The ability to form ZnO nanowire arrays with dedicated morphological properties is crucial for the development of efficient piezoelectric devices such as piezoelectric nano -generators and sensors. However, their integration typically requires the use of metallic seed layers for their synthesis by chemical bath deposition, from which their morphological control is still very limited. In this context, the formation mechanisms of ZnO nanowires from Au seed layers are carefully investigated for different precursor (i.e., zinc nitrate and hexamethylenetetramine (HMTA)) concentrations in the range of 1-100 mM, where drastic variations of the morphological properties are observed. By coupling in situ pH measurements and thermodynamic computations, we perform an in-depth analysis of the thermodynamic properties of the chemical bath, where the predominant role of the NO3- ions in the evolution of the pH of the chemical bath is revealed. An original approach is further developed to carefully determine the hydrolysis ratio of HMTA molecules, which is found to vary in the range of 20-45% with the precursor concentration, and to directly impact the supersaturation ratio of Zn(II) species. From these results, we identify the presence of three different growth regimes depending on the precursor concentrations, each of them giving rise to ZnO nanowire arrays with specific morphological properties. These results highlight the critical importance of the thermodynamic properties of the chemical bath in the formation process of ZnO nanowires from Au seed layers and provide key elements of understanding to efficiently optimize their morphology for their integration into piezoelectric devices.

The formation of nanowires by chemical bath deposition is of great interest for a wide variety of optoelectronic, piezoelectric, and sensing devices, from which the theoretical description of their elongation process has emerged as a critical issue. Despite its strong influence on the nanowire growth kinetics, reactor size has typically not been taken into account in the theoretical modeling developed so far. We report a new theoretical description of the axial growth rate of nanowires in dynamic conditions based on the solution of Fick's diffusion equations, implementing a sealed reactor of finite height as a varying parameter. The theoretical model is applied in various chemical bath deposition conditions in the case of the growth of ZnO nanowires, from which the influence of the reactor height is investigated and compared to experimental data. In particular, it is found that the use of reactor heights smaller than 2 cm significantly decreases the ZnO nanowires' axial growth rate in typical experimental conditions due to the faster depletion of reactants. The present approach is further used predictively, showing its high potential for the design of batch reactors for a wide variety of chemical precursors and semiconductor materials in applied research and industrial production.

The controlled incorporation of dopants like copper into ZnO nanowires (NWs) grown by chemical bath deposition (CBD) is still challenging despite its critical importance for the development of piezoelectric devices. In this context, the effects of the addition of copper nitrate during the CBD of ZnO NWs grown on Au seed layers are investigated in detail, where zinc nitrate and hexamethylenetetramine are used as standard chemical precursors and ammonia as an additive to tune the pH. By combining thermodynamic simulations with chemical and structural analyses, we show that copper oxide nanocrystals simultaneously form with ZnO NWs during the CBD process in the low-pH region associated with large supersaturation of Cu species. The Cu(II) and Zn(II) speciation diagrams reveal that both species show very similar behaviors, as they predominantly form either X2+ ions (with X = Cu or Zn) or X(NH3)42+ ion complexes, depending on the pH value. Owing to their similar ionic structures, Cu2+ and Cu(NH3)42+ ions preferentially formed in the low- and high-pH regions, respectively, are able to compete with the corresponding Zn2+ and Zn(NH3)42+ ions to adsorb on the c-plane top facets of ZnO NWs despite repulsive electrostatic interactions, yielding the significant incorporation of Cu. At the highest pH value, additional attractive electrostatic interactions between the Cu(NH3)42+ ion complexes and negatively charged c-plane top facets further enhance the incorporation of Cu into ZnO NWs. The present findings provide a deep insight into the physicochemical processes at work during the CBD of ZnO NWs following the addition of copper nitrate, as well as a detailed analysis of the incorporation mechanisms of Cu into ZnO NWs, which are considered beyond the only electrostatic forces usually driving the incorporation of dopants such as Al and Ga.

DNA nanotechnology has shown great promise for nanopatterning applications thanks to the ability to nanoengineer rationally designed two and three-dimensional (3D) nano-objects of complex shapes with subnanometer precision and high degree of rigidity [1]. Recently, a self-assembled DNA origami allowing sub-10 nm pattern transfer into SiO2 has been demonstrated [2]. We report here a mechanistic study of a high resolution (10 nm) and high density (10 nm) DNA pattern transfer into a Si substrate. In order to exploit their full potential for lithographic application, the deterministic positioning of the DNA nanostructures on a predefined substrate is still a major challenge to overcome. In a second part of this paper, we present a hybrid nanopatterning process by combining locally chemically modified substrate by top-down technics with bottom- up self-assembly of DNA nanostructures in order to deterministically fix DNA origamis on the substrate. Chemical contrast is formed using conventional lithography in order to create DNA affine and adverse parts on the substrate. The pattern transfer of the DNA nanostructures in the inorganic under layer is demonstrated as well. Thus, DNA origami appears to be a promising emerging approach for the engineering of hard masks for patterning.

Desoxyribonucleic acid (DNA) origami architectures are a promising tool for ultimate lithography because of their ability to generate nanostructures with a minimum feature size down to 2 nm. In this paper, we developed a method for silicon (Si) nanopatterning to face up current limitations for high-resolution patterning with standard microelectronic processes. For the first time, a 2 nm-thick 2D DNA origami mask, with specific design composed of three different square holes (with a size of 10 and 20 nm), is used for positive pattern transfer into a Si substrate using a 15 nm-thick silicon dioxide (SiO2) layer as an intermediate hard mask. First, the origami mask is transferred onto the SiO2 underlayer, by an HF vapor-etching process. Then, the Si underlayer is etched using an HBr/O2 plasma. Each hole is transferred in the SiO2 layer and the 20 nm-sized holes are transferred into the final stack (Si). The resulting patterns exhibited a lateral resolution in the range of 20 nm and a depth of 40 nm. Patterns are fully characterized by atomic force microscopy, scanning electron microscopy, focused ion beam-transmission electron microscopy, and ellipsometry measurements.

DNA nanotechnology has shown great promise for nanopatterning applications thanks to the ability to nanoengineer rationally designed two and three-dimensional (3D) nano-objects of complex shapes with subnanometer precision and high degree of rigidity [1]. Recently, a self-assembled DNA origami allowing sub-10 nm pattern transfer into SiO2 has been demonstrated [2]. We report here a mechanistic study of a high resolution (10 nm) and high density (10 nm) DNA pattern transfer into a Si substrate. In order to exploit their full potential for lithographic application, the deterministic positioning of the DNA nanostructures on a predefined substrate is still a major challenge to overcome. In a second part of this paper, we present a hybrid nanopatterning process by combining locally chemically modified substrate by top-down technics with bottom-up self-assembly of DNA nanostructures in order to deterministically fix DNA origamis on the substrate. Chemical contrast is formed using conventional lithography in order to create DNA affine and adverse parts on the substrate. The pattern transfer of the DNA nanostructures in the inorganic under layer is demonstrated as well. Thus, DNA origami appears to be a promising emerging approach for the engineering of hard masks for patterning.

The chemical bath deposition of nanowires is of high interest for a wide variety of optoelectronic, piezoelectric, and sensing devices, but a theoretical description of the elongation process is still missing despite its critical importance. By solving Fick's diffusion equations in combination with thermodynamic computations, we determine the expression of the axial growth rate of nanowires and its temporal dependence under dynamic conditions, namely, in a sealed reactor, where the depletion of chemical reactants occurs. The theoretical model is found to be in very good agreement with a large set of experimental data specifically collected in the case of the chemical bath deposition of ZnO nanowires. In particular, an activation energy of 198 +/- 24 kJ/mol is deduced for the elongation process of ZnO nanowires, involving the energy barriers for both the dehydration process of Zn(II) species (i.e., [Zn(H2O)(6)](2+) ions) and their subsequent direct incorporation onto the c-plane top faces. This shows its high potential to enable in-depth investigation of the physicochemical processes at work in the chemical bath. By using the theoretical model as a predictive approach, a complete growth diagram reporting the evolution of the length of ZnO nanowires vs effective growth time and temperature is also obtained over a broad range of conditions, revealing its additional high potential for applied research and industrial purposes. The present general approach is further compatible with a broad range of chemicals in solution and of semiconducting materials grown by chemical bath deposition.

ZnO nanowires are considered as attractive building blocks for piezoelectric devices, including nano-generators and stress/strain sensors. However, their integration requires the use of metallic seed layers, on top of which the formation mechanisms of ZnO nanowires by chemical bath deposition are still largely open. In order to tackle that issue, the nucleation and growth mechanisms of ZnO nanowires on top of Au seed layers with a thickness in the range of 5–100 nm are thoroughly investigated. We show that the ZnO nanowires present two different populations of nano-objects with a given morphology. The majority primary population is made of vertically aligned ZnO nanowires, which are heteroepitaxially formed on top of the Au (111) grains. The resulting epitaxial strain is found to be completely relieved at the Au/ZnO interface. In contrast, the minority secondary population is composed of ZnO nanowires with a significant mean tilt angle around 20° with respect to the normal to the substrate surface, which are presumably formed on the (211) facets of the Au (111) grains. The elongation of ZnO nanowires is further found to be limited by the surface reaction at the c-plane top facet in the investigated conditions. By implementing the selective area growth using electron beam lithography, the position of ZnO nanowires is controlled, but the two populations still co-exist in the ensemble. These findings provide an in-depth understanding of the formation mechanisms of ZnO nanowires on metallic seed layers, which should be taken into account for their more efficient integration into piezoelectric devices.

Patterning surface with structural DNA origami mask presents a major interest for nanolithography due to its modularity and high ability to achieve a high resolution with 3-5 nm. In this paper, we demonstrate a sub-ten-nanometer lithography process using anhydrous HF vapor into a SiO2 substrate (figure 1). After optimizing rinsing conditions on SiO2 substrate and HF etching process, we reach a high density (<20 nm pitch) and high resolution (~10 nm CD) patterned surface with a fast etching rate of 0.2 nm.s-1. The resulting SiO2 patterns are used as hard mask in HBr/O2 plasma of Si substrate. Origami pattern features are conserved: lateral dimensions, morphology and structure. For the first time, we developed a high resolution (~10 nm) and high contrast (~65 nm) transfer of patterns into Si substrate. We will highlight the challenges brought by this new technology and demonstrate the feasibility to control this patterning technique. AFM technique has been previously tested to confirm the pattern fidelity. Using all the available imaging capabilities on the CDSEM, we will establish the best method for each layer to achieve the precision required for the targeted nodes of this technology. Beyond the resolution capabilities, the precise placement of the DNA pattern on the substrate is investigated. Based on a pre-patterning step using the nanoimprint technology, the affinity of the DNA with respect to the substrate is locally modified and its influence is analyzed. Thus, DNA origami appears like a promising approach for emerging and engineering of hard mask for patterning.

Deoxyribonucleic acid (DNA) is presented as a potential candidate to develop nanopackaging solutions in the field of microelectronics by a bottom-up approach. Such an approach could overcome the miniaturization limitations of the current top-down approaches. By its particular and unique properties of self-assembling and the capability to be functionalized, DNA is a versatile biological material that can be used in many different ways to build multiscale nanostructures and especially conductive nanowires (NWs). These NWs could be implemented as potential future nanoscale interconnections.

Metallic conductive nanowires (NWs) with DNA bundle core are achieved, thanks to an original process relying on double-stranded DNA alignment and physical vapor deposition (PVD) metallization steps involving a silicon substrate. First, bundles of DNA are suspended with a repeatable process between 2 µm high parallel electrodes with separating gaps ranging from 800 nm to 2 µm. The process consists in the drop deposition of a DNA lambda-phage solution on the electrodes followed by a naturally evaporation step. The deposition process is controlled by the DNA concentration within the buffer solution, the drop volume, and the electrode hydrophobicity. The suspended bundles are finally metallized with various thicknesses of titanium and gold by a PVD e-beam evaporation process. The achieved NWs have a width ranging from a few nanometers up to 100 nm. The electrical behavior of the achieved 60 and 80 nm width metallic NWs is shown to be Ohmic and their intrinsic resistance is estimated according to different geometrical models of the NW section area. For the 80 nm width NWs, a resistance of about few ohms is established, opening exploration fields for applications in microelectronics.

Ultra-high vacuum (UHV) investigations have demonstrated a successful development of atomic nanostructures. The scanning tunneling microscope (STM) provides surface study at the atomic scale. However, the surface preparation is a crucial experimental step and requires a complex protocol conducted in situ in a UHV chamber. Surface contamination, atomic roughness, and defect density must be controlled in order to ensure the reliability of advanced UHV experiments. Consequently, a packaging for nanoscale devices has been developed in a microelectronic clean room environment enabling the particle density and contaminant concentration control. This nanopackaging solution is proposed in order to obtain a Si(001)-(2×1):H reconstructed surface. This surface is protected by a temporary silicon cap. The nanopackaging process consists in a direct bonding of two passivated silicon surfaces and is followed by a wafer dicing step into 1-cm2 dies. Samples can be stored, shipped, and in situ opened without any additional treatment. A specific procedure has been developed in order to open the nanopackaged samples in a UHV debonder, mounted in the load-lock chamber of a low-temperature STM system (LT-STM). Statistical large scan LT-UHV-SEM images and LT-UHV-STM images have been obtained enabling the surface study at the atomic resolution.

With their attractive intrinsic properties, such as morphology, autoassembling properties, and tailorability, nano-objects could provide alternative and innovative routes to current microelectronics and nanoelectronics. Further insight on their electrical properties, especially in terms of statistics and reproducibility, as well as on their potential integration into silicon-based electronics is, however, often required to be able to fully exploit their potential. This paper proposes an innovative approach using a generic structure allowing the study of nano-objects electrical properties. Regarding the nano-objects integration, a homogeneous approach is presented with the in situ fabrication of atomic wires as a possible planar interconnection system. A heterogeneous approach is described as well with the characterization and preliminary integration of biological material, such as deoxyribonucleic acid-based nanowires or amyloid fibers.

In the wide range of emergent nanotechnologies, DNA-based microelectronics has shown an important potential for components miniaturization and auto-assembling approaches applicable to future silicon-based electronic circuits [1]. In order to pursue the Moore's law, interconnections must be indeed addressed at the nanoscale, with a good control of their size, location and electrical & thermal performances. With its natural auto-assembling property, its 2-nm-double-helix diameter and its several metallization possibilities, DNA is a promising candidate to build bio-inspired electronic components [1]. DNA has been first metallized by Erez Braun in 1998 using a silver electroless method [2]. Since 1998, several groups have worked on DNA metallization using different chemistries with metals such as Pd, Pt, Au, Ag and Cu [3]. Most of these works have presented electrical and morphological characterizations of few metallic nanowires. However, in order to initiate DNA-based-nanowires integration on silicon technologies, we must start to implement nanowires on silicon at wafer scale. We have thus developed a platform based on silicon technologies providing morphological and electrical characterizations of copper nanowires built from DNA [4]. This platform will allow us to simultaneously characterize a large number of nanowires, returning a statistic of their electrical performance, and thus allowing the optimization of the copper nanowire metallization process. Two main approaches are proposed to fabricate and contact a large number of copper nanowires with metallic electrodes in order to study their electrical behavior. In both approaches, a linear 16-μm-length DNA phage is used. The first approach consists in aligning DNA wires on a hydrophobic silicon oxide surface by a method called DNA combing. On a second time, aligned DNA wires are all metallized by electroless process [4]. 5-nm-diameter copper nanowires have been so far achieved by this method and focus on improving the metallization process is currently at stake. Finally, Ti/Au electrodes are fabricated on the nanowires by a classical lift-off process in order to electrically connect them. The advantage of this approach is the very accurate nanowires alignment and their homogeneity over the surface. However, the low number of aligned nanowires per surface unit (10–20μm−2) and the high electrical resistance of each (>kohms) makes the electrical characterization quite complex. On the other side, the second approach consists in fabricating the Ti/Au electrodes first and then aligning or randomly depositing the copper nanowires at their surface. Same protocols are used to align and metallize the DNA nanowires for both approaches. The advantage of this second approach is a higher nanowire density deposited on the electrodes. However, a higher contact resistance and a lower control of nanowires alignment are obtained. Both approaches are currently explored and permit to explore a wide range of parameters for copper nanowires metallization process improvement.