RU2764379C1 - Scanning probe microscope and controller of the scanning probe microscope - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: group of inventions relates to scanning probe microscopy. The scanning probe microscope includes a vibrating probe sensor, a vertical drive for reciprocal movement of the sensor and the sample perpendicular to the scanning plane, a measuring transmitter of signals from the vibrating probe sensor, containing a controller including at least one feedback circuit including a digital signal processor connecting the output of the measuring transmitter of signals from the vibrating probe with the vertical drive, a programmable gate array programmed to execute direct digital synthesis of a variable signal, a USB unit for communication with a computer, means for processing the signal from the measuring transmitter of signals from the vibrating probe sensor using at least one dual phase synchronous mixer and low-pass filters. A galvanic separation unit is introduced before the USB unit. At least one dual analogue phase synchronous mixer is installed on the board of the digital signal processor and is configured to supply an output signal first to a third-order analogue filter, then to a multiplexer, then to a digital signal processor for digital filtering.

EFFECT: creation of a functional scanning probe microscope.

8 cl, 1 dwg

Description

The invention relates to scanning probe microscopy, to devices that provide control of scanning probe microscopes. The group of inventions can be used to scan the surface of a sample in order to determine the topography of its surface, to determine the dimensions of characteristic features on its surface, etc.

Known scanning probe microscope, including a vibration probe sensor, a vertical drive for the mutual movement of the sensor and the sample perpendicular to the scanning plane, a measuring converter of signals from a vibration probe sensor, containing a control unit that includes at least one feedback circuit, including a digital signal processor that connects the output a vibration probe signal transducer and a vertical drive, a programmable gate array programmed to perform direct digital synthesis of an alternating signal, a USB block for communication with a computer, means for processing a signal from a vibration probe signal transducer using a dual phase synchronous mixer, a signal and low-frequency filters, and a galvanic isolation unit (RU 2428700 C2) is inserted in front of the USB unit. This scanning probe microscope has a fairly broad functionality. The disadvantage is a rather high level of noise.

Known application in image processing in microscopy low-pass filtering (RU 2296387 C1), analog and digital filters (CN 102833462 B).

The technical problem is the level of noise, the above devices do not eliminate this problem.

The device according to RU 2428700 C2 can be taken as the closest analogue.

A scanning probe microscope controller is proposed, including at least one feedback circuit, including a digital signal processor, connecting the output of a measuring transducer of signals from a vibration probe sensor and a vertical drive, a programmable gate array programmed to perform direct digital synthesis of an alternating signal, a USB block for communication with a computer, means for processing a signal from a measuring converter of signals from a vibration probe sensor using a dual phase synchronous mixer, a signal and low-frequency filters, and a galvanic isolation unit is inserted in front of the USB block. A dual analog phase synchronous mixer is mounted on a digital signal processor board and is configured to feed the output signal first to a third-order analog filter, then to a multiplexer, then to a digital signal processor for digital filtering.

Accordingly, this controller is intended for use in a scanning probe microscope.

Thus, a scanning probe microscope is also proposed, including a vibration probe sensor, a vertical drive for mutual movement of the sensor and the sample perpendicular to the scanning plane, a measuring converter of signals from the vibration probe sensor, containing a control unit, including at least one feedback circuit, including a digital processor signal converter, connecting the output of the measuring signal converter from the vibration probe sensor and the vertical drive, a programmable gate array programmed to perform direct digital synthesis of an alternating signal, a USB block for communication with a computer, means for processing the signal from the measuring signal converter from the vibration probe sensor using a dual phase synchronous mixer, signal and low-pass filters, with a galvanic isolation block inserted in front of the USB block. The dual analog phase synchronous mixer is installed on the digital signal processor board and is configured to feed the output signal first to the third order analog filter, then to the multiplexer, then to the digital signal processor for digital filtering.

The technical result is to reduce the noise level.

The technical result is achieved by sequential signal processing in a certain way. The dual analog phase synchronous mixer is installed on the digital signal processor board and is configured to feed the output signal first to the third order analog filter, then to the multiplexer, then to the digital signal processor for digital filtering.

The controller of a scanning probe microscope is designed to ensure the operation of a scanning probe microscope: organization of scanning, feedback, control of parameters, registration of signals, including signals from a probe sensor, and also for communication with a workstation (computer).

The controller of a scanning probe microscope performs the following functions: converts control signals coming from the control program, generates signals for the scanner, stepper motors, measuring heads and thermal stage, and processes signals from measuring heads.

The controller is designed to ensure the operation of scanning probe microscopes of various configurations in various modes (scanning probe microscope in the configuration for scanning with a probe, for scanning with a sample), capable of supporting work with various measuring heads designed to work with various types of probe probes: vibration probes, optical fiber probes for scanning near-field optical microscopy, etc. (the indicated parts - measuring heads, probe sensors - are not included in the controller of the scanning probe microscope).

The most important parameters of a scanning probe microscope controller are the number of recorded signals, their frequency characteristics, output signals and their characteristics, speed, type and characteristics of feedback circuits (connections), internal switching capabilities, internal analog (amplification, filtering) and digital signal processing capabilities.

Below is an embodiment of the devices of the group of inventions (one of the possible options, the devices can be made in a different way, with the presence of all the elements indicated in the claims, with the achievement of a technical result).

The controller has a modular design. The standard package includes a backplane with the following installed on it: a power supply, an AFM board and a high-voltage amplifier board. In addition, the backplane has 6 slots (4 large and 2 small) that can accommodate expansion boards. When installing additional cards in small slots, keep in mind that they do not receive analog signals, and there are also restrictions on digital signals.

For signal processing, the AFM board has a floating point digital signal processor operating at a frequency of 320 MHz (Floating point DSP 320 MHz).

For data exchange between the signal processor and its periphery, data exchange with USB, signal generation, ADC control, a programmable gate array is installed on the AFM board.

The method of processing signals from the measuring head is their synchronous detection. The AFM board contains a synchronous detector for this. The synchronous detector consists of a pair of phase synchronous mixers (multipliers of the signal at the input of the synchronous detector by the corresponding reference signals Sin and Cos) and a low-pass filtering system. Each multiplier is based on the AD734 microcircuit manufactured by Analog Devices, is analog and is structurally soldered on the AFM board along with other components, while the autonomous or decoupled power supply of the AD734 microcircuits is not provided. Further, in the form of MSin and MCos projections, through a low-pass filter (20 kHz), the signal is fed to the multiplexer before the ADC.

The low pass filtering is multi-stage. Low-frequency filtering of the output signal of the mixers is carried out by a third-order analog filter. After the multiplexer and ADC digitization, the signal is additionally filtered digitally. The digital part of the filtering is carried out in a digital signal processor.

The controller is connected via cable connections to the computer and the measuring unit.

The measuring unit can be equipped with various additional devices. When working with some of them, for example, such as a thermal table or a nanosclerometric head, the controller is equipped with additional expansion boards, and the connection diagram changes.

To carry out measurements with sample heating, a thermal stage is installed in the measuring unit on the sample holder.

Analog signals intended for transmission from the high-voltage amplifier board to the AFM board:

- HV_X (normalized);

- HV_Y (normalized);

- HV_Z (normalized);

- X sensor;

-Y sensor;

-Z sensor;

- Res2;

- Res4.

- Analog signals intended for transfer from AFM board to board

high voltage amplifiers:

- Out X;

- Output Y;

- Out Z;

-Ex6;

- sample.

The controller can be installed, for example, board AFM 9.0 (figure 1).

Signals A-C, B-D (outputs from a four-section photodiode) are converted into signals DFL = (A-C) - (B-D) and LF = (A-C) + (B-D). The original signals A-C and B-D are no longer used.

Signals HV_X, HV_Y, HV_Z (normalized), Gnd (device ground), Laser, Ex2, Ex3, Res1, Res2, Res3, Res4 go directly to the input of the multiplexer before the ADC and are available for measurement (digitization).

X sensor, Y sensor, Z sensor signals are mixed with signals from programmable bias DACs (Bias) and go to the input of the multiplexer before the ADC through a programmable amplifier with gains ×1, 10, 100, 1000.

DFL and LF signals are mixed with signals from programmable bias DACs (Bias) and go to the input of the multiplexer before the ADC through a programmable amplifier with gains ×1, 10, 100, 1000. In addition, these signals, before bias and gain, go to filters high frequencies (170 Hz) and amplifiers with gains ×1, 10 and further to the matrix of variable signals (synchronous detector input).

The EX1 signal goes directly to the input of the multiplexer before the ADC and is available for measurement (digitization). In addition, this signal goes to a high-pass filter (170 Hz) and an amplifier with a gain of ×1, 10, and then to a matrix of variable signals (synchronous detector input).

The STM signal goes to the input of the multiplexer before the ADC with a gain of ×10 and is available for measurement (digitization). In addition, this signal, before amplification, goes to a high-pass filter (170 Hz) and with gains ×1, 10, and then to a matrix of variable signals (synchronous detector input).

The outputs from the matrix of variable signals go to the synchronous detector.

The synchronous detector consists of a pair of phase synchronous mixers (multipliers of the signal at the input of the synchronous detector by the corresponding reference signals Sin and Cos) and a low-pass filtering system. Each multiplier is based on the AD734 microcircuit manufactured by Analog Devices, is analog and is structurally soldered on the AFM 9.0 board along with other components, while the autonomous or decoupled power supply of the AD734 microcircuits is not provided. Further, in the form of MSin and MCos projections, through a low-pass filter (20 kHz), the signal is fed to the multiplexer before the ADC. The low pass filtering is multi-stage. Low-frequency filtering of the output signal of the mixers is carried out by a third-order analog filter. After the multiplexer and ADC digitization, the signal is additionally filtered digitally. The digital part of the filtering is carried out in a digital signal processor.

All generators available on the AFM board are arranged in a similar way.

The output signal of the generator, which is then used to feed the probe, the sample, to drive the probe, or as a reference signal for the synchronous detector, is taken from the output of the DAC, the digital input signal of which is formed in the gate array (FPGA).

After the matrix of variable signals, there are also high-pass filters.

At the input of the matrix of variable signals in front of the synchronous detector, after amplifiers with gains ×1, 10, signals from generators Gen1 and Mod (the same in characteristics) also come.

Outputs of the matrix of variable signals (except for those going to the synchronous detector): Ut_mod, Ceram (Probe), EXT6. The last two signals go directly to the output connector, and the Ut_mod signal is mixed with the BV DAC output.

The resulting BV signal goes through the relay system to the external connectors -+AMP and Sample. The relays are independent, and the BV signal can be applied to one of these outputs, or both at once. The Sample output can also be connected to an external Ex5 input, with the +AMP output either grounded or BV signaled.

The signal DAC BV is a system of three DACs - Value BV, Scale BV and Offset BV.

A 16-bit ADC with a frequency of 500 kHz measures the signals coming to it in the order specified by the matrix from the BrdSignals.ini file. An increased signal measurement frequency means an increase in the accuracy of its measurement - virtual (used to calculate the Mag and Phase signals), SensorX, SensorY (used to work in the mode with closed feedback loops that control the scanner movements along the X, Y axes (Close Loop mode)) and the SensorZ signal (used to calculate the SensorHeight signal) are measured with the highest priority.

The AFM board has two analog outputs on the back (BNC sockets).

The OUT AC jack can be used to output (observe with an external oscilloscope) variable signals, namely, signals coming to the input of the variable signal matrix, i.e. DFL, LF, STM, EX1, as well as signals from generators Gen1 and Mod. At this output, only the variable components of these signals. The cutoff frequency of the high-pass filter is 170 Hz.

The OUT DC jack can output constant (low frequency) signals from the DSP via the OSC_DAC (16-bit) DAC. The frequencies of these signals are up to 16 kHz.

The 50-pin connectors output the ResDAC signal (16 bits) from the DSP.

Also up to 16 kHz.

To generate scanner control signals, four DACs are used for each channel (X, Y, Z). The signals from the Value and Gen DACs are mixed and fed to the Scale amplifier, and then the Offset signal is added to them.

The resulting signals Output X, Output Y, Output Z go through the backplane buses to the high-voltage amplifier board. The HV amp and LV amp amplifiers are on the high voltage amplifier board.

Modification of the AFM board can include a second phase synchronous mixer, which ensures more efficient operation of the controller, lower noise level.

The board of high-voltage amplifiers is designed to amplify the scanner control signals to the values required for supply to piezoceramics, to process signals from displacement sensors and to control one stepper motor.

The board of high-voltage amplifiers can be made, for example, as follows.

There are two connectors on the back of the board.

Signals Output X, Output Y, Output Z, received on the board of high-voltage amplifiers through the backplane, get to the amplifier system.

Output X, Output Y signals can be converted to X+, X- (Y+, Y-) signals of ±150 V each (4 kHz bandwidth) or to LV_X+, LV_X- (LV_Y+, LV_Y-) signals of ±5 V each ( bandwidth 10 kHz). The switching of signals is carried out by a programmable relay, the signals go to the same contacts in the connectors.

The Output Z signal is converted into Z+ and Z- signals with a voltage of ± 150 V, each with a bandwidth of 12 kHz. The relay in this case disables one of the channels - Z-.

The board also contains three blocks for processing signals from displacement sensors and two DACs that provide the operation of one stepper motor.

The power supply unit of the controller is connected to the external power supply network with a standard cable. External network voltage 110/220 V, 50/60 Hz. Depending on the voltage of the external network, it is necessary to set the switch on the back of the controller near the power connector to the desired position. The switch only affects the voltage that is supplied to the transformers of the high voltage amplifier board.

The power supply provides the controller with the necessary voltages to power the electronic components +/-15 V and +5 V. Other voltages are already generated on the backplane. All voltages, including those for the HV board, go to the backplane.

Grounding is provided through the ground contact of the power connector, as well as a special grounding clamp on the rear cover of the controller. Both grounds are equivalent.

As one of the possible options, the controller can have the following parameters:

overall dimensions, mm 160×445×500,

weight, kg 12.0,

supply voltage, V 90÷240 (+10%/-15%), 50/60 Hz,

power consumption (without additional power supplies), not more than, W 80,

USB 2.0 interface Full speed.

The use of this controller in a scanning probe microscope provides measurement accuracy, noise reduction, which, in turn, enhances the functionality of scanning probe microscopy, ensuring the study of both hard and soft objects.

Claims (8)

1. A scanning probe microscope, including a vibration probe sensor, a vertical drive for mutual movement of the sensor and the sample perpendicular to the scanning plane, a measuring converter of signals from the vibration probe sensor, containing a controller that includes at least one feedback circuit, including a digital signal processor that connects the output a vibration probe signal transducer and a vertical drive, a programmable gate array programmed to perform direct digital synthesis of an alternating signal, a USB block for communication with a computer, means for processing a signal from a vibration probe signal transducer using at least one dual phase synchronous mixer and low-frequency filters, and before the USB block, a galvanic isolation block is inserted, characterized in that at least one dual analog phase synchronous with The mixer is installed on the digital signal processor board and is configured to supply the output signal first to the third-order analog filter, then to the multiplexer, then to the digital signal processor for digital filtering. 2. Scanning probe microscope according to claim 1, characterized in that the microscope controller has a modular design. 3. Scanning probe microscope according to claim 1, characterized in that the microscope controller includes a cross-board and a power supply unit installed on it, an AFM board and a high-voltage amplifier board. 4. Scanning probe microscope according to claim 1, characterized in that the microscope controller further includes a second dual phase synchronous mixer. 5. A scanning probe microscope controller, including at least one feedback circuit, including a digital signal processor, connecting the output of the measuring signal converter from the vibration probe sensor and a vertical drive, a programmable gate array programmed to perform direct digital synthesis of an alternating signal, a USB block for communication with a computer, means for processing a signal from a measuring converter of signals from a vibration probe sensor using at least one dual phase synchronous mixer and low-frequency filters, and a galvanic isolation unit is inserted in front of the USB unit, characterized in that at least one dual analog phase synchronous the mixer is installed on the digital signal processor board and is configured to supply the output signal first to the third-order analog filter, then to the multiplexer, then to the digital signal processor for chi frovoy filtration. 6. The controller according to claim 5, characterized in that it has a modular design. 7. The controller according to claim 5, including a backplane and a power supply, an AFM board and a high-voltage amplifier board installed on it. 8. The controller of claim 5, further including a second dual phase synchronous mixer.

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