Variable Temperature UHV SPM Benchmarking UHV STM and AFM Technology - The VT XA Series • 50 K – 500 K / 650 K • True pA STM • Improved dI/dV Spectroscopy • Beam Deflection AFM • QPlus AFM • In-situ Evaporation

VT Series: Major Product Releases: 1994 VT STM 1998 VT with Beam Deflection AFM 2003 Sub-pA STM & improved spectroscopy 2008 VT with QPlus AFM Variable Temperatures After a period of rapid development, Scanning Probe Microscopy (SPM) has become a standard analysis technique in surface science. The Omicron VT SPM is the established microscope in many research labs. It won the prominent R&D 100 award in 1996 and to the present day more than 500 instruments have been delivered and successfully installed around the world. The design concept and ultimate performance as well as the concept of easy...

Heating and Cooling Concept for Temperatures from 50 K to 650 K The thermal connection (copper braid) between flow cryostat and sample stage is fixed and thermally isolated from the microscope stage. An embedded solid-state heater element in the sample stage allows indirect radiative heating of samples. The stage is equipped with a temperature sensor to measure the sample temperature. A temperature range between 50 K and 500 K is possible. Instruments without cooling option can heat the sample up to 650 K. Sample Plates using standard Omicron samples plates. The pilosophy with many different...

The VT-series enables the mounting of up to two EFM evaporators on the VT-chamber for in-situ materials growth even during imaging. The Omicron patented piezo inertia drive allows the same sample area to be relocated and imaged even after the sensor has been retracted during evaporation. Before Evaporation After Evaporation surface, image size: 80 nm x Data courtesy: M. Hupalo and M. C. Tringides, Dept. of Physics Iowa State Univ., Ames Lab. USDOE, USA, PHYSICAL REVIEW B, VOLUME 65 Easy and Safe Sensor Exchange 1) The transfer plate is inserted into the sample stage to pick up a sensor using...

True pA STM and Tunneling Spectroscopy All instruments of the VT series are equipped with state-of-the-art STM and STM spectroscopy capabilities. It is possible to extend this with AFM functionality, and the VT instruments can be used either with Beam Deflection AFM, the ‘QPlus‘ AFM, or with both types of AFM. Capacitive compensation Bias current compensation Frequency select / Low pass 330 nA range: 80 kHz / 3 kHz 3 nA range: 800 Hz / 200 Hz IT monitor, direct IT Offset compensation 100 nm Growth of multilayer ice films and the formation of cubic ice imaged with STM at IT = 0.4 pA. Ice films...

Capacitive Compensation via Preamplifier Technology Optimized for Modulation Spectroscopy Internal switch (Software controlled) R1 Sample R1 = 3 GΩ 3 nA Range R2 = 30 MΩ 330 nA Range R2 Sensor-sample intrinsic (floating) - capacitance IT + UMod (AC) UGap (DC) Internal capacitive compensation Schematic of VT-series pre-amplification and internal capacitive compensation. 6 with sub-monolayer coverage obtained in the low-current mode. Set-point values IT = 2.5 pA, UGap = 1.4 V. The white and black dotted circles highlight the first polymer layer and a partially nucleated second layer, respectively....

Non-Contact Modes Non-contact mode Non-Contact Operation Modes: The sensor is forced to oscillate or is excited to oscillate at its resonance frequency (eigenfre- quency). There are two basic modes of operation; amplitude modulation (AM) and frequency modulation (FM). FM is the pre- ferred mode in-vacuum, as the quality factors of the sensors (q-factors) are typically higher than in air. Magnetic Force Microscopy (MFM): Non-contact AFM can be used to measure magnetic forces. The magnetic dipole interac- tion is recorded at a constant tip-sample distance. The typical distance between tip and surface...

Lock-in amplifier PI-feedback ~ Low-pass filter Frequency demodulator Tip height control + SKPM Sample Polymer Source Insulator Gate U=UDC+UAC sin (2π f2t) Id Vq z (nm) Scanning Kelvin Probe Microscopy (SKPM): In SKPM an AC and a DC voltage are applied between tip and sample. The lock-in technique provides information on work function changes on a surface and correlates it with the simultaneously recorded topography information. Detection at frequency 2f2 can be used for Scanning Capacitance Microscopy (SCM). Drain Vd 200 Source 0 Drain 0V 0 Vd -1 V -2 V -3 V -4 V -5 V -6 V -7 V -8 V Vt (V) -2...

Oscillation amplitude 3 Fts(z) (nN), It(z) (nA) 2 1 0 -1 Contact Mode Short-range force (Morse potential) -2 Long-range (νdW) force Total force -3 Contact mode Tunneling current 0 0.5 1 z (nm) 1.5 2 Plot of tunnelling current and typical force potentials as a function of Sample distance between surface and front sensor atom. For AFM, interaction involves many more tip atoms than for STM. Shaded area: small QPlus oscillation amplitudes in combination with specific df setpoints allow for tuning the sensitivity to various force ranges. Contact Mode: Non-Contact AFM with Small Oscillation Amplitudes...

Forces in Atomic Force Microscopy AFM Multi-Mode Multi-mode operation Normal forces FN Deflection Lateral forces FL detection Δ f frequency shift Excitation Amplitude regulation Sample It detection Damping Tunneling current IT Multi-Mode Operation & Spectroscopy: Multi-mode operation uses simultaneous data collection of several signals. Tunnelling current, normal force, lateral force, frequency shift, and damping signals are available simultaneously with the MATRIX SPM controller. Furthermore, external inputs can be selected in order to obtain useful multi-mode spectroscopy combinations. The...

Beam Deflection AFM The classical Beam Deflection AFM method uses a microscale cantilever with a sharp tip at its end. The cantilever is typically silicon or silicon nitride with a tip radius curvature on the order of several nanometers. The force interaction between the tip and the sample surface leads to a deflection of the cantilever. In a Beam Deflection AFM the deflection is measured using a laser spot reflected from the top surface of the cantilever into an array of photodiodes. Depending on the application it is possible to operate in the static contact mode or in the dynamic non contact...