J. E. Hilliard

Bio: J. E. Hilliard is an academic researcher from Northwestern University. The author has contributed to research in topics: Elastic modulus & Diffusion (business). The author has an hindex of 3, co-authored 4 publications receiving 519 citations.

Enhanced elastic modulus in composition‐modulated gold‐nickel and copper‐palladium foils

Abstract: The biaxial elastic modulus Y[111] has been measured by bulge testing in Au‐Ni and Cu‐Pd foils containing short‐wavelength one‐dimensional composition modulations produced by vapor deposition. As compared with homogeneous foils of the same average composition, the modulated foils exhibited an appreciable increase in modulus—from 0.21 to 0.46 TPa for Au‐Ni and from 0.27 to 1.31 TPa for Cu‐Pd. For the latter system, the increase was found to be proportional to the square of the amplitude of the modulation. The enhancement of the modulus decreased with increasing wavelength and for wavelengths greater than 3 nm the modulus was the same as that for homogeneous foils. It was also observed that the deformation was non‐Hookian; the slope of the stress‐strain curves decreased with increasing strain.

Elastic modulus in composition‐modulated copper‐nickel foils

Abstract: The biaxial elastic modulus Y[111] was measured by bulge testing on Cu‐Ni thin foils containing short‐wavelength composition modulations produced by vapor deposition. In the wavelength range of 1.3–3.0 nm, we observed a twofold increase in the modulus as compared with homogeneous foils. The increase was proportional to the square of the composition amplitude. The maximum modulus occurred at a wavelength of 1.7 nm and an average composition of 45 at. % Cu. The stress‐strain curves of the modulated foils were reversible but non‐Hookean, while homogeneous foils displayed a Hookean behavior with moduli in good agreement with those calculated from the single‐crystal elastic constants of bulk Cu‐Ni alloys.

Effect of long‐range interaction on diffusion in copper‐nickel composition‐modulated alloys

Abstract: Vapor deposited Cu–Ni films were produced containing composition modulations with wavelengths between 0.8 to 5.0 nm. The foils, deposited on mica substrates, exhibited a strong 〈111〉 texture and produced satellite peaks in the x‐ray diffraction patterns. The interdiffusivities in the range of 375–450 °C, which were measured from the decay rate of the x‐ray diffraction satellite intensities, yielded an activation energy of 2.7×105 J/mol. This value is in good agreement with that obtained by tracer diffusivities at high temperatures. The effective diffusion coefficient DB at 400 °C [as a function of the dispersion relation B2(h)] showed a minimum at a wavelength of about 1.5 nm in contrast with the linear or monotonic behavior of several other systems. A new formulation of DB in a power series of B2 was developed and the first six interaction energies were calculated from short‐range order parameters.

Interdiffusion in composition modulated copper-nickel thin films

Abstract: Interdiffusivities were measured in vapor-deposited Cu-Ni foils containing [ I l l ] composition modulations with wavelengths between 0.8 and 5 nm. The interdiffusivities in the range of 375-450 O C , measured from the decay rate of X-ray diffraction satellite intensities, were in good agreement with an extrapolation of existing high temperature data obtained with conventional diffusion specimens. The effective diffusion coefficient D, at 400 OC as a function of the dispersion relation B '(h) showed a minimum, in contrast with the behavior of several other systems investigated so far. A new formulation of D, in powers of B Z was developed and six interatomic potentials were calculated from short range order parameters which yielded a,minimum in D, at approximately 1.6 nm as was observed experimentally. Screening singularities showed up in the D, by the appearance of a sharp peak at a wavelength 2.5 nm. Introduction. According to the linearized treatquantity D\", is an interdiffusion coefficient which, in a ment of diffusion the amplitude, A(t), of a composition derivation to be published elsewhere, can be related to modulation defined by the wavevector : the diffusion coefficient, D\", measured in a macroscopic k = h1 bl + h2 bz + h, bg , will vary with time, t.. according to : couple by : A(t) = A(0) exp[a(h) t] , where f \" is the second derivative with respect to composition of the Helmholtz free energy per unit where a(h) is an amplification factor defined by : volume, o is a coherency strain term [l] which depends on the elastic constants and the variation of lattice ~ ( h ) = B2(h) BB, (2) parameter with composition and the K's are gradientenergy coefficients. Eq. (4) is a generalization of an in which BZ(h) is the dispersion relationship : expression [2] which included only the first term in the summation and this, in turn, was a generalization of a B2(h) = (lla2) C [I cos k(h).x(r)] (3) continuum model developed by Cahn [l] that is valid for the limit gZ(h) -t 0. Expressions for the K's in in which a is the lattice parameter and the summation terms of the interatomic potentials have been derived is over the nearest neighbor sites to the origin. The for the [l 1 l] and [loo] directions in a ~.c.c. lattice. (*) Currently at : Rutgers, The State University of New Jersey, Experimental procedure and results. ComposiDepartment of Mechanics and Materials Science, College of Engltion were prepared by neering, Piscataway, New Jersey 08854, U.S.A. evaporating the two components through a rotating Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1977781 INTERDIFFUSION IN COMPOSITION MODULATED COPPER-NICKEL THIN FILMS C7-405 pinwheel shutter onto a mica substrate ; details of the technique have been given elsewhere [3]. The foils had a strong [l111 texture and the modulations were coherent. The wavelength (0.8-5 nm) and amplitude of the modulations were determined from the location and intensity (I) of the satellites about the 111 Bragg peak. The diffusivity DB was estimated from the terminal slope of a plot of In [I(t)/I(O)] versus isothermal annealing time. The variation of BB with B2(h) is shown in figure 1. It will be noted that the dependence is strongly nonlinear indicating that the higher-order terms in Eq. (4) are significant. We believe that the strong peak at a wavelength of 2.5 nm is not due to the gradientenergy coefficients but instead is a result of a large increase in the elastic modulus that we have observed (and will be reporting elsewhere) in composition modulated Cu-Ni foils having wavelengths S 2.5 nm. The increase in the .modulus increases the coherency-strain term o in Eq. (4) and hence the value of BB. An increase in elastic modulus has also been observed [4] in Au-Ni and Cu-Pd composition modulated foils and we FIG. 1. Diffusivities DB versus BZ for 50 at. pct. Cu-Ni foils at 400 oC. believe that the effect is due to change in the band structure resulting from the introduction of a new Brillouin zone. The following values for the first four gradientenergy coefficients were estimated from a fit of Eq. (4) to figure 1 using a value of 7.2 X 108 J/m3 for f\" As previously noted, the K's can be related to the interatomic potentials. The first six of these were calculated from short-range order parameters determined by Vrijen, van Dijk and Radelaar [5]. The values derived for K, , K, and K, agreed with the observed ones in respect to sign but were smaller by approximately an order of magnitude. There was a corresponding discrepancy . in the values of DB calculated from Eq. (4) but they did exhibit a minimum at about the same wavelength as the experimental values plotted in figure 1. The differences between the observed and calculated quantities 'are probably due to the omission of higher-order interatomic potentials since these are heavily weighted in the expressions for the K's. The results described here for the Cu-Ni system differ from those so far observed in other systems in two respects, both of which are related to the longrange interactions in Cu-Ni. First, in all systems so far studiedK, has the same sign as the heat of mixing whereas in Cu-Ni it is of opposite sign. Secondly, in measurements of Dg in A U ' ~ g [3] and Cu-Pd* [6] composition modulated foils the data could be adequately .fitted using only the first term of the summation in Eq. (4). Acknowledgments. This research was supported by the National Science Foundation through the Northwestern University Materials Research Center.

Field-Induced Layering of Colloidal Crystals

Abstract: An electrohydrodynamic methodology has been developed that makes possible the precise assembly of two- and three-dimensional colloidal crystals on electrode surfaces. Electrophoretically deposited colloidal particles were observed to move toward one another over very large distances (greater than five particle diameters) to form two-dimensional colloidal crystals for both micrometer- and nanometer-size particles. This coalescence of particles with the same charge is opposite to what is expected from electrostatic considerations and appears to result from electrohydrodynamic fluid flow arising from an ionic current flowing through the solution. The ability to modulate this "lateral attraction" between particles, by adjusting field strength or frequency, facilitates the reversible formation of two-dimensional fluid and crystalline colloidal states on the electrode surface. Further manipulation allows controlled structures to be assembled.

Stresses and deformation processes in thin films on substrates

Abstract: The stresses that develop in thin films on substrates can be detrimental to the reliability of thin film electronic devices. In order to design these devices for improved mechanical reliability, an...

Mechanical deflection of cantilever microbeams: A new technique for testing the mechanical properties of thin films

Abstract: The mechanical deflection of cantilever microbeams is presented as a new technique for testing the mechanical properties of thin films. Single-layer microbeams of Au and SiO2 have been fabricated using conventional silicon micromachining techniques. Typical thickness, width, and length dimensions of the beams are 1.0,20, and 30 μm, respectively. The beams are mechanically deflected by a Nanoindenter, a submicron indentation instrument that continuously monitors load and deflection. Using simple beam theory and the load-deflection data, the Young’s moduli and the yield strengths of thin-film materials that comprise the beams are determined. The measured mechanical properties are compared to those obtained by indenting similar thin films supported by their substrate.

Young’s modulus measurements of thin films using micromechanics

Abstract: Electrostatically deflectable cantilever beams (1000–9000 A thick, 120–8.3 μm long) have been fabricated from a number of thin insulating films prepared by a variety of deposition methods. Measurements of the transverse mechanical resonant frequencies of these beams have been used to calculate Young’s modulus of the insulating thin films. This new technique is relatively simple and accurate and is applicable to a wide range of materials and deposition procedures.