Nanopillars fabricated by Nano Imprint Lithography
Layer thickness determination by X-ray reflectometry
Nanobeams with thin coating films
Nanoparticles
Nanoclusters
Micro-Electro-Mechanical-Systems (MEMS) for the stiffness calibration of cantilevers
Siliconnitride nanobeams fabricated by e-beam lithography
Instrumented Indentation Technique (IIT)
Embedded nano-objects
Nanowires (NW) and nanotubes (NT)
for mechanical AFM measurements
New silicon reference spring artefact for cantilever calibration
The aim of this workpackage is to supply nano-object samples for mechanical measurements using nanoindenters and AFMs. Different routes to create nano-objects which can be handled and used for nanomechanical measurements, will be followed. One challenge will be the attachment of the nano-objects during mechanical measurement, so that the contact force measurements are not disturbed.
Approaches will include the creation of 
nanopillars (Task 1.1) or nanobeams (Task 1.2) starting from homogenous substrates or large area thin layer systems, respectively. By using X-Ray Reflectometry (XRR) and the Instrumented Indentation Technique (IIT) the uniformity of the thickness of these substrates, or large area thin layer systems, and their mechanical properties, respectively, will be easily measured in this Joint Research Project (JRP).
In the next step, nanobeams of various sizes down to several tens of nanometres will be fabricated using electron beam lithography and Focussed Ion Beam (FIB). By using sandwich like thin film structures the surface films of the free standing bridge will be used to obtain information about surface effects on small structures. In order to localise these tiny structures using nanoindenters certain marker structures will need to be added. A very important question that will be answered will be how the surface layers influence the mechanical properties of nano-objects. Therefore, different nanobeam coating materials will be tested, and in order to avoid surface tension effects, the coating will be applied on both sides of the thin membranes.
Another approach will investigate embedded nano-objects as a means of attaching the structures to a stiff substrate (Task 1.3).
Nanoparticles and nanowires will be manufactured by different approaches including electron beam lithography, membrane filtration, drying, chemical fixation by surface denaturation, electrostatic precipitation of aerosols and thermal precipitation (Task 1.4).
Nanoclusters of some hundred atoms will also be investigated (Task 1.5).
For all nano-objects, this WP will investigate the influence of surface-to-volume ratio, of size (length, width, height of nano-objects), of coating thickness, of hydrophilic/hydrophobic coatings and of humidity on the mechanical properties. The preparation of testing materials (Task 1.6) is important for comparison measurements but also for determining instrument parameters such as the area function and tip radius of AFM-tips or the compliance of the AFM.
Moreover, for traceable mechanical measurements with AFMs the traceability of measured force is very important. New silicon reference spring artefacts will be developed which will enable an easy calibration of the cantilever’s normal stiffness.
Metrological AFM of NPL
Principle of PTB's Nanoforce measurement facility
PTB Micro-Electro-Mechanical-System for cantilever stiffness calibration
Task 2.1 Traceability of force of AFM
The aim of this task is to choose procedures used to calibrate instruments and their cantilevers depending on the environment (air, liquid, vacuum) and to provide a matrix for the calibration of cantilevers depending on their use. In order to achieve measurement uncertainties of the normal spring constant of AFM cantilevers in industry and research laboratories below 10 % three different methods will be further developed.
Two methods “cantilever on reference cantilever” and “cantilever on reference spring” will be further developed because users can simply copy the methods and use them. The third method will involve directly calibrating the cantilevers using a nanoindenter, a compensation mass balance and a primary nanoforce measuring device. All methods will be used for the traceable calibration of the cantilever normal spring constant and the results will be compared in order to verify the measurement uncertainties.
Particular emphasis will be placed on the cantilever on reference spring method using active MEMS[1] since this method
This method denoted as “cantilever on reference MEMS spring” will be further developed in order to achieve a measurement uncertainty below 5 %. The MEMS actuator allows simultaneous deflection and deflection measurement of the cantilever by some micrometres. The accessible force range of these reference spring sensors is between some pN and some µN.
The main focus of the MEMS development will be on the improvement of the deflection resolution which currently amounts to 8.4 nm in a bandwidth of 1 kHz. A high resolution Fabry-Perot interferometer will be integrated into the MEMS, so as to detect the in-plane displacement of the MEMS with picometre resolution.
The MEMS reference spring actuator is expected to have high calibration accuracy for cantilevers with spring constants from 0.01 N/m to 50 N/m.
[1] S. Gao, Z. Zhang, Y. Wu and K. Herrmann: Towards quantitative determination of the spring constant of a scanning force microscope cantilever with a microelectromechanical nano-force actuator. Meas. Sci. Technol. 21 (2010) 015103 (8pp)
Task 2.2 Calibration of tip properties
The aim of this task is to develop procedures to determine the AFM tip radius, tip form, contact area and the wear of the tip. Different tips will be investigated.
Task 2.3 Set-up of AFM instrumentation
The aim of this task is to provide one AFM to measure small objects with very high accuracy and another AFM to measure mechanical properties.
The tip shapes will be characterised using the available artefacts or the heterostructures developed in
Task 2.2. Firstly investigations of Au and other nanoparticles, line width structures and topography-less analytical samples will be made to estimate the range of tip effects on dimensional measurements. This task includes investigations and improvements of the resolution of the laser interferometers and the optical detection system of the AFM as well as further reduction of the signal-to-noise ratio of the detection/feedback system.
Mechanical properties will be measured by AFMs using the contact mode and by applying bending methods and CR-FM for elastic modulus measurements and indentation for hardness measurements. An available high precision metrology AFM will be upgraded in order to realise the CR-FM technique.
Task 2.4 Set-up of AFM to measure under different humidity conditions
The aim of this task is to develop an instrument for traceable dimensional and force measurements under different humidity conditions. Special attention will be given to a fast, in situ calibration of cantilever stiffness and tip properties.
The aim of this workpackage is to provide theoretical and numerical support for workpackages 1 and 2. Nanoindentations in nano-objects positioned on a substrate are modelled, to simulate the whole measurement process and to determine the mechanical properties of the nano-objects. Special focus will be on the size dependence of these properties. Indentations in nanobeams/tubes/rods under special geometric conditions and in samples where nanoparticles are fixed or embedded in an appropriate material layer as a function of embedding depth are carried out. The results of the Molecular Dynamic Calculations and the Finite Element Modelling are compared.
Task 3.1: Finite Element Modelling (FEM) of nano-objects on substrates
The aim of this task is to model nanoindentations in nano-objects positioned on a substrate, to simulate the whole measurement process and to determine the mechanical properties of the nano-objects. Special focus will be on the size dependence of these properties.
The nano-objects modelled in this task will include nanoparticles and core-shell nanorods. The chosen material is gold on SiO2 for the nano-objects and diamond, tungsten and silicon for tips. There are several size effects that will be addressed: overall size for nanoparticles, radius, thickness and length/diameter ratio for rods. Deformations of the tips and/or substrate will be modelled as well, and their effect on the measured elastic properties will be described.
Task 3.2: Finite Element Modelling (FEM) of indentation in nanopillars and nanorods and bending of nanobeams
The aim of this task is to study indentations in nanobeams/tubes/rods under special geometric conditions. In order to reduce the demands on computer speed and memory, a two-dimensional model will be studied first. The effect of the radius of the rod and the shell thickness will be studied. A simple theoretical model is available for cantilevers with one or both ends fixed and it can be compared with the results of the FEM simulations (D3.2.3). The tip will be modelled first, as a perfect rigid body. Its deformation will be included in a second step. In a further step any deformation of the substrate to which the nanobeam/tube/rod is attached will be studied. Due to the fairly simple setup the results from this task will be used for comparison with experiments.
Task 3.3: Theoretical modelling of tethering of nano-objects by embedding
The aim of this task is to study indentations, in samples where nanoparticles are fixed or embedded in an appropriate material layer (prepared in Task 1.3), as a function of embedding depth. The tip will be modelled first as a perfect rigid body. Its deformation will be included in a second step. The results from this task will be used for comparison with the experiments in Task 4.7.
Task 3.4: Molecular Dynamics of nanoparticles and nanowires
The aim of this task is to study, in detail, nanoindentations in nano-objects using MDC. The main areas of interest will be: mechanical properties, effects of non-ideal conditions (roughness, irregularities, defects) and humidity.
Within this task mechanical properties of supported nanowires and nanoparticles will be simulated, as well as the measurement where the nano-object is subject to load from a model AFM tip. The main materials simulated will be Au nanowires on SiO2 surfaces. The same materials will be studied experimentally in WP4. Silicon, tungsten and diamond tips, for example, of different sizes and different sharpness will be used. The studied properties will be elastic modulus and the size dependence of it, as a function of nanowire diameter, shape and length (up to 20 nm). Results will be compared to finite element models and to experiments in Tasks 4.5 and 4.7.
Ambient humidity spontaneously forms capillaries in small scale voids and gaps between objects. As shown by earlier research, including our experimental and computational work, this may have a strong, even dominant effect on contact forces in nanoscale measurements made at normal ambient humidity, and therefore it can affect measurements including those of mechanical properties of nanowires.
Task 3.5: Large scale molecular dynamics calculations
The aim of this task is to develop models that can bridge the gap between the Finite Element Analysis and Molecular Dynamics. Large scale molecular dynamics will be used for simulating the nanoindentation process on different nano-objects. A graphics card based supercomputer code for multimillion atoms molecular dynamics will be combined with a Finite Element method solver giving proper boundary conditions. Calculations will be run for instrumented indentation and AFM indentation tests of nanoparticles, nanowires and different nanoscale objects found on solid surfaces (like atomic steps).
Task 3.6: Comparison of Molecular Dynamic Calculations and Finite Element Modelling
The aim of this task is to compare and analyse the results of both MDC and FEM calculations. The similarities and differences will be studied. The appropriateness of each method used for a given test case as studied in Tasks 3.1. – 3.5. (e.g. the nanoindentation in a nanoparticle or nanowire) will be discussed and advice on the choice of the method will be provided to the JRP-Partners involved and will ultimately be published.
The aim of this workpackage is to quantify the effects of material and tip on the determination of dimensional measurements and to quantify the mechanical properties of all test bulk-like samples, composite samples and thin film test structures (nanopillar as well as nanobeam), and real nano-objects such as nanoparticles and nanowires.
Task 4.1: Dimensional measurements on structured samples and small objects by AFM to identify effects due to adhesion
The aim of this task is to investigate the effects of tip shape and material properties on the determination of geometrical properties. Tip characterisers used in Task 2.1 will be investigated to determine the shape of the tip during topographical measurements. Furthermore, special nanoscale-like structures (e.g. chromium lines on glass) will be used to investigate the effects of different materials. For this, optimised samples comprising selected materials will be used to enhance adhesion effects. Also the effect of water films caused by different air humidity levels will be investigated.
Task 4.2: Measurement on unstructured samples and nanopillars
The aim of this task is to characterise bulk-like and unstructured homogenous substrates, samples with thin film layer systems (as selected in WP1) and structured surfaces with pillars of various diameter and height using the instrumentation indentation technique, and the cantilever and CR-FM techniques. All techniques will use well characterised indenters or tips. The results obtained will be compared.
Task 4.3: Measurement on samples with nano-particles fixed or embedded in a layer
The aim of this task is to measure the properties of nanoparticles fixed or embedded in a layer (as selected and prepared in Task 1.3) by IIT. Additional parts of the samples will be investigated by FIB and SEM to provide geometrical parameters and additional information about the embedded quality.
Task 4.4: Measurements on structured nanoscale objects by AFM
The aim of this task is to characterise the elastic properties of the thin film structures by instrumented indentation and AFM methods (D2.3.7) and to compare these with calculations performed by FEM methods for these layer systems (D3.2.2).
Task 4.5: Measurement on real nano-objects on flat substrates and variation of humidity
The aim of this task is to measure nanoparticles with regard to their geometrical and mechanical properties under different conditions of humidity (20 %RH – 60 %RH). Experimental and numerical data from FEM and MDC calculations will be compared.
Task 4.6: Measurement on real nanowires on flat and structured samples prepared by FIB under different humidity conditions
The aim of this task is to measure the geometrical and mechanical properties of nano-wires prepared on a range of flat and structured sample surfaces. Nano-wires will either not be attached to the surfaces or they will be attached by FIB. The investigation will be performed under a range of different humidity conditions and bending will be done using a piezo actuator. The results obtained experimentally, and by numerical calculations using FEM and MDC, will be compared.
Task 4.7: Comparison of experimental and numerical results
The aim of this task is to compare and analyse the results obtained during this JRP. Experimental, and theoretical investigations by MDC and FEM calculations in D3.6.1 will be compared and analysed.
The results of the JRP will be provided to a wide range of research laboratories, institutes, companies and universities in Europe. Task 5.1 generates direct impact for the stakeholders involved in the case studies in the field of material science and biology/pharmacy/medicine. Therein the results together with the outlines of the Good Practice Guides will be applied by interested stakeholders.
Task 5.1 Case Study
The aim of this task is to apply the techniques evaluated during the JRP together with Collaborators and other stakeholders from nanotechnology-related industries and institutes to ensure the practicality of the techniques and of the draft Good Practice Guide. Two case studies will be carried out:
1. Case study about the calibration of cantilevers used for force measurements on nano-objects.
2. Case study about the calibration of cantilevers for biological science.
The latter is of great interest, because AFM are very frequently used in universities, research institutes and industry for investigations of molecules, polymers, etc. for biology, pharmacy, medicine, etc. It has been shown that the inconsistencies in the results obtained by non-traceable cantilever stiffness lead to a great delay (at least half a year) in research, since much work has to be performed to realise and to identify the problem (comparing to other techniques, round-robin, post calibration of cantilevers and instruments) . Participants in each case study are Collaborators, invited stakeholders and other interested labs in universities, and industry. If you are interested in taking part in one of these case studies please contact the coordinator of this project (Uwe Brand).