Thermal Acoustic Cabinet

High Performance Thermal Cabinet for NT-MDT Microscopes

Improved Stability of SPM Experiments

Thermal Acoustic Cabinet – Brochure (1.0 MB) Visit Suppliers Website

Scanning probe microscopes give researchers visualization tools for the future. When scanning at the nano-scale, high precision is an absolute, users require an environment that is free of the external interferences caused by mechanical and acoustic vibration. Important factors for high quality scans include the temperature stability of the microscope and low thermal drift of samples during experiments.Low thermal drift of samples enables researchers to examine surface regions of singular samples using  multiple AFM modes, this collective group of examinations ensure comprehensive surface analysis delivering extremely accurate results. Atomic Force Microscopy (AFM) and Scanning Tunneling Microscopy (STM) use a relatively slow feedback mechanism in the majority of the techniques. A large number of experiments such as imaging at the atomic-scale, profiling of corrugated surfaces and collection of local force curve in the force volume operation etc. are experiments that need to be conducted in low thermal drift environments. To address the need for accurate, temperature stable and vibration free environments the ‘TAC’ (Thermal Acoustic Cabinet) has been designed to deliver a breakthrough environment capable of producing new levels of accuracy, reliability and stability.  The temperature of the sample location within the cabinet is electronically-controlled at the set-point level with a precision of 0.02 degree C. This is achieved by raising the cabinet environment to slightly above room temperature, the embedded heaters then support the set-point temperature using a specialized convection system thereby eliminating the requirement on mechanical fans and eliminating the introduction of mechanical noise within the cabinet.The following pages contain an overview of the cabinet and its technical specifications followed by several practical examples of AFM data obtained with microscopes operating inside the cabinet.

Thermal Cabinet Microscope Placement

Improved Stability of SPM Experiments

The Thermal Acoustic Cabinet can accommodate a range of NT-MDT scanning probe microscopes including the NEXT/Titanium devices and the NTEGRA Prima. Designed with a full 270 degree of easy access to provide unlimited access during the installation and adjustment of microscopes or cable connections.(Figure 1a-b)The cabinet’s structure is assembled from high grade aluminum, this increases the rigidity of the cabinet and creates an environment capable of reducing external interference and ensuring maximum stability throughout scanning. The walls of the cabinet are designed using customized acoustic foam which delivers further suppression and absorption of external acoustic noise.The cables that connect the microscope with the exterior electronic units run through a specialized port on the rear wall of the cabinet, this is equipped with a damping fixture that prevents outside vibrations being transmitted by the cables. The microscope can either be installed using an active anti-vibration table for example the TS-150, placed on the floor of the chamber, or be positioned on the custom-designed bungee system. The bungee system is specifically designed for the Thermal Acoustic Cabinet and is attached to the ceiling of the chamber. The platform for the bungee system incorporates a leveling system that is designed to accommodate and stabilize microscopes including the NEXT/ Titanium and NTEGRA Prima.

Thermal Cabinet Performance and Readings

Improved Stability of SPM Experiments

The internal temperature of the cabinet is maintained to a user defined set point by means of a closed loop system, this system includes both external and internal temperature sensors (the internal sensor can be located by the user to any location within the cabinet) and special heat convection tunnels located in the rear of the cabinet.The temperature readings and various settings are displayed on a screen at the front. The actual microscope temperature is shown with 6 digit precision and the noise level is approximately at 0.25 millidegree. The control unit has a USB port located at the back of the cabinet for communication with an external computer for recording the long-term temperature changes.  The performance of the cabinet has been comprehensively investigated to determine the level of damping of all external acoustic noise, vibration protection and temperature stability. The graph in Figure 2 demonstrates a substantial reduction of the sensor signal in the broad frequency range when comparing between the open and closed environments.  In another test shown in table 1 the AFM deflection signal of a probe having spring constant of 12 N/m, which stayed in contact with a sample, was measured to determine the mechanical vibrations caused by environmental noise near the cabinet. (A vacuum pump, was placed on the same table as the cabinet to provide a controlled vibration source).Deflection measurements were performed under a number of different conditions to test the various anti-vibration options available with the cabinet for sale. A microscope was placed on the bungee cords’ and on the active vibration protection tablet NS-150 in “off” and “on” conditions. The comparative deflection signal values, which were obtained in these experiments, are shown in Table 1.  

Thermal Cabinet Temperature Stability and Thermal Drift

Improved Stability of SPM Experiments

The most important test is to determine temperature stability and thermal drift of the microscope inside the cabinet. Typically, the set-point temperature at the sample stage of the microscope is chosen 3-4 degrees above the room temperature. As room temperature oscillates and can be regulated by air-conditioning these temperatures changes can be as large as 3 degrees.Such changes are on the extreme side but can be successfully damped by the cabinet so that the variations of the microscope temperature are only in the 0.02 degrees range. This situation is illustrated by the graphs in Figure 3.  

The temperature variations proceed rather slowly with time constant around 50 minutes. Even more important to notice is that such temperature conditions can lead to very small thermal drift values in AFM images, which were obtained in the continuous scanning of the 200-nm area containing self-assemblies on semifluorinated alkanes. Such temperature drift (approx. 0.2 nm/min) was recorded in these and other studies with the thermal cabinet. The situation is further improved when the room temperature variations are smaller (down to 1 degree) and the temperature stability of 0.005 degrees has been achieved in such cases. When the cabinet door is opened in order to change a probe or a sample, which takes a couple of minutes, the microscope temperature dropped, and it recovers to the set-point level within an hour. Yet this process proceeds gradually and it has a minimal influence on thermal drift.  

Thermal Cabinet Microscope AFM Images

Improved Stability of SPM Experiments

Several AFM images were chosen to illustrate the microscope performance at the low thermal drift conditions. They include the atomic-scale image of mica (Figure 4a), the image of normal alkane C22H46 on graphite (Figure 4b) and a series of images of semifluorinated alkanes F14H20 (Figure 5a-b). These height images were recorded in different modes with the scanning rate in the 1-2 Hz range that allows precise recording of the surface corrugations reflecting atomic and molecular arrangement in these samples. A practically “immobile” position of the defect in the images of lamellae of semifluorinated alkanes on graphite and stable visualization of semifluorinated self-assemblies on mica (Figure 5a-b) underlines low thermal drift of the microscope.