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Kinetic energy is usually the entry point for the study of energy in physics and is often perceived as unproblematic. We present evidence, however, that some learners who seem to have accepted the concept, from elementary school students to college physics majors and in-service teachers, nevertheless do not consistently attribute kinetic energy to moving objects that are being pushed or carried by other objects. Factors that seem to contribute to this idea include that the passive object is not moving "on its own"; the lack of attributes, like wheels, that suggest the ability to move on its own; and the perception that it would stop immediately if the driving object were to stop or disappear. We interpret these observations in terms of a model of a conceptual change via assimilation rather than accommodation and suggest some possible instructional implications.

Abundant research leaves little question that pedagogical approaches involving active student engagement with the material, and opportunities for student-to-student discussions, lead to much better learning outcomes than traditional instructor-led, expository instructional formats, in physics and in many other fields. In introductory college physics classes, some departments have departed radically from conventional lecture-recitation-laboratory course structures, but many, including my own, retain the basic format of large-group classroom sessions (lectures) supplemented by smaller-group meetings focused on problem solving (recitations) and separate laboratory meetings. Active student engagement in the lectures is encouraged through approaches such as Peer Instruction and Interactive Lecture Demonstrations, and these approaches have been demonstrably successful.

This paper reports observations that show a significant effect of class meeting time on student evaluations of teaching for an introductory college physics class. Students in a lecture section with an early-morning meeting time gave the class and instructors consistently lower ratings than those in an otherwise nearly identical section that met an hour later, even for aspects of the course that were seemingly identical across the two sections.

We report results and impressions from a three-day inquiry-based workshop for K-8 teachers, aimed at improving their understanding of energy from a science and engineering perspective. Results suggest that the teachers made significant gains in understanding and appreciation of important energy concepts, but their comprehension of some key ideas remained incomplete. The dissipation of energy into thermal energy of the environment proved to be a particularly difficult idea, and one that represents a serious obstacle to understanding the principle of the conservation of energy.

The adsorption behavior of CO on Ni islands grown on Au(111) was studied with a combination of temperature programmed desorption, Fourier transform infrared spectroscopy, and surface resistivity measurements. The Au(111) herringbone reconstruction provides a template for the growth of ordered Ni islands, with evidence for the presence of strain and Au atoms within the islands. The islands grow radially until θNi ≈ 0.3 ML, after which subsequent Ni atoms contribute primarily to a second layer. We study saturated CO adsorption at 227 K over a range of Ni island sizes and find layer-dependent adsorption properties. For single-layer islands at low Ni coverage, CO adsorbs primarily in the atop position and desorbs at lower temperatures than on pure Ni, with a saturation CO coverage of about 0.5 CO/Ni. As second layer Ni grows, saturated CO coverages on the Ni approach unity, with higher desorption temperatures, but still with primarily atop CO. Based on previous studies, we propose that in the first Ni layer, ligand effects from the Au substrate and possibly Au in the islands and strain due to the Ni/Au lattice mismatch affect the Ni—CO bonds. CO adsorption behavior on the two-layer islands is qualitatively explained by a decrease in Au nearest neighbors and the presence of a more expanded/corrugated structure. [ABSTRACT FROM AUTHOR]

The change in surface resistivity due to the formation of nickel islands on gold(111) was studied by measuring the resistance of a thin film of Au as a function of Ni coverage, ϴ. Previous studies showed that the Au(111) herringbone reconstruction provides a template for the periodic growth of ordered islands. Ni islands grow radially until ϴ ≈ 0.3 ML, after which subsequent Ni atoms contribute primarily to a second layer. Since Ni atoms on Au(111) grow in ordered nanoclusters, a nonlinear dependence of resistance on ϴ might be anticipated. Our results, however, show a linear dependence for Ni atoms in the first layer, as if they were independent point scatterers. Above ϴ ≈ 0.3 ML, there is little change in resistivity, which we attribute to Ni atoms in the second layer making no significant contribution to the resistivity. Although we did not directly image the islands, our results are consistent with the growth model and structures previously observed with scanning tunneling microscopy. Our results serve as an indirect probe of the growth kinetics of this system, as well as determining the contributions of Ni islands to the surface resistivity of the Au film. [ABSTRACT FROM AUTHOR]

Issues concerning the effects of a partial Au monolayer on the kinetics of water formation and adsorption on a stepped Pt(335) surface are presented.

Infrared spectroscopy of adsorbed CO was used to characterize the dependence of surface structure on deposition temperature during homoepitaxial growth on Cu(100). Intensity borrowing due to dipole coupling greatly enhances the absorption signal due to defect-bonded CO, making it possible to detect and quantify defect concentrations at the level of a few percent. For deposition temperatures between 300 and 400 K, the defect density increases slightly with decreasing deposition temperature but remains below 2%. There is a sharp increase in defect density, up to 5%-6%, as the deposition temperature is decreased from 300 to 250 K. At lower deposition temperatures, there is some sign of a leveling off in defect density, but the IR absorption spectrum becomes so broad that meaningful analysis becomes impractical, while visible degradation of the low-energy electron diffraction pattern indicates worsening surface order. No indication of 're-entrant' ordering at low temperatures was observed for deposition temperatures down to 150 K. [ABSTRACT FROM AUTHOR]

We report several experiments under ultrahigh vacuum conditions that elucidate the role of oxygen in the functioning of silicon carbide field-effect gas sensors with nonporous platinum gates. The devices studied are shown to be sensitive both to hydrogen and to propene. All of the results are consistent with oxygen acting through its surface reactions with hydrogen. Three specific aspects are highlighted: the need, under some conditions, for oxygen to reset the device to a fully hydrogen-depleted state; competition between hydrogen oxidation and hydrogen diffusion to metal/oxide interface sites, leading to steplike behavior as a function of the oxygen:hydrogen ratio (λ-sensing); and the removal of sulfur contamination by oxygen. [ABSTRACT FROM AUTHOR]

Measurements of surface resistivity as a function of coverage for oxygen adsorbed on sulfur-predosed Cu(100) films reveal two types of interactions between sulfur and oxygen: S–O repulsion and short-range suppression of the surface resistivity change induced by oxygen adsorption. The repulsive interaction causes oxygen atoms to first occupy adsorption sites far from the sulfur atoms, beyond second-nearest-neighbor sites, where the oxygen-induced surface resistivity is unaffected by sulfur. As a result the low-coverage variation of surface resistivity with oxygen coverage is indistinguishable from the linear dependence observed for oxygen on clean Cu(100). As the oxygen coverage increases, oxygen begins to occupy sites close to sulfur. At the nearest-neighbor sites, the resistivity change due to added oxygen is completely suppressed, and the sample resistance levels off, remaining unchanged even as oxygen continues to adsorb. This resistivity suppression may involve both a reduction of oxygen’s direct effect on the resistivity and an oxygen-induced reduction in the resistivity due to the already adsorbed sulfur. With increasing sulfur precoverage both the maximum resistivity change and the oxygen coverage at which the leveling occurs decrease, because the number of sites unaffected by sulfur is reduced. Both the sulfur-oxygen repulsion and the resistivity suppression presumably arise from a through-metal coupling involving adsorbate-induced modifications of the local electronic structure. [ABSTRACT FROM AUTHOR]

We have investigated the effects of sulfur contamination on a Pt-gate silicon carbide based field-effect gas sensor, under ultrahigh vacuum conditions, at a temperature of 527 °C. Exposure to hydrogen sulfide, even in the presence of hydrogen or oxygen at partial pressures of 20–600 times greater than the H2S level, rapidly coated the gate with a monolayer of sulfur. Sulfur contamination reduced the magnitude of the sensor’s response to alternating hydrogen and oxygen pulses by about 70%, as compared to the uncontaminated gate. There was no evidence of irreversible changes in device behavior due to sulfur deposition and removal. The adsorbed sulfur could not be removed by exposure to hydrogen at the pressures accessible. Oxygen was effective at removing the sulfur. The rate of sulfur oxidation was suppressed at high sulfur coverages, but not as strongly as on low-index single-crystal surfaces. These results are discussed in the context of prior experiments on Pt crystals and films. [ABSTRACT FROM AUTHOR]

The authors have measured the contribution of CO adsorbed on different bonding sites to the resistivity of epitaxial Cu(100) films. Through an analysis of the correlation between surface resistivity and temperature-programed desorption measurements, CO on terraces is found to affect the resistance much more strongly than CO on defect sites. Two possible explanations are considered: a reduced scattering cross section of defect CO owing to the different local electronic structure at defect sites or strong scattering by the bare defect that is not significantly affected by the adsorption of CO. [ABSTRACT FROM AUTHOR]

We compare CO’s response to electric fields at edge and terrace sites on the stepped Pt(335) surface. The comparison is made at zero frequency and at the frequency of the C–O stretch vibration. Atop-bonded CO is observed with reflection–absorption ir spectroscopy (RAIRS), electroreflectance vibrational spectroscopy (EVS), and high-resolution electron energy loss spectroscopy (HREELS). Coadsorbed H or O is used to control the CO adsorption site. With both RAIRS and HREELS the measured vibrational cross-section of atop CO at the step edge is 2.0±0.2 times greater than for CO on the terrace. The vibrational Stark effect—the change of CO’s vibrational frequency with externally applied electrostatic field—is also a factor 2.0±0.2 larger for atop CO at the step edge than it is for atop CO on the terrace. Because the vibrational cross section varies as the square of the field while the Stark effect is linear, a model in which CO responds to the screened local field at a single point cannot simultaneously explain the observed site dependence of both the vibrational Stark effect and the vibrational cross section. The most plausible explanation is that CO’s response to electric fields is nonlocal. A simple model is presented that can account for our data. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have studied CO and H coadsorbed on the stepped Pt(335) surface in vacuum to learn about their interaction at steps and to compare with previous electrochemical studies. Both electroreflectance and conventional reflectance absorption vibrational spectra were obtained of atop bonded CO. Its stretch vibrational frequency ν, Stark tuning rate (dν/dE), and integrated absorbance S were all studied as functions of CO and H coverage. With CO only on step edges, S for atop CO decreases to zero with increasing H coverage. The CO affected by H is in a mixed phase and is bridge bonded. Atop CO’s (dν/dE) decreases with increasing CO coverage but is unaffected by coadsorbed H. In the low CO coverage limit (dν/dE)=88±9 cm-1/(V/Å), in agreement with theory and with previous measurement. The standard model of dipole–dipole screening is unable to explain the CO coverage dependence of both (dν/dE) and S. The vibrational polarizability of CO increases with coverage. We also compare our results with spectroelectrochemical data from CO on Pt(335) in aqueous electrolyte. Our measured (dν/dE) is too small to explain the variation of CO’s ν with electrode potential [lowercase_phi_synonym] in the electrochemical experiments if (dE/d[lowercase_phi_synonym]) in the double-layer is taken from conventional models. The effect of coadsorbed H is also different; in vacuum H has no effect on CO’s (dν/dE) but in electrolyte, at low CO coverage, (dν/d[lowercase_phi_synonym]) drops to zero at the potential where H adsorption begins. [ABSTRACT FROM AUTHOR]

Electron energy loss spectroscopy is used to compare atop CO at two sites on Pt(335): on the flat (111) terrace and on the step edge. The cross section for the C–O stretch overtone of the terrace species is not significantly larger than that of the edge species. Previous experiments have shown that the vibrational frequency of terrace CO responds much less to applied electrostatic field than does edge CO, even though their ir cross sections are about the same. The present experiment shows that CO has similar molecular properties at the two sites: a chemical explanation for the different Stark tuning rates is ruled out. The difference could be due to spatial variation of the electric field. Local screening of almost all the static electric field at terrace sites is one possibility, but a simple jellium model is unable to explain the observed effect. Interaction of the molecular quadrupole moment with the spatially varying field near the surface is also important. [ABSTRACT FROM AUTHOR]

Investigates the crystal structure, surface morphology and electrical conductance of copper films grown on hydrogen-terminated silicon(100). Techniques used in determining film structure and surface morphology; Description on atomic force microscopic images obtained from the samples; Measurements of four-wire direct current resistance on selected films during deposition.