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Schematic diagram of noncontact AFM using the FM detection method. The cantilever oscillation is performed by using a positive feedback loop composed of the deflection detector of a cantilever, AGC circuit, a phase shifter, and a piezoelectric actuator.
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We present the design and performance of a noncontact atomic-force microscope (AFM) operating at low temperatures (LTNCAFM). For the first time, a “top bath” cryostat is used to avoid long-distance translation of the AFM unit, while protecting the fragile optical fiber, and to reduce outgassing. The top bath cryostat is optimized by using three rad...
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... Fig. 8 we show a schematic diagram of the NCAFM with the FM detection technique. In the FM technique the cantilever serves as a mechanically oscillating element. The cantilever oscillation is performed by using a positive feed- back loop composed of an optical fiber interferometer, a variable gain amplifier with an automatic gain control AGC ...
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Citations
... All the experiments were performed in a UHV chamber under a pressure of 5.0 × 10 −10 torr at 85 K (UNISOKU-based custom-built ncAFM/STM). The details of the system were described elsewhere (38). The STM observation was performed with a PtIr tip (UNISOKU) in constant current mode. ...
Understanding the precise atomic structure of ice surfaces is critical for revealing the mechanisms of physical and chemical phenomena at the surfaces, such as ice growth, melting, and chemical reactions. Nevertheless, no conclusive structure has been established. In this study, noncontact atomic force microscopy was used to address the characterization of the atomic structures of ice Ih(0001) and Ic(111) surfaces. The topmost hydrogen atoms are arranged with a short-range (2 × 2) order, independent of the ice thickness and growth substrates used. The electrostatic repulsion between non-hydrogen-bonded water molecules at the surface causes a reduction in the number of the topmost hydrogen atoms together with a distortion of the ideal honeycomb arrangement of water molecules, leading to a short-range-ordered surface reconstruction.
... Since fiber optic interferometer based systems do not require the installation of electronic components into or next to the deflection sensor region for measurements, they are convenient and versatile to use for a variety of applications. Atomic resolution imaging in either ultrahigh vacuum (UHV) 1,2 or liquid, 3,4 high resolution imaging of biological samples in liquids, 5 low temperature (LT) AFM imaging, 6,7 LT magnetic force microscope (MFM) imaging in high magnetic field, [8][9][10][11] and LT-UHV applications 12 are typical examples utilizing the advantages of the fiber optic interferometers. All these systems use one of the two typical interferometric measurement methods: Michelson or Fabry-Pérot (FP). ...
In this publication, we describe the design of a new fiber Fabry-Pérot interferometer and employ this to a low temperature atomic force/magnetic force microscope (LT-AFM/MFM) operating in the 4–300 K temperature range. A multilayer dielectric mirror coated optical fiber is used to achieve unprecedented 1 fm/Hz noise level, while the shot noise limit is 0.51 fm/Hz. The cavity length is adjustable, and the fiber can be brought within a very close proximity of the cantilever using a dedicated 2 mm stroke piezonanopositioner integrated on the piezotube scanner. The same nanopositioner also is used to park the fiber at a safe parking location during cantilever exchange. We demonstrate the performance of the LT-AFM/MFM by imaging the ITO thin film at 300 K, atomic steps on HOPG at 300 K, magnetic bits on the hard disk at 15 K, and the Abrikosov vortex lattice in the BSCCO(2122) single crystal at 4 K.
... The experiments were performed with a homemade LT-NC-AFM apparatus operated in UHV [22]. The cryostat has three shields with the two fold shutters. ...
... All experiments were performed using our custom atomic force microscopy apparatus equipped with an optical fibre interferometer system operating at room temperature under ultrahigh vacuum (UHV) below 3 × 10 −9 Pa (ref. 33). The cleaned Ge(001) surface (As-doped, 0.5-0.6 cm) was obtained via several cycles of Ar + sputtering at 1 keV followed by annealing at 973-1,073 K in the UHV chamber. ...
Probing physical quantities on the nanoscale that have directionality, such as magnetic moments, electric dipoles, or the force response of a surface, is essential for characterizing functionalized materials for nanotechnological device applications. Currently, such physical quantities are usually experimentally obtained as scalars. To investigate the physical properties of a surface on the nanoscale in depth, these properties must be measured as vectors. Here we demonstrate a three-force-component detection method, based on multi-frequency atomic force microscopy on the subatomic scale and apply it to a Ge(001)-c(4 × 2) surface. We probed the surface-normal and surface-parallel force components above the surface and their direction-dependent anisotropy and expressed them as a three-dimensional force vector distribution. Access to the atomic-scale force distribution on the surface will enable better understanding of nanoscale surface morphologies, chemical composition and reactions, probing nanostructures via atomic or molecular manipulation, and provide insights into the behaviour of nano-machines on substrates.
... chamber was the same as that developed by Suehira. 17 Liquid nitrogen of 3.8 l and liquid helium of 4.6 l can be stored in the outer and inner Dewars. In addition, the three radiation shields shut off light and heat from outside to allow the experiment to be performed at 4 K. 17 Figure 2(c) shows a schematic view of the AFM unit. ...
... 17 Liquid nitrogen of 3.8 l and liquid helium of 4.6 l can be stored in the outer and inner Dewars. In addition, the three radiation shields shut off light and heat from outside to allow the experiment to be performed at 4 K. 17 Figure 2(c) shows a schematic view of the AFM unit. In the OBD system, to achieve highly sensitive force detection, the focused optical beam should be adjusted accurately on the back side of the cantilever, and the reflected optical beam should be adjusted in the center of the four-segmented photodiode. ...
The atomic force microscopy (AFM) is a very important tool for imaging and investigating the complex force interactions on sample surfaces with high spatial resolution. In the AFM, two types of detection systems of the tip-sample interaction forces have been used: an optical detection system and an electrical detection system. In optical detection systems, such as optical beam deflection system or optical fiber interferometer system, both the lateral and the vertical tip-sample forces can be measured simultaneously. In electrical detection systems, such as qPlus or Kolibri sensors, either the lateral or vertical forces can be measured. Simultaneous measurement of the lateral and vertical interaction forces effectively allows investigation of force interactions because the force is a vector with magnitude and direction. In this study, we developed a low-temperature, frequency-modulation AFM using an optical beam deflection system to simultaneously measure the vertical and lateral forces. In this system, the heat sources, such as a laser diode and a current-to-voltage converter, for measuring the photocurrent of the four-segmented photodiode are located outside the observation chamber to avoid a temperature increase of the AFM unit. The focused optical beam is three-dimensionally adjustable on the back side of the cantilever. We demonstrate low-noise displacement measurement of the cantilever and successful atomic resolution imaging using the vertical and lateral forces at low temperatures.
... Last but not least, a number of very interesting physical phenomena only occur below a certain critical temperature, e.g., magnetic ordering or superconductivity. Therefore, many low temperature force microscopes have been realized in the past [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] . Some sub-Kelvin AFM-type set-ups dedicated to rather special experiments, like magnetic resonance force microscopy 25 , have been presented in the past. ...
The design of an atomic force microscope with an all-fiber interferometric detection scheme capable of atomic resolution at about 500 mK is presented. The microscope body is connected to a small pumped 3He reservoir with a base temperature of about 300 mK. The bakeable insert with the cooling stage can be moved from its measurement position inside the bore of a superconducting 10 T magnet into an ultra-high vacuum chamber, where tip and sample can be exchanged in-situ. Moreover, single atoms or molecules can be evaporated onto a cold substrate located inside the microscope. Two side chambers are equipped with standard surface preparation and surface analysis tools. The performance of the microscope at low temperatures is demonstrated by resolving single Co atoms on Mn/W(110) and by showing atomic resolution on NaCl(001).
... All experiments were carried out by a home-made NC-AFM operating under ultrahigh vacuum (UHV) conditions at 78 K, with an optical interferometer system and a sample-and tipcleaning system equipped in the UHV chamber [12,58]. The FM technique was used to detect the tip-sample force interaction. ...
We present an experimental study of coexisting p(2 x 1) and c(6 x 2) phases on an oxygen-terminated Cu(110) surface by noncontact atomic force microscopy (NC-AFM) at 78 K. Ball models of the growth processes of coexisting p(2 x 1)/c(6 x 2) phases on a terrace and near a step are proposed. We found that the p(2 x 1) and c(6 x 2) phases are grown from the super Cu atoms on both sides of O-Cu-O rows of an atomic spacing. In this paper, we summarize our investigations of an oxygen-terminated Cu(110) surface by NC-AFM employing O-and Cu-terminated tips. Also, we state several problems and issues for future investigation.
... The apparatus was operated in an ultrahigh-vacuum (UHV) chamber. 21) The AFM imaging was conducted at 78 K, where the thermal drift was less than 0.05 # A/min. The base pressure of the system was less than 2:0 Â 10 À11 Torr. ...
... NaCl (Wako Pure Chemical Industries) with a purity of approximately 99.99% was deposited on the Cu surface. Atomic deposition is typically carried out by heating or ion sputtering in UHV; 2,21) the former method was used in this experiment. An NaCl film was grown on a clean Cu(111) surface at 300 K using an EFM3 evaporator (Omicron). ...
A new atomic force microscopy (AFM) force mapping technique has been
used to investigate insulating thin (100) films of NaCl on conducting
Cu(111) substrate at 78 K. This technique was able to map the
interaction forces between the AFM tip and the surface ions of the
sample. The site-specific force curves of the (100) surface of the NaCl
thin films are presented. We observed only an attractive short-range
interaction force at the Na+ and Cl- sites. We
propose simple models to explain the behavior of the force curves at the
different ion sites.
... Since fiber optic interferometer based systems do not require the installation of electronic components into or next to the deflection sensor region for measurements, they are convenient and versatile to use for a variety of applications. Atomic resolution imaging in either ultrahigh vacuum (UHV) 1,2 or liquid, 3,4 high resolution imaging of biological samples in liquids, 5 low temperature (LT) AFM imaging, 6,7 LT magnetic force microscope (MFM) imaging in high magnetic field, [8][9][10][11] and LT-UHV applications 12 are typical examples utilizing the advantages of the fiber optic interferometers. All these systems use one of the two typical interferometric measurement methods: Michelson or Fabry-Pérot (FP). ...
Fiber interferometrik ölçüm sistemleri, düşük sıcaklık atomik kuvvet mikroskop (DS-AKM) sistemlerinde, kuvvet algılayıcısı olarak kullanılan yayların sapmalarını ölçmede yaygın olarak kullanılır. Tipik bir Michelson interferometresi şeklinde çalışan bu ölçüm sistemlerinde elde edilen ölçüm hassasiyeti ~100fm/√Hz mertebesindedir. Bir interferometre ölçüm sistemi, ucu elmas bir kesiciyle düzlenmiş bir fiber ve fibere dik olacak şekilde hizalanmış bir yaydan oluşur. 1320 nm dalga boyundaki bir lazer demeti, 2x2 %50‟lik bir fiber çiftleyiciye gelerek burada ikiye ayrılır: birinci kısım fiber kablo aracılığıyla taşınarak, ucu düzlenmiş fibere gelerek %2–3‟lük kismi buradan geri yansır. Kalan kısım dışarıya yayılarak, yaya çarpar ve yansıyarak geri döner ve fiber kabloya girerek ilerler. Bu iki demet, fiber kablo içerisinde ilerleyerek bir phodedektöre ulaşır ve burada bir girişim deseni oluşturarak bir akım oluşturur. Bu akım, i =io[1–Vcos(4πd/λ)] şeklinde ifade edilir. Denklemdeki V parametresi „görünürlük‟, d ise fiber ile yay arasındaki mesafeyi ifade etmektedir. Bu iki parametre, bir fiber interferometrenin hassasiyetini belirleyen iki ana unsurdur.
Bu çalışmada, DS-AKM‟de kuvvet etkileşimlerinden doğan yay sapmalarını ölçmek için Michelson türü bir interferometre geliştirdik. RF modülasyonu uyguladığımız laser demeti DS-AKM sisteminde ~25 fm/√Hz mertebesinde bir hassasiyet elde ettik. Bu hassasiyet mertebesinde elde ettiğimiz Manyetik Kuvvet Mikroskobu (MKM) görüntülerinde, 10 nm mertebesinde bir çözünürlük elde ettik. Örnek olarak yüksek yoğunluklu bilgisayar hard disklerini kullandık. Elde ettiğimiz MKM çözünürlüğünü artırmak için, DS-AKM‟nin hassasiyetini artırmak ve gürültü seviyesini düşürmek gerekmektedir. Bu amaçla iki önemli eylem önerisini ortaya koyduk: (1) düzlenmiş fiberin %2–3 seviyesinde olan yansımasını artırmak, (2) fiber ile yay arasındaki mesafeyi azaltmak. Bu amaçla, düzlenmiş fiberi dielektrik malzemelerle çok katmanlı bir şekilde kaplayarak yansımayı ~%50 seviyesine çıkardık. Fiber ile yay arasındaki mesafeyi azaltmak için, tarayıcı piezo tüpü kullancak şekilde bir kaydırak mekanizması geliştirdik. Bu şekilde fiber, z-doğrultusunda yaya göre ileri ve geri yönde hareket kabiliyeti kazandı. Mevcut tasarımdaki 30–40 μm olan yay–fiber mesafesi bu mekanizma ile ayarlanabilir hale getirildi ve mesafe ~2–3 μm‟a düşürüldü.
Çok katmanlı dielektrik kaplama fiber–yay arasında, çoklu yansımalar oluşmasını sağlayarak bir Fabry–Perot interferometresi olarak çalışmaya başladı. Bu şekilde yaptığımız gürültü ölçümlerinde oda sıcaklığında ~8 fm/√Hz mertebesinde hassasiyet ölçmüş bulunmaktayız. Shot noise adını verdiğimiz gürültü tabanımız ise ~2 fm/√Hz olarak hesaplandı. Yeni sistem ile devam eden çalışmalarımızda, hassasiyeti daha da artırmayı ve 5–6 nm seviyesinde MKM çözünürlüğü elde etmeyi amaçlamaktayız.
... Typically, atomic corrugations in the range of 100 pm are observed during imaging in NC-AFM feedback mode on the Si1117 7 surface using the KolibriSensor, as shown in Figs. 3 and 4. This is in good agreement with the values observed in silicon-cantilever-based NC-AFM experiments conducted at cryogenic temperatures, 30,31 underlining the high performance of the SPM 150 Aarhus microscope in combination with the KolibriSensor in NC-AFM imaging. Furthermore, this also suggests that despite the fact that a metallic tip was used throughout our studies, imaging in NC- AFM feedback mode was presumably governed by a silicon- terminated tip created by slight touches of the surface during imaging. ...
Combined atomic-resolution scanning tunneling microscopy (STM) and noncontact atomic-force microscopy (NC-AFM) studies are carried out with the piezoelectric KolibriSensor in ultrahigh vacuum at room temperature. The sensor exhibits a very low spectral deflection noise density of only 6.5 fm/ Hz which favors in combination with its high spring constant of 540 000 N/m stable NC-AFM operation at subnanometer oscillation amplitudes. The authors present atomic-resolution imaging on the Si (111) (7×7) surface recorded in STM and NC-AFM feedback mode. They find that the tip surface distance during atomic-resolution imaging on silicon is much smaller for NC-AFM compared to STM. It is shown that atomic-resolution NC-AFM and dynamic STM images of the same area on the Si (111) (7×7) surface enable a discrimination of vacancies and adsorbates. Furthermore, the topography of graphite imaged in dynamic STM and NC-AFM feedback mode is compared.
