Looks like you are currently in Finland but have requested a page in the United States site. Would you like to change to the United States site? Elton N. Kaufmann Editor. He has been with Argonne since and has served in several positions. Kaufmann holds a B.
Prior to joining Argonne, Dr. Kaufmann is a member of the Materials Research Society in which he held several positions including President Kaufmann has published approximately technical papers in refereed journals and books. Table of contents Forward.
This provides valuable information on the near-surface crystallography of the sample, which can be correlated with the growth conditions used or surface modifications applied, without the need for time-consuming sample preparation. CL spectra can also be acquired in spot mode, which show features attributable to excitons, donor—acceptor pairs or impurities. The information content of CL images and spectra includes the location of recombination sites such as dislocations and precipitates, and the presence of doping-level inhomogeneities.
This can be amplified and an image of the recombination activity displayed as the electron beam is rastered across the sample. The resolution of extended defects achieved using EBIC and CL techniques is limited by the penetration depth of the electron beam, the effect of beam spreading and the diffusion length of minority carriers.
The constraint of minority carrier diffusion length is removed due to the close proximity of the sample foil surfaces, and resolution depends on the incident probe size, the width of the electron hole pair generation zone and recombination velocity at the free surface.
Before presenting some material characterization case studies based on electron beam techniques, we now discuss the preparation of electron transparent foils that are free from artefacts and suitable for TEM investigation. We should initially consider whether destructive or nondestructive preparative techniques need to be applied. Accordingly, the focus of this section is to introduce techniques used to prepare samples for TEM investigation, since the requirement is for specimens that are typically submicrometer in thickness and free of preparation artefacts.
The idea being to minimize or eliminate artefacts from the preparation process, to ensure that the sample being investigated is representative of the starting bulk material. Care is also needed to avoid artefacts that might be introduced through interaction of the high-energy electron beam with the sample. In this context, it is interesting to note how TEM sample preparation techniques have developed over the years.
Characterization of Materials (formerly Methods in Materials Research) provides comprehensive up-to-date coverage of materials characterization techniques. A thoroughly updated and expanded new edition, this work features a logical, detailed, and self-contained coverage of the latest materials characterization.
Biological samples fashioned by enzymatic digestion, staining and microincineration were also possible by Glass and diamond knife microtomes were introduced in the s and used to section soft biological materials. Advances in the controlled preparation of inorganic materials were made upon the introduction of argon ion beam thinning in the late s, which allowed for cross-sectional observation of semiconductor heterostructures when combined with sequential mechanical polishing and dimpling.
Significant development work in this area appears throughout the literature from the s.
The problem of surface amorphization, introduced by the argon sputtering process, was minimized by adopting low-voltage milling techniques to define the final electron-transparent sample foil. Low stacking fault energy semiconductors, such as II—VI compounds which are easily damaged or InP-based compounds that suffer from In droplet formation with conventional milling techniques, were also successfully prepared for TEM observation using the technique of iodine reactive ion beam etching RIBE , otherwise known as chemically assisted ion beam etching CAIBE , developed in the s.
The s, however, saw the development of the most effective raft of sample preparation techniques for functional materials and complex semiconductor device structures in particular: i.
The integrity of the layer growth and the orientation relationship with the substrate. The nature of the structural defects within the epilayer, arising, e. Modification of the microstructure due to subsequent processing, such as contact formation and device usage. The following examples emphasize the need to apply complementary material characterization techniques in support of the development of semiconductor science and technology.
The emergence of the In,Ga,Al N system for short-wavelength light-emitting diodes, laser diodes and high-power field effect transistors has been the semiconductor success story of recent years.
In parallel with the rapid commercialization of this technology, nitride-based semiconductors continue to provide fascinating problems to be solved for future technological development. CBED analysis confirmed the feature to be an inversion domain. As shown earlier, the selectivity of the FIB technique enables cross-sections through emergent cores of the hillocks to be obtained, thereby allowing nucleation events associated with these features to be isolated and characterized. Low-magnification cross-sectional TEM imaging also revealed the presence of faceted column-shaped defects beneath the apices of these growth hillocks Fig.
It was presumed that these features originated at the original epilayer-substrate interface since no other contrast delineating the region of this homoepitaxial interface could be discerned. Thus, the defect cores were identified as having Ga-polar growth surfaces embedded within an N-polar GaN matrix. Competition between growth and desorption rates of Ga and N-polar surfaces allowed the gross hexagonal pyramids to evolve. This initial approach of applying electron diffraction and imaging techniques thus enabled the nature of the inversion domains to be identified and their propagation mechanism established in order to explain the development of the hillocks.
However, more detailed chemical analysis was required to ascertain the nature of the source of the inversion domains and how this related to substrate preparation and the growth process. Accordingly, these defect sources were attributed to remnant contamination from the chemomechanical polishing technique used to prepare the substrates prior to growth.
The CL technique is ideally suited to studies of luminescence uniformity and spectral purity. The STEBIC technique was originally demonstrated in the late s, using dedicated STEM instrumentation to obtain information on the electrical properties of dislocation core structures within Ga,Al As,P , thereby providing the first evidence that nonradiative recombination processes at dislocations are related to jogs and kink sites.
STEBIC imaging of an electron-transparent foil allows the electrical and structural properties of defects to be observed simultaneously. The availability of electron sources with high brightness in modern scanning TEM instruments compensates for the main problem of small generation volume and provides an accessible way to perform STEBIC experiments.
The samples incorporated buried p—n junctions to assist with charge collection and surmount the problem of surface recombination effects. This type of considered approach to materials characterization is required in order to break free of the black-box mentality that can develop if one is too trusting of the output generated by automated or computerized instrumentation systems. One should always bear in mind the process of signal generation that provides the information content. This in turn helps us to develop an appreciation of performance parameters such as spatial or spectral resolution, in addition to sensitivity, precision and detection limits.
One should consider technique calibration and the appropriate use of standards in order to ensure that the data acquired is appropriate and reproducible to the problem being addressed. Consideration should also be given to the form and structure of the data being acquired and how the data sets are analyzed. In this context, distinction should be made between the processing of analog and digital information and the consequences of data conversion.
Auger Depth Profile Using an energetic ion beam to remove layers of the material, Auger spectra are collected at each depth to determine composition. However, the structural integrity of the interface between GaN and sapphire can be appraised, along with the presence of nanometer-scale, three-dimensional growth islands formed during the initial stages of epitaxy, prior to layer coverage. Quantifying the angle of misalignment between large grains to other situations where knowing the precise crystallographic orientation is needed. Permanent deformation For year, over the large thirty elements, American, medical and considerable type examples do ahead biased on econometrics that are negatively close in frequency and industry. The rational understanding of these results is impossible without the Raman map of the PS band Figure 10c.
Issues regarding the interpretation or misinterpretation of results often stem from the handling of experimental errors. There are clearly differences between qualitative assessment and the more rigorous demands of quantitative analysis. The level of effort invested often reflects the nature of the problem that is being addressed. To summarize, an awareness of the methodology used in any investigation is required to establish confidence in the relevance of the results obtained. As ever, there are many people one wishes to acknowledge for their involvement in the growth, processing and underpinning characterisation research programmes drawn from to illustrate this chapter.
University of Nottingham: with thanks to Tom Foxon, T. University of Warwick: with thanks to Richard Kubiak and E. Skip to main content Skip to sections. Advertisement Hide. Download chapter PDF. Different parts of the electromagnetic spectrum will interact with matter in different ways, according to the energy states within the material, allowing absorption or ionization effects to occur. The salient features of these various radiation—material interaction processes are summarized in the schematics shown in Fig.
Open image in new window. As the quantum energy increases from radio waves, through microwaves, to infrared and visible light, absorption increases, whilst specific quantized ionization effects come into play upon moving further into the ultraviolet and x-ray parts of the spectrum. Microwave and infrared radiation, for example, can interact with the quantum states of molecular rotation and torsion, leading to the generation of heat.
Strong absorption also occurs within metallic conductors, leading to the induction of electric currents. Visible and ultraviolet light can elevate electrons to higher energy levels in what is known as the photoelectric effect, which is essentially the liberation of electrons from matter by short-wavelength electromagnetic radiation when all of the incident radiation energy is transferred to an electron. At lower 0.
In practical terms, the process of sputtering is most efficient when the masses of the incident and ejected particles are similar, whilst it is also dependent on the sputtering gas pressure, the energy spread of the particles, the bias conditions and the sample geometry. By way of comparison, Fig.
In order to make sense of the origins of the many different signals, we must consider the phenomenon of electron scattering, which underpins them all. Elastically scattered electrons contribute to the formation of diffraction patterns and diffraction contrast images in TEM. The signatures from plasmon-scattered electrons can dominate the low-energy regimes of EEL spectra, providing information on sample thickness. Table The basic principles of diffraction in reflection, transmission or glancing angle geometries may be introduced with reference to x-ray scattering and interference.
The positions of the resultant maxima in scattering intensity may be used to deduce crystal plane spacings and hence the structure of an unknown sample when correlated with database values. The path difference between the x-rays reflected from successive planes must be equivalent to an integer number of wavelengths n for constructive interference to occur.
The crystallographic structure of an unknown material can, nevertheless, be analyzed via the diffraction of x-rays of known wavelength. By way of example, Fig.
If we consider the objective lens shown in Fig. For the combined projection optical microscope system shown in Fig. The path of travel of the electron beam through the entire electron-optic column must be under conditions of high vacuum, considering the ease of absorption of electrons in air. An accelerated, high-energy electron acquires significant kinetic energy and momentum. When charting the historical development of TEM, improvements in resolution have depended on the construction of microscopes operating at higher voltages, in order to capitalize on the benefits from the reduced electron wavelength.
This spread in path lengths of rays traveling from an object to the image plane is termed spherical aberration. The weak beam technique allows for complex dislocation tangle to be resolved more clearly.