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Raman Spectroscopy through the Indenter Working as an Optical Objective
Abstract
The transparent indenter which can used as an optical objective were tested to obtained a spectra during the indentation. A special device which comprises the transparent indenter and actuator was developed and embedded into the Raman spectrometer. An indentation into the silicon sample was performed and phases that exist under the load and without it were identified.
Fig. 4 Raman spectra obtain during and after the unloading part of the indentation. Fullsize Image
... All maps in the following sections are presented for only one sector, the rest parts of the image differ only due to the indenters manufacturing shortcomings. The ability of the tip to transmit the light can be used to combine mechanical and spectroscopy measurements [3]. Similar simultaneous opto-mechanical measurements were known before, however, they didn't make use of the light passing through the tip. ...
... Work [4] considers an indentation of the transparent sample when spectra are collected from the bottom side of the sample, work [5] describes an indentation near the sample's edge with the collection of spectra in perpendicular direction. Current approach, which is described in [3], isn't limited to near-edge indentation and can be used for the opaque samples. ...
... Raman mapping was performed using specially designed unit [3], that fits into the Renishaw InVia Raman spectroscope and allows applying the load by means of the stepper motor actuator and measuring the force acting on the indenter by means of the load cell. A silicon covered with a ~200 nm thick DLC coating was chosen as a sample for investigation. ...
Transparent diamond tip described elsewhere allows combining mechanical indentation measurement with optical methods, including not only surface observation, but also spectroscopy measurements, in particular, Raman spectroscopy. Current work considers the possibilities of creating Raman maps, which give an information about the pressure distribution and ratio of material phases. Corresponding maps are presented for the case of indentation of DLC film on a silicon sample.
... These pyramids actually form three planeparallel plates through which a quasi-parallel beam of light from the microscope passes, without undergoing complete internal reflection, both to the sample and back. 11,12 This approach, which allows observing the surface through an indenter, can be implemented for tips in the form of Vickers, Knoop, and any other self-similar indenters. The indenter-objective can also be in the form of a rotation figure, which is especially valuable when studying the stress-strain diagram by the method of instrumental indentation. ...
Modern trends in the development of experimental research methods imply not only an increase in the accuracy of a specific technique but also the possibility of combining diverse measurements in the course of one experiment. While optical spectroscopy remains one of the most powerful tools used in the chemical and physical sciences to study the structure of a wide range of materials, it is impossible to imagine a single study of local mechanical properties without instrumental indentation. A powerful investigation technique is the in situ combination of these two methods within one experiment. This can be made by focusing the laser either through the transparent sample or through the transparent indenter tip of the special geometry preventing the total internal reflection in diamond. This Tutorial discusses the preparation and characterization of such a transparent diamond indenter. The obtained experimental results and promising application areas of simultaneous measurement of optical spectra during indentation are considered.
... The special issue covers new methodologies of in situ indentation testing with various observation methods, including transparent optical microscopy, 2) photoelastic evaluation, 3) Raman spectroscopy, 4,5) and macroscopic 2D observation with a wedge indenter. 6,7) Other topics include elasticity modeling for conical and pyramidal indenters, 8) evaluation of the conventional yield stress and field, 9) and measurements in harsh environments e.g., at elevated temperatures. ...
This paper presents the current research trends in indentation techniques, especially on the micro- and nanoscales, and the application of such techniques for the mechanical characterization of various materials. The survey was carried out based on the special issue of Materials Transactions (Vol. 60, No. 8), published in August 2019. The indentation techniques have diversified, and they have been implemented in instrumentation specialized for in situ measurements, environmental control including elevated temperatures, and mechanical property evaluation of soft materials. These techniques can also be applied in a more fundamental manner to assist the physical modeling of plastic deformation and fracture. For each of the various topics, a brief introduction is given to the cutting-edge methods and novel approaches in characterization that offer opportunities for innovative developments in materials science.
Fig. 1 Trend of the decennial number of publications on indentation-related research since around 1900. (Data were used from Scopus on Nov. 2020). Fullsize Image
... Modern developers of testing facilities intended for industrial operations are in demand to accelerate and simplify the measurement algorithms, as well as to increase the reliability and the accuracy of measurements. One of these promising methods is the use of a transparent indenter [13,14], which allows one to observe the formation of various phases of the material under the indenter during the test [15]. The global aim of developers is the creation of a tool that is able to measure automatically a broad range of materials with different hardness and Young's-modulus values. ...
An instrument capable of assessing the hardness of materials by instrumental indentation under industrial-production conditions, including pipelines and parts of working mechanisms (bridges, railroad tracks, ship mechanisms, and other products), which operate outdoors, is described. The key components of the device are: a load-applying element (electromagnetic actuator), a displacement sensor (a capacitive sensor mounted on the working rod) and an indenter (a Berkovich diamond tip with a diameter of 500 μm and a radius of 100 nm). The largest force that can be applied to the sample is 10 N, and the maximum movement of the indenter reaches 150 μm. For the convenience of measuring both bulk and thin samples, a portable hardness tester is equipped with two different nozzles. The main peculiar feature of the device is measurement of the hardness and the Young’s modulus of the material within a single working cycle. The device is tested on various materials: steels of grades 40Cr13 and 08Cr18N10T (including samples that underwent aging), aluminum, fused silica, polycarbonate, and laminated chipboard. The roughness of the tested surfaces and the range of loads required to carry out instrumental indentation with a portable device are determined as well. The values of the hardness and elastic modulus are consistent with data obtained by means of laboratory hardness testers.
Transparent indenter’s tip proposed elsewhere allows to observe sample surface before, after and during an indentation measurements. Such an ability allows not only to select the indentation with the real-time optic image and observe residual imprints, but also conduct spectroscopic measurements. Current work shows an examples of the tip application, in particular the possibility to observe a cracks during a scratching.
Using high numerical aperture lenses, we detected doublet optical phonon, forbidden by selection rules, in Raman spectra of Si strained in the (001) plane (bulk Si as well as strained Si device structure grown on SiGe). This allowed us to quantitatively determine stress and its distribution in strained Si with the ∼ 10% accuracy, assuming symmetric biaxial stress. At the same time, we demonstrate some deviations of the real stress from the assumed model. For better accuracy, one has to consider these deviations as well as a possibility of improvement of available Si phonon deformation potential values.
Instrumented indentation is a widely used technique to study the mechanical behavior of materials at small length scales. Mechanical tests of bulk materials, microscopic, and spectroscopic studies may be conducted to complement indentation and enable the determination of the kinetics and physics involved in the mechanical deformation of materials at the crystallographic and molecular level, e.g., strain build-up in crystal lattices, phase transformations, and changes in crystallinity or orientation. However, many of these phenomena occurring during indentation can only be observed in their entirety and analyzed in depth under in situ conditions. This paper describes the design, calibration, and operation of an indentation device that is coupled with a Raman microscope to conduct in situ spectroscopic and optical analysis of mechanically deformed regions of Raman-active, transparent bulk material, thin films or fibers under contact loading. The capabilities of the presented device are demonstrated by in situ studies of the indentation-induced phase transformations of Si thin films and modifications of molecular conformations in high density polyethylene films.
Using high resolution angle-dispersive X-ray powder diffraction at station 9.1 of Daresbury SRS, a new phase of silicon (Si-XII) has been observed. The structure has been solved and refined using Rietveld refinement techniques.
Si XII is related to the primitive rhombohedral cell of the body-centred cubic (Si III) phase, but has a larger rhombohedral angle than the 109.47 degrees required for the cubic structure. A volume collapse of around 2% at about 2GPa, shows that the transition is first order, and the existence of the phase is seen in both pressure increase and decrease from the previous phases. Internal atomic rearrangements involve a shortening of the next-nearest neighbour distance in the Si III phase, which produces an unusual 5-fold and 6-fold ring bonding topology. This has the effect of producing a wide spread of bond angles within the structure, making Si XII the most complex, tetrahedrally-bonded crystalline phase of silicon. Simulated transition mechanisms have shown that the transition from the cubic Si-III phase to Si-XII involves one bond breakage and one new bond formation per unit cell.
Phase transformations occurring in materials under high pressures are important for a wide range of problems in materials
science and solid-state physics. Most of the results in this area have been obtained using various sophisticated high-pressure
cells. We studied solid-state phase transformations and amorphisation under high non-hydrostatic pressures in very simple
experiments using a combination of hardness indentation tests with micro-Raman spectroscopy. Amorphisation of diamond, that
did not occur under hydrostatic loading, has been observed. Shearing and distortion of cubic diamond structure above 100 GPa
resulted not only in its amorphisation, but also in the formation of threefold coordinated carbon. A carbon film that was
squeezed between a SiC substrate and diamond indenter lost its graphitic structure and produced a Raman band typical of diamond-like
carbon (DLC). Even for such a well-studied material as Si, principally new data have been obtained. High spatial resolution
of the method allowed us to show that the Raman spectrum that was previously ascribed to a metastable Si-III phase originates
from two different high-pressure phases of Si. Up to five different phases of Si were found within a single impression. Studies
of reversible transformations that occur upon unloading or heating of samples by the laser beam have also been carried out.
Amorphisation and/or phase transformations have been observed for some other materials, such as SiC, quartz, Ge, GaAs and
other. The combination of indentation tests with micro-Raman spectroscopy provides a powerful and fast tool for in-situ and
ex-situ monitoring of pressure-induced phase transformations in materials.
Unloading rate and maximum load have been previously shown to affect the response of silicon to sharp indentation, but no such study exists for spherical indentation. In this work, a statistical analysis of over 1900 indentations made with a 13.5-mum radius spherical indenter on a single-crystal silicon wafer over a range of loads (25–700 mN) and loading/unloading rates (1–30 mN/s) is presented. The location of “pop-in” and “pop-out” events, most likely due to pressure-induced phase transformations, is noted, as well as pressures at which they occur. Multiple occurrences of pop-in and pop-out events are reported. Raman micro-spectroscopy shows a higher intensity of metastable silicon phases at some depth under the surface of the residual impression, where the highest shear stresses are present. A stability range for Si-II is demonstrated and compared with previous results for Berkovich indentation.
A new approach to the design of transparent diamond indenters is proposed, which allows one to obtain a full optical image of the investigated area of the sample surface, including images directly during measurements by applying the indentation and scratching methods. In this case, it is not required to use immersion liquids that fill the region between the sample and the indenter. The measured area is observed with an optical microscope with illumination through an objective lens. Using an indenter in the form of a trihedral Berkovich pyramid, images of the surface of a test structure and the residual indentation are reconstructed and an image of the surface during its deformation under the application of a load to the indenter is obtained.
The ability to correlate mechanical and chemical characterization techniques in real time is both lacking and powerful tool for gaining insights into material behavior. This is demonstrated using a novel nanoindentation device equipped with Raman spectroscopy to explore the deformation-induced structural changes in piroxicam crystals. Mechanical anisotropy was observed in two major faces (0¯1 1) and (011) which are correlated to changes in the inter-layer interaction from in situ Raman spectra recorded during indentation. This study demonstrates the considerable potential of an in situ Raman nanoindentation instrument for studying a variety of topics, including stress-induced phase transformation mechanisms, mechanochemistry, and solid state reactivity under mechanical forces which occur in molecular and pharmaceutical solids.
Depth-sensing nanoindentation tests were made on single-crystal silicon wafers at various loads using a sharp Berkovich indenter, and the resulting indents were studied using transmission electron microscope and selected area diffraction techniques. The results indicated that the shape of the unloading parts of the load–displacement curves was affected by indentation load. The geometry and the size of the phase transformation region were also dependent on the indentation load. A strong correlation between the indentation load and the microstructure change of silicon was confirmed. A small load (∼20mN) leads to a complete amorphous indent after unloading, whereas a big load (∼50mN) produces a mixture of amorphous and nano-crystalline structure around the indent. The critical load for this transition to occur was approximately 30mN. These results provide information for ductile regime machining technologies of silicon parts.
Ruffell et al. [ Phys. Rev. B 83 075316 (2011)] have reported that within residual nanoindentations in films of amorphous silicon both Si-III and Si-XII phases exist in the ratio of about 20:80. It is shown here that, in the light of the existing experimental evidence, the material within the residual indentations cannot have the Si-XII phase in it, and instead the material is almost 100% Si-III with possibly a very small fraction of the Si-I phase.
Silicon wafers subject to depth-sensing indentation tests have been studied using Raman microspectroscopy. We report a strong correlation between the shape of the load-displacement curve and the phase transformations occurring within a nanoindentation. The results of Raman microanalysis of nanoindentations in silicon suggest that sudden volume change in the unloading part of the load-displacement curve (“pop-out” or “kink-back” effect) corresponds to the formation of Si–XII and Si–III phases, whereas the gradual slope change of the unloading curve (“elbow”) is due to the amorphization of silicon on pressure release. The transformation pressures obtained in nanoindentation tests are in agreement with the results of high pressure cell experiments. © 2000 American Institute of Physics.
Nanoindentation has been used widely to study pressure-induced phase transformations in Si. Here, a new aspect of the behavior is examined by making nanoindentations on (1 0 0) single crystals using a series of triangular pyramidal indenters with centerline-to-face angles varying from 35.3° to 85.0°. Effects of indenter angle, maximum load, and loading/unloading rate are systematically characterized from nanoindentation load–displacement data in conjunction with micro-Raman imaging spectroscopy of the residual hardness impressions. Results are discussed in terms of prevailing ideas and models for indentation-induced phase transformations in silicon.
Interaction between two material surfaces in a real environment is a complex process that may involve material fracture, deformation, mechanochemical interactions, and phase transformations. These processes must be considered together because of the existing synergy between them. Interaction between two material surfaces in a real environment is a complex process that may involve material fracture, deformation, mechanochemical interactions, and phase transformations. These processes must be considered together because of the existing synergy among them. This chapter reviews phase transformations in semiconductors, including pressure-induced metallization. Mechanisms of phase transformations in ceramics can be different from those in semiconductors, but pressure- or deformation-induced amorphization has been observed for both classes of materials.
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