auger electron spectroscopy (AES)
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auger electron spectroscopy (AES)
- 3. Lise Meitner Pierre Auger
- 4. The Auger Process K L M Vacuum Level Eject core electron Higher electron falls into hole Another higher level electron is ejected to carry away excess energy. Measure kinetic energy of ejected electron. Incident Electron Beam (5 kV) Ekinetic = E(K) - E(L) - E(L)
- 5. KE of Auger electron ~ -EA – EB EC Emitted energy of relaxed electron Energy needed to overcome BE of Auger electron NOTE: KE of Auger electron is not proportional to the primary beam energy Different from XPS Kinetic Energy Of The Auger Electron
- 6. KLM Source of auger electron Origin of relaxing electron Initial core hole Four main Auger series: KLL, LMM, MNN, NOO As the atomic number increases, the number possible electron transfers are also high.
- 7. Auger yield
- 9. In addition, the entire system must be shielded from the earth’s magnetic field AES instrument schematic configuration
- 17. (HSA) henmispherical scefor alualyser
- 18. Read-out system
- 19. • Qualitative Identification of Elements Analytical Information Ex: From the differential AES spectrum Ni, Fe and Cr have been identified. Ni Fe Cr
- 20. Chemical Shift Auger spectra from elemental silicon and oxidized silicon showing the chemical shift which occurs in the oxide
- 21. Quantification External standard (1 Sensitivity factor(2
- 22. Sensitivity factor of elements
- 23. Surface Analysis Auger Electron Spectroscopy (AES) Depth Profiling E- Gun Ar+ Sputter Gun
- 25. •The primary electron beam is focussed on the surface and scanned (similarly to SEM). •At each point (pixel), an Auger spectrum is recorded. •Peaks that correspond to a specific element are indentified and their intensity measured. •A colour is assigned to each element •The brightness of colour at each pixel is proportional to the intensity of the corresponding Auger peak. •Result: multicoloured images as chemical element maps. Scanning auger microscopy(SAM):
- 27. XPS vs. Auger
Notas do Editor
- Pierre Auger, in 1925 observed (at first in the cloud chamber, then in photographic plates) the occurrence of electrons with precisely determined energies. These electrons have been later named Auger electrons) may serve to identify their parent atoms. 1953 J. J. Lander – the idea of using the Auger electrons in surface analysis.The AES has been implemented as an analytic toolin 1967 (Larry Harris), after increasing the method sensitivity by using differential spectra to discriminate the tiny Auger peaks in the electronic spectra. 1968 – Auger spectrometer with CMA in modern configuration.
- KLL برای عناصر با z=3 تا z=14 .LMMبرای عناصر با z=14 تا z=40 .MNN برای عناصر با z=40 تا z=79 .NOOبرای عناصر سنگین مطرح می باشد.
- Escape depth is independent of the primary electron energy used. The unique dependence of λon Auger electron energyalso distinguishes top monolayer chemistry from the layers below. The scattering of electrons depends on the electrondensity of the solid material and on kinetic energyThe most useful kinetic energy range of Auger electrons is from 20 to 2500 eV andcorresponds to electrons with high scattering cross sections in solids.
- The peaks are relatively small because only0.1% of the total current is typically contained in Auger peaks
- The ease of electron generation using high primary electron currentsfrom 0.05 to 5 μA and the ability to focus and deflect electrons electrically are among the chief advantages
- The Auger electrons appear as peaks on a smooth background of secondary electrons. If the specimen surface is clean, the main peaks would be readily visible and identified. However, smaller peaks and those caused by trace elements present on the surface may be difficult to discern from the background. Because the background is usually sloping, even increasing the gain of the electron detection system and applying a zero offset is often not a great advantage. Therefore the Auger spectra are usually recorded in a differential form. In the differential mode it is easy to increase the system gain to reveal detailed structure not directly visible in the undifferentiated spectrum.
- از آنجا كه اين روش اثر بازتاب الكترون ها و ضخامت بحراني كه الكترون ها از آن مي توانند بگريزند را در نظر نمي گيرد بهاين روش شبه كمّي مي گويند. در اين روش به منظور عدم نياز به استاندارد هاي مختلف از اتم نقره خالص به منظور معياراستفاده مي شود و فاكتور حساسيت عناصر ديگر را نسبت به آن مي سنجند . از آنجا كه اطلاعا در نهايت به شكلديفرانسيلي نمايش داده مي شوند نياز است تا Ix به صور peak-to-peak محاسبه شود و اين فقط وقتي ميسر است كهشكل پيك ها در زمينه تغيير نكند يعني عنصر مورد نظر در نمونه يكنواخت پراكنده شده باشد
- In the Auger map the different region: titanium (blue), sulphur (green) and silicon (red) are clearly visible with very good spatial resolution (the horizontal dimension
- Sample charging :which induces high secondary electron emission and therefore minimizes surface charge buildup, is used tminimize charging effects. Use of low electron beam currents, optimizing voltages, and large-area rastering often helps tominimize surface charging. Another practice involves masking the surface with a conductive metal grid, which acts as alocal sink to the electron chargeSpectral peak overlap is a problem in relatively few situations in AES. This occurs when one of the elements ispresent in a small concentration and its primary peaks are overlapped by peaks of a major constituent in the sample. Oftenthe effect is significant degradation of sensitivity. For example, titanium and nitrogen, iron and manganese, and sodiumand zinc are frequently encountered combinations in which peak overlap is of concern. This problem is the most severewhen one of the elements has only one peak, such as nitrogen. In most cases, one or both of the elements have severalpeaks, and the analysis can be performed using one of the nonoverlapping peaks, although it may be a minor peak in thespectrum. Peak overlap problems may also be solved by acquiring the data in the N(E) mode, followed by spectralstripping to separate the peaks.