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We investigate interaction effects which occur in scanning tunneling microscopy (STM) by performing local force spectroscopy with an oscillating tip while imaging Si(111)7 x 7 terraces in the dynamic lever STM mode (constant time-averaged current). It is found that true atomic resolution is achieved close to the minimum of the resonance frequency vs. distance curve and even closer to the sample. On the other hand true atomic resolution in noncontact AFM (constant frequency shift) is expected several nm away from this minimum, in the range where the frequency shift becomes more negative with decreasing distance.

Decision-making logic based on fuzzy logic and an adaptive PI-controller was inserted into the feedback loop of a combined atomic force microscope/scanning tunneling microscope (AFM/STM), which is able to measure the frequency shift Delta f of the cantilever-type spring and the mean tunneling current (I) over bar(t) simultanously. Depending on the conductivity of the surface the fuzzy logic controller decides whether it has to use the AFM feedback or the STM feedback. On conductive regions of the sample STM mode is used, whereas on poorly conducting regions the non-contact AFM mode is preferred. This allows one to scan over heterogenous surfaces avoiding a tip crash.

We performed scanning force microscopy (SFM) in ultrahigh vacuum (UHV) on AgBr thin films which were in situ deposited on NaCl(001) substrates. The morphology of the initial growth stage and the nanotribological properties of these thin films are characterized and discussed. The lateral (frictional) forces are measured as a function of normal load. The local friction coefficients are extracted by means of the two-dimensional histogram technique. In the low load regime, friction coefficients of 0.33 ± 0.07 and

The surfaces of in situ cleaved NaF crystals have been studied by scanning force microscopy (SFM) in ultrahigh vacuum (UHV). Operating the UHV force microscope in the contact mode, the surface structure with extended terraces interrupted by steps of typically 0.25 nm and 0.5 nm in height is revealed. Atomic-scale resolution is achieved on the terraces as well as at monatomic steps of the ionic crystal. The square surface lattice shows a periodicity of 0.45+/-0.04 nm that corresponds well to the spacing between equally charged ions along the [100] directions in the bulk phase. From the SFM data at cleavage steps the imaging area of the sensing tip is estimated to be less than 1 nm2. Some aspects of the contrast mechanism in the lateral and normal force images are discussed. The SFM data are complemented by low-energy-electron-diffraction measurements on NaF(001) carried out in the same compact UHV system.

Scanning force microscopy has been employed to investigate static and dynamic surface structures on ferroelectric crystals of GASH and TGS. On the crystal cleavage faces two sets of complementary results are obtained depending on the operation mode of the force microscope: (1) In the contact mode, static domain structures and superimposed cleavage structures are imaged on GASH(0001), whereas on TGS(010) specific domain erosion due to water adsorption is observed. Additionally, molecular resolution has been achieved on GASH surfaces. (2) In the non-contact mode, domain walls are revealed and the motions of the walls due to heat treatment are documented.

Scanning force microscopy (SFM) has been used to study the (0001) cleavage faces of ferroelectric crystals of GASH (guanidinium aluminium sulfate hexahydrate). For the first time, the surface and domain structures of a ferroelectric material has been imaged directly from the micrometer down to the molecular scale. On the micrometer scale SFM reveals the elementary cleavage structure with typical zig-zag-shaped steps. Superimposed on this topographic structure are ferroelectric domain structures which could be imaged with SFM operating the force microscope in the repulsive contact mode. On the nanometer scale, molecular resolution has been achieved on the atomically flat terraces. The imaged surface lattice with spacings of 0.68 nm reflects the threefold symmetry of the unreconstructed GASH (0001) surface.

A polycrystalline diamond film was etched down to a depth corresponding to the grain size with 193 nm excimer laser radiation. Below a graphitic surface layer (GL) we have observed a highly stable layer (SL) which is conducting. Atomic force microscope measurements were made in order to characterize the topography and microfriction of these two surface layers. Features of the diamond facet structure are still visible in spite of smoothening by the laser etch process. An approximation for the friction coefficient of both surface layers yields values of between 0.01 and 0.1. The friction pictures of the GL show a local period length of about 70 nm, which could be a typical diameter for micrographitic grains. The SL is more disrupted than the GL and the appearance of a period length of about 70 nm has faded discernibly.

Recent developments in the field of scanning-probe methods show increasing demand for controlling and storing many different experimental parameters in addition to topographic information. In order to be able to perform these experiments (e.g. force spectroscopy, surface modification, friction measurements, etc.) we have designed a versatile acquisition system. Up to four different channels can be measured and displayed at the same time. Scan parameters are under software control, and additional output signals can be easily generated to meet experimental requirements. This flexibility allows the straightforward incorporation of new conditions and modes of measurement. We use a PC/386 system based principally on commercially available electronics. As an illustration of its performance we present the application of this system to a bidirectional atomic-force microscope. With this particular microscope it is important to control lateral as well as normal forces independently. Topography and friction information can be acquired and viewed simultaneously. The versatility of this data-acquisition system also makes it well suited for a variety of other tribological/micromechanical experiments such as friction loops, force-distance curves and surface wear.

A feedback mechanism based on fuzzy logic has been applied to operate a combined atomic force microscope (AFM)/scanning tunneling microscope (STM), which is able to measure the resonance frequency shift Δf of the cantilever-type spring and the mean tunneling current Īt simultaneously. Using a decision making logic, the microscope can be scanned over a heterogeneous surface without tip crash. On the conductive parts of the sample, the STM mode is preferred, whereas the noncontact (nc)-AFM mode is used on the poorly conductive parts of the surface. The transition from the STM mode to nc-AFM mode is performed smoothly with the fuzzy logic feedback.

We demonstrate 10 dB gain enhancement in S-band optical parametric amplification, 10 dB net conversion efficiency enhancement, and S/C band wavelength conversion by simultaneous Raman amplification using a highly nonlinear fiber. Numerical simulations support the experimental results.

Using a noncontact atomic-force and scanning-tunneling microscope in ultrahigh vacuum, we have measured the switching energy of a single molecule switch based on the rotation of a di-butyl-phenyl leg in a Cu-tetra-3,5 di-tertiary-butyl-phenyl porphyrin. The mechanics and intramolecular conformation of the switched leg is controlled by the tip apex of the noncontact atomic-force microscope. The comparison between experimental and calculated force curves shows that the rotation of the leg requires an energy less than 100 x 10(-21) J, which is 4 orders of magnitude lower than state-of-the-art transistors.

A scanning force/tunneling microscope (SFM/STM) for remote controlled operation in ultrahigh vacuum (UHV) is described. The lateral forces, normal forces, and tunneling currents between probe tip and sample can all be measured simultaneously. The optical beam deflection detector and the sample position can be adjusted by means of three compact inertial stepping motors. An UHV‐compatible light emitting diode is introduced as a general alternative to the widely used laser diode in the detector. Images, taken at 5×10−11 mbar on Si(111) with STM and noncontact SFM, and on NaF(001) with contact SFM, are presented.

We report the first observation of intense visible upconversion luminescence from Cs/sub 3/Lu/sub 2/Cl/sub 9/:Er/sup 3+/ crystals excited by a 1.53-/spl mu/m tunable cw diode laser amplified by an erbium-doped fiber amplifier. Spectral and dynamic properties between 15 and 300 K as well as changes along the chloride sample series are discussed.

Scanning force microscopy for studying ferroelectric domain structures is applied. The force microscope was operated in the contact static mode (repulsive force regime) and in the noncontact dynamic mode (attractive force regime). These two techniques were applied to study cleavage faces of ferroelectric crystals of GASH (guanidinium aluminum sulfate hexahydrate) and TGS (triglycine sulfate) crystals. Using the contact mode, the positive and negative domains are revealed by opposite contrast. In the dynamic noncontact mode, the domain walls are revealed. The experimental setup allows in situ experiments to study the dynamics of ferroelectric domains. First results on the time dependence of the domains motion in TGS will be presented.

The technique of operating the scanning force microscope in the dynamic noncontact mode (dynamic force microscopy) has been improved. Home-built instruments based on an optical beam deflection scheme in two different environments were used. The two force microscopes were operated in ambient air and in ultrahigh vacuum, respectively. In order to control the oscillating cantilever different methods were applied: slope-detection (lock-in amplifier, RMS-to-DC converter) and frequency modulation (FM) technique as well. The advantages of this nondestructive technique are demonstrated on different samples, such as soft organic matter (hexagonally packed intermediate layer, Langmuir-Blodgett film), layer-structured compounds (CdI2), n-doped Si(111), and ferroelectric crystals [triglycine sulfate (TGS), guanidinium aluminum sulfate hexahydrate (GASH)]. On TGS and GASH cleavage faces, the ferroelectric domains and domain walls could be imaged. From experimental data a spatial resolution of about 1-2 nm in lateral and

Highly ionized plasmas (degree of ionization 0.1,...,0.5) with electron temperatures kTe≳4 eV are required for high‐power generation from ion lasers. In stationary low‐pressure arcs, however, these requirements are limited by discharge instabilities. The stability limits are investigated in the case of Ar and Hg low‐pressure discharges. It is shown that the main limitation processes are due to neutral gas depletion by ionization and axial plasma inhomogeneities. The stability ranges of ion‐laser discharges are represented using the geometry‐independent parameters jR and pR ( j: discharge current density; p: filling pressure; R: discharge radius). These instabilities, together with saturation effects in the laser mechanism, limit the output power of ion lasers by restricting the operational range of the discharges.

The influence of axial magnetic fields on ion-laser discharges of large diameter (tube radiusR=0.6 cm) has been investigated. At modest power levels (jR 150 A/cm) axial magnetic fields cannot increase the laser output.

Excitation and decay rates of the 4880 A-ArII-laser transition pumped in a low-pressure arc yield a power limit for ArII high power lasers (arc diameter >1 cm), caused mainly by radiation trapping. Maximum power of the 4880 A laser is Φ/L=70W/m±25%.

Plasma temperatures of the wall-stabilized low pressure Ar-arc, which has been optimized for maximum inversion density of the Ar II 4p- 4s laser transitions (i.e.kTe≅4 eV), have been determined experimentally and compared with literature data. Ion temperature is obtained from the Doppler linewidths of Ar II transitions, which have been measured both spectroscopically and indirectly by measuring the gain of the 4880 a laser line. Neutral temperature is obtained from the Doppler linewidths of Ar-I-transitions and by relating fill pressure and calculated values of the corresponding gas density.

An Ar low‐pressure high‐current discharge (length=1.7 m, diameter=12 mm) was used for continuous high‐power operation of uv laser lines (λ=351.1 nm, 363.8 nm). The measured maximum output power of 18 W for both lines combined was restricted by thermal mirror degradation. Based on gain measurements, a maximum power of 35 W is predicted. It appears that this value is limited by discharge instabilities.

High‐power cw laser radiation from nine Ar and five Kr laser transitions in the spectral range 275

High power cw laser oscillation on 7 ArIII and 3 KrIII lines below 350 nm is reported. The active medium used is a highly ionized low pressure dc discharge (length: 1.7 m, radius: 6mm) from which 75 Watts in the combined 351.1 nm and 363.8 nm ArIII lines can be extracted. For every line under investigation the output increases without saturation up to the available discharge current i = 480 A. The maximum power values are: 17 W (ArIII 333–335 nm); 3.8 W (ArIII 300–305 nm) and 0.4 W (ArIII 275 nm).

In the last 10 years forces in scanning probe microscopy (SPM) have been an interesting topic with continuing progress. The recently achieved true atomic resolution in dynamic force microscopy in ultrahigh vacuum (UHV) allows a comparison of scanning force microscopy (SFM) with scanning tunneling microscopy (STM) on Si(111)7x7 surfaces. The range of atomic resolution by SFM coincides with the stable tunneling range of STM. Wide area images of a quality comparable to STM have been obtained with a cleaned Si tip on stepped areas of the Si(111)7x7 and on surfaces of ionic crystals. The Magnetic Force Microscope yields new information on the magnetic domain structure of thin magnetic layers and on single flux lines and their pinning in high temperature superconductors. New visions to extend today’s SFM devices to create new sensors and detectors (nano-age mechanics) are discussed.

A low-pressure Ar arc discharge (length = 1.7 m, diameter = 12 mm) was used for continuous high-power generation of UV laser lines ( \lambda = 351.1 nm, 363.8 nm). Low-loss mirror coatings and stabilization of the discharge with a magnetic field enabled a maximum output power of 40 W to be achieved from the combined lines.

A continuous rhodamine 6G jet stream dye laser was pumped by a high-power multimode argon laser. Using water with a viscosity-raising additive as a solvent, no thermooptical problems arose up to the available pump power of 110 W. The maximum output power of the CW dye laser was 33 W at an efficiency of 30 percent.