Nanoscale Techniques Research Articles

An Overview of Nanoscale Techniques for Photovoltaics and Solar Cell Fabrication

An Overview of Nanoscale Techniques for Photovoltaics and Solar Cell Fabrication

Engineered low-dimensional nanomaterials for sensors, actuators, and electronics

We present an overview of our research on nanoelectronics and nanomechanics based on low-dimensional materials, including carbon nanotubes and graphene. Our primary research focus is on carbon nanotube and graphene architectures for electronics, energy harvesting, and sensing applications. We are also investigating an atomically precise graphene nanomachining method as well as a high-throughput desktop nanolithography process. In addition, we are exploiting nanomechanical actuators and nanoscale measurement techniques for reconfigurable arrayed nanostructures with applications in THz antennas, remote detectors, and biomedical nanorobots. Last, we are studying the effect of antibody functionalized nickel nanowires to improve cell separation techniques. These design, nanofabrication, manipulation, and characterization processes will enable next-generation nanoelectronics that have a wide range of applications including sensors, detectors, system-on-a-chip, system-in-a-package, programmable logic controls, energy storage systems, and all-electronic systems.

At the nanoscale: nanohemostat, a new class of hemostatic agent

Three basic categories of hemostats are widely used in surgery today: chemical agents, thermal devices, and mechanical methods that use pressure or ligature to slow bleeding. Each has its benefits and limitations. However, nanotechnology is rapidly ushering in new medical technologies. This review focuses on the 'nanohemostat', a new class of hemostatic agent that stops bleeding in less than 15 seconds by using (RADA)4, referred to as nanohemostat-1 (NHS-1), a synthetic biological material that self-assembles at the nanoscale when applied to a wound, and compares it to the characteristics of the 'ideal hemostat'.

PROBING INDIVIDUAL CHEMICAL EVENTS

FLUORESCENCE MICROSCOPY can pinpoint individual chemical reactions in real time as they occur at the interface between a solution and the surface of a key industrial catalyst support, according to a study by researchers at the University of California, Irvine ( J. Am Chem. Soc., DOI: 10.1021/ja105517d). The technique provides molecularly resolved maps and live-action movies depicting the chemical evolution of discrete metal complexes as they bind to functionalized silica surfaces. The products could serve as models of supported metal catalysts. That level of detail cannot be obtained from analytical methods that survey average properties of large numbers of molecules or from nanoscale techniques that probe static chemical systems. To monitor the single-molecule events, UC Irvine chemists N. Melody Esfandiari, Yong Wang, Suzanne A. Blum, and coworkers treated glass (silica) microscope coverslips with a triethoxysilyl thiourea compound. The team carried out that preparation step in a manner that patterned t...

Characterising gate dielectrics in high mobility devices using novel nanoscale techniques

Strained Si and strained SiGe layers can increase the speed of MOS devices through enhanced electron and hole mobilities compared with bulk Si. However, epitaxial growth of strained Si and SiGe layers induces surface roughness which impacts gate dielectric properties including leakage, breakdown and interface traps. Gate dielectric quality is conventionally studied at a macroscopic level on individual transistors or capacitors. To understand precisely the effect of roughness on the quality and reliability of dielectrics on high mobility substrate devices requires high spatial resolution characterisation techniques. Device processing modifies the dielectric/semiconductor interface compared with its initial form. Therefore nanoscale analysis on completed devices is necessary. In this work, we present new techniques to enable gate leakage analysis on a nanoscale in fully processed high mobility MOSFETs. This is achieved by careful selective removal of the gate from the dielectric followed by C-AFM measurements on the dielectric surface. Raman spectroscopy, AFM and SEM (EDX) confirmed complete layer removal. The techniques are applied to strained Si devices which have different surface morphologies and different macroscopic electrical data. Dielectric reliability is also assessed through device stressing.

Powder diffraction with spin polarized neutrons

The polarized neutron diffraction (PND) and spherical neutron polarimetry (SNP) techniques are very powerful tools and provide arguably the most sensitive methods for determining magnetization distributions at all the positions of the chemical. However, they can only apply to single crystals. Because of the difficulties encountered in growing sufficiently large samples of molecular magnets, and the inability to measure efficiently powder samples and more specifically nanoscale systems, the PND and SNP techniques are inadequate for a number of highly interesting subjects. We present a new technique taking advantage of the recent progress of the polarized 3He neutron spin filters that should overcome these limitations and which we propose to call the ‘flipping difference method’. We describe the measurement strategy, the data analysis technique and preliminary analysis of the results of the first measurements.

Axon repair: surgical application at a subcellular scale

Injury to the nervous system is a common occurrence after trauma. Severe cases of injury exact a tremendous personal cost and place a significant healthcare burden on society. Unlike some tissues in the body that exhibit self healing, nerve cells that are injured, particularly those in the brain and spinal cord, are incapable of regenerating circuits by themselves to restore neurological function. In recent years, researchers have begun to explore whether micro/nanoscale tools and materials can be used to address this major challenge in neuromedicine. Efforts in this area have proceeded along two lines. One is the development of new nanoscale tissue scaffold materials to act as conduits and stimulate axon regeneration. The other is the use of novel cellular-scale surgical micro/nanodevices designed to perform surgical microsplicing and the functional repair of severed axons. We discuss results generated by these two approaches and hurdles confronting both strategies.

Characterization of core-shell GaAs/AlGaAs nanowire heterostructures using advanced electron microscopy

To explore the unique properties of the nanoscale, advanced fabrication and characterization techniques are required. Specifically analyses in two orthogonal directions, plan-view and cross-section, were used to prove the core-shell morphology of GaAs/AlGaAs nanowires and determine their cross-section to be hexagonal. High-resolution transmission electron microscopy and high angle annular dark field scanning transmission electron microscopy confirmed the core-shell interface to be defect-free, coherent, and sharp (<1nm). Energy dispersive X-ray spectroscopy determined the shell composition to be Al0.9Ga0.1As uniformly along the length of the nanowire. These results demonstrate the power of electron microscopy to aid the development of semiconductor nanotechnology.

New modes for subsurface atomic force microscopy through nanomechanical coupling

Non-destructive, nanoscale characterization techniques are needed to understand both synthetic and biological materials. The atomic force microscope uses a force-sensing cantilever with a sharp tip to measure the topography and other properties of surfaces. As the tip is scanned over the surface it experiences attractive and repulsive forces that depend on the chemical and mechanical properties of the sample. Here we show that an atomic force microscope can obtain a range of surface and subsurface information by making use of the nonlinear nanomechanical coupling between the probe and the sample. This technique, which is called mode-synthesizing atomic force microscopy, relies on multi-harmonic forcing of the sample and the probe. A rich spectrum of first- and higher-order couplings is discovered, providing a multitude of new operational modes for force microscopy, and the capabilities of the technique are demonstrated by examining nanofabricated samples and plant cells.

Micro- and Nanoscale Control of the Cardiac Stem Cell Niche for Tissue Fabrication

Advances in stem cell (SC) biology have greatly enhanced our understanding of SC self-renewal and differentiation. Both embryonic and adult SCs can be differentiated into a great variety of tissue cell types, including cardiac myocytes. In vivo studies and clinical trials, however, have demonstrated major limitations in reconstituting the myocardium in failing hearts. These limitations include precise control of SC proliferation, survival and phenotype both prior and subsequent to transplantation and avoidance of serious adverse effects such as tumorigenesis and arrhythmias. Micro- and nanoscale techniques to recreate SC niches, the natural environment for the maintenance and regulation of SCs, have enabled the elucidation of novel SC behaviors and offer great promise in the fabrication of cardiac tissue constructs. The ability to precisely manipulate the interface between biopolymeric scaffolds and SCs at in vivo scale resolutions is unique to micro- and nanoscale approaches and may help overcome limitations of conventional biological scaffolds and methods for cell delivery. We now know that micro- and nanoscale manipulation of scaffold composition, mechanical properties, and three-dimensional architecture have profound influences on SC fate and will likely prove important in developing the next generation of "transplantable SC niches" for regeneration of heart and other tissues. In this review, we examine two key aspects of micro- and nanofabricated SC-based cardiac tissue constructs: the role of scaffold composition and the role of scaffold architecture and detail how recent work in these areas brings us closer to clinical solutions for cardiovascular regeneration.

Special Issue on Dynamic Modeling, Control and Manipulation at the Nanoscale

Special Issue on Dynamic Modeling, Control and Manipulation at the Nanoscale

Nanoparticles in sentinel lymph node mapping

The lymph nodes and lymphatic vessels are more difficult to access than most vascular structures. Interstitial injection of imaging agents is often necessary to opacify the lymphatics. Traditionally, radionuclide methods of sentinel node imaging have dominated this field, however, limitations in resolution and exposure to radiation have encouraged the development of newer imaging methods. Among these are magnetic resonance lymphography in which a Gadolinium labeled nanoparticle is injected and imaged providing superior anatomic resolution and assessment of lymphatic dynamics. Optical imaging employing various nanoparticles including quantum dots also provide the capability of mapping each lymphatic basin in another "color". Taken together this "toolbox" of lymphatic imaging agents is poised to improve our understanding of the lymphatic system.

Beyond the optical resolution in living cell: Biomedical applications of Scanning Ion Conductance Microscopy

317 Molecular biology has advanced: we know much about the individual molecular components that make up living cells down to the level of the individual atoms. The challenge, however, is to fully understand the functional integration of these components. This requires determining how the molecular machines that make up a living cell are organized and interact together not at the atomic length scale but on a nm scale. To do this we need to develop and apply nanoscale techniques for the visualisation and quantification of cell machinery in real-time and on living cells. This will lead to detailed, quantitative models of subcellular structures and molecular complexes under different conditions for both normal and diseased cells. This approach ultimately requires the development of novel biophysical methods. We have recently pioneered the development of an array of new and powerful biophysical tools based on Scanning Ion Conductance Microscopy that allow quantitative measurements and non-invasive functional imaging of single protein molecules in living cells. Scanning ion conductance microscopy and a battery of associated innovative methods are unique among current imaging techniques, not only in spatial resolution of living and functioning cells, but also in the rich combination of imaging with other functional and dynamical interrogation methods. These methods, crucially, will facilitate the study of integrated nano-behaviour in living cells in health and disease. Beyond the Optical Resolution in Living Cell: Biomedical Applications of Scanning Ion Conductance Microscopy

Capturing the nanoscale complexity of cellular membranes in supported lipid bilayers

The lateral mobility of cell membranes plays an important role in cell signaling, governing the rate at which embedded proteins can interact with other biomolecules. The past two decades have seen a dramatic transformation in understanding of this environment, as the mechanisms and potential implications of nanoscale structure of these systems has become accessible to theoretical and experimental investigation. In particular, emerging micro- and nano-scale fabrication techniques have made possible the direct manipulation of model membranes at the scales relevant to these biological processes. This review focuses on recent advances in nanopatterning of supported lipid bilayers, capturing the impact of membrane nanostructure on molecular diffusion and providing a powerful platform for further investigation of the role of this spatial complexity on cell signaling.

Prospects and developments in cell and embryo laser nanosurgery

Recently, there has been increasing interest in the application of femtosecond (fs) laser pulses to the study of cells, tissues and embryos. This review explores the developments that have occurred within the last several years in the fields of cell and embryo nanosurgery. Each of the individual studies presented in this review clearly demonstrates the nondestructiveness of fs laser pulses, which are used to alter both cellular and subcellular sites within simple cells and more complicated multicompartmental embryos. The ability to manipulate these model systems noninvasively makes applied fs laser pulses an invaluable tool for developmental biologists, geneticists, cryobiologists, and zoologists. We are beginning to see the integration of this tool into life sciences, establishing its status among molecular and genetic cell manipulation methods. More importantly, several studies demonstrating the versatility of applied fs laser pulses have established new collaborations among physicists, engineers, and biologists with the common intent of solving biological problems.

Ethical, Legal and Social Aspects of Brain-Implants Using Nano-Scale Materials and Techniques

Nanotechnology is an important platform technology which will add new features like improved biocompatibility, smaller size, and more sophisticated electronics to neuro-implants improving their therapeutic potential. Especially in view of possible advantages for patients, research and development of nanotechnologically improved neuro implants is a moral obligation. However, the development of brain implants by itself touches many ethical, social and legal issues, which also apply in a specific way to devices enabled or improved by nanotechnology. For researchers developing nanotechnology such issues are rather distant from their daily work in the lab, but as soon as they use their materials or devices in medical applications such as therapy of brain diseases they have to be aware of and deal with them. This paper is intended to raise sensitivity for the ethical, legal and social aspects (ELSA) involved in applying nanotechnology in brain implants or other devices by highlighting the short term problems of testing and clinical trials within the existing regulatory frameworks (A), the short and medium-term questions of risks in the application of the devices (B) and the long-term perspectives related to problems of enhancement (C). To identify and address such issues properly nanotechnologists should involve ethical, legal and social experts and regulatory bodies in their research as early as possible. This will help to remove pressure from regulatory bodies, to settle public concern and to prevent non-acceptable developments for the benefit of the patients.

Nano-optics with spin waves at microwave frequencies

With the recent development in nanoscale patterning techniques, the potential of practical applications of nanometer-size structures for signal processing has been growing continuously. Experimental findings on the manipulation of optical signals in nanostructures have recently given rise to a widely addressed scientific area—subwavelength nano-optics. Here, we demonstrate that spin waves in microscopic ferromagnetic film structures represent a superb object for realization of the principles of nano-optics in the microwave frequency range. We show experimentally that by using the unique properties of spin waves, one can easily channelize, split, and manipulate submicrometer-width spin-wave beams propagating in microscopic magnetic-film waveguides.

Physical IC debug – backside approach and nanoscale challenge

Abstract. Physical analysis for IC functionality in submicron technologies requires access through chip backside. Based upon typical global backside preparation with 50–100 µm moderate silicon thickness remaining, a state of the art of the analysis techniques available for this purpose is presented and evaluated for functional analysis and layout pattern resolution potential. A circuit edit technique valid for nano technology ICs, is also presented that is based upon the formation of local trenches using the bottom of Shallow Trench Isolation (STI) as endpoint for Focused Ion Beam (FIB) milling. As a derivative from this process, a locally ultra thin silicon device can be processed, creating a back surface as work bench for breakthrough applications of nanoscale analysis techniques to a fully functional circuit through chip backside. Several applications demonstrate the power and potential of this new approach.

Magnetic microposts for mechanical stimulation of biological cells: Fabrication, characterization, and analysis

Cells use force as a mechanical signal to sense and respond to their microenvironment. Understanding how mechanical forces affect living cells requires the development of tool sets that can apply nanoscale forces and also measure cellular traction forces. However, there has been a lack of techniques that integrate actuation and sensing components to study force as a mechanical signal. Here, we describe a system that uses an array of elastomeric microposts to apply external forces to cells through cobalt nanowires embedded inside the microposts. We first biochemically treat the posts' surfaces to restrict cell adhesion to the posts' tips. Then by applying a uniform magnetic field (B<0.3 T), we induce magnetic torque on the nanowires that is transmitted to a cell's adhesion site as an external force. We have achieved external forces of up to 45 nN, which is in the upper range of current nanoscale force-probing techniques. Nonmagnetic microposts, similarly prepared but without nanowires, surround the magnetic microposts and are used to measure the traction forces and changes in cell mechanics. We record the magnitude and direction of the external force and the traction forces by optically measuring the deflection of the microposts, which linearly deflect as cantilever springs. With this approach, we can measure traction forces before and after force stimulation in order to monitor cellular response to forces. We present the fabrication methods, magnetic force characterization, and image analysis techniques used to achieve the measurements.

Colloidal silver fabrication using the spark discharge system and its antimicrobial effect on Staphylococcus aureus

Nanoscale techniques for silver production may assist the resurgence of the medical use of silver, especially given that pathogens are showing increasing resistance to antibiotics. Traditional chemical synthesis methods for colloidal silver (CS) may lead to the presence of toxic chemical species or chemical residues, which may inhibit the effectiveness of CS as an antibacterial agent. To counter these problems a spark discharge system (SDS) was used to fabricate a suspension of colloidal silver in deionized water with no added chemical surfactants. SDS-CS contains both metallic silver nanoparticles (Ag 0) and ionic silver forms (Ag +). The antimicrobial affect of SDS-CS on Staphylococcus aureus was studied. The results show that CS solutions with an ionic silver concentration of 30 ppm or higher are strong enough to destroy S. aureus. In addition, it was found that a solution's antimicrobial potency is directly related to its level of silver ion concentration.