SPM Tip Research Articles

Interaction of wedge-like domains created by local polarization reversal on nonpolar cut of lithium niobate

The formation of stripe domains as a result of domain merging during local switching by a conductive SPM tip on Y cut of lithium niobate doped by MgO was studied. The stripe domains with proper length can be created by application of a positive voltage pulse after a negative one in the point displaced on a certain distance in Z + direction. The length of the stripe domain is exactly limited by the distance between the points of voltage application. The creation of periodical structures of the stripe domains with 1 μm period and 0.5 duty cycle was demonstrated.

Decay of domains created by local switching on non-polar cut of MgO doped LiNbO3 single crystals

Decay of isolated wedge-like domains with charged domain walls during local switching by a biased SPM tip on non-polar cut of lithium niobate doped by MgO was studied using piezoresponse force microscopy. It was found that domain imaging led to domains length reduction, whereas domain width did not change. Domain decay without scanning was also revealed. All the obtained effects were attributed to influence of injected charges, residual depolarization field, and AC voltage. Spatial distribution of electric field near SPM tip was simulated numerically. The obtained results provide new understanding of domain decay problem for nanodomain engineering.

Self-Organized Formation of Quasi-Regular Ferroelectric Nanodomain Structure on the Nonpolar Cuts by Grounded SPM Tip.

The understanding of self-organization processes at the micro- and nanoscale is of fundamental interest and is important to meet the great challenges in further miniaturization of electronic devices to the nanoscale. Here, we report self-organized quasi-regular nanodomain structure formation on the nonpolar cut of a ferroelectric lithium niobate single crystal. These structures were formed along the trajectory of grounded scanning probe microscope tip approaching or moving away from the freshly switched region. Detailed analysis of the formed structures revealed internal organization by the length of the needle-like domains, which ranged from uniform to quasi-periodic and even chaotic modes as a function of distance from the switched region. Comprehensive investigations and numerical simulations allowed to attribute explored phenomena to charge injection during the field application and further switching under the action of electric field induced by injected charges near the tip. Self-organization and quasi-periodicity were explained by the effective screening and long-range electrostatic interaction between the individual needle-like domains.

Vacuum scanning capillary photoemission microscopy

We demonstrate the use of a conical capillary in a scanning probe microscopy for surface analysis. The probe can measure photoemission from a substrate by transmitting photoelectrons along the capillary as a function of probe position. The technique is demonstrated on a model substrate consisting of a gold reflecting layer on a compact disc which has been illuminated by an unfocused laser beam with a wavelength 400nm, from a femtosecond laser with a beam size of 4mm. A quartz capillary with a 2-µm aperture has been used in the experiments. The period of gold microstructure, shown to be 1.6µ, was measured by the conical probe operating in shear force mode. In shear force regime, the dielectric capillary has been used as a “classical” SPM tip, which provided images reflecting the surface topology. In a photoelectron regime photoelectrons passed through hollow tip and entered a detector. The spatial distribution of the recorded photoelectrons consisted of periodic mountain-valley strips, resembling the surface profile of the sample. Submicron spatial resolution has been achieved. This approach paves the way to study pulsed photodesorption of large organic molecular ions with high spatial and element resolution using the combination of a hollow-tip scanner with time-of-flight technique.

Chemical State Evolution in Ferroelectric Films during Tip-Induced Polarization and Electroresistive Switching.

Domain formation and ferroelectric switching is fundamentally inseparable from polarization screening, which on free surfaces can be realized via band bending and ionic adsorption. In the latter case, polarization switching is intrinsically coupled to the surface electrochemical phenomena, and the electrochemical stage can control kinetics and induce long-range interactions. However, despite extensive evidence toward the critical role of surface electrochemistry, little is known about the nature of the associated processes. Here we combine SPM tip induce polarization switching and secondary ion mass spectrometry to explore the evolution of chemical state of ferroelectric during switching. Surprisingly, we find that even pristine surfaces contain ions (e.g., Cl-) that are not anticipated based on chemistry of the system and processing. In the ferroelectric switching regime, we find surprising changes in surface chemistry, including redistribution of base cations. At higher voltages in the electroforming regime significant surface deformation was observed and associated with a strong ion intermixing.

Diamond as Advanced Material for Scanning Probe Microscopy Tips

AbstractSynthetic diamond and conductive, doped forms of diamond are ideally suited materials for scanning probe microscopy tips due to their inherent physical, chemical, and mechanical properties. In particular for atomic force microscopy (AFM) and related techniques, which require a conductive tip in permanent contact to the sample surface, boron‐doped diamond (BDD) is an excellent material. Only few examples have so far been demonstrated using boron‐doped diamond microelectrodes as probes for scanning electrochemical microscopy (SEM) or AFM‐SECM. This review focuses on the state‐of‐the‐art using diamond‐coated SPM tips and conductive boron‐doped diamond as probe material discussing advantages and disadvantages.

Framed carbon nanostructures: synthesis and applications in functional SPM tips.

We present a synthesis method to fabricate framed carbon-based nanostructures having highly anisotropic shapes, in particular, the nanofork and nanoscalpel structures which are obtained systematically under optimized growth conditions. A theoretical model is developed to explain the formation of such nanostructures on Si cantilevers and W etched wires exposed to a focused electron beam. We then demonstrate the potentials of these nanostructures as functional tips for scanning probe microscopy. Owing to their anisotropic shapes, such tips can be very useful for nanolithography, nanosurgery of biological objects, and precise manipulation with surface particles. Overall, our method provides a simple and robust way to produce functional scanning probe microscopy tips with variable shapes and enhanced capabilities for different applications compared to standard cantilevers.

Optical near-field excitation at commercial scanning probe microscopy tips: a theoretical and experimental investigation

A systematic study of the influence of the excitation angle, the light polarization and the coating thickness of commercial SPM tips on the field enhancement in an apertureless scanning near-field optical microscope is presented. A new method to optimize the alignment of the electric field vector along the major tip axis by measuring the resonance frequency was developed. The simulations were performed with a MNPBEM toolbox based on the Boundary Element Method (BEM). The influence of the coating thickness was investigated for the first time. Coatings below 40 nm showed a drastic influence both on the resonance wavelength and the enhancement. A shift to higher angles of incidence for the maximum enhancement could be observed for greater tip radii.

An analytical approach for scanning probe microscope-tip electrostatic field distribution accounting for dead layer and domain wall

We have proposed a new theoretical approach for the determination of the electric field distribution in the ferroelectric/dielectric system with the presence of the SPM tip. The initial statement of the model has only a numerical solution. To find an analytical solution of the problem, some assumptions are introduced: the domain wall thickness can be considered to be much smaller than the domain size, and we use a high ferroelectric dielectric permittivity. The developed approach allows us to obtain explicit formulas for the polarization and electric field intensity. We have calculated and then analyzed the tip capacitance as a function of the distance from the ferroelectric interface. Additionally, different forms of the SPM tip are considered. It is demonstrated that in the presence of charges at the domain, the results differ from those obtained with the widely used dielectric model by 30%.

Toward Mechanosynthesis of Diamondoid Structures: X. Commercial Capped CNT SPM Tip as Nowadays Available C2 Dimer Placement Tool for Tip-Based Nanofabrication

Toward Mechanosynthesis of Diamondoid Structures: X. Commercial Capped CNT SPM Tip as Nowadays Available C2 Dimer Placement Tool for Tip-Based Nanofabrication

Account for Mutual Influence of Electrical, Elastic, and Thermal Phenomena for Ferroelectric Domain Wall Modeling

The theoretical model of the ferroelectric domain wall motion has been developed. It is demonstrated that for a proper phenomenon description it is necessary to consider the thermoelectroelasticity gradient terms. It is shown that in the linear approximation the general solution of three-dimensional problem in transversely isotropic thermoelectroelastic media can be obtained by means of five newly introduced harmonic potential functions. As an example of the proposed model applicability, the electroelastic field induced by a sphere (SPM tip) located near a plane boundary of two half-spaces is considered and described.

Toward Mechanosynthesis of Diamondoid Structures: VII. Simple Strategy of Building Atomically Perfect SPM Tip Through Attachment of C60 Molecule to Commercial Silicon Tip by Controlled Hydrogen Atom Desorption from Tip Asperity Si(111) Silicon Surface

Toward Mechanosynthesis of Diamondoid Structures: VII. Simple Strategy of Building Atomically Perfect SPM Tip Through Attachment of C<SUB>60</SUB> Molecule to Commercial Silicon Tip by Controlled Hydrogen Atom Desorption from Tip Asperity Si(111) Silicon Surface

Shape of Local Hysteresis Loops Measured by Means of Piezoresponse Force Microscopy

Shape of local hysteresis loops was studied by scanning probe microscopy using pulsed and in-field modes. Intermediate states on the loops measured in pulsed mode were revealed and explained by partial backswitching in the area under SPM tip. The obtained slope of the loops measured in the in-field mode was explained taking into account the interaction between two types of charges: induced in sample by switching voltage and in cantilever by modulation voltage. Dependence of loops slope on the position of the laser spot on the cantilever was found. Computer simulation was used for explanation of the observed data.

Fabrication of sub-100 nm conducting polyaniline wire on a polymer substrate based on friction nanolithography

Friction Nanolithography (FRNL) is used to fabricate polyaniline nano-wire on a flexible, insulating, and highly transparent substrate. FRNL uses SPM tip to scratch the substrate to form a trench with higher friction force. Polyaniline nano-wire is selectively deposited on the trench. Sub-100 nm polyaniline wire is fabricated based on FRNL.

Self-assembled polystyrene nanospheres for the evaluation of atomic force microscopy tip curvature radius

In this paper, self-assembled polystyrene nanospheres are proposed as a shape characterizer sample for SPM tips. Ordered arrays or 2D islands of polystyrene spheres may be prepared either by sedimentation or by crystallization of the colloidal spheres' suspension. The self-assembling mechanism guarantees high reproducibility; thus the characterizer sample can be ‘freshly’ prepared at each use, avoiding the problem of time and use deterioration and reducing the problem of sample structure fidelity that occurs when lithographic structures are employed. The spheres could also be deposited on the sample itself in order to speed up the characterization process in applications requiring frequent tip characterizations. We present numerical calculations of geometrical convoluted profiles on the proposed structures showing that, for a variety of different tip shapes, at the border between a couple of touching spheres the tip flanks do not come into contact with the spheres. Due to this behaviour, touching spheres are an optimum characterizer sample for SPM tip curvature radius characterization, enabling a straightforward procedure for calculating the curvature radius from the amplitude of tip oscillation along profiles connecting spheres' centres. The new procedure for the characterization of SPM probes was assessed exploiting different kinds of self-assembled structures and comparing results to those obtained by spiked structures and SEM observations.

Micro fabrication by electrochemical process in citric acid electrolyte

This paper describes micro electrochemical machining of stainless steel in an environmentally friendly electrolyte of citric acid. Electrochemical dissolution region is minimized by applying a few hundred nanosecond duration pulses between the tungsten SPM tip and the work material. Electrochemical machining (ECM) characteristics according to citric acid concentration, feed speed and electric conditions such as pulse amplitude, pulse frequency, and tool electrode baseline potential are investigated through a series of experiments. Micro holes of 60 μm in diameter with the depth of 50 μm and 90 μm in diameter with the depth of 100 μm are perforated using citric acid electrolyte. Square and circular micro cavities are also fabricated by electrochemical milling. This research may contribute to the development of safe and eco-friendly micro manufacturing technology.

Modification and Characterization of Metallized Tips for Scanning Probe Microscopy

Abstract The characterization of nanoscale regions in present and future device structures of leading-edge microelectronic products requires probes with dedicated features tailored on the nanoscale. SPM tips are used not only for conventional AFM characterization, but also for electrical, thermal and optical investigation of devices. For particular applications as nano-Raman spectroscopy or conductive AFM, highly reproducible metal tips or metallized tips are needed. In this paper, new approaches to tailor those tips using the FIB technique, and to characterize the tips using dedicated structures and adapted AFM methods are described. Based on a numerical procedure, the tip quality is described quantitatively. The described preparation and calibration techniques offer new possibilities for the routine application of nanostructures and nanodevices as needed for advanced SPM techniques and nanosensors.

One-Step Polymer Grafting from Silicon Nitride SPM Probes: From Isolated Chains to Brush Regime

We show that a reactive polymer can be directly grafted from commercial Si3Nx SPM tips, without any intermediate layer. The conditions can be chosen to achieve either an isolated mushroom regime, with only one or a few chains accessible at the tip apex, or a brush regime.

Ss-LrpB from Sulfolobus solfataricus Condenses about 100 Base Pairs of Its Own Operator DNA into Globular Nucleoprotein Complexes

Ss-LrpB from the hyperthermoacidophilic crenarchaeote Sulfolobus solfataricus P2 is a member of the Lrp-like family of Bacterial/Archaeal transcription regulators that binds its own control region at three regularly spaced and partially conserved 15-bp-long imperfect palindromes. We have used atomic force microscopy to analyze the architecture of Ss-LrpB.DNA complexes with a different stoichiometry formed with the wild type operator and with an operator mutant. Binding of dimeric Ss-LrpB to all three target sites is accompanied by the formation of globular complexes, in which the protein induces strong DNA deformations. Furthermore, DNA contour length foreshortening of these complexes indicates DNA wrapping, with about 100 bp being condensed. The average bending angle is 260 degrees . The establishment of protein-protein contacts between Ss-LrpB dimers in these globular complexes will contribute to the cooperativity of the binding. The profound remodeling of the control region is expected to have a strong impact on gene expression and might constitute the key element in the autoregulatory process.

Observation of Ge2Sb2Te5 thin film phase transition behavior according to the number of cycles using Transmission Electron Microscope and Scanning Probe Microscope

ABSTRACTRecently, the development of information technology (IT) increases the demands of memory devices. Phase change random access memory (PRAM), based on the reversible phase change of the chalcogenide alloy, Ge2Sb2Te5, is widely regarded as a favourite candidate for the next generation memory. Because of PRAM has a simple cell structure with high scalability; it is non-volatile, has a relatively high read/write operation speed (Â50ns). The PRAM operation relies on the fact that chalcogenide-based materials can be reversible switched from an amorphous phase to a crystalline state by an external electrical current. It is important to study the electrical property with set/reset cycles, since film thickness shrinkage occurs with the phase transition.In this work, we fabricated the 100nm amorphous Ge2Sb2Te5 thin film on TiN/Ti/Si substrate using dc-magnetron sputtering. The 50X50§2 isolated Ge2Sb2Te5 cell was lithographed by the lift-off pattern and wet etching. And TiN top electrode was deposited using pattern align process at room temperature after the SiO2 insulator CMP. Phase transition behavior with the set/reset cycle was observed using I-V measurement and transmission electron microscope (TEM) on isolated Ge2Sb2Te5 cell. The set/reset programming was operated using tungsten SPM tip which was fabricated using focused ion beam (FIB) lithography. I-V curve which was observed by the I-V probe clearly showed that the phase transition was occurred by applying the electric field through the I-V probe. The resistivity difference between amorphous and crystal state was more than 102. After the phase transition, it was also demonstrated with transmission electron microscope (TEM) analysis. For the preparation of TEM specimen of the amorphous and crystalline cell, focused ion beam (FIB) lithography was adopted.