Direct photoluminescence probing of ferromagnetism in monolayer two-dimensional CrBr3

Atomically thin magnets are the key element to build up spintronics based on two-dimensional materials. The surface nature of two-dimensional ferromagnet opens up opportunities to improve the device performance efficiently. Here, we report the intrinsic ferromagnetism in atomically thin monolayer CrBr3, directly probed by polarization resolved magneto-photoluminescence. The spontaneous magnetization persists in monolayer CrBr3 with a Curie temperature of 34 K. The development of magnons by the thermal excitation is in line with the spin-wave theory. We attribute the layer-number dependent hysteresis loops in thick layers to the magnetic domain structures. As a stable monolayer material in air, CrBr3 provides a convenient platform for fundamental physics and pushes the potential applications of the two-dimensional ferromagnetism.Comment: 27 pages, 10 figure

Consumer perceptions of company environmental requests : an experimental examination of hotel reuse programs

x, 177 leaves ; 29 cmConsumer response toward companies’ corporate social responsibility (CSR) efforts has received much attention in the consumption context. However, little is known in the anti-consumption context. The present research studies one anti-consumption CSR program – reusing, which suggests that customers in a hotel use towels and linens more than once in order to reduce the use of fresh water and the generation of waste water. The impact of source credibility, argument strength, and fit on consumer response was assessed. It was found that a high credibility source (i.e., the hotel source) generated less egoistic attributions than a low credibility source (i.e., the Project Planet source). Regardless of the charity type, making a charitable donation can positively influence subjects’ attitudes toward the hotel and value-driven attributions, while negatively influenced egoistic attributions. Moreover, subjects’ perceived strong arguments positively influenced attitude, behavior intention, value-driven, strategic, and stakeholder-driven attributions, while negatively influenced counterarguments

Hysteresis of Electronic Transport in Graphene Transistors

Graphene field effect transistors commonly comprise graphene flakes lying on SiO2 surfaces. The gate-voltage dependent conductance shows hysteresis depending on the gate sweeping rate/range. It is shown here that the transistors exhibit two different kinds of hysteresis in their electrical characteristics. Charge transfer causes a positive shift in the gate voltage of the minimum conductance, while capacitive gating can cause the negative shift of conductance with respect to gate voltage. The positive hysteretic phenomena decay with an increase of the number of layers in graphene flakes. Self-heating in helium atmosphere significantly removes adsorbates and reduces positive hysteresis. We also observed negative hysteresis in graphene devices at low temperature. It is also found that an ice layer on/under graphene has much stronger dipole moment than a water layer does. Mobile ions in the electrolyte gate and a polarity switch in the ferroelectric gate could also cause negative hysteresis in graphene transistors. These findings improved our understanding of the electrical response of graphene to its surroundings. The unique sensitivity to environment and related phenomena in graphene deserve further studies on nonvolatile memory, electrostatic detection and chemically driven applications.Comment: 13 pages, 6 Figure

The negative side of corporate social responsibility

Although corporate social responsibility (CSR) has become increasingly important to a company’s success, the relationship between CSR and corporate financial performance is equivocal. The purpose of this research is to explore additional conditions under which CSR can lead to negative outcomes for both the firm and consumers. Specifically, different from other papers examining the negative effects of CSR that focus on either perceived negative motivations or perceived unethical behavior by the firm, this research examines how CSR that is, on the surface, perceived positively by consumers, leads to negative outcomes. The first paper, “Who’s working in the kitchen today”, explores the potential for CSR activities to lead to negative financial outcomes through producer contagion between stigmatized populations and products they produce. The results show that although consumers admire companies that hire stigmatized populations, they actually tend to avoid products produced by stigmatized populations. Consumers believe that this CSR practice decreases the value of products because stigmatized populations may contaminate the products by transferring their negative properties to the products through the production process. Further research identifies the mediating effect of disgust and the moderating effects of product intimacy and end user vulnerability. Finally, a choice task reveals that the negative producer contagion effect can be mitigated by implicit information such as color. The second paper, “Can ‘Real’ Men Consume Ethically?” complements the first paper by examining the outcomes from the consumers’ perspective. This paper examines how observers make judgments about consumers on the basis of their CSR support. Across four experiments it reveals that, in addition to being viewed as socially responsible, consumers are viewed as less masculine and more feminine when they consume ethical products. It also identifies two boundary conditions to this effect, including the use of self-benefit advertising appeals and the use of descriptive norms to signal gender appropriate behavior. It also identifies how consumers resolve the conflict of prosocial and gender-congruent impression management objectives. It shows that when consumers are in the presence of observers of the opposite sex, they are more likely to prioritize prosocial identity even when it threatens their gender orientation

Ultrafast optical studies on graphene and graphene oxide

In this thesis, ultrafast optical properties of graphene and graphene oxide materials have been studied by use of steady-state and time-resolved spectroscopic techniques. Carrier dynamics of monolayer graphene, stacked and suspended few-layer graphene films were measured in the broad visible spectral range by femtosecond pump/probe spectroscopy. The time scales of carrier-carrier scattering, carrier-optical phonon scattering and optical phonon-acoustic phonon scattering have been obtained and their roles in carrier relaxation process are distinguished. Meanwhile, there are several unusual quasiparticle interactions in graphene samples, including optical phonon emission and absorption, coherent phonon generation, interband triple-resonance electron-phonon scattering and stimulated two-phonon emission. On the other side, the broadband fluorescence from as-prepared graphene oxide in water has been investigated in detail. Ultrafast fluorescence (~1 ps) of graphene oxide was determined for the first time by femtosecond fluorescence upconversion technique. The origin of the fluorescence is attributed to electron-hole recombination from the bottom of the conduction band and nearby localized states to the valance band. Structurally, the GO emission is from the non-oxidized sp2 regions and the boundary of oxidized sp3 regions.DOCTOR OF PHILOSOPHY (SPMS

Optical properties of 2D semiconductor WS2

2D semiconductor tungsten disulfide (WS2) attracts significant interest in both fundamental physics and many promising applications such as light emitters, photodetectors/sensors, valleytronics, and flexible nanoelectronics, due to its fascinating optical, electronic, and mechanical properties. Herein, basic exciton properties of monolayer WS2 are reviewed including neutral excitons, charged excitons, bounded excitons, biexcitons, and the effects of electrostatic gating, chemical doping, strain, magnetic field, circular polarized light, and substrate on these excitonic structures. Besides basic excitonic emission, single‐photon emission, exciton–polaritons, and stimulated emission in monolayer WS2 are also discussed. The understanding of these optical phenomena is critical for the development of potential optical applications in electronic and optoelectronic devices. Finally, a summary and future prospective of the challengers and developments regarding 2D semiconductor WS2 is presented.MOE (Min. of Education, S’pore