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Intelligent Micro-Nano-Fabrication INTELLIGENT MICRO-NANO-FABRICATION Prof. PhD Eng. EurEng. Gh. Ion Gheorghe1, PhD Stu...

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Intelligent Micro-Nano-Fabrication

INTELLIGENT MICRO-NANO-FABRICATION Prof. PhD Eng. EurEng. Gh. Ion Gheorghe1, PhD Student Iulian Ilie2 General Manager– INCD Mechatronics & Measurement Technique, Bucharest Associated Prof. in U. Valahia of Târgovişte, U.T.M Bucharest and U. P. Bucharest Scientific Doctorates Coordinator in Doctoral School of Mechanical Engineering, U. V. of Târgovişte Corresponding Member of the Academy of Technical Sciences in Romania 2 INCD Mechatronics & Measurement Technique, Bucharest 1

Abstract:Innovations in the field of intelligent micro-nano-fabrication created unique opportunities for micro-nano-products for micro-nano-processing on micro and nano scale micro-nano-structures. This micro-nano-size range is applicable to new electronic, optical, magnetic, mechanical, chemical and biological micro-nano-devices, to micro-nano-sensors, for control, etc.. Important techniques used to manufacture micro-nano-fabrication structures occur in a range from a few microns to a few nanometers. Important steps have been taken in the field of micro- and nano-structures by developing microcomponents of complex organic structures and micro-components of micro- and nano- polymers and dendrimers, with high micro-mechanical and micro-optic properties by applying new advanced technologies and an ultra-precise architecture at micro and nano level. Trends regarding these micro- and nano-components, refer to future research for obtaining new micro- and nano-technological steps, to address the new blocks of copolymers in molecular and atomic compositions, to address the new new nano-crystalls for obtaining new method, semiconductors, magnets, by colloidal chemical processes and micro-technologies and condensed matter physics. Obtaining new materials, also as a future trend, has been driven by scientific discoveries in which the most important was the discovery of "carbon nanotubes", which applies in building matrices for the discovery of new materials, benefitting not only from the construction, topology of interatomic bonds, but also from the absence of surface effects, together with excellent electrical, optical and mechanical properties. Keywords:micro-nano-fabrication, micro-nano-structures, micro-nano-mechatronics.,

1. Introduction By approaching new micro- and nano-technologies through a controlled process for obtaining microparticles, new micro- and nano-scale structures can be obtained in various fields of materials, particularly in ceramics, in various forms, such as clusters, characterized by a unique morphology when it comes to fractal dimension, single bond energy and the coordination number. Processing micro- and nano-structures depends mainly on advanced developments of "auto-assembly methodologies", that further allow the development of "methods for obtaining micro- and nano-structures." In this respect, micro- and nano-structure design is based on the application and implementation of microand nano-technologies for obtaining micro-lithography templates and samples meant to develop new methods and ways of producing, assembling and binding macromolecules and nano-objects. The discovery of new bio-compatible micro- and nanomaterials, with very sophisticated properties, depends more and more on their synthesis by new approaches, type"bottom-top", borrowing a lot of supra-molecular chemistry techniques, colloidal techniques, soil-gel techniques, genetic engineering tehniques, biological /

molecular bio-chemistry techniques, overlapping the new methods of manipulation and synthesis with laser beams, etc.. The evolution of intelligent mechatronic nanoprocessing micro-systems or intelligent mechatronic micro-systems with nanometric and sub-nanometric precision has seen spectacular shifts, as the new principles of micro- and nano-processing, the new principles of micro- and nano-constructive solutions, the new smart materials with superior (physical, chemical, mechanical, tribological, etc..) properties and the new approaches for micro- and nano-sized products were discovered. The evolution of intelligent mechatronic nanoprocessing or processing micro-systems has also experienced dramatic shifts in terms of the accuracy of nano-processing, leading to precision and accuracy below 1 nm. Research work from all over the world have adressed the new micro- and nano-technology that have lead to new mechatronic intelligent technological microsystems appropriate for the new current requirements, such as the minimization of systematic and random , the optimization of the process capability index and the systematization of nano-technology. Of this research work from all the world, we highlight

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Intelligent Micro-Nano-Fabrication the following: • intelligent mechatronic micro-systems for processing silicon plates; • intelligent mechatronic micro-systems for integrated circuits assembly--processing; • intelligent mechatronic micro-systems for corrosion in dry process and wet process; • intelligent mechatronic micro-systems for mask processing; • intelligent mechatronic micro-systems for disc printing; • etc. As a further evolution, intelligent mechatronic nanoprocessing or processing micro-systems will head to higher atom by atom processing nano-technologies. 8.2 Micro-nano-technologies for intelligent manufacturing Micro-nano-fabrication µnmechatronic techniques are adapted for the fabrication of mechatronic devices within the range of 1 µm - 1 nhm. Nano-structures provide a tool for studying the electrical, magnetic, optical, thermal and mechanical properties of matter, at nanoscale.

These include important quantum mechanical phenomena (such as conductance quantification and Coulomb blockade) arising from the limitation of electrical charge transporters in structures, quantum dots, fig. 1. From a practical perspective, the use of nano-structures in electronics / optics and sensors can lead to significant improvements in performance. In the field of devices, the investigators relied on manufacturing nanometer-sized transistors, in anticipation of the technical difficulties provided by Moore's Law for a resolution of more than 100 nm. In addition, optical sources and detectors with nano-sized dimensions have improved features that are not achievable in larger devices (lower threshold powers, improved dynamic behavior and improved wavelenght of line emission in quantum dots lasers). These improvements create major opportunities for the next generation of communication and computing devices. In the field of sensorics, the decrease in size beyond conventional optical litography can provide an improved sensitivity and selectivity.

Fig. 1. Important quantum structures: a) quantum cavity, b) wire, c) quantum dots. The various mechatronic nano-fabrication techniques nanofabricare mechatronic techniques can be divided into top-down and buttom-up teniques. The first approach starts with a thin film or bulk material which removes selective regions in order to manufacture nano-structures (similar to microprocessing techniques). The second method is based on molecular recognition and self-assembly and used to manufacture nano-structures from smaller pieces (molecules, colloids and groups). The top-down approach is a branch of standard lithography techniques 72

micro-processing. The bottom-up approach, on the other hand, is more strongly influenced by chemical engineering and materials science and is based on fundamentally different principles. Therefore, five major mechatronic nano-fabrication techniques will be presented, including: i) fabrication with electron beam and nanoprint ii) force engineering and epitaxy iii) mechatronic sample scanning techniques iv) self-assembly and template fabrication; v) chemical techniques for the fabrication of nano-particles and nano-wires.

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Intelligent Micro-Nano-Fabrication 2.μnFabrication with electron beam and nano-print There are various important litography techniques used in micro-nano-fabrication and MEMS. These include various forms of UV lithography (normal, active and extreme) and X-ray. Due to the lack of resolution (for UV) or difficulties in mask making and sources of radiation (X rays), these techniques are not suitable for nano-scale fabrication. Electron ray lithography is an attractive alternative technique for making nanostructures. It uses an electron beam to expose an electron-sensitive coating layer such as polimetilmetacrilate (PMMA), dissolved in trichlorobenzene (positive) or policlorometilstirene (negative). The electron beam gun is usually part of a scanning electronic microscope (SEM), but transmission electron microscopes can also be used. While Ȧ wavelengths are easily reached, electron scattering in the protective layer limits the resolution that can be achieved to > 10 nm. Beam control and template generation is done through a computer interface. Electron beam lithography is serial and therefore has poor results. Although this is not a major concern when manufacturing devices used in the study of fundamental micro-physics, it severely limits nano-fabrication on a

large scale. Electron beam lithography, in connection with the lifting, etching and electro-deposition processes can be used for obtaining various nano-structures. A new interesting mechatronic technique that fights back the serial and small limitations electron beam lithography for manufacturing nanostructures is known as nanoimprint technology. This technique uses a stamp (template) made up of a strong material and manufactured using electron beams to punch and deform a polymer protective layer (coating). This is usually followed by a reactive ion etching phase meant to transfer the template to the substrate. This technique is superior economically as a single stamp can be used repeatedly to manufacture a large number of nano-structures. Figure 2 shows a scheme of nano-imprint manufacturing. First, a stamp from a hard material (like silicon or SiO 2) is created using electron beam lithography and etching with reactive ion. Then, a substrate coated with a protective layer is stamped and, finally, an anisotropic RIE (reactive ion etching) is performed to remove the residues from the protective layer, in the stamped area. At this point, the process is complete and the substrate can be stamped or, if metal structures are used, the metal evaporates and the lifting is done.

Fig. 2. Nano-imprint manufacturing scheme is cooled below T g before the stamp is removed. The coating used in nanoimprint technology can Similarly, UV and heat resistant coatings are be thermoplastic, a UV-curable polymer, or a heat completely cleaned before the stamp is separated. resistant polymer. The available resolution in nano-imprint For a thermoplastic coating (such as PMMA), technology is limited by the strength of both the powder the substrate is heated more than the glass transition and the polymer, and may be of 10 nm. temperature (T g) of the polymer before stamping and it The Romanian Review Precision Mechanics, Optics & Mechatronics, 2014, No. 46

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Intelligent Micro-Nano-Fabrication A nanoimprint technique recently used for stamping a silicon substrate in less than 250 ns using XeCl laser (308 nm) and a quartz mask (LADI - laser assisted direct imprint), fig. 3.

Fig.3. Very fast silicon nano-print using a XeCl laser Figure 4 shows the SEM micro-diagrames of the quartz print and the silicon substrate printed with lines of 140 nm obtained using LADI. Nano-print lithography processes were also modified for nano-fluid channel fabrication (for manipulating DNA) and multilayer polymer structures. Figure 5 shows a cross section of nano-fluidic channels fabricated using imprint lithography.

3. μnFabrication quantum structure using epitaxis on moulded substrates Precise atomic deposition techniques like molecular beam epitaxy (MBE) and chemical deposition of metal-organic vapours (MOCVD) have proven to be useful means for the fabrication of confined quantum structures and devices (including quantum source lasers, photodetectors and resonant unnel diode). Although quantum sources and super-structures are structures that are the most suitable for these techniques (Fig. 1a), quantum wires and quantum dots were also made by adding additional steps such as etching or selective growth. Quantum cavity and super-structures fabrication using epitaxial growth is a mature and well developed field. Various ways were used to manufacture wires and quantum dots using epitaxial layers. The simplest method involves electron ray lithography and etching a epitaxially grown layer (such as InGaAs on a GaAs substrate). Due to damages and / or contamination occurring during lithography, this method is very suitable for the active fabrication of the device (of lasers with quantum dots, for example). Various other methods involving epitaxial layers growth over uneaven surfaces as side-stair, split-ende and shaped substrate were used to fabricate quantum wires and dots without the need for the lithography and etching of the quantum structure. These templates of the uneaven surace can be produced in a variety of ways, such as etching through a mask or split along the crystallographic planes.

Fig.4. a, b. SEM Micro-diagrames of: a. a quartz template and b) a silicon surface printed using LADI

Subsequent epitaxial growth on top of these structures results in a set of planes with different growth rates depending on the geometry or surface diffusion and adsorption effects. These effects can increase or limit the growth rate in various planes, resulting in shaping and limiting of lateral epitaxial layers deposited and the formation of quantum wires (in channel V) and dots (in inverted pyramids). Figure 6 shows a schematic section of an InGaAs quantum wiresfabricated in a V channel of InP. As can be seen, the growth rate on the sidewalls is less than in the surfaces from the top and the bottom. Therefore, a thinner InGaAs layer from the basis of the V channel forms a quantum wire limited at the edges with a thinner layer with a larger gap between the bands.

Fig.5 Solar rays of a nano-fluidic channel using nanoimprint lithography 74

Figure 7 shows a quantum wire formed using epitaxial growth over a dielectric planar shaped substrate. Quantum cavity creation isnrelatively eassy using any of these techniques; however, in order to create wires and quantum dots, electron beam lithography is still necessary to mold channels and window templates.

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Fig. 6. (A) Fabricated InGaAs Quantum Wires in a V channel of InP and (B) AlGaAs quantum wire fabricated by epitaxial growth on a masked GaAs substrate 4. Quantum structure μnfabrication using selfassembly induced by bending A more recent mechatronic technique for manufacturing quantum wires and dots involoves selfassembly induced by bending. „Self-assembly” is a process where a 2D curved system decreases in energy by changing a 3D morphology. The combination of materials most commonly used in this technique is the In x Ga 1-x As / GaAs system, which offers a large network mismatch (7.2% between InAs and GaAs), although the Ge dots on the Si substrate have attracted attention recently. This method is based on network mismatch between the epitaxial layer and its substrate, resulting in the formation of a multitude of quantum dots and wires. Figure 8 shows a scheme of selfassembly process induced by bending. When the network constants of the substrate and the constants of the epitaxial layer are markedly different, only the first few monolayers deposited epitaxially crystallizes in curved layers in which network constants are equal. When a critical thickness is reached, a significant bending occurs in the layer, resulting in breaking the spontaneous formation of ordered structures and spontaneously distributed islands with regular shapes and similar sizes. This growth is usually known as Stranski-Krastanow mode. The size, separation and height of the quantum dot depends on deposition parameters (total amount of material deposited, growth rate and temperature) and the combinations of materials. As one can see, this is a very convenient method to grow perfect crystalline nanostructures over a large area without lithography or etching. A major drawback of this technique is the random distribution of quantum dots. This technique can also be used in the fabrication of quantum wires by relaxing the bending at the ends of the phase.

Fig. 7. Stranski-Krastanow growth method, (A) 2D wett layer, (b) increasing the raw side and breaking, (C) coherent 3D self-assembly 5. Sample scanningμntechniques The invention of sample scanning microscopy (SPM) was a revolution in imaging and spectroscopy at atomic scale. In particular, scanning tunneling microscopes (scanning through tunneling) and atomic force microscopes (STM and AFM) have applications in physics, chemistry, materials science and biology. The ability to perform atomic-scale manipulation, lithography and nano-processing using such probes has been considered from the beginning and has evolved considerably in the last decade. Sample scanning microscopy systems involve the controlof the movement of an atomic sharp tip near or in contact with a surface with sub-nanometer accuracy. Piezoelectric positioning systems are usually used to achieve such precision. High resolution images can be obtained by scanning tips over a surface, while monitoring the tip-surface interaction. In tunnelling scanning microscopic systems, a polarized voltage is applied to the sample and the tip is positioned close enough to the surface for a tunneling current to develop across the hole (Fig. 8a). Because this current is sensitive to the distance between the tip and the surface, scanning the tip in the xy plane while recording the tunneling current allows drafting surface topography with atomic scale resolution. In a more common operation, an amplified current signal is connected to the piezoelectric positioning system on the z-axis by a reverse loop connection, so that the current and the distance are kept constant during scanning. In this configuration, the surface topography image is obtained by recording the vertical position of the tip in each xy position. The STM works only for conductive surfaces and establishes a tunneling current. Atomic force microscopy, on the other hand, provides a conductive surface observation and conducting.

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Intelligent Micro-Nano-Fabrication In AFM, the tip is attached to a cantilever is flexible and brought into contact with the surface (Fig. 9b). The force between the tip and thesurface is detected by sensing the beam deflection in the console. A topographic image is obtained by plotting the surface deviation as a function of the x-y position. In a more common operation, a loop with reverse connection is used to maintain a constant deflection while topographic information is obtained by moving vertically the beam in console. Some sample-scanning systems use a combination of the AFM and STM modes: the tip is mounted in a beam with a console with an electrical connection so that the surface force and tunneling current are controlled or monitored. STM systems can be functional in ultra-high vacuum (UHV STM) or in the air, while AFM systems are only operational in the air. When a sample scanning system is operational in the air, the water absorbed on the surface of the sample accumulates under the tip, forming a meniscus between the tip and the surface. The water meniscus plays an important role in some of the sample scanning techniques described below.

Fig. 8. a, b sample scanning systems: (a) STM and (b) AFM • Oxidation induced by scanning the sample Nano-scale local oxidation of various materials can be achieved using air samples and functional scanned samples and polarized at a high enough voltage, fig. 9. Polarizations of -2 to-10V are normally used, with writing speeds of 0.1 - 100 mm / s in an ambient humidity of 20% - 40%.

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Fig. 9. SEM image of a reverse truncated pyramid surface fabricated on a SOI silicon capsule by SPM oxidation and subsequent etching in TMAH (lift is of 500 nm) It is assumed that the water meniscus formed at the point of contact serves as electrolyte so that the tip polarized oxidizes a small surface area such as an anode. The most common application of this principle is inactivated silicon oxidation with hydrogen. To inactivate the surface of silicon with hydrogen atoms, it is often dipped in HF solution. Oxide templates "written" on a silicon surface can be used as a mask in wet and dry etching. Templates with line diameters of 10 nm were successfully transferred on a silicon substrate in this way. Different metals were also anodized locally (aluminum or titanium, for example) using this method. An interesting variation of this process is deposited amorphous silicon anodization. Amorphous silicon can be deposited at low temperatures on a variety of materials. The deposited silicon layer can be modeled and can be used as, for example, a 0.1 mm CMOS transistor gate or can be used as a mask to shape a support film. The biggest drawback of this technique is poor reproducibility due to tip wear during anodization. However, the application of AFMs in non-contact mode has helped to overcome this problem. • Protective layer exposure to scanning and litography Electrons emitted from a polarized SPM tip can be used to expose a protective layer in a manner similar to electron beam lithography (Fig. 10). Various systems were used in this lithographic technique, including constant-current STM systems, AFM and non-contact AFM systems with constant tipprotective layer force and constant current.

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Intelligent Micro-Nano-Fabrication Systems using beams in console have the advantage that AFM observation and alignment can be achieved without exposing the protective layer. Coatings that are well characterized for electron beam lithography (as PMMA or SAL601) lithography were used to scan the sample for accurate lithography below 100 nm. The procedure for this process is as follows. The capsules are cleaned and the native oxide (silicon or poly) is removed with HF dipping. A coating with a thickness of 35-100 nm is then deposited on the surface. Exposure is achieved by moving the SPM tip over the surface while applying a polarized voltage that is large enough to produce the emission of electrons from the top (a few tens of volts). The protective layer is developed in a standard solution subsequent to exposure. Features with a thickness of more than 50 nm were obtained with this procedure.

Fig. 10. Sample scan lithography with a protective organic coating • Dip-pen lithography (litography by dipping the tip) In dip-pen nano-lithography (DPN) a functional AFM tip is "stained with ink" with a certain chemical and brought in contact with a surface. The molecules of ink flow from the tip to the surface as a in a pen. The water meniscus formed between tip and the surface allows a natural diffusion and transport of molecules, as shown in Fig. 11.

Fig. 11. Scheme of the operating principle of dip-pen nano-litography

Ink staining can be done by dipping the tip in a solution containing a small concentration of molecules followed by a drying step (difluoroetane drying, for example). Lines with widths of up to 12 nm and spatial resolution of 5 nm have been demonstrated with this technique. Samples shaped with DPN include conducting polymers, gold, dendrimer, DNA, organic dyes, antibodies and alcanitiolsi. Alcantiols were used as an organic etching mask in a gold monolayer and then in the engraving of the exposed silicon substrate. The beam in cantilever of the AFM can also be used to control the deposition of solid organic ink. This technique was recently reported by Sheehan and his colleagues, where 100 nm lines of octadecilfosforic acid (melting point 100 ° C) were written using a sample AFM head. • Other techniques nanofabricare by scanning the sample A variety of mechatronic nano-fabrication techniques based on sample scanning systems were demonstrated. Some of these demonstrations prove the concept and must be assessed as viable and repeatable manufacturing processes. For example, a substrate can be machined using STM / AFM tips operating as planes or engraving devices. They can be used directly to create structures in the substrate, although it is more convenient to use them to shape a protective layer for the subsequent etching, an elimination or electrodeposition phase. Mechanical Nano-processing of SPM samples can be facilitated by heating the tip for glass transition for a polymer substrate. This circumstance was applied to data storage systems based on SPMs in polycarbonate substrates. Electric fields strong enough to induce atomic emission from the tip can be easily generated by applying voltage pulses greater than 3V. This strategy was used to transfer material from the tip to the surface and vice-versa. Ten to twenty nanoscale stacks of metals as Au, Ag and Pt were deposited on a surface or moved on a surface in this way. The same path was used to extract single atoms from the surface of the semiconductor and re-deposit them elsewhere. Manipulation of nanoparticles, molecules and atoms on a surface alone was also achieved by simply pushing or sliding them with the SPM tip. Metals can also be locally deposited using the STM chemical vapor submission technique. In this technique, an organo-metallic precursor gas is introduced into the STM chamber. A voltage pulse is applied between the tip and thesurface dissociates the precursor gas in a thin layer of metal. Local electrochemical etching and electrodeposition are also possible using SPM systems. A drop of the appropriate solution is placed on the substrate. Then the STM tip is immersed in the drop and a voltage is applied. To reduce Faradic currents, the tip is coated with wax so that only the tip is exposed to the solution. Characteristic sizes below 100 nm were

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Intelligent Micro-Nano-Fabrication obtained with this technique. Using a single peak to produce in series the desired changes in one area leads to very slow manufacturing processes that are not practical for mass production. Many of the techniques developed so far for scanning the sample, however, could also be reploaced by an area of peaks, which would increase their result and would make them more competitive with other nano-fabrication processes. This way has been demonstrated for observation, lithography and data storage using both uni-dimensional areas and bidimensional areas of scanned samples. With the development of larger areas, with individual advances in force, vertical position and current control, many of these techniques can be used in standard industrial manufacturing. 6. Self-assembly and template fabrication Self-assembly is a nano-fabrication technique involving nanoparticle colloidal aggregation in the desired final structure. This aggregation can be spontaneous (entropic) and due to minimum thermodynamic value constraints (minimizing energy) or due to the chemical and complementary binding of organic molecules and supra-moleculels (molecular self-assembly). Molecular self-assembly is one of the most important techniques used to develop complex functional structures in biology. Since these techniques require that the target structures are thermodynamically stable, it is going to produce structures that are free from defects and selfhealing. Self-assembly is by no means limited to molecules or nano scale and can be performed at any scale, as a strong (multi-ordination) manufacturing method. Another attractive feature of this technique refers to the possibility of combining self-assembly properties of organic molecules with electronic, magnetic and photonic properties of inorganic components. The fabrication of the basic template is another technique that uses top-bottom deposition (CVD electroplating, and others) in nano-templates to manufacture nanostructures. The nano-templates used in this technique are usually prepared using selfassembly techniques. The following sections will discuss various techniques of self-assembly and production of templates investigated intensively.

of the system. In addition to spontaneous thermal selfassembly, gravitational forces, convection and electrohydro-dynamic forces can also be used to induce aggregation in complex 3D structures. Chemical selfassembly requires the attachment of a single organic molecular layer (monolayer self-assembled or SAM) of (organic or inorganic) colloidal particles and subsequent self-assembly of these components in a complex structure using molecular recognition and binding. • Physical self-assembly This is a method based on the entropy driven by the spontaneous organization of colloidal particles in a relatively stable structure through non-covalent interactions. For example, polystyrene colloidal spheres can be assembled into a 3D structure on a substrate that is held vertically in the colloidal solution, Fig. 12. After evaporation of the solvent, the spheres aggregate in a hexagonal closely packed (HCP) structure. The interstitial pore size and density are determined by the size of the polymer sphere. Polymer spheres can be engraved in smaller sizes after the formation of HCP surfaces, thereby altering pore printing separations. This technique can produce large areas modeled in a fast, simple and economic manner. A classic example is the assembly of on-chip natural silicon photonic crystals that are capable to reflect the incoming light in any direction over a certain wavelength domain. In this method, a thin layer of colloidal silica spheres are assembled on a silicon substrate. This is done by placing a vertical silicon capsule in a vial containing an ethanolic suspension of silica spheres. A temperature gradient over the vial helps pick up the silica spheres. Figure 13 shows a cross-sectional SEM image of an oval flat thin template assembled directly on the silicon capsule of the 855 nm spheres. Once such a template is prepared, LPCVD can be used to fill the interstitial spaces with silicon, so that high refractive index silicon zones provide the necessary width.

• Physical and chemical self assembly The central theme behind the self-assembly process is the spontaneous (physical) or chemical aggregationof colloidal nanoparticles. Spontaneous self-assembly exploits the tendency of sub-micro-colloidal nano-or mono-dispersate spheres to self-organize in a network with acentered cubic facade (FCC). The force that generates this process is the urge to achieve a thermodynamically stable state (minimum free energy) 78

Fig. 12. Self-assembly of colloidal particles on solid substrates after drying in a vertical position.

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Intelligent Micro-Nano-Fabrication When the aqueous dispersion is let to dehydrate slowly across the cell, the capillary force exerted over the liquid pushes the colloidal spheres across the surface of the basic subsatre until they are blocked by the template. If the concentration of colloidal dispersion is sufficiently high, the template will be filled with the maximum number of colloidal particles determined by the geometric limit. This method can be used to manufacture a variety of polygonal and polyhedral aggregates that are otherwise difficult to generate. • Chemical self-assembly

Fig. 13. SEM image of a cross section of an oval flat thin template (spheres with a 855 nm diameter) assembled directly on a silicon capsule. You can also store colloidal particles on a shaped substrate (template-assisted self-assembly). This method is based on the principle that when an aqueous dispersion of colloidal particles is let to dehydrate on a solid surface which is already modeled, colloidal particles are blocked by deep regions and assembled in aggregates of shapes and sizes determined by the geometrical limitation provided the template. Templates modeled surfaces can be manufactured using conventional photo-lithography to ensure the control of the shapes and sizes of templates, thus allowing the assembly of complex structures of colloidal particles. A cross section of a fluidic cell used in TASA is shown in Figure 14.

Fig. 14. Cross section view of a fluidic cell used for template-assisted self-assembly The fluidic cell has two parallel glass substrates to limit the aqueous dispersion of the colloidal particles. The surface from the basis of the substrate is modeled with a 2D templates surface.

Organic and super-molecular SAM plays a critical role in the self-assembly of colloidal particles. SAMs are organic molecules that are absorbed chemically by robust solid substrates. They often have a hydrophilic head (polar), which can be linked to various solid surfaces and a long hydrophobic (nonpolar) tail that lies outside. SAMs are formed by immersing a substrate in a diluted solution of the molecule in an organic solvent. The resulting film is a dense organization of molecules arranged to expose the final group. SAM sustainability is strongly dependent on the strenght of anchoring to the surface of the substrate. SAMs have been studied intensively since the end group can be functionalized to form molecular surfaces arranged specifically for applications ranging from simple insulators and plain lubricants to biological sensors. SAMs use chemical self-assembly or supramolecular organic binding and recognition as areas for the fabrication of complex 3D colloidal nanoparticles. The most common organic monolayers used include: 1) organosiliconate compounds on glass surfaces and silicon oxide layers, 2) alcantiolsi, Dialkyl disulfide and gold Dialkyl sulfide, 3) fatty acids on aluminum oxide and other metal oxides and 4) DNA. Octadeciltriclorosilane (OTS) is the most commonly used to form SAM organosilane mainly because it is not heavy and forms dense layers. Alchiltriclorosilane monolayers can be prepared on silica capsules with silicon oxide surface (SiOH groups with nearly 5.10 14 / cm 2). Fig. 15 shows a schematic representation of the formation of monolayers by adsorption of alchiltriclorosilan solution on substrates of Si / SiO 2. Since the silicon-chlorine contact is susceptible to hydrolysis, the amount of water in the system must be limited to obtain monolayers of good quality. Monolayers made of methyl-and vinylalchilsilanes are autophobic in hydrocarbon solution and thus appear wet in the solution used for their formation. The disadvantage of this method is the fact that a cloudy film is deposited on the surface (due to the formation of a polymer gel in siloxane) if the alchiltriclorosilane in the solvent adherent to the substrate is exposed to water.

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Intelligent Micro-Nano-Fabrication

Fig. 15. (A) Alchilsiloxane made from the adsorbtion of alchitriclorosilanei formed on the Si / SiO 2 substrates. (B) Schematic representation of the process Alcantioli (X (CH 2) n SH, where x is the final group) on gold form another important group of organic SAM systems. A major advantage of using gold as the substrate material is that it does not have a stable oxide and can thus be operated in ambient conditions. When a fresh, clean, hydrophilic gold substrate is immersed (for a few minutes to several hours) in a dilute (10 -3 M) of organic sulfur compounds (alcantioli) in a solvent inorganic monolayers oriented, well-packed can be obtained. Sulfur is used as group head due to strong interaction with the gold substrate (44 kcal / mol), resulting in the formation of an ordered monolayer, well packaged. The final grouping of alcantioli can be changed to show hydrophobic or hydrophilic properties to the adsorbed layer. Another method for SAM alcantioli deposition is soft lithography. This technique is based on staining an alcantiol PDMS template with ink and then transfering it to planar and non-planar substrates. Alcantiol functionalized surfaces (planar, non-planar, spherical) can also be used to self-assemble a variety of complex 3D structures. Carboxylic acid derivatives self-assemble on surfaces (like glass, Al 2 O 3 and Ag 2 O) by acid-base reaction, giving rise to fatty acid monolayers. The time required to form a complete monolayer increases with decreasing concentration. Higher concentrations of carboxylic acids are necessary to form a monolayer on gold rather than on Al 2 O 3. This is due to different affinities of these substances of the COOH group (higher affinity for Al 2 O 3 and glass than gold) and also the concentrations of surface oxides that are salt makers in the two substances. In the case of amorphous metal oxide surfaces, the chemical adsorbtion of alcanoic acids is not unique. For example, on Ag 2 O, the two atoms of carboxylic oxygen substrate binds in a nearly symmetrical bond, resulting 80

in ordered monolayers with a chain tilt angle of 15 º to 25 º. However, on CuO and Al 2 O 3 , oxygen atoms bind symmetrically and chain angle is close to 0 °. The structure of monolayers is thus the result of a balance between various interactions that occur between polymer chains. The deoxyribonucleic acid (DNA) – the skeleton on which all life is built - can be used in self-assemble nano-materials into macroscopic aggregates that show a number of useful physical properties desired. DNA consists of two chains that are wrapped around one another to form a double helix. Single chains of nucelotides are left when the two chains are wrapped. These nucleotides are composed of a sugar (pentose ring), a phosphate (PO 4) and a nitrogen base. The right order and the architecture of these components are essential for achieving a proper structure of nucleotides. Four nucleotides form usually the DNA, adenine (A), guanine (G), cytosine (C) and thymine (T). A basic property of the structure of DNA nucleotides describes is that they bind specifically to a different nucleotide in the double helix when they selfassembly (A binds to T and C bins to G). This specific binding capability can be used to assemble the material in nano-phase and nanostructures. For example, nucleotides functionalized with gold nanoparticles were assembled in complex 3D structures by attaching DNA chain to gold through a binding molecule or a bond. In another work, the DNA was used to assemble nano-particles inmacroscopic materials. This method uses alkane ditiol as biding molecule to connect the DNA to the nano-particule. Thiol groups at each end of the molecule are attached covalently to the colloidal particles to form aggregate structures. • Template fabrication Template fabrication refers to a set of techniques that can be used in the fabrication of organic and inorganic 3D structures from a nano-template. These templates differ in material, template, sizes, features, full size template and regularity. Although nano-templates can be manufactured using electron beam lithography, the serial nature of this technique prohibits its application. Self-assembly is the preferred technique since it can produce high surface nano-templates. A series of nano-templates were investigated for use in the fabrication of templates. These include colloidal polymer spheres, aluminum membranes and nuclear membranes with engraving traces. Colloidal spheres can be deposited on a regular 3D surface using the techniques described above. Aluminum oxide porous membranes can be produced by anodic oxidation of aluminum. The oxidized film consists of coloumnar surfaces from hexagonal pores separated by distances comparable with pore size. By controlling the electrolyte species, temperature, voltage and time, pores wkith sizes, densities and heights can be obtained.

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Intelligent Micro-Nano-Fabrication Pore size and depth can be adjusted by a proper acid corrosion. Porous polycarbonate templates or membranes can be fabricated by etching traces of nuclear membranes. This technique is based on the transfer of high energy fragments from a radioactive source to a dielectric material. Particles leave behind traces which can then be chemically active and can create corroded pores through the membrane. Pores separation and thus pore density is thus depending on pore size. The pore density is determined only by the irradiation. After the fabrication of the template, the interstitial spaces (in colloidal spheres) or pores (in aluminum oxide and polycarbonate membranes) in the template are filled with the desired material. This can be done using a variety of deposition techniques, like electroplating and CVD. The final structure may be a composite of the nano-template and of the dmaterial, or the template can be selectively etched resulting in a complex 3D structure filled with air. For example, nickel, iron and cobalt nano-wires were grown electrochemically in a porous mould. Threedimensional photonic crystals were fabricated by electrochemical depositing of CdSe and silicon in polystyrene and colloidal assemblies of silicon oxide. An interesting example is the synthesis of metallic barcode with nanometric dimensions. These nano-barcodes are prepared by the electrochemical reduction of metal ions in the pores of the aluminum oxide membrane followed by their release by etching the templates. This procedure is illustrated schematically in Figure 16.

multi-band Au-Ag bar code (Ag strips with lengths of 60-240 nm that are separated by segments of 550 nm can be seen). These encoded fnano-particles can be used in luorescent surfaces and surfaces based on mass spectroscopy, allowing a wide variety of bio-analytic measures.

Fig. 17. Multi-band Au-Ag particle images (a) Optical and (b) FE-SEM In conclusion, various techniques for micro / nano-fabrication used for fabrication of structures covering a wide variety of sizes (mm-nm) were presented. Starting with some of the most common micro-fabrication techniques (lithography, deposition and etching), a sum of micro-processor technologies and MEMS that can be used to manufacture microstructures up to ≈ 1μm were pre sented. These techniques have reached an adequate level of maturity that allows the production of commercial products based on MEMS (pressure sensors, accelerometers, gyroscopes, etc.). More recently, nano-sized structures have attracted much interest due to their electrical, magnetic, optical, thermal and mechanical properties. This could lead to a variety of electronic, photonic and detection devices with superior performance compared to macro devices. Nano-fabrication techniques were presented. Thus, electron beam lithography and other lithography types with high resolution can be used to produce nanometerscale structures. Other potential techniques are selfassembly and nano-print lithography. Of these, selfassembly is the most promising due to its low cost and the ability to produce nano-structures at different length scales. 6.Foundation and future of intelligent micro-nanofabrication

Fig. 16. Barcode particles synthesis parciculelor A film of silver on the back is used as the working electrode to reduce the metal ions (silver and gold in this case) of the solution. Over seven different metal segments of 10 nm and several micrometers long, with 13 strips, can be distinguished using this technique. Optical reflectivity is used to read the template encoded in the metalic particles. Figure 17 shows optical microscope images and electron emission scanning microscope images of a

The substantiation of intelligent micro-nanofabrication in the future is based on the new generative techniques and technologies at micro and nano-scale, together with the prediction of the implications of the new discoveries of the fields but also of the products and technologies in the micro-nano area. The new advanced areas in which the intelligent advanced micro-nano-fabrications will be implemented are still listed and identified as follows: The concept of "nanotechnology" provides its applications in its advanced generation and evolution in the following areas:

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Intelligent Micro-Nano-Fabrication • in the field of biological systems for membranes, enzymes and other cellular generated components; • in the field of carbon structures (eg nano-structures); • in the field of silicon structures and other enzymatic substances fabrication; • in the field of nano-materials and nano-semiconductors fabrication; • in the field of the production of nano-computers; • in the field of artificial intelligence approaching; • in the field of the production of MEMS AND NEMS; ● in the field of BIOMEMS AND BIONEMS; • in the field of the realization of bio-sensors / biomicro-sensors/ bio-nano-sensori; • in in the field of micro-nano-devices that achieve high-speed and are characterized by great flexibility; • in the field of diamond tubes production; • in the field of "assemblers" for new materials with micro-structures; • in the field of "re-producers" for finished products, such as micro-nano-machines; • in the field of nano-sized "nano-computers"; • in the field of block co-polymers; • in the field of nano-crystals; • in the field of the production of clusters of nanoparticles;

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in the field of of aerogels; • in the field of intelligent uniforms made from materials improved with polymers; • in the field of "computer- clothes" ; • in the field of intelligent clothes realization meant to prevent aging, made from the new "NanoDew" material. References: [1] Albrecht, A. et. al., “Mikrobewegungssysteme”, Mikroelectronik, 1993 (5), Fachbeilage “Mikrosystemtechnik” [2] Altrock, K., “Signalverarbeitung fur Sensorsysteme”, Mikroelectronik, 1993 (3), Fachbeilage “Mikrosystemtechnik” [3] Brugger, J. et al., Microfabricated tools for nanoscience, Jour-nal of Micromechanics and Microengineering, 1993 (4), Vol. 3 [4] Brugger, J. et al., “Nanopositioniersystem”, Mikroelektronik, 1993 (5), Fachbeilage “Mikrosystemtechnik” [5] Buker, H., “Glasfasersensorik als neue Disziplin der Mikrosensorik”, 7. IAR Kolloquium, Tagungs-band, Universitat Duisburg, 1993 [6] Burns, V. , “Mikroelectromechanical Systems (MEMS) and SPC Market Study” mst news.

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