0000000000033813
AUTHOR
Rünno Lõhmus
Analysis of static friction and elastic forces in a nanowire bent on a flat surface: A comparative study
ZnO nanowires bent to a complex shape and held in place by static friction force from supporting flat surface are investigated experimentally and theoretically. The complex shapes are obtained by bending the nanowires inside a scanning electron microscope with a sharp tip attached to a nanopositioner. Several methods previously described in the literature are applied along with author's original method to calculate the distributed friction force and stored elastic energy in the nanowires from the bending profile. This comparative study evidences the importance of the usage of appropriate models for accurate analysis of the nanowires profile. It is demonstrated that incomplete models can lea…
Devices based on semiconductor nanowires
Recently, nanoelectromechanical systems (NEMS) have attracted much attention due to their unique properties and possible applications that differ greatly from those of microelectromechanical systems. NEMS operating frequencies may achieve giga- and terahertz levels and their power consumption and heat capacity is extremely low. Moreover, integration levels may reach 1012 devices per cm−2. In this review, we present techniques for integrating semiconductor materials in NEMS. In particular, we examine fabrication, structure, properties and potential applications of two main classes of NEMS, namely, resonators and switches.
Modeling of kinetic and static friction between an elastically bent nanowire and a flat surface
Friction forces for a nanowire (NW) elastically bent on flat substrate were investigated both theoretically and experimentally. Models based on elastic beam theory were proposed considering balance of external, frictional, and elastic forces along the NW. The distributed friction force was determined for two cases: (i) the NW was uniformly dragged at its midpoint and bent by kinetic friction forces and (ii) the NW was held in a bent state by static friction forces. The first case considers a uniform distribution of kinetic friction along the NW and enables the measurement of the friction force from the elastically deformed NW profile. The second case exploits the interplay between static fr…
Elasticity and yield strength of pentagonal silver nanowires: In situ bending tests
This paper reports in situ mechanical characterization of silver nanowires (Ag NWs) inside a scanning electron microscope using a cantilevered beam bending technique. Measurements consisted in controlled bending of a cantilevered NW by the tip of an atomic force microscope glued to the force sensor. Relatively high degree of elasticity followed by either plastic deformation or fracture was observed in bending experiments. Experimental data were numerically fitted into the model based on the elastic beam theory and values of Young modulus and yield strength were extracted. Measurements were performed on twenty Ag NWs with diameters from 76 nm to 211 nm. Average Young modulus and yield streng…
Phase and structural transformations in annealed copper coatings in relation to oxide whisker growth
Abstract We describe structural and phase transformation in copper coatings made of microparticles during heating and annealing in air in the temperature range up to 400 °C. Such thermal treatment is accompanied by intensive CuO nanowhisker growth on the coating surface and the formation of the layered oxide phases (Cu 2 O and CuO) in the coating interior. X-ray diffraction and focused ion beam (FIB) are employed to characterize the multilayer structure of annealed copper coatings. Formation of volumetric defects such as voids and cracks in the coating is demonstrated.
Mechanical properties of sol–gel derived SiO2 nanotubes
The mechanical properties of thick-walled SiO2 nanotubes (NTs) prepared by a sol–gel method while using Ag nanowires (NWs) as templates were measured by using different methods. In situ scanning electron microscopy (SEM) cantilever beam bending tests were carried out by using a nanomanipulator equipped with a force sensor in order to investigate plasticity and flexural response of NTs. Nanoindentation and three point bending tests of NTs were performed by atomic force microscopy (AFM) under ambient conditions. Half-suspended and three-point bending tests were processed in the framework of linear elasticity theory. Finite element method simulations were used to extract Young’s modulus values…
Electron beam induced growth of silver nanowhiskers
Abstract In this paper we report an electron beam induced rapid (up to several tens of nm/s) growth of silver nanowhiskers from silver nanowire networks coated with TiO 2 by sol–gel method. Different growth conditions are tested and it is demonstrated that growth is optimal for samples with the film thickness in the range 50–200 nm and previously annealed at 400 °C for 5–10 min. Growth mechanism is attributed to cooperative effect of several factors including diffusion of Ag into TiO 2 matrix during annealing, electromigration of Ag atoms caused by strong electric field, and presence of mechanical stresses at interfaces enhanced by thermal expansions due to local heating under e-beam illumi…
Real-time measurements of sliding friction and elastic properties of ZnO nanowires inside a scanning electron microscope
Abstract A real-time nanomanipulation technique inside a scanning electron microscope (SEM) has been used to investigate the elastic and frictional (tribological) properties of zinc oxide nanowires (NWs). A NW was translated over a surface of an oxidised silicon wafer using a nanomanipulator with a glued atomic-force microscopic tip. The shape of the NW elastically deformed during the translation was used to determine the distributed kinetic friction force. The same NW was then positioned half-suspended on edges of trenches cut by a focused ion beam through a silicon wafer. In order to measure Young’s modulus, the NW was bent by pushing it at the free end with the tip, and the interaction f…
Force interactions and adhesion of gold contacts using a combined atomic force microscope and transmission electron microscope
Force interactions and adhesion of gold contacts using a combined atomic force microscope and transmission electron microscope
Complex tribomechanical characterization of ZnO nanowires: nanomanipulations supported by FEM simulations
In the present work, we demonstrate a novel approach to nanotribological measurements based on the bending manipulation of hexagonal ZnO nanowires (NWs) in an adjustable half-suspended configuration inside a scanning electron microscope. A pick-and-place manipulation technique was used to control the length of the adhered part of each suspended NW. Static and kinetic friction were found by a 'self-sensing' approach based on the strain profile of the elastically bent NW during manipulation and its Young's modulus, which was separately measured in a three-point bending test with an atomic force microscope. The calculation of static friction from the most bent state was completely reconsidered…
Mechanical characterisation of pentagonal gold nanowires in three different test configurations: A comparative study.
Abstract Mechanical characterisation of individual nanostructures is a challenging task and can greatly benefit from the utilisation of several alternative approaches to increase the reliability of results. In the present work, we have measured and compared the elastic modulus of five-fold twinned gold nanowires (NWs) with atomic force microscopy (AFM) indentation in three different test configurations: three-point bending with fixed ends, three-point bending with free ends and cantilevered-beam bending. The free-ends condition was realized by introducing a novel approach where the NW is placed diagonally inside an inverted pyramid chemically etched in a silicon wafer. In addition, all thre…
Manipulation of nanoparticles of different shapes inside a scanning electron microscope
In this work polyhedron-like gold and sphere-like silver nanoparticles (NPs) were manipulated on an oxidized Si substrate to study the dependence of the static friction and the contact area on the particle geometry. Measurements were performed inside a scanning electron microscope (SEM) that was equipped with a high-precision XYZ-nanomanipulator. To register the occurring forces a quartz tuning fork (QTF) with a glued sharp probe was used. Contact areas and static friction forces were calculated by using different models and compared with the experimentally measured force. The effect of NP morphology on the nanoscale friction is discussed.
Metal nanodumbbells for nanomanipulations and tribological experiments
Nanomanipulation experiments were carried out on nanodumbbells (NDs) to study their kinetic behavior and tribological properties. Ag, Au and Cu NDs were produced by laser-induced melting of corresponding nanowires (NWs). NDs were characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Manipulation experiments were performed first with atomic force microscope (AFM) at ambient conditions, and then inside SEM at high vacuum conditions. Different regimes of motion were observed. In-plane and out-of-substrate-plane rotation were identified as the most preferred motion types of NDs.
The effect of heat treatment on the morphology and mobility of Au nanoparticles
This work was supported by The Centre National de la Recherche Scientifique (CNRS) of France and the French Embassy Program. The authors are also grateful for partial support by COST Action CA15216, the Estonian Science Foundation (grants PUT1689 and PUT1372), the Estonian Centre of Excellence in Zero Energy and Resource Efficient Smart Buildings and Districts, ZEBE, grant 2014-2020.4.01.15.0016 and Latvian Science Council grant lzp-2018/2-0083.
Effect of cobalt doping on the mechanical properties of ZnO nanowires
Abstract In this work, we investigate the influence of doping on the mechanical properties of ZnO nanowires (NWs) by comparing the mechanical properties of pure and Co-doped ZnO NWs grown in similar conditions and having the same crystallographic orientation [0001]. The mechanical characterization included three-point bending tests made with atomic force microscopy and cantilever beam bending tests performed inside scanning electron microscopy. It was found that the Young's modulus of ZnO NWs containing 5% of Co was approximately a third lower than that of the pure ZnO NWs. Bending strength values were comparable for both materials and in both cases were close to theoretical strength indica…
Mechanical and structural characterizations of gamma- and alpha-alumina nanofibers
Abstract We investigate the applicability of alumina nanofibers as a potential reinforcement material in ceramic matrix compounds by comparing the mechanical properties of individual nanofibers before and after annealing at 1400 °C. Mechanical testing is performed inside a scanning electron microscope (SEM), which enables observation in real time of the deformation and fracture of the fibers under loading, thereby providing a close-up inspection of the freshly fractured area in vacuum. Improvement of both the Young's modulus and the breaking strength for annealed nanofibers is demonstrated. Mechanical testing is supplemented with the structural characterization of the fibers before and afte…
Some aspects of formation and tribological properties of silver nanodumbbells.
In this paper, metal nanodumbbells (NDs) formed by laser-induced melting of Ag nanowires (NWs) on an oxidized silicon substrate and their tribological properties are investigated. The mechanism of ND formation is proposed and illustrated with finite element method simulations. Tribological measurements consist in controllable real-time manipulation of NDs inside a scanning electron microscope (SEM) with simultaneous force registration. The geometry of NDs enables to distinguish between different types of motion, i.e. rolling, sliding and rotation. Real contact areas are calculated from the traces left after the displacement of NDs and compared to the contact areas predicted by the contact m…
Shape restoration effect in Ag-SiO2 core-shell nanowires.
The combination of two different materials in a single composite core–shell heterostructure can lead to improved or even completely novel properties. In this work we demonstrate the enhancement of the mechanical properties of silver (Ag) nanowires (NW) achieved by coating them with a silica (SiO2) shell. In situ scanning electron microscope (SEM) nanomechanical tests of Ag–SiO2 core–shell nanowires reveal an improved fracture resistance and an electron-beam induced shape restoration effect. In addition, control experiments are conducted separately on uncoated Ag NWs and on empty SiO2 shells in order to gain deeper insight into the peculiar properties of Ag–SiO2. Test conditions are simulate…
Real-time manipulation of ZnO nanowires on a flat surface employed for tribological measurements: Experimental methods and modeling
Elastic and tribological properties of zinc oxide nanowires (NWs) on Si wafer and highly oriented pyrolytic graphite (HOPG) are experimentally investigated and theoretically interpreted. Measurements are performed inside a scanning electron microscope (SEM) using real-time manipulation technique that enables two possible ways of data registration: “external” force registration with quartz tuning fork (QTF) based sensor and “internal” force registration utilizing in situ observed elastic deformation of NWs. Young modulus is determined by loading half-suspended NW at its free end and then employed for the following tribological experiments. Maximal static friction force is estimated when NW i…
Application of Tuning Fork Sensors for In-situ Studies of Dynamic Force Interactions Inside Scanning and Transmission Electron Microscopes
Mechanical properties of nanoscale contacts have been probed in-situ by specially developed force sensor based on a quartz tuning fork resonator (TF). Additional control is provided by observation of process in scanning electron microscope (SEM) and transmission electron microscope (TEM). A piezoelectric manipulator allows precise positioning of atomic force microscope (AFM) probe in contact with another electrode and recording of the TF oscillation amplitude and phase while simultaneously visualizing the contact area in electron microscope. Electrostatic control of interaction between the electrodes is demonstrated during observation of the experiment in SEM. In the TEM system the TF senso…
Structural factor in bending testing of fivefold twinned nanowires revealed by finite element analysis
In this study, we performed finite element method simulations to investigate the effect of the structure on the elastic response of Ag and Au nanowires (NWs) with a fivefold twinned crystal structure in bending tests. Two different models of a pentagonal NW were created: a 'uniform model' having an isotropic continuous structure and a 'segmented model' consisting of five anisotropic domains. Two asymmetrical mechanical test configurations were simulated: cantilevered beam bending and 3-point bending. The dimensions of the NW, the test configurations, as well as the force and the displacement ranges were based on the previously obtained experimental data. The results of the simulations demon…
Mechanical characterization of TiO2 nanofibers produced by different electrospinning techniques
Abstract In this work TiO2 nanofibers produced by needle and needleless electrospinning processes from the same precursor were characterized and compared using Raman spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and in situ SEM nanomechanical testing. Phase composition, morphology, Young's modulus and bending strength values were found. Weibull statistics was used to evaluate and compare uniformity of mechanical properties of nanofibers produced by two different methods. It is shown that both methods yield nanofibers with very similar properties.
Enhanced flexibility and electron-beam-controlled shape recovery in alumina-coated Au and Ag core–shell nanowires
The proper choice of coating materials and methods in core–shell nanowire (NW) engineering is crucial to assuring improved characteristics or even new functionalities of the resulting composite structures. In this paper, we have reported electron-beam-induced reversible elastic-to-plastic transition in Ag/Al2O3 and Au/Al2O3 NWs prepared by the coating of Ag and Au NWs with Al2O3 by low-temperature atomic layer deposition. The observed phenomenon enabled freezing the bent core–shell NW at any arbitrary curvature below the yield strength of the materials and later restoring its initially straight profile by irradiating the NW with electrons. In addition, we demonstrated that the coating effic…
Tribological Aspects of In Situ Manipulation of Nanostructures Inside Scanning Electron Microscope
This chapter is dedicated to manipulation of nanostructures inside a scanning electron (SEM) microscope employed for real-time tribological measurements. Different approaches to force registration and calculation of static and kinetic friction are described. Application of the considered methodology to Au and Ag nanoparticles, as well as ZnO and CuO nanowires, is demonstrated. Advantages and limitations of the methodology in comparison to traditional AFM-based manipulation techniques are discussed.
Real-time manipulation of gold nanoparticles inside a scanning electron microscope
Abstract The forces needed to overcome static friction and move 150 nm diameter Au nanoparticles on an oxidized Si substrate were measured in Normal and Shear oscillation modes inside a scanning electron microscope (SEM) in real time. The experimental setup consisted of a quartz tuning fork (QTF) mounted onto a high-precision 3D nanomanipulator used with a glued silicon or tungsten tip as a force sensor. Static friction was found to range from tens of nN to several hundred nN. Large variations in static friction values were related to differences in particle shape. Kinetic friction tended to be close to the detection limit and in most cases did not exceed several nN. The influence of therma…