An automated technique is presented for mechanically exfoliating single-layer and few-layer transition metal dichalcogenides using controlled shear and normal forces imposed by a parallel plate rheometer. A thin sample that is removed from bulk MoS₂ or MoTe₂ is initially attached to the movable upper fixture of the rheometer using blue dicing tape while the lower base plate also has the same tape to capture and exfoliate samples when the two plates are brought into contact then separated. A step-and-repeat exfoliation process is initiated using a preprogrammed contact force and liftoff speed. It was determined that atomically thin films of these materials could be obtained reproducibly using this technique, achieving single-layer and few-layer thicknesses for engineering novel two-dimensional transistor devices for future electronic technologies. We show that varying the parameters of the rheometer program can improve the mechanical exfoliation process.

Flexible microfluidics have found extensive utility in the biological and biomedical fields. A leading substrate material for compliant devices is polydimethylsiloxane (PDMS). Despite its many advantages, PDMS is inherently hydrophobic and consequently its use in passive (pumpless) microfluidics becomes problematic. To this end, many physical and chemical modifications have been introduced to render PDMS hydrophilic, ranging from amphiphilic molecule additions to surface plasma treatments. However, when transitioning from lab benchtop to realized medical devices, these modifications must exhibit long-term stability. Unfortunately, these modifications are often presented but their mechanisms and long-term stability are not studied in detail. We have investigated an array of PDMS modifications, utilizing contact angle goniometry to study surface energy over a 30-day evolution study. Samples were stored in air and water, and Fourier Transform Infrared-Attenuated Total Reflectance (FTIR-ATR) analysis was used to confirm surface functional group uniformity. We have identified preferred modification techniques for long-lasting PDMS devices and characterized often overlooked material stability.

In nanotechnology, understanding the effect of interfaces and defects becomes critically important in determining a material's properties and device performance. Many one-dimensional and two-dimensional materials exhibit excellent physical, electrical, thermal, and optical properties, making them highly desirable for a wide array of applications. However, their low dimensionality also means their performance can be susceptible to defects in the material and the interfaces they form with other device components. Carbon nanotubes are often used in sensing applications, typically, in a field-effect transistor configuration (CNTFET). The interface between the contact electrode metal and the nanotube forms a Schottky barrier, which plays an important role in both transistor and sensor characteristics. Modifications to this interface by the environment can modulate the barrier and produce a change in device characteristics. Transistor operation can also be modified by the presence of defects in the carbon nanotube sidewall structure. This paper explores how defects in single-wall carbon nanotubes can affect the sensing mechanism of CNTFET gas sensing devices. Gas exposure measurements were performed on as-grown near pristine (low defect) nanotube devices and compared with plasma irradiated, highly defective nanotube devices. By utilizing selective passivation to isolate structural components that contribute to the sensing mechanism, the study shows that the presence of defects, and their relative densities, has a critical role in gas sensing performance. Recognizing the presence of these defects, even in as-grown nanotubes, can help reconcile seemingly contradictory results in the literature regarding the gas sensing mechanism. This work represents an important step toward understanding the effect of both interfaces and defects for carbon nanotube sensor development.

Objective: Modern diagnostics is pivoting towards less invasive health monitoring in dermal interstitial fluid, rather than blood or urine. However, the skin's outermost layer, the stratum corneum, makes accessing the fluid more difficult without invasive, needle-based technology. Simple, minimally invasive means for surpassing this hurdle are needed. Methods: To address this problem, a flexible, Band-Aid-like patch for sampling interstitial fluid was developed and tested. This patch uses simple resistive heating elements to thermally porate the stratum corneum, allowing the fluid to exude from the deeper skin tissue without applying external pressure. Fluid is then transported to an on-patch reservoir through self-driving hydrophilic microfluidic channels. Results: Testing with living, ex-vivo human skin models demonstrated the device's ability to rapidly collect sufficient interstitial fluid for biomarker quantification. Further, finite-element modeling showed that the patch can porate the stratum corneum without raising the skin's temperature to pain-inducing levels in the nerve-laden dermis. Conclusion: Relying only on simple, commercially scalable fabrication methods, this patch outperforms the collection rate of various microneedle-based patches, painlessly sampling a human bodily fluid without entering the body. Significance: The technology holds potential as a clinical device for an array of biomedical applications, especially with the integration of on-patch testing.