EP0604415A1 - Dispositif de detection d'electrons pour les analyses spectroscopiques de surfaces soumises a une excitation par rayons x - Google Patents

Dispositif de detection d'electrons pour les analyses spectroscopiques de surfaces soumises a une excitation par rayons x

Info

Publication number
EP0604415A1
EP0604415A1 EP91916107A EP91916107A EP0604415A1 EP 0604415 A1 EP0604415 A1 EP 0604415A1 EP 91916107 A EP91916107 A EP 91916107A EP 91916107 A EP91916107 A EP 91916107A EP 0604415 A1 EP0604415 A1 EP 0604415A1
Authority
EP
European Patent Office
Prior art keywords
sample
diode
conversion
detector
ray
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP91916107A
Other languages
German (de)
English (en)
Inventor
José GOULON
Christophe Gauthier
Louis Leclerc
Alain Retournard
Robert Cortes
Marie Odile Lampert
Roland Henck
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
EUROPEAN ECONOMIC COMMUNITY EEC
European Economic Community
Original Assignee
EUROPEAN ECONOMIC COMMUNITY EEC
European Economic Community
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by EUROPEAN ECONOMIC COMMUNITY EEC, European Economic Community filed Critical EUROPEAN ECONOMIC COMMUNITY EEC
Publication of EP0604415A1 publication Critical patent/EP0604415A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
    • G01T1/16—Measuring radiation intensity
    • G01T1/28—Measuring radiation intensity with secondary-emission detectors
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
    • G01N23/22—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material
    • G01N23/227—Measuring photoelectric effect, e.g. photoelectron emission microscopy [PEEM]
    • G01N23/2273—Measuring photoelectron spectrum, e.g. electron spectroscopy for chemical analysis [ESCA] or X-ray photoelectron spectroscopy [XPS]

Definitions

  • This invention refers to an electron detector device optimized for structural surface analyses using X-ray excita ⁇ tion spectroscop .
  • the device operated under vacuum condi ⁇ tions, comprises basically a large size silicon diode that can detect both the X-ray fluorescence photons and the conversion electron resulting from the irradiation of the sample by the incident X-ray photons.
  • X-ray absorption fine structures (“XAFS" spectra, as referred to in the scientific literature) are classically measured by monitoring the intensity of the X- ray fluorescence photons, or the intensity of the conversion electrons as a function of the energy of the monochromatic exciting X-ray beam. This requires, however, some suitable, detector.
  • the detector output signal associated with each energy data point is digitized and stored in a computer memo- ry.
  • the whole XAFS spectrum (corresponding to a complete scan of the monochromator) is finally reconstructed and analyzed according to more or less standard procedures so as to recover the structural information.
  • the secondary emissions are most often collected with- in a restricted solid angle along a detection axis rotated by about 90° with respect to the incident X-ray beam exciting the sample.
  • Standard detectors will respond not only to the con ⁇ version electrons, but also to the X-ray fluorescence photons, and, even worse, to a "variable" background of X-ray photons directly scattered or diffracted by the sample.
  • the primary aim of the invention is to eliminate any radiative contribution and thus to enhance the "near-surface sensitivity" of the structural information.
  • Figure 1 shows a schematic top-view of a device cor ⁇ responding to the invention.
  • Figure 2 presents a functional diagram of a photodiode used in the detection device shown in Figure 1.
  • Figure 3 is a top view of the photodiode considered in Figure 2.
  • Figure 4 reproduces typical experimental spectra re- corded with a device corresponding to the invention. These spectra contain all the desired near-surface structural infor ⁇ mation. In this particular experiment, the sample was bulk tungsten metal with an oxidized overlayer.
  • the sample 1 is suspended from a sample holder (not shown) inside a vacuum tight sample chamber 2 which also incorporates the whole detector assembly.
  • An electrostatic screen 3 made of preformed copper foils or metallic grids, is disposed all around the sample except in the direction of the detector.
  • An entrance slit 4 is cut into this electrostatic screen in order to allow the incident X-ray beam to strike the surface of the absorbing sample 1.
  • the plane of incidence of the exciting X-ray beam is set horizont ⁇ al in the proposed experimental arrangement: this is usually preferable in terms of polarization of the incident beam but, alternatively, it could be set vertical as well (with only minor mechanical modifications).
  • the detection assembly itself is set always perpendi ⁇ cular to the plane of incidence of the exciting X-ray beam impinging on the sample at about 90° from the direction of the X-ray beam.
  • the first element of the detector assembly is a microchannel plate 5 set vertically. It is held in a support frame 6 machined from a highly insulating material (e.g. tef ⁇ lon), which carries also a large size photodiode 9 which is a non-standard component described below with reference to Figu- res 2 and 3 and which is the heart of the detection system.
  • the primary function of the microchannel plate (MCP) 5 is to pre-amplify the signal of the conversion electrons. It is operated at a very low difference of potential between the polarization terminals 7 and 8, i.e. about 500 eV which re- suits in a very modest gain ( ⁇ 1000) compared to the standard operation mode recommended by the channel plate manufacturers and corresponding to typical gains of 10 5 to 10 8 . Under such operating conditions, the MCP 5 presents an extremely linear amplification characteristic which is essential for the pre- sent application. A further amplification is obtained by acce ⁇ lerating the intensified electron beam leaving the MCP before these electrons reach the photodiode.
  • Second scan Second scan
  • MCP terminal 7 -1900V ⁇ U ⁇ 1500V
  • MCP terminal 7 -1900V ⁇ U ⁇ 1500V
  • MCP terminal 8 -1000 V
  • MCP terminal 8 -1000V Si-diode front-face:.0 V Si-diode front-face: 0 V Si-diode back-face: ground Si-diode back-face: ground
  • the distance between the sample 1 and the MCP 5 may be, for example, 60 mm; the distance between the MCP 5 and the Si-diode may be 5 mm.
  • the radiative emission i.e. X-ray scattering + X-ray fluorescence
  • the radiative emission is entirely absorbed but a quite significant amount of secondary electrons can still be generated inside the channels and be amplified to ⁇ gether with the conversion photoelectrons which are of direct interest for the required analyses.
  • the measured XAFS spectrum recorded at the output of the Si-diodes is "pol- luted" and distorted by signatures which are due to the radia ⁇ tive emission and not relevant to the surface of the sample.
  • Figure 4 reproduces' the characteristic FT spectrum, of the XAFS data measured during the first scan (dashed line) and the FT spectrum corresponding to the difference discussed above (continuous line): a detailed interpretation of these spectra would fall far beyond the scope of the present disclo ⁇ sure but it is clearly apparent that a strong signature asso ⁇ ciated with the metallic tungsten substrate. (i.e. the W...W interatomic distance) is missing in the difference spectrum which is left with the only contribution of the oxide over- layer.
  • Figure 4 is thus a good illustration of the typical "contamination" of the structural information contained in the surface sensitive contribution of the ' conversion photoelec ⁇ trons by spectral features due to the bulk sample and result- ing from the unwanted X-ray fluorescence contribution.
  • the "key component” which is the Si- diode. It is made of a high resistivity n-type silicon wafer (280 um thick; 53x53 mm 2 ). As summarized in Figure 2, the junction results from the creation of a ion implanted p * layer 11, the interface zone between the n-type substrate 10 and the p* layer 11 constituting the space charge region 12. The thick ⁇ ness of the p * layer 11 is about 1300A.
  • the active area of the front face is not coated with a protective aluminium layer: there are only provided a narrow peripheral strip plus a few axial strips 14 projecting therefrom towards the center of the free surface (see Figure 3).
  • the aluminium strips disposed as described above are required to collect the detected charges and allow electrical contacts to be taken using ultra-sonic wire bonding techniques.
  • the whole back face can be protected with an aluminium coating. Connections can then be made from both faces with a low noise electrometer (not shown) used for ultra-low current measurements.
  • the thickness of the p * layer 11 has to be minimized: this is because the charges created in this p* layer need to diffuse to reach the junction with some probability to recombine without inducing any current detected by the elec ⁇ trometer. No Si0 2 nor aluminium protective coatings are provi ⁇ ded. However, due to the absence of such an overall protective layer on top of the active area, special care must be taken during operation: this means that the diode has to be kept under vacuum (just as the MCP!) and that water condensation and adsorption on the cold front face is not tolerated.
  • the absence of Si0 2 overlayer minimizes the risk of damaging the junction when intense beams of electrons strike the active area: this is because, as established over the recent years, fixed charges tend to accumulate in the oxide and generate strong electric fields destructing the junction. This consideration may lead to protect the passivated Si0 2 strip 134 with a special teflon frame not shown in Figures 1 and 2.
  • the very thin overlayer of native oxide on top of the p * layer 11 does not induce any notable degradation of the diode characteristics, e.g. any spectacular increase of the "dark" current.
  • the Si-diode It is strongly recommended to operate the Si-diode at low temperature, typically at 150 K, in order to reduce the dark current generated in the diode but also in order to in ⁇ crease the equivalent shunt resistor of the diode which has to be made as large as possible so as to minimize the noise due to the residual offset voltage of the J-FET used as input stage of the electrometer (not discussed in this document).
  • the detector should preferably be operated under good vacuum.
  • the components of the detector asembly are all bake- able under a good primary vacuum at 400 K.
  • the detector is compatible with the conventional, ultrahigh vacuum (UHV) requirements. This is a serious advantage of the present devi ⁇ ce over many classical detectors which do not survive high temperatures involved during the baking operation of the sa p- le chamber/detector prior to use.
  • V 0 - 2250 V _+ 300 V): in this con- figuration the conversion photoelectrons emitted by the sample are synchroneously accelerated and blocked depending on the value of V B and the ac component of the signal delivered by the Si-diode should be directly proportional to the surface sensi ⁇ tive contribution of the conversion photoelectrons. It is noteworthy that the operation of the device without the pre-intensifying MCP proved also to be quite pos ⁇ sible in cases where the signal is very large. This simplifi ⁇ cation may find useful applications when the experiment is coupled to very intense synchrotron radiation X-ray sources of the 3rd generation.

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  • Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Biochemistry (AREA)
  • Analytical Chemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Molecular Biology (AREA)
  • Analysing Materials By The Use Of Radiation (AREA)

Abstract

L'invention concerne un dispositif détecteur d'électrons pour les analyses spectroscopiques de surfaces soumises à une excitation par rayons-X monochromatiques; ce détecteur comprend: (i) une diode au silicium (9) capable de détecter avec un gain 1 des électrons secondaires accélérés; (ii) une galette de micro-canaux (5) conçue pour pré-amplifier les photo-électrons de conversion remis par l'échantillon (1) et qui est utilisée avec un gain très bas mais avec d'excellentes caractéristiques de linéarité. Le composant-clé est une diode au silicium refroidie faite avec du silicium de type n à haute résistivité avec une couche (11) à ions P+ implantés d'environ 1300 Å d'épaisseur. Ses performances dans la détection d'électrons énergétiques résultent de l'absence de couches mortes supplémentaires (revêtement de SiO2 passivé ou d'aluminium protecteur); seules quelques bandes d'aluminium (14) étant prévues pour optimiser l'accumulation des charges. Un procédé différent exploitant les excellentes performances de ce détecteur mais nécessitant deux balayages successifs, permet de distinguer l'effet des photo-électrons de conversion à surface sensible de l'effet de radiation, c'est-à-dire celui de l'émission fluorescente de rayons X qui contient les informations structurelles sur l'échantillon massif.
EP91916107A 1991-09-17 1991-09-17 Dispositif de detection d'electrons pour les analyses spectroscopiques de surfaces soumises a une excitation par rayons x Withdrawn EP0604415A1 (fr)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/EP1991/001771 WO1993006470A1 (fr) 1991-09-17 1991-09-17 Dispositif de detection d'electrons pour les analyses spectroscopiques de surfaces soumises a une excitation par rayons x

Publications (1)

Publication Number Publication Date
EP0604415A1 true EP0604415A1 (fr) 1994-07-06

Family

ID=8165610

Family Applications (1)

Application Number Title Priority Date Filing Date
EP91916107A Withdrawn EP0604415A1 (fr) 1991-09-17 1991-09-17 Dispositif de detection d'electrons pour les analyses spectroscopiques de surfaces soumises a une excitation par rayons x

Country Status (6)

Country Link
EP (1) EP0604415A1 (fr)
JP (1) JPH06510115A (fr)
CA (1) CA2118921A1 (fr)
IE (1) IE922607A1 (fr)
PT (1) PT100869A (fr)
WO (1) WO1993006470A1 (fr)

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5326978A (en) * 1992-12-17 1994-07-05 Intevac, Inc. Focused electron-bombarded detector
GB9520384D0 (en) * 1995-10-06 1995-12-06 Univ Leicester Detector and method for autoradiography
GB0321039D0 (en) 2003-09-09 2003-10-08 Council Cent Lab Res Councils Ionising particle analyser
US9822166B2 (en) 2013-03-15 2017-11-21 Dana-Farber Cancer Institute, Inc. Flavivirus neutralizing antibodies and methods of use thereof
EP4426730A1 (fr) 2021-11-05 2024-09-11 Dana-Farber Cancer Institute, Inc. Anticorps monoclonaux humains contre la grippe largement réactifs et leurs procédés d'utilisation

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9306470A1 *

Also Published As

Publication number Publication date
CA2118921A1 (fr) 1993-04-01
JPH06510115A (ja) 1994-11-10
PT100869A (pt) 1994-05-31
WO1993006470A1 (fr) 1993-04-01
IE922607A1 (en) 1993-03-24

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