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Microscopia por geração de soma de frequências em interfaces líquidas e sólidas; Sum frequency generation microscopy at liquid and solid interfaces

Oiticica, Pedro Ramon Almeida
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 12/02/2015 PT
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Estudos em interfaces são importantes para o completo entendimento de muitos processos em química, física e biologia. Esses sistemas são governados principalmente pelas propriedades interfaciais dos materiais. Nas duas últimas décadas, o desenvolvimento de novos métodos experimentais melhorou o nosso entendimento das propriedades interfaciais. O advento de uma série de técnicas de espectroscopia a laser baseadas em óptica não linear e o desenvolvimento das técnicas de microscopia por ponta de prova, possibilitaram estudos antes inimagináveis em superfícies e interfaces. Entre as técnicas de espectroscopia não linear, destacamos a espectroscopia por Geração de Soma de Frequências (espectroscopia SFG). Essa técnica foi desenvolvida por Shen et al. em 1987 e, desde então, é aplicada a muitos estudos em superfícies e interfaces. A espectroscopia SFG pode fornecer informações sobre a natureza química por meio do espectro vibracional e sobre o ordenamento médio das moléculas em uma única monocamada. O sinal SFG só pode ser gerado em meios não centrossimétricos, isso inclui superfícies ou interfaces entre meios centrossimétricos, onde há quebra da simetria de inversão. A combinação da espectroscopia SFG com a microscopia óptica tem sido proposta como uma nova técnica experimental para obter imagens em interfaces com sensibilidade química pelo espectro vibracional e contraste pela orientação e ordenamento das moléculas. Neste trabalho...

Nanostructured films of perylene derivatives: High performance materials for taste sensor applications

Constantino, C. J L; Antunes, P. A.; Venancio, E. C.; Consolin, N.; Fonseca, F. J.; Mattoso, L. H C; Aroca, R. F.; Oliveira, O. N.; Riul, A.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 95-101
ENG
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Four perylene derivatives (PTCD) have been used as transducing materials in taste sensors fabricated with nanostructured Langmuir-Blodgett (LB) films deposited onto interdigitated gold electrodes. The Langmuir monolayers of PTCDs display considerable collapse pressures, with areas per molecule indicative of an edge-on or head-on arrangement for the molecules at the air/water interface. The sensing units for the electronic tongue were produced from 5-layer LB films of the four PTCDs, whose electrical response was characterized with impedance spectroscopy. The distinct responses of the PTCDs, attributed to differences in their molecular structures, allowed one to obtain a finger printing system that was able to distinguish tastes (salty, sweet, bitter and sour) at 1 μM concentrations, which, in some cases, are three orders of magnitude below the human threshold. Using Principal Component Analysis (PCA) data analysis, the electronic tongue also detected trace amounts of a pesticide and could distinguish among samples of ultrapure, distilled and tap water, and two brands of mineral water. © 2004 by American Scientific Publishers. All rights reserved.

Thermodynamics and kinetics of ceramic/metal interfacial interactions

Arróyave, Raymundo, 1975-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 248 p.; 2606346 bytes; 5680171 bytes; application/pdf; application/pdf
ENG
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Ceramic/metal interfaces occur in a great number of important applications, such as ceramic/metal composites, microelectronics packaging, ceramic/metal seals, and so forth. Understanding the formation and evolution of such interfaces is therefore essential for the better design and optimization of these technologies. In this thesis, a methodology for the study of the thermochemical interactions at ceramic/metal interfaces, during both their formation and evolution, is proposed. Because of the importance of zirconia-based ceramics in increasingly important applications such as structural composites, thermal barrier coatings and Solid Oxide Fuel Cells, it was decided to illustrate the concepts developed in this thesis through the study of the interactions between zirconias and active metals. Semi-empirical thermodynamic models of all the phases likely to take part in the ceramic/metal interfacial interactions studied were developed. Phase diagram data and thermochemical information were critically assessed and use to adjust the thermodynamic parameters that allowed the description of the Ag-Cu-Ti, Cu-Ti-Zr, Ti-Zr-O, Cu-Ti-O and Cu-Zr-O systems. The thermodynamic models were used to predict the diffusion paths across zirconia/active metal interfaces through metastable phase diagrams calculations. Additionally...

Symmetry principles in the physics of crystalline interfaces

Kalonji, Gretchen Lynn
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 113 leaves; 5706553 bytes; 5706314 bytes; application/pdf; application/pdf
ENG
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by Gretchen Lynn Kalonji.; Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1982.; MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE; Includes bibliographical references.

Enhanced performance of optical sources in III-V materials using photonic crystals

Erchak, Alexei A. (Alexei Andrew), 1976-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 216 p.; 25911085 bytes; 25910844 bytes; application/pdf; application/pdf
ENG
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This thesis applies the unique properties of photonic crystals to enhance the performance of several III-V optical sources. Emphasis is placed on the primary limitation of using photonic crystals for III-V optical sources: nonradiative recombination pathways introduced at the high dielectric contrast interfaces of the photonic crystal. Chapter 1 begins the thesis by providing a theoretical and historical framework for photonic crystals, and lays the foundation for the design of the novel optical sources presented in the later chapters. Chapter 2 develops a framework for improving the external efficiency of a semiconductor LED using photonic crystals. The design, fabrication, and testing of a novel high-efficiency semiconductor LED is described in detail. To improve coupling to radiation modes without introducing nonradiative surface recombination pathways, a triangular lattice photonic crystal in two-dimensions is etched into the top layer of an asymmetric InGaP/InGaAs quantum well structure emitting at 980 nm. Enhanced injection and external efficiency of the LED is demonstrated. Chapter 3 develops methods of laterally steam oxidizing AlAs into A1203 to form large-area wide stop-band one-dimensional Al203/GaAs photonic crystals. The mechanical stability of the high-dielectric contrast interface determines the quality of the photonic crystal and is therefore explored in detail by examining the AlAs steam oxidation process. The A1203/GaAs photonic crystal is integrated with an InP/InGaAs absorber region and used to self-start ultra-short 35 femtosecond pulses in a Cr4+:YAG laser. Chapter 4 develops the design...

New polymeric biomaterial interfaces for biosensor applications

Kim, Heejae
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 133 leaves; 8373299 bytes; 8378865 bytes; application/pdf; application/pdf
ENG
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To fabricate living cell-based immunological sensors, we have examined two PEO-based biomaterials that can be patterned to generate cellular array templates: poly(allylamine)-g- poly(ethylene glycol) graft-copolymer and poly(ethylene glycol) dimethacrylate hydrogel. Poly(allylamine)-g-poly(ethylene glycol) polycation graft-copolymers were designed, synthesized, and characterized in order to combine bio-functionality with patternability on charged polyelectrolyte multilayer surfaces. Polymer-on-polymer stamping (POPS) techniques were used to create micron scale patterned regions on negatively charged multilayer surfaces via direct stamping of these graft copolymers. The long PEG side chains effectively resisted adsorption of antibodies or other proteins, and created a bio-inert area when patterned by POPS. On the other hand, desired proteins can be covalently attached to the graft copolymer by introducing proper coupling agents. Arrays of proteins were produced by either simple adsorption or coupling of proteins onto the graft copolymer patterned surfaces. The protein arrays were utilized as templates in fabricating cellular arrays of non-adherent B cells.; (cont.) Poly(ethylene glycol) dimethacrylate hydrogel precursors were photopolymerized into 3D rmicrowell array templates via micromolding. After the floors of microwells were decorated with antibodies...

Orientation Dependent Ion Beam Mixing of Ta/Si Interfaces

Berky, W; Gottschalk , S; Elliman, Robert; Balogh, A G
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
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Ta/Si interfaces were systematically studied concerning ion beam mixing effects. Tantalum was evaporated on silicon of (1 0 0) and (1 1 1) orientation using the molecular beam epitaxy (MBE) method. The samples were then irradiated with 1.85 MeV and 6 MeV

Electronically coupled complementary interfaces between perovskite band insulators

Huijben, M.; Rijnders, G.; Blank, D. H. A.; Bals, S.; Van Aert, S.; Verbeeck, J.; Van Tendeloo, G.; Brinkman, A.; Hilgenkamp, H.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 04/03/2006
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Perovskite oxides exhibit a plethora of exceptional electronic properties, providing the basis for novel concepts of oxide-electronic devices. The interest in these materials is even extended by the remarkable characteristics of their interfaces. Studies on single epitaxial connections between the two wide-bandgap insulators LaAlO3 and SrTiO3 have revealed them to be either high-mobility electron conductors or insulating, depending on the atomic stacking sequences. In the latter case they are conceivably positively charged. For device applications, as well as for basic understanding of the interface conduction mechanism, it is important to investigate the electronic coupling of closely-spaced complementary interfaces. Here we report the successful realization of such electronically coupled complementary interfaces in SrTiO3 - LaAlO3 thin film multilayer structures, in which the atomic stacking sequence at the interfaces was confirmed by quantitative transmission electron microscopy. We found a critical separation distance of 6 perovskite unit cell layers, corresponding to approximately 2.3 nm, below which a decrease of the interface conductivity and carrier density occurs. Interestingly, the high carrier mobilities characterizing the separate electron doped interfaces are found to be maintained in coupled structures down to sub-nanometer interface spacing.

Multi-phase-field analysis of short-range forces between diffuse interfaces

Wang, N.; Spatschek, R.; Karma, A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 23/12/2009
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We characterize both analytically and numerically short-range forces between spatially diffuse interfaces in multi-phase-field models of polycrystalline materials. During late-stage solidification, crystal-melt interfaces may attract or repel each other depending on the degree of misorientation between impinging grains, temperature, composition, and stress. To characterize this interaction, we map the multi-phase-field equations for stationary interfaces to a multi-dimensional classical mechanical scattering problem. From the solution of this problem, we derive asymptotic forms for short-range forces between interfaces for distances larger than the interface thickness. The results show that forces are always attractive for traditional models where each phase-field represents the phase fraction of a given grain. Those predictions are validated by numerical computations of forces for all distances. Based on insights from the scattering problem, we propose a new multi-phase-field formulation that can describe both attractive and repulsive forces in real systems. This model is then used to investigate the influence of solute addition and a uniaxial stress perpendicular to the interface. Solute addition leads to bistability of different interfacial equilibrium states...

A Dynamic Multiscale Phase-field Model for Structural Transformations and Twinning: Regularized Interfaces with Transparent Prescription of Complex Kinetics and Nucleation

Agrawal, Vaibhav; Dayal, Kaushik
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 29/12/2014
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The motion of microstructural interfaces is important in modeling materials that undergo twinning and structural phase transformations. Continuum models fall into two classes: sharp-interface models, where interfaces are singular surfaces; and regularized-interface models, such as phase-field models, where interfaces are smeared out. The former are challenging for numerical solutions because the interfaces need to be explicitly tracked, but have the advantage that the kinetics of existing interfaces and the nucleation of new interfaces can be transparently and precisely prescribed. In contrast, phase-field models do not require explicit tracking of interfaces, thereby enabling relatively simple numerical calculations, but the specification of kinetics and nucleation is both restrictive and extremely opaque. This prevents straightforward calibration of phase-field models to experiment and/or molecular simulations, and breaks the multiscale hierarchy of passing information from atomic to continuum. We present the formulation of a phase-field model -- i.e., a model with regularized interfaces that do not require explicit numerical tracking -- that allows for easy and transparent prescription of complex interface kinetics and nucleation. The key ingredients are a re-parametrization of the energy density to clearly separate nucleation from kinetics; and an evolution law that comes from a conservation statement for interfaces. This enables clear prescription of nucleation through the source term of the conservation law and of kinetics through an interfacial velocity field. A formal limit of the kinetic driving force recovers the classical continuum sharp-interface driving force...

Enhancing Graphene-derived Materials through Multimodal and Self-healable Interfaces

Liu, Yilun; Xu, Zhiping
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 24/08/2013
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Recent studies have shown that graphene-derived materials not only feature outstandingly multifunctional properties, but also act as model materials to implant nanoscale structural engineering insights into their macroscopic performance optimization. Functionalizing the interfaces between graphene sheets by interlayer crosslinks has been proven to be an effective route to tune the mechanical properties. Here we explore the graphene-derived material with a layer-by-layer structure and multiple crosslinking mechanisms. The effects of multimodal and self-healable crosslinks are assessed in terms of interlayer loading transfer capability. The results show that the brick-and-motar hierarchy and synergetic effects from different crosslinks enable synergetic enhancement in the strength and toughness. The findings here could shed light on the development of high-performance paper-, fiber- or film-like macroscopic materials from monolayer nanosheets with nanoengineerable interfaces.

Electron behavior in topological insulator based P-N overlayer interfaces

Wray, L. A.; Neupane, M.; Xu, S. -Y.; Xia, Y. -Q.; Fedorov, A. V.; Lin, H.; Basak, S.; Bansil, A.; Hor, Y. S.; Cava, R. J.; Hasan, M. Z.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 05/06/2012
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Topological insulators (TIs) are novel materials that manifest spin-polarized Dirac states on their surfaces or at interfaces made with conventional matter. We have measured the electron kinetics of bulk doped TI Bi$_2$Se$_3$ with angle resolved photoemission spectroscopy while depositing cathodic and anodic adatoms on the TI surfaces to add charge carriers of the opposite sign from bulk dopants. These P-N overlayer interfaces create Dirac point transport regimes and larger interface potentials than previous N-N type surface deposition studies, revealing unconventional Rashba-like and surface-bulk electron interactions, and an unusual characteristic distribution of spectral weight near the Dirac point in TI Dirac point interfaces. The electronic structures of P-N doped topological interfaces observed in these experiments are an important step towards the understanding of solid interfaces with topological materials.; Comment: Submitted to Phys. Rev. B. 12 pages, including supplemental material. This is a substantially revised version of arXiv:1105.4794

The net charge at interfaces between insulators

Bristowe, N. C.; Littlewood, P. B.; Artacho, Emilio
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 15/02/2011
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The issue of the net charge at insulating oxide interfaces is shortly reviewed with the ambition of dispelling myths of such charges being affected by covalency and related charge density effects. For electrostatic analysis purposes, the net charge at such interfaces is defined by the counting of discrete electrons and core ion charges, and by the definition of the reference polarisation of the separate, unperturbed bulk materials. The arguments are illustrated for the case of a thin film of LaAlO$_3$ over SrTiO$_3$ in the absence of free carriers, for which the net charge is exactly 0.5$e$ per interface formula unit, if the polarisation response in both materials is referred to zero bulk values. Further consequences of the argument are extracted for structural and chemical alterations of such interfaces, in which internal rearrangements are distinguished from extrinsic alterations (changes of stoichiometry, redox processes), only the latter affecting the interfacial net charge. The arguments are reviewed alongside the proposal of Stengel and Vanderbilt [Phys. Rev. B {\bf 80}, 241103 (2009)] of using formal polarisation values instead of net interfacial charges, based on the interface theorem of Vanderbilt and King-Smith [Phys. Rev. B {\bf 48}...

Orientation-Dependent Transparency of Metallic Interfaces

Xu, P. X.; Xia, K.; Zwierzycki, M.; Talanana, M.; Kelly, P. J.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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As devices are reduced in size, interfaces start to dominate electrical transport making it essential to be able to describe reliably how they transmit and reflect electrons. For a number of nearly perfectly lattice-matched materials, we calculate from first-principles the dependence of the interface transparency on the crystal orientation. Quite remarkably, the largest anisotropy is predicted for interfaces between the prototype free-electron materials silver and aluminium for which a massive factor of two difference between (111) and (001) interfaces is found.

Metallic conduction at organic charge-transfer interfaces

Alves, H. Dias; Molinari, A. S.; Xie, H.; Morpurgo, A. F.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 02/10/2008
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The electronic properties of interfaces between two different solids can differ strikingly from those of the constituent materials. For instance, metallic conductivity, and even superconductivity, have been recently discovered at interfaces formed by insulating transition metal oxides. Here we investigate interfaces between crystals of conjugated organic molecules, which are large gap undoped semiconductors, i.e. essentially insulators. We find that highly conducting interfaces can be realized with resistivity ranging from 1 to 30 kOhm square, and that, for the best samples, the temperature dependence of the conductivity is metallic. The observed electrical conduction originates from a large transfer of charge between the two crystals that takes place at the interface, on a molecular scale. As the interface assembly process is simple and can be applied to crystals of virtually any conjugated molecule, the conducting interfaces described here represent the first examples of a new class of electronic systems.; Comment: 21 pages, 5 figures

Why Some Interfaces Cannot be Sharp

Nakagawa, Naoyuki; Hwang, Harold Y.; Muller, David A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 18/10/2005
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A central goal of modern materials physics and nanoscience is control of materials and their interfaces to atomic dimensions. For interfaces between polar and non-polar layers, this goal is thwarted by a polar catastrophe that forces an interfacial reconstruction. In traditional semiconductors this reconstruction is achieved by an atomic disordering and stoichiometry change at the interface, but in multivalent oxides a new option is available: if the electrons can move, the atoms don`t have to. Using atomic-scale electron energy loss spectroscopy we find that there is a fundamental asymmetry between ionically and electronically compensated interfaces, both in interfacial sharpness and carrier density. This suggests a general strategy to design sharp interfaces, remove interfacial screening charges, control the band offset, and hence dramatically improving the performance of oxide devices.; Comment: 12 pages of text, 6 figures

Wave Scattering by Metamaterial Wedges and Interfaces

Sukhorukov, Andrey; Shadrivov, Ilya; Kivshar, Yuri
Fonte: John Wiley & Sons Inc Publicador: John Wiley & Sons Inc
Tipo: Artigo de Revista Científica
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We outline specific features of numerical simulations of metamaterial wedges and interfaces. We study the effect of different positioning of a grid in the Yee method, which is necessary to obtain consistent convergence in modelling of interfaces with metamaterials characterized by negative dielectric permittivity and negative magnetic permeability. We demonstrate however that, in the framework of the continuous-medium approximation, wave scattering on the wedge may result in a resonant excitation of waves with infinitely large spatial frequencies, leading to non-convergence of the simulation results that depend on the discretization step.

Fractal Analysis Methods for Solid Alkane Monolayer Domains at SiO 2 /Air Interfaces

Knuefing, Lydia; Schollmeyer, Hauke; Riegler, Hans; Mecke, K
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
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A systematic evaluation of various fractal analysis methods is essential for studying morphologies of finite and noisy experimental patterns such as domains of long chain alkanes at SiO2/air interfaces. The derivation of trustworthy fractal dimensions crucially relies on the definition of confidence intervals for the assumed scaling range. We demonstrate that the determination of the intervals can be improved largely by comparing the scaling behavior of different morphological measures (area, boundary, curvature). We show that the combination of area and boundary data from coarse-grained structures obtained with the box-counting method reveals clear confidence limits and thus credible morphological data. This also holds for the Minkowski density method. It also reveals the confidence range. Its main drawback, the larger swing-in period at the lower cutoff compared to the box-counting method, is compensated by more details on the scaling behavior of area, boundary, and curvature. The sandbox method is less recommendable. It essentially delivers the same data as box-counting, but it is more susceptible to finite size effects at the lower cutoff. It is found that the domain morphology depends on the surface coverage of alkanes. The individual domains at low surface coverage have a fractal dimension of ≈ whereas at coverages well above ≈the scaling dimension is 2 with a large margin of uncertainty at ≈coverage. This change in morphology is attributed to a crossover from a growth regime dominated by diffusion-limited aggregation of individual domains to a regime where the growth is increasingly affected by annealing and the interaction of solid growth fronts which approach each other and thus compete for the alkane supply.

Heavy Ion Induced Intermixing at Ta/Si and Ta/SiO 2 Interfaces

Berky, W; Balogh, A G; Elliman, Robert
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
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46.99218%
Systematic ion beam mixing experiments have been performed on Ta/SiO 2 and Ta/Si interfaces. Tantalum was evaporated on silicon and SiO2/silicon substrates by means of molecular beam epithaxy. Samples were subsequently irradiated with 500 keV Si, 100 keV

Printed instructional materials for distance education: interfaces with the language practices; Materiales educativos impresos de educación a distancia: Interfaces con prácticas de lenguaje; Materiais didáticos impressos para educação a distância: interfaces com práticas de linguagem

Albuquerque, Michele Rodrigues de; Silva, Ivanda Maria Martins
Fonte: ETD - Educação Temática Digital Publicador: ETD - Educação Temática Digital
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; ; Pesquisa Empírica; Pesquisa Empírica Formato: application/pdf
Publicado em 05/11/2012 POR
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This paper intends to analyze the production of printed instructional materials for Distance Education, it being understood as a form of distance education students and teachers are physically separated, but united virtually through technological and educational resources. Even with the advances in digital technologies, the print media plays an important role in the processes of mediation between teachers and students. In Distance Education, the physical distance between teachers and students can be minimized, considering the language dialogic in the production of printed instructional materials. The paper will present the key features that guide the production of printed instructional materials on Distance Education. We also discuss concepts such as: a dialogic practice in the production of printed instructional materials and the design of text as a mediator and interactive distance learning.; Pretende-se aqui analisar a produção de material didático impresso para Educação a Distância (EAD), compreendendo a EAD como modalidade em que alunos e professores estão fisicamente separados, mas unidos virtualmente por meio de recursos tecnológicos e pedagógicos. Mesmo com os avanços das tecnologias digitais, a mídia impressa assume papel de destaque nos processos de mediação entre docentes e discentes. Na EAD...