Strong Quantum Confinement Effect Research Articles

High perovskite-to-manganese energy transfer efficiency in single-component white-emitting Mn-doped halide perovskite quantum dots

Taking advantages of negligible reabsorption and no phase separation, single-component white-emitting phosphors are believed as new promising color conversion materials for white light-emitting diodes. As a potential candidate, Mn-doped lead halide perovskites are studied intensively, but rare works can realize pure white emission with a single component due to the challenge for realizing sufficient energy transfer efficiency from perovskite to Mn at the desirable emission wavelengths. In this work, we reported the synthesis of single-component white light halide perovskite quantum dots (QDs) by doping Mn into the host of CsPb(Cl/Br)3@CsPb(Cl/Br)x core–amorphous shell (CAS). The small size of zero-dimensional core in CAS structure has a strong quantum confinement effect, which can enhance the energy transfer efficiency from halide perovskite to Mn impurity dramatically. Our result shows 19.3 times higher energy transfer efficiency for Mn-doped CAS than that of ordinary Mn-doped CsPb(Cl/Br)3 nanocubes. As a result, as-prepared Mn-doped CAS QDs give rise to a white light emission with Commission Internationale de l’Eclairage (CIE) color coordinates of (0.37, 0.33). After blending with polystyrene (PS), Mn-doped CAS QDs can be used as a single-component color conversion material for assembling white light LEDs.

Effects of Material Dimensionality on the Optical Properties of CsPbBr3 Nanomaterials

Inorganic perovskites such as CsPbBr3 have attracted intensive research attention due to their excellent thermal stability and high photoluminescence quantum efficiency. With the decrease of the material’s dimension, quantum confinement effects will take place, which will induce many interesting properties. Here, quasi two-dimensional perovskite nanoplatelets (NPLs) and three-dimensional perovskite nanocrystals (NCs) have been grown, and their optical properties have been compared and discussed. It is interesting to find that the photon energy of CsPbBr3 NPLs hardly changes with temperature due to strong electron–phonon interaction. At the same time, the strong quantum confinement effect results in a smaller Stokes shift and a faster fluorescence lifetime. In addition, although the NPLs have many surface defects, they exhibit a relatively strong negative thermal quenching effect of emission. These results demonstrate the unique optical properties of perovskite NPLs that can pave the way for future nanosca...

Size and temperature dependence of photoluminescence of hybrid perovskite nanocrystals.

In this work, we studied the effects of particles' size and temperature on the photoluminescence (PL) of CH3NH3PbBr3 perovskite nanocrystals (PNCs), with the PNC size controlled by varying the surface passivating ligands. The structural and optical properties of the PNCs were investigated using UV-Vis and PL spectroscopy, revealing strong quantum confinement effects. Temperature dependent PL measurements showed the spectral blue shift of the PL peak for the small PNCs (3.1 ± 0.2 nm) with decreasing temperature from 300 K to 20 K, which is opposite to the red shift with decreasing temperature observed for large- (9.2 ± 0.5 nm) and middle-sized (5.1 ± 0.3 nm) PNCs. The PL lifetime also increased with increasing temperature for the larger PNCs, while it remained about the same for the small and middle-sized PNCs. This increase in lifetime with temperature is attributed to exciton dissociation to free carriers at higher temperatures and to the formation of polar domains in the PNCs. However, the small and middle-sized PNCs did not show such a trend, which may be due to efficient defect passivation as higher concentration of 3-aminopropyl trimethoxysilane (APTMS) was used and to the role of particle size in surface state delocalization. Cryo-X-ray diffraction showed no new peak formation or peak splitting as temperature was varied, which suggests efficient crystal phase stabilization in PNCs of all three sizes controlled by the concentration of APTMS. These results emphasize the importance of size and surface properties of PNCs in their optical properties such as PL quantum yield, PL lifetime, and crystal phase stability.

Tuning hyperthermia efficiency of MnFe2O4/ZnS nanocomposites by controlled ZnS concentration

Magneto-fluorescence MnFe2O4/ZnS nanocomposite with varying ZnS concentration were successfully synthesized by co-precipitation method. Its structural, morphological, optical and magnetic properties are comprehensively characterized by XRD, HRTEM, FTIR, UV-Vis, Photoluminescence (PL) spectroscopy and VSM techniques. XRD Results indicates that the prepared nanocomposite comprises of cubic Spinel structure of MnFe2O4 and cubic zinc blende structure of ZnS. FTIR analysis exhibits conjugation of ZnS with surface of MnFe2O4 nanoparticles through surfactant PEG. The photoluminescence study shows the shifting of emission peaks due to strong quantum confinement effect and the absorption spectra shows the trend of increasing band gap with increasing concentration of ZnS. Room temperature magnetic study shows that the saturation magnetization increases with increasing ZnS concentration. The prepared nanocomposite investigated for hyperthermia application at different concentration of ZnS. The result infer that the nanocomposite is a promising material for hyperthermia and also heating efficiency can be tuned by changing the ZnS concentration in the MnFe2O4/ZnS nanocomposite.

Electronic properties and oxygen reduction reaction catalytic activity of h-BeN2 and MgN2 by first-principles calculations

Currently, identifying suitable oxygen reduction reaction (ORR) catalysts in novel two-dimensional (2D) materials has attracted more and more research attention. Here, we have studied the catalytic activities of 2D h-BeN2 and MgN2 monolayers for ORR by using first-principles calculations. The calculated results reveal that the direct quasiparticle bandgap of BeN2 monolayer is 3.32 eV, and the indirect bandgap of MgN2 is 3.42 eV. 2D h-BeN2 and MgN2 exhibit high exciton binding energies of 1.07 and 0.83 eV respectively, and their optical properties are determined by bound exciton transitions due to the strong quantum confinement effects. Importantly, h-BeN2 and MgN2 monolayers with positive-charged (+1.6 e) metal atom (Be/Mg) on the surface exhibit excellent adsorption ability for O2 and ORR intermediates, and show better CO tolerance than Pt(111). The calculated free energy plots are always downhill for ORR catalyzed by BeN2 in both acid and alkaline environments, and by MgN2 in alkaline environments. The detailed reaction mechanism analyses show that high-efficient four-electron pathway is the optimal pathway for ORR catalyzed by BeN2 in acid environments. Surprisingly, there is a low overpotential of 0.45 eV for ORR catalyzed by BeN2 in the acid solution and no overpotential in the alkaline solution. Our studies found for the first time that 2D h-BeN2 shows huge potential as a non-precious metal ORR catalyst in acid and alkaline environments.

High Yield Controlled Synthesis of Nano-Graphene Oxide by Water Electrolytic Oxidation of Glassy Carbon for Metal-Free Catalysis.

The strong quantum confinement effect as well as abundant edges and oxygen functional groups enable nano-graphene oxide (NGO) a variety of intriguing applications such as catalysis, bioimaging, drug delivery and photovoltaic devices. However, the development of NGO is severely hindered because of the difficulty in controlled mass production. Here, we report the efficient synthesis of NGO with a high yield of ∼40 wt % by water electrolytic oxidation of glassy carbon (GC). The NGO shows a high oxidation degree (C/O atomic ratio, ∼1.4) and excellent dispersion stability. Moreover, its size can be easily tuned by the graphitization degree of GC, which enables the controlled synthesis of NGO with average size of 4, 8, and 13 nm and different oxygen functional groups. As metal-free catalysts, the 13 nm sized NGO is found to be beneficial for the oxidative coupling reaction of benzylamine, while the 4 nm sized NGO shows a conversion rate of 88 times higher than 13 nm sized NGO for the oxidation reaction of benzene. In addition, the water electrolytic oxidation mechanism of graphitic materials is systematically studied. It is found that sulfuric acid has a protective effect on the graphite electrode during the water electrolytic oxidation process, and 50 wt % sulfuric acid solution well balances the protection and oxidation processes, leading to the highest oxidation efficiency and production rate.

Hot-Tailoring of Carbon Nitride Dots with Redshifted Photoluminescence for Visual Double Text Encryption and Bioimaging.

The fabrication of carbon dots and their doped forms by top-down chemical cleavage has attracted considerable attention in the efforts to meet the increasing demands for optoelectronic applications ranging from biosensing to electro- and photocatalysis. However, due to strong quantum confinement effects, the size decrease often leads to an increase in the band gap, even in the emission of deep-ultraviolet (DUV) light, which greatly limits their applications. Here, we report a facile hot-tailoring strategy for fabricating carbon nitride nanodots (CNDs) with redshifted intrinsic photoluminescent (PL) emission, compared with the pristine bulk precursor. It has been found that the different leaving abilities of the C,N-containing groups during the pyrolysis stage and the chemical passivation during the liquid-collection stage played vital roles. Due to the redshifted photoluminescence and other attractive features, the as-obtained CNDs were successfully applied in visual double text encryption with higher security and also in bioimaging with photostability superior to traditional dyes. This work highlights the great potential of the hot-tailoring method in modulating carbon-based nanostructures and offsetting band-gap widening as the size decreases.

Ultrahigh-Performance Optoelectronics Demonstrated in Ultrathin Perovskite-Based Vertical Semiconductor Heterostructures.

Two-dimensional (2D) atomic layered semiconductor (e.g., transition metal dichalcogenides, TMDCs) heterostructures display diverse novel interfacial carrier properties and have potential applications in constructing next generation highly compact electronics and optoelectronics devices. However, the optoelectronic performance of this kind of semiconductor heterostructures has difficulty reaching the expectations of practical applications, due to the intrinsic weak optical absorption of the atomic-thick component layers. Here, combining the extraordinary optoelectronic properties of quantum-confined organic-inorganic hybrid perovskite (PVK), we design an ultrathin PVK/TMDC vertical semiconductor heterostructure configuration and realize the controlled vapor-phase growth of highly crystalline few-nanometer-thick PVK layers on TMDCs monolayers. The achieved ultrathin PVKs show strong thickness-induced quantum confinement effect, and simultaneously form band alignment-engineered heterointerfaces with the underlying TMDCs, resulting in highly efficient interfacial charge separation and transport. Electrical devices constructed with the as-grown ultrathin PVK/WS2 heterostructures show ambipolar transport originating from p-type PVK and n-type WS2, and exhibit outstanding optoelectronic characteristics, with the optimized response time and photoresponsivity reaching 64 μs and 11174.2 A/W, respectively, both of which are 4 orders of magnitude better than the heterostructures with a thick PVK layer, and also represent the best among all previously reported 2D layered semiconductor heterostructures. This work provides opportunities for 2D vertical semiconductor heterostructures via incorporating ultrathin PVK layers in high-performance integrated optoelectronics.

Novel synthesis of porous β-In2S3 ultrathin nanosheets with large lateral size

We report a novel hot-injection route to synthesize meso/macroporous β-In2S3 ultrathin nanosheets (UTNSs) with about 1.2 nm in thickness and a few micrometers in lateral dimensions using oleic acid (OA) as capping agent and liquid paraffin (LP) as reductive solvent. A reasonable formation mechanism involving redox reaction and oriented-growth was proposed: sulphur powder is reduced to S2− in LP by dehydrogenation process, and then reacts with In3+ to form In2S3 UTNSs under the inductive agent of OA and chloride ion. The large band gap (∼2.34 eV) and obvious blue-shifted absorption edge in the UV-Vis diffuse reflectance spectrum indicate a strong quantum confinement effect resulted from ultra-thinness structure. This low-cost and environment-friendly synthesis strategy provides an extended route to synthesize chalcogenide nanomaterials with ultrathin sheet-structure.

Halide Perovskite Nanocrystals for Next-Generation Optoelectronics.

Colloidal perovskite nanocrystals (PNCs) combine the outstanding optoelectronic properties of bulk perovskites with strong quantum confinement effects at the nanoscale. Their facile and low-cost synthesis, together with superior photoluminescence quantum yields and exceptional optical versatility, make PNCs promising candidates for next-generation optoelectronics. However, this field is still in its early infancy and not yet ready for commercialization due to several open challenges to be addressed, such as toxicity and stability. Here, the key synthesis strategies and the tunable optical properties of PNCs are discussed. The photophysical underpinnings of PNCs, in correlation with recent developments of PNC-based optoelectronic devices, are especially highlighted. The final goal is to outline a theoretical scaffold for the design of high-performance devices that can at the same time address the commercialization challenges of PNC-based technology.

Tuning the Electrochemical Property of the Ultrafine Metal‐oxide Nanoclusters by Iron Phthalocyanine as Efficient Catalysts for Energy Storage and Conversion

Nanoclusters (NCs) have been demonstrated of outstanding performance in electrochemical energy storage and conversion technologies due to their strong quantum confinement effects and strong interaction with supports. Here, we developed a class of ultrafine metal‐oxide (MOx, M = Fe, Co and Ni) NCs incorporated with iron phthalocyanine (FePc), MOx/FePc‐G, supported on graphene as high‐performance catalysts for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and carbon dioxide reduction (CO2RR). The high activities for ORR and OER are attributed to the electron donation and accepting ability of the highly redox active of FePc‐G that could tune the properties of MOx. The FeOx/FePc‐G exhibits an extremely positive half‐wave potential (E1/2) of 0.888 and 0.610 V for ORR in alkaline and neutral conditions, respectively, which is around 60 mV more positive than that of Pt/C. And NiOx/FePc‐G shows similar OER activity with the state‐of‐the‐art catalysts, Ir/C, and better performance than NiFeO NCs supported on graphene. Remarkably, the CoOx/FePc‐G and NiOx/FePc‐G show high activity and selectivity to reduce CO2 into CO with a low onset potential of −0.22 V (overpotential is 0.11 V).

Z-scan studies of Sn doped CuO nano-colloidal suspension

We report synthesis and characterization of l-valine capped Sn doped CuO nanoparticles (NPs). Pure and Sn doped CuO NPs were obtained by chemical co-precipitation method and were calcined at 500 °C for 2 h. X-ray diffraction (XRD) shows formation of crystalline CuO having monoclinic phase with average particle size of 8 nm. Utraviolet-visible (UV-vis) spectroscopy attests the formation of NPs and strong blue shift in the excitonic absorption has been observed for both uncalcined and calcined NPs. All samples show broad excitonic absorption in the wavelength range 351–654 nm due to inter band surface states transitions in CuO NPs. Fourier transform infra-red (FT-IR) spectroscopy confirms the role of l-valine as capping agent. Energy dispersive X-ray (EDX) spectroscopy confirms Sn doping into CuO. Transmission electron microscopy (TEM) attest the formation of CuO NPs having uniform near spherical shape. Third order NLO properties of undoped and Sn doped CuO NPs in the form of colloidal suspension have been investigated using Z-scan technique employing the fundamental wave at 1064 nm of a 7ns mode-locked Nd-YAG laser operating at 10 Hz. Sample with 5% Sn doping is found to possess strong nonlinear optical absorption and refraction due strong quantum confinement effect, TPA, ESA, etc. processess.

External stokes shift of perovskite nanocrystals enlarged by photon recycling

Lead halide perovskite nanocrystals (NCs) have rapidly emerged as promising materials for low-cost and high-efficiency photovoltaic, optoelectronic, and photonic devices. The Stokes shift is a crucial parameter affecting their performance. In this work, we find that the external Stokes shift is strongly dependent on photon recycling. Due to the nonlinear nature of the quantum confinement effect (QCE), the bandgap distribution becomes extremely broad when the sizes are ultra-small, resulting in many repetitions of photon recycling and substantial emission redshift. Thereby, the smaller NCs exhibit larger external Stokes shifts. In detail, for the small NCs with the most probable size of 6.4 nm, the intrinsic Stokes shift is about 71 meV, but the observed external Stokes shift becomes 143.4 meV in the concentrated solution, whereas the intrinsic and apparent Stokes shifts are 69 and 97.6 meV for large NCs of 9.7 nm. Therefore, photon recycling significantly contributes to the external Stokes shift of perovskite NCs, in particular for the ultra-small sizes with strong QCE. This finding will add to the growing fundamental physical understanding of perovskites, which is of great interest due to their applications in photovoltaics and other fields.

Large exciton binding energy, high photoluminescence quantum yield and improved photostability of organo-metal halide hybrid perovskite quantum dots grown on a mesoporous titanium dioxide template

Herein, we demonstrated a novel synthetic route to grow size-tunable hybrid perovskite (CH3NH3PbI3 and CH3NH3PbBr3) quantum dots (QDs) using a Fluorine-doped TiO2 (F-TiO2) mesoporous template and these QDs exhibit large exciton binding energy, high photoluminescence quantum yield and improved photostability. The pore size in F-TiO2 template is tuned by varying the HF molar concentration during its solvothermal growth and size of the perovskite QDs embedded in F-TiO2 pores is tuned in the range 1.7–5.1 nm, as revealed from the TEM analysis. A systematic blue-shift in UV–visible absorption edge, as well as photoluminescence (PL) spectrum, is observed with the reduced size of the perovskite QDs due to strong quantum confinement. The CH3NH3PbI3 QD with average size ∼1.7 nm exhibits ∼47 nm blue shift in the PL spectra, ∼43 fold enhancement in PL intensity and ∼25% PL quantum yield (QY). On the other hand, CH3NH3PbBr3 QD of similar size exhibits dramatically enhanced (∼124 times) PL emission with narrow line width and a PLQY of ∼57%, which is significant for the template-assisted growth of perovskite QDs film. The quantitative analysis of the PL emission energy vs QD size shows an excellent fit with the Brus equation confirming the strong quantum confinement effect in the perovskite QDs. Analysis of low-temperature PL spectra reveals very high exciton binding energy (162–272 meV) for the QDs as compared to the bulk film (32 meV) due to the high effective dielectric constant, and high electron-hole recombination probability in the QDs, which is consistent with the extremely high PLQY and stable emission from the QDs. The blue shift of the PL peak with increasing temperature is explained on the basis of localization effect. Time-resolved PL analysis for both the perovskite QDs reveals faster life time compared to their bulk counterparts, confirming the significant radiative recombination of carriers in the QDs at the room temperature. The CH3NH3PbBr3 QDs embedded in porous F-TiO2 template maintain its initial PL intensity up to several hours (≥10 h) under the UV laser exposure (18mW), while that of the bulk film decreases to <67%. Thus, template grown hybrid perovskite QDs exhibiting high photostability and very high PLQY demonstrated here are promising for the next generation optoelectronic applications.

Hydrothermal-solvothermal cutting integrated synthesis and optical properties of MoS2 quantum dots

In this work, uniform MoS2 quantum dots (QDs) are fabricated by a novel hydrothermal-solvothermal cutting integrated route. The resulting products possess few-layer thickness with an average size about 2.6 nm. Due to the strong quantum confinement effect, the obtained MoS2 QDs showed an enlarged band gap of 3.90 eV and a good photoluminescence property. Furthermore, this cost-effective and efficacious method may provide a potential advance for preparation of other layered material QDs.

Morphology Control and Growth Mechanism Study of Quantum-Sized ZnS Nanocrystals from Single-Source Precursors

The growing demand of metal sulfides using in various applications has in turn greatly stimulated basic research to develop novel nanomaterials with controlled size, shape, phase and desired properties. Specifically, ultrathin ZnS nanowires with diameter of less than 2 nm have attracted significant interest because of their considerable promise in sensors, phosphor host materials, photodetectors, and other devices. A novel method for the synthesis of controlled morphology, phase and size of ZnS nanocrystals has been developed. Especially, ultrathin ZnS nanowires with 1.5 nm in diameter were synthesized from single-source precursor zinc dicarbazoledithiocarbamate using oleylamine as capping ligand and solvent. Strong quantum confinement effects related to the unique nature of these ultrathin ZnS nanowires were observed. More importantly, we have presented the evidence for the assembly of ultra-small ZnS nanoparticles in 1-D polymer-like structures achieved by oriented attachment mechanism for synthesis of ultrathin ZnS nanowires.

Ultrasmall and Monolayered Tungsten Dichalcogenide Quantum Dots with Giant Spin-Valley Coupling and Purple Luminescence.

Monolayered tungsten dichalcogenide quantum dots (WS2 QDs) have various potential applications due to their large spin–valley coupling and excellent photoluminescence (PL) properties. What is expected is that with the decrease in lateral size of QDs, the stronger quantum confinement effect will dramatically strengthen the spin–valley coupling and widen the band gap. However, ultrasmall monolayered WS2 QDs prepared by ion intercalation unavoidably undergo the problem of structural defects, which will create defect levels and significantly change their properties. In this study, we report that by annealing defective monolayered WS2 QDs in sulfur vapor, pristine monolayered WS2 QDs with an ultrasmall lateral size of ca. 1.8–3.8 nm can be obtained. The results show that the ultrasmall monolayered WS2 QDs exhibit a giant spin–valley coupling of ca. 821 meV. Moreover, the pristine ultrasmall monolayered WS2 QDs show purple PL centered at 416 nm, and the defect PL peaks in defective WS2 QDs can be effectively removed by annealing. All of these results afford the ultrasmall monolayered QDs various applications such as in optoelectronics, spintronics, valleytronics, and so on.

UV induced synthesis of starch capped CdSe quantum dots: Functionalization with thiourea and application in sensing heavy metals ions in aqueous solution

Herein, a highly facile, rapid and one-pot approach has been applied for the synthesis of water soluble starch capped CdSe quantum dots (QDs) by using UV irradiation in the aqueous solution containing cadmium sulphate, sodium selenosulfate, acetone and 2-propanol. No external reducing agents were added to the solution, as the radicals generated in situ upon photoirradiation i.e., 2-hydroxy-2-propyl radicals, (CH3)2COH could reduce the precursor ions for the synthesis of these QDs. These QDs were characterised by various techniques such as UV–Vis absorption, XRD, Raman, FTIR, TEM and SEM measurements. The presence of strong quantum confinement effects could be realized from their very small size i.e., ∼3 nm as revealed by TEM studies. Besides, these QDs were found to exhibit photoluminescence (PL) in the longer wavelength region. The PL intensity as well as the charge carrier lifetime values could be conveniently tuned by simply varying the Cd to Se precursor ratio during the synthesis. Furthermore, a relatively novel approach has been adopted to extract these QDs from the colloidal solution by freezing it to 0 °C followed by de-freezing to room temperature. The extracted QDs were functionalized with thiourea in order to increase the PL quantum yield and the stability of the QDs. The effects of pH and temperature on the PL intensity of functionalized CdSe QDs were also investigated to explore their applicability in sensing of heavy metal ions. Interestingly, the QDs displayed highly selective PL quenching in the presence of Cu2+, Cr6+ and Hg2+ metal ions. The limits of detection for these metal ions have been determined and a probable PL quenching mechanism is postulated.

Novel Two-Dimensional Semiconductor SnP3 with High Carrier Mobility, Good Light Absorption, and Strong Interlayer Quantum Confinement

We propose a novel two-dimensional (2D) SnP3 crystal that possesses low indirect band gaps of 0.67 eV (monolayer) and 1.03 eV (bilayer) and high kinetic and thermal stability until 500 K. The 2D SnP3 shows strong interlayer quantum confinement effects, resulting in a band gap increase from mono- to bilayer, and then a band gap decrease from bi- to triple layer leading to a semiconductor–metal transition. Monolayer SnP3 has large hole mobility (992 cm2 V–1 s–1), whereas bilayer SnP3 has high electron mobility (8002 cm2 V–1 s–1) which is comparable to that of phosphorene. The static dielectric constants of mono- and bilayer SnP3 are 3.21 and 5.24, respectively. Both monolayer and bilayer SnP3 show strong light absorption in the visible and ultraviolet regions. The indirect band gap of monolayer SnP3 decreases under biaxial compressive strain and increases under biaxial tensile strain. Especially, when the biaxial compressive strain reaches to 6%, monolayer SnP3 has a transition from semiconductor to metal. ...

Red emissive Ag2Se quantum dots (QDs) with room-temperature synthesis of both orthorhombic and superionic cubic phases via stirring approach

In this research Ag2Se quantum dots (QDs) were synthesized with just a stirring room-temperature approach, using AgNO3 and Na2SeO3 as precursors and thioglycolic acid (TGA) as capping agent molecule. Synthesized QDs were characterized by means of XRD, FTIR, FESEM, EDS, HRTEM, UV–Vis and PL analyses. Synthesized QDs were in orthorhombic phase of Ag2Se (β-Ag2Se) with a uniform size distribution histogram between 1.8 and 2.5 nm. Synthesized QDs indicated two sharp exciton absorption peaks at 440 and 607 nm at room temperature and a narrow red emission between 600 and 800 nm with a peak at about 673 nm and FWHM of about 57 nm. The quantum yield was obtained about 4.48% which is highest among reported values. It was found that orthorhombic (β-Ag2Se) and superionic cubic (α-Ag2Se) phases can simply be formed at room temperature only by changing the sequence of addition of TGA capping agent. The cubic phase co-exists with orthorhombic phase was identified by XRD and it revealed also exciton absorption bands at room temperature due to strong quantum confinement effects.