Modulated microwave microscopy and probes used therewith

A microwave microscope probe, comprising:

• a probe tip having a semiconductor barrier formed therein and having an apex positionable adjacant a surface of a sample;
• and
• a cantilever arm supported on proximal end of the arm and supporting the probe tip projecting in a first direction toward the apex from a bottom surface on a distal end of the arm, wherein the arm comprises
• a first conductive layer dispose in the first direction on top surface of the arm opposition the bottom surface and extending between the proximal and distal ends,
• a dielectric layer disposed in the first direction on the first conductive layer and extending between the proximal and distal ends, and
• a first conductive strip formed in the first direction on the dielectric layer, extending between the proximal and distal ends, and electrically connected to the apex of the probe tip for conveying a microwave signal which passes through the semiconductor barrier.

A microwave microscope, comprising:

• a probe tip;
• a cantilever arm supported near its proximal end by an actuator positioned near the proximal end, and supporting the probe tip on its distal end;
• a source of microwave signal at a microwave frequency of greater than 100 MHz coupled to the probe tip and interacting with a sample adjacent the probe tip;
• means for modulating at a modulation frequency less than 10% of the microwave frequency a coupling of the microwave signal from the probe tip to a sample while the probe tip is vertically separated from the sample;
• and
• sensing circuitry receiving and electrically interacting microwave radiation reflected from the sample with an oscillatory electrical signal from the modulating means, for producing a differential of the received microwave radiation relative to at least two non-zero vertical separations of the probe tip from the sample.

A microwave microscope for characterizing a sample, comprising:

• a probe tip;
• a cantilever arm supported near its proximal end by an actuator positioned near the proximal end, and supporting the probe tip on its distal end adjacent the sample;
• a source of microwave signal coupled to the probe tip and as an oscillatory first electrical signal and interacting with the sample adjacent the probe tip;
• a source of an oscillatory second electrical signal applied to the probe tip;
• means including a non-linear electrical element apart from the sample for modulating a coupling of the microwave signal from the probe tip to the sample according to the second electrical signal;
• and
• sensing circuitry, receiving microwave radiation reflected from the sample, detecting an amplitude of a signal at a sideband frequency having a first value determined between a second value of a frequency of the microwave signal and a third value of a frequency of the second electrical signal.

A microscope, comprising

• a probe tip;
• a cantilever arm supported near its proximal end by an actuator positioned near the proximal end, and supporting the probe tip on its distal end;
• a source of microwave signal coupled to the probe tip and interacting with a sample adjacent the probe tip;
• a low-frequency oscillatory source producing a vertical oscillation signal of vertical oscillation frequency lower than that of the microwave source;
• an actuator controlled according the vertical oscillation signal and controlling a vertical motion of the probe tip perpendicular to a sample surface;
• and
• a control system receiving and electrically interacting microwave radiation reflected from the sample with an electrical signal of vertical oscillation frequency from the low-frequency source for producing a differential of the received microwave radiation relative to at least two vertical separations of the probe tip from the sample surface.

A probe tip for use in a microwave microscope, comprising:

• a mount;
• a cantilever flexible in a vertical direction, supported on one end thereof by the mount, supporting on the other end thereof a probe tip projecting in the vertical direction from the cantilever, and including a transmission line carrying a microwave signal and extending along the cantilever between the probe tip to the mount, wherein the probe tips includes
• a body including a tapered section terminating in an apex, and
• a semiconductor barrier disposed in the body and across which the microwave signal passes.

A method of operating a microscope, comprising the steps of:

• coupling a microwave excitation signal at a microwave frequency of greater than 100 MHz through a probe tip onto a localized area of a sample;
• modulating the coupling of the excitation signal according to a modulation signal at a modulation frequency of less then 10% of the microwave frequency;
• detecting a reflected microwave signal from the sample resulting from the excitation signal;
• and
• demodulating the reflected microwave signal resulting from the microwave excitation signal according to the modulation signal.