Sobre a Faixa de Pedestres

The interference colors resulting from thin films of Al 2O 3 deposited by atomic layer deposition (ALD) on silicon have been rigorously analyzed using a recently developed robotic gonioreflectometer. A series of eleven increasingly thick films was deposited, up to 1613 Å, and their reflectance values obtained for the visible spectrum. A comparison of these values with the predictions of computer simulations employing Fresnel equations has revealed that while there was generally good agreement between predicted and measured spectra, there are some spectral regions that exhibit large deviations from predicted reflectances, typically at near-normal measurement angles and shorter wavelengths. The effect of these discrepancies on color appearance was investigated in the CIE L*a*b* color space for the daylight illuminant D65. Large iridescence is both predicted and measured for most film thicknesses. Chroma and hue differences as large as 20 CIELAB units between the predicted and the measured color centers were obtained. Simulation also predicts larger iridescence than what is actually measured. A likely cause for the observed discrepancies is that the dielectric constants of the ALD films deviate from the literature values for the bulk material

Anisotropic effective permittivity of an ultrathin gold coating on optical fiber in air, water and saline solutions

The optical properties of an ultrathin discontinuous gold film in different dielectric surroundings are investigated experimentally by measuring the polarization-dependent wavelength shifts and amplitudes of the cladding mode resonances of a tilted fiber Bragg grating. The gold film was prepared by electron-beam evaporation and had an average thickness of 5.5 nm ( ± 1 nm). Scanning electron imaging was used to determine that the film is actually formed of individual particles with average lateral dimensions of 28 nm ( ± 8 nm). The complex refractive indices of the equivalent uniform film in air at a wavelength of 1570 nm were calculated from the measurements to be 4.84-i0.74 and 3.97-i0.85 for TM and TE polarizations respectively (compared to the value for bulk gold: 0.54-i10.9). Additionally, changes in the birefringence and dichroism of the films were measured as a function of the surrounding medium, in air, water and a saturated NaCl (salt) solution. These results show that the film has stronger dielectric behavior for TM light than for TE, a trend that increases with increasing surrounding index. Finally, the experimental results are compared to predictions from two widely used effective medium approximations, the generalized Maxwell-Garnett and Bruggeman theories for gold particles in a surrounding matrix. It is found that both of these methods fail to predict the observed behavior for the film considered

Amidinates, guanidinates and iminopyrrolidinates: Understanding precursor thermolysis to design a better ligand

The thermolysis of metal compounds incorporating amidinate-type ligands (RN(H)C(X)NR, where R is any alkyl and X is an alkyl or an amido) show a great complexity and diversity. Amidinates and guanidinates of copper(I), aluminium(III) and gallium(III) can undergo thermal decomposition by two main routes: elimination of carbodiimide (here called "deinsertion") and by abstraction of a β-hydrogen. In general terms carbodiimide deinsertion tends to be a low temperature and solution-based thermolysis route, and β-hydrogen elimination tends to be a high temperature and gas phase thermolysis path. Th

Surface chemistry of group 11 atomic layer deposition precursors on silica using solid-state nuclear magnetic resonance spectroscopy

The use of chemical vapour deposition (CVD) and atomic layer deposition (ALD) as thin film deposition techniques has had a major impact on a number of fields. The deposition of pure, uniform, conformal thin films requires very

The Chemistry of Inorganic Precursors during the Chemical Deposition of Films on Solid Surfaces

Conspectus The deposition of thin solid films is central to many industrial applications, and chemical vapor deposition (CVD) methods are particularly useful for this task. For one, the isotropic nature of the adsorption of chemical species affords even coverages on surfaces with rough topographies, an increasingly common requirement in microelectronics. Furthermore, by splitting the overall film-depositing reactions into two or more complementary and self-limiting steps, as it is done in atomic layer depositions (ALD), film thicknesses can be controlled down to the sub-monolayer level. Thanks to the availability of a vast array of inorganic and metalorganic precursors, CVD and ALD are quite versatile and can be engineered to deposit virtually any type of solid material. On the negative side, the surface chemistry that takes place in these processes is often complex, and can include undesirable side reactions leading to the incorporation of impurities in the growing films. Appropriate precursors and deposition conditions need to be chosen to minimize these problems, and that requires a proper understanding of the underlying surface chemistry. The precursors for CVD and ALD are often designed and chosen based on their known thermal chemistry from inorganic chemistry studies, taking advantage of the vast knowledge developed in that field over the years. Although a good first approximation, however, this approach can lead to wrong choices, because the reactions of these precursors at gas-solid interfaces can be quite different from what is seen in solution. For one, solvents often aid in the displacement of ligands in metalorganic compounds, providing the right dielectric environment, temporarily coordinating to the metal, or facilitating multiple ligand-complex interactions to increase reaction probabilities; these options are not available in the gas-solid reactions associated with CVD and ALD. Moreover, solid surfaces act as unique "ligands", if these reactions are to be viewed from the point of view of the metalorganic complexes used as precursors: they are bulky and rigid, can provide multiple binding sites for a single reaction, and can promote unique bonding modes, especially on metals, which have delocalized electronic structures. The differences between the molecular and surface chemistry of CVD and ALD precursors can result in significant variations in their reactivity, ultimately leading to unpredictable properties in the newly grown films. In this Account, we discuss some of the main similarities and differences in chemistry that CVD/ALD precursors follow on surfaces when contrasted against their known behavior in solution, with emphasis on our own work but also referencing other key contributions. Our approach is unique in that it combines expertise from the inorganic, surface science, and quantum-mechanics fields to better understand the mechanistic details of the chemistry of CVD and ALD processes and to identify new criteria to consider when designing CVD/ALD precursors

Trends in copper precursor development for CVD and ALD applications

The continued dominance of copper in microelectronic manufacturing is due in part to the techniques that have kept pace with the relentless trend towards smaller feature sizes. Pure and defect-free copper features can be created at these and smaller scales using gas phase deposition methods such as chemical vapor deposition (CVD) and atomic layer deposition (ALD). Here we review the deposition processes and in particular surface chemistry for depositing copper metal by CVD and ALD. A summary of known processes is given, and new trends in copper film deposition research are discussed. As well, process parameters and properties of copper films deposited from precursors using key ligand systems such as aminoalkoxides, amidinates, guanidinates, betadiketonates and betaketoiminates are presented. Surface chemistry is examined from the point of view of the similarities of CVD and ALD, considering precursors that can be used in both types of processes. This serves to highlight trends in decomposition mechanisms and illuminates some interesting similarities in process temperature and other parameters

Synthesis and characterization of copper(I) amidinates as precursors for atomic layer deposition (ALD) of copper metal

A series of copper(I) amidinates of the general type [(R′NC(R) NR″)Cu]2 (R′ and R″ = n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl; R = methyl, n-butyl) have been synthesized and characterized. These compounds are planar dimers, bridged by nearly linear N-Cu-N bonds. Their properties (volatility, low melting point, high thermal stability, and self-limited surface reactivity) are well-suited for atomic layer deposition (ALD) of copper metal films that are pure, highly conductive, conformal, and strongly adherent to substrates

Principles of precursor design for vapour deposition methods

Chemical vapour deposition (CVD) and atomic layer deposition (ALD) are attractive techniques for depositing a wide spectrum of thin solid film materials, for a broad spectrum of industrial applications. These techniques rely on volatile, reactive, and thermally stable molecular precursors to transport and deposit growth materials in a kinetically controlled manner, resulting in uniform, conformal, high purity films. Developments in these fields depend on careful precursor design. We discuss the qualities that make successful CVD or ALD precursors (low melting point, high volatility, stability and specific reactivity) and the widely applicable design principles used to achieve them, through examples of group 11 and 13 precursors including amidinates, guanidinates and iminopyrrolidinates. We highlight the most valuable techniques that we use to asses potential precursors on the basis of the discussed qualities, and to elucidate relevant mechanisms of decomposition and surface reactivity. There is a strong focus on thermogravimetric analysis (TGA), and solid state (SS) and solution NMR studies