3D printing and additive manufacturing for the industry of the future

Resume : Volatile organic compounds (VOCs) are major air pollutants, which are found especially inside buildings and can be harmful to humans. A lot of efforts are directed towards the development of devices measuring the level of VOCs in ambient air. Commercially available sensors are mostly based on silicon chips including metal oxides to interact with the pollutants at elevated temperatures. In this study we present a microsensor for VOC monitoring fabricated with 3D printing based on two-photon polymerization. The supporting structures as well as the sensing structures are made of photosensitive resin, polymerized during the printing process. A conductive polymer mesh is suspended between two electrodes and the exposure to various organic compounds leads to their uptake and the swelling of the polymer. The geometrical changes of the sensitive mesh cause a change of its electrical resistivity. The metal electrodes are sputtered and their shape can be easily modified during the development of the sensor by using PDMS sputtering masks based on 3D printed masters. This method makes the fabrication of the electrodes faster and easier by avoiding a lithography step. Taking advantage of the high resolution of two-photon polymerization, the sensitive mesh can be precisely shaped to maximize the effect of the VOC uptake on the electrical signal and therefore increase the sensitivity. Using polymer both as a sensitive material and as a structural material allows the fabrication of cheap and light sensors. The 3D printing process affords high degree of design freedom, flexible modification and fast implementation for the sensor development.

Resume : While 3D printing of objects down to the micrometer scale is already well established in research and development, techniques for controlled additive manufacturing at the nanoscale are only few [1]. Based on the progress in recent years, Focused Electron Beam Induced Deposition (FEBID) has evolved into a true 3D nanoprinting technology, allowing mask-less, direct-write fabrication of even complex 3D nano-architectures on almost any material and substrate morphology. The growing availability of different precursor types continuously expand the functionalities of FEBID based structures from electrically over magnetically towards optically active purposes. Together with its 3D ability at the nanoscale, this approach paves the way for applications, which have been very challenging or even impossible in the past [2]. In this contribution, we introduce the audience into 3D-nanopringing via focused electron beams and sketch possibilities and limitations. In the following, we focus on recent advances in accuracy and predict-ability based on local nano-heating effects [3]. As an important step towards a generic 3D printing technology, we discuss simulations on 3D growth and 3D-FEBID software solutions. Finally, we present selected applications of such 3D-nanoprinted structures in research and industry. [1] Hirt et al., Adv. Mater. (2017) 201604211, 1 [2] Winkler et al., J. Appl. Phys. (2019), in print [3] Mutunga et al., ACS Nano (2019), in print

Resume : Focused electron beam induced deposition (FEBID) is an aspiring technology for next-generation direct-write fabrication on the nano-scale. FEBID-based fabrication of mesh-like nano-architectures has already reached a high level of precision, predictability and reliability [1,2], we now take the next logical step towards closed and semi-closed 3D nano-architectures. This opens up numerous possibilities as well as new challenges that will need further research in the future. To gain fundamental understanding of their growth behavior, we studied the dependency of spatial inclination angles on width, height and shape of systematically built 3D structure series, designed with a new pattern generating software we are currently developing. Complimentary heat diffusion simulations (OpenFOAM) revealed the implications of thermal effects, which recently turned out to play a major role [3]. The goal of this combined approach between experiments and simulation is not only to get a closer insight into the underlying mechanisms of 3D FEBID but also to develop a general model for compensation. This will lead to predictable and reproducible fabrication of even complex 3D nano-architectures as essential element on the route towards a generic 3D nano-printing technology for future applications in various fields of research and development. [1] Winkler et al., J. Appl. Phys., 2019, in print [2] Fowlkes et al., ACS Appl. Nano Mat. 1(3), 2018 [3] Mutunga et al., ACS Nano, 2019, in print

Resume : Atomic Force Microscopy (AFM) is an essential tool in research and development due to quantitative 3D surface characterization with sub-nanometer resolution and the possibility to access magnetic, mechanical, optical, electrical or thermal surface properties. In contrast, AFM is analytically blind, which requires complementary techniques such as Scanning Electron Microscopy (SEM). Based on the motivation to combine both worlds, GETec Microscopy Inc. has designed an AFM system for seamless integration in highly space confined SEMs. The core elements of this technology are self-sensing cantilever, which enable electrical readout of the cantilever deflection, eliminating space consuming optical detection systems. In the past, the available measurements modes were restricted to morphological and mechanical characterisation. To overcome this limitation, we jointly develop new nano-probe concepts to access electric, magnetic and thermal surface properties. This talk starts with an introduction of our nanoprobe fabrication, using 3D nanoprinting via focused electron beam. We present our latest 3D nano-thermistor concept in detail. This range from simulation of the most stable geometry followed 3D fabrication over mechanical tuning for stable AFM operation towards thermal probing. As demonstrated, a 3D nano-thermistors allow for scan speeds up to 80 µm/s and quantitative temperature measurements with an accuracy of ±1 C° and fast dynamic responses of about 32 ms/K.

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Resume : 4D printing is an emerging technology where a ‘smart material’ can respond in a pre-programmed way to external stimuli. Significant advances in computer aided design, additive manufacturing and materials science have opened up the possibilities of self-assembly systems, and complex geometries with multi-functional properties. The current materials capable of ‘4D printing’ deliver exciting proof of concepts for future designs, however further development and qualifications are needed for their use in the space environment. The reliability of 4D printing materials for space applications is assessed, together with a consideration of the impact due to long-term storage on the ground and its effect on 4D printing functionalities. A FDM high temperature (420oC) dual extruder which is capable of printing space qualified materials and other high strength thermoplastics, is being utilized to print a variety of proof of concept composite structures. Up to now a study of all printing parameters for each type of filament such as optimal printing speed, printing direction, the design; length /angle, and printing temperatures has been completed. Two phenomena occur when heating bi-layer materials with different CTE and modulus. Once heated the modulus of the stiffer polymer decreases at its glass transition temperature and the internal stress stored in the combined printed layer is released. The difference of the CTE between the materials increases the bending motion further, in line with the printing direction. 4D printing could feature in numerous aspects in the design of a satellite, but more specifically in the design of a deployment mechanism which has fewer components, is simpler to control and has a lower risk of mechanical failure. Deployment mechanisms may only have to operate once or multiple times throughout their service life. The reliability and precision of deployment is paramount, thus understanding how 4D printed materials behave and how the fixity, repeatability and reversibility is affected by microgravity, radiation exposure and extreme temperatures is a significant challenge. In this paper several examples of on-going 4D printing work at ESA will be presented. It will also highlight the specific challenges of using such materials in a space environment.

Resume : Focused Electron Beam Induced Deposition (FEBID) is a very promising technique for 3D-printing at the nanoscale, as it enables mask-less, direct-write fabrication of 3D nano-architectures. For precision and reliability, local precursor coverage is of highest importance, as it determines the incremental growth rates and by that reproducibility. Recently, reduced residence times of precursor molecules due to local beam heating was demonstrated, which explains observed stability problems for larger 3D structures [1]. While FEBID at cryogenic temperatures were studied before [2], we here focus on temperatures from room temperature down to 1 °C. For that, we designed, fabricated and tested a variable temperature stage using Peltier elements, which allows us to investigate the precursor dynamics in a range of +/- 30 K around room temperatures. The results do not only explain the origin of previously observed growth rate variations without any heating/cooling but also point out the importance of temperature stability for precision and reliability during 3D nanoprinting. We present FEBID experiments in dependency on temperature, which clearly shows a massive growth rate increase when approaching 1 °C. The focus lies on quasi-1D pillars and 3D multi-pod architectures, to demonstrate the boost in deposition rates at low temperatures. References: [1] Mutunga et al., ACS Nano 2019, in print [2] Bresin et al., Nanotechnology, 24, 2013

Resume : The fabrication of micro and nanopatterned surfaces on polymers have been an area gathering a lot of interest from research and industrial parties. On the one hand, alternatives involving direct writing with charged particles or different kinds of illumination sources have demonstrated to provide an enormous design flexibility and modularity, but with a low throughput. On the other hand, industrial fabrication techniques such as injection moulding, while allowing a high throughput, were proven to bring an extremely low flexibility for changes in the fabrication pattern. In this work we will introduce the parallelization of a direct laser writing technique like two photon induced photopolymerization (TPP) as fabrication technique that may combine both; high throughput and fabrication flexibility. Diffractive Optical Elements (DOEs) were used for splitting the original laser beam into arrays of 3×3,11×11, 51×51 and 101×101 parallel beams. An ultrashort pulsed laser (280 ps) emitting visible radiation (515nm) was used for the photopolymerization of a commercial photoresist (Ormocomp©). In this way, large patterned areas were produced by single exposure steps with the parallel laser beams. Very well defined structures were fabricated with the 3×3 and 11×11 DOEs, proving the reliability of the technique. However, the proximity effect limited the definition of the structures fabricated with the larger DOEs. Still, a very high fabrication throughput was achieved for the fabrication of repetitive patterns with a high design flexibility.

Resume : Directed-energy-deposition (DED) Additive manufacturing (AM) has many advantages for production of large scale engineering structures with significantly reduced manufacturing costs and lead times. This has proven particularly true for the Wire + Arc AM (WAAM) process. The presentation will cover how, based on 12 years of intensive world-leading research into all aspects of WAAM, we have printed critical airframe components up to 6m in aluminium and 2m in titanium, by developing a mature industrial ecosystem, which can also be translated to other DED processes. We will present the key elements of this system (software, machines, innovative sensors), and how it has been applied to large scale metallic parts (flanges, wing ribs, pressure vessels, landing gears, etc). The business benefits will be explained, with the support of industrially-relevant metrics, such as reduction of lead times from over a year to a few weeks, and reduction in cost of as much as 60%. A roadmap for future development, including WAAM commercialisation and industrialisation, will be announced.

Resume : NiTi alloy is the most used shape memory alloy used in a wide variety of applications such as in actuators, aerospace, automobiles and biomedical industries. The high strength, better corrosion resistance and biocompatibility of this material makes it a suitable candidate for biomedical application as stents, orthopedic implants, root canal instruments, and orthodontic archwires. In the present work, microstructure evolution and the consequent property development of an additively manufactured (Laser Engineered Net Shaping (LENS)) NiTi is investigated systematically. Effect of laser energy density on modifying the physical and mechanical properties have been included in the study. Increasing laser power increases microstructure homogeneity, as well as a decrease in porosity, have been observed. Austenite at room temperature is confirmed by DSC analysis which shows the materials intent to show pseudoelastic behavior. Furthermore, the effect of porosity developed during deposition plays a vital role in modifying mechanical properties. The mechanical properties are evaluated using indentation (spherical and Berkovich) and uniaxial tensile testing. Optimized processing conditions in terms of laser scan speed and rate are identified that yields the best pseudoelasticity. Indentation stress-strain curves are generated further from the nanoindentation results that closely match with the tensile stress-strain curves. Indentation size effect, as well as the size effect of tensile testing, have also been studied.

Resume : In the context of cost reduction, the increase of power to mass ratio of aircraft engines is a key issue that requires the development of light-weight, high temperature alloys. Due to their low density and strong hot mechanical properties and corrosion resistance, γ-TiAl are good candidates to replace nickel-based superalloys in the low-pressure turbine of the aircraft engines. The conventional processing route strongly limits the γ-TiAl achievable geometries and direct additive manufacturing, such as the DED-CLAD® process, is a good substitute to fabricate large scale complex functional parts. Due to their low thermal shock resistance, the key issue for their direct additive manufacturing is the control of the thermal gradient during and after powder deposition. In this work, a high temperature heating device with integrated control of the heating and cooling rate has been used. The model material is a first generation TiAl alloy, the composition of which is Ti48Al48Cr2Nb2, produced by gas atomisation. By using a 400 and 900°C heated substrate, a process operating point has been identified, which allowed to build massive blocks. They show very few unmelted particles, some micron-sized pores and a good cohesion to the substrate. In this work, the effects of the preheating temperature have been investigated. The beneficial effects of using temperatures above the brittle/ductile transition on the as-deposited microstructure soundness and mechanical properties are discussed.

Resume : The Directed Energy Deposition - Construction Laser Additive and Direct (DED-CLAD®) technique is a free-form metal deposition process, which allows generating near-net shape structures through the interaction of a powder stream and a laser beam. With increasing industrial interest and significance of DED-CLAD®, the importance for profound process knowledge increases, so that large scale parts can be manufactured. Therefore, three different numerical thermal models for DED-CLAD® are presented named as Material Activation, Arbitrary Lagrangian Eulerian (ALE) free surface motion (horizontal) and Arbitrary Lagrangian Eulerian free surface motion (vertical) that allows a detailed study of the temperature evolution in the build part. Considering thin wall builds, numerical results obtained with COMSOL Multiphysics software are successfully compared with experimental data available in literature such as melt-pool dimensions, and thermocouple temperature measurements. Furthermore, a possible way to reduce the computation time and to increase the accuracy is also proposed. Keywords: DED-CLAD®, LMD, ALE, modeling, Simulation, Heat Source, Additive manufacturing, Material Activation

Resume : Additive Manufacturing, (AM), the industrial version of 3D printing is changing the way of manufacturing and delivering products. Laser metal deposition (LMD), a promising technique that falls in the category of AM direct energy deposition (DED), consists in fuse materials by melting as they are being deposited. Usually AM techniques was used when the component can´t be built by traditional processes or for in some cases, properties improvement, as in this case. The main goal of this work is to study the influence of process parameters and path planning on mechanical properties and microstructure. Samples made of stainless steel 316L powder were manufactured with a Trudisk Laser of 16kW and a BEO D70 head (TRUMPF) and a GTV powder feeder. The process parameters were maintained constant while different trajectories were explored, then we did the opposite. Sample microstructure were studied trough Optical and Scanning Microscopy. The cooling rate was studied with an infrared camera (Flir) and an on axis infrared sensor to measure the cooling rate of solidification area. On the other hand, microhardness measurements were also made on samples on the building and the scanning direction while tensile specimens were extracted from different planes and tested following the ASTM E8 Standard.

Resume : The interaction of the fast moving laser beam and the metal powder during Laser Powder Bed Fusion (LPBF) can result in strong process fluctuations leading to the formation of weld defects, which significantly reduce the quality of the generated parts. In order to analyse these process fluctuations during the LPBF-process a model arrangement was set up, which allowed the simultaneous use of different monitoring tools for the observation of the interaction of the laser beam and the powder bed as well as the surrounding area. High-speed imaging in the visible wavelength range with high magnification and framerates of up to 10,000 fps was used to observe the interaction of the laser beam and the powder bed. High-speed imaging in the infrared wavelength range with up to 1,500 fps was used to analyse the temperature distribution and the solidification of the melt pool and the previous vectors. Additionally, off-axis Pyrometers and several on-axial diodes were used and the information obtained from the different sensors was compared. The results of the high-speed online process monitoring will be presented and discussed for each monitoring tool. Furthermore, it will be shown that the use of a closed-loop control system may be advantageous to achieve high part qualities.

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Resume : In recent years Additive Manufacturing (AM), commonly called 3D printing, is of particular interest to the aerospace and biomedical device industries, due to the ability to manufacture low-volume, complexly-shaped parts with fine structures and gradient mechanical properties. Therefore, it is desirable to obtain sufficient rendering accuracy and surface quality of additively manufactured objects. In view of the nature of AM, unmelted powder particles become attached to each part’s outer surface. In order to obtain the required surface finish, those particles must be removed by postprocessing methods. In this study chemical polishing for 3D printed titanium and its alloys were studied. For each material, different concentrations were selected and investigated. As a result HF-HNO3 solutions for pure titanium as well as titanium alloys were determined in order to obtain the best surface quality and fabrication that is accurate to the original CAD dimensions of the part. Depending on a part geometry, concentration of the solutions and the time of polishing up to 30% of mass loss of the samples have been observed. Scanning Electron Microscopy of samples surface revealed the removal of powder particles and surface smoothing. Fabrication accuracy was determined by Micro Computed Tomography scanning of the samples before and after chemical etching and it showed high improvement of dimensions accuracy of the CAD model of chemically polished samples regarding to as- fabricated samples.

Resume : The centrifugal atomization technology was developed for the fabrication of nuclear fuel powders such as Uranium Silicide and Uranium Molybdenum alloys by Korea Atomic Energy Research Institute (KAERI). The centrifugal atomization technology has several advantages compared to comminuting method for the powder fabrication. The powder which made by the atomization has very uniform and fine spherical shape as well as high purity with high yield rate, over 95%. KAERI has supplied the atomized powders to research institutes and commercial companies around the world such as ANL, INL, BWXT, CEA, CERCA, SCK∙CEN, and CNEA for the development of research reactor fuels. Due to the good external characteristic of the centrifugally atomized powder, it is very suitable for additive manufacturing technologies with metallic materials.

Resume : Atomic Force Microscopy (AFM) is an essential tool in research and development due to quantitative 3D surface characterization with sub-nanometer resolution and the possibility to access magnetic, mechanical, optical, electrical or thermal surface properties. In contrast, AFM is analytically blind, which requires complementary techniques such as Scanning Electron Microscopy (SEM). Based on the motivation to combine both worlds, GETec Microscopy Inc. has designed an AFM system for seamless integration in highly space confined SEMs. The core elements of this technology are self-sensing cantilever, which enable electrical readout of the cantilever deflection, eliminating space consuming optical detection systems. In the past, the available measurements modes were restricted to morphological and mechanical characterisation. To overcome this limitation, we jointly develop new nano-probe concepts to access electric, magnetic and thermal surface properties. This talk starts with an introduction of our nanoprobe fabrication, using 3D nanoprinting via focused electron beam. We present electric and magnetic nanoprobe concepts briefly, followed by our latest 3D nano-thermistor concept in more detail. This range from 3D fabrication over mechanical tuning for stable AFM operation towards thermal probing. As demonstrated, a 3D nano-thermistors allow for scan speeds up to 80 µm/s and quantitative temperature measurements with an accuracy of ±1 C° and fast dynamic responses of about 32 ms/K.

Resume : 3D printing or additive manufacturing is expected to revolutionize the manufacturing of components in short period time. Specially, these techniques can be used various application fields, which are making prototypes for electronics, aerospace, automotive, and so on. In order to 3D printing technology to be applied to an electronic device or an automobile, a thermal-mechanical stability over 300oC must be secured. However, almost of commercialized 3D printers do not provide thermal-mechanical stability over 300oC due to thermoplastic properties. Therefore, we have designed a hybrid organic-inorganic composite material suitable for high temperatures stability and successfully made thermoplastic filaments using a mini-extruder machine for fused deposition modelling (FDM) printer. Also, we studied various composite materials, which are glass fiber, carbon fiber, and modified Basalt fiber for improving thermal, mechanical. The house-made filaments, including various composites, and 3D printed samples were measured by thermal mechanical analyzer (TMA), bending strength with micro-universal testing machine. Surface morphology and x-ray tomography of those are measured by scanning electron microscope (SEM) and X-ray microscopy (XRM). We will present the detailed experiment results and other analysis results for improved 3D printing materials. This work was partly supported by Institute for Information & communications Technology Promotion (IITP) grant funded by the Korea government (MSIT) (No.2018-0-01164, Development of high-speed(10g/hr) deposition source for OLED electrode) and Electronics and Telecommunications Research Institute (ETRI) (No.19ZB1900, Developments of organic-inorganic hybrid polymer material and packaging process for 3D Printing over 350 ℃)

Resume : X-ray computing tomography (XCT) is used to probe the fresh and recycled metallic powders for 3D printing applications. We have used XCT technique to characterize the particle size distribution and pore size distribution in both virgin and recycled powder and have shown that the recycled powder has a broader size distribution and the pore formation is more probable in a broad range of sizes from 2-10um. The particle size changes during the manufacturing of the parts and we can observe a broader range of sizes from 10-30um. XCT is a powerful technique to reveal also the pore formation inside the particles although the particles seem to be unaffected and have a perfectly spherical shape or clean surface. This understanding greatly serves to reuse the powders in the 3D printing process in order to reduce power consumption. There is no such compelling technique to visualize the porosity formation inside the powder particles in 3D format. Our characterizations indicate that the powder collection from the 3D printing machine must follow a protocol to separate the most affected and least affected particles as possible in order to retain the highly desired mechanical properties of the parts printed from recycled powders. XCT method has greatly shown that the in or out-diffusion of chemical elements can be a reason for pore formation inside the particles during the 3D printing process.

Resume : The degree of crystallinity hence mechanical properties polyetheretherketone (PEEK), strongly depends on the processing parameters and the post-process thermal treatment. The aim of this work was to determine influence of the size and the filling degree of the 3D printed by FDM (Fused Deposition Modeling) technology PEEK subjected to thermal post-processing. For this purpose, three sizes of cylindrical shapes were printed: 1x0.1 cm; 2.5x2.5 cm; 5x5 cm with two filing degree levels: 50 and 100%. Tested samples were annealed to increase their degree of crystallinity to create an element with the same content of crystalline phase in the entire volume and minimize the anisotropy of mechanical properties. The degree of crystallinity was specified by determining the enthalpy of the crystalline phase melting by DSC (differential scanning calorimetry). The surface of the samples and their internal areas were analyzed. Our studies have shown that post-process thermal treatment of 3D printed PEEK increase the degree of crystallinity, but the content of the crystalline phase may vary depending on the sampling site. This effect can be caused by different heat conduction during fabrication and heat treatments. Results of our study showed that there is a high need to optimize the thermal post-processing of elements with different architectures manufactured using the FDM method from PEEK.

Resume : Sanitary ceramic ware usually present small visible defects in the outer glaze layer that hinder their commercialization. Nowadays, the solution to remove these defects requires a further firing of the entire piece. This process involves high energetic costs and high CO2 emission. This way, the development of a technological solution based on the localized repair of defects is strongly desirable. Laser technology accomplishes this requisite, since it provides a highly localized heat source, thus enabling obvious economic and environmental advantages. In this work, the interaction between a continuous wave CO2 laser and the glaze material to be repaired was studied. Different experimental conditions were explored, including several repair materials, distinct laser heating cycles, laser powers and intensities, among others. Although local glaze melting was successfully attained, some cracks appeared in the repaired area due to high thermal stresses. To attenuate this phenomenon, an additional diffused irradiation heat source from an infra-red lamp was explored. This combination significantly reduced the number of cracks and their dimensions in small samples, strongly reducing the defect perceptibility. However, in real pieces this approach leads to fatal damage by breakage due to unavoidable strong thermal stresses build-up. In alternative, a second firing at lower temperature was considered, using tailored compositions for the glaze filling of the defects.

Resume : Polyetherimide (ULTEM) resin offers superior mechanical properties for a thermoplastic in fused deposition modeling (FDM) technology. Thermoplastic gears used at high velocity and loading in machine run is occurred to damages as wearing and fracture gear. In recent years, as a result of improvements in 3D printers, very complex and diverse parts can be manufactured. In this study, gears were produced by using additive manufacturing by using ULTEM material and damages of thermoplastic gears produced with FDM method, tested at the loading. In addition, thermoplastic gear and thermoplastic pair gear was investigated. As a result of this study, wearing depth occurred at the gear profile under the SEM microscope was examined. The opportunities and limitations of ULTEM material for the fabrication of gears are discussed in this paper.

Resume : Over the past 20 years, the interest in organic and printed electronics has increased exponentially. Low-cost printed electronics seek to minimize the area limitations and number of steps associated with conventional silicon processing for applications that do not require high performances [1]. By using printing technologies, the process becomes all-additive without the need of expensive lithography or vacuum processes, resulting in a reduction of production costs. Furthermore, the development of novel multi-functional nanocomposites materials has gained tremendous research interest on using low-cost and renewable raw materials, to produce sustainable, biodegradable, and eco-friendly biomaterials to be used in electronic applications [2]. In this work, organic rectifying diodes fabricated by means of inkjet printing on nanopaper environmentally friendly substrates are presented. Figure 1a shows the scheme of the proposed structure: following a work recently published by our group [3], plastic substrates and bottom metal electrodes were substituted by the conductive nanopapers for the fabrication of organic rectifying diodes. Nanocellulose changes its electrical properties from being an insulator to a semiconductor and, eventually, becoming a conductor by the addition of conductive fillers [4]. Conductive nanopapers were obtained from two different cellulose pulps (high-purity softwood cellulose pulp CNF5 and eucalyptus pulp CNF15) adding conductive polymers (polythiophene (PT2, PH500) and polypyrrole (PPy) or Multi-Walled Carbon NanoTubes (MWCNTs). Poly-4vinylphenol (PVP), an epoxy insulator (SU8), and high permittivity (HK) Epoxy/Nanosilica insulator (UTDots) were investigated as the polymeric insulator layer. A commercial amorphous polymer (Merck Lisicon® SP400) was employed as the p-type semiconductor. The top electrodes were patterned using a commercial silver conductive paint (SCP03B). The quality of the printed film was highly affected by the roughness of the nanopapers. In some cases, a non- homogenous insulator layer results in a short-circuit through the structure. Figure 1b shows the best results obtained employing CNF5 as the substrate. Rectification Ratio (RR) is defined as the ratio of the maximum forward current to the maximum reverse current registered at the same voltage. The electrical performances of the diodes seem to be more dependent on the choice of the insulator than on the nanopaper formulations. The ternary formulation with the combination of PH500 mixed with PPy as substrate and UTDots as the insulator showed a maximum forward current of 2µA and a maximum reverse current of 1nA (Figure 1C). As a result, extremely high RR value was obtained (2000).