Nanometer-scale Objects Research Articles

Resolving three-dimensional shape of sub-50 nm wide lines with nanometer-scale sensitivity using conventional optical microscopes

We experimentally demonstrate that the three-dimensional (3-D) shape variations of nanometer-scale objects can be resolved and measured with sub-nanometer scale sensitivity using conventional optical microscopes by analyzing 4-D optical data using the through-focus scanning optical microscopy (TSOM) method. These initial results show that TSOM-determined cross-sectional (3-D) shape differences of 30 nm–40 nm wide lines agree well with critical-dimension atomic force microscope measurements. The TSOM method showed a linewidth uncertainty of 1.22 nm (k = 2). Complex optical simulations are not needed for analysis using the TSOM method, making the process simple, economical, fast, and ideally suited for high volume nanomanufacturing process monitoring.

Designing a symmetry-protected molecular device

Realizing a quantum transistor built of molecules or quantum dots has been one of the most ambitious challenges in nanotechnology. Even though remarkable progress has been made, being able to gate and control nanometer scale objects, as well to interconnect them to achieve scalability remains extremely difficult. Most experiments concern a single quantum dot or molecule, and they are made at ultra low temperature to avoid decoherence and tunneling. We propose to use canonical transformations to design quantum devices that are protected by symmetry, and therefore, may be operational at high temperatures. We illustrate the idea with examples of quantum transistor architectures that can be connected both in series and parallel.

Carbon origami

A reaction that folds up large aromatic molecules and fixes them into bowl shapes expands opportunities for making nanometre-scale objects from single sheets of carbon. Such objects have potential applications in electronics.

Faltkunst mit DNA-Origami

Many processes in biology rely fundamentally on the relative position and orientation of interacting molecules. It is notoriously difficult to observe, let alone control, the position and orientation of molecules because of their small size and the constant thermal fluctuations that they experience. Molecular self-assembly with DNA origami enables building customshaped nanometer-scale objects with molecular weights in the megadalton regime. It provides a unique route for placing molecules and constraining their fluctuations in user-defined ways and thus opens up completely new avenues for scientific exploration.

Self-assembly of polylactic acid and cholesterol-modified dextran into hollow nanocapsules

Abstract A study of the direct preparation of hollow polymer nanocapsules which composed of the biocompatible and biodegradable polymers, polysaccharide and polylactic acid (PLA), was presented. By the dialysis of a DMSO solution of cholesterol-modified dextran (Chol-Dex) and poly( d , l -lactic acid) against water, hollow polymer nanocapsules with a highly stable structure and relatively narrow size distribution were obtained. The formation mechanism and the effects of various factors such as PLA molecular weight and the weight ratio of Chol-Dex to PLA on the formation of hollow polymer nanocapsules were investigated by SEM, TEM and 1 H NMR analysis. The results showed that hollow capsules were obtained when the weight ratio of Chol-Dex to PLA was between 3:1 and 1:1, and when PLA of molecular weights greater than 360 Da were used. The hollow capsules with a sandwich shell structure derived from deposition of PLA and some amphiphilic polysaccharide on the internal interface of the polysaccharide-coated aggregates, which were formed through phase separation during the initial phase of the dialysis. This novel approach to hollow polymer nanocapsule formation represents a rare example of the self-assembly of two biocompatible polymers into nanometer-scale objects with interesting structures, shapes and morphology through a simple assembly process.

Raman Spectroscopy of Lithographically Patterned Graphene Nanoribbons

Nanometer-scale graphene objects are attracting much research interest because of newly emerging properties originating from quantum confinement effects. We present Raman spectroscopy studies of graphene nanoribbons (GNRs), which are known to have nonzero electronic bandgap. GNRs of width ranging from 15 to 100 nm have been prepared by e-beam lithographic patterning of mechanically exfoliated graphene followed by oxygen plasma etching. Raman spectra of narrow GNRs can be characterized by an upshifted G band and a prominent disorder-related D band originating from scattering at the ribbon edges. The D-to-G band intensity ratio generally increases with decreasing ribbon width. However, its decrease in width of <25 nm, partly attributed to amorphization at the edges, provides a valuable experimental estimate on D mode relaxation length of <5 nm. The upshift in the G band of the narrowest GNRs can be attributed to confinement effect or chemical doping by functional groups on the GNR edges. Notably, GNRs are much more susceptible to photothermal effects resulting in reversible hole doping caused by atmospheric oxygen than bulk graphene sheets. Finally we show that the 2D band is still a reliable marker in determining the number of layers of GNRs despite its significant broadening for very narrow GNRs.

A primer to scaffolded DNA origami

Molecular self-assembly with scaffolded DNA origami enables building custom-shaped nanometer-scale objects with molecular weights in the megadalton regime. Here we provide a practical guide for design and assembly of scaffolded DNA origami objects. We also introduce a computational tool for predicting the structure of DNA origami objects and provide information on the conditions under which DNA origami objects can be expected to maintain their structure.

Standardization of Excitation Efficiency in Near-field Scanning Optical Microscopy

Near-field scanning optical microscope (NSOM or SNOM) is a form of scanning probe microscope (SPM), which is used to observe the optical properties of a sample surface with a nanometer-scale spatial resolution. Since the near-field light strongly interacts with the sample surface, or with nanometer-scale objects on the substrate's surface, NSOM is advantageous to excite only the vicinity of a sample surface. From the view point of surface chemical analysis, a discussion about the light energy concentration within a nanometer-scale region, and an estimation of its efficiency are indispensable for accurate measurements of the optical properties in a nanometer-scale region. In this paper, we describe the concept, the cautions and the general guidelines of a method to measure the excitation efficiency of aperture-type NSOM instruments.

Direct Synthesis of Polymer Nanocapsules: Self-Assembly of Polymer Hollow Spheres through Irreversible Covalent Bond Formation

A detailed study of the direct synthesis of polymer nanocapsules, which does not require any template, and core removal, is presented. Thiol-ene "click" reaction between a CB[6] derivative (1) with 12 allyloxy groups at the periphery and dithiols directly produced polymer nanocapsules with a highly stable structure and relatively narrow size distribution. Based on a number of observations including the intermediates detected by DLS, TEM, and SEM studies, a mechanism of the nanocapsule formation was proposed, which includes 2D oligomeric patches turning into a hollow sphere. A theoretical study supports that the formation of a hollow sphere from a disk-shaped intermediate can be thermodynamically favorable under certain conditions. In particular, the effects of various factors such as monomer concentration, reaction temperature, and medium on the formation of polymer nanocapsules have been investigated, which qualitatively agree with those predicted by our theoretical model. An interesting feature of the polymer nanocapsules was that the polymer shell made of a CB[6] derivative allows facile tailoring of its surface properties in a noncovalent and modular manner by virtue of the unique recognition properties of the accessible molecular cavities exposed on the surface. Furthermore, this approach appears to be applicable to any building unit with a flat core and multiple polymerizable groups at the periphery which can direct polymer growth in lateral directions. Other reactions, such as amide bond formation, can be used for the synthesis of polymer nanocapsules in this approach. This novel approach to polymer nanocapsules represents a rare example of self-assembly of molecular components into nanometer-scale objects with interesting structures, shapes, and morphology through irreversible covalent bond formation.

Surface hydrophilization of electrospun PLGA micro-/nano-fibers by blending with Pluronic® F-108

Poly(lactide-co-glycolide) (PLGA) has been widely explored as scaffolds in tissue engineering. However, its hydrophobicity can adversely affect events such as protein adsorption and downstream cell adhesion in tissue engineering applications. Although surface modification techniques (high energy radiation/chemical treatment) to modify the hydrophobicity of PLGA can be useful at the macroscopic scale, their usefulness for micro-/nano-meter scale objects can be limited due to adverse affects on physical properties. Therefore, in this study we report the surface hydrophilization of electrospun micro-/nano-fiber meshes of PLGA (85:15) by blending with small quantities (0.5–2%) of a non-ionic surfactant Pluronic® F-108 (PF-108). The blended fiber meshes showed a decrease in surface contact angle when compared to pure PLGA fiber meshes demonstrating an improvement in surface hydrophilicity due to blending. This was corroborated by XPS analysis that demonstrated surface enrichment of PF-108. Thermal and mechanical studies demonstrated that blending with small quantities of PF-108 do not compromise the bulk properties of PLGA. Therefore these studies demonstrated the feasibility of hydrophilization of electrospun PLGA micro-/nano-fibers, without compromising the bulk properties (thermal and mechanical) of native PLGA.

Glyconanomaterials: synthesis, characterization, and ligand presentation.

Glyconanomaterials, nanomaterials carrying surface-tethered carbohydrate ligands, have emerged and demonstrated increasing potential in biomedical imaging, therapeutics, and diagnostics. These materials combine the unique properties of nanometer-scale objects with the ability to present multiple copies of carbohydrate ligands, greatly enhancing the weak affinity of individual ligands to their binding partners. Critical to the performance of glyconanomaterials is the proper display of carbohydrate ligands, taking into consideration of the coupling chemistry, the type and length of the spacer linkage, and the ligand density. This article provides an overview of the coupling chemistry for attaching carbohydrate ligands to nanomaterials, and discusses the need for thorough characterization of glyconanomaterials, especially quantitative analyses of the ligand density and binding affinities. Using glyconanoparticles synthesized by a versatile photocoupling chemistry, methods for determining the ligand density by colorimetry and the binding affinity with lectins by a fluorescence competition assay are determined. The results show that the multivalent presentation of carbohydrate ligands significantly enhances the binding affinity by several orders of magnitude in comparison to the free ligands in solution. The effect is sizeable even at low surface ligand density. The type and length of the spacer linkage also affect the binding affinity, with the longer linkage promoting the association of bound ligands with the corresponding lectins.

AFM Observation of Single Membrane Proteins and its Application to Nano Biodevices

Recent progress on nanotechnology including nanostructure fabrication and nanometer-scale measurement techniques, and work on biomolecules whose size is equivalent to that covered by nanotechnology, are expected to result in the creation of a new research field called nano-bio science. This article introduces our recent work on the observation of single biomolecule; reconstituted a receptor protein into an artificial lipid membrane using an atomic force microscope (AFM). An AFM is a measurement tool that enables us to observe nanometer-scale objects in a liquid environment. We also examine the orientation of the proteins in proteoliposomes with the dynamic light scattering technique (DLS). Most receptor proteins have orientations in molecules, for example the extracellular and intracellular domains. Determining the protein orientation is essential for nano-biodevice fabrication if we wish to utilize the protein's function. We also introduce our recent attempt to realize a nano-bio device; a very small device obtaining and utilizing biological functions; using our state-of-the-art nanofabrication technique and a technique for handling receptor proteins. Thus, by combining nanotechnology and biotechnology to realize nano-biodevices, we can produce ultra-small biological sensors for implantation. Further improvements are expected.

Nanotech: Bigger isn't better

Over the years, scientists haven't settled for merely observing worlds existing on grains of sand, they've also created them. Once, all motors, engines, or pumps were noisy iron masses that could only be moved with great difficulty. Now, some are delicate wisps that can only be seen under an electron microscope. When researchers at ATT they prefer to be part of the assembly line. The microscopes that now enable them to see nanometer-scale objects offer this opportunity. The tiny probe of a scanning tunneling microscope flies above the surface of an object, sensing individual atoms. The same probes can give scientists a hand to push the atoms around. One futuristic application of nanotechnology might produce tiny surgical robots to repair the body from the inside, improving on its natural healing machinery. These tiny medical teams could even do a search-and-destroy on a virus, Peterson proposes. Currently, the sweetest fruits of nanotechnology still live in the world of dreams, but scientists are not slumbering. Soon, they will move their human-made nanoworlds out from under the microscope to invigorate the macroscopic world. Then, nanotechnology's benefits-and pitfalls-will be visible to the naked eye. D

The RHEED tracking of the droplet epitaxial grown quantum dot and ring structures

Self-assembled strain-free GaAs quantum dot and quantum ring structures grown by droplet epitaxy were investigated by the RHEED technique. The temporal evolution of these nanometer-scale objects were tracked in situ manner during the growth process. The initial stage of the surfaces was the same for both kinds of quantum objects. We have compared step by step the RHEED pattern in [ 1 1 ¯ 0 ] direction in the case of both quantum objects. After the Ga deposition the pattern becomes diffuse. Almost at the same time with the offering of arsenic the RHEED pattern changed from diffuse to spotty and later changed slowly to spots with chevrons in case of the quantum dot. In case of the quantum ring the situation is quite different. The pattern, which consists of streaks and spots, evaluate slowly and continuously. The different patterns and their different temporal evaluations can be explained with the shape and the kinetic of development of different quantum objects.

Multiple Exciton Generation in InAs Nanocrystals

Limitations of the efficiency of the existing solar cells motivate continuous search for new technological solutions that might lead to more efficient photovoltaic conversion. Among systems that are investigated for possible use in solar energy conversion devices are semiconductor quantum dots. A few ways of employing these nanometer-scale objects in the photoconversion process have been proposed [1, 2], one of which is multiple exciton generation in nanocrystals. Such an effect, consisting in generation of two or more electron–hole pairs by a single absorbed photon, has been observed in a few recent experiments performed on nanocrystals formed of various narrow-gap semiconductors [3–5]. It is a matter of discussion whether the excitons are created coherently during the absorption process or incoherently, due to carrier kinetics involving some kind of dissipative processes at a later time. In any case, the process results from the Coulomb coupling between electron and trion states. As a result, an intraband transition (relaxation) of the electron may be accompanied by the creation of another electron–hole pair, as shown in Fig. 1a. This Auger-type process is referred to as impact ionization. Let us note that the hole, which is initially created in the same confined state as the electron, does not take part in the impact ionization process. In this paper we formulate and study a simple theoretical model of coherent multiple exciton generation by a single high-energy photon absorbed in an InAs nanocrystal. We calculate the interband Coulomb matrix element between an excited electron state and a ground state trion. We determine the degree of mixing

Nanometer-Scale Manipulation and Ultrasonic Cutting Using an Atomic Force Microscope Controlled by a Haptic Device as a Human Interface

We describe a nanometer-scale manipulation and cutting method using ultrasonic oscillation scratching. The system is based on a modified atomic force microscope (AFM) coupled with a haptic device as a human interface. By handling the haptic device, the operator can directly move the AFM probe to manipulate nanometer scale objects and cut a surface while feeling the reaction from the surface in his or her fingers. As for manipulation using the system, nanometer-scale spheres were controllably moved by feeling the sensation of the AFM probe touching the spheres. As for cutting performance, the samples were prepared on an AT-cut quartz crystal resonator (QCR) set on an AFM sample holder. The QCR oscillates at its resonance frequency (9 MHz) with an amplitude of a few nanometers. Thus it is possible to cut the sample surface smoothly by the interaction between the AFM probe and the oscillating surface, even when the samples are viscoelastics such as polymers and biological samples. The ultrasonic nano-manipulation and cutting system would be a very useful and effective tool in the fields of nanometer-scale engineering and biological sciences.

Reconsideration of Continuum Thermomechanical Quantities in Atomic Scale Simulations

As motivation builds to consider mechanics of nanometer scale objects, it is increasingly advantageous to implement models with finer resolution than standard continuum approaches. For such exercises to prove fruitful, these models must be able to quantify continuum thermomechanical quantities; furthermore, it may be necessary to do so on a sub-system level in order to assess gradients or distributions in a given property. Herein we review the calculation of stress, heat flux, and temperature in atomic scale numerical simulations such as the molecular dynamics method.

Supramolecular Assembly of Nanoparticles at Liquid–Liquid Interfaces

At the interface: The supramolecular organization of nanometer-scale objects is of great interest in the field of applied nanotechnology. Liquid–liquid interfaces can provide an alternative to current methods for the formation of highly ordered structures through the self-assembly of nanoparticles, nanocrystals, and even viruses (see picture). The concept is generally applicable and can be transferred to other interfaces, such as those of polymers.

Inside-Out Disruption of Silica/Gold Core−Shell Nanoparticles by Pulsed Laser Irradiation

Near-infrared (NIR) femtosecond laser irradiation of metallodielectric core-shell silica-gold (SiO(2)-Au) nanoparticles can induce extreme local heating prior to the rapid dissipation of energy caused by the large surface area/volume ratio of nanometer-scale objects. At low pulse intensities, the dielectric silica core is removed, leaving an incomplete gold shell behind. The gold shells with water inside and out still efficiently absorb NIR light from subsequent pulses, showing that a complete shell is not necessary for absorption. At higher pulse intensities, the gold shell itself is melted and disrupted, leading to smaller, approximately 20-nm gold nanoparticles. Spectroscopic measurements show that this disruption is accompanied by optical hole burning of the peak at 730 nm and formation of a new peak at 530 nm. The silica removal and gold shell disruption confirms significant temperature rise of the core-shall nanoparticle. However, the entire process leads to minimal heating of the bulk solution due to the low net energy input.

Nanoantennas for Light Emission

Radio antennas have long been used to increase the amount of radiated power and modify the emission direction of the radio waves. In his Perspective, Greffet discusses recent attempts to apply these ideas to the design of optical antennas, which could find applications in quantum information processing and spectroscopy of nanometer-scale objects. The author highlights the report by MA¼hlschlegel et al. , who show that although optical antennas face challenges that are not encountered at radio wavelengths, radio antenna designs can nevertheless be reproduced successfully at optical wavelengths. Many other designs are being investigated in this rapidly expanding field.