BACKGROUND

An electron microscope may comprise various systems and methods for delivering an electron dose. For example, in transmission electron microcopy, high-energy electrons may pass through a sample from above and form an image on a detector below. This process, which is intended to measure the properties of a sample, may change the sample and may even damage the sample.

SUMMARY

Applicant has recognized that there is an unmet need for new methods and systems for temporally modulating the electron dose on a transmission electron microscope. Systems and methods of the present disclosure allow the functional form and timescale of the dose (e.g., an electron dose waveform) to be tailored to the dynamics of the sample in a fast, precise, and repeatable fashion. Methods and systems disclosed herein may be used to reduce or control the effects of the electron dose during a transmission electron microscopy (TEM) measurement.

Systems and methods disclosed herein may improve on methods of adjusting the electron dose that operate, for example, by modulating electron optical settings of the electron beam. Such settings may include beam current, convergence angle, and aperture size. Adjusting the electron optical settings may not allow for an electron dose to be modulated on a fast timescale. Further, aligning electron optics for transmission electron microscopy to achieve atomic resolution may be complex and may involve adjusting multiple interconnected parameters within the electron optical system.

Systems and methods disclosed herein may provide at least some of the following, non-limiting advantages: allowing the average dose to be adjusted on a fast timescale; allowing the average dose to execute an arbitrary function with respect to time; allowing the average dose (e.g., the duty cycle) to be continuously varied across a range from 0 to 100% dose transmission; allowing the dose waveform to be synchronized to a detector, a stimulus to the sample, or a change in the electron-optical conditions of the microscope; allowing the dose waveform to be calculated and adjusted by an algorithm which may consider one or more of information about the sample, deflection electronics, detectors involved in the measurement, and the determined waveform input into the control software by the user; allowing the temporal profile of the pump pulse, probe pulse, or both to be customized in a pump-probe experiment; reducing limitations on the dose waveform created by the physical constraints of ultrafast pulsed electron sources such as laser-driven cathodes and radio-frequency pulsers, e.g., a limited dynamic range and/or duration for the waveform; allowing the dose waveform to be applied at a selectable accelerating voltage available for the electron beam; and allowing the pulses which comprise the dose waveform to occur at a nonuniform repetition rate.

In an aspect, the present disclosure provides a device. The device may comprise: an electron source directed toward a sample area; a detector for receiving an electron signal or an electron-induced signal; and a deflector positioned between the electron source and the sample, wherein the deflector modulates an intensity of the electron source directed to the sample area according to an electron dose waveform having a continuously variable temporal profile.

In another aspect, the present disclosure provides a device. The device may comprise: an electron source directed toward a sample area; a detector for receiving an electron signal or an electron-induced signal; and a deflector positioned between the electron source and the sample, wherein the deflector modulates an intensity of the electron source directed to the sample area according to an electron dose waveform having a variable temporal profile, the variable temporal profile comprising: a selectable non-regular pulse width, a selectable non-regular repetition rate, or both.

In some embodiments, the electron dose waveform comprises an arbitrarily defined temporal profile. In some embodiments, the waveform comprises a series of waypoints. In some embodiments, the series of waypoints are individually or collectively selectable to construct the arbitrarily defined temporal profile. In some embodiments, the series comprises greater than 1000 waypoints. In some embodiments, the arbitrarily defined temporal profile comprises a temporal resolution of less than 10 ns. In some embodiments, the arbitrarily defined temporal profile is indicated by a user.

In some embodiments, the deflector comprises a driving electrode and an electrode at a fixed voltage. In some embodiments, the deflector comprises two driving electrodes. In some embodiments, the electron dose waveform modulates an average intensity of the electron source directed toward the sample area. In some embodiments, the average intensity is modulated substantially without change to other image conditions. In some embodiments, the device comprises a physical or virtual knob to adjust the average intensity. In some embodiments, the average intensity is controllable independently of a driving voltage of the electron source. In some embodiments, the average intensity is continuously variable across a range from 0 to 100% dose transmission.

In some embodiments, the electron dose waveform comprises a periodic waveform. In some embodiments, the electron dose waveform is aperiodic. In some embodiments, the electron dose waveform comprises a pump and a probe pulse. In some embodiments, the electron dose waveform is a square wave. In some embodiments, a transition time between a high voltage and a low voltage is less than about 50 ns, defined as a sum of a ringing time plus a slope time. In some embodiments, a transition time between a high voltage and a low voltage is less than about 10 ns, defined as a slope time from about 10% to about 90% a transition voltage. In some embodiments, a pulse width of the square wave is aperiodic. In some embodiments, the electron dose waveform comprises a shortest exposure time of about 100 ns.

In some embodiments, the device comprises: a pattern generator configured to produce an electrical signal representative of the electron dose waveform; and a driver electronics configured to receive the electrical signal from the pattern generator and supply a voltage comprising the electron dose waveform to the deflector. In some embodiments, the device comprises one or more computer processors comprising instructions that when executed are configured to: receive an indication of the electron dose waveform; and deliver the indication to the pattern generator.

In some embodiments, the one or more computer processors comprise instructions to adjust a shape of the electron dose waveform according to one or more parameters. In some embodiments, the one or more parameters comprise information about one or more of a property of an image from the detector, a property of the deflector, a property of the driver electronics, a property of the detector, and the indication of the electron dose waveform. In some embodiments, the one or more parameters comprises an indication of a minimum, a maximum or a fixed value for a pulse width or a pulse repetition rate of the electron dose waveform.

In some embodiments, the one or more parameters comprises a timing constraint of the deflector, the driver electronics, or the pattern generator. In some embodiments, the one or more parameters comprises a characteristic timescale of a sample or a process within the sample. In some embodiments, the one or more parameters comprises a time-dependent voltage bias or temperature. In some embodiments, the one or more parameters comprises a dose rate or a timing consideration of the detector. In some embodiments, the one or more parameters comprises an indication of a data signal quality from a collected or a real-time measurement. In some embodiments, the one or more parameters comprises an indication an effect of the intensity of the electron dose waveform on a sample from a collected or a real-time measurement.

In some embodiments, the one or more processors comprises instructions to adjust a timing of the electron dose waveform relative to a collection time of the detector, a location of one or more sub-portions of the detector, an arrival time of a stimulus to the sample area, or a change in an electron-optical condition of the device. In some embodiments, the pattern generator is an analog or a digital pattern generator. In some embodiments, the pattern generator comprises an analog to digital converter.

In another aspect, the present disclosure provides a method for modulating a dose in a transmission electron microscope image. The method may comprise: providing an electron source directed toward a sample area; receiving an electron dose waveform at a deflector disposed between the electron source and the sample area, wherein the electron dose waveform modulates an intensity of the electron source directed to the sample area according to the electron dose waveform; and outputting an electron signal or an electron-induced signal relating to at least a portion of the modulated intensity.

In some embodiments, the electron dose waveform comprises a continuously temporal variable profile. In some embodiments, the electron dose waveform comprises an arbitrarily defined temporal profile. In some embodiments, the waveform comprises a series of waypoints. In some embodiments, the series of waypoints are individually or collectively selectable to construct the arbitrarily defined temporal profile. In some embodiments, the series comprises greater than 1000 waypoints. In some embodiments, the arbitrarily defined temporal profile comprises a temporal resolution of less than 10 ns. In some embodiments, the method comprises receiving an indication of the arbitrarily defined temporal profile from a user. In some embodiments, the method further comprises providing the device of any aspect or embodiment.

In another aspect, the present disclosure provides a computer implemented method for modulating an electron dose on a transmission electron microscope (TEM). The method may comprise: (a) receiving at a processor an indication of an electron dose waveform comprising a representation of a temporal profile of an intensity of an electron dose directed to a sample area within the TEM; (b) transmitting the indication to the TEM, wherein an electrical signal representative of the indication drives a deflector within the TEM, thereby modulating the temporal profile of the electron dose; (c) receiving one or more tunable parameters, the one or more tunable parameters comprising information about one or more of: a property of a TEM image, a property of the deflector, a property of a driver electronics within the TEM, a property of a detector within the TEM, and the indication of the electron dose waveform; and (d) updating the indication of the electron dose waveform based on the one or more parameters.

In some embodiments, the method may comprise continuously updating the indication of the electron dose waveform. In some embodiments, the method further comprises providing the device of any aspect or embodiment.

Another aspect of the present disclosure provides a system comprising one or more computer processors and computer memory coupled thereto. The computer memory comprises machine executable code that, upon execution by the one or more computer processors, implements any of the methods above or elsewhere herein.

Additional aspects and advantages of the present disclosure will become readily apparent to those skilled in this art from the following detailed description, wherein only illustrative embodiments of the present disclosure are shown and described. As will be realized, the present disclosure is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the disclosure. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.

INCORPORATION BY REFERENCE

All publications, patents, and patent applications mentioned in this specification are herein incorporated by reference in their entirety to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference in its entirety. In the event of a conflict between a term herein and a term in an incorporated reference, the term herein controls.

