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The stress-related ferroelectric properties have been studied on the Triglycine sulfate (TGS) by scanning probe microscope (SPM). Together with normal stress of the tip, the lateral stress is applied to the sample with piezoelectric transducers. With this study, we characterized the way the ferroelectricity of TGS responds to the axis-specific stress. Specially, the b-directional stress applicable to the surface can amount to several GPa such that the polarization switching by mechanical stress is observable. Although the lateral stress is not strong enough to view such phenomena, a-axis(c-axis) stress still affects the polarization value so as to fortify (lessen) the electric field inside, respectively. These contrasting results can be explained by the sign relation of piezo-coefficients about the individual axis. This work can be a touchstone of future researches in characterizing the elelctromechanical properties of more popular ferroelectrics such as PZT or BTO.

Lead-free piezoceramics Bi0.5(Na1-xKx)0.5TiO3 (x = 0.00~1.00) has been investigated by using scanning probe microscope with lock-in technique. Superior to other bulk measurements, this technique gives not only the topological but the piezo/ferroelectric properties without any convolutions. By the appropriate selection of lock-in channel and spectra analysis, we can get the trend of the magnitude and phase of polarization with different x value. And this enables us to find the morphotropic phase boundary successfully.

The physical and chemical properties of metallic electrodes on Pb(Zr,Ti)O3 (PZT) are investigated by atomic force microscopy. Pt, a catalyst, tends to change itself into a dielectric oxide. Such a passive layer should cause a depolarization field driving the domain structure into the polystate. Therefore, the effective thickness of the Pt electrode becomes smaller than that of Ir electrode. Thus, we observed an opposite domain contrast around a region covered by thin Pt on PZT, which implied the failure of the screening of the depolarizing field. This multidomain configuration can cause a suppression of the remnant polarization of PZT capacitors. Also, Ir is better than Pt in regard to film smoothness, indicating that the adhesion property of Ir on PZT is superior to that of Pt on PZT. We prove it using height–height correlation function. This study is significant on the scaling issues of ferroelectric capacitors, such as the thickness limit of the electrode and the requirement for high surface smoothness of ferroelectric films.

We fabricated high quality (Ga,Mn)As epilayers by low-temperature molecular beam epitaxy and studied the magnetic and magneto-transport properties in detail. In particular, we investigated the relation between the longitudinal and the transverse Hall resistivity over a wide range of temperatures. It turned out that the anomalous Hall coefficient scaled linearly with the longitudinal resistivity, which seems to imply that the skew scattering is the primary source of the anomalous Hall effect in (Ga,Mn)As if we consider classical models only. However, we cannot rule out other mechanisms because of the narrow range of resistivity investigated. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The effect of crystalline defects on the formation of ferroelectric domains in triglycine sulfate (TGS) crystals has been investigated using a dynamic contact electrostatic force microscopy. This detection method, based on the Coulomb interaction between the charge on the tip and the surface charge on the sample, yields a good spatial resolution as well as a complete separation between the topography and the domain image. The crystal imperfections, degraded surface, and strain in the crystal affect strongly the static domain configuration. Comparison of the topography to the domain image reveals a deterministic behavior in the formation of the equilibrium domain configuration, which is determined by twin boundaries in the crystal. Surface imperfections appear different depending on the polarization direction. Positively polarized regions show circular islands, whereas negatively polarized region shows circular holes as well as islands of various shapes. When TGS samples were cooled below the Curie temperature from a paraelectric state, the relaxation rate of the domains from the nonequilibrium configuration to the equilibrium configuration is substantially decreased forthe sample that contains many defects, indicating a pinning effect by the crystal imperfections such as the degraded surface and stress in the crystal.

A La 0.7 Sr 0.3 MnO 3 thin film epitaxially grown on a LaAlO 3 (001) substrate by pulsed laser deposition has been investigated by means of low-temperature magnetic force microscopy under high stability conditions. The ferromagnetic film exhibits a stress-induced perpendicular easy axis of magnetization. The domain structure was imaged at zero field after (i) thermal demagnetization, (ii) saturation in an in-plane field and (iii) saturation in an out-of-plane magnetic field, respectively. Stripe domains were observed in all cases, however, contrast and domain width are increased after out-of-plane saturation while alignment of stripe domains in field direction occurs after in-plane saturation. A quantitative analysis of the image contrast suggests a variable in-plane component of the magnetization, dependent on the magnetic history of the sample. Calculations of domain width and contrast from the relevant energy contributions are compared with experimental results.

A magnetic flux-guide in the form of a sharp needle is known to enhance the spatial resolution of the scanning SQUID microscope. We investigated the properties of a soft ferromagnetic tip as a flux-guide by measuring the local field of the tip end. The effects of the flux-guide, such as the transmission of a magnetic signal, length dependence, and nonlinear distortion, were observed. We also present the design and construction of a HTS scanning SQUID microscope with a flux-guide and a planar gradiometer. The gradiometer with a flux-guide is an appropriate solution for improving the performance of the scanning SQUID microscope with a flux-guide as regards the prevention of external field noise without magnetic shields.

We report an optical spectroscopic method to monitor NiAs-type MnAs (α-MnAs) nanocrystals in (Ga,Mn)As diluted magnetic semiconductors. We utilize Mn ion implantation of low temperature (LT) GaAs epitaxial thin films followed by rapid thermal annealing (RTA) to yield embedded ferromagnetic α-MnAs nanoclusters in a GaAs:Mn matrix. As-implanted samples are paramagnetic and become ferromagnetic with Curie temperature of ∼320 K after RTA at 750 °C. No peaks of potential secondary phases could be observed in x-ray diffraction measurements. However, in optical spectra, the annealed samples show resonant absorption at 0.9 eV photon energy, due to resonant surface plasma oscillation of spherical metallic phases embedded in LT GaAs. Since the absorption peak position in the photon energy has a direct relation to the value of the plasma frequency of metallic inclusions, the metallic clusters in LT GaAs are identified as α-MnAs nanocrystals by comparing them with simulations based on Maxwell–Garnett theory. We sugge...

Bulk single crystals of Sn-doped ZnO were implanted with Co or Mn at doses designed to produce transition metal concentrations of 3–5 at.% in the near-surface (� 2000 A region. The implantation was performed at � 350 Ct o promote dynamic annealing of ion-induced damage. Following annealing at 700 C, temperature-dependent magnetization measurements showed ordering temperatures of � 300 K for Co- and � 250 K for Mn-implanted ZnO. Clear hysteresis loops were obtained at these temperatures. The coercive fields were 6 100 Oe for all measurement temperatures. X-ray diffraction showed no detectable second phases in the Mn-implanted material. One plausible origin for the ferromagnetism in this case is a carrier-induced mechanism. By sharp contrast, the Co-implanted material showed evidence for the presence of Co precipitates with hexagonal symmetry, which is the cause of the room temperature ferromagnetism. Our results are consistent with the stabilization of ferromagnetic states by electron doping in transition metal-doped ZnO predicted by Sato and Katayama–Yoshida [Jpn. J. Appl. Phys. 40 (2001) L334]. This work shows the excellent promise of Mn-doped ZnO for potential room temperature spintronic applications. 2003 Elsevier Ltd. All rights reserved.

Growth by molecular-beam epitaxy (MBE) of the dilute-magnetic alloy GaMnN is reported. The Mn concentration, as determined by Auger electron spectroscopy (AES), is found to be linear with increasing Mn-cell temperature up to ∼43at.%Mn. No second phases are observed for Mn levels below 9 at.%. The cubic-phase Mn4N is found to be the thermodynamically stable phase at the growth conditions used to produce GaMnN. Hysteresis in M versus H is observed in both GaMnN and GaMnN:C grown on both sapphire and metal-oxide chemical-vapor deposition (MOCVD) GaN at several growth temperatures. Magnetotransport results show the anomalous Hall effect, negative magnetoresistance, and magnetic hysteresis, indicating that Mn is incorporating into the GaN and forming the ferromagnetic-semiconductor GaMNN. Room-temperature hysteresis is obtained in magnetization measurements with an optimum Mn concentration of ∼3 at.%.

We report on the magnetic and structural properties of epitaxial metal organic chemical vapor deposition grown p-GaN:Mg/Al2O3 implanted with Co, Cr, and V ions at varying high doses at 350 °C. Magnetic and structural properties were investigated after a short anneal at 700 °C to remove implantation damage. Magnetic properties determined from superconducting quantum interference device magnetometer measurements indicate ferromagnetic-like ordering for Co and Cr doped samples up to 320 K, while V doped samples show paramagnetic behavior for all temperatures considered. For all samples studied, structural characterization techniques such as x-ray diffraction, high-resolution cross-sectional transmission electron microscopy, and selected area diffraction pattern, indicate no second phases that may contribute to the magnetic properties measured. Transport measurements (resistivity as a function of temperature) reveal all samples to show insulating-like behavior.

We have studied vortex dynamics in Bi2Sr2CaCu2O8 single crystal with low density columnar defects by using a magnetic force microscope. Single crystal Bi2Sr2CaCu2O8 sample was irradiated by 1.3 GeV uranium ion to form artificial pinning centers along the crystalline c-axis. The irradiation dose corresponded to a matching field of 20 gauss. The radius of an individual vortex is approximately 140 nm, which is close to the penetration depth of this material. Magnetic force microscope (MFM) images show that intrinsic crystalline defects such as stacking fault dislocations are very effective pinning centers for vortices in addition to the pinning centers due to ion bombardment. By counting the number of vortex, we found that the flux trapped at each pinning center is a single flux quantum. At higher magnetic field, the vortex structure showed an Abrikosov lattice disturbed only by immobile vortices located at pinning centers. When increasing or decreasing the external magnetic field, the spatial distribution of vortices showed a Bean model like behavior.

We measured the superconducting gap of MgB2 thin films and pellets by utilizing point contact Andreev reflection method with a gold tip. From more than 100 measurements, we obtained the distribution of the superconducting gap of the material. This distribution shows two peaks, one at 2–3 meV and the other around 6–8 meV while BCS weak coupling limit predicts 5.9 meV. From temperature dependence measurements, we observed energy gap to nearly follow BCS-like behavior. These results also seem to agree well with the recent anisotropic energy gap estimation based on the ab initio calculation from the band structure of MgB2.

Scanning probe microscope with a dc bias and an ac modulation signal applied to the probing tip has been quite successful for investigating the characteristics in a sub-micron scale for the high density ferroelectric memory application field. The degradation of ferroelectric films—PbZr 0.4 Ti 0.6 O 3 (PZT) and Bi 3.25 La 0.75 Ti 3 O 12 (BLT)—caused by the hydrogen forming gas annealing is investigated in a microscopic scale by using an electrostatic force microscope (EFM). From the first harmonic signal of EFM, we obtained different polarization behaviors from as-grown and hydrogen-annealed ferroelectric films. We found that the hydrogen forming gas annealing is degrading the ferroelectric film with no catalyst top electrode on top of the film. It is believed that the annealing process causes the diffusion of hydrogen into the ferroelectric film resulting in the destruction of polarization in these materials. We speculate that the different degradation behavior among these materials (PZT and BLT) is due to the different cohesivity of hydrogen in these materials.

Our studies show that hydrostatic pressure causes a substantial increase in Kondo temperature TK and suppresses the magnetic order of the Ce-rich side of (Ce,U)Al2. For example, the magnetic transition of (Ce0.7U0.3)Al2 disappears above 5.5 kbar. Spin fluctuations dominant in the U-rich side become suppressed too, and simultaneously the U-rich systems are driven with pressure towards a simple metallic regime. A new scaling is found of the pressure-dependent resistivity of U-rich samples.

We have investigated domain structure and dynamics of a triglycine sulfate (TGS) single crystal with a dynamic contact mode electrostatic force microscope (DC-EFM), which is operated in contact mode. DC-EFM can overcome a problem in conventional noncontact EFM measurement. The temperature dependence of surface charge density was measured by a nulling technique. We also investigated local domain switching behaviors of TGS single crystal and PZT thin film. Complex pattern was written on a PZT thin film by the polarization reversal. A writing capability such as a writing speed and voltage dependence in PZT film has been studied by DC-EFM.

Dynamic contact mode electrostatic force microscopy (DC-EFM) was developed as a new operation mode of scanning probe microscope (SPM). By operating EFM in a contact mode with an ac modulation bias, we have improved the spatial resolution and also achieved a complete separation of the topographic effect from other electrostatic force effect overcoming the mixing problem of a topographic effect with other electrostatic effects frequently encountered in the conventional noncontact EFM measurement. DC-EFM can be utilized either as a force microscopy for the surface hardness, or as a potentiometry for the surface potential distribution, or as a charge densitometry for the surface charge density study. This is also applicable to the measurement and control of the domain structure in ferroelectric materials that have a bound surface charge.

Atomically flat SrTiO 3 (STO) substrates can be prepared by oxygen-annealing, however, step structures are known to be difficult to control. Various step structures of original substrates could be modified by growth of homoepitaxial films using laser molecular beam epitaxy (MBE). On substrates with a mixture of 1 and 2 unit cell (uc) steps, two kinds of films were grown: their growths were interrupted at either a top or a bottom of reflection high-energy electron diffraction (RHEED) intensity oscillations. The step structure of the top-interrupted film was similar to that of the substrate. However, in the bottom-interrupted film, bunched steps could be removed after deposition of only 2.5 monolayers (ML) and 1 uc steps could be generated. The recovery of the RHEED intensities reflecting the step height modification was found out to have a strong azimuthal dependence of incident electron-beam (e-beam) direction with respect to the step direction.

In the core of quantum Hall effect, intrinsic anomalous Hall effect (AHE), and intrinsic spin Hall effect lies the Berry phase, a quantum mechanical phase associated with an adiabatic change of the system. However, experimental evidences supporting this new recognition are scarce in three-dimensional systems. We report here that the anomalous Hall conductivity of metallic GaMnAs samples, when properly scaled by the carrier concentration, remains constant regardless of the ferromagnetic transition temperature from 50 to 160 K. In addition, the constant agrees with the theoretical prediction quite well. These qualitative and quantitative agreements support the idea of intrinsic AHE originated from momentum-space Berry phase firmly. Furthermore, the tunability of intrinsic AHE in the diluted magnetic semiconductors can be utilized in the semiconductor spintronics applications.

We report the synthesis and characterization of Mn 12 O 12 ( PhCO 2 ) 15 ( 3 - thiopheneCO 2 ) ( H 2 O ) 4 (1) single-molecule magnet (SMM) and its monolayer film on gold substrate. Out of 16 ligands encapsulating Mn 12 O 12 core, one specific ligand is terminated by sulfur in this compound. While the general magnetic properties of Mn12 SMMs are retained in 1, the arrangement of the molecules in the film is much improved compared to the case of other Mn12 complexes. Current–voltage curves of the molecular junction of 1 obtained by using an atomic force microscopy show the step-like features which seem indicative of the molecular energy levels of 1.

A dynamic contact mode operation of electrostatic-force microscopy (EFM) with an ac modulation has been developed and used to investigate the domain strucutre and dynamics of a triglycine sulfate single crystal. Well-separated topographic and domain contrast images have been obtained by detecting the force instead of the force gradient in the dynamic contact mode operation of EFM. Surface charge density and the anisotropic domain wall thickness have been measured. The evolution of domains embedded in an oppositely polarized larger domain indicates the existence of a significant interaction between domains of the same polarity.

We have studied the effect of barrier strength on the tunneling magnetoresistance of MnAs/GaMnAs heterostructures with double AlAs barriers. The epitaxial structures were grown by low-temperature molecular beam epitaxy. The vertical magnetotransport properties were studied for various GaAs spacer thicknesses. We find that the junction resistivities of double barrier samples increase exponentially as the barrier strength increases, implying that direct tunneling process governs the transport properties. In contrast, the tunneling magnetoresistance depends primarily on the number of interfaces rather than on the barrier strength.

The effects of surface morphology on domain formation and relaxation in ferroelectric materials have been investigated. Comparison of the topography of triglycine sulfate with its ferroelectric domain image reveals a deterministic behavior in the formation of the equilibrium domain configuration. It is observed that defects such as crystal imperfections, cleavage steps and strained lines make ferroelectric state more stable by suppressing short-range repulsion, which results in domain pinning. On the other hand, it can be seen that long-range interaction is screened by free carriers in the metallic film. For this reason, we can see the domain movement beneath the metallic film is faster than that in bare surface.

We report a noninvasive high speed voltage sampling technique by using atomic force microscope. This technique is based on the mixing of interaction forces between a conductive probe-tip and a device interconnect line. Mixing phenomena allow measurements of signals with frequencies far above the mechanical resonance frequency of the cantilever. To increase the sensitivity and stability of the signal detection in ambient environment, we employed a delayed pulse sampling and lock-in amplifier detection of the small electrostatic force resulting from a high frequency signal on integrated circuits. The probing pulse is first modulated by a low frequency sinusoidal voltage using a double-balanced diode mixer. The junction between probe-tip and integrated circuit interconnection line works as the second mixer which mixes the probing voltage with the high speed waveform in the interconnection line. This technique can sense voltage signals even through a passivation layer of a 0.5 μm in thickness. We sampled an 8...

The photoresponse of a YBa2Cu3Ox grain‐boundary junction has been measured as a function of chopping frequency and bias current in a temperature range of 2 K≤T≤70 K. The response was found to be mostly bolometric, but a nonbolometriclike component was also identified, which appeared as a chopping‐frequency independent signal while immersing the sample in the superfluid helium. The bias‐current dependence of the response showed a peak at a current corresponding to the critical current of the junction, and the peak values remained constant for 30 K≤T≤70 K. However, below 15 K the peak of the photoresponse increased very sharply with decreasing temperature following a 1/T3 dependence, consistent with the temperature dependence of the thermal boundary resistance between the film and the substrate.

Using force spectroscopy in the dynamic mode at low temperature, we have measured the interaction between a magnetic tip and an individual single vortex trapped by an artificial columnar defect in a Bi2Sr2CaCu2O8+δ single crystal. From spectroscopy data obtained along a line that intersects a vortex, we get quantitative information about the vertical and lateral magnetostatic forces between tip and vortex. Particularly, we estimate the lateral dragging force exerted on the vortex by the magnetic tip to about 1.5pN.

Tunneling spectra of a single crystalline YNi 2 B 2 C ( T c = 15.4 K) and LuNi 2 B 2 C ( T c = 15.7 K) have been measured by a point-contact spectroscopy using a low-temperature scanning tunneling microscope. The conductance curve of these materials shows a smeared gap structure with an almost linear density of states inside of the gap region as well as a sizable zero-bias conductance. The linear conductance inside the gap region has been explained by a proximity-induced energy gap in the degraded surface normal layer. The resulting energy gap at 4.2 K is 3.2 meV and 3.3 meV for YNi 2 B 2 C and LuNi 2 B 2 C, respectively. A simple analysis using a smeared BCS density of states, on the other hand, yields energy gap of 2.55 meV and 2.65 meV. Temperature dependence of the energy gap in LuNi 2 B 2 C shows a reasonable agreement with the BCS type temperature dependence except a slight deviation near T c .

The magnetic and structural properties of cobalt-implanted ZnO single crystals are reported. High-quality, (110)-oriented single-crystal Sn-doped ZnO substrates were implanted at ∼350 °C with Co to yield transition metal concentrations of 3–5 at. % in the near-surface (∼2000 A) region. After implantation, the samples were subject to a 5 min rapid thermal annealing at 700 °C. Magnetization measurements indicate ferromagnetic behavior, with hysteresis observed in the M vs H behavior at T=5 K. Coercive fields were ⩽100 Oe at this measurement temperature. Temperature-dependent magnetization measurements showed evidence for ordering temperatures of >300 K, although hysteresis in the M vs H behavior was not observed at room temperature. Four-circle x-ray diffraction results indicate the presence of (110)-oriented hexagonal phase Co in the ZnO matrix. From the 2θ full width at half maximum (FWHM) of the Co (110) peak, the nanocrystal size is estimated to be ∼3.5 nm, which is below the superparamagnetic limit at ...

The field-dependent domain structure of epitaxial La0.7Ca0.3MnO3−δ thin films grown on a LaAlO3(001) substrate has been studied as a function of film thickness (50 and 100 nm) and oxygen content (optimum and deficient) by means of magnetic force microscopy at 5.2 K. The epitaxially grown films show a stress induced out-of-plane anisotropy. All samples exhibit a maze type domain structure at zero field. Domain size and contrast depend on film thickness. The effect of oxygen content could not clearly been determined. Field-dependent measurements were performed by ramping a perpendicular magnetic field of up to 800 mT continuously during imaging. Domain nucleation and growth takes place by discrete reorientation of regions, which have diameters similar to the final domain width.

The surface structure of an anatase Ti0.94Co0.06O2 (001) film, grown epitaxially on a Nb-doped SrTiO3 (001) substrate, was investigated using in situ scanning tunneling microscopy. For the as-grown film, a (1×n) (n=3, 4, 5, and 6) reconstructed surface was observed that shows (n−2) faint rows between adjacent bright rows. After annealing at 650 °C, nanoparticles appeared, mostly on the step edges. From the I–V curves measured by scanning tunneling spectroscopy, the tunneling gap of Co:TiO2 was estimated to be about 3.0 eV, consistent with the band gap (Eg=3.2 eV) of pure anatase TiO2. However, on nanoparticles, the I–V curve showed a much smaller gap, suggesting that the particle must be different from TiO2.

Tunneling spectra of a polycrystalline bulk ${\mathrm{HgBa}}_{2}$${\mathrm{Ca}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{8+\mathrm{\ensuremath{\delta}}}$ with ${\mathit{T}}_{\mathit{c}}$=132 K have been measured by point-contact spectroscopy using a low-temperature scanning tunneling microscope. Unlike other high-${\mathit{T}}_{\mathit{c}}$ superconductors, the conductance of this material shows a BCS-like gap structure with a relatively small smearing parameter \ensuremath{\Gamma}. Conductances with a linear density of states for \ensuremath{\Vert}eV\ensuremath{\Vert}a small cusp at the gap are also observed. From a simple calculation based on the assumption that the surface is covered with a normal layer, we explained the linear dI/dV for \ensuremath{\Vert}eV\ensuremath{\Vert}obtained two distinctively different energy gaps \ensuremath{\Delta}=48 meV and 22 meV with the resultant 2\ensuremath{\Delta}/${\mathit{k}}_{\mathit{B}}$${\mathit{T}}_{\mathit{c}}$=8.5 and 3.9, respectively.

GaMnN thin films were synthesized using gas-source molecular-beam epitaxy. Mn concentrations between 3 and 12 at. % were investigated. No evidence of second-phase formation was observed by powder x-ray diffraction or high-resolution cross section transmission electron microscopy in films with 9% or less Mn. The films were n type as determined by capacitance–voltage or Hall analysis. Magnetic characterization performed using a squid magnetometer showed evidence of ferromagnetic ordering at room temperature for all samples. In agreement with theoretical predictions, material with 3% Mn showed the highest degree of ordering per Mn atom. At 320 K, the samples show a nonzero magnetization indicating a TC above room temperature.

We report effects of heating to the intensities of Raman modes in the spectra of single-crystals embedded in ceramic YBa2Cu3O7−δ pellets, and compare the results with those from YBa2Cu3O7−δ thin-films. Heating was done by either increasing the laser-beam power or resistively heating in a heating cell. From the measurements on a single-crystal in z(xx)\(\bar z\) polarization, we find that the relative intensity of the B1g mode of the plane oxygens to that of the A1g mode of apical oxygens decreases strongly as the samples are heated. For a crystal in near x(zz)\(\bar x\) polarization, the relative intensity of the two modes increases up to certain value. In thin-films, however, no such change was observed even when heated to higher temperatures than the crystals were. Therefore, we interpret that the change in the relative intensity of the two modes of single-crystals is not due to electronic or structural changes nor thermal decomposition in the heated samples. We propose that a single-crystal, when heated, is fractured into many “micro-crystals” and these micro-crystals thermally fluctuate in orientations. For thin-films, such fluctuation in orientations might be hindered because there are only a few layers of micro-crystals on top of the substrate. Scanning electron micrographs (SEM) of the heated part of the samples seem to provide the evidence of the micro-crystals.

We report our experimental setup for the shot noise thermometry system at KRISS. Precision RF measurement setup in the frequency range of about 1 GHz has been installed in a He-3 refrigerator, which can be cooled down to 300 mK. The shot noise of Al-AlOx-Al tunnel junction, fabricated by two angle- evaporation technique, was measured and compared with theoretical curve. The inferred temperature from the noise curve agrees well with the measured temperature.

Charge trapping induced by hot carriers in a metal–oxide–semiconductor capacitor was studied with a scanning capacitance microscope (SCM). The local charge trapping/detrapping and the readout of the trapped charge in SiO2 was performed using a SCM combined with an atomic force microscope. When applying a voltage between the conductive probe tip and the p-type silicon substrate, hot carriers injected from silicon substrate into the SiO2 generated a positive trapped charge in the 10-nm-thick SiO2 layer. The resulting shift in capacitance–voltage (C–V) curves due to the locally trapped charge was measured by the high-frequency C–V measurement. For an application to the ultrahigh density data storage field, we investigated how the charge trapping and detrapping characteristics depend on the writing speed and bias voltage.

Investigating the scaling behavior of annealed ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{As}$ anomalous Hall coefficients, we note a universal crossover regime where the scaling behavior changes from quadratic to linear. Furthermore, measured anomalous Hall conductivities in the quadratic regime when properly scaled by carrier concentration remain constant, spanning nearly a decade in conductivity as well as over 100 K in ${T}_{C}$ and comparing favorably to theoretically predicated values for the intrinsic origins of the anomalous Hall effect. Both qualitative and quantitative agreements strongly point to the validity of new equations of motion including the Berry phase contributions as well as the tunability of the anomalous Hall effect.

We visualized the flux distribution of a ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ single crystal in transversal geometry by using low temperature magnetic force microscopy in the dynamic mode. With increasing external magnetic field, the magnetic flux density exhibited a distribution, which generally followed the Bean model. When the propagating flux front passed through the imaging area, we could observe a shift of the magnetic force microscopy signal toward an unexpected direction. The origin of this shift was studied by considering very long-range magnetic force due to the specific flux and current distribution near the propagating flux front.

Investigating the scaling behavior of annealed Ga1-xMnxAs anomalous Hall coefficients, we note a universal crossover regime where the scaling behavior changes from quadratic to linear. Furthermore, measured anomalous Hall conductivities in the quadratic regime when properly scaled by carrier concentration remain constant, spanning nearly a decade in conductivity as well as over 100 K in T_[C] and comparing favorably to theoretically predicated values for the intrinsic origins of the anomalous Hall effect. Both qualitative and quantitative agreements strongly point to the validity of new equations of motion including the Berry phase contributions as well as the tunability of the anomalous Hall effect.

We report on the anomalous Hall coefficient and longitudinal resistivity scaling relationships on a series of annealed Ga1-xMnxAs epilayers (x~0.055). As-grown samples exhibit scaling parameter n of ~ 1. Near the optimal annealing temperature, we find n ~ 2 to be consistent with recent theories on the intrinsic origins of anomalous Hall Effect in Ga1-xMnxAs. For annealing temperatures far above the optimum, we note n > 3, similar behavior to certain inhomogeneous systems. This observation of atypical behavior agrees well with characteristic features attributable to spherical resonance from metallic inclusions from optical spectroscopy measurements., 3 pages, 3 figures

We have developed a simple tapping mode in atomic force microscopy using a capacitive electrostatic force. In this technique, the probe‐to‐sample distance is modulated by the capacitive force between tip and sample induced by a sinusoidal bias applied to the conductive probe instead of a conventional mechanical vibration. The electrostatic force versus distance curve of the probe indicates that it is necessary to use a rather stiff cantilever to prevent the snapping of the tip into the surface due to the adhesive force at the surface. We have succeeded in obtaining topographic images of a conductive surface as well as a soft polystyrene sample with a low tracking and lateral force through this method.

We have studied the vortex structure in Bi 2 Sr 2 CaCu 2 O 8 single crystal with low-density artificial columnar defects formed by the irradiation of 1.3 GeV uranium ions by using a low-temperature magnetic force microscope.We observed that some of the topographic steps are acting as strong line pinning centers for magnetic vortices in this material. We confirmed that these line steps correspond to the stacking fault dislocations. The stacking fault dislocation showed a direction dependent pinning behavior due to the line-shape geometry of the dislocation. The movement of the vortices across the dislocation line is impeded, while the movement along the dislocation line is quite free.

Highly p-type GaAs:C was ion implanted with Mn at differing doses to produce Mn concentrations in the 1--5 at. % range. In comparison to LT-GaAs and ${n}^{+}\mathrm{GaAs}:\mathrm{Si}$ samples implanted under the same conditions, transport and magnetic properties show marked differences. Transport measurements show anomalies, consistent with observed magnetic properties and with epi-LT-(Ga,Mn)As, as well as the extraordinary Hall effect up to the observed magnetic ordering temperature ${(T}_{C}).$ Mn ion-implanted ${p}^{+}\mathrm{GaAs}:\mathrm{C}$ with as-grown carrier concentrations $g{10}^{20}{\mathrm{cm}}^{\ensuremath{-}3}$ show remanent magnetization up to 280 K.

Ferroelectric Bi4Ti3O12 thin films have been grown on MgO (100) and MgO(110) substrates by the pulsed laser deposition. X‐ray diffraction studies show that the films on both substrates have preferential crystallographic orientation such that most of their c axes are close to the substrate normal direction. The film on MgO(110) shows quadratic and hysteretic electro‐optic characteristics with the effective coefficient of about 3.8×10−15 m2/V2.

A uniform pattern of quantum dots and nanowires were reproducibly fabricated by creating holes in a two-layer structure using atomic force microscopy (AFM) indentation, dry-etching of polymer resists, and metal deposition through the indentation holes. The two-layer structure was created by depositing a thin gold layer onto a polymethyl methacrylate (PMMA) layer on a silicon substrate. The indentation depth was set so that the AFM tip penetrated the thin gold layer without the tip contacting the silicon substrate. This two-layer indentation was used to create a pattern of holes in the thin gold layer. Then, the PMMA was exposed to an isotropic O2 plasma etchant through the holes in the indentation pattern to form an undercut between the substrate and the gold layer. Quantum dots were subsequently created through the deposition of gold on the exposed silicon substrate through the indentation holes. Gold nanowires were also fabricated by creating indentation holes consecutively and optimizing the distance between the holes using the same two-layer indentation method. The topographic and electrical measurements of the fabricated gold nanowires suggest that our method is capable of making uniform and reproducible nanowires. The scanning electron microscopy images of the tips confirmed that the consecutive-hole-indentation method is less invasive than the conventional ploughing method, where constant tip contact occurs with the substrate during the formation of nanowires.

Heavily carbon-doped GaAs ( p ∼3×10 20 cm −3 ) layers were implanted with Mn ions. The structural and transport properties of the as-implanted samples were investigated using the high resolution X-ray diffraction and AC magneto-transport measurements. The results show there are no known secondary phases in the samples and indicate anomalous Hall effect at intermediate temperatures.

We present a mechanical memory device based on dynamic motion of a nanoelectromechanical (NEM) resonator. The NEM resonator exhibits clear nonlinear resonance characteristics which can be controlled by the dc bias voltage. For memory operations, the NEM resonator is driven to the nonlinear resonance region, and binary values are assigned to the two allowed states on the bifurcation branch. The transition between memory states is achieved by modulating the nonlinear resonance characteristics with dc bias voltage. Our device works at room temperature and modest vacuum conditions with a maximum operation frequency of about 5 kHz.

A detection method using a self-sensing cantilever is more desirable than other detection methods (optical fiber and laser beam bounce detection) that are bulky and require alignment. The advantage of the self-sensing cantilever is its simplicity, particularly its simple structure. It can be used for the construction of an atomic force microscopy system with a vacuum, fluids, and a low temperature chamber. Additionally, the self-actuating cantilever can be used for a high speed scanning system because the bandwidth is larger than the bulk scanner. Frequently, ZnO film has been used as an actuator in a self-actuating cantilever. In this paper, we studied the characteristics of the self-sensing and self-actuating cantilever with an integrated Wheatstone bridge circuit substituting the ZnO film with a lead zirconate titanate (PZT) film as the actuator. We can reduce the leakage current (to less than 10(-4) A/cm(2)) in the PZT cantilever and improve sensor sensitivity through a reduction of noise level from the external sensor circuit using the Wheatstone bridge circuit embedded into the cantilever. The self-sensing and actuating cantilever with an integrated Wheatstone bridge circuit was compared with a commercial self-sensing cantilever or self-sensing and actuating cantilever without an integrated Wheatstone bridge circuit. The measurement results have shown that sensing the signal to noise level and the minimum detectable deflection improved to 4.78 mV and 1.18 nm, respectively. We believe that this cantilever allows for easier system integration and miniaturization, provides better controllability and higher scan speeds, and offers the potential for full automation.