Ultrafine Aerosol Particle Sizer Based on Piezoresistive Microcantilever Resonators with Integrated Air-Flow Channel

To monitor airborne nano-sized particles (NPs), a single-chip differential mobility particle sizer (DMPS) based on resonant micro cantilevers in defined micro-fluidic channels (µFCs) is introduced. A size bin of the positive-charged fraction of particles herein is separated from the air stream by aligning their trajectories onto the cantilever under the action of a perpendicular electrostatic field of variable strength. We use previously described µFCs and piezoresistive micro cantilevers (PMCs) of 16 ng mass fabricated using micro electro mechanical system (MEMS) technology, which offer a limit of detection of captured particle mass of 0.26 pg and a minimum detectable particulate mass concentration in air of 0.75 µg/m3. Mobility sizing in 4 bins of a nebulized carbon aerosol NPs is demonstrated based on finite element modelling (FEM) combined with a-priori knowledge of particle charge state. Good agreement of better than 14% of mass concentration is observed in a chamber test for the novel MEMS-DMPS vs. a simultaneously operated standard fast mobility particle sizer (FMPS) as reference instrument. Refreshing of polluted cantilevers is feasible without de-mounting the sensor chip from its package by multiply purging them alternately in acetone steam and clean air

Calibrating a high-speed contact-resonance profilometer

A European EMPIR project, which aims to use large-scale, 5 mm × 200 µm × 50 µm (L×W×H), piezoresistive microprobes for contact resonance applications, a well-established measurement mode of atomic force microscopes (AFMs), is being funded. As the probes used in this project are much larger in size than typical AFM probes, however, some of the simplifications and assumptions made for AFM probes are not applicable. This study presents a guide on how to systematically create a model that replicates the dynamic behavior of microprobes. The model includes variables such as air damping, nonlinear sensitivities, and frequency dependencies. The finished model is then verified by analyzing a series of measurements

Sampling and Mass Detection of a Countable Number of Microparticles Using on-Cantilever Imprinting.

Liquid-borne particles sampling and cantilever-based mass detection are widely applied in many industrial and scientific fields e.g., in the detection of physical, chemical, and biological particles, and disease diagnostics, etc. Microscopic analysis of particles-adsorbed cantilever-samples can provide a good basis for measurement comparison. However, when a particles-laden droplet on a solid surface is vaporized, a cluster-ring deposit is often yielded which makes particles counting difficult or impractical. Nevertheless, in this study, we present an approach, i.e., on-cantilever particles imprinting, which effectively defies such odds to sample and deposit countable single particles on a sensing surface. Initially, we designed and fabricated a triangular microcantilever sensor whose mass m0, total beam-length L, and clamped-end beam-width w are equivalent to that of a rectangular/normal cantilever but with a higher resonant frequency (271 kHz), enhanced sensitivity (0.13 Hz/pg), and quality factor (~3000). To imprint particles on these cantilever sensors, various calibrated stainless steel dispensing tips were utilized to pioneer this study by dipping and retracting each tip from a small particle-laden droplet (resting on a hydrophobic n-type silicon substrate), followed by tip-sensor-contact (at a target point on the sensing area) to detach the solution (from the tip) and adsorb the particles, and ultimately determine the particles mass concentration. Upon imprinting/adsorbing the particles on the sensor, resonant frequency response measurements were made to determine the mass (or number of particles). A minimum detectable mass of ~0.05 pg was demonstrated. To further validate and compare such results, cantilever samples (containing adsorbed particles) were imaged by scanning electron microscopy (SEM) to determine the number of particles through counting (from which, the lowest count of about 11 magnetic polystyrene particles was obtained). The practicality of particle counting was essentially due to monolayer particle arrangement on the sensing surface. Moreover, in this work, the main measurement process influences are also explicitly examined

In-line measurement of the surface texture of rolls using long slender piezoresistive microprobes

Long slender piezoresistive silicon microprobes are a new type of sensor for measurement of surface roughness. Their advantage is the ability to measure at speeds of up to 15 mm/s, which is much faster than conventional stylus probes. The drawbacks are their small measurement range and tendency to break easily when deflected by more than the allowed range of 1 mm. In this article, previously developed microprobes were tested in the laboratory to evaluate their metrological properties, then tested under industrial conditions. There are several industrial measurement applications in which microprobes are useful. Measurement of the roughness of paper machine rolls was selected for testing in this study. The integration of a microprobe into an existing roll measurement device is presented together with the measurement results. The results are promising, indicating that measurements using a microprobe can give useful data on the grinding process

Small force metrology for AFM, stylus instruments, CMM and nanoindenter via reference springs and sensors

With the increasing spread of soft polymer products the calibration of probing forces of atomic force microscopes, stylus instruments, coordinate measuring machines and nanoindenters becomes more and more important in order not to scratch the surface of these products during quality control. New sensors and reference springs for force calibration and new calibration methods for these devices will be presented along with some comparison measurements revealing the status of force and stiffness calibration. The contribution closes with an outlook on the current status of probing force standardization

Quantitative scanning spreading resistance microscopy on n-type dopant diffusion profiles in germanium and the origin of dopant deactivation

Diffusion profiles of arsenic and antimony in undoped and carbon doped germanium (Ge), respectively, were analysed by means of scanning spreading resistance microscopy (SSRM). Whereas earlier secondary ion mass spectrometry analyses have determined the distribution of the chemical concentration of dopants and carbon, the electrically active defect concentration is quantified by SSRM using appropriate calibration samples and a preparation technique that reduces the surface roughness and its density of electronic states. Pronounced differences between the chemical and electrical dopant profiles are observed and consistently described by the formation of inactive dopant defect complexes in the framework of the vacancy mediated diffusion of donor atoms in Ge. This reveals that donor deactivation occurs during dopant diffusion at elevated temperatures

Imaging the mechanical properties of nanowire arrays

Dimensional and contact resonance (CR) images of nanowire (NW) arrays are measured using our new-developed CR imaging (CRI) setup. Then a reference method is employed to calculate the indentation modulus of NWs (Mi,NW) representing the elasticity of NWs, by measuring NW arrays (NWAs) and reference samples at the same static probing force. Furthermore, topography is imaged in combination with CR and Mi,NW separately by software, whereby the relation between both parameters of NWAs is visualized. As typical examples, 3D imaging of topography and Mi,NW is performed with Si pillar, Cu and ZnO NWAs. The novel method allows for fast mechanical performance measurements of large-scale vertically-aligned NW arrays (NWAs) without releasing them from their substrates

Design of Miniaturized, Self-Out-Readable Cantilever Resonator for Highly Sensitive Airborne Nanoparticle Detection

In this paper, a self-out-readable, miniaturized cantilever resonator for highly sensitive airborne nanoparticle (NP) detection is presented. The cantilever, which is operated in the fundamental in-plane resonance mode, is used as a microbalance with femtogram resolution. To achieve a maximum measurement signal of the piezo resistive Wheatstone half-bridge, the geometric parameters of the sensor design were optimized by finite element modelling (FEM). Struts at the sides of the cantilever resonator act as piezo resistors and enable an electrical read-out of the phase information of the cantilever movement whereby they do not contribute to the resonators rest mass. For the optimized design, a resonator mass of 0.93 ng, a resonance frequency of ~440 kHz, and thus a theoretical sensitivity of 4.23 fg/Hz can be achieved. A μ-channel guiding a particle-laden air flow towards the cantilever is integrated into the sensor chip. Electrically charged NPs will be collected by an electrostatic field between the cantilever and a counter-electrode at the edges of the μ-channel. Such μ-channels will also be used to accomplish particle separation for sizeselective NP detection. Throughout, the presented airborne NP sensor is expected to demonstrate significant improvements in the field of handheld, MEMS-based NP monitoring devices

Cantilever Sensors

A cantilever is considered the most basic mechanical spring-mass system and has enormous application potential for sensors [...