Surface Potential Images Research Articles

Regulation of the Surface Potential of Silicon Substrates in Micrometer Scale with Organosilane Self-Assembled Monolayers

Microstructures composed of two types of organosilane self-assembled monolayers (SAMs) terminated with different functional groups have been constructed on silicon substrates covered with native oxide. Surface potential images of these microstructures were acquired by Kelvin-probe force microscopy (KFM). By chemical vapor deposition (CVD), the SAMs were fabricated from n-octadecyltrimethoxysilane (ODS) [H3C(CH2)17Si(OCH3)3], fluoroalkylsilane (FAS), that is, heptadecafluoro-1,1,2,2-tetrahydro-decyl-1-trimethoxysilane [F3C(CF2)7(CH2)2Si(OCH3)3], and n-(6-aminohexyl)aminopropyltrimethoxysilane (AHAPS) [H2N(CH2)6NH(CH2)3Si(OCH3)3]. Through a photolithographic technique, binary microstructures consisting of ODS/FAS and ODS/AHAPS were constructed. A surface potential contrast of the two SAMs in each of the binary microstructures was clearly detected by KFM. The surface potential of the FAS-terminated region was ca. 180 mV lower than that of the ODS-terminated region, while the potential of the AHAPS-terminated...

Surface potential images of self‐assembled monolayers patterned by organosilanes: ab initio molecular orbital calculations

AbstractSelf‐assembled monolayers (SAMs) with different function terminal groups were prepared on substrates of n‐type silicon by chemical vapour deposition (CVD) from n‐octadecyltrimethoxysilane (ODS: H3C(CH2)17Si(OCH3)3), heptadecafluoro‐1,1,2,2‐tetrahydro‐decyl‐1‐trimethoxysilane (FAS: F3C(CF2)7 (CH2)2Si(OCH3)3), n‐(6‐aminohexyl)aminopropyltrimethoxysilane (AHAPS: H2N(CH2)6NH(CH2)3 Si(OCH3)3) and 4‐(chloromethyl)phenyltrimethoxysilane [CMPS: H2ClC(C6H4)Si(OCH3)3]. The sample surfaces covered with ODS‐SAM were irradiated under a reduced pressure of 10 Pa with vacuum ultraviolet (VUV) light through a photomask. Then, the irradiated areas with the ODS‐SAM removed were covered with another SAM by CVD. Surface potential images of the patterned areas were measured by Kelvin probe force microscopy (KPFM) and explained by ab initio molecular orbital (MO) calculations. The KPFM measurements showed that the surface potential contrasts of the FAS‐, AHAPS‐ and CMPS‐SAMs against the ODS‐SAM were about −170, +50 and −30 mV, respectively. The surface potentials as a function of area occupied by a molecule were predicted using the respective dipole moments perpendicular to substrates, which were obtained by the ab initio MO calculations. The predicted surface potentials of the FAS‐, CMPS‐ and AHAPS‐SAMs approximately agreed with the measured values at areas of about 1.5, 1.6 and 0.6 nm2 per molecule. The ab initio MO calculations also showed differences in surface potentials appearing due to the differences in Fermi levels of the respective SAMs. Copyright © 2002 John Wiley & Sons, Ltd.

Surface Potential Nanopatterning Combining Alkyl and Fluoroalkylsilane Self-Assembled Monolayers Fabricated via Scanning Probe Lithography

A coplanar nanostructure composed of two types of organosilane molecules has been fabricated by a method that combines scanning probe lithography and molecular self-assembly. Regulation of the surface potential on the nanometer scale is focussed on and investigated using Kelvin-probe force microscopy (see Figure for a surface potential image).

Imaging mechanism of piezoresponse force microscopy of ferroelectric surfaces

In order to determine the origin of image contrast in piezoresponse force microscopy (PFM), analytical descriptions of the complex interactions between a small tip and ferroelectric surface are derived for several sets of limiting conditions. Image charge calculations are used to determine potential and field distributions at the tip-surface junction between a spherical tip and an anisotropic dielectric half plane. Methods of Hertzian mechanics are used to calculate the response amplitude in the electrostatic regime. In the electromechanical regime, the limits of strong (classical) and weak (field-induced) indentation are established and the relative contributions of electroelastic constants are determined. These results are used to construct ``piezoresponse contrast mechanism maps'' that correlate the imaging conditions with the PFM contrast mechanisms. Conditions for quantitative PFM imaging are set forth. Variable-temperature PFM imaging of domain structures in ${\mathrm{BaTiO}}_{3}$ and the temperature dependence of the piezoresponse are compared with Ginzburg-Devonshire theory. An approach to the simultaneous acquisition of piezoresponse and surface potential images is proposed.

The elimination of the ‘artifact’ in the electrostatic force measurement using a novel noncontact atomic force microscope/electrostatic force microscope

We investigate the ‘artifact’ included in Kelvin probe force microscopy (KPFM). We theoretically show that the artifact due to the applied AC field cannot be canceled by conventional KPFM and that the artifact signal can be detected from the force signal through the second harmonic component of AC field. We made an experiment to simultaneously obtain the topography, the spatial distribution of the surface potential and the artifact signal on Si(1 1 1) surface using our noncontact atomic force microscope (NC-AFM). The result indicates that topography includes the artifact signal and that the surface potential image reflects the charge density of Si adatoms. We propose the novel method to completely eliminate the artifact due to the electrostatic force.

Imaging Transport Disorder in Conducting Arrays of Metallic Quantum Dots: An Experimental and Computational Study

Surface potential imaging (see Figure) reveals the transition to collective behavior in a two-dimensional quantum dot solid. As described in this communication, an electrical potential gradient is applied across the film, and various scanning probe and electron microscopy images are correlated to interrogate the role of disorder in the transition from local to collective behavior.

New approaches to the imaging of surface potentials

Towards the goal of recording and analysing the elastically filtered intensity of 4–50 keV electrons within the two-dimensional reflection rocking curves (convergent-beam RHEED patterns), preliminary experiments with a one-dimensional serial energy filter have been performed. Zero-loss and plasmon-loss filtered linescans through the specular disc of a CB-RHEED pattern from the Si(001)-2 × 1 surface at 4 kV are shown and compared with dynamical calculations. Energy-filtered detection of CB-RHEED patterns is necessary for quantitative analysis of the surface potential.

Critical Temperature and LE/G Phase Transitions in Monolayer Films of the Amphiphilic TEMPO Derivatives at the Air/Water Interface

Phase behavior of five members of a homologous series of 4-alkaneamido-2,2,6,6-tetramethyl-1-piperidinyloxy (CnTEMPO with n = 14, 16, 18, 20, 22) was investigated with classical Langmuir monolayer techniques and with Brewster angle microscopy and 2D voltammetry. Surface potential data, BAM images, and 2D voltammetry showed that only C20- and C22TEMPO monolayers have a 2D LE/G critical point above room temperature and that the remaining three compounds with shorter alkane chains form supercritical monolayers. The unusually low values of the critical temperature for these amphiphiles was explained in terms of the molecular structure of their headgroup featuring two polar groups (the nitroxy and the amide moieties) located in the opposite positions of a bulky piperidine ring. The presence of the two polar groups causes a change of orientation of the headgroup during monolayer expansion and results in a substantial increase (ca. 50−100 Å2/molecule) of the cross sectional area of these amphiphiles. As a result, in the expanded monolayers, the van der Waals attraction between the alkane chains is weakened as they can only partially align. The decreased cohesion within the monolayers leads to the observed decrease of their 2D critical temperature. Analysis of the plots of BAM reflected light intensity as a function of amphiphile's surface concentration obtained at different temperatures yielded the C20TEMPO critical temperature of 28 °C. BAM and 2D voltammetry can both be used to precisely determine the position of the C22TEMPO LE/G phase transition (98.5 Å2/molecule at 23.5 °C). The proximity of the C20TEMPO critical point to the room-temperature results in a less precise value of this phase transition (127−130 Å2/molecule at 23.5 °C). A remarkably consistent ability of fresh line microelectrodes used in 2D voltammetry to nucleate the 2D gas phase makes this method less ambiguous and thus superior to BAM in determining the position of the LE/G phase transitions.

Near-field fluorescence imaging and simultaneous observation of surface potentials.

We present a new detection method to measure simultaneously surface potential and fluorescence intensity distributions using a combined scanning near-field optical microscope-atomic force microscope (SNOM-AFM). A surface potential image of phospholipid monolayers was obtained in non-contact mode using the SNOM-AFM with a thin-step etched optical fibre probe. For applying this technique, a phospholipid of dipalmitoylphosphatidylethanolamine labelled at the head with a nitrobenzoxadiazole group was used as a fluorescent and single component Langmuir-Blodgett film. It is well known that aggregation of the lipid molecules and their fluorescence intensities are very sensitive to its environmental conditions such as humidity and temperature. We demonstrated for the first time the near-field optical imaging and simultaneous observation of surface potentials with Maxwell stress microscopy.

Ion Irradiation Effect on the Microscopic Potential Distribution of MgO Surface

The microscopic surface potential images of ion-bombarded MgO films, as a model of the protecting layer of a plasma display panel (PDP) in operation, are observed for the first time with a scanning Maxwell-stress microscope. From the obtained images and their temporal variations, we find that ion bombardment induces the uniform shift and the speckled distribution of the MgO surface potential, which are considered to be due to weakly bound and strongly trapped charges, respectively. The results indicate that ion bombardment causes the modification of the local electronic structure and the huge electric patch field near the surface.

Electrical Features of Surface Structure in Polymer Monolayers by Smm

Recent development in scanning probe microscope techniques has made it possible to investigate, not only microscopic surface topography, but also physical and chemical properties on the nanometer-scale. We observed the surface potential distribution and molecular ordering in monolayers. The SMM surface potential image clearly shows the existence of micron-sized domains in the polymer monolayers with a good correspondence to the topographical features. This is a first step towards understanding electrical phenomena in organic and inorganic materials with SMM.

Surface potential measurement of self-assembled InAs dots by scanning Maxwell stress microscopy

We have imaged surface potential of InAs self-assembled quantum dots on GaAs (001) surface by scanning Maxwell stress microscopy. Simultaneously obtained constant tip–sample capacitance image and surface potential image were compared with atomic force microscope (AFM) image, and was found that the surface potential on large dots of about 100-nm diameter is ∼610mV which is 30–40 mV lower than that on regular size dots. This result well coincides with previously reported Schottky barrier heights which were estimated from current versus voltage measurements with the same type of samples using conductive probe AFM.

Spatially localized dynamic properties of individual interfaces in semiconducting oxides

Local electronic property variations at individual interfaces have been determined using scanning surface potential microscopy, a variant of atomic force microscopy in conjunction with locally applied electric fields. Micropatterning is used to isolate individual interfaces and position contacts so that biases can be controlled locally. Positional variations in the voltage dependent interface charge and density of states in polycrystalline zinc oxide are determined from surface potential imaging.

Nanometer‐Scale Variations in Interface Potential by Scanning Probe Microscopy

The local electrical potential at individual grain boundaries and the potential distributions across polycrystalline samples have been measured by using scanning surface potential imaging with an atomic force microscope. Individual grain boundaries are isolated for measurement by micropatterning an array of contacts onto the surface of a ZnO‐based varistor material. Quantification of the voltage dependence of the local voltage decrease and resistivity is illustrated. Comparisons are made by using optical and electron microscopy and spectroscopy. On a larger scale, potential distributions are mapped in a polycrystalline ZnO‐NiO system that exhibits positive temperature coefficient of resistivity behavior.

Investigation of Surface Potential of Ferroelectric Organic Molecules by Scanning Probe Microscopy

The surface potential of ferroelectric copolymer films of vinylidene fluoride and trifluoroethylene was investigated by scanning probe microscopy. The results reveal that the as-deposited copolymer films on a graphite substrate show a negative surface potential. The surface potential is ascribed to the substrate-induced effect, which causes frozen dipoles in the copolymer films. We made locally poled areas in the films using a conductive cantilever tip and measured the piezoelectric response of the films with a modified scanning force microscope. The observed asymmetric behavior of the piezoelectric response of the thin films can be consistently explained by the frozen ferroelectric layer in the films. Both surface potential and piezoresponse images of locally polarized areas were also obtained. The results indicate that the charge transferred from the tip overcompensated for the oriented dipoles and that the surface potential of the poled regions was attributed to the excess charge.

Measuring and modifying the electric surface potential distribution on a nanometre scale: a powerful tool in science and technology

The combination of atomic force microscopy (AFM) and Kelvin probe technology is a powerful tool to obtain high-resolution maps of the electric surface potential distribution on conducting and non-conducting samples. We show that potential maps of composite metal films and semiconductors show a clear chemical contrast and can be used to differentiate between different materials with a lateral resolution of a few 10 nm. Because AFM tips are not point-like structures, we establish a simple model to correlate the measured quantities with the true surface potential distribution, and compare numerical simulations of the three-dimensional tip-specimen model with experimental data from test structures. For the first time, we combine the electrostatic surface potential and the topography data to derive the local electrostatic field strength on active transistors. Using suitable substrates, trapped surface charges can be generated by applying short voltage pulses between the tip and the sample surface. These surface charges can be detected in the electric surface potential image and might be used as bits in new data storage systems or as target sites in self-assembly processes.

Characterization of Ferroelectric BaTiO3 (100) Surfaces by Variable Temperature Scanning Surface Potential Microscopy and Piezoresponse Imaging

AbstractVariable temperature atomic force microscopy (AFM), scanning surface potential microscopy (SSPM) and piezoresponse imaging were applied to the characterization of a model BaTiO3(100) surface. The influence of the domain structure on surface topography, surface potential and piezoresponse image is discussed. The domain induced surface corrugations and piezoelectric response were found to disappear above the Curie temperature in full agreement with theoretical expectations. Relaxation of apparent surface potential after the transition to paraelectric state on heating and during the transition to ferroelectric state on cooling was observed. The kinetics of potential relaxation was orders of magnitude slower than that of the transition.

3PD056 電気化学走査型マックスウエル顕微鏡を用いた表面電位分布イメージング

3PD056 電気化学走査型マックスウエル顕微鏡を用いた表面電位分布イメージング

High Voltage and High Resolution Surface Potential Imaging using Scanning Electrostatic Force Microscope

A newly developed technique for high voltage surface potential imaging having high resolution capability using Scanning Electrostatic Force Microscope(SEFM) is described. It can measure both electrostatic surface potential distribution of several hundred volts on the dielectric film and topography independently and simultaneously in high resolution of some tens of μm, in the air, quantitatively and without affecting charge distribution. The result of measuring surface potential distribution formed by spark discharge on a dielectric film is shown and compared to the results by a conventional electrostatic voltmeter and by toner method.

Surface potential imaging for magnetoresistive head development

We demonstrate the first applications of scanning surface potential microscopy to magnetoresistive (MR) thin-film devices. Images are presented on active devices showing 2D maps of the surface potential of energized MR read-head stripes taken from the production line at the puck level. We have found that surface potential line scans (voltage vs. distance) along MR spin valve stripes show slight deviations from linearity, possibly due to nonuniform film magnetization along the length of the stripe.