Zurich Instruments Newsletter - Edition Q1/2013
- Editorial: Happy New Year!
- Customer Interview: Prof. Angelika Kühnle, University of Mainz, on Molecular Self-assembly
- Reduce Lab Setup Complexity: HF2PLL Free Product Upgrade 2013
- Premium Customer Support: New Software Release Available for Download
- Reduce Lab Complexity: The History of the Lock-in Amplifier (Part 2)
- Tips & Tricks: AM and FM Signal Generation and Frequency Chirping with the HF2LI
- Company Agenda
Happy New Year!
This first newsletter of the year focuses on SPM and AFM applications with the hope of stimulating the interest also of non-users.
The SPM/AFM market is highly specialized and competitive. There is hardly a G20 country without its own microscope producer, and it is easy to list about 30 relevant vendors. There are a lot of niche applications and suppliers specialize in fancy combinations of methods, but the competition is fierce as many companies are supported directly or indirectly by state funding. In a market that is not particularly growing, consolidation is the consequence and we have seen some evidence of this last year when Oxford Instruments acquired first Omicron and recently Asylum Research1.
Given the large number of SPM/AFM equipment suppliers, only a handful of independent electronics manufacturers make it to the top, among them Zurich Instruments. Being in no particular competition to microscope companies, Zurich Instruments offers high-end lock-in amplifiers and phase-locked loops that combine with, in principle, any system. The electronics from Zurich Instruments support advanced imaging and non-imaging modes and allows scientists to expand the capabilities of existing setups.
1 Oxford Instruments plc: Acquisition of Asylum Research Corp., 17 December 2012, Link
Prof. Angelika Kühnle, University of Mainz, on Molecular Self-assembly
Your research area is molecular self-assembly and molecular manipulation. This is fast-paced, bleeding-edge science. Which frontiers are you pushing?
An important aspect in our research is exploring molecular self-assembly on bulk insulators. Especially from an application-oriented point of view, it is of highest interest to extend the range of substrates from metals to non-conducting surfaces. As an example, when considering a molecular wire for future molecular electronics, electronic decoupling from the supporting substrate is mandatory. To control molecular self-assembly on bulk insulating surfaces, we tune the balance of intermolecular versus molecule-surface interactions. To this end, a very important aspect of our work is identifying suitable functionality for substrate templating.
Recently we have been focusing on reactions on surfaces. Inducing covalent bonds between molecules on surfaces opens further exciting possibilities to increase structural complexity and functionality.
Which applications heavily rely on molecular self-assembly?
For example molecular electronics. Miniaturization of integrated circuits will require incorporating molecular devices. A one-by-one manipulation process to assemble these structures from single molecules is too time consuming by far. Thus, we need to come up with ideas that will enable us to create functional units from the molecules "themselves" through a clever design of the molecular building blocks.
Which recent techniques and instrumentation technologies are currently helping progress your research?
Our work is based on high-resolution non-contact atomic force microscopy, as this is the method of choice when it comes to direct imaging at the atomic scale. Therefore, we constantly improve our instruments to measure at the physical resolution limits. Recently we implemented an atom-tracking system that allows us to measure three-dimensional force data at room temperature, which requires the utmost drift stability. Our home-built solutions benefit from fruitful cooperations as well as from high-end commercial instruments.
You also perform liquid AFM. How do the challenges differ from UHV AFM also with respect to instrumentation?
High-resolution frequency modulation atomic force microscopy imaging in liquids implies pushing the instrument's performance to its limit. Because of the high damping of the surrounding liquid, detecting the resonance frequency requires optimizing the signal-to-noise ratio as much as possible. An increasingly recognized issue is cantilever excitation. While piezoacoustic excitation leads to a large number of fake resonance peaks, direct drive methods such as photothermal excitation yield a well-defined resonance curve. There is still a lot of trial and error constructing, testing and rebuilding and constant improvements. This requires skilled experimentalist who construct prototype solutions.
Which of your publications is your favorite?
On-Surface Covalent Linking of Organic Building Blocks on a Bulk Insulator, ACS Nano 5 (2011) 8420
In this work we have demonstrated the covalent linking of organic molecules by thermal activation on a bulk insulator. The resulting products constitute conjugated molecular structures, which serve as prototype "wires" on a truly insulating support.
Can you tell us about what drives you and what excites you in your research activities?
Curiosity and teamwork! I am always excited to learn what is behind the things we see ... and behind the things we do not see. Further it is a great pleasure to work together with my students, who always come up with new crazy and brilliant ideas.
Reduce Lab Setup Complexity
HF2PLL Free Product Upgrade 2013
Zurich Instruments has the objective of reducing the complexity of laboratory setups by accommodating a wide offer of functionality into its instruments, therefore improving the ease of use and expanding the application support on a continuous basis. For 2013 a new feature package has been made available that elevates the HF2PLL to a level making it the absolute equipment of choice for SPM applications.
We are particularly proud to introduce the support for amplitude and frequency modulated KPFM (AM-KPFM and FM-KPFM) and that already two papers from Osaka  and Mainz  have been published. In the first paper, the team around Sugawara-sensei investigated the combination of amplitude-modulation KPFM and heterodyne technique to reduce the effect of stray capacitance. The method also improved the sensitivity on short range forces. In the second paper Angelika Kühnle shows evidence of a molecular reaction called deprotonation in the form of near atomic-resolution images. Several other papers using HF2PLL are currently being prepared. More information can be found on the Scanning probe application page.
Further we announce the capability to perform dual-frequency resonance tracking (DFRT), permitting oscillator resonance tracking for applications where the phase of the acquired signal is location dependent making the use of phase-locked loops impractical. This is for instance the case in piezoresistive material analysis or for oscillators whose operation experiences phase jumps. We are now looking forward to enabling many scientists to use this alternative tracking method.
Also other features are available with the new HF2PLL upgrade:
- Q-Control enables flexible scan speed control of high-Q cantilevers, faster frequency sweeping of high Q resonators and support for highly-damped applications
- Tip protection permits avoiding unwanted operation, therefore enabling scan continuity with safe unattended operation and automatic resume and saving on AFM hardware
- PLL Peak Analyzer (Q-Factor extractor) is an integrated tool for measuring the Q-Factor of resonators (e.g. cantilevers), with a standardized method providing repeatability of results
- PID Sideband Analyzer increases the signal-to-noise by a factor of √2 in KPFM and SNOM
- Cascaded PID improves speed and loop stability
 Yasuhiro Sugawara, Lili Kou, Zongmin Ma, Takeshi Kamijo, Yoshitaka Naitoh, and Yan Jun Li, Osaka University, Japan, "High potential sensitivity in heterodyne amplitude-modulation Kelvin probe force microscopy", Applied Physics Letters 100, 223104 (2012), doi:10.1063/1.4723697
 M. Kittelmann, P. Rahe, A. Goudon, A. Kühnle, Johannes Gutenberg Universität Mainz, "Direct Visualization of Molecule Deprotonation on an Insulating Surface", ACS Nano 6, 7406-7411 (2012), doi:10.1021/nn3025942
Premium Customer Support
New Software Release Available for Download
One of the core product philosophies at Zurich Instruments is "Premium Customer Support" and, to reinforce this philosophy, all of our customers benefit from the Customer Care Premium package (HF2-CCP or UHF-CCP) when they purchase one of our instruments. Included in this package are software updates for the lifetime of the instrument.
Our most recent software release 12.08 includes a number of improved features for users of all of Zurich Instruments’ products and also added functionality for customers using the HF2LI-PLL, HF2LI-PID, and HF2LI-RT options. Let’s take a brief look at some of the recent changes:
- Arbitrary input scaling, useful for when you want to relate a demodulator voltage to a different unit such as current. This is a unique feature of the HF2LI and one of our Application Scientists has written a blog entry arbitrary input scaling and units in lock-in amplifiers with a few brief examples showing where this feature can help.
- Reworked sweeper tool with multi-quantity support so that phase, amplitude and offset can be swept in addition to frequency. It’s now also possible to sweep in different directions.
- Improved spectroscope tool with frequency analysis support
- Reworked spectrum analyzer, with new analysis tools and operating modes.
- For the PID option, the input can now have a choice of units and we’ve also added the PID advisor for straightforward and hassle-free PID parameter setting. There is also now a choice of complex quantities to put to the auxiliary outputs.
- The PLL advisor has been updated to make use of the PID improvements.
- Improved real-time performance.
In conjunction with the software upgrade, we’ve also updated the user manual with some new tutorial chapters, a more comprehensive specifications section and an extensive chapter on signal processing basics.
We’re happy to hear what you think about the latest features and changes.
Reduce Lab Complexity
The History of the Lock-in Amplifier (Part 2)
In one of our previous newsletters, Q3/2011, we discussed some of the early history of the lock-in amplifier. Despite often being attributed to Dr. Robert H. Dicke, a founding member of Princeton Applied Research (PAR), it’s now quite clear that the fundamentals of the lock-in technique were established long before the formation of PAR and that the term "lock-in amplifier" was in use as early as 1941.
It also seems that that decade saw work on both the theoretical and practical aspects of lock-in amplifiers. In a technical report from 1949 , an analysis of the low frequency output spectrum of the lock-in amplifier was made, noting possible improvements in S/N ratio if a low-pass filter was added after the lock-in amplifier (which at the time essentially consisted of a pentode convertor). This, of course, later became standard practice in lock-in amplifier instruments.
Interestingly, Stutt also reported significant S/N ratio improvements for amplitude modulated signals, where the desired signal is the modulation rather than the carrier. It was also concluded that similar S/N ratio improvements could not be made using a simple signal multiplier.
 C.A. Stutt, Technical Report No. 105, Research Laboratory of Electronics, Massachusetts Institute of Technology, March 26, 1949
Tips & Tricks
AM and FM Signal Generation and Frequency Chirping with the HF2LI
In this article we would like to describe a non-obvious application of the PID controller option for the HF2LI lock-in amplifier. Users are effectively enabled to modulate the signal output amplitude or signal frequency. Available patterns include amplitude (AM), frequency (FM) modulation and frequency chirping (FC). Instrumentation wise this requires an HF2LI Instrument unit plus the HF2LI-PID option.
Step-by-step amplitude modulation:
1. Enter the desired modulation signal into the auxiliary input on the back panel of the instrument (tip: the sinusoidal signal could be generated with one of the HF2LI signal outputs)
2. In the PID control panel select this auxiliary input as the input unit and the set point to 0 V
3. Use the proportional part of the PID as adjustment for the modulation amplitude (set I and D values to zero). The product of input amplitude and scaling factor P determines the overall modulation amplitude M (sideband amplitude)
4. Select one of the signal amplitudes as PID output (e.g. Signal 1: Amplitude and Demodulator 7)
5. Choose the PID output center value to define the carrier amplitude value A (if set to zero the instruments acts as a frequency mixer and simply multiplies the two signals) and make sure the output range settings covers the whole desired amplitude range
6. Check the generated signal on the built-in oscilloscope in the time domain, or use the FFT spectrum analyzer to analyze a defined portion of the spectrum around the carrier frequency. One should expect a carrier signal with 2 sidebands. The resulting modulation index calculates as m = M/A
Performance: the bandwidth bottleneck is likely to be the PID controller. The rate at which the PID controller updates the output values defines the upper limit for the modulation frequency. The actual rate at which the output is updated is indicated by the rate field on the top left in the PID tab and has a maximum value of 153.4 kSa/s in the case where only one of the four PID controllers is enabled. The maximum bandwidth of the auxiliary inputs is 100 kHz.
Similarly, the PID output can be used to change the frequency of one of the internal oscillators generating a frequency modulated signal. For a sinusoidal input signal this leads to a frequency modulation at the output, with the frequency deviation defined by the amplitude of the modulation input signal and the multiplication factor P defined in the PID. Along the same lines, frequency chirping can be implemented by applying a linear voltage ramp as an input signal to the PID.
Tip: the HF2LI FFT spectrum analyzer has the peak hold function which can be used in connection with frequency chirping to determine and display resonances.
- Joint MMM/Intermag Conference 2013, Chicago, USA, January 14-18, 2013
- MEMS 2013, Taipei, Taiwan, January 20-24, 2013
- Photonics West 2013, San Francisco, USA, February 5-7, 2013
- AAFMT 2013 - 4th workshop advanced AFM techniques, Karlsruhe, Germany, March 4-5, 2013
- DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM), Regensburg, Germany, March 19-21, 2013
- Forum Sonde Locale 2013, Spa, Belgium, March 25-29, 2013
- JSAP Spring 2013 Meeting, Kanagawa/Tokyo, Japan, March 27-30, 2013