Atomic Force Microscope Profiler Research Articles

Reconstructing Local Profile of Exciton-Emission Wavelengths across a WS2 Bubble beyond the Diffraction Limit.

Air bubbles formed between layers of two-dimensional (2D) materials not only are unavoidable but also emerge as an important means of engineering their excitonic emission properties, especially as controllable quantum light sources. Measuring the actual spatially resolved optical properties across such bubbles is important for understanding excitonic physics and for device applications; however, such a measurement is challenging due to nanoscale features involved which require spatial resolution beyond the diffraction limit. Additional complexity is the involvement of multiple physical effects such as mechanical strain and dielectric environment that are difficult to disentangle. In this paper, we demonstrate an effective approach combining micro-photoluminescence measurement, atomic force microscope profile mapping, and a theoretical strain model. We succeeded in reconstructing the actual spatial profiles of the emission wavelengths beyond the diffraction limit for bubbles formed by a monolayer tungsten disulfide on boron nitride. The agreements and consistency among various approaches established the validity of our approach. In addition, our approach allows us to disentangle the effects of strain and dielectric environment and provides a general and reliable method to determine the true magnitude of wavelength changes due to the individual effects across bubbles. Importantly, we found that micro-optical measurement underestimates the red and blue shifts by almost 5 times. Our results provide important insights into strain and screening-dependent optical properties of 2D materials on the nanometer scale and contribute significantly to our understanding of excitonic emission physics as well as potential applications of bubbles in optoelectronic devices.

Study of interface reactions between Ti/Al/Ni/Au metallization and AlGaN/GaN heterostructures

Abstract The electrical characteristics, and the range of interface metal-semiconductor reactions of Ti/Al/Ni/Au metallization with AlGaN/GaN heterostructures at various annealing temperatures ranging from 715°C to 865°C, have been investigated. The relation between the depth of the interface solid state reaction and the current-voltage (I-V) characteristics of the ohmic contact, have been studied. It was observed, that the transition from nonlinear to linear I-V behaviour occurred after the annealing at 805°C. The structural changes in AlGaN/GaN heterostructures beneath the metallic contact after the thermal treatment, were investigated. After removing the metallization by etching, the atomic force microscope profiles and scanning electron microscope images, were studied to define the depth to which the interfacial solid state reactions between the metallization and the semiconductor structure take place. It was observed, that the changes in the heterostructures, caused by the interface m-s reactions, were observed up to a depth of 180 nm at 865°C. In the worst case, this could result in the complete removal of the two-dimensional electron gas under the metallization of the ohmic contacts. To study the influence of the annealing process parameters on the properties of the two-dimensional electron gas, the van der Pauw Hall mobility measurement was performed.

Surface modification of cyclic olefin copolymer substrate by oxygen plasma treatment

Cyclic olefin copolymer (COC) substrate surface was modified by plasma treatment under oxygen atmosphere. The surface properties were evaluated by contact angle measurement, atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS). It was found that the surface acquired oxygen containing polar functional groups such as C–O, C = O, which increased in number as the plasma treatment time increased. As revealed by AFM profile, these changes were accompanied by a slightly increase in roughness. The adhesive ability between the coating layer (ITO) and the COC surface can be improved after optimum plasma treating procedure, which can be proofed by the optical microscope observation after boiling test.

Tribological modification of metal counterface by rubber

Sulphur vulcanizates of styrene-budadiene rubber (SBR) filled with 80 phr of silica were rubbed extensively against iron Armco or magnesium alloy (AZ 31), and chemical modification of the surface layer of metals studied. Secondary Ion Mass Spectrometer (s-SIMS) spectra revealed fragments containing sulphur. Also Raman spectra, obtained with the surface focused confocal microscope, apart metal oxides, contained absorption peaks indicated on metal sulfides and sulfates. Depth of the modification, calculated from Atomic Force Microscope profiles of ion-etched samples (s-SIMS depth profiling) reached several tens of nanometers, what corresponds to several monolayers. The thickness of modified layer was higher for magnesium alloy, due to its higher electronegative character in comparison to iron.

Refractive index profiles of Ge-doped optical fibers with nanometer spatial resolution using atomic force microscopy

We show a quantitative connection between Refractive Index Profiles (RIP) and measurements made by an Atomic Force Microscope (AFM). Germanium doped fibers were chemically etched in hydrofluoric acid solution (HF) and the wet etching characteristics of germanium were studied using an AFM. The AFM profiles were compared to both a concentration profile of the preform determined using a Scanning Electron Microscope (SEM) and a RIP of the fiber measured using a commercial profiling instrument, and were found to be in excellent agreement. It is now possible to calculate the RIP of a germanium doped fiber directly from an AFM profile.

Long-range AFM profiler used for accurate pitch measurements

A long-range atomic force microscope (AFM) profiler system was built based on a commercial metrology AFM and a home-made linear sample displacement stage. The AFM head includes a parallelogram-type scanner with capacitive position sensors for all three axes. A reference cube located close to the tip acts as the counter electrode for the capacitive sensors. Below this metrology AFM head we placed a linear sample displacement stage, consisting of monolithic flexures forming a double parallelogram. This piezo actuated stage provides a highly linear motion over m. Its displacement is simultaneously measured by a capacitive position sensor and a differential double-pass plane mirror interferometer; both measuring systems have subnanometre resolution capability. For the measurement of periodical structures two operating modes are possible: a direct scanning mode, in which the position of the displacement stage is increased point by point while the AFM head measures the height, and a combined scanning mode where the displacement stage produces offsets which are multiples of the pitch to be measured while the AFM head is simultaneously scanning to locate an edge or a line centre position. Construction details, system characteristics and results from first pitch measurements are presented. The estimated relative combined uncertainties for pitch values on different standards are in the range to . Laser diffraction measurements of comparable uncertainty were performed on the same standards and show a very good agreement.

Thickness measurements of Si 1 − xGe x thin layers deposited on Si mesa structures

A partially relaxed Si 0.6Ge 0.4 620 Å thick layer has been deposited on a patterned Si substrate containing mesas of width ranging from 2 to 200 μm. Raman spectra at various points on the sample were taken, and an evaluation of layer thickness has been performed, showing different values in different areas of the mesas. This can be explained as being a consequence of the different growth rates on different crystal planes. Atomic force microscope profiles of the mesas were taken, showing a flat, smooth (001) crystal plane on the top of the mesa, and steep side walls, close to the (110) plane. The stress was measured from Raman shift, and was found to be constant through the sample within the 7000 Å diameter spot of the laser.

Comparison of surface roughness measurements by stylus profiler, AFM and non-contact optical profiler

Surface roughness measurements were performed on a glass-ceramic disk substrate by stylus profiler (SP), atomic force microscope (AFM) and non-contact optical profiler (NOP). Results of surface measurements are presented and the differences between SP, AFM and NOP roughness measurements are discussed. The effects of stylus size, scan size and sampling interval on roughness parameters are investigated. The methodology of choosing the scan size and sampling interval is suggested. AFM is concluded to be the most suitable surface measuring instrument for roughness measurement on the glass-ceramic substrate. If SP is used to make the measurement, the tip radius should be in the order of 0.2 μ. However, localized damage to the test surface may occur owing to high contact stress. NOP using an objective magnification of 40 or lower is not recommended because the glass-ceramic substrate contains submicron roughness.

Overcoming the pseudomorphic critical thickness limit using compliant substrates

We demonstrated the high-quality molecular beam epitaxy growth of exceedingly thick In0.14Ga0.86As pseudomorphic layers on thin, free-standing, compliant GaAs substrates. We first fabricated 800-Å-thick compliant platforms before growing a lattice-mismatched layer on the platform. The layer we grew exceeds its usual critical thickness by about twenty times without strain relaxation. X-ray analysis confirms a shift in the InGaAs peaks grown on the compliant substrate, indicating an unrelaxed strain of 0.9%. Moreover, atomic force microscope profiles verify that layers grown on compliant substrates are much smoother than layers grown on a plain substrate.