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PbTe and PbSe are among the most promising thermoelectric materials used in the mid-temperature (400–900 K) power generation range. In these materials the efficiency increase in thermoelectric performance is critically related to the lowering of lattice thermal conductivity (κL), without compromising the electronic power factor. By means of state-of-the-art equilibrium molecular dynamics (EMD), we investigate heat transport in several nanostructured PbTe/PbSe models as a function of material morphology. Layered composites show a reduction of the average κL of about 35 % with respect to the bulk. The insertion of PbSe nanoparticles into a PbTe matrix, or viceversa PbTe into PbSe reduces κL by up to 45 % while in more anisotropic nanocomposites the reduction exceeds PbSe/PbTe alloys. Layered composites show the lowest lattice thermal conductivity in the direction of layer stacking, for which an optimal thickness is identified. Along this line we provide a full account of the impact of alloying and (sub)nanostructuring on heat transport for this important class of materials. Particularly anisotropic nano-dot morphologies and layered (sub)nanocomposites emerge as a paradigm for outstanding thermoelectric materials.

In the confined zone between a bidimensional material and a metal surface, unexpected effects can take place. In this study, we show that when a nonregular two-dimensional h-BN layer is grown on a Cu(111) surface, metal adatoms spontaneously pop up from the bulk to fill the holes in the structure. We provide ample theoretical support to our findings based on a large set of dispersion-corrected density functional theory calculations and on a detailed analysis of the electronic properties and of the chemical processes at this peculiar interface. The observation can be rationalized in terms of a high affinity of Cu adatoms toward N-donor species. Defective h-BN, exposing N-terminated edges, behaves like a giant multi-N-donor macrocyclic ligand that can encapsulate metal atoms as a consequence of a huge stabilization deriving from the Cu–N bond formation. Our conclusions could apply to other metal surfaces and could even stimulate the idea of trapping different metal atoms from those of the underlying surface (e.g., more precious but more active metals) for catalytic purposes

Metal-doped and metal-supported two-dimensional materials are attracting a lot of interest as potentially active electrocatalysts for reduction and oxidation processes. Previously, when a non-regular 2 D h-BN layer was grown on a Cu(111) surface, metal adatoms were found to spontaneously emerge from the bulk to fill the atomic holes in the structure and become available for surface catalysis. Herein, computational electrochemistry is used to investigate and compare the performance of Cu-doped and Cu-supported pristine and defective h-BN systems for the electrocatalytic water oxidation reaction. For the various model systems, the intermediate species of this multistep oxidation process are identified and the free-energy variations for each step of reaction are computed, even for those steps that do not involve an electron or a proton transfer. Both associative and O2 direct evolution mechanisms are considered. On this thermodynamic basis, the potential-determining step, the thermodynamic-determining step, and consequently the theoretical overpotential are determined for comparison with experiments. Small Cu clusters (tetramers) trapped in the h-BN defective lattice on a Cu(111) support are found to be very active for the water oxidation reaction since such systems are characterized by a low overpotential and by a small energy cost for O2 release from the catalyst, which is often observed to be a major limit for other potential electrocatalysts.

Functionalizing nanoparticles (NPs) with biological molecules is apromising modern strategy in bionanotechnology to build up smart bioinorganicdevices for medical applications. Bifunctional linkers provide an interesting andductile bioconjugation approach especially because they behave not only asanchoring and tethering agents but also as spacers between the NP and thebiomolecules, which helps in maintaining their 3D structural and functionalproperties. In this work, by means of a wide set of density functional theory(DFT) electronic structure calculations and density functional tight binding(DFTB) molecular dynamics simulations, we provide an all-round investigation ofthe functionalization of realistic curved TiO2 NPs (2−3 nm size with∼800atoms) with a catechol derivative, such as dopamine and DOPAC. We span fromsingle-molecule adsorption to the full coverage regime. For the low coverage, weachieve a detailed description of the mechanisms of molecular adsorption, of theinterfacial electronic charge-transfer effects, and of the processes following visiblelight irradiation (exciton formation, trapping, charge carrier diffusion, or recombination). We then consider a growing molecularlayer on the NP and analyze the self-assembling mechanism and the effects on the electronic properties of the complex. Finally,for the maximum coverage (46 molecules per NP) we perform molecular dynamics runs at 300 K to compare the molecularconfiguration and electronic properties of the NP/linker complex interface before and after thermal treatment to better accountfor the competition between molecule/surface and molecule/molecule interactions. The use of curved NP surfaces combinedwith dopamine, with respect to aflat one and DOPAC, respectively, is found to be more effective for bioconjugation

TiO2 nanoparticles (NPs) are attracting materials for biomedical applications, provided that they are coated with polymers to improve solubility, dispersion and biocompatibility. Conformation, coverage density and solvent effects largely influence their functionality and stability. In this work, we use atomistic molecular dynamics simulations to study polyethylene glycol (PEG) grafting to highly curved TiO2 NPs (2-3 nm) in different solvents. We compare the coating polymer conformations on NPs with those on (101) flat surfaces. In water, the transition from mushroom to brush conformation starts only at high density ({\sigma} = 2.25 chains/nm2). In dichloromethane (DCM), at low-medium coverage ({\sigma} < 1.35 chains/nm2), several interactions between the PEG chains backbone and undercoordinated Ti atoms are established, whereas at {\sigma} = 2.25 chains/nm2 the conformation clearly becomes brush-like. Finally, we demonstrate that these spherical brushes, when immersed in water, but not in DCM, follow the Daoud-Cotton (DC) classical scaling model for the polymer volume fraction dependence with the distance from the center of star-shaped systems.

The ability to actively regulate heat flow at the nanoscale could be a game changer for applications in thermal management and energy harvesting. Such a breakthrough could also enable the control of heat flow using thermal circuits, in a manner analogous to electronic circuits. Here we demonstrate switchable thermal transistors with an order of magnitude thermal on/off ratio, based on reversible electrochemical lithium intercalation in MoS2 thin films. We use spatially-resolved time-domain thermoreflectance to map the lithium ion distribution during device operation, and atomic force microscopy to show that the lithiated state correlates with increased thickness and surface roughness. First principles calculations reveal that the thermal conductance modulation is due to phonon scattering by lithium rattler modes, c-axis strain, and stacking disorder. This study lays the foundation for electrochemically-driven nanoscale thermal regulators, and establishes thermal metrology as a useful probe of spatio-temporal intercalant dynamics in nanomaterials., Thermal transistors can enable game changing applications in energy harvesting and heat routing. Here, the authors demonstrate reversible thermal modulation of nearly 10 times by ion intercalation in MoS2 nanofilms. A new thermal microscopy technique allows operando imaging of Li ion segregation.

Heterogeneous photocatalysis is vital in solving energy and environmental issues that this society is confronted with. Although photocatalysts are often operated in the presence of water, it has not been yet clarified how the interaction with water itself affects charge dynamics in photocatalysts. Using water-coverage-controlled steady and transient infrared absorption spectroscopy and large-model (∼800 atoms) ab initio calculations, we clarify that water enhances hole trapping at the surface of TiO2 nanospheres but not of well-faceted nanoparticles. This water-assisted effect unique to the nanospheres originates from water adsorption as a ligand at a low-coordinated Ti–OH site or through robust hydrogen bonding directly to the terminal OH at the highly curved nanosphere surface. Thus, the interaction with water at the surface of nanospheres can promote photocatalytic reactions of both oxidation and reduction by elongating photogenerated carrier lifetimes. This morphology-dependent water-assisted effect provides a novel and rational basis for designing and engineering nanophotocatalyst morphology to improve photocatalytic performances.

Despite the many successful syntheses and applications of dopamine-functionalized TiO 2 nanohybrids, there has not yet been an atomistic understanding of the interaction of this 1,2-dihydroxybenzene derivative ligand with the titanium dioxide surfaces. In this work, on the basis of a wide set of dispersion-corrected hybrid density functional theory (DFT) calculations and density functional tight binding (DFTB) molecular dynamics simulations, we present a detailed study of the adsorption modes, patterns of growth, and configurations of dopamine on the anatase (101) TiO 2 surface, with reference to the archetype of 1,2-dihydroxybenzene ligands, i.e., catechol. At low coverage, the isolated dopamine molecule prefers to bend toward the surface, coordinating the NH 2 group to a Ti 5c ion. At high coverage, the packed molecules succeed in bending toward the surface only in some monolayer configurations. When they do, we observe a proton transfer from the surface to the ethyl-amino group, forming terminal NH 3+ species, which highly interact with the O atoms of a neighboring dopamine molecule. This strong Coulombic interaction largely stabilizes the self-assembled monolayer. On the basis of these results, we predict that improving the probability of dopamine molecules being free to bend toward the surface through thermodynamic versus kinetic growth conditions will lead to a monolayer of fully protonated dopamine molecules.

Computational modeling of titanium dioxide nanoparticles of realistic size is extremely relevant for the direct comparison with experiments but it is also a rather demanding task. We have recently worked on a multistep/scale procedure to obtain global optimized minimum structures for chemically stable spherical titania nanoparticles of increasing size, with diameter from 1.5 nm (~300 atoms) to 4.4 nm (~4000 atoms). We use first self-consistent-charge density functional tight-binding (SCC-DFTB) methodology to perform thermal annealing simulations to obtain globally optimized structures and then hybrid density functional theory (DFT) to refine them and to achieve high accuracy in the description of structural and electronic properties. This allows also to assess SCC-DFTB performance in comparison with DFT(B3LYP) results. As a further step, we investigate photoexcitation and photoemission processes involving electron/hole pair formation, separation, trapping and recombination in the nanosphere of medium size by hybrid DFT. Finally, we show how a recently defined new set of parameters for SCC-DFTB allows for a proper description of titania/water multilayers interface, which paves the way for modeling large realistic nanoparticles in aqueous environment.

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The presence of defects in the graphenic layers deposited on metal surfaces modifies the nature of the interaction. Unsaturated carbon atoms, due to vacancies in the lattice, form strong organometallic bonds with surface metal atoms that highly enhance the binding energy between the two materials. We investigate by means of a wide set of dispersion-corrected density functional theory calculations how such strong chemical bonds affect both the electronic properties of these hybrid interfaces and the chemical reactivity with water, which is commonly present in the working conditions. We compare different metal substrates (Cu vs Pt) that present a different type of interaction with graphene and with defective graphene. This comparative analysis allows us to unravel the controlling factors of water reactivity, the role played by the carbon vacancies and by the confinement or "graphene cover effect". Water is capable of breaking the C-Cu bond by dissociating at the undercoordinated carbon atom of the vacancy, restoring the weak van der Waals type of interaction between the two materials that allows for an easy detachment of graphene from the metal, but the same is not true in the case of Pt, where C-Pt bonds are much stronger. These conclusions can be used to rationalize water reactivity at other defective graphene/metal interfaces.

A detailed understanding of the relation between microscopic structure and phonon propagation at the nan oscale is essential to design materials with desired phononic and thermal properties.Here we uncover a new mechanism of phonon interaction in surface oxidized membranes, i.e., native oxide layers interact with phonons in ultra-thin silicon membranes through local resonances. The local resonances reduce the low frequency phonon group velocities and shorten their mean free path. This effect opens up a new strategy for ultralow thermal conductivity design as it complements the scattering mechanism which scatters higher frequency modes effectively. The combination of native oxide layer and alloying with germanium in concentration as small as 5% reduces the thermal conductivity of silicon membranes to 100 time lower than the bulk. In addition, the resonance mechanism produced by native oxide surface layers is particularly effective for thermal condutivity reduction even at very low temperatures, at which only low frequency modes are populated., Comment: 6 pages, 5 figures, Accepted for publication in Physical Review B

Structural, electronic and transport properties of defect-free, defected and functionalized armchair and zig-zag graphene nanoribbons (GNRs) are investigated with density functional theory and non-equilibrium Green's function calculations and rationalized in terms of Clar's theory of the aromatic sextet. Calculations suggest a tight relationship between the transport properties of nanoribbons and the underlying bond patterning as described by valence bond and Clar sextet theory. Namely, armchair GNRs exhibit a strong dependence of the transport properties on the ribbon width, as a consequence of different valence bond representations. The occurrence of localized defects involving electron pairs does not significantly alter this behavior. Conversely, transport properties of zigzag GNRs are less affected by morphological details, such as width and occurrence of defects, as expected from the application of Clar's theory. However, controlled edge functionalization and morphology modifications in zigzag GNRs can potentially lead to localization of aromatic sextets and, consequently, to strong changes in the transport properties. Our work indicates Clar sextet theory as a powerful and accurate tool to rationalize and predict the electronic and transport properties of complex carbon nanostructures based on GNRs. These principles can be extended to the design of novel systems with potential applications in nanoelectronics. (C) 2014 Elsevier Ltd. All rights reserved.

Carbon is a surprising material in all respects. In this Review, we present results of metadynamics calculations for crystal structure prediction of novel carbon polymorphs with even and odd rings. So-called superhard graphite results from cold-compressing graphite. We review the results of molecular dynamics simulations on the graphite-to-diamond phase transition, that yields Oganov's M-carbon. The latter, like some of the modifications predicted by metadynamics, features five- and seven-membered odd rings. We identify the role of odd rings at times of phase nucleation, and we speculate on the preference for odd-membered rings over even motifs in a context of nucleation and phase growth.

Understanding magnetism in defective graphene is paramount to improve and broaden its technological applications. A single vacancy in graphene is expected to lead to a magnetic moment with both a σ (1 μB) and a π (1 μB) component. Theoretical calculations based on standard LDA or GGA functional on periodic systems report a partial quenching of the π magnetization (0.5 μB) due to the crossing of two spin split bands at the Fermi level. In contrast, STS experiments ( Phys. Rev. Lett. 2016, 117, 166801) have recently proved the existence of two defect spin states that are separated in energy by 20–60 meV. In this work, we show that self-interaction corrected hybrid functional methods (B3LYP-D*) are capable of correctly reproducing this finite energy gap and, consequently, provide a π magnetization of 1 μB. The crucial role played by the exact exchange is highlighted by comparison with PBE-D2 results and by the magnetic moment dependence with the exact exchange portion in the functional used. The ground state ferromagnetic planar solution is compared to the antiferromagnetic and to the diamagnetic ones, which present an out-of-plane distortion. Periodic models are then compared to graphene nanoflakes of increasing size (up to C383H48). For large models, the triplet spin configuration (total magnetization 2 μB) is the most stable, independently of the functional used, which further corroborates the conclusions of this work and puts an end to the long-debated issue of the magnetic properties of an isolated C monovacancy in graphene

TiO2 nanoparticles (NPs) are nowadays considered fundamental building blocks for many technological applications. Morphology is found to play a key role with spherical NPs presenting higher binding properties and chemical activity. From the experimental point of view, the characterization of these nano-objects is extremely complex, opening a large room for computational investigations. In this work, TiO2 spherical NPs of different sizes (from 300 to 4000 atoms) have been studied with a two-scale computational approach. Global optimization to obtain stable and equilibrated nanospheres was performed with a self-consistent charge density functional tight-binding (SCC-DFTB) simulated annealing process, causing a considerable atomic rearrangement within the nanospheres. Those SCC-DFTB relaxed structures have been then optimized at the DFT(B3LYP) level of theory. We present a systematic and comparative SCC-DFTB vs DFT(B3LYP) study of the structural properties, with particular emphasis on the surface-to-bulk sites ratio, coordination distribution of surface sites, and surface energy. From the electronic point of view, we compare HOMO-LUMO and Kohn-Sham gaps, total and projected density of states. Overall, the comparisons between DFTB and hybrid density functional theory show that DFTB provides a rather accurate geometrical and electronic description of these nanospheres of realistic size (up to a diameter of 4.4 nm) at an extremely reduced computational cost. This opens for new challenges in simulations of very large systems and more extended molecular dynamics.

In biomedical applications, TiO2 nanoparticles are generally coated with polymers to prevent agglomeration, improve biocompatibility, and reduce cytotoxicity. Although the synthesis processes of such composite compounds are well established, there is still a substantial lack of information on the nature of the interaction between the titania surface and the organic macromolecules. In this work, the adsorption of polyethylene glycol (PEG) on the TiO2 (101) anatase surface is modeled by means of dispersion-corrected density functional theory (DFT-D2) calculations. The two extreme limits of an infinite PEG polymer [−(OCH2CH2)n], on one side, and of a short PEG dimer molecule [H(OCH2CH2)2OH], on the other, are analyzed. Many different molecular configurations and modes of adsorption are compared at increasing surface coverage densities. At low and medium coverage, PEG prefers to lay down on the surface, while at full coverage, the adsorption is maximized when PEG molecules bind perpendicularly to the surface and interact with each other through lateral dispersions, following a mushroom to brush transition. Finally, we also consider the adsorption of competing water molecules at different coverage densities, assessing whether PEG would remain bonded to the surface or desorb in the presence of the aqueous solvent.

Finite-length models of chiral semiconducting carbon nanotubes based on Clar sextet theory allowed carrying out accurate calculations, performed by application of gradient-corrected density functional theory, on the energetic of sidewall reactions. In particular, we analyzed the addition of atomic fluorine and carbene (CH2) to (6,4) and (6,5) nanotubes, finding excellent convergence of reaction energies with respect to the model length and good agreement with literature data. Our study demonstrates the importance of using models of carbon nanotubes based on chemical considerations to evaluate consistently the electronic and reactive properties of the sidewall.

In biomedical applications, TiO2 nanoparticles are generally coated with polymers to prevent agglomeration, improve biocompatibility, and reduce cytotoxicity. Although the synthesis processes of such composite compounds are well established, there is still a substantial lack of information on the nature of the interaction between the titania surface and the organic macromolecules. In this work, the adsorption of polyethylene glycol (PEG) on the TiO2 (101) anatase surface is modeled by means of dispersion-corrected density functional theory (DFT-D2) calculations. The two extreme limits of an infinite PEG polymer [-(OCH2CH2)n], on one side, and of a short PEG dimer molecule [H(OCH2CH2)2OH], on the other, are analyzed. Many different molecular configurations and modes of adsorption are compared at increasing surface coverage densities. At low and medium coverage, PEG prefers to lay down on the surface, while at full coverage, the adsorption is maximized when PEG molecules bind perpendicularly to the surface and interact with each other through lateral dispersions, following a mushroom to brush transition. Finally, we also consider the adsorption of competing water molecules at different coverage densities, assessing whether PEG would remain bonded to the surface or desorb in the presence of the aqueous solvent. (Chemical Equation Presented).

Thermoelectric materials are strategically valuable for sustainable development, as they allow for the generation of electrical energy from wasted heat. In recent years several strategies have demonstrated some efficiency in improving thermoelectric properties. Dopants affect carrier concentration, while thermal conductivity can be influenced by alloying and nanostructuring. Features at the nanoscale positively contribute to scattering phonons, however those with long mean free paths remain difficult to alter. Here we use the concept of hierarchical nano-grains to demonstrate thermal conductivity reduction in rocksalt lead chalcogenides. We demonstrate that grains can be obtained by taking advantage of the reconstructions along the phase transition path that connects the rocksalt structure to its high-pressure form. Since grain features naturally change as a function of size, they impact thermal conductivity over different length scales. To understand this effect we use a combination of advanced molecular dynamics techniques to engineer grains and to evaluate thermal conductivity in PbSe. By affecting grain morphologies only, i.e. at constant chemistry, two distinct effects emerge: the lattice thermal conductivity is significantly lowered with respect to the perfect crystal, and its temperature dependence is markedly suppressed. This is due to an increased scattering of low-frequency phonons by grain boundaries over different size scales. Along this line we propose a viable process to produce hierarchical thermoelectric materials by applying pressure via a mechanical load or a shockwave as a novel paradigm for material design.

We explore the effect of isotropic strain on the electronic structure of graphene. It is shown that the interplay between one-particle band narrowing and sizable multiorbital Coulomb interactions induces a transition from a Dirac-liquid semimetal to an orbital selective metal characterized by narrow $\ensuremath{\pi}$-orbital Kondo clouds and abrupt downshift of ${\ensuremath{\sigma}}^{*}$ states. The correlated electronic structure we derive is promising in the sense that it leads to results that might explain the reshaped electronic structure of graphene nanobubbles probed in scanning tunneling microscopy. Our proposal is a key step in understanding the intricate and interdependent changes in orbital and electronic degrees of freedom of strained materials with hexagonal lattice structure.

Review: discussion of crystal structure predictions of novel carbon polymorphs with even and odd rings; 47 refs.

The existence of polymorphs or chemical element allotropes is a fact of nature that remains surprising. On the one hand, it is unevenly distributed, with only some compounds or elements distinguished by a large number of polymorphs or allotropes. On the other hand, many crystal structure are predicted, which can exist in principle. We argue that this imbalance may derive form an imperfect knowledge of transformation mechanisms, which solely determine the formation of a certain product. Especially in a scenario of nucleation and growth, reasoning on the mechanical stability of the final product only may mislead the overall judgement on the accessibility of a particular compound. We illustrate mechanistic analysis of selected reconstructive phase transitions by state of the art accelerated molecular dynamics techniques. We emphasize the role of nucleation in phase selection, and stress the necessary inclusion of details on intermediate steps for a more capable crystal structure prediction activity.

By means of ab initio metadynamics runs we explored the lower-pressure region of the phase diagram of germanium. A monoclinic germanium phase with four-membered rings, less dense than diamond and compressible into \beta-tin phase (tI4) was found. A metallic bct-5 phase, mechanically stable down to room conditions appeared between diamond and tI4. mC16 is a narrow-gap semiconductor, while bct-5 is metallic and potentially still superconducting in the very low pressure range. This finding may help resolving outstanding experimental issues., Comment: 6 figures

We use ab initio density-functional calculations to determine the interaction of a graphene monolayer with the Si(111) surface. We find that graphene forms strong bonds to the bare substrate and accommodates the 12% lattice mismatch by forming a wavy structure consisting of free-standing conductive ridges that are connected by ribbon-shaped regions of graphene, which bond covalently to the substrate. We perform quantum transport calculations for different geometries to study changes in the transport properties of graphene introduced by the wavy structure and bonding to the Si substrate. Our results suggest that wavy graphene combines high mobility along the ridges with efficient carrier injection into Si in the contact regions. DOI: 10.1103/PhysRevLett.110.176805

Four sp3 carbon allotropes with six, eight, and 16 atoms per primitive cell have been derived using a combination of metadynamics simulations and topological scan. A chiral orthorhombic phase oC16 (C2221) was found to be harder than monoclinic M-carbon and shows excellent stability in the high-pressure range. A second orthorhombic phase of Cmmm symmetry, by \sim 0.028 eV/atom energetically lower than W-carbon, can be formed from graphite at \sim 9 GPa. In general, the mechanical response under pressure was found to depend on the structure topology, which reflects the way rings are formed from an initial graphene layer stacking., Comment: 5 pages, 5 figures

We investigate the interaction of a graphene monolayer with the C(111) diamond surface using ab initio density functional theory. To accommodate the lattice mismatch between graphene and diamond, the overlayer deforms into a wavy structure that binds strongly to the diamond substrate. The detached ridges of the wavy graphene overlayer behave electronically as free-standing polyacetylene chains with delocalized π electrons, separated by regions containing only sp(3) carbon atoms covalently bonded to the (111) diamond surface. We performed quantum transport calculations for different geometries of the system to study how the buckling of the graphene layer and the associated bonding to the diamond substrate affect the transport properties. The system displays high carrier mobility along the ridges and a wide transport gap in the direction normal to the ridges. These intriguing, strongly anisotropic transport properties qualify the hybrid graphene-diamond system as a viable candidate for electronic nanodevices.

Using molecular dynamics simulations and a Density Functional based Tight Binding method, the metastable germanium allotropes hR8 and cI16 are shown to interconvert by means of two sets of quasi-1D chains. The first set hosts sequences of SN2 inversions of Ge tetrahedral centers, and represents the activated step. The second set does not imply any reconstruction, but assists the first one in propagating the reconstruction. The overall process is commenced by bond nucleation, followed by chain formation and reconstruction into either structure. A novel intermediate metastable phase is visited in the process. Elementary steps of chemical reactivity are accessible due to the appropriate time and spatial resolution of the methods used. This paves the way for a chemical understanding of structure reconstruction and metastable phase formation in solid materials.

The possibility of tuning the electronic properties of graphene by tailoring the morphology at the nanoscale or by chemical functionalization opens interesting perspectives towards the realization of devices for nanoelectronics. Indeed, the integration of the intrinsic high carrier mobilities of graphene with functionalities that are able to react to external stimuli allows in principle the realization of highly efficient nanostructured switches. In this paper, we report a novel approach to the design of reversible switches based on functionalized graphene nanoribbons, operating upon application of an external redox potential, which exhibit unprecedented ON/OFF ratios. The properties of the proposed systems are investigated by electronic structure and transport calculations based on density functional theory and rationalized in terms of valence-bond theory and Clar's sextet theory.

PEGylation of metal oxide nanoparticles is the common approach to improve their biocompatibility and in vivo circulation time. In this work, we present a combined experimental and theoretical study to determine the operating condition that guarantee very high grafting densities, which are desirable in any biomedical application. Moreover, we present an insightful conformational analysis spanning different coverage regimes and increasing polymer chain lengths. Based on 13C NMR measurements and molecular dynamics simulations, we show that classical and popular models of polymer conformation on surfaces fail in determining the mushroom-to-brush transition point and prove that it actually takes place only at rather high grafting density values.