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Electrical conductivity measurements were performed on structurally anisotropic thin films deposited using the glancing angle deposition apparatus [K. Robbie and M. J. Brett, J. Vac. Sci. Technol. A 15, 1460 (1997); K. Robbie, J. Sit, and M. J. Brett, J. Vac. Sci. Technol. B 16, 1115 (1998); K. Robbie and M. J. Brett, US Patent No. 5,866,204 (2 February 1999)]. The films were comprised of bilayers of titanium over silica, engineered as a chevron morphology. Samples were evaporated at various incident vapor deposition angles α, in order to investigate the effects of morphology and voiding on the behavior of conductivity. A rapid decline in the conductivity, accompanied by an increase in conduction anisotropy in the plane of the substrate, was observed with increasing α. A random walk model was developed to model the transport properties of the films, and applied to microstructures predicted by a three-dimensional ballistic thin film simulator. In order to generate reasonable agreement between the modeling ...

A method of producing relatively monodisperse, small-diameter (sub-500 nm diameter) aerosol fibers is described. This method involves the separation of porous thin films from their substrate. It was found that fibers with diameters of less than several hundred nm and lengths of several micrometers can be formed that do not adhere to one-another. Two μ m thick columnar thin films were fabricated and processed, yielding aerosol fibers with lengths up to 2 μm and diameters up to 170 nm. Diameter and length distributions of a collected aerosol showed that a broad range of fiber lengths and diameters are formed by this method. Further modification of the method, however, is expected to greatly narrow the range of effective diameters and lengths obtained.

Recent experimental work by a number of researchers has demonstrated that unusual high porosity thin films may be obtained in physical deposition systems by combining glancing angle deposition with in situ substrate motion control. The microstructure of these films consists of isolated columns engineered into shapes such as helices, posts, or chevrons. Due to the isolated nature of the columns, the films present a unique opportunity to study fundamental thin film growth behavior and, in particular, the influence of the self-shadowing mechanism in three dimensions. Apart from this academic motivation, there is the need to characterize the physical constraints imposed on the engineering of these films. In particular, this study will have implications for the realization of isolated, periodically arranged nanostructures envisioned for certain applications such as photonic band gap crystals. Results from an ongoing study of growth dynamics, morphology, porosity, and scaling behavior, and the dependence of these features on deposition parameters are presented.

The effectiveness of debris reduction using magnetically guided pulsed laser deposition (MGPLD) is reported here. KrF laser pulses (248 nm) of 100 mJ energy were focused to intensities of 6×109 W/cm2 onto the surface of a copper or a carbon source target and a magnetic field of 0.3 T as used to steer the plasma around a curved arc of 0.5 m length to the deposition substrate. Debris counts were compared for films produced by the MGPLD and conventional PLD (nonguided) techniques. A significant reduction in particulates of size greater than 0.1 μm was achieved using MGPLD. For the copper films, particulate count was reduced from 150 000 particles/cm2/nm to 50 particulates/cm2/nm and for diamond-like carbon thin films particulate count was reduced from 25 000 particles/cm2/nm to 1200 particles/cm2/nm.

A new approach is described in the deposition of thin films for thermal barrier applications. Using controlled substrate motion, porous layers and capping layers were vacuum deposited in an alternating fashion, creating a new, multilayered film structure. Direct measurements of the thermal properties of these multilayers were made using the 3ω and Mirage techniques. In the 3ω technique, heat is introduced into the coating by an AC current flowing through an evaporated resistor with a frequency ω. A fit of resistor voltage as a function of frequency yields the thermal conductivity. In the Mirage technique, an oscillating temperature is induced immediately above the film using a pulsed laser. A second probe laser aligned parallel to the surface is deflected by these temperature variations, and the thermal diffusivity is then found by fitting amplitude and phase shift data to the solution of the three-dimensional diffusion equation. Typically, the 3ω and Mirage techniques measure thermal constants in directions normal and parallel to the substrate, respectively. Measurements using these methods led to estimates of a reduction in thermal diffusivity of as little as 9% of that of films deposited entirely at normal incidence. Thermal simulations of similar structures also predicted a substantial decrease in overall thermal conductivity. In a specific case, an improved conductivity of 18% of that of films deposited by standard techniques was estimated.

Pulsed laser deposition (PLD) has been used together with the Glancing Angle Deposition (GLAD) technique [1,2] for the first time to produce highly porous structured films. A laser produced carbon plasma and vapour plume was deposited at a highly oblique incident angle onto rotating Si substrates, resulting in films exhibiting high bulk porosity and controlled columnar microstructure. By varying the substrate rotation rate, the shape of the microcolumns can be tailored. These results extend the versatility of the GLAD process to materials not readily deposited by means of traditional physical vapour deposition techniques.

The production of highly porous films by oblique deposition has attracted recent attention because of the possible applications of such films. The morphology of obliquely evaporated films is thought to be determined mainly by the mechanisms of self-shadowing and surface diffusion. The thin film process simulator GROFILMS has been used to verify the importance of these effects, and clarify some aspects of how they interact to determine the final film morphology. Good agreement between simulations and actual films has been achieved. Temperature control of the film during deposition is shown to be an important consideration for the production of structurally engineered films.

Thin films with microstructures controlled on a nanometer scale have been fabricated using a recently developed process called glancing angle deposition (GLAD) which combines oblique angle evaporation with controlled substrate motion. Critical to the production of GLAD thin films is the requirement for a narrow angular flux distribution centered at an oblique incidence angle. We report here recent work with low-pressure, long-throw sputter deposition with which we have succeeded in fabricating porous titanium thin films possessing “zig-zag,” helical, and “pillar” microstructures, demonstrating microstructural control on a level consistent with evaporated GLAD. The use of sputtering for GLAD simplifies process control and should enable deposition of a broader range of thin film materials.

Summary form only given, as follows. The guiding of plasma produced by a KrF laser and Nd:YAG laser using straight and curved solenoidal magnetic field has been studied as a means of giving a debris free, controlled deposition source for the production of thin films. Details on the deflection and guiding of the laser produced plasma in curved and straight magnetic fields and initial coating results will be presented. These results will be presented and compared to predictions of plasma guiding using 2D and 3D numerical plasma simulation mode.

A new fully three dimensional (3D) ballistic deposition simulator 3D-FILMS has been developed for the modeling of thin film deposition and structure. The simulator may be implemented using the memory resources available to workstations. In order to illustrate the capabilities of 3D-FILMS, we apply it to the growth of engineered porous thin films produced by the technique of GLancing Angle Deposition (GLAD).

Recent experimental work has demonstrated that unique high porosity thin films may be ob- tained in physical deposition systems by combining glancing angle deposition with in situ sub-strate motion control [1-7]. The microstructure of these films consists of isolated columns engineered into shapes such as helices, posts, or chevrons. Due to the isolated nature of the columns, the films present a unique opportunity to study fundamental thin film growth behaviour and, in particular, the influence of the self shadowing mechanism in three dimensions. Apart from this academic motivation, there is the need to characterize the physical constraints imposed on the engineering of these films. In particular, this study will have implications for the realization of isolated, periodically arranged nanostructures envisioned for certain applications. Preliminary results from an ongoing study of growth dynamics, morphology, porosity, and scaling behaviour, and the dependence of these features on deposition parameters are presented below.

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

Unique thin film microstructures have been fabricated with the Glancing Angle Deposition (GLAD) technique. These porous,thin films can be engineered with a variety of different morphologies to sub-micron dimensions, including helical, post, andchevron or zigzag microstructures. This paper reports some recent results in study and application of films deposited usingGLAD, namely: the use oflow pressure, long throw sputtering to produce porous titanium films; deposition ofporous, structuredZr02 films for use as thermal barriers; and measurement of the mechanical response of chiral or "microspring" thin films.Keywords: glancing angle deposition, thermal barrier, porous films, sputtering, mechanical properties 1. INTRODUCTION The Glancing Angle Deposition (GLAD) technique has been used to fabricate thin films by physical vapour deposition"2'3.This technique involves the deposition ofthin films onto unheated substrates oriented at highly oblique angles to the vapourflux. Under these conditions, two main mechanisms dominate the growth process: enhanced self-shadowing and limitedadatom diffusion3'4'5. When flux first arrives at the substrate, the film begins nucleating at the surface, and as additional fluxreaches the substrate, areas of previous film growth physically shadow the areas behind them. This initiates the formation ofnanometer scale, columnar structures. Because the substrates are unheated, the diffusion length of the adsorbed atoms islimited, and they do not fill in the areas which were shadowed. As the film further evolves, it develops into isolated columnsof material which can be grown with a variety of different microstructures through the utilization of computer controlledsubstrate motion. These microstructures include arrays of posts, zig-zags, helices, periodically bent nematics6'7 (s-shapes)and many other morphologies (sometimes called Sculptured Thin Films2), with control over the shape attainable on ananometer scale. Whereas earlier researchers have reported film deposition at oblique incidence4'5'8 (near 700 from

A new approach to deposition of thin films for thermal barrier applications is described. During electron beam evaporation, the extreme shadowing effect that is present at highly oblique incidence is employed to introduce porosity into thin films of zirconia. Using controlled substrate motion a solid capping layer may be applied to these porous films. By depositing layers of porous material and capping in an alternating fashion a new structure is produced which warrants evaluation as an improved thermal barrier coating.

We describe the fabrication of porous chevron thin films deposited at glancing incidence and report some common growth peculiarities of the microstructure. In particular, the second (and additional) chevron arms of porous chevron thin films are consistently inclined at angles significantly greater than the corresponding first arms. This effect is observed in both real and simulated films and has important implications in the fabrication of optical coatings. A simple theoretical model is developed to describe this effect, and a technique for achieving consistent column angles is presented.

A novel three-dimensional (3D) ballistic deposition simulator 3D-FILMS has been developed for the modeling of thin film deposition and structure. The simulator features a ballistic transport algorithm to model incident species with angular distributions appropriate to physical vapor deposition systems. Two-tiered data structuring is employed in order to enable the simulator to run using memory resources available to workstations. The simulator has been applied to a unique class of thin films grown by the technique of glancing angle deposition (GLAD). These films exhibit low bulk density due to an internal structure consisting of isolated microcolumns, which can be engineered into a variety of 3D forms. Because of their inherent 3D morphology, created by a combination of complex substrate motion and 3D shadowing, GLAD films represent an ideal test subject for 3D simulation. Scanning electron microscope images of films are presented together with simulation results, which correctly reproduce aspects of colu...

A nanoindentation technique has been applied to demonstrate the mechanical actuation of thin films fabricated by glancing angle deposition. The films were comprised of a porous layer whose microstructures consisted of helical columns that resembled springs. Surmounting the porous layer was a dense capping layer which served to redistribute the force of the nanoindenter tip and prevent it from penetrating the microstructured film. Atomic force microscope images and force versus displacement curves confirmed that there was an elastic regime to the displacements in the films when low forces were applied. The loading behavior of the porous films was compared with that of dense, unstructured films and revealed a marked difference between the two. A study of the measurements and results enabled such properties as the spring constant and resonant frequencies to be estimated, establishing a basis for future developments and applications in wave-type devices or resonators constructed from these microstructured thin films.