Bose-Einstein condensation (BEC) has been observed in a dilute gas of sodium atoms. A Bose-Einstein condensate consists of a macroscopic population of the ground state of the system, and is a coherent state of matter. In an ideal gas, this phase transition is purely quantum-statistical. The study of BEC in weakly interacting systems which can be controlled and observed with precision holds the promise of revealing new macroscopic quantum phenomena that can be understood from first principles.

Bose-Einstein condensation in a gas of sodium atoms

Biomolecular motors such as F 1 –adenosine triphosphate synthase (F 1 -ATPase) and myosin are similar in size, and they generate forces compatible with currently producible nanoengineered structures. We have engineered individual biomolecular motors and nanoscale inorganic systems, and we describe their integration in a hybrid nanomechanical device powered by a biomolecular motor. The device consisted of three components: an engineered substrate, an F 1 -ATPase biomolecular motor, and fabricated nanopropellers. Rotation of the nanopropeller was initiated with 2 mM adenosine triphosphate and inhibited by sodium azide.

https://science.sciencemag.org/content/sci/290/5496/1555.full.pdf

Powering an Inorganic Nanodevice with a Biomolecular Motor

Nanofabrication by electron beam lithography and its applications

In the past decade, the feature size in ultra large-scale integration (ULSI) has been continuously decreasing, leading to nanostructure fabrication. Nowadays, various lithographic techniques ranging from conventional methods (e.g. photolithography, x-rays) to unconventional ones (e.g. nanoimprint lithography, self-assembled monolayers) are used to create small features. Among all these, resist-based electron beam lithography (EBL) seems to be the most suitable technique when nanostructures are desired. The achievement of sub-20-nm structures using EBL is a very sensitive process determined by various factors, starting with the choice of resist material and ending with the development process. After a short introduction to nanolithography, a framework for the nanofabrication process is presented. To obtain finer patterns, improvements of the material properties of the resist are very important. The present review gives an overview of the best resolution obtained with several types of both organic and inorganic resists. For each resist, the advantages and disadvantages are presented. Although very small features (2-5 nm) have been obtained with PMMA and inorganic metal halides, for the former resist the low etch resistance and instability of the pattern, and for the latter the delicate handling of the samples and the difficulties encountered in the spinning session, prevent the wider use of these e-beam resists in nanostructure fabrication. A relatively new e-beam resist, hydrogen silsesquioxane (HSQ), is very suitable when aiming for sub-20-nm resolution. The changes that this resist undergoes before, during and after electron beam exposure are discussed and the influence of various parameters (e.g. pre-baking, exposure dose, writing strategy, development process) on the resolution is presented. In general, high resolution can be obtained using ultrathin resist layers and when the exposure is performed at high acceleration voltages. Usually, one of the properties of the resist material is improved to the detriment of another. It has been demonstrated that aging, baking at low temperature, immediate exposure after spin coating, the use of a weak developer and development at a low temperature increase the sensitivity but decrease the contrast. The surface roughness is more pronounced at low exposure doses (high sensitivity) and high baking temperatures. A delay between exposure and development seems to increase both contrast and the sensitivity of samples which are stored in a vacuum after exposure, compared to those stored in air. Due to its relative novelty, the capabilities of HSQ have not been completely explored, hence there is still room for improvement. Applications of this electron beam resist in lithographic techniques other than EBL are also discussed. Finally, conclusions and an outlook are presented.

/pdf/resists-for-sub-20-nm-electron-beam-lithography-with-a-focus-kriwryl4od.pdf

Resists for sub-20-nm electron beam lithography with a focus on HSQ: state of the art.

Ligand exchange reactions of 1.5-nm triphenylphosphine-stabilized nanoparticles with omega-functionalized thiols provides a versatile approach to functionalized, 1.5-nm gold nanoparticles from a single precursor. We describe the broad scope of this method and the first mechanistic investigation of thiol-for-phosphine ligand exchanges. The method is convenient and practical and tolerates a surprisingly wide variety of technologically important functional groups while producing very stable nanoparticles that essentially preserve the small core size and size dispersity of the precursor particle. The mechanistic studies reveal a novel three-stage mechanism that can be used to control the extent of ligand exchange. During the first stage of the exchange, AuCl(PPh3) is liberated, followed by replacement of the remaining phosphine ligands as PPh3 (assisted by gold complexes in solution). The final stage involves completion and reorganization of the thiol-based ligand shell.

Thiol-Functionalized, 1.5-nm Gold Nanoparticles through Ligand Exchange Reactions: Scope and Mechanism of Ligand Exchange

New nonpolymer materials, calixarene derivatives were tested as high‐resolution negative resists for use in electron beam lithography. Arrays of 12‐nm‐diam dots with a 25 nm pitch were fabricated easily. The sensitivity of calixarene in terms of area dose ranged from 700 to 7000 μC/cm2, and the required dose for dot fabrication was about 105 electrons/dot. The standard area dose for calixarene is almost 20 times higher than that for polymethyl methacrylate (PMMA), but the electron spot dose for dot fabrication by calixarene is almost the same as that for PMMA and other highly sensitive resists such as SAL (chemically amplified negative resist for electron beam made by Shipley). The electron spot dose for such extremely small dots does not seem to depend on standard area dose, but any resist tends to require the same dose under exposure in a 50 keV electron beam writing system. We propose a qualitative exposure model that suggests a tradeoff of dose and dot size. The calixarene seems to be promising materi...

Nanometer‐scale resolution of calixarene negative resist in electron beam lithography

New electron beam (EB) resists made of calixarene resists are introduced. Typical sensitivities of calixarene resists range from 700 µ C/cm2 to 7 mC/cm2. High-density dot arrays with 15 nm diameter constructed using calixarene resist were easily delineated using a point EB lithography system. Our results suggest that the resolution limit of calixarene resists is dominated by a development process such as adhesion to a substrate rather than by the EB profile. Calixarene resists are resistant to etching by halide plasma. We also demonstrated nanoscale devices processed by using calixarene resists. Calixarene resists are promising materials for nanofabrication.

Calixarene Electron Beam Resist for Nano-Lithography

The device feature size in Si ULSIs has been reduced over the years, and sooner or later we will probably enter the so-called nanoelectronics era. Two nanofabrication technologies, electron-beam lithography and atomic-beam holography, which are expected to play an important role in the coming era, are discussed first. In order to get finer patterns with electron-beam lithography, improvements in the characteristics of organic resists are crucially important. Organic negative resists with a fine resolution have been developed, and a high-quality resist line pattern with a width as small as 7 nm has been successfully formed. A new atom manipulation technique called atomic-beam holography has been proposed for nanofabrication. It enables direct pattern formation on a substrate by passing laser-cooled atoms through a computer-generated hologram. It is expected to be a technique with a fine resolution, reaching the atomic scale, and a high throughput. Nano-size devices are developed from two standpoints. One pursues the miniaturization limit of MOS transistors: in this context, we discuss the fabrication of MOS transistors with gate length down to 14 nm and their electrical characteristics. The other approach is to explore `breakthrough devices' that utilize quantum effects: single electron devices are one type of such devices. We discuss the operation of an all-metallic single-electron memory cell along with the electrical characteristics of a single-electron transistor made of aluminium.

http://iopscience.iop.org/article/10.1088/0957-4484/10/2/306/pdf

Nanofabrication toward sub-10 nm and its application to novel nanodevices

We studied nanometer-scale patterning using a polystyrene negative resist in electron beam lithography We found that the use of a low-molecular-weight polystyrene enables 10-nm-level patterning at low-acceleration voltage We also found that the spot dose of such ultrasmall patterns formed at a 5 kV acceleration voltage was one-tenth of that formed at 50 kV Low-voltage electron beam lithography is a suitable technique for organic resist nanopatterning The Charlesby theory can still be applied to nanodot formation, and we can therefore estimate the dot sensitivity for various polystyrene molecular weights We suppose that an exposure model is based on polymer aggregation to explain the formation of a 10-nm-level pattern with a height of 40 nm can be formed by using a small molecule, not a large one

https://iopscience.iop.org/article/10.1143/JJAP.36.7773/pdf

Nanometer-Scale Patterning of Polystyrene Resists in Low-Voltage Electron Beam Lithography

Calixarene is a promising high-resolution negative electron-beam resist having a resolution of the order of 10nm because of its low molecular weight. We have made a purified calixarene resist containing metal contaminants whose concentrations are measured in parts per billion and which therefore do not degrade the performance of silicon devices. The purity of the calixarene itself was also improved and we obtained high-purity calix[6]arene and high-purity calix[7]arene, in both of which contain the main component is more than 95% of all the calixarene present. The resolution of both purified calixarene resists is almost same as that the nonpurified calixarene, but the sensitivity of calix[7]arene is higher than that of calix[6]arene because its molecular weight is higher.

Eiichi Nomura

Papers

Nanometer‐scale resolution of calixarene negative resist in electron beam lithography

Calixarene Electron Beam Resist for Nano-Lithography

Nanofabrication toward sub-10 nm and its application to novel nanodevices

Nanometer-Scale Patterning of Polystyrene Resists in Low-Voltage Electron Beam Lithography

High-resolution, High-purity Calix[n]arene Electron Beam Resist.