of 5 ML instead of 1 M.L. The present controversy on the presence or absence of antiferromagnetic and oscillatory indirect coupling in the Co/Cu (111) -system is discussed in the light of these experiments. The discussion shows that the oscillatory coupling is an intrinsic property of ideal (111)-structures, and can be understood by the RKKY-type theory of indirect coupling between ferromagnetic Monolayers. The usual application of this theory to the coupling between thicker films is justified. However, in the fcc (111) -system there is apparently a specific barrier against complete coalescence, resulting in a tendency to retain holes and channels in the Cu-spacer. This tendency is stronger in flat single-crystal samples than in sputtered films with high densities of atomic steps. Apparently, this results in competing ferromagnetic hole coupling which may more or less completely obscure the intrinsic oscillatory coupling, preferentially in samples grown on extremely flat single crystal surfaces.

Spin Polarized Electron Spectroscopies of 3d and 4f Systems

AbstractRecent results from spin polarized electron spectroscopie studies of surfaces and ultrathin films are presented. The Magnetic coupling of 3d transition Metals (Cr,Mn) to the Fe (100) surface is studied by spin polarized electron energy loss spectroscopy. The first atomic layer of Cr and mn aligns antiparallel to the Fe. For larger thicknesses we find evidence for layer-by-layer antiferromagnetic order. In the range of 1–6 atomic layers the behavior is more complex with the surface of the Cr films showing preferential ferromagnetic alignment while the mn surface aligns antiparallel to the Fe substrate.Secondary electrons from Gd (0001) surfaces are shown to be highly spin polarized. However, no enhancement mechanism at low kinetic energy as in the 3d transition metals is observed indicating the absence of strongly spin dependent inelastic scattering in Gd. Temperature dependent spin polarized 4f photoemis-sion results show almost complete polarization demonstrating ferromagnetic surface coupling. However, a perpendicular surface magnetization component is found indicating surface spin canting. A large enhancement of the surface Curie temperature is also present.

Influence of roughness on magnetic surface anisotropy in ultrathin films

A magnetostatic model for shape anisotropy of an ultrathin film with surface roughness is presented. Apart from the usual volume anisotropy, an additional perpendicular surface anisotropy results from the surface roughness. For a continuous film, the shape anisotropy follows the famous 1/t behavior. By considering the correlation between the surfaces, the perpendicular surface anisotropy can be further increased. When the film thickness is less than a certain value, the magnetic layer may become a discontinuous or island-like structure and the shape anisotropy is proportionally lower with decreasing film thickness. With a nonzero quality factor (Q=Kc/2πMs2), a marked kink in the dependence Kefft on the film thickness gradually appears with increasing roughness. Observed results agree qualitatively with predictions based on the present model.

Dynamics of photothermal surface expansion and diffusivity using laser-induced holographic gratings

The transient thermal expansion of a GaAs surface was measured directly using a two color reflection transient grating technique. Isolation of the expansion signal requires the selection of wavelengths which pump and probe different regions of the absorption bands in the sample. The surface thermal diffusivity was also determined to be equivalent to the bulk value above 50 K. Below 50 K, D/sub s/ was determined to be up to an order of magnitude slower than the bulk diffusivity due to increased phonon boundary scattering. It is demonstrated that the expansion signal perpendicular to the surface can be modeled with moderate success using a straightforward one-dimensional analytic theory. The work reported is restricted to expansion perpendicular to the surface, validating the applicability of this technique for measuring the perpendicular expansion signal and surface diffusivity. However, the true power of the reflection transient grating technique lies in its ability to measure phenomena in and out of the plane of the surface simultaneously by varying the fringe spacing of the grating.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Mössbauer studies of Fe(100)/Ag(100) multilayers grown on NaCl(100) by molecular beam epitaxy

Fe(100)/Ag(100) heterostructures, with varying Fe bilayer thicknesses equal to 3, 6 and 9 monolayers (ML) and a constant Ag bilayer thickness equal to 40 ML, were grown on suitably prepared monocrystalline NaCl(100) substrates by molecular beam epitaxy. The multilayer moncrystallinity was verified with in situ reflection high energy electron diffraction. Transmission Mössbauer measurements revealed a perpendicular surface anisotropy for the Fe(100) bilayers at 4.2 K. This behavior is unlike that of Fe(100)/Ag(111) ultrathin films of about the same thickness.

Bulk and surface Debye temperatures in relation to cohesive energy and Lennard-Jones potentials

A simple model is presented which relates bulk Debye temperatures to cohesive energy, atomic mass and atomic radius by means of a Lennard-Jones type of potential. Good agreement is obtained for the various groups of the periodic table. The model can be extended to describe surface Debye temperatures as well. It explains why the perpendicular surface Debye temperatures of fcc (111). (100) and (110) surfaces are virtually equal for a given element. Experimentally determined surface Debye temperatures are lower than predicted, which is explained in terms of surface relaxation and anharmonicity of the surface oscillations.

Magnetic properties of Fe/Cr and Fe/Cu superlattices (abstract)

Both the static and dynamic magnetic properties of sputtered Fe/Cr and Fe/Cu superlattices are compared. The static magnetization is measured by vibrating sample and SQUID magnetometry as well as conversion electron Mössbauer spectroscopy. The spin-wave spectra are measured by Brillouin light scattering (BLS). Although the structure of these two systems as determined by x-ray diffraction are similar, the magnetic properties differ greatly. In Fe/Cr, the Fe layers couple antiferromagnetically (AF), which can be correlated with an enhanced magnetoresistance. Both the strength of AF coupling and the size of the magnetoresistance are found to have a maximum value for Cr thicknesses of 11 Å and increase with decreasing Fe thickness. Broad spin-wave spectra are observed by BLS and there is little indication of surface anisotropy. In contrast, Fe/Cu shows no indication of AF coupling of the Fe and a perpendicular surface anisotropy is observed. Very well-resolved spin-wave modes showing the band structure expected for a ferromagnetically coupled magnetic superlattice are observed in the BLS spectra. The relationship between the interface structure and the varying magnetic properties will be discussed.