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Abstract
Although small structures can be fabricated by deposition, lithography and etching, in
some cases their intrinsic variability precludes their use as elements in useful arrays.
Manufacture is a proper subset of fabrication. We show that structures with 3 nm design
rules can be fabricated but not manufactured in a top-down approach—they do not have
the reproducibility to give a satisfactory yield to a pre-ordained specification. It is also
shown that the transition from manufacturability to intrinsic unmanufacturability takes
place at nearer 7 nm design rules.
... Due to the layered nature of fabrication processes, the top-down approach is mainly limited to 2D or 2.5D structures in manufacturing. Structures can be fabricated by repeated material deposition and removal processes, supporting very accurate manufacturing, but present manufacturability problems when the length scale is less than a few nanometers [216,217]. ...
... • All other figures in this chapter were originally published under a CC-BY license and appropriately cited, were original to this work, or were from official US Government documents and therefore not subject to copyright in the United States. 217 ...
Doctoral Dissertation: In the manufacturability-driven design (MDD) perspective, manufacturability of the product or system is the most important of the design requirements. In addition to being able to ensure that complex designs (e.g., topology optimization) are manufacturable with a given process or process family, MDD also helps mechanical designers to take advantage of unique process-material effects generated during manufacturing. One of the most recognizable examples of this comes from the scanning-type family of additive manufacturing (AM) processes; the most notable and
familiar member of this family is the fused deposition modeling (FDM) or fused filament fabrication (FFF) process. This process works by selectively depositing uniform, approximately isotropic beads or elements of molten thermoplastic material (typically structural engineering plastics) in a series of pre-specified traces to build each layer of the part. There are many interesting 2-D and 3-D mechanical design problems that can be explored by designing the layout of these elements. The resulting structured, hierarchical material (which is both manufacturable and customized layer-by-layer within the limits of the process and material) can be defined as a manufacturing process-driven structured material (MPDSM). This dissertation explores several practical methods for designing these element layouts for 2-D and 3-D meso-scale mechanical problems, focusing
ultimately on design-for-fracture. Three different fracture conditions are explored: (1) cases where a crack must be prevented or stopped, (2) cases where the crack must be encouraged or accelerated, and (3) cases where cracks must grow in a simple pre-determined pattern. Several new design tools, including a mapping method for the FDM manufacturability constraints, three major literature reviews, the collection, organization, and analysis of several large (qualitative and quantitative) multi-scale datasets on the fracture behavior of FDM-processed materials, some new experimental equipment, and the refinement of a fast and simple g-code generator based on commercially-available
software, were developed and refined to support the design of MPDSMs under fracture
conditions. The refined design method and rules were experimentally validated using a series of case studies (involving both design and physical testing of the designs) at the end of the dissertation. Finally, a simple design guide for practicing engineers who are not experts in advanced solid mechanics nor process-tailored materials was developed from the results of this project.
... In Figure 4 we summarize the constraints related to the operating frequency of Si exchangeonly qubits for realistic devices, including the technological limit of manufacturability at 3 nm (orange line). This limit was discussed and quantified by Kelly in 2011 by considering a number of arguments based on the intrinsic variability of top-down fabrication processes, on the unwanted electron tunneling and on the parasitic interferences, leading to a limit on the manufacturability at around 3 nm [2]. Furthermore, we highlight the physical bounds imposed by the requirements of adiabaticity, coherence and node-dependent minimum operation time, which hamper quantum computing in the blue, red and grey area respectively. ...
Even the quantum simulation of simple molecules such as FeS requires more than 10 qubits. In order to assess such a multimillion scale of identical qubits and control lines, the silicon platform seems to be one of the most indicated routes as it provides the capability of nanometric, serial and industrial quality fabrication. The maximum amount of quantum information per unit surface and the consequent space constraints on qubit operations are key parameters towards fault-tolerant quantum information processing (QIP) with Si qubits. Such maximum density of quantum information is expressed for the compact exchange-only Si double quantum dot qubit architecture as a function of the CMOS technology node. The size scale optimizing both physical qubit operation time and quantum error correction (QEC) requirements is assessed by reviewing the physical and technological constraints. We determine the workable operation frequency range of a Si-CMOS quantum processor to be within 1 and 100 GHz, which limits its feasibility only to the most advanced nodes. The compatibility with classical control circuitry is discussed, focusing on the cryogenic CMOS operation required to bring the classical controller as close as possible to the quantum processor and to enable interfacing thousands of qubits on the same chip. The operation time range prospected for cryogenic control electronics is found to be compatible with the qubit operation time. By combining the forecast of technology development with operation time and classical circuitry constraints, we derive a maximum quantum information density for logical qubits of 2.8 and 4 Mqb/cm for the 10-nm and 7-nm technology nodes respectively for the Steane code. The density is one and two orders of magnitude less for surface and concatenated codes respectively. Such values provide a benchmark for the development of Si-based fault tolerant QIP.
... Due to the layered nature of fabrication processes, the top-down approach is mainly limited to 2D or 2.5D structures in manufacturability. Structures can be fabricated by repeated material deposition and removal processes, supporting very accurate manufactur-ing, but presenting manufacturability problems when the length scale is less than a few nanometers [164,165]. The bottom-up approach places material at the desired locations, similar to 3-D printing processes. ...
Design-for-manufacturing (DFM) concepts have traditionally focused on design simplification; this is highly effective for relatively simple, mass-produced products, but tends to be too restrictive for more complex designs. Effort in recent decades has focused on creating methods for generating and imposing specific , process-derived technical manufacturability constraints for some common problems. This paper presents an overview of the problem and its design implications, a discussion of the nature of the manufacturability constraints, and a survey of the existing approaches and methods for generating/enforcing the minimally-restrictive manufacturability constraints within several design domains. Four major design perspectives were included in the study, including the system design (top-down), the product design (bottom-up), the manufacturing process-dominant approach (specific process required), and the part-redesign approach. Manufacturability constraints within four design levels were explored as well, ranging from macro-scale to sub-micro-scale design. Very little previous work was found in many areas, but it is clear from the existing literature that the problem and a general solution to it are very important to explore further in future DFM and design automation work.
... This approach represents so far the main path in terms of robustness and efficiency although it is remarkably costly, both in terms of time and cost of the required facilities. 16,17 Colloidal lithography is emerging as a "bottom-up" fabrication technique, thanks to the possibility of producing patterns on large scales 18,19 even though control on the size and the shape still needs to be optimized. 20,21 An alternative "bottom-up" approach that is quickly emerging as a valuable and cost-efficient strategy is the one where small precursor molecules interact between each other forming nanostructures. ...
Thanks to the spontaneous interaction between noble metals and biological scaffolds, nanomaterials with unique features can be achieved following relatively straightforward and cost-efficient synthetic procedures. Here, plasmonic silver nanorings are synthesized on a ring-like Peroxiredoxin (PRX) protein and used to assemble large arrays of functional nanostructures. The PRX protein drives the seeding growth of metal silver under wet reducing conditions, yielding nanorings with outer and inner diameters down to 28 and 3 nm, respectively. The obtained hybrid nanostructures can be deposited onto a solid-state membrane in order to prepare plasmonic nanopores. In particular, the interaction between graphene and PRX allows for the simple preparation of ordered arrays of plasmonic nanorings on a 2D-material membrane. This fabrication process can be finalized by drilling a nanometer scale pore in the middle of the ring. Fluorescence spectroscopic measurements have been used to demonstrate the plasmonic enhancement induced by the metallic ring. Finally, we support the experimental findings with some numerical simulations showing that the nanorings are endowed with a remarkable plasmonic field within the cavity. Our results represent a proof of concept of a fabrication process that could be suitable for nanopore-based technologies such as next-generation sequencing and single-molecule detection.
... For arrays of nanometer half-pitch, ¼ 12%, highlighting a clearly intolerable variation for the electronic transport or optical properties of arrays made of elements with such intrinsic variability. Even if we could successfully fabricate such arrays by heroic processing, at very high cost, one must noteVatom by atom with a force microscope of sortsVthat there would never be such an array to write, store, or read information as the electrons and photons would leak extensively over extremely short timescales [48]. ...
Thin-film electronics in its myriad forms has underpinned much of the technological innovation in the fields of displays, sensors, and energy conversion over the past four decades. This technology also forms the basis of flexible electronics. Here we review the current status of flexible electronics and attempt to predict the future promise of these pervading technologies in healthcare, environmental monitoring, displays and human–machine interactivity, energy conversion, management and storage, and communication and wireless networks.
... There is lesson for mainstream nanotechnology [2]. We face the unsolved problem of insufficient uniformity and reproducibility of nanoscale artefacts-for example, the length and chirality of nanotubes, the shape and volume of quantum dots, the shape and area of graphene flakes, and the positioning of active dopant atoms within nanoparticles. ...
For a science to become a technology, a certain level of control has to have been established over the way items are fabricated for manufacture and use. Here we first consider the challenge of making and using a LEGO® brick scaled down by a factor of 10n
for n = 0–6 in each spatial dimension, i.e. from millimetres to nanometres. We consider both the manufacture and the subsequent properties of the nanobricks that pertain to their use in constructing and dismantling structures. As n increases, the ability to use fails first, to manufacture fails second and to fabricate fails last. Applied to the vast literature in nanoscience, this process emphasises the unmanufacturability of most nanoscale artefacts.
... Transistors have been fabricated with gate lengths as short as 3 nm [1], and a plethora of new architectures have been either proposed or demonstrated where devices can be grown in a bottom-up fashion using nanowires [2,3], wrapped-gates [4,5] and various other modalities [6,7]. Of course, the cost of making such devices combined with their reduced efficiency and yield is somewhat of a bottleneck in terms of mass-production, and at present, it appears as if this is a fundamental rather than technical issue [8]. Therein lies the renewed interest in molecular systems. ...
An approach to reproducibly fabricate molecular electronic devices is presented. Lateral nanometer-scale gaps with high yield are formed in Au/Pd nanowires by a combination of electromigration and Joule-heating-induced thermomechanical stress. The resulting nanogap devices are used to measure the electrical properties of small numbers of two different molecular species with different end-groups, namely 1,4-butane dithiol and 1,5-diamino-2-methylpentane. Fluctuations in the current reveal that in the case of the dithiol molecule devices, individual molecules conduct intermittently, with the fluctuations becoming more pronounced at larger biases.
... NEMS devices are most frequently made using silicon microfabrication technology so it is important to study the fabrication of conducting nanowires on silicon or related substrates like SiO 2 /Si or Si 3 Ni 4 /Si to develop robust methods for producing them under varying surface conditions and to ensure that they are ultimately manufacturable. 3 Focused ion beam (FIB) is an important tool for rapid prototyping of nanoscale devices and the work reported here presents results of using FIB as a lithography tool to produce gold nanowires on technically important surfaces in order to study the structural integrity of these nanowires as a function of their width and substrate surface conditions. We show that, below a certain width, the fabrication methods can lead to liquid-like instabilities in the FIB patterned nanowires. ...
Observation of liquid-like instabilities is reported in Au nanowires formed by nanopatterning of Au films using focused ion beam (FIB) on different types of Si substrates including those passivated with SiO2 or Si3N4 surfaces. The onset of the instability, which can ultimately lead to break up of the FIB patterned nanowires into gold islands, occurs when the diameter of the nanowire is below a critical range, which depends on the conductivity of the substrate and the extent of native oxide present on it. We also observe the formation of Taylor cones on very narrow nanowires grown on insulating substrates at the onset of instabilities. This effect is further strong evidence of liquid behaviour and is the result of charging of the wires during FIB nanofabrication.
... For arrays of nanometer half-pitch, ¼ 12%, highlighting a clearly intolerable variation for the electronic transport or optical properties of arrays made of elements with such intrinsic variability. Even if we could successfully fabricate such arrays by heroic processing , at very high cost, one must noteVatom by atom with a force microscope of sortsVthat there would never be such an array to write, store, or read information as the electrons and photons would leak extensively over extremely short timescales [48]. Consider quantum wires. ...
Thin-film electronics in its myriad forms has underpinned much of the technological innovation in the fields of displays, sensors, and energy conversion over the past four decades. This technology also forms the basis of flexible electronics. Here we review the current status of flexible electronics and attempt to predict the future promise of these pervading technologies in healthcare, environmental monitoring, displays and human–machine interactivity, energy conversion, management and storage, and communication and wireless networks.
Design-for-manufacturing (DFM) concepts have traditionally focused on design simplification; this is highly effective for relatively simple, mass-produced products, but tends to be too restrictive for more complex designs. Effort in recent decades has focused on creating methods for generating and imposing specific, process-derived technical manufacturability constraints for some common problems. This paper presents an overview of the problem and its design implications, a discussion of the nature of the manufacturability constraints, and a survey of the existing approaches and methods for generating/enforcing the minimally-restrictive manufacturability constraints within several design domains. Five major design perspectives or viewpoints were included in the survey, including the system design (top-down), product/component design (bottom-up), the manufacturing process-dominant case (product/component design under a specific process), the part-redesign perspective, and sustainability perspective. Manufacturability constraints within four design levels or scales were explored as well, ranging from macro-scale to sub-micro-scale design. Very little previous work was found in many areas, revealing several gaps in the literature. What is clearly needed is a more general, design-method-independent approach to collecting and enforcing manufacturability constraints.
The spontaneous interaction between noble metals and biological scaffolds enables simple and cost‐effective synthesis of nanomaterials with unique features. Here, plasmonic silver nanorings are synthesized on a ring‐like protein, i.e., a peroxiredoxin (PRX), and used to assemble large arrays of functional nanostructures. The PRX drives the seeding growth of metal silver under wet reducing conditions, yielding nanorings with outer and inner diameters down to 28 and 3 nm, respectively. The obtained hybrid nanostructures are selectively deposited onto a solid‐state 2D membrane made of graphene in order to prepare plasmonic nanopores. In particular, the interaction between the graphene and the PRX allows for the simple preparation of ordered arrays of plasmonic nanorings on a 2D‐material membrane. This fabrication process can be finalized by drilling a nanometer scale pore in the middle of the ring. Fluorescence spectroscopic measurements in combination with numerical simulations demonstrate the plasmonic effects induced in the metallic nanoring cavity. The prepared nanopores represent one of the first examples of hybrid plasmonic nanopore structures integrated on a 2D‐material membrane. The diameter of the nanopore and the atomically thick substrate make this proof‐of‐concept approach particularly interesting for nanopore‐based technologies and applications such as next‐generation sequencing and single‐molecule detection.
The 2D directed self-assembly of micron-sized hard spherical particles within square confinements is studied theoretically and experimentally. Grand Canonical Monte Carlo simulations are used to predict the equilibrium packing structures of particles in square wells of specific dimensions. Spin coating and mechanical rubbing processes are used for the directed self-assembly of a monolayer of particles. The precision of the graphoepitaxy decreases as template size increases. Both simulations and experiments show that graphoepitaxy of square lattices vanishes with square templates of side length greater than five times the particle diameter. Missing particles and polydispersity of particles are two main causes disrupting the square packing structure in cells of three to five particle diameter side length.
Even the quantum simulation of simple molecules such as FeS requires more than 10 qubits. In order to assess such a multimillion scale of identical qubits and control lines, the silicon platform seems to be one of the most indicated routes as it provides the capability of nanometric, serial and industrial quality fabrication. The maximum amount of quantum information per unit surface and the consequent space constraints on qubit operations are key parameters towards fault-tolerant quantum information processing (QIP) with Si qubits. Such maximum density of quantum information is expressed for the compact exchange-only Si double quantum dot qubit architecture as a function of the CMOS technology node. The size scale optimizing both physical qubit operation time and quantum error correction (QEC) requirements is assessed by reviewing the physical and technological constraints. We determine the workable operation frequency range of a Si-CMOS quantum processor to be within 1 and 100 GHz, which limits its feasibility only to the most advanced nodes. The compatibility with classical control circuitry is discussed, focusing on the cryogenic CMOS operation required to bring the classical controller as close as possible to the quantum processor and to enable interfacing thousands of qubits on the same chip. The operation time range prospected for cryogenic control electronics is found to be compatible with the qubit operation time. By combining the forecast of technology development with operation time and classical circuitry constraints, we derive a maximum quantum information density for logical qubits of 2.8 and 4 Mqb/cm for the 10-nm and 7-nm technology nodes respectively for the Steane code. The density is one and two orders of magnitude less for surface and concatenated codes respectively. Such values provide a benchmark for the development of Si-based fault tolerant QIP.
Artefacts in widespread use in electronic and optoelectronic systems have been manufactured by low-cost, high-volume processes. This chapter reviews recent progress and lack of progress on manufacturability of several nanoscale systems using the criteria: tunnel devices, split-gate transistors/quantum point contacts, and other nanoscale systems. For any real-world applications, such as in charge pumps for quantum metrology or specific quantum information processing systems, one needs a strategy to narrow the standard deviation of the device parameters. Of the attributes specific to manufacturability, reproducibility needs further improvement, simple simulations are available, and reliability and service life can be inferred from earlier cryogenic experiments. There are many examples of papers working on the new forms of carbon, fullerenes, nanotubes, and graphene, but these are still in the realms of one-offs in terms of individual or few devices, or very small and primitive integrated circuits. The same applies to other quasi-monolayer electron systems.
In this chapter, the author considers the borderline between manufacturability and unmanufacturability, and then examines the consequences on nanoelectronic device performance. As present, there are two distinct routes to manufacture of nanoscale artefacts. The dominant route is top-down, sculpting and adding selective volumes of materials to a starting substrate, using combinations of deposition (including epitaxy), etching and lithography. The other manufacturing approach is the bottom-up route, where small structures, such as nanowires or complex molecules, are deposited in arrays. The problems include the uniformity of the fabricated nanowires, or the lack of 5-nines purity starting molecular materials of any level of non-trivial internal complexity, the precise positional ordering of the nanostructures or molecules to achieve long range translational order without point or line defects, tight local orientation order, and the process of wiring up the array elements for addressing. epitaxial growth; nanoelectronics; performance evaluation; semiconductor device manufacture; zeolites
It is fairly easy to list the likely technical impacts of nanotechnology. The focus on applications to information processing, energy and health implies that these are the areas in which the greatest impact is foreseen. The most important impacts will, however, be on a broader plane, because nanotechnology epitomizes a deeper, more rational view of the universe, including all the practical aspects of our environment. Nevertheless, it is far from certain that humanity will take up the challenge of the new opportunities, the most potentially disruptive of which is the possibility for everyone to participate in shaping his or her own environment, as much a producer as a consumer. For this reason, those who hold this vision and see such a development as the only alternative offering a sustainable way forward for humanity (in other words for promoting its long-term survival) have a special responsibility to cultivate the vision and its realization.
We review the theoretical and experimental advances in nanometric-scale devices and single atom systems. Few electron devices are currently obtained either by fabricating nanometric-scale semiconductor FinFETs and quantum dots, or by doping them with few impurity atoms. Devices of such size, originally realized by employing either pre-industrial or laboratory processes, are now being fabricated in commercial 14 nm node architecture. They have lead, starting from the 90's, to the observation of classical non-linear effects, to spin- and orbital-related quantum effects, manipulation of few qubits and to many-body quantum effects. As scaling of devices continues, the natural question is whether single atom and few electron devices will represent the ultimate scaled technology. We highlight high points and major constraints and limitations to state-of-the-art fabrication based on lithography and doping, and their possible integration with different methods such as self-assembly, inspired by biology and natural systems. "At the atomic level, we have new kinds of forces and new kinds of possibilities, new kinds of effects. The problems of manufacture and reproduction of materials will be quite different. I am, as I said, inspired by the biological phenomena in which chemical forces are used in repetitious fashion to produce all kinds of weird effects (one of which is the author). R. Feynman, 1957"
This chapter examines the future of bionanotechnology from the perspective of public health, describing priority areas, a framework of risk governance, and ethics. It explains the precautionary principle from its origins in epidemiology, using asbestos as an example of where an early warning was given for a future public health issue. A brief history of chemistry, an outline of the developing process of nano-bio’s divergence from and convergence with nanotechnology, and the evolution of nano-bio in Japan as a societal issue, are also considered here. Nanotechnology, as well as nano-bio, will drastically change our relationship with nature. Nanotechnology and nanoscience involving nano-bio force us to reconsider the boundaries between nature and artifact. The chapter provides an overview of nanotechnology’s areas of application from the electrical and mechanical industries to biotechnology, medicine, nutrition, and public health. Biodevices and biosystems such as nanofabrication processes, nanomaterials, including analytical tools that can be applied to bionanotechnology, and bioimaging in nanomedicine are all examined.
Between a promising initial result in a laboratory and the commercial availability of a product there are many hoops to jump through, and indeed there is a severe attrition rate so that few results actually make it to products. In this article, I want to focus on the technical aspects of achieving a manufacturable prototype, but it must be remembered that commercial success is based on customers actually wanting to buy the product in the market place at the price on offer. I am particularly concerned about the issue of manufacturability precisely because is not the concern of the authors of the vast majority of papers that appear under the title of nanotechnology, and the subset in nanoelectronics. Indeed I think that the problem is so serious that there will be a welldeserved backlash against the whole of nanoscience if it is not rectified soon.
Only a small fraction of contemporary nanoscience will ever emerge as a functioning and commercial nanotechnology. Far too little attention is paid to the hoops and hurdles presented by the transition from science to technology by those who assert that their work will find applications. A systematic protocol is developed for appropriate investigations.
Self-assembled copper-silicide (Cu-Si) nanowires were prepared by the evaporation of Cu onto Si(001) under high vacuum conditions. The Cu-Si nanowires were studied in situ by scanning electron microscopy. Crystallographic, structural, and chemical properties of the nanowires were investigated by transmission electron microscopy at cross-sections of these nanowires fabricated by focused ion beam. In addition, chemical of nanowires were also studied by scanning transmission electron microscopy. The morphology of Cu-Si nanowires due to oxidation at ambient conditions was investigated as well. Experimental results obtained from the Cu-Si nanowires were compared to bulk data reported previously by other authors.
Developments in nanotechnology are making increasing demands on our ability to manipulate materials to designed patterns and structures. Patterning at increasingly diminished scales becomes very challenging, particularly with a view to manufacturing reproducible structures en masse. In fact Kelly recently argued that 'There are strict limits for which one-off fabrication is possible, but manufacture is not' [1]. Kelly was referring to top-down manufacturing processes and while activity in the field remains high and fruitful, there is at least as much research into bottom-up processes including self-assembly. In this issue, researchers at SASTRA University in India report programmable biomimetic self-assembly of carbon nanotubes (CNTs) using proteins [2]. The process uses changes in the surface charge and conformation of an unfolding protein, showing promise for biomedical applications and nanobiotechnology. Since the discovery of carbon nanotubes in 1990, their exceptional properties have inspired a cornucopia of applications, from the realms of science fiction with space elevators [3, 4], to more commercial merchandise such as tennis rackets [5]. A lot of applications based on CNTs use composites, and the properties of these composites can vary significantly depending on the manner in which the nanotubes are assembled. Researchers in the US recently reported experimental and simulation studies of thermal transport in carbon nanotubes [6]. Their work dealt with the discrepancy between the exceedingly high conductivity predicted and observed in single nanotubes and that reported for large assemblies. The work highlights some of the factors which diminish thermal conductivity in carbon nanotube assemblies, as well as identifying some optimal structures for maximizing thermal properties. The possible biomedical properties of carbon nanotubes have also attracted interest. However there has been debate over the potential for carbon nanotubes to support cell growth versus their potential toxicity. Researchers in New Jersey in the US have tackled these issues with a study of primary calvaria osteoblastic cell growth on single-walled carbon nanotube thin film substrates [7]. They describe a mechanism through which carbon nanotubes not only induce toxicity but also promote bone cell differentiation, leading to the formation of bone nodules. Bioapplications of nanomaterials often require bio-sympathetic methods for their production. The self-assembly achieved by viruses attracted the attention of Bancroft and his colleagues in the late 1960s [8, 9]. Since then a number of biomimetic approaches inspired by nature have been developed that allow fabrication of controlled complex structures with the potential for mass production [10, 11]. The tobacco mosaic virus has been demonstrated as one example of a useful biological template for simple and versatile nanopatterning [12]. Structures patterned using this biological toolbox may have applications in fields as broad as gas sensing and Li-battery electrodes. Researchers in Finland have also demonstrated the fabrication of complex protein structures using a DNA origami technique [13]. As the authors point out, controlled assembly of proteins has great potential for a range of biological applications and is also important for understanding fundamental biomolecular interactions. Many approaches to CNT assembly taken so far have required pre-patterning of a suitable substrate with a structure-directing agent to promote assembly of the nanotubes. However, as Nithiyasri et al in India point out in this issue, 'Assembly of CNTs in the dispersion medium would be more advantageous in terms of overcoming patterning hardships and cost as well as being suitable for a wide range of applications like biosensors, tissue engineering scaffolds and devices requiring high-density aligned domains of CNTs'. Their biomimetic approach uses thermally reversible denaturation of bovine serum albumin without the need for pre-patterning. In 1959 in his famous lecture 'There's plenty of room at the bottom', Feynman said 'What I want to talk about is the problem of manipulating and controlling things on a small scale' [14]. Fifty years later people are still talking about this, and as the work reported in this issue demonstrates so well, research in the field is still brimming with exciting developments. However, the paper by Nithiyasri et al does more than report an interesting phenomenon; it also proposes a mechanism for explaining how it happens. Feynman was also famous for his ability to explain things at an elementary level, and perhaps that was largely attributable to his genius for in-depth understanding of complex subjects. In fact he once remarked 'I couldn't do it', after an attempt to prepare a first-year student lecture on why spin one-half particles obey Fermi-Dirac statistics. He added, 'I couldn't reduce it to the freshman level. That means we don't really understand it.' What makes the developments in nanotechnology today so exciting is not just the advances in our ability to manipulate very small things, but our increasingly deepening understanding of how these processes operate. References [1] Kelly M J 2011 Intrinsic top-down unmanufacturability Nanotechnology 22 245303 [2] Nithiyasri P, Balaji K, Brindha P and Parthasarathy M 2012 Programmable self-assembly of carbon nanotubes assisted by reversible denaturation of a protein Nanotechnology 23 465603 [3] Clarke A C 1979 The Fountains of Paradise (London: Victor Gollancz) [4] Audacious & Outrageous: Space Elevators http://science.nasa.gov/science-news/science-at-nasa/2000/ast07sep_1/ [5] Babolat® NS™ Drive Tennis Racket http://www.nanotechproject.org/inventories/consumer/ browse/products/5130/ [6]Aliev A E, Lima M H, Silverman E M and Baughman R H 2010 Thermal conductivity of multi-walled carbon nanotube sheets: radiation losses and quenching of phonon modes Nanotechnology 21 035709 [7] Tutak W, Park K H, Vasilov A, Starovoytov V, Fanchini G, Cai S-Q, Partridge N C and Chhowalla M 2009 Toxicity induced enhanced extracellular matrix production in osteoblastic cells cultured on single-walled carbon nanotube networks Nanotechnology 20 255101 [8] Bancroft J B, Hills G J and Markham R 1967 A study of the self-assembly process in a small spherical virus formation of organized structures from protein subunits in vitro Virology 31 354-79 [9] Bancroft J B 1970 The self-assembly of spherical plant viruses Adv. Virus Res. 16 99-134 [10] Sarikaya M, Tamerler C, Jen A K-Y, Schulten K and Baneyx F 2003 Molecular biomimetics: nanotechnology through biology Nature Mater. 2 577-85 [11] Dickerson M B, Sandhage K H and Naik R R 2008 Protein- and peptide-directed syntheses of inorganic materials Chem. Rev 108 4935-78 [12] Gerasopoulos K, McCarthy M, Banerjee P, Fan X, Culver J N and Ghodssi R 2010 Biofabrication methods for the patterned assembly and synthesis of viral nanotemplates Nanotechnology 21 055304 [13] Kuzyk A, Laitinen K T and T¨orm¨a P 2009 DNA origami as a nanoscale template for protein assembly Nanotechnology 20 235305 [14] Feynman R P 1959 Plenty of room at the bottom www.its.caltech.edu/ ~feynman/plenty.html.
Starting from the conventional self-organized arrays of flat Co dots on Au(111), we extended the growth vertically to fabricate Co pillars. The principle is to deposit sequentially a fraction x of an atomic layer (AL) of Co and 1-x AL of Au. At each step, the deposited Co atoms aggregate on top of the previous dots, increasing their height by 1 AL. Pillars with a 2:1 vertical aspect ratio were achieved. Because of the large number of atoms per pillar, the superparamagnetic blocking temperature is 300 K in the pillars, whereas it is only 20 K in conventional flat dots with the same lateral density.
We consider charge qubit monitoring (continuous-in-time weak measurement) by a single-electron transistor (SET) operating in the sequential-tunneling regime. We show that commonly used master equations for this regime are not of the Lindblad form that is necessary and sufficient for guaranteeing valid physical states. In this paper we derive a Lindblad-form master equation and a corresponding quantum trajectory model for continuous measurement of the charge qubit by a SET. Our approach requires that the SET-qubit coupling be strong compared to the SET tunneling rates. We present an analysis of the quality of the qubit measurement in this model (sensitivity versus back action). Typically, the strong coupling when the SET island is occupied causes back action on the qubit beyond the quantum back action necessary for its sensitivity, and hence the conditioned qubit state is mixed. However, in one strongly coupled, asymmetric regime, the SET can approach the limit of an ideal detector with an almost pure conditioned state. We also quantify the quality of the SET using more traditional concepts such as the measurement time and decoherence time, which we have generalized so as to treat the strongly responding regime.
Hybrid mode-locking in monolithic quantum dot (QD) lasers is studied experimentally and theoretically. A strong asymmetry of the locking range with respect to the passive mode locking frequency is observed. The width of this range increases linearly with the modulation amplitude for all operating parameters. Maximum locking range found is 30 MHz. The results of a numerical analysis performed using a set of delay-differential equations taking into account carrier exchange between QDs and wetting layer are in agreement with experiments and indicate that a spectral filtering element could improve locking characteristics.
We propose a new drive mechanism for carbon nanotube (CNT) motors, based upon the torque generated by a flux of electrons passing through a chiral nanotube. The structure of interest comprises a double-walled CNT formed from, for example, an achiral outer tube encompassing a chiral inner tube. Through a detailed analysis of electrons passing through such a "windmill," we find that the current, due to a potential difference applied to the outer CNT, generates sufficient torque to overcome the static and dynamic frictional forces that exist between the inner and outer walls, thereby causing the inner tube to rotate.
Electronic devices based on carbon nanotubes are among the candidates to eventually replace silicon-based devices for logic applications. Before then, however, nanotube-based radiofrequency transistors could become competitive for high-performance analogue components such as low-noise amplifiers and power amplifiers in wireless systems. Single-walled nanotubes are well suited for use in radiofrequency transistors because they demonstrate near-ballistic electron transport and are expected to have high cut-off frequencies. To achieve the best possible performance it is necessary to use dense arrays of semiconducting nanotubes with good alignment between the nanotubes, but techniques that can economically manufacture such arrays are needed to realize this potential. Here we review progress towards nanotube electronics for radiofrequency applications in terms of device physics, circuit design and the manufacturing challenges.
This paper presents a study of sequence specific electronic conduction through short (15-base- pair) double-stranded (ds) DNA molecules, measured by immobilizing 3'-thiol-derivatized DNAs in nanometre scale gaps between gold electrodes. The polycation spermidine was used to stabilize the ds-DNA structure, allowing electrical measurements to be performed in a dry state. For specific sequences, the conductivity was observed to scale with the surface density of immobilized DNA, which can be controlled by the buffer concentration. A series of 15-base DNA oligonucleotide pairs, in which the centre sequence of five base pairs was changed from G: C to A: T pairs, has been studied. The conductivity per molecule is observed to decrease exponentially with the number of adjacent A: T pairs replacing G: C pairs, consistent with a barrier at the A: T sites. Conductance-based devices for short DNA sequences could provide sensing approaches with direct electrical readout, as well as label-free detection.
This text is a first attempt to pull together the whole of semiconductor science and technology since 1970 in so far as semiconductor multilayers are concerned. Material, technology, physics and device issues are described with approximately equal emphasis, and form a single coherant point of view. The subject matter is the concern of over half of today's active semiconductor scientists and technologists, the remainder working on bulk semiconductors and devices. It is now routine to design and the prepare semiconductor multilayers at a time, with independent control over the dropping and composition in each layer. In turn these multilayers can be patterned with features that as a small as a few atomic layers in lateral extent. The resulting structures open up many new ares of exciting solid state and quantum physics. They have also led to whole new generations of electronic and optoelectronic devices whose superior performance relates back to the multilayer structures. The principles established in the field have several decades to go, advancing towards the ultimate of materials engineering, the design and preparation of solids atom by atom. The book should appeal equally to physicists, electronic engineers and materials scientists.
We study the yield and reproducibility of quantized conductance in short one-dimensional quantum wires in split-gate transistors. In order to get an unambiguous assessment, more than 500 split gates have been fabricated and tested at 1.4 K. The study clearly shows that the devices are too sensitive to the inherent dopant structures and to variations of processing. The limitations of split gates also have been revealed through the fluctuations of the pinch-off voltage and the characteristics of the first quantized plateau.
The engineering of tunnel barriers has not yet succeeded to the point where low cost high volume manufacture of tunnel devices can be undertaken. We analyse one overriding reason for the unacceptable variability in device performance and suggest that engineered tunnel barriers are unlikely to play a role in extending the CMOS Roadmap, as has recently been suggested.
Carbon nanotubes are very attractive for a wide range of potential applications. However, many applications require the growth of aligned/micropatterned carbon nanotubes with or without a modified nanotube surface. Simple pyrolytic methods for large scale production of aligned/micropatterned carbon nanotube arrays perpendicular to the substrate surface have been developed. These aligned carbon nanotube arrays can be transferred onto various substrates of particular interest in either a patterned or non-patterned fashion. The perpendicularly-aligned structure provides advantages for not only an efficient device construction but also surface functionalisation (both the inner and outer wall) while their alignment structure can be largely retained. These aligned carbon nanotubes with tunable surface characteristics are of great significance to various practical applications, ranging from plastic optoelectronics to bioceramics. Examples include biomolecule immobilised carbon nanotube biosensors, synthetic polymer supported aligned carbon nanotube chemical vapour sensors, metal nanoparticle decorated carbon nanotubes, and aligned coaxial nanowires of carbon nanotubes sheathed with titanium dioxide (TiO2) nanoparticles or thin films. These newly synthesised carbon nanotubes decorated with polymers, metal nanoparticles, and/or TiO2 coatings were demonstrated to show novel optoelectronic properties and should possess good bioactive behaviours with enhanced tissue attachment attractive for functional optoelectronic and bioceramic applications. This article reviews recent work carried out in the authors group on the preparation of nanocomposites based on aligned carbon nanotubes functionalised with polymers or metal (oxide) nanoparticles. Their potential applications as plastic optoelectronics and bioceramics will also be discussed.
The fabrication of very narrow metal lines by the lift-off technique, especially below sub-10 nm, is challenging due to thinner resist requirements in order to achieve the lithographic resolution. At such small length scales, when the grain size becomes comparable with the line-width, the built-in stress in the metal film can cause a break to occur at a grain boundary. Moreover, the line-width roughness (LWR) from the patterned resist can result in deposited metal lines with a very high LWR, leading to an adverse change in device characteristics. Here a new approach that is not based on the lift-off technique but rather on low temperature hydrogen reduction of electron-beam patterned metal naphthenates is demonstrated. This not only enables the fabrication of sub-10 nm metal lines of good integrity, but also of low LWR, below the limit of 3.2 nm discussed in the International Technology Roadmap for Semiconductors. Using this method, sub-10 nm nickel wires are obtained by reducing patterned nickel naphthenate lines in a hydrogen-rich atmosphere at 500 °C for 1 h. The LWR (i.e., 3 σLWR) of these nickel nanolines was found to be 2.9 nm. The technique is general and is likely to be suitable for fabrication of nanostructures of most commonly used metals (and their alloys), such as iron, cobalt, nickel, copper, tungsten, molybdenum, and so on, from their respective metal–organic compounds.
Semiconductor nanostructures with sizes down to a few nanometers can be defined in different, highly parallel processes with
the aid of polymers. In a "top-down" approach, either micelles formed by diblock-copolymers or other self-assembled patterns
like "breath figures" or imprints of colloids in polymer films are used for the formation of metal masks of different sizes
on semiconductors in a first preparation step. These metal masks are then used in an anisotropic dry-etching process for the
shaping of pillars in the semiconductor material. After additional evaporation and etching steps, dense patterns of nano-holes
in metal films can be produced. In a "bottom-up" approach, micelles act as nano-reactors for the formation of metal clusters
of Zn, Cd, Mg or Cu which then can be oxidized so as to form nanocrystals of the oxidic semiconductors ZnO, CdO, MgO, and
CuO. When Au salts are added to the micelles, Au dots remain after removal of the organic compounds. These can be used as
catalysts for the growth of ZnO nanopillars with high aspect ratio. Even ring-shaped (Zn,Cd)O semiconductor patterns can be
formed starting with nanoporous polymer membranes, which are loaded by appropriate metal salts and then removed in an oxygen
plasma, leaving "donut"-like (Zn,Cd)O rings. Production, structure and optical properties of these nanostructures are discussed.
A status report on optical negative-index-metamaterial fabrication is given. The advantages, drawbacks and challenges of different fabrication techniques including electron-beam lithography (EBL), focused-ion beam (FIB) milling, interference lithography (IL) and nanoimprint lithography (NIL) and direct laser writing are outlined. Since the possibility of creating a truly three-dimensional (3D) metamaterial is critical for real-life applications and the future of this research area, the recent developments on large-scale, multiple-functional-layer metamaterials are discussed in detail, and alternative methods for 3D fabrication of complex structures are mentioned. Throughout the report, main breakthroughs in fabrication of optical negative-index metamaterials are described, as well as challenges facing future manufacturing of optical metamaterials.
For many potential applications, carbon nanotubes must be chemically modified, but the reactions involved aren't easily controlled. The discovery of a reversible modification process is a step towards such control.