Undercooled State Research Articles

Discovery of Q-BN and Direct Conversion of h-BN into c-BN and Formation of Epitaxial c-BN/Diamond Heterostructures

ABSTRACTWe review the discovery of a new phase BN (named Q-BN) which has been created by nanosecond laser melting in the super undercooled state and quenching rapidly with rates exceeding several billion degrees per second. This phase, sequel to our earlier discovery of Q-Carbon, has amorphous structure from which phase-pure c-BN is formed in the form of nanodots, microcrystals, nanoneedles, and microneedles. Large-area single c-BN are formed by providing a template for epitaxial growth during quenching of super undercooled liquid BN. Since there is a rapid crystal growth from liquid, both n- and p-type dopants can be incorporated into electrically active substitutional sites with concentrations exceeding solubility limits through the phenomenon of solute trapping. We have grown diamond on c-BN by pulsed laser deposition of carbon at 500°C without the presence of hydrogen, and created c-BN and diamond epitaxial composites. We discuss the mechanism of epitaxial c-BN and diamond growth on lattice matching c-BN template under pulsed laser evaporation of amorphous carbon. This discovery on direct conversion of h-BN into phase-pure c-BN at ambient temperatures and pressures in air, represents a seminal contribution to the field of boron nitride, which is quite complementary to our discovery of graphite to diamond conversion. We have bypassed thermodynamics with the help of kinetics and time control. This research represents a major breakthrough for c-BN and diamond based high-power electronic and photonic devices, and host of other applications related to high-speed machining, deep-sea drilling, field-emission displays and biomedical applications.

Retraction Note to: Fundamental Discovery of New Phases and Direct Conversion of Carbon into Diamond and hBN into cBN and Properties

We review the discovery of new phases of carbon (Q-carbon) and BN (Q-BN) and address critical issues related to direct conversion of carbon into diamond and hBN into cBN at ambient temperatures and pressures in air without any need for catalyst and the presence of hydrogen. The Q-carbon and Q-BN are formed as a result of quenching from super undercooled state by using high-power nanosecond laser pulses. We discuss the equilibrium phase diagram (P vs T) of carbon, and show that by rapid quenching, kinetics can shift thermodynamic graphite/diamond/liquid carbon triple point from 5000 K/12 GPa to super undercooled carbon at atmospheric pressure in air. Similarly, the hBN-cBN-Liquid triple point is shifted from 3500 K/9.5 GPa to as low as 2800 K and atmospheric pressure. It is shown that nanosecond laser heating of amorphous carbon and nanocrystalline BN on sapphire, glass, and polymer substrates can be confined to melt in a super undercooled state. By quenching this super undercooled state, we have created a new state of carbon (Q-carbon) and BN (Q-BN) from which nanocrystals, microcrystals, nanoneedles, microneedles, and thin films are formed depending upon the nucleation and growth times allowed and the presence of growth template. The large-area epitaxial diamond and cBN films are formed, when appropriate planar matching or lattice matching template is provided for growth from super undercooled liquid. The Q-phases have unique atomic structure and bonding characteristics as determined by high-resolution SEM and backscatter diffraction, HRTEM, STEM-Z, EELS, and Raman spectroscopy, and exhibit new and improved mechanical hardness, electrical conductivity, and chemical and physical properties, including room-temperature ferromagnetism and enhanced field emission. The Q-carbon exhibits robust bulk ferromagnetism with estimated Curie temperature of about 500 K and saturation magnetization value of 20 emu g−1. We have also deposited diamond on cBN by using a novel pulsed laser evaporation of carbon and obtained cBN/diamond composites, where cBN acts as template for diamond growth. Both diamond and cBN grown from super undercooled liquid can be alloyed with both p- and n-type dopants. This process allows carbon to diamond and hBN to cBN conversions and formation of useful nanostructures and microstructures at ambient temperatures in air at atmospheric pressure on practical and heat-sensitive substrates in a controlled way without need for any catalysts and hydrogen to stabilize sp3 bonding for diamond and cBN phases.

Direct conversion of h-BN into c-BN and formation of epitaxial c-BN/diamond heterostructures

We have created a new state of BN (named Q-BN) through rapid melting and super undercooling and quenching by using nanosecond laser pulses. Phase pure c-BN is formed either by direct quenching of super undercooled liquid or by nucleation and growth from Q-BN. Thus, a direct conversion of hexagonal boron nitride (h-BN) into phase-pure cubic boron nitride (c-BN) is achieved by nanosecond pulsed laser melting at ambient temperatures and atmospheric pressure in air. According to the P-T phase diagram, the transformation from h-BN into c-BN under equilibrium processing can occur only at high temperatures and pressures, as the hBN-cBN-Liquid triple point is at 3500 K/9.5 GPa or 3700 K/7.0 GPa with a recent theoretical refinement. Using nonequilibrium nanosecond laser melting, we have created super undercooled state and shifted this triple point to as low as 2800 K and atmospheric pressure. The rapid quenching from super undercooled state leads to the formation of a new phase, named as Q-BN. We present detailed characterization of Q-BN and c-BN layers by using Raman spectroscopy, high-resolution scanning electron microscopy, electron-back-scatter diffraction, high-resolution TEM, and electron energy loss spectroscopy, and discuss the mechanism of formation of nanodots, nanoneedles, microneedles, and single-crystal c-BN on sapphire substrate. We have also deposited diamond by pulsed laser deposition of carbon on c-BN and created c-BN/diamond heterostructures, where c-BN acts as a template for epitaxial diamond growth. We discuss the mechanism of epitaxial c-BN and diamond growth on lattice matching c-BN template under pulsed laser evaporation of amorphous carbon, and the impact of this discovery on a variety of applications.

Research Update: Direct conversion of h-BN into pure c-BN at ambient temperatures and pressures in air

We report a direct conversion of hexagonal boron nitride (h-BN) into pure cubic boron nitride (c-BN) by nanosecond laser melting at ambient temperatures and atmospheric pressure in air. According to the phase diagram, the transformation from h-BN into c-BN can occur only at high temperatures and pressures, as the hBN-cBN-Liquid triple point is at 3500 K/9.5 GPa. Using nanosecond laser melting, we have created super undercooled state and shifted this triple point to as low as 2800 K and atmospheric pressure. The rapid quenching from super undercooled state leads to formation of super undercooled BN (Q-BN). The c-BN phase is nucleated from Q-BN depending upon the time allowed for nucleation and growth.

RETRACTED ARTICLE: Fundamental Discovery of New Phases and Direct Conversion of Carbon into Diamond and hBN into cBN and Properties

We review the discovery of new phases of carbon (Q-carbon) and BN (Q-BN) and address critical issues related to direct conversion of carbon into diamond and hBN into cBN at ambient temperatures and pressures in air without any need for catalyst and the presence of hydrogen. The Q-carbon and Q-BN are formed as a result of quenching from super undercooled state by using high-power nanosecond laser pulses. We discuss the equilibrium phase diagram (P vs T) of carbon, and show that by rapid quenching, kinetics can shift thermodynamic graphite/diamond/liquid carbon triple point from 5000 K/12 GPa to super undercooled carbon at atmospheric pressure in air. Similarly, the hBN-cBN-Liquid triple point is shifted from 3500 K/9.5 GPa to as low as 2800 K and atmospheric pressure. It is shown that nanosecond laser heating of amorphous carbon and nanocrystalline BN on sapphire, glass, and polymer substrates can be confined to melt in a super undercooled state. By quenching this super undercooled state, we have created a new state of carbon (Q-carbon) and BN (Q-BN) from which nanocrystals, microcrystals, nanoneedles, microneedles, and thin films are formed depending upon the nucleation and growth times allowed and the presence of growth template. The large-area epitaxial diamond and cBN films are formed, when appropriate planar matching or lattice matching template is provided for growth from super undercooled liquid. The Q-phases have unique atomic structure and bonding characteristics as determined by high-resolution SEM and backscatter diffraction, HRTEM, STEM-Z, EELS, and Raman spectroscopy, and exhibit new and improved mechanical hardness, electrical conductivity, and chemical and physical properties, including room-temperature ferromagnetism and enhanced field emission. The Q-carbon exhibits robust bulk ferromagnetism with estimated Curie temperature of about 500 K and saturation magnetization value of 20 emu g−1. We have also deposited diamond on cBN by using a novel pulsed laser evaporation of carbon and obtained cBN/diamond composites, where cBN acts as template for diamond growth. Both diamond and cBN grown from super undercooled liquid can be alloyed with both p- and n-type dopants. This process allows carbon to diamond and hBN to cBN conversions and formation of useful nanostructures and microstructures at ambient temperatures in air at atmospheric pressure on practical and heat-sensitive substrates in a controlled way without need for any catalysts and hydrogen to stabilize sp3 bonding for diamond and cBN phases.

Structural changes during a liquid-liquid transition in the deeply undercooledZr58.5Cu15.6Ni12.8Al10.3Nb2.8bulk metallic glass forming melt

Using high energy synchrotron x-ray radiation combined with electrostatic levitation, in situ structural analysis of a bulk metallic glass forming liquid is performed from above the liquidus temperature down to the glass transition. The data indicate a liquid-liquid transition (LLT) in the deeply undercooled state at $T/{T}_{g}\ensuremath{\sim}1.2$ which manifests as a maximum in the heat capacity and an abrupt shift in the first peak position of the total structure factor in the absence of a pronounced density change. Analysis of the corresponding real-space data shows that the LLT involves changes in short- and medium-range order. The structural changes on the length scale of medium-range order imply a fragile-strong transition in agreement with experimental viscosity data.

Novel phase of carbon, ferromagnetism, and conversion into diamond

We report the discovery of a new phase of carbon (referred to as Q-carbon) and address fundamental issues related to direct conversion of carbon into diamond at ambient temperatures and pressures in air without any need for catalyst and presence of hydrogen. The Q-carbon is formed as result of quenching from super undercooled state by using high-power nanosecond laser pulses. We discuss the equilibrium phase diagram (P vs. T) of carbon and show that by rapid quenching kinetics can shift thermodynamic graphite/diamond/liquid carbon triple point from 5000 K/12 GPa to super undercooled carbon at atmospheric pressure in air. It is shown that nanosecond laser heating of diamond-like amorphous carbon on sapphire, glass, and polymer substrates can be confined to melt carbon in a super undercooled state. By quenching the carbon from the super undercooled state, we have created a new state of carbon (Q-carbon) from which nanodiamond, microdiamond, microneedles, and single-crystal thin films are formed depending upon the nucleation and growth times allowed for diamond formation. The Q-carbon quenched from liquid is a new state of solid carbon with a higher mass density than amorphous carbon and a mixture of mostly fourfold sp3 (75%–85%) with the rest being threefold sp2 bonded carbon (with distinct entropy). It is expected to have new and improved mechanical hardness, electrical conductivity, chemical, and physical properties, including room-temperature ferromagnetism (RTFM) and enhanced field emission. Here we present interesting results on RTFM, enhanced electrical conductivity and surface potential of Q-carbon to emphasize its unique properties. The Q-carbon exhibits robust bulk ferromagnetism with estimated Curie temperature of about 500 K and saturation magnetization value of 20 emu g−1. From the Q-carbon, diamond phase is nucleated and a variety of micro- and nanostructures and large-area single-crystal diamond sheets are grown by allowing growth times as needed. Subsequent laser pulses can be used to grow nanodiamond into microdiamond and nucleate other nanostructures of diamond on the top of existing microdiamond and create novel nanostructured materials. The microstructural details provide insights into the mechanism of formation of nanodiamond, microdiamond, nanoneedles, microneedles, and single-crystal thin films. This process allows carbon-to-diamond conversion and formation of useful nanostructures and microstructures at ambient temperatures in air at atmospheric pressure on practical and heat-sensitive substrates in a controlled way without need for any catalysts and hydrogen to stabilize sp3 bonding for diamond formation.

Research Update: Direct conversion of amorphous carbon into diamond at ambient pressures and temperatures in air

We report on fundamental discovery of conversion of amorphous carbon into diamond by irradiating amorphous carbon films with nanosecond lasers at room-temperature in air at atmospheric pressure. We can create diamond in the form of nanodiamond (size range <100 nm) and microdiamond (>100 nm). Nanosecond laser pulses are used to melt amorphous diamondlike carbon and create a highly undercooled state, from which various forms of diamond can be formed upon cooling. The quenching from the super undercooled state results in nucleation of nanodiamond. It is found that microdiamonds grow out of highly undercooled state of carbon, with nanodiamond acting as seed crystals.

Effect of Static Magnetic Field on Recalescence and Surface Velocity Field in Electromagnetically Levitated Molten CuCo Droplet in Undercooled State

The recalescence events of phase-separated Co-rich phases in undercooled molten CuCo droplets electromagnetically levitated under various static magnetic fields were observed directly using a high-speed camera, and also the surface velocities on the levitated droplets were measured by tracing the trajectories of the phase-separated Co-rich phases as tracer particles. In addition, numerical simulations of melt convection in a spherical electromagnetically levitated CuCo droplet exposed to a static magnetic field were performed assuming laminar flow. We observed the emergence of many intermittent bright spots due to recalescence on the entire surface of the levitated droplet, and the frequency of the bright spots decreased markedly as the static magnetic field increased, with no bright spots observed at fields larger than 1.5 T. Also, the Reynolds numbers were evaluated from the measured and calculated velocities in the droplet for various static magnetic fields and compared with the critical Reynolds number of approximately 600, at which the laminar–turbulent transition of a magnetohydrodynamic (MHD) flow in an electromagnetically levitated droplet occurs, as proposed by Hyers et al. The above results clearly revealed that the marked change in the phase separation structures in undercooled molten CuCo droplets at approximately 1.5 T is due to a convective transition from turbulent flow to laminar flow in the levitated droplets, as speculated in our previous work.

Measurement of Density of Fe-Co Alloys Using Electrostatic Levitation

The density of a series of five different iron-cobalt alloys was measured using electrostatic levitator processing. Each sample was processed through multiple thermal cycles and the liquid density was measured, while the superheated sample was cooled down to its undercooled state. The volume of the sample was estimated by analyzing captured high-speed video data of the projected shape of the sample. The mass change during the melt cycle was also tracked using Langmuir’s equation of mass evaporation. The density was then calculated as a function of temperature based on these measurements of volume and mass. Density values obtained showed higher precision than existing data from the literature obtained using a variety of different techniques, although the accuracy was consistent.

Surface tension and density data for Fe–Cr–Mo, Fe–Cr–Ni, and Fe–Cr–Mn–Ni steels

The temperature dependence of surface tension and density for Fe–Cr–Mo (AISI 4142), Fe–Cr–Ni (AISI 304), and Fe–Cr–Mn–Ni TRIP/TWIP high-manganese (16 wt% Cr, 7 wt% Mn, and 3–9 wt% Ni) liquid alloys are investigated using the conventional maximum bubble pressure (MBP) and sessile drop (SD) methods. In addition, the surface tension of liquid steel is measured using the oscillating droplet method on electromagnetically levitated (EML) liquid droplets at the German Aerospace Centre (DLR, Cologne). The data of thermophysical properties for Fe–Cr–Mn–Ni is of major importance for modeling of infiltration and gas atomization processes in the prototyping of a “TRIP-Matrix-Composite.” The surface tension of TRIP/TWIP steel increased with an increase in temperature in MBP as well as in SD measurement. The manganese evaporation with the conventional measurement methods is not significantly high within the experiments (∆Mn < 0.5 %). The temperature coefficient of surface tension (dσ/dT) is positive for liquid steel samples, which can be explained by the concentration of surface active elements. A slight influence of nickel on the surface tension of Fe–Cr–Mn–Ni steel was experimentally observed where σ is decreased with increasing nickel content. EML measurement of high-manganese steel, however, is limited to the undercooling state of the liquid steel. The manganese evaporation strongly increased in excess of the liquidus temperature in levitation measurements and a mass loss of droplet of 5 % was observed.

Experimental platform for solidification and in-situ magnetization measurement of undercooled melt under strong magnetic field.

An experimental platform for solidification of undercooled melt and synchronous measurement of magnetization under strong magnetic field is reported. The facility can be used for in-situ measurement of the magnetization of the undercooled melts and to studying the non-equilibrium solidification from deeply undercooled metals and alloys in magnetic field. The key advantages of this apparatus are first, we can obtain large undercooling in high fields by glass fluxing technique in combination with cyclical superheating and supercooling method, which is comparable to the maximum undercooling obtained by traditional method without magnetic field. Second, we can have a controlled thermal history with linear heating and cooling speed with high accuracy. Third, the temperature and magnetization measurement system are fast and on-line, which is very suitable for the investigation of both the structure transitions in the liquid in a wide temperature range (overheated and undercooled state) and the solid state phase transformations.

Interplay between the structure and dynamics in liquid and undercooled boron: an ab initio molecular dynamics simulation study.

In the present work, the structural and dynamic properties of liquid and undercooled boron are investigated by means of ab initio molecular dynamics simulation. Our results show that both liquid and undercooled states present a well pronounced short-range order (SRO) mainly due to the formation of inverted umbrella structural units. Moreover, we observe the development of a medium-range order (MRO) in the undercooling regime related to the increase of inverted umbrella structural units and of their interconnection as the temperature decreases. We also evidence that this MRO leads to a partial crystallization in the β-rhombohedral crystal below T = 1900 K. Finally, we discuss the role played by the SRO and MRO in the nearly Arrhenius evolution of the diffusion and the non-Arrhenius temperature dependence of the shear viscosity, in agreement with the experiment.

Creep or tensile stress induced anisotropy in FINEMET-type ribbons?

Continuous stress annealing can be performed on FINEMET-type (Fe 73.5 Cu 1 Nb 3 Si 15.5 B 7 ) ribbons. Here we report experiments conducted in a cheap open tubular furnace as a function of pulling velocity ( v ). We achieved up to v =120 m/min that is almost 100 times higher than previously reported for this kind of equipments. In this report we show for the first time how the properties are depending on the pulling velocity. While the achieved relative permeability µ r remained constant without changing any other parameter than v , the elongation of the ribbon and the contraction of the ribbon width were monotonically changing as v was increased. The results support that the creep is not determined exclusively by the applied stress, but it is determined by the details of the amorphous–nanocrystalline transformation, which is influenced by the pulling velocity. The bigger the pulling velocity is, the higher the onset temperature of the amorphous–nanocrystalline transformation is, and the wider the associated exothermic peak is, resulting in increased elongation of the ribbon due to a short time formation of undercooled liquid state. • We report detailed investigations as a function of pulling velocity in a dynamical stress annealing process. • The inverse effective permeability is linearly depending on the applied stress, in accordance with Herzer’s back-stress theory. • The creep is not uniquely determined by the stress, but depends also on the pulling velocity. • The permeability is independent from the elongation of the ribbon. • The induced anisotropy does not depend on the creep.

Fabrication of Barium Titanate Based Ferroelectrics by Containerless Processing

Lead-free ferroelectric materials are desired in our lives owing to the environmental problem, and are anticipated to replace conventional ferroelectrics such as Pb(Zr,Ti)O3(PZT) ceramics. Many researchers have attempted to develop lead-free ceramics whose ferroelectric properties would surpass those of PZT ceramics. Recently, it has been reported that oxygen-deficient hexagonal-BaTiO3which is metastable state of perovskite-BaTiO3exhibits giant dielectric constants over the wide temperature range. Such a metastable material has capability as a lead-free dielectric material with high performance. The containerless processing has an advantage over the other conventional methods in synthesizing metastable materials. It can suppress heterogeneous nucleation from the container wall, and produce the undercooled state below the solidification point of the metastable phase, which is lower than that of the stable phase. The purpose of this study is to synthesize barium titanate based ferroelectrics by the containerless processing as lead-free metastable materials. We developed the aerodynamic levitation furnace which enables us to levitate and melt a sample about 1-3 mm in diameter in containerless condition. Figure 1 shows a schematic view of the aerodynamic levitation furnace. The samples are levitated by the gas jet nozzle, and are melted using the CO2laser radiation. The metastable crystals of the barium titanate based ferroelectrics were fabricated by the aerodynamic levitation furnace. The crystal structure is demonstrated by analyzing high energy synchrotron radiation powder diffraction data. We discuss the prospects of the ferroelectricity on the basis of the determined crystal structure.

Formation of spherulites and pentagonal quasicrystals in metals being electrodeposited

The aim of the work was experimental verification of validity of the phenomenon of phase formation through a stage of liquid state in metals being electrodeposited. The idea of the work was based on the known fact, that at minor undercooling of melt solidification of metal usually occurs in dendritic form, and at significant undercooling of melt dendritic form transfers to spherulite one. At that spherulites, as a rule, are being formed on the interface between metal and a melting-pot. Besides, superfast solidification of greatly undercooled melt causes formation of quasicrystals with pentagonal symmetry. Therefore, if metals being electrodeposited really pass through a stage of undercooled liquid state and rapidly solidify at the deposition temperature, than spherulite forms of crystallization and pentagonal quasicrystals should be detected in their layers adjacent to the cathode. As the result of experimental investigations accomplished by the method of scanning electron microscopy formation of spherulites and pentagonal quasicrystals in the adjacent to the cathode layers of metals (copper, lead and cobalt) being electrodeposited was discovered. It is shown, that presence of spherulites and pentagonal quasicrystals in electrodeposited metals is the result of superfast solidification of undercooled liquid metallic phase being formed during electrochemical deposition of metals. Formation of spherulites and pentagonal quasicrystals in the adjacent to the cathode layers of metals being electrodeposited proves the validity of the phenomenon of phase formation through a stage of liquid state in metals being electrodeposited.

On the entropic nucleation barrier in a martensitic transformation

The nucleation of martensite in alloys is hindered by a free energy nucleation barrier, hence comprising contributions of the potential energy and the entropy. The leading effect is commonly attributed to the potential energy barrier due to strain fields. In this contribution, we investigate the nature of the entropic barrier by means of molecular dynamics (MD) simulations. We study a transformation process of an undercooled single crystal and examine two nucleation events observed under adiabatic conditions using vibrational mode analysis of the atomic trajectories. Our analysis shows that martensitic nucleations are indicated by transit from a state of uncorrelated into a state of correlated atomic motions. This correlation process is built up locally by a small group of atoms even before the product lattice can be recognized morphologically and it produces vibrational ‘soft’ modes along transformation paths. Phase space analyses unveil that the correlation process is characterized by narrow domains – ‘nucleation channels’ – the atomic trajectories have to pass, connecting the phase space domains of the parent and the product lattice. For a successful nucleation event, the nucleus atoms have to pass this channel collectively, which stochastically represents a rare event. Thermal fluctuations prevent finding the channel at elevated temperature and give rise for entropic stabilization of the parent phase. This ‘entropic nucleation barrier’ is reduced in the undercooled state but still effective, thus preventing the parent phase from collapsing into the product. The entropic barrier may be interpreted as the probability of a group of atoms to simultaneously pass the nucleation channel. Such group then represents a nucleus.

Formation of Cu-rich crystalline/NiNb-rich amorphous composite induced by liquid phase separation

Liquid phase separation phenomena give rise to a unique opportunity in developing the crystalline/amorphous composites using melt-spinning method. In this study, a new crystalline/amorphous composite with a droplet-type microstructure is investigated in Cu–Ni–Nb immiscible system. It is found that the Cu30(Ni38Nb62)70 alloy undergoes liquid–liquid phase separation in the undercooled liquid state, and then solidifies into Cu-rich crystalline phase and NiNb-based amorphous phase. The fcc Cu-rich crystalline droplets are dispersed in the NiNb-based amorphous matrix. The grain size of Cu-rich droplets is in the range between nanometer dimension order and micrometer order. On the other hand, an obvious layer without Cu-rich nanoparticles is observed near the wheel side. The indentation testing of Cu30(Ni38Nb62)70 ribbon shows a larger elastic–plastic deformation area and much smaller Vickers hardness, due to the formation of softer Cu-rich particles. Further results indicate that the formation of droplet-type microstructure could be attributed to the liquid phase separation and amorphous phase formation.

Crystal nucleation in undercooled melts of PdZr2

Crystal nucleation in undercooled melts of the stoichiometric PdZr2 compound is studied by measuring the nucleation undercooling of small droplets processed by containerless electrostatic and electromagnetic levitation. Owing to the avoidance of container walls usually acting as heterogeneous nuclei, large undercoolings are achieved. The statistics of crystal nucleation is investigated by measuring the nucleation undercooling of at least 100 melting and solidification cycles for both sets of experiments. The results are analyzed within a statistical approach based on the classical nucleation theory. Out of this two important parameters can be extracted. These are the activation energy, which needs to be overcome to form critical nuclei and, the pre-factor in the nucleation rate equation, which measures the number of potential nucleation sites per unit volume. The results are discussed with respect to the different experimental conditions, short-range order in the undercooled liquid state and its impact to the glass forming ability of this alloy.

Dynamic properties of liquid and undercooled aluminum

First-principles molecular dynamics simulations of liquid and undercooled aluminum have been performed to study the evolution of dynamic properties across the melting point. Single-atom as well collective dynamic properties are determined and are related to the structural evolution of the liquid phase. The temperature dependence of the self-diffusion coefficient is computed from both the mean square displacement and the velocity autocorrelation function. Self-diffusion coefficients follow an Arrhenius law with the single activation energy of 250 meV, consistent with experimental results for the liquid phase. Moreover, we show that the Arrhenius relation can also be applied to the undercooled state at T = 875 K. Finally, a direct calculation of the shear viscosity from the transverse current correlation function shows that the Stokes–Einstein relation can be applied over the temperature range investigated.