EP0296262A1
Expired / Lapsed
EP
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Method for investigating surfaces at nanometer and picosecond resolution and laser-sampled scanning tunneling microscope for performing said method
Assignee: International Business Machines Corp
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Filing: 1987-06-22
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Granted: —
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Expires: 2007-06-22
Abstract
Abstract For observing material structures and/or dynamic processes at surfaces, the known scanning tunneling microscope (STM) is combined with a photoexcitation process leading to photon-assisted tunneling. Thereby, the very fine spatial resolution of the STM is combined with the picosecond or even femtosecond time resolution of laser pulses. The tunnel tip (20) of a scanning tunneling microscope is positioned at tunnel distance with respect to the surface of the sample (27) to be investigated, with an appropriate potential (U t ) applied across the gap between tunnel tip (20) and sample (27). The tunneling current is gated by means of at least one pulsed laser beam (26) directed at the tunneling region and/or at the tunnel tip (20). In one embodiment, by a first laser beam a bunch of hot-electrons is excited in the sample to an energy just below the material's work function and caused to travel within the sample. A second laser beam at the location of the tunnel tip gates the tunneling current in accordance with the pulse pattern of the lasers. In another embodiment, the gating action occurs at the tunnel tip (20) where a laser beam (26) is used to change the resistance of a photoconductor layer (23) arranged between the tunnel electrode (22) and the associated electronics (24, 25).
Inventors
- 👤 Johannes Georg Dr. Beha
- 👤 Armin Udo Dr . Blacha
- 👤 Rolf Dr. Clauberg
- 👤 Rolf Bernd Georg Dr. Möller
- 👤 Wolfgang Dieter Dr. Pohl
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-07 14:44
CPC Classifications
G; G01; G01Q; G01Q60/00; G01Q60/10; G01Q60/12; G01Q60/16; Y; Y10; Y10S; Y10S977/00; Y10S977/84; Y10S977/849; Y10S977/86; Y10S977/861; Y10S977/868
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
144 words
Method for investigating dynamic processes and/or the material structure at the surface of a sample (3, 6, 12, 27, 58), with a spatial resolution in the nanometer range, and with a time resolution in the picosecond range, characterized by the steps of: - positioning the tunnel tip (1, 7, 13, 20, 30, 38, 45) of a scanning tunneling microscope relative to the surface of the sample (3, 6, 12, 27, 58) to be investigated, applying a predetermined electrical potential (U t ) across the gap between the tunnel tip (1, 7, 13, 20, 30, 38, 45) and said sample (3, 6, 12, 27, 58); and - gating the tunneling current by means of at least one pulsed laser beam (4, 5, 9, 16, 26, 35, 44, 51, 55) directed at the tunneling region and/or said tunnel tip (1, 7, 13, 20, 30, 38, 45).
Claim 2
Dependent Claim
144 words
Method for investigating dynamic processes and/or the material structure at the surface of a sample (3, 6, 12, 27, 58), with a spatial resolution in the nanometer range, and with a time resolution in the picosecond range, characterized by the steps of: - positioning the tunnel tip (1, 7, 13, 20, 30, 38, 45) of a scanning tunneling microscope relative to the surface of the sample (3, 6, 12, 27, 58) to be investigated, applying a predetermined electrical potential (U t ) across the gap between the tunnel tip (1, 7, 13, 20, 30, 38, 45) and said sample (3, 6, 12, 27, 58); and - gating the tunneling current by means of at least one pulsed laser beam (4, 5, 9, 16, 26, 35, 44, 51, 55) directed at the tunneling region and/or said tunnel tip (1, 7, 13, 20, 30, 38, 45).
Claim 3
Dependent Claim
178 words
Method in accordance with claim 1, characterized in that the electrical potential (U t ) across the tunneling gap is maintained at a level below the one at which the tunneling current normally starts to flow, that a first laser beam (4) is directed at the surface of the sample (3, 6, 12) under investigation, at a predetermined distance from the surface spot opposite the tunnel tip (1, 7, 13) so as to excite traveling hot-electrons at the surface of said sample (3, 6, 12), that a second laser beam (5, 9, 16) is applied at or in the vicinity of said surface spot at which the tunnel tip (1, 7, 13) is placed, said second laser beam ( 5, 9, 16) having a known time relationship with respect to said first exciting laser beam (4), and that the behavior of the time variation of the tunneling current occurring between said surface spot and said tip (1, 7, 13) in response to said hot-electrons which were further excited by said second laser beam (5, 9, 16), is determined.
Claim 4
Dependent Claim
166 words
Method in accordance with claim 1, characterized in that the electrical potential (U t ) between the tunnel tip (20, 30, 38, 45) and the surface of the sample (27, 58) under investigation is maintained at a level normally permitting a tunneling current to flow, that a tunnel tip (20, 30, 38, 45) is used which carries a photoconductor (23, 34, 40, 48) between the conductive point (22, 32, 39, 47) thereof and the terminal (24, 38, 43, 49) to which the said tunnel potential (U t ) is applied, wherein said photoconductor (23, 34, 40, 48) has a relatively high dark resistance and a relatively low light resistance, and that the said laser beam (26, 35, 44, 51) is directed onto said photoconductor (23, 34, 40, 48) so as to render the same conductive when said laser beam (26, 35, 44, 51) is sampled, thus enabling the tunneling current (i t ) to flow in the presence of a laser pulse (26, 35, 44, 51).
Claim 5
Dependent Claim
124 words
Laser-sampled scanning tunneling microscope for performing the method in accordance with claim 1, characterized in that the tunnel tip (1, 7, 13, 20, 30, 38, 45) is held at tunneling distance over the area of interest of the sample (3, 6, 12, 27, 58) being investigated, that a tunneling voltage (U t ) is applied between the tunnel electrode (1, 7, 15, 22, 32, 37, 47) and said sample (3, 6, 12, 27, 58), and that at least one pulsed laser is provided, the beam (5, 9, 16, 26, 35, 44, 51, 55) of the laser being directed at the said area of interest of said sample (3, 6, 12, 27, 58) and/or at said tunnel tip (1, 7, 13, 20, 30, 38, 45).
Claim 6
Dependent Claim
152 words
Scanning tunneling microscope in accordance with claim 4, characterized in that a first pulsed laser is arranged such that its beam (4) impinges upon a location of said sample (3, 6, 12) remote by a predetermined distance from said tunnel tip (1, 7, 13), said beam (4) having an energy sufficient to excite hot-electrons in said sample (3, 6, 12), said energy being insufficient for the excited hot-electrons arriving at a location opposite said tunnel tip (1, 7, 13) to reach their work function, that a second pulsed laser is arranged such that its beam (5, 9, 16) impinges upon said sample (3, 6, 12) at the location of said tunnel tip (1, 7, 13), and that means (V) are provided for measuring the variation of the tunnel voltage (U t ) occurring at the time of arrival of the excited hot-electrons at the place of the tunnel tip (1, 7, 13).
Claim 7
Dependent Claim
58 words
Scanning tunneling microscope in accordance with claim 5, characterized in that said sample (6) is transparent to the light of said second laser beam (9), and that said second laser beam (9) is arranged so as to shine through said sample (6) from the side opposite said tunnel tip (7) and in axial alignment with the latter (Fig.2).
Claim 8
Dependent Claim
85 words
Scanning tunneling microscope in accordance with claim 5, characterized in that said tip (13) consists of a transparent body (14) coated with a thin metal layer (15) having a narrow aperture at the apex (17) of said coated body (14, 15), that said laser beam (16) is coupled into the rear end of said transparent body (14) and exits at the apex (17) thereof, and that the tunneling voltage (U t ) is applied between said metal layer (15) and said sample (12; Fig. 3).
Claim 9
Dependent Claim
78 words
Scanning tunneling microscope in accordance with claim 4, characterized in that said tip (13) consists of an insulating body (21) carrying an electrically conductive, pointed electrode member (22) at one end, and a photoconductor layer (23) along one side and in contact with said electrode member (22) as well as with an electrode (24), and that said laser beam (26) is aligned to impinge upon a window (28) through which said photoconductor layer (23) is exposed (Fig. 4).
Claim 10
Dependent Claim
88 words
Scanning tunneling microscope in accordance with claim 4, characterized in that said tip (30) consists of an insulating body (31) having a pointed shape with a tunnel electrode (32) fixed onto one face of said point, that said electrode is in connection with a photoconductor layer (34) which in turn is partly covered by a contact electrode (33), that part of the photoconductor layer (34) is exposed through a window (36) is said contact electrode (33) to a laser beam (35) aligned with said window (36, Fig. 5)
Claim 11
Dependent Claim
80 words
Scanning tunneling microscope in accordance with claim 4, characterized in that said tip (38) comprises an insulating body (42) having a pointed shape with a tunnel electrode (37) consisting of a photoconductor material fixed onto one face (41) of said point, that said tunnel electrode (37) is partly covered by, and in electrical connection with, a contact electrode (43) and that a corner (39) of the photoconductor layer (40) is exposed to an appropriately aligned laser beam (44; Fig. 6).
Claim 12
Dependent Claim
186 words
Scanning tunneling microscope in accordance with claim 4, characterized in that said tip (45) comprises an insulating body (46) with a tunnel electrode (47) fixed to one end thereof and having electrical contact with a first photoconductor layer (48) to which a first electrode (49) is attached, partly covering said photoconductor layer (48) but leaving a first window (50) for exposure of part of said first photoconductor layer (48) to a first laser beam (51), that a second photoconductor layer (52) is coated onto said body (46) and is, in turn covered by a second electrode (53) having a second window (54) for exposing part of said second photoconductor (52) to a second laser beam (55), said second photoconductor (52) being in electrical contact with a metal shield (56) coated onto an insulating layer (57) covering said tunnel electrode (47) except for an aperture (60) at the apex of said tunnel elctrode (47), said second laser beam (55) controlling the potential of said metal shield (56) which is normally governed by a resistor (59) connected between said metal shield (56) and the sample (58) being investigated.
References Cited (Backward Citations)
EP0027517A1
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EP0112401A1
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