Rethinking the Characterization of Nanoscale Field‐Effect Transistors: A Universal Approach

Standard methods for calculating transport parameters in nanoscale field‐effect transistors (FETs), namely carrier concentration and mobility, require a linear connection between the gate voltage and channel conductance; however, this is often not the case. One reason often overlooked is that shifts in chemical and electric potential can partially compensate each other, commonly referred to as quantum capacitance. In nanoscale FETs, capacitance is often unmeasurable and an analytical formula is required, which assumes the conducting channel as metallic and common methods of determining threshold voltage no longer couple properly into transport equations. As present and future FET structures become smaller and have increased channel‐gate coupling, this issue will render standard methods impossible to use. This work discusses the validity of common methods of characterization for nanoscale FETs, develops a universal model to determine transport properties by only measuring the threshold voltage of an FET and presents a new parameter to easily classify FETs as either quantum capacitance‐limited or metallic approximated charge transport. Also considered in this work is electrical hysteresis from trap states and, in combination with the proposed universal model, novel techniques are introduced to measure and remove the errors associated with these effects often ignored in literature.     

Equal-Channel Angular Extrusion of a Low-Density High-Entropy Alloy Produced by High-Energy Cryogenic Mechanical Alloying

In this study, we demonstrate the feasibility of forming a bulk consolidated, low-density high-entropy alloy, namely AlFeMgTiZn, which shows reasonable mechanical properties and high hardness. The fabrication of the high-entropy alloy from powdered precursors via high-energy mechanical alloying as a function of milling time is presented. In turn, the evolution of the alloy microstructure with postmilling anneal treatment is elucidated. Last, the severe plastic deformation processing methodology, i.e., equal-channel angular extrusion, chosen for consolidation, is described and shown to result in a bulk product with good results.     

Insomnia and well-being.

Most Americans have occasional problems with insomnia. The relationship of insomnia to illness is well known. However, insomnia may also relate to lower levels of well-being. Although there are various definitions of well-being, one of the most clearly articulated and comprehensive models identifies 2 overarching constructs, psychological well-being and subjective well-being. The purpose in the present study was to assess the relationship between insomnia symptoms and the dimensions of psychological and subjective well-being, adjusting for the potential confound of comorbid physical and psychological illness. The data for the present study came from the National Survey of Midlife Development in the United States, a survey of community-dwelling adults. After adjustment for demographic characteristics and a wide range of chronic mental and physical health conditions, insomnia symptoms were found to have a significant relationship with both psychological and subjective well-being but a stronger relationship to subjective well-being. These data suggest that insomnia symptoms have a stronger relationship to enjoying life than to the perception that one has a meaningful life. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mechanical properties of electrodeposited nanocrystalline copper using tensile and shear punch tests

Characterization of the mechanical properties of electrodeposited nanocrystalline Cu with an average grain size of 74 nm was carried out using two different testing techniques, shear punch tests and tensile tests. The grain size distribution was broad and the volume fraction of larger grains was appreciable. The electrodeposited Cu had a high yield strength combined with moderate ductility and strain hardening. Scatter in the ductility values was attributed to residual porosity and inhomogeneity in the microstructure. Measurements of the strain rate sensitivity showed a significant increase in the rate sensitivity and a decrease in the activation volume for the deformation of nanocrystalline Cu compared with similar tests on coarse-grained cold worked Cu.     

Healthcare provider smoking cessation advice among US worker groups

Objective

Among workers in dusty occupations, tobacco use is particularly detrimental to health because of the potential synergistic effects of occupational exposures (for example, asbestos) in causing disease. This study explored the prevalence of smoking and the reported smoking cessation discussion with a primary healthcare provider (HCP) among a representative sample of currently employed US worker groups.

Methods

Pooled data from the 1997–2003 National Health Interview Survey (NHIS) were used to estimate occupation specific smoking rates (n = 135 412). The 2000 NHIS Cancer Control Module was used to determine (among employed smokers with HCP visits) the prevalence of being advised to quit smoking by occupation (n = 3454).

Results

The average annual prevalence of current smoking was 25% in all workers. In 2000, 84% of smokers reported visiting an HCP during the past 12 months; 53% reported being advised by their physician to quit smoking (range 42%–66% among 30 occupations). However, an estimated 10.5 million smokers were not advised to quit smoking by their HCP. Workers with potentially increased occupational exposure to dusty work environments (including asbestos, silica, particulates, etc), at high risk for occupational lung disease and with high smoking prevalence, had relatively low reported discussions with an HCP about smoking cessation, including farm workers (30% overall smoking prevalence; 42% told to quit), construction and extractive trades (39%; 46%), and machine operators/tenderers (34%; 44%).

Conclusion

The relatively low reported prevalence of HCP initiated smoking cessation discussion, particularly among currently employed workers with potentially synergistic occupational exposures and high current smoking prevalence, needs to be addressed through educational campaigns targeting physicians and other HCPs.     

Photochemical fate of sulfa drugs in the aquatic environment: sulfa drugs containing five-membered heterocyclic groups

The photochemical fate of five sulfa drugs with varying five-membered heterocyclic substituents (sulfamethoxazole, sulfisoxazole, sulfamethizole, sulfathiazole, and sulfamoxole) was investigated in aqueous solution. The rate of direct photolysis of these compounds is dependent upon the identity of the heterocyclic R group as well as the pH of the solution. Matrix deconvolution methods were employed to determine the absorption spectrum and photolysis rate of each protonation state (cationic, neutral, and anionic). From these data, quantum yields for direct photodegradation were calculated for each protonation state of the sulfa drugs. The quantum yields calculated range from <0.005 for the neutral state of sulfamethizole to 0.7 +/- 0.3 for the protonated state of sulfisoxazole. The protonation state that is most photoreactive varies among the sulfa drugs and cannot be attributed to the rate of photon absorption. Products arising from the direct photolysis of the sulfa drugs were also investigated. For all the compounds, sulfanilic acid was observed as a common product. The singlet oxygen quenching rates of the sulfa drugs were determined by laser flash photolysis and range from (2 +/- 1) x 10(4) M(-1) s(-1) for sulfamethoxazole to (3.0 +/- 0.7) x 10(8) M(-1) s(-1) for sulfamoxole. Reaction of the sulfa drugs with hydroxyl radical is not modulated by the R group, and the rate constants are all near the bimolecular diffusion-controlled limit of 10(10) M(-1) s(-1). The photodegradation of the sulfa drugs in natural water samples of Lake Josephine (St. Paul, MN) and Lake Superior was attributed solely to direct photolysis. This study indicates thatthese similarly structured antibiotics will be subject to a wide range of photodegradation rates with sulfathiazole degrading relatively quickly, sulfisoxazole and sulfamethizole degrading moderately, and sulfamethoxazole degrading much more slowly.     

Characterizing Heat Release Rates Using an Inverse Fire Modeling Technique

A ubiquitous source of uncertainty in fire modeling is specifying the proper heat release rate (HRR) for the fuel packages of interest. An inverse HRR calculation method is presented to determine an inverse HRR solution that satisfies measured temperature data. The methodology uses a predictor-corrected method and the Consolidated Model of Fire and Smoke Transport (CFAST) zone model to calculate hot gas layer (HGL) temperatures in single compartment configurations. The inverse method runs at super-real-time speeds while calculating an inverse HRR solution that reasonably matches the original HRR curve. Examples of the inverse method are demonstrated by using a multiple step HRR case, complex HRR curves, experimental temperature data with a constant HRR, and a case with an experimentally measured HRR. In principle, the methodology can be applied using any reasonably accurate fire model to invert for the HRR.     

Near IR scanning angle total internal reflection Raman spectroscopy at smooth gold films

Total internal reflection (TIR) Raman and reflectivity spectra were collected for nonresonant analytes as a function of incident angle at sapphire or sapphire/smooth 50 nm gold interfaces using 785 nm excitation. For both interfaces, the Raman signal as a function of incident angle is well-modeled by the calculated interfacial mean square electric field (MSEF) relative to the incident field times the thickness of the layer being probed in the Raman measurement (D(RS)). The Raman scatter was reproducibly enhanced at the interface containing a gold film relative to the sapphire interface by a factor of 4.3-4.6 for aqueous pyridine or 2.2-3.7 for neat nitrobenzene, depending on the analyzed vibrational mode. The mechanism for the increased Raman signal is the enhanced MSEF at incident angles where propagating surface plasmons are excited in the metal film. The background from the TIR prism was reduced by 89-95% with the addition of the gold film, and the percent relative uncertainty in peak area was reduced from 15 to 1.7% for the 1347 cm(-1) mode of nitrobenzene. Single monolayers of benzenethiol (S/N = 6.8) and 4-mercaptopyridine (S/N = 16.5) on gold films were measured by TIR Raman spectroscopy with 785 nm excitation (210 mW) without resonant enhancement in 1 min.     

In situ mechanical property measurements of amorphous carbon-boron nitride nanotube nanostructures

To understand the mechanical properties of amorphous carbon (a-C)/boron nitride nanotube (BNNT) nanostructures, in?situ mechanical tests are conducted inside a transmission electron microscope equipped with an integrated atomic force microscope system. The nanotube structure is modified with amorphous carbon deposited by controlled electron beam irradiation. We demonstrate multiple in situ tensile, compressive, and lap shear tests with a-C/BNNT hybrid nanostructures. The tensile strength of the a-C/BNNT hybrid nanostructure is 5.29?GPa with about 90?vol% of a-C. The tensile strength and strain of the end-to-end joint structure with a-C welding is 0.8?GPa and 5.2% whereas the lap shear strength of the side-by-side joint structure with a-C is 0.25?GPa.