Stability of an oscillating tip in Non-Contact Atomic Force Microscopy: theoretical and numerical investigations

This paper is a theoretical and a numerical investigation of the stability of a tip-cantilever system used in Non-Contact Atomic Force Microscopy (NC-AFM) when it oscillates close to a surface. No additional dissipative force is considered. The theoretical approach is based on a variationnal method exploiting a coarse grained operation that gives the temporal dependence of the nonlinear coupled equations of motion in amplitude and phase of the oscillator. Stability criterions for the resonance peak are deduced and predict a stable behavior of the oscillator in the vicinity of the resonance. The numerical approach is based on results obtained with a virtual NC-AFM developped in our group. The effect of the size of the stable domain in phase is investigated. These results are in particularly good agreement with the theoretical predictions. Also they show the influence of the phase shifter in the feedback loop and the way it can affect the damping signal

POLA PENGGUNAAN OBAT PADA PASIEN STROKE HEMORAGIK DI RSUP PROF. DR. R.D. KANDOU MANADO PERIODE JANUARI-DESEMBER 2018

ABSTRACK Hemorrhagic stroke is a stroke caused by intracerebral hemorrhage or subarachniod hemorrhage due to rupture of cerebral blood vessels in certain areas, so that blood fills the brain tissue. The selection and use of drugs must be rational, so that treatment can achieve maximum therapy with minimal side effects. The purpose of this study was to determine the characteristics and patterns of drug use in hemorrhagic stroke patients at Prof. RSUP Dr. R.D. Kandou Manado. This study uses a descriptive method with a retrospective research design. The sample of this study were 83 patients, including 70 intracerebral hemorrhagic stroke patients and 13 subarachnoid hemorrhagic stroke patients. Patient characteristics were mostly male as many as 46 patients (55.42%) and female as many as 37 patients (44.58%). The largest age range of hemorrhagic stroke patients at the age of 55-64 years was 27 patients (32.52%). The duration of treatment with the highest prevalence was 1-5 days in 37 patients (44.57%). Hypertension is the most common comorbid disease of 60 patients (40.27%), and cholesterol of 15 patients (10.06). The pattern of drug use based on the evaluation of the right indication as many as 83 patients (100%), the right patients as many as 83 patients (100%), the right drugs as many as 82 patients (98.8%), and the right dosage of 73 patients (87.95%). Keywords: Hemorrhagic stroke, drug use ABSTRAK Stroke hemoragik adalah stroke yang disebabkan oleh perdarahan intraserebral atau perdarahan subarakhniod karena pecahnya pembuluh darah otak pada area tertentu, sehingga darah memenuhi jaringan otak. Pemilihan dan penggunaan obat harus secara rasional, sehingga pengobatan dapat mencapai terapi yang maksimal dengan efek samping minimal. Tujuan dari penelitian ini untuk mengetahui karakteristik dan pola penggunaan obat pada pasien stroke hemoragik di RSUP Prof. Dr. R.D. Kandou Manado. Penelitian ini menggunakan metode deskriptif dengan desain penelitian retrospektif. Sampel penelitian ini sebanyak 83 pasien, diantaranya terdapat 70 pasien stroke hemoragik intraserebral dan 13 pasien stroke hemoragik subarakhnoid. Karakteristik pasien sebagian besar adalah laki-laki sebanyak 46 pasien (55,42%) dan perempuan sebanyak 37 pasien (44,58%). Rentang usia pasien stroke hemoragik terbesar pada usia 55-64 tahun sebanyak 27 pasien (32,52%). Lama perawatan dengan prevalensi paling banyak, yaitu 1 – 5 hari pada 37 pasien (44,57%). Hipertensi merupakan penyakit penyerta yang paling banyak diderita sebesar 60 pasien (40,27%), dan kolestrol sebanyak 15 pasien (10,06). Pola penggunaan obat berdasarkan evaluasi tepat indikasi sebanyak 83 pasien (100%), tepat pasien sebanyak 83 pasien (100%), tepat obat sebanyak 82 pasien (98,8%), dan tepat dosis sebanyak 73 pasien (87,95%). Kata kunci : stroke hemoragik, pola penggunaan oba

Distance dependence of force and dissipation in non-contact atomic force microscopy on Cu(100) and Al(111)

The dynamic characteristics of a tip oscillating in the nc-AFM mode in close vicinity to a Cu(100)-surface are investigated by means of phase variation experiments in the constant amplitude mode. The change of the quality factor upon approaching the surface deduced from both frequency shift and excitation versus phase curves yield to consistent values. The optimum phase is found to be independent of distance. The dependence of the quality factor on distance is related to 'true' damping, because artefacts related to phase misadjustment can be excluded. The experimental results, as well as on-resonance measurements at different bias voltages on an Al(111) surface, are compared to Joule dissipation and to a model of dissipation in which long-range forces lead to viscoelastic deformations

Temperature dependence of the energy dissipation in dynamic force microscopy

The dissipation of energy in dynamic force microscopy is usually described in terms of an adhesion hysteresis mechanism. This mechanism should become less efficient with increasing temperature. To verify this prediction we have measured topography and dissipation data with dynamic force microscopy in the temperature range from 100 K up to 300 K. We used 3,4,9,10-perylenetetracarboxylic-dianhydride (PTCDA) grown on KBr(001), both materials exhibiting a strong dissipation signal at large frequency shifts. At room temperature, the energy dissipated into the sample (or tip) is 1.9 eV/cycle for PTCDA and 2.7 eV/cycle for KBr, respectively, and is in good agreement with an adhesion hysteresis mechanism. The energy dissipation over the PTCDA surface decreases with increasing temperature yielding a negative temperature coefficient. For the KBr substrate, we find the opposite behaviour: an increase of dissipated energy with increasing temperature. While the negative temperature coefficient in case of PTCDA agrees rather well with the adhesion hysteresis model, the positive slope found for KBr points to a hitherto unknown dissipation mechanism

Influence of noncontact dissipation in the tapping mode: Attempt to extract quantitative information on the surface properties with the local force probe method

In the Tapping mode, a variation of the oscillation amplitude and phase as a function of the tip sample distance is the necessary measurement to access quantitatively to the properties of the surface. In the present work, we give a systematic comparison between experimental data recorded on two surfaces, phase and amplitude, and theoretical curves. With an interaction between the tip and the surface taking into account an attractive and a repulsive term, the analytical approach is unable to properly describe the relationship between the phase variation and the oscillation amplitude variation. When an additional dissipation term is involved, due to the attractive interaction between the tip and the surface, the model gives a good agreement with the recorded data. Particularly, the trends in the phase variations related to the noncontact situations have been found to be amenable to an analysis based upon a simple viscoelastic behavior of the surface

Dynamic condensation of water at crack tips in fused silica glass

Water molecules play a fundamental role in the physics of slow crack propagation in glasses. It is commonly understood that, during stress-corrosion, water molecules that move in the crack cavity effectively reduce the bond strength at the strained crack tip and, thus, support crack propagation. Yet the details of the environmental condition at the crack tip in moist air are not well determined. In a previous work, we reported direct evidence of the presence of a 100 nm long liquid condensate at the crack tip in fused silica glass during very slow crack propagation (10^-9 to 10^-10 m/s). These observations are based on in-situ AFM phase imaging techniques applied on DCDC glass specimens in controlled atmosphere. Here, we discuss the physical origin of the AFM phase contrast between the liquid condensate and the glass surface in relation to tip-sample adhesion induced by capillary bridges. We then report new experimental data on the water condensation length increase with relative humidity in the atmosphere. The measured condensation lengths were much larger than what predicted using the Kelvin equation and expected geometry of the crack tip.Comment: Accepted in JNCS. In pres

Analytical Approach to the Local Contact Potential Difference on (001) Ionic Surfaces: Implications for Kelvin Probe Force Microscopy

An analytical model of the electrostatic force between the tip of a non-contact Atomic Force Microscope (nc-AFM) and the (001) surface of an ionic crystal is reported. The model is able to account for the atomic contrast of the local contact potential difference (CPD) observed while nc-AFM-based Kelvin Probe Force Microscopy (KPFM) experiments. With the goal in mind to put in evidence this short-range electrostatic force, the Madelung potential arising at the surface of the ionic crystal is primarily derived. The expression of the force which is deduced can be split into two major contributions: the first stands for the coupling between the microscopic structure of the tip apex and the capacitor formed between the tip, the ionic crystal and the counter-electrode; the second term depicts the influence of the Madelung surface potential on the mesoscopic part of the tip, independently from its microscopic structure. These short-range electrostatic forces are in the range of ten pico-Newtons. When explicitly considering the crystal polarization, an analytical expression of the bias voltage to be applied on the tip to compensate for the local CPD, i.e. to cancel the short-range electrostatic force, is derived. The compensated CPD has the lateral periodicity of the Madelung surface potential. However, the strong dependence on the tip geometry, the applied modulation voltage as well as the tip-sample distance, which can even lead to an overestimation of the real surface potential, makes quantitative KPFM measurements of the local CPD extremely difficult

Observation of individual molecules trapped on a nanostructured insulator

For the first time, ordered polar molecules confined in monolayer-deep rectangular pits produced on an alkali halide surface by electron irradiation have been resolved at room temperature by non-contact atomic force microscopy. Molecules self-assemble in a specific fashion inside pits of width smaller than 15 nm. By contrast no ordered aggregates of molecules are observed on flat terraces. Conclusions regarding nucleation and ordering mechanisms are drawn. Trapping in pits as small as 2 nm opens a route to address single molecules

Canopy precipitation interception in a lowland tropical forest in relation to stand structure

It is generally accepted that vegetation provides important ecosystem services especially in term of rainfall partitioning. This study aims to evaluate the influence of canopy structure namely crown area (CA), diameter at breast height (DBH), tree height (TH) and crown spread (CS) and stand density on the partitioning of rainfall. Twelve throughfall plots of 20 x 20 m with 64 gauges randomly placed within each plot were established. For stemflow measurements, all trees within a 100 m2 plot within the study area were collared. Interception loss was computed as the difference between precipitation and throughfall plus stemflow. Throughfall ranged from 73.47 - 82.32 % of the gross rainfall. Stemflow was found to be roughly around 2.01% of the gross rainfall. Highest interception was 24.52 % attributed to the plot having the highest above ground biomass (AGB) density. The relation between canopy interception and forest structure were analyzed by regression method. Multiple regression analysis on the potential influence of stand structure to the throughfall percentage shows that all the forest structures variables measured in this study are negatively correlated to the amount of throughfall generated. This study suggests that forests with higher value of DBH, CA, CS and TH had higher interception rate