Delay time modulation femtosecond time-resolved scanning probe microscope apparatus

#The present invention relates to an apparatus for measuring a physical phenomenon by photoexcitation, which has an ultimate resolution both temporal and spatial. More specifically, the invention relates to a delay time modulated and time-resolved, scanning probe microscope apparatus.

#Attempts to develop next-generation devices having unprecedented functions by controlling structures on nanoscale have been growing rapidly in late years. Among others, creating a functional device and an ultrafast device utilizing photophysical properties is one of particularly important targets. To this end, it becomes necessary and essential to elucidate a photoexcited physical phenomenon in a local area of nanoscale, including a transient response therein. In this connection, it has been proposed to introduce a new measurement technique that combines a scanning probe microscopic technique providing an ultimate spatial resolution with a laser pulse technique providing an ultimate temporal resolution, which has already led to important achievements such as elucidations of photoexcited emission and tunneling current light emission from a single molecule and a semiconductor superlattice structure, an elucidation of a local band structure and an analysis of the point defect. See Journal of Applied Physics Vol.83, No. 7, 1 Apr. 1998, page 3453 ff.; Journal of Applied Physics Vol. 88, No. 8, 15 Oct. 2000, pages 4851; Solid State Communications Vol.6 of 107, page 281 ff., 1998; and Hyomen-Kagaku (Surface Science) 20, page 337 SHIGEKAWA, hidemi “Photoexciting STM”.

#A scanning probe microscope, e.g., a scanning tunneling microscope, is an apparatus in which the probe apex having a radius of curvature in the order of angstroms is brought proximate to a surface of a specimen across a distance in the order of angstroms and a tunnel junction is formed between the probe apex and the specimen surface to measure a morphology of the surface on an atomic level from a tunneling current passing through the tunnel junction. The scanning tunneling microscope, using a piezo stage that allows scanning with a precision in the order of angstroms, is capable of obtaining a surface morphology at an ultimate spatial resolution.

#The present invention will better be understood from the following detailed description and the drawings attached hereto showing certain illustrative forms of implementation of the present invention. In this connection, it should be noted that such forms of implementation illustrated in the accompanying drawings hereof are intended in no way to limit the present invention but to facilitate an explanation and understanding thereof. In the drawings, in connection with the first object:

#FIG. 1 is a diagram illustrating the construction of a delay time modulated and femtosecond time-resolved scanning probe microscope apparatus constituting a first form of implementation of the present invention;

#FIG. 2 is a diagram illustrating results of measurement of the probe signal flowing through a Au (111) thin film deposited on mica in an apparatus of the present invention;

#Hereinafter, the present invention will be described in detail with reference to certain suitable forms of implementation thereof illustrated in the drawing figures.

#Mention is first made of a delay time modulated and femtosecond time-resolved scanning probe microscope apparatus constituting a first form of implementation of the present invention.

#FIG. 1 is a diagram illustrating the construction of a delay time modulated and femtosecond time-resolved scanning probe microscope apparatus constituting a first form of implementation of the present invention. In the Figure, the delay time modulated and femtosecond time-resolved scanning probe microscope apparatus of the present invention designated by reference numeral 1 comprises an ultrashort laser pulse generator 2 for producing a series of ultrashort laser pulses 3; a delay time modulating circuit 6 which splits an ultrashort laser pulse 3 produced by the ultrashort laser pulse generator 2 into two ultrashort laser pulses 4 and 5 and which also modulates a delay time td between ultrashort laser pulses 4 and 5 with a frequency ω; a scanning probe microscope 7 for scanning a specimen 18 over a surface area thereof with a probe 19 in which the probe 19 is disposed just above the specimen 18 so that a tunnel junction is formed between a probe 19's apex and the specimen 18 irradiated with the ultrashort laser pulses 4 and 5 with the delay time td modulated with the frequency ω; and a lock-in detection unit 8 which performs lock-in detection with the modulation frequency ω of a probe signal 11 that is a tunneling current passing between the probe 19's apex and the specimen 18 and modulated by irradiation of the ultrashort laser pulses 4 and 5 thereon.