2017 New's Items

Preventing Thin Film Dewetting via Graphene Capping

P. Cao
P. Bai
A. Omrani
Y. Xiao
K. Meaker
H. Tsai
A. Yan
H. Jung
R. Khajeh
G. Rodgers
Y. Kim
A. Aikawa
M. Kolaczkowski
Y. Liu
A. Zettl
2017

A monolayer 2D capping layer with high Young's modulus is shown to be able to effectively suppress the dewetting of underlying thin films of small organic semiconductor molecule, polymer, and polycrystalline metal, respectively. To verify the universality of this capping layer approach, the dewetting experiments are performed for single‐layer graphene transferred onto polystyrene (PS), semiconducting thienoazacoronene (EH‐TAC), gold, and also MoS2 on PS. Thermodynamic modeling indicates that the exceptionally high Young's modulus and surface conformity of 2D...

Ferroelectricity in Pb1+δZrO3 Thin Films

R. Gao
S. E. Reyes-Lillo
R. Xu
A. Dasgupta
Y. Dong
L. Dedon
J. Kim
S. Saremi
Z. Chen
C. R. Serrao
H. Zhou
J. B. Neaton
L. W. Martin
2017

Antiferroelectric PbZrO3 is being considered for a wide range of applications where the competition between centrosymmetric and noncentrosymmetric phases is important to the response. Here, we focus on the epitaxial growth of PbZrO3 thin films and understanding the chemistry–structure coupling in Pb1+δZrO3 (δ = 0, 0.1, 0.2). High-quality, single-phase Pb1+δZrO3 films are synthesized via pulsed-laser deposition. Although no...

Excitation-Wavelength-Dependent Small Polaron Trapping of Photoexcited Carriers in α-Fe2O3

L. M. Carneiro
S. K. Cushing
C. Liu
Y. Su
P. Yang
A. P. Alivisatos
S. R. Leone
2017

Small polaron formation is known to limit ground-state mobilities in metal oxide photocatalysts. However, the role of small polaron formation in the photoexcited state and how this affects the photoconversion efficiency has yet to be determined. Here, transient femtosecond extreme-ultraviolet measurements suggest that small polaron localization is responsible for the ultrafast trapping of photoexcited carriers in haematite (α-Fe2O3). Small polaron formation is evidenced by a sub-100 fs splitting of the Fe 3p core...

Tunable Anisotropic Photon Emission from Self-Organized CsPbBr3 Perovskite Nanocrystals

M. J. Jurow
T. Lampe
E. Penzo
J. Kang
T. Zechel
Z. Nett
M. Brady
L-W. Wang
A. P. Alivisatos
S. Cabrini
W. Brutting
Y. Liu
2017

We report controllable anisotropic light emission of photons originating from vertically aligned transition dipole moments in spun-cast films of CsPbBr3 nanocubes. By depositing films of nanocrystals on precoated substrates we can control the packing density and resultant radiation pattern of the emitted photons. We develop a technical framework to calculate the average orientation of light emitters, i.e., the angle between the transition dipole moment vector (TDM) and the substrate. This model is applicable to any emissive material with a known refractive...

Dissecting and Modeling Zeaxanthin- and Lutein-Dependent Nonphotochemical Quenching in Arabidopsis Thaliana

M. Leuenberger
J. M. Morris
A. M. Chan
L. Leonelli
K. K. Niyogi
G. Fleming
2017

Photosynthetic organisms use various photoprotective mechanisms to dissipate excess photoexcitation as heat in a process called nonphotochemical quenching (NPQ). Regulation of NPQ allows for a rapid response to changes in light intensity and in vascular plants, is primarily triggered by a pH gradient across the thylakoid membrane (∆pH). The response is mediated by the PsbS protein and various xanthophylls. Time-correlated single-photon counting (TCSPC) measurements were performed on Arabidopsis thalianato quantify the dependence of the response of NPQ to changes...

Density Tunable Graphene Aerogels Using a Sacrificial Polycyclic Aromatic Hydrocarbon

S. Turner
H. Long
B. Shevitski
T. Pham
M. Lorenzo
E. Kennedy
S. Aloni
M. Worsley
A. Zettl
2017

Raman and photoluminescence (PL) spectroscopy are used to investigate dynamic structure–function relationships in methylammonium lead iodide (MAPbI3) perovskite. The intensity of the 150 cm–1 methylammonium (MA) librational Raman mode is found to be correlated with PL intensities in microstructures of MAPbI3. Because of the strong hydrogen bond between hydrogens in MA and iodine in the PbI6 perovskite octahedra, the Raman activity of MA is very sensitive to structural distortions...

Large Bulk Photovoltaic Effect and Spontaneous Polarization of Single-Layer Monochalcogenides

T. Rangel
B. M. Fregoso
B. S. Mendoza
T. Morimoto
J. E. Moore
J. B. Neaton
2017

We use a first-principles density functional theory approach to calculate the shift current and linear absorption of uniformly illuminated single-layer Ge and Sn monochalcogenides. We predict strong absorption in the visible spectrum and a large effective three-dimensional shift current (∼100μA/V2...

Nanoscience — Potential and Threats

A. P. Alivisatos
2017

As the world’s population continues to expand, scientists are working to address the energy needs and challenges that accompany growth with environmentally responsible approaches. Nanoscience is helping to provide solutions to energy and environmental concerns in a number of ways.

Bandgap Engineering in Semiconductor Alloy Nanomaterials with Widely Tunable Compositions

C. Ning
L. Dou
P. Yang
2017

Over the past decade, tremendous progress has been achieved in the development of nanoscale semiconductor materials with a wide range of bandgaps by alloying different individual semiconductors. These materials include traditional II–VI and III–V semiconductors and their alloys, inorganic and hybrid perovskites, and the newly emerging 2D materials. One important common feature of these materials is that their nanoscale dimensions result in a large tolerance to lattice mismatches within a monolithic structure of varying composition or between the substrate and target material, which...