1,721,011 research outputs found
Tip-based nanofabrication
No full textAlternative lithographic techniques, in particular those based on scanning probe microscopy, have shown a great potential for fabricating nanostructures using various material and allowing high spatial resolution, alignment capabilities and high-resolution imaging during the different lithographic steps. More specifically, atomic force microscope (AFM) and scanning tunneling microscope (STM) have been in the recent past employed to image and modify at nanometer scale a new carbon material discovered in 2004 and called graphene, a single layer of carbon atoms arranged in a honeycomb crystal lattice. In this chapter a review of recent results obtained by scanning probe based nanofabrication on graphene nanostructures is presented. It is focused in particular on nanomanipulation, local anodic oxidation (LAO), electrochemical or thermal-stimulated desorption, static or dynamic ploughing as well as other AFM and STM based techniques on imaging, lithography and spectroscopy
Coherent transport in Nb/d-doped-GaAs hybrid microstructures
No full textCoherent transport in Nb/GaAs superconductor-semiconductor microstructures is presented. The structure fabrication procedure is based on δ-doped layers grown by molecular-beam-epitaxy near the GaAs surface, followed by an As cap layer to protect the active semiconductor layers during ex situ transfer. The superconductor is then sputter deposited in situ after thermal desorption of the protective layer. Two types of structures in particular will be discussed, i.e. a reference junction and the engineered one that contains an additional insulating AlGaAs barrier inserted during the growth in the semiconductor. This latter configuration may give rise to controlled interference effects and realizes the model introduced by de Gennes and Saint-James in 1963. While both structures show reflectionless tunneling-dominated transport, only the engineered junction shows additionally a low-temperature single marked resonance peaks superimposed to the characteristic Andreev-dominated subgap conductance. The analysis of coherent magnetotransport in both microstructures is successfully performed within the random matrix theory of Andreev transport and ballistic effects are included by directly solving the Bogoliubov–de Gennes equations. The impact of junction morphology on reflectionless tunneling and the application of the employed fabrication technique to the realization of complex semiconductor-superconductor systems are also discussed
Scanning probe nanoimprint lithography
No full textThe present paper reports on a novel lithographic approach at the nanoscale level, which is based on scanning probe microscopy (SPM) and nanoimprint lithography (NIL). The experimental set-up consists of an atomic force microscope (AFM) operated via software specifically developed for the purpose. In particular, this software allows one to apply a predefined external load for a given lapse of time while monitoring in real-time the relative distance between the tip and the sample as well as the normal and lateral force during the embossing process. Additionally, we have employed AFM tips sculptured by means of focused ion beam in order to create indenting tools of the desired shape. Anti-sticking layers can also be used to functionalize the tips if one needs to investigate the effects of different treatments on the indentation and de-molding processes. The lithographic capabilities of this set-up are demonstrated on a polystyrene NIL-patterned sample, where imprinted features have been obtained upon using different normal load values for increasing time intervals, and on a thermoplastic polymer film, where the imprint process has been monitored in real-time
Nanowear of polymers
No full textThe use of viscoelastic materials, such as polymers, constantly increases in the field of nanotechnology. These materials are softer than metallic and inorganic ones, and, because of that, they are easier to deform and wear off. The wear mechanisms occurring for viscoelastic materials are rather complex, and, generally, present more complications for a direct investigation with respect to metals or ceramics materials. With the advent of Scanning Probe Microscopy (SPM), well characterized forces can be applied to a surface with a nanometer-scale spatial resolution. In particular Atomic ForceMicroscopy (AFM), working at high contact forces, can significantly modify many surfaces. Polymers are soft enough to be modified by hard AFM tips, such as those of silicon, silicon nitride or diamond. For these reasons, the AFM is today the main tool employed to investigate wear occurrence on polymer surfaces. The wear of a polymer surface caused by an AFM tip in a regime of single asperity contact is an articulate process that depends on conditions such as, namely, the applied forces, the tip shape, size and the relative velocity. Since the influence of all these parameters is in close connection with the sample properties, one can expect a dependence of the wearing process on the mechanical properties of the sample surfaces. These properties can vary significantly from the bulk properties, if cross linking is made or, on contrary, residual solvents are present in the specimens. This chapter is divided in three sections following a general introduction. Specifically, the first section deals with wear induced by means of AFM tips to study the mechanical properties of films at the nanoscale; the second one regards the exploitation of wear for the creation of nanolithographic patterns; the last one is finally dedicated to an applicative field such as the characterization ofwear of polymers for biomedical applications at the meso- and nanoscales
Nanoscale rippling on polymer surfaces induced by AFM manipulation
Full text linkNanoscale rippling induced by an atomic force microscope (AFM) tip can be observed after performing one or many scans over the same area on a range of materials, namely ionic salts, metals, and semiconductors. However, it is for the case of polymer films that this phenomenon has been widely explored and studied. Due to the possibility of varying and controlling various parameters, this phenomenon has recently gained a great interest for some technological applications. The advent of AFM cantilevers with integrated heaters has promoted further advances in the field. An alternative method to heating up the tip is based on solvent-assisted viscoplastic deformations, where the ripples develop upon the application of a relatively low force to a solvent-rich film. An ensemble of AFM-based procedures can thus produce nanoripples on polymeric surfaces quickly, efficiently, and with an unprecedented order and control. However, even if nanorippling has been observed in various distinct modes and many theoretical models have been since proposed, a full understanding of this phenomenon is still far from being achieved. This review aims at summarizing the current state of the art in the perspective of achieving control over the rippling process on polymers at a nanoscale level
Nanosized Optical "Devices" for Applications in Proteomics and Biomolecular Electronics: Engineered Green Fluorescent Proteins
No full textFunctional Nanomaterials is the first and unique compilation of the state-of-the-art review chapters covering all aspects of functional nanomaterials and their applications. Nanotechnology has led to a profound paradigm shift after the developments in recent years and after being classified as one of the most important areas of impending technology by the U.S. government. Novel functional nanomaterials are the basis of newly emerging nanotechnologies for various device applications. This book with 30 chapters reflects the tremendous world-wide interest in functional nanostructured materials. The wide variety of topics covered in this book is interesting for professionals working in the fundamental and applied research. The book covers major classes of nanomaterials such as carbon nanotubes, carbon and polymer nanofibers, nanoparticles, nanocomposites, nanosheets, fullerenes, supramolecular and self-assembled nanostructures, and many other types of nanomaterials. In addition, this book highlights various physico-chemical properties of different nanostructures such as catalytic, dielectric, magnetic, fluorescent and luminescent properties as well as applications of nanomaterials in sensors, photonics, drug delivery, proteomics, biomolecular electronics, and Homeland Security
Local anodic oxidation studied by spectroscopic microscopy
No full textAtomic force microscope(AFM) induced local oxidation is a versatile and promising nanofabrication process used successfully to produce quantum devices. Nevertheless, little information is available on the chemical and structural properties of the grown oxide. We address this open issue by a spectromicroscopic study of nanoscopic oxide patterns grown by AFM anodic oxidation on n-type silicon substrate. We show that AFMoxidation produces chemically uniform, stoichiometric SiO2, and that its chemical and structural properties do not depend on the applied voltage. The observed electrostatic shift of the oxide binding energies allows a simple estimation of the electrical properties of the AFM induced oxide
Cantilever deflection measurement and actuation by an interdigitated transducer
Full text linkA scheme that allows all-electrical high-bandwidth readout of a cantilever deflection by means of an integrated interdigitated transducer is presented. The present approach takes advantage of the piezoelectricity of the chosen cantilever substrate material to generate and detect surface-acoustic-waves by means of an interdigitated transducer (IDT) and to determine cantilever deflections. We shall also show that the same IDT can be used to excite the oscillation modes of the lever. Our scheme is compatible with implementations exploiting wireless excitation and readout and in mass sensing applications.A scheme that allows all-electrical high-bandwidth readout of a cantilever deflection by means
of an integrated interdigitated transducer is presented. The present approach takes advantage
of the piezoelectricity of the chosen cantilever substrate material to generate and detect
surface-acoustic-waves by means of an interdigitated transducer IDT and to determine cantilever
deflections. We shall also show that the same IDT can be used to excite the oscillation modes of the
lever. Our scheme is compatible with implementations exploiting wireless excitation and readout
and in mass sensing applications
Use of polystyrene brushes to investigate the role of interface between substrates and thin homogeneous films
No full textThe viscoelastic properties of thin polystyrene (PS) films depend on confinement, as it can modify the molecular dynamics affecting the glass transition. In the recent past, the authors have investigated the region next to the free interface by means of an atomic force microscope suitably modified to monitor the indentation of a tip into a film during a given lapse of time while applying a constant load. Herein, to explore the interface with the substrate, the authors report on experiments in which PS brushes grafted to native silicon oxide were used. It was found that the film wettability on brushes and H-terminated silicon can be highly improved when compared with native silicon oxide. In addition, the glass transition temperature of thin films increases up to the bulk value in the case of film/brush combinations with high molecular weight or films with high molecular weight on H-terminated silicon. Data are discussed according to hypotheses such as residual solvent presence, interface free volume, and molecular mechanical coupling. These observations can be of great interest for nanotechnological applications, especially in those instances where one needs to tailor the temperature dependence of viscoelastic properties of thin films
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