attocfm I for Surface Quality Inspection NANOSCOPY APPLICATION NOTE M01 RELATED PRODUCTS G

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1 APPLICATION NOTE M01 attocfm I for Surface Quality Inspection Confocal microscopes work by scanning a tiny light spot on a sample and by measuring the scattered light in the illuminated volume. First, the resolution obtained is better in comparison with the microscope operated conventionally, since a pinhole removes the out-of-focus information. Second, by scanning many thin sections through a sample, one can build up a very clean three-dimensional image of the sample. Finally, the non-contact method prevents from destruction or degradation of the sample. Because confocal microscopy is a three-dimensional, high-resolution, and non-destructive tool, it is ideal for high resolution defect analysis and topography profiles (examples are shown in the pictures on the right). Fig. 1: Confocal picture of GaAs-substrate: Inspection of a cleaved surface; the size of the image is 20 x 20 microns. The highly modular and flexible attocfm I features fully adjustable excitation and collection ports enabling easy handling and filtering of the excitation and collection signal for raman spectroscopy. The attocfmiopens up new possibilities in quantitative surface characterization in the micron / sub-micron range. Fig. 2: Confocal picture of a chess board grating (SiO 2 on Si) with a period of 2 microns, recorded in reflection mode. The sample has some defects on the surface structure. Fig. 4: Complete attocfm system and the confocal microscope head. Fig. 3: The aluminum on glass grating is damaged at certain locations. Left: size 30 x 30 microns; right: size 45 x 45 microns. attocfm I ANPxyz100/LT ANSxy100 ANC200 attoscan attoview highly modular and flexible confocal microscope high precision piezoelectric scanner electronic scan controller data acquisition software data viewing software attocube systems AG, Königinstrasse 11 A (RGB), D München, Germany, Tel. +49 (0) , Fax. +49 (0)

2 APPLICATION NOTE M02 attocfm I: Spectroscopy on Quantum Dots Confocal microscopes enable fluorescence measurements of thin sections in thick samples. In conventional fluorescence microscopy, outof-focus fluorescence tends to overwhelm details in the actual image plane. In confocal microscopy, a tiny light spot is focused and scanned in a defined image plane of the sample to excite fluorescence. The use of a blocking pinhole in the conjugate plane eliminates the degrading out-of-focus information. The application shown here is high resolution spectroscopy on a single quantum dot at 4 K in high magnetic fields. The precise measurements of a single quantum ring reported in Nature prove that quantum rings indeed behave as artificial atoms (Nature 405, ). The measurements of single quantum rings provide the definite proof of the atom like behavior of the quantum structures. In addition, the Nature paper reports detection of the emission energy of excitons to which various numbers of electrons have been added. These emission energies appear to be quantized. Khaled Karrai of the Center for NanoScience at Ludwig-Maximilians University, Munich, and Richard J. Warburton of Heriot-Watt University, Edinburgh, show that semiconductor quantum dots act like artificial atoms because they display sharp, discrete spectral lines when the confined electrons and holes that are analogous to the quantum energy levels of atoms recombine. The team examined the behavior of dots with singly, doubly or triply charged excitons and discovered that they conformed to that of artificial hydrogen, helium and lithium atoms. Further work examines the polarization of the photons which may be used to control the spin of the electrons in the dots, enabling applications in spintronics. Fig. 1: A laser beam is coupled into an illumination fiber and focused on the sample. The reflected light from the sample is then collected by the collection fiber, which is also the blocking pinhole aperture for the confocal setup. The signal detection is then achieved by a photon counting system or CCD-camera. The collaboration of scientists use one prototype of the attocfmi microscope, that operates at temperatures between 1.6 and 300 K and is machined entirely from titanium to resist magnetically induced perturbations. Karrai noted that the instrument is so stable that it enables the investigation of a single quantum dot for months at a time without drifting out of focus. Related article: Optical emission from a char-ge-tunable quantum ring by R. J. Warburton, C. Schäflein, D. Haft, F. Bickel, A. Lorke, K. Karrai, J.M. Garcia, W. Schoenfeld, Nature 405, 926 (2000). Fig. 2: A color-scale plot of the photoluminescence (PL) versus gate voltage showing the discrete spectral lines of a quantum dot. attocfm I ANPxyz100/LT highly modular and flexible confocal microscope attocube systems AG, Königinstrasse 11 A (RGB), D München, Germany, Tel. +49 (0) , Fax. +49 (0)

3 APPLICATION NOTE M03 3D - Imaging with attocfm II The confocal imaging system achieves out-of-focus rejection by two strategies: By illuminating a single point of the specimen with a focused beam, so that illumination intensity drops off rapidly above and below the plane of focus. By the use of a blocking pinhole in the conjugate plane of the previous plane of focus in order to eliminate the degrading out-of-focus information. By scanning many thin sections through your sample, you can build up a very clean three-dimensional image of the sample. Confocal imaging can offer another advantage in favourable situations (small pinhole size, bright specimen): the resolution obtained is better than the resolution obtained with any microscope operated conventionally. In practice, the best horizontal resolution of a confocal microscope is (at λ=630 nm illumination) about 200 nm, and the best vertical resolution is less than 500 nm. Fig. 1: Confocal picture of a chess board with 2 microns of period recorded in reflection mode. Fig. 3: The attocfm II microscope sensor head. Fig. 2: Confocal picture of a tweezers structure; the tweezers are freely suspended. The size of the image is 30x30 microns recorded in reflection mode. The 200 nm wide structures are resolved with an excitation laser source of 630 nm! (C. Meyer et al., IEEE Nano 2004). attocfm II ANPxyz100/LT ANSxy100 ANC200 attoscan attoview highly stable and compact confocal microscope high precision piezoelectric scanner electronic scan controller data acquisition software data viewing software attocube systems AG, Königinstrasse 11 A (RGB), D München, Germany, Tel. +49 (0) , Fax. +49 (0)

4 APPLICATION NOTE M04 attocfm II: Fiber Quality Control - Fluorescence Imaging The attocfm II is an ultra compact confocal microscope which is miniaturized for in situ analysis. The microscope is highly stable at low temperature, high magnetic field and high vacuum. A laser beam is coupled on one arm of a single mode optical fiber coupler. The fiber end of the second arm is placed in a ceramic ferrule, to guarantee an accurate position of the fiber in front of the objective and to minimize the optical aberrations. This single mode fiber illuminates the sample and plays the role of the blocking pinhole aperture when collecting the fluorescent or scattered light from the sample. Moreover, the mechanical parts are highly stable against thermal drift. Finally, the design is optimized to minimize the light losses and to collect the maximum amount of light scattered by the illuminated point of the sample. In the application shown here, this method is applied to a single mode optical fiber (see pictures on the left). The measurement of the fluorescent light in the core of the optical fiber provides information on the doping elements location and spatial distribution inside the core of the fiber. Fig. 1: Schematic drawing of the attocfm II microscope Fig. 2: Fluorescence of the core of a single mode fiber measured by the confocal setup. Left above: topography of the cleaved fiber end without any illumination. Right above: the through-the-fiber transmitted light is detected. Below: the distribution of the doping elements in the core of the fiber is clearly resolved. attocfm II ANPxyz100/LT ANSxy100 ANC200 attoscan attoview highly stable and compact confocal microscope high precision piezoelectric scanner electronic scan controller data acquisition software data viewing software attocube systems AG, Viktualienmarkt 3, D München, Germany, Tel. +49 (0) , Fax. +49 (0)

5 APPLICATION NOTE M10G First 4 K Closed Cycle Cryostat Combined with Confocal Microscopy... The use of cryogen-free cryostats is desired for many applications e.g. where liquid Helium is not available or not desired. For use in conjunction with high-resolution low-temperature microscopy, one requirement is performance with low vibration. Ideally, the cryostat should also provide short cool-down times and easy handling. Such a system has been developed and tested successfully in a collaboration of attocube systems and VeriCold Technologies. The confocal microscope attocfm II was used in conjunction with the low-vibration pulse tube cryostat from VeriCold to determine the system vibrations at the one hand, and perform confocal microscopy at 4 K, at the other hand (see page 2). Confocal Microscope (attocube systems) The attocfm II confocal microscope is thermally compensated and guarantees stability for spectroscopy over long periods of time. Ultra compact versions for 1 bore liquid Helium dewars and larger versions for 2 bore cryostats or similar chambers are available. The confocal objectives, specially developed for low-temperature and high-vacuum use, are diffraction limited and optimized for high-resolution imaging and/or spectroscopy measurements at visible and infrared wavelengths. Cryogen-free 4 K cryostat (VeriCold Technologies) The low-vibration pulse tube based cryostat from Vericold Technologies replaces any 4 K Helium bath cryostat where liquid Helium is neither available nor desired. The system has been especially adapted for very low vibration needs by eliminating moving parts in the cold head. An initial cool down time of < 4 hours and a sample cool down time of < 2 hours from room temperature to 4 K allow fast cycle times maximizing your productivity. Vibration measurement technique The system vibrations are measured optically by means of confocal microscopy. Having an ideally flat, reflecting sample, the optical signal reaches a maximum when the sample surface lies in the focal plane. By positioning the fiber at half maximum of the signal, a change in Z-position (e.g. vibrations) will change the intensity of the measured reflected light significantly, thus providing information on the system vibrations. attocfm II highly stable confocal microscope for low temperatures ANPxyz100/LT attostep data acquisition software cryostat closed cycle cryostat (VeriCold T.) 2005 VeriCold Technologies GmbH attocube systems AG, Viktualienmarkt 3, D München, Germany, Tel. +49 (0) , Fax. +49 (0) VeriCold Technologies GmbH, Bahnhofstr. 21, D Ismaning, Tel. +49 (0) , Fax-: +49 (0)

6 APPLICATION NOTE 10G Vibrations of the system The vibrations of the complete system including the cryostat and the confocal microscope were recorded at different temperatures and with the cooler on and off. Figure 1 (top) illustrates the vibrations as a function of time recorded at 4 K with the cooler on. The corresponding vibration spectrum recorded under the same conditions is shown in Figure 1 (bottom). The vibrations corresponding to the operating frequency of the cooler were typically below 10 nm. Performing the same experiment at 300 K showed vibrations in the range of nm (data not shown). The vibrations as a function of the time recorded at 4 K with the cooler switched off are shown in Figure 2 (top). In this case, the vibrations corresponding to the operating frequency were determined to be below 5 nm. Figure 2 (bottom) illustrates the vibration spectrum recorded under the same conditions. Confocal imaging The attocfm II is an ultra-compact confocal microscope which is highly stable at low temperatures, high magnetic fields and in high vaccum. A laser beam is coupled into one arm of a 50/50 single mode optical fiber coupler. The fiber end of the second arm is placed in a ceramic ferrule, to guarantee an accurate position with respect to the objective and to minimize optical aberrations. This single mode fiber illuminates the sample and is used as the blocking pinhole aperture when collecting the scattered light from the sample. The mechanical parts are highly stable against thermal drift and the design is optimized to minimize light losses as well as to collect the maximum amount of light scattered by the illuminated point on the sample. Figure 1: Vibrations (top) and vibration spectrum (bottom) of the complete system (confocal microscope inside the cryostat) recorded at 4 K with the cooler on. The images in Figure 3 were recorded with the attocfmii in reflection mode. The illumination wavelength was chosen to be 1330 nm. As a sample, a SiO 2 on Si grating with a period of 4 µm and a chess board with a period of 2 µm was used. The image on the left was recorded at 300 K with the cooler on. The sample features are clearly resolved despite the higher vibrations at this temperature. The other two images were recorded at low temperature (4 K) with the cooler running (middle) and switched off (right). Due to the low vibrations of the cryostat and the highly stable microscope, absolutely stable measurements over several hours were enabled. Furthermore, fast cycle times and easy, cryogen- free handling add to the simplicity of this complete low temperature confocal microscopy system. 300 K cooler on Figure 2: Vibrations (top) and vibration spectrum (bottom) of the complete system (confocal microscope inside the cryostat) recorded at 4 K with the cooler off. 4 K cooler on 4 K cooler off Figure 3: (left) CFM image of a SiO 2 on Si sample recorded at 300 K with the cooler on. The grating has a period of 4 µm and the chess board a period of 2 µm. The step scan range is 30 x 30 µm. (middle) CFM image of a SiO 2 on Si chess board sample recorded at 4 K with the cooler on. The chess board has a period of 2 µm. The step scan range is 10 x 10 µm. (right) CFM image of a SiO 2 on Si chess board sample recorded at 4 K with the cooler off. The chess board has a period of 2 µm. The step scan range is 10 x 10 µm VeriCold Technologies GmbH attocube systems AG, Viktualienmarkt 3, D München, Germany, Tel. +49 (0) , Fax. +49 (0) VeriCold Technologies GmbH, Bahnhofstr. 21, D Ismaning, Tel. +49 (0) , Fax-: +49 (0)

7 APPLICATION NOTE M11 attocfm II for Photoluminescence Measurements on Semiconductor Quantum Dots Introduction The attocfmii confocal microscope is thermally compansated guaranteeing unreached stability required e.g. for single quantum dot spectroscopy over long periods of time. At the same time, extremely high optical resolution is provided. It incorporates the ANPxyz100/LT stage that is needed for bringing the sample into focus and for positioning over areas as big as 5x5 mm². Magnetic field and low temperature compatibility of the attocfm II are of course guaranteed. Compared with the attocfm I, which is very flexible and can easily be modified to introduce additional optics like filters and polarizers, the attocfm II is much more compact and easy-to-use. Photoluminescence Measurements on Single Quantum Dots Recently, the nano-optics group of Khaled Karrai at the University of Munich, together with cooperating groups throughout the world, presented ground-breaking photoluminescence measurements on semiconductor quantum dots, a model system which is often called and related to as artificial atoms. In the measurements, which they performed with the attocfmii, the magnetic field dependence behaves as predicted for the uncharged exciton (bound electron-hole pairs), as well as for the singly and doubly charged ones. But for the triply charged exciton new effects not predicted by this comparison appear, as a special magnetic field dependence is seen. This way is was shown that quantum dots can also possess electronic states that go far beyond the artificial atom model. Figure 1: The ultra-compact attocfm II. The researchers say that the anti-crossings are due to the interaction of the excitons with the continuum of states above the quantized energy levels. This kind of interaction is not known in the case of atoms, as there such states are not bound to the nucleus. But in the case of the semiconductor quantum dots there is a layer of material (the so-called wetting layer) that carries those interacting electrons. Hence, different rules seem to apply for quantum dots compared with real atoms. Following K. Karrai, the instrument used in their setup convinces by having an unreached stability with at the same time very high optical resolution. Without the ultra-stable microscope head, he says, measuring the properties of a single quantum dot over a period of more than three months would not have been possible. Related article: Hybridization of electronic states in quantum dots through photon emission by K. Karrai, R. J. Warburton, C. Schulhauser, A. Högele, B. Urbaszek, E. J. McGhee, A.O. Govorov, J. M. Garcia, B. D. Gerardot, P. M. Petroff, Nature (2004) 247, 8, 135. Figure 2: The graph above shows the photoluminescence intensity of a triply charged InAs quantum dot vs. magnetic field (red corresponds to high intensity). The interesting dependence is not predicted by the model of an artificial atom. attocfm II ANPxyz100/LT highly stable confocal microscope for low temperatures attocube systems AG, Königinstrasse 11 A (RGB), D München, Germany, Tel. +49 (0) , Fax. +49 (0)

8 APPLICATION NOTE M13 Confocal Microscopy in Combination with a Solid Immersion Lense for Enhanced Resolution Confocal microscopy provides several advantages over conventional wide field optical microscopy including elimination of image degrading out-of-focus information and the ability to acquire serial optical images in successive thin sections from thick specimen. Confocal microscopy relies on wo strategies: a) Illumination of a single point of the specimen at a time with a focused beam so that the illumination intensity drops rapidly above and below the plane of focus and b) using a blocking pinhole aperture in a conjugate focal plane to the specimen eliminating degrading out-of-focus information. Solid immersion microscopy, where light is focused inside a high refractive-index lens close to a sample, offers a method for achieving resolution well below the diffraction limit in air. Combining these techniques, major improvement of resolution and light throughput are achieved in addition to offering a very simple experimental setup compared to other high resolution optical techniques, e.g. scanning near-field optical microscopy (SNOM). In the confocal setup, the solid immersion lens is applied directly on the surface of the investigated sample, which was a SiO 2 on Si chess board with two microns in period. A schematic drawing of the experimental setup is shown in Figure 1. The confocal microscope attocfm II was used first to acquire an image of a sample without the solid immersion lens, and second, to acquire an image with the solid immersion lens. The purpose is to determine the increase in the resolution. The wavelength used was 635 nm. The diffraction limited confocal objective had a numerical aperture of 0.55, thus leading to a lateral resolution of 700 nm. Figure 2 shows the image and a line cut recorded without the solid immersion lens. The micrometer sized structures are clearly resolved. Figure 3 shows the image acquired using the solid immersion lens. The measured resolution was about 160 nm. This ultra-high resolution is also attributed to the confocal setup using a pinhole that leads to an additional enhancement of the resolution. Figure 2: 3D-view and line cut of the image acquired with the attocfm II confocal microscope. The sample is a chess board with 2 microns in period. Figure 1: Schematic drawing of the attocfm II setup including the solid immersion lens. Figure 3: 3D-view and line cut of the image acquired with the attocfm II in combination with the solid immersion lens. attocfm II ANPxyz100 ANSxy100 ANC200 attoscan attoview highly stable confocal microscope ANhigh precision piezoelectric scanner electronic scan controller data acquisition software data viewing and editing software attocube systems AG, Königinstrasse 11 A (RGB), D München, Germany, Tel. +49 (0) , Fax. +49 (0)

9 Optical absorption on a single semiconductor quantum dot with a magnetic field applied in Voigt geometry. The modular design of the attocfm III represents a highly flexible and versatile system for high resolution spectroscopy. In these experiments, the setup has been modified to accommodate an inverted geometry. A special confocal objective was designed that redirects the incoming light by 90 to impinge onto the sample perpendicular to the externally applied magnetic field, i.e. in Voigt geometry (see Fig. 1). The measured spot diameter of ~ 1.5 μm is only slightly larger than that of a standard axial confocal objective. The light transmitted through the sample is measured by a photo detector directly behind the sample. All parts are made from Titanium, so that the microscope maintains its high stability during cool-down to cryogenic temperatures and exposure to magnetic fields of up to 8 T. The optical setup allows performing high resolution laser spectroscopy on a single, self-assembled quantum dot (QD). Fig. 2(a) shows the optical spectra of a QD charged with a single electron (X 1- ), measured with different laser polarizations at 0.7 T in Voigt geometry. According to the respective optical selection rules, the unpolarized resonance line of the X 1- splits into four lines (Fig. 2a-i), where two transitions are mediated by linear polarized light parallel to the external magnetic field (π 0 ; see Fig. 2a-ii), and two by light polarized perpendicular to the magnetic field (π 90; ; see Fig. 2a-iii). Transmission spectroscopy allows direct probing of these optical selection rules. In Fig. 3, the magnetic field dispersion of all four resonances is shown as a function of the applied magnetic field. The ground states (one electron in the QD; electron depicted by a filled triangle; direction indicating spin arrangement) and excited states (two electrons with anti-parallel spin and one hole; hole indicated by an open triangle) are spilt according to their Landée g-factors. Optically allowed transitions connect all four levels leading to four resonances lines with comparable oscillator strength. The presented experimental setup allows studying the anisotropic magnetic properties of single self-assembled quantum dots with high degree of precision (Fig. 2(b)) [1]. Furthermore, the resonant optical pumping offers a spin shelving scheme for the resident electron in the QD [2,3], which was already demonstrated to be orders of magnitude more efficient if the magnetic field is applied in Voigt geometry rather than in Faraday geometry [3,4]. The equally strong coupling of the two Zeeman split ground states to either of the excited states opens the way for quantum optical coherent spin manipulation schemes as they are known from atom optics [3]. References [1] M. Bayer, et al., Physical Review B 65, (2002). [2] M. Atatüre, et al. Science 312, 551 (2006). [3] M. Kroner, et al. prepared for publication [4] Xu, et al., Physical Review Letters 99, (2007). The data was generously provided by M. Kroner from the Department of Physics, Ludwig-Maximilians University, Germany. attocube systems explore your nanoworld Single Mode Fiber Fig. 1: Diffraction limited, fiber-based confocal microscope for high resolution spectroscopy in Voigt geometry, based on the CFM III design Fig. 2: (a) Transmission spectra of a single negatively charged quantum dot at a magnetic field of 0.7 T applied perpendicular to the quantum dot symmetry axis. The resonance line splits in four linear polarized lines (i). The outer resonances are resonant to light polarized parallel to the applied magnetic field direction (ii). The inner lines are polarized perpendicular (iii). (b) The Zeeman splitting of the electron (E Z,e ) and hole (E Z,h ) states of the quantum dot as a function of the magnetic field. The energies can be obtained directly from the spectra as shown in (a). Fig. 3: Magnetic field dispersion of the X 1- resonance energies as a function of the magnetic field applied in Voigt geometry. The inset depicts the electronic and excitonic levels, interconnected by four optical transitions which are indicated by the arrows. attocube systems AG, Königinstrasse 11 A (Rgb), D München, Germany, Tel. +49 (0) , Fax. +49 (0) Transmission (0.0001/ division) Energy (ev) (i) σ (ii) π 0 (iii) π Detector Sample Mirror E Z,h 1 z-axis y-axis x-axis Helium bath cryostat and magnet coil E Z,e (a) Energy (ev) 3,, 4 2 Splitting (µev) (b) 0 1 B (T) E Z,e E Z,h B (T) attocube systems AG All rights reserved.

10 nanotooling Solutions for extreme Environments APPLICATION NOTE PS03 Compact confocal microscope integrated into the attouhvchamber. Based on the design of the attocube s low temperature compatible attocfm I a confocal microscope setup has been integrated into the attouhvchamber. The tests show superior performance of the optical microscope while enabling an easy optical access for sensitive applications such as Bose-Einstein Condensates, the detailed characterization of waveguides. The measurements have been performed using a standard confocal head together with a special lens setup for the attouhvchamber. The optical beam from the confocal setup was guided into the UHV chamber though an optical broadband window. A laser with a 635 nm wavelength and a UHV compatible objective with the following properties have been used: focal length of 1.56 mm and an NA of 0.68 which results in a theoretical spot size of ~ 600 nm and resolution of at best ~ 450 nm. The confocal head and the objective were stationary, while the sample was mounted on an ANPxyz101 positioner set for coarse alignment in combination with an ANSxy100 scanner for scanning purposes. The sample was a standard chess board structure with ~ 60 nm high SiO 2 structures on Si substrate with 2 µm periodicity. The whole setup was at room temperature and UHV conditions, with the pressure less than 1E-9 mbar. Fig. 1: Image of the chess-board grating with 2 µm periodicity. Red corresponds to high, black to low intensity. From the graph, one can see that the spot is very good circular. In Figure 1 the result of the measurement is shown. The image shows clearly the periodicity of the grating at good contrast. Additionally, the image shows that the circular spot size of the setup has no distortions or aberrations. In summary, it has been shown that the attouhv chamber can be easily combined with the confocal attocfm I setup with no compromises on the quality of the measurement. Fig. 2: Image of the chess-board grating with 2 µm periodicity.??????????????????????????????????????????????????????????????????????????????????????????????????? attouhvchamber attocfm I ANPxyz101/UHV ANC150 miniaturized UHV chamber confocal microscope inertial positioners attocube systems AG, Königinstrasse 11 A (Rgb), D München, Germany, Tel. +49 (0) , Fax. +49 (0) attocube systems AG All rights reserved.