Kinetic Regime Research Articles

Magnetospheric Multiscale Observations of Markov Turbulence on Kinetic Scales

In our previous studies we have examined solar wind and magnetospheric plasma turbulence, including Markovian character on large inertial magnetohydrodynamic scales. Here we present the results of the statistical analysis of magnetic field fluctuations in the Earth’s magnetosheath, based on the Magnetospheric Multiscale mission at much smaller kinetic scales. Following our results on spectral analysis with very large slopes of about −16/3, we apply a Markov-process approach to turbulence in this kinetic regime. It is shown that the Chapman–Kolmogorov equation is satisfied and that the lowest-order Kramers–Moyal coefficients describing drift and diffusion with a power-law dependence are consistent with a generalized Ornstein–Uhlenbeck process. The solutions of the Fokker–Planck equation agree with experimental probability density functions, which exhibit a universal global scale invariance through the kinetic domain. In particular, for moderate scales we have the kappa distribution described by various peaked shapes with heavy tails, which, with large values of the kappa parameter, are reduced to the Gaussian distribution for large inertial scales. This shows that the turbulence cascade can be described by the Markov processes also on very small scales. The obtained results on kinetic scales may be useful for a better understanding of the physical mechanisms governing turbulence.

Operando kinetics of hydrogen evolution and elemental dissolution I: The dissolution of galvanized steel in hydrochloric acid

A new approach to the simultaneous measurement of the hydrogen evolution reaction (HER) and elemental dissolution rates is presented and applied to the reaction of galvanized steel coatings with HCl solution. Dissolution profiles revealed several kinetic regimes including the dissolution of the intact coating, the dissolution of the nanometric Fe2Al5 intermetallic layer, and the corrosion of the steel substrate. The HER and Zn dissolution rates were in excellent agreement, and the quantities of interfacial Fe and Al were consistent with the predicted 50 nm thick Fe2Al5 intermetallic film, demonstrating the analytical capabilities of the atomic emission spectroelectrochemistry (AESEC) technique.

High-temperature oxidation behavior of TaTiCr, Ta4Ti3Cr, Ta2TiCr, and Ta4TiCr3 concentrated refractory alloys

This study reports the unique microstructures and high-temperature oxidation behavior of TaTiCr, Ta4Ti3Cr, Ta2TiCr, and Ta4TiCr3 concentrated refractory alloys and elucidates the effect of moderate composition changes on oxidation performance. All alloys investigated in this study formed bcc solid solution matrices with second phase Laves precipitates (except for Ta4Ti3Cr, being single-phase bcc).The alloys were tested for 24 h at 1200 °C, of which: TaTiCr exhibited superior oxidation performance for the duration of the test; Ta4TiCr3 showed moderate oxidation resistance, with both parabolic and linear kinetic regimes; and Ta4Ti3Cr and Ta2TiCr both exhibited poor oxidation performance, with Ta2TiCr being completely oxidized after testing. All alloys formed complex oxides; however, the excellent performance of the TaTiCr alloy can be attributed to the compact, continuous nature of the oxide scale, the combination of complex oxides and protective Cr2O3 formation, and the complex internal nitride morphology, slowing oxygen ingress and reducing the depth of internal oxidation.

Effect of chemical chaperones on processes of protein aggregation proceeding in different kinetic regimes

The formation and accumulation of protein aggregates adversely affect intracellular processes in a living cell and are a negative factor in the production and storage of protein preparations. Chemical chaperones can prevent protein aggregation, but this property is not universal and depends on the structure of the target protein and the kinetics of its aggregation. In this work, we studied the effect of betaine (Bet) and lysine (Lys) on test systems based on thermal aggregation of muscle glycogen phosphorylase b (Phb) at 48°C, UV-irradiated Phb (UV-Phb) at 37°C and apo-form of Phb (apo-Phb) at 37°C and characterized by the order of aggregation with respect to the protein (n) equal to 0.5, 1 or 2, respectively. Dynamic light scattering, differential scanning calorimetry, and analytical ultracentrifugation have shown that Bet protects Phb and apo-Phb from aggregation, but accelerates the aggregation of UV-Phb. At the same time, Lys prevents UV-Phb and apo-Phb aggregation, but increases the rate of Phb aggregate formation. The mechanisms of chemical chaperone action on the tertiary and quaternary structures and the kinetics of thermal aggregation of the target proteins are discussed. Comparison of the effect of chemical chaperones on test systems with different kinetic regimes of aggregation provides more complete information about the mechanism of their action.

On the importance of reactions in the proximity of the gas–water interface: Application to direct ozone reactions of antibiotics in water

A comparison between kinetic models of the direct ozonation in water of a mixture of fifteen antibiotics has been carried out by considering both the reactions in the proximity of gas–water interface (film reactions) and in the water bulk. Stoichiometric coefficients and rate constants of the O3-antibiotic reaction were determined following standard procedures and compared to the values reported in the literature. The importance of stoichiometric coefficients in the establishment of the ozone kinetic regimes and kinetic modelling has been discussed. Most of the antibiotics studied react under fast or moderate regime with ozone at the conditions applied. The significance of these reactions in the proximity of gas–water interface is discussed sustained in the application of film theory. Results have been compared to those obtained from the kinetic approach where ozone reactions in the film are not taken into account. The importance of reactions in the film represents >60% of antibiotics consumption. Deviations between experimental and simulated concentrations of antibiotics are due to the contribution of reaction intermediates to ozone consumption, which is not considered in the kinetic model.

The influence of sample mass (scaling effect) on the synthesis and structure of non-graphitizing carbon (biochar) during the analytical pyrolysis of biomass.

The porous non-graphitizing carbon (NGC) known as biochar is derived from the pyrolytic conversion of organic precursors and is widely investigated due to its multifunctional applications. At present, biochar is predominantly synthesized in custom lab-scale reactors (LSRs) to determine the properties of carbon, while a thermogravimetric reactor (TG) is utilized for pyrolysis characterization. This results in inconsistencies in the correlation between the structure of biochar carbon and the pyrolysis process. If a TG reactor can also be used as an LSR for biochar synthesis, then the process characteristics and the properties of the synthesized NGC can be simultaneously investigated. It also eliminates the need for expensive LSRs in the laboratory, improves the reproducibility, and correlatability of pyrolysis characteristics with the properties of the resulting biochar carbon. Furthermore, despite numerous TG studies on the kinetics and characterization of biomass pyrolysis, none have questioned how the properties of biochar carbon vary due to the influence of the starting sample mass (scaling) in the reactor. Herein, with a lignin-rich model substrate (walnut shells), TG is utilized as an LSR, for the first time, to investigate the scaling effect starting from the pure kinetic regime (KR). The changes in the pyrolysis characteristics and the structural properties of the resultant NGC with scaling are concurrently traced and comprehensively studied. It is conclusively proven that scaling influences the pyrolysis process and the NGC structure. There is a gradual shift in pyrolysis characteristics and NGC properties from the KR until an inflection mass of ∼200 mg is reached. After this, the carbon properties (aryl-C%, pore characteristics, defects in nanostructure, and biochar yield) are similar. At small scales (≲100 mg), and especially near the KR (≤10 mg) carbonization is higher despite the reduced char formation reaction. The pyrolysis is more endothermic near KR with increased emissions of CO2 and H2O. For a lignin-rich precursor, at masses above inflection point, TG can be employed for concurrent pyrolysis characterization and biochar synthesis for application-specific NGC investigations.

How droplets move on laser-structured surfaces: Determination of droplet adhesion forces on nano- and microstructured surfaces.

Lateral adhesion forces are a fundamental property of liquid-solid interactions and a key aspect of dynamic droplet mobility. But, commonly applied conventional wetting analysis is limited to static and quasi-static methods and cannot resolve dynamic and spatial liquid-solid interactions. However, droplet mobility is assumed to be affected by chemical and topographic surface inhomogeneities introduced by femtosecond laser treatment. In this study, we used a customized droplet adhesion force instrument to determine lateral adhesion forces on various femtosecond laser-structured surface designs to obtain a deeper understanding of the dynamic droplet motion with regard to chemical and topographic surface features. We show that the droplet motion was highly affected by the chemical and topographical surface design and local inhomogeneities. The droplet mobility on femtosecond laser-structured surfaces could be classified into a static, a transfer, and a kinetic regime, which is essential for designing surfaces with extreme wetting characteristics and a wide range of scientific and industrial processes. Furthermore, with proper tailoring of surface structures and chemical modification, we were able to provoke adhesion forces on self-organized laser microstructures similar to those found on the natural lotus leaves.

Transport of double-stranded ribonucleic acids (dsRNA) and deoxyribonucleic acids (DNA) in sand and iron oxide-coated sand columns under varying solution chemistries.

Assessing ecological risks associated with the use of genetically modified RNA interference crops demands an understanding of the fate of crop-released insecticidal double-stranded RNA (dsRNA) molecules in soils. We studied the adsorption of one dsRNA and two double-stranded DNA as model nucleic acids (NAs) during transport through sand- and iron oxide-coated sand (IOCS)-filled columns over a range of solution pH and ionic compositions. Consistent with NA-sand electrostatic repulsion, we observed only slight retention of NAs in sand columns. Conversely, pronounced NA retention in IOCS columns is consistent with strong and irreversible NA adsorption involving electrostatic attraction to and inner-sphere complex formation of NAs with iron oxide coatings. Adsorption of NAs to iron oxides revealed a fast and a slow kinetic adsorption regime, possibly caused by the excluded-area effect. Adsorption of NAs to sand and IOCS increased in the presence of dissolved Mg2+ and with increasing ionic strength, reflecting cation-bridging and screening of repulsive electrostatics, respectively. The co-solute phosphate and a pre-adsorbed dissolved organic matter isolate competitively suppressed dsRNA adsorption to IOCS. Similar adsorption characteristics of dsRNA and similarly sized DNA suggest that existing information on DNA adsorption to soil particles helps in predicting adsorption and fate of dsRNA molecules in soils.

Kinetic and structural insights into the grain boundary phase transitions in Ni-Bi alloys

Kinetic and structural changes associated with grain boundary phase transition induced by Bi alloying in dilute Ni–Bi alloys (0–0.3 at.% of Bi) are investigated in a concerted manner. Grain boundary diffusion of Ni in the Ni-Bi alloys is measured in Harrison's B- and C-type kinetic regimes applying the radiotracer technique and utilizing the 63Ni radioisotope. The measurements are performed across the single phase towards two-phase regions of the bulk phase diagram. In case of the single phase region it is the Ni(Bi) solid solution. In case of two phase areas these are Ni(Bi) solid solution + liquid Bi above 927 K or Ni(Bi) solid solution + NiBi below 927 K. Three distinct regions of the dependence of the Ni grain boundary diffusion rates on the Bi concentration are distinguished. A slight increment in Ni grain boundary diffusion is observed at lower Bi contents which is driven by Bi grain boundary segregation. Beyond a critical Bi concentration and still within the single-phase solid solution region, the Ni diffusivity starts to enhance dramatically with increasing Bi content. This is correlated with the appearance of multi-layer Bi segregation along the grain boundaries. It is substantiated by high-angle annular dark-field scanning transmission electron microscopy combined with energy dispersive X-ray spectroscopy measurements. At higher Bi concentrations, which corresponds to the appearance of a liquid layer of Bi at the grain boundaries, the Ni diffusivity attains the highest values. A serial of structural transitions between the different grain boundary phases is for the first time demonstrated to be accompanied by remarkable changes of the grain boundary diffusion rates. The present results highlight a close correlation between the atomic transport and structure modifications due to grain boundary phase transitions in the Ni–Bi alloys. Utilizing the present experimental results, a Ni–Bi grain boundary diffusion map is proposed.

Crystallization Kinetics in an Immiscible Polyolefin Blend.

Motivated by the problem of brittle mechanical behavior in recycled blends of high density polyethylene (HDPE) and isotactic polypropylene (iPP), we employ optical microscopy, rheo-Raman, and differential scanning calorimetry (DSC) to measure the composition dependence of their crystallization kinetics. Raman spectra are analyzed via multivariate curve resolution with alternating least-squares (MCR-ALS) to provide component crystallization values. We find that iPP crystallization behavior varies strongly with blend composition. Optical microscopy shows that three crystallization kinetic regimes correspond to three underlying two-phase morphologies: HDPE droplets in iPP, the inverse, and cocontinuous structures. In the HDPE droplet regime, iPP crystallization temperature decreases sharply with increasing HDPE composition. For cocontinuous morphologies, iPP crystallization is delayed, but the onset temperature changes little with the exact blend composition. In the iPP droplet regime, the two components crystallize nearly concurrently. Rheological measurements are consistent with these observations. DSC indicates that the enthalpy of crystallization of the blends is less than the weighted values of the individual components, providing a possible clue for the decreased iPP crystallization temperatures.

Cyanate Ester Polymerization: Overview of Mechanistic and Kinetic Aspects

AbstractThis article reviews both time‐honored and most recent studies of the mechanisms and kinetics of cyanate esters polymerization. Different types of processes, including catalytic, non‐catalytic, bulk, solution, and nanoconfined ones are covered. The mechanistic and empirical models suitable for describing the kinetic and diffusion regimes of polymerization are discussed at length. Recent advances in methodology of the analysis of multistep polymerization reactions by means of model‐fitting and isoconversional techniques are considered as applied to cyanate esters. The importance of the calorimetric measurements in polymerization studies is emphasized.

Growth and Performance of High-Quality SWCNT Forests on Inconel Foils as Lithium-Ion Battery Anodes.

Large-scale production of vertically aligned single-walled carbon nanotubes (VA-SWCNTs) on metal foils promises to enable technological advancements in many fields, from functional composites to energy storage to thermal interfaces. In this work, we demonstrate growth of high-quality (G/D > 6, average diameters ∼ 2-3 nm, densities > 1012 cm-2) VA-SWCNTs on Inconel metal for use as a lithium-ion battery (LIB) anode. Scale-up of SWCNT growth on Inconel 625 to 100 cm2 exhibits nearly invariant CNT structural properties, even when synthesis is performed near atmospheric pressure, and this robustness is attributed to a growth kinetic regime dominated by the carbon precursor diffusion in the bulk gas mixture. SWCNT forests produced on large-area metal substrates at close to atmospheric pressure possess a combination of structural features that are among the best demonstrated so far in the literature for growth on metal foils. Leveraging these achievements for energy applications, we demonstrate a VA-SWCNT LIB anode with capacity >1200 mAh/g at 1.0C and stable cycling beyond 300 cycles. This robust synthesis of high-quality VA-SWCNTs on metal foils presents a promising route toward mass production of high-performance CNT devices for a broad range of applications.

Kinetics of HSA crystallization and its relationship with the phase diagram

Using the protein human serum albumin (HSA) and the trivalent salt cerium chloride (CeCl3) to tune the effective interactions, we induce crystallization and connect the crystallization kinetics to different regions of the phase diagram. The nucleation density, the nucleation rate, as well as the crystal size show maxima slightly above the specific salt concentration c∗ for aggregation. The comparison with data of the reduced second virial coefficient suggests that B2/B2HS alone is insufficient to explain the observed trends. We thus discuss further aspects impacting the crystallization behavior. We are able to link and distinguish the kinetic regimes regarding their relative distance to phase boundaries, namely c∗ as well as the liquid–liquid phase separation (LLPS) border.

β‐Myrcene Coordination Polymerization: Experimental and Kinetic Modeling Study

AbstractThe present work presents phenomenological models to describe the coordination polymerization of β‐myrcene using the Ziegler–Natta catalyst system composed by neodymium versatate (NdV3), diisobutylaluminum hydride (DIBAH), and dimethyldichlorosilane. The kinetic parameters required to simulate the reactions are estimated, and the amount of DIBAH used as a chain transfer agent (CTA) is obtained by a data reconciliation strategy since it can participate in side reactions. Several experiments are performed at different conditions to evaluate the impact of key operation variables on the control of monomer conversion and average molar masses. It is shown that the initial NdV3, β‐myrcene, and DIBAH concentrations exert strong influences on the course of the polymerization. The kinetic mechanism of Coordinative Chain Transfer Polymerization (CCTP) fits well with the data of final average molar masses and monomer conversion, while the dynamic trajectories of these variables are fitted better by kinetic mechanisms of more conventional coordination polymerizations, considering site deactivation and termination by chain transfer. In all cases, the proposed models are able to predict the experimental data well after successful parameter estimation and reconciliation of CTA concentrations, indicating that the kinetic mechanism can be characterized by different kinetic regimes.

Application of similarity laws to dual-frequency capacitively coupled radio frequency plasmas with the electrical asymmetry effect

Similarity laws (SLs) are useful for correlation and prediction of plasma parameters at different scales, which have been verified for geometrically symmetric capacitive radio-frequency (rf) discharges in nonlocal kinetic regimes. In this work, we demonstrate the applicability of SLs to dual-frequency rf discharges and confirm that similarity relations still hold considering the electrical asymmetry effect (EAE). By simultaneously tuning the control parameters (the gas pressure p, discharge gap d, and driving frequency f), we examine the similarity relations in rf plasmas via fully kinetic particle-in-cell simulations with the external circuits coupled and solved self-consistently. The validity of the SL scalings in dual-frequency rf plasmas with the EAE is confirmed for parameters such as the electron/ion density, ion flux, dc self-bias, ion energy distribution function, and power absorption. Although adjusted by the EAE, the dc self-bias and ion energy distribution functions are identified as similarity invariants under similar discharge conditions. Furthermore, the plasma series resonance phenomenon, filamentation of power depositions of electrons and ions in bulk plasma, and electric field reversal are observed in dual-frequency discharges with the EAE, which can also be exactly replicated under similar discharge conditions. The results further extend the application of SL scaling to dual-frequency rf plasmas, providing a more comprehensive understanding of the scaling characteristics in rf plasmas.

Measurements of Rayleigh–Brillouin scattering spectra of Ar, N[formula omitted], and CH[formula omitted] at pressures up to 20 atm

This paper describes the spectral measurement of Rayleigh–Brillouin scattering (RBS) in Ar, N2, and CH4 at 300 K and pressures up to 20 atm, which is relevant for the application of filtered Rayleigh scattering (FRS) diagnostics at elevated pressure. The measurement scheme for RBS spectra was relatively novel, based on an air-spaced virtually imaged phased array (VIPA), capable of rapid acquisition at high resolution. However, the VIPA’s nonuniform dispersion, irregular instrument response function, and sensitivity to local ambient conditions challenged the reconstruction of high-fidelity lineshapes in frequency space. Nonuniform dispersion was addressed using the VIPA dispersion function, and sensitivity of the air-spaced optic to the refractive index of air was minimized by tracking local temperature and pressure during measurements. Irregular instrument response was remedied with a computational model of the VIPA’s optical field, and by deconvolution. A comparison of experimental lineshapes with model predictions by Tenti S6 yielded good agreement. In the kinetic and nominal transition regimes, local residuals were within 3% for Ar and N2, and 5–10% for CH4. Beyond the transition regime, experimental lineshapes continued to display good qualitative agreement, with frequency shifts of the Brillouin peaks representing the main deviation from model prediction. Artifacts in the experimental data from uncertainty and the deconvolution algorithm were identified and discussed. This work establishes an experimental foundation for future measurements of RBS spectra, which will assist in the development of FRS diagnostics of reacting flows at high pressure.

One-Pot Synthesis of Menthol from Citral and Citronellal Over Heterogeneous Catalysts

One-pot synthesis of menthol from citronellal or citral was summarized. Both batch and continuous reactors have been recently applied. This reaction is very complex and a bifunctional catalyst exhibiting especially Lewis acid sites for cyclisation of citronellal to isopulegol are needed, while metal particles are required for its hydrogenation to menthols. Typically, too mild acidity of the catalyst and small particles do not catalyze menthol formation. Furthermore, too high acidity causes catalyst deactivation and dehydration of menthol. Very high menthol yields have been obtained in batch reactor over nobel and transition metal supported bifunctional catalysts. Shape selectivity was demonstrated for Ni-supported on Zr-modified beta zeolite, which gave high diastereoselectivity to the desired L-menthol. Recently one-pot synthesis of menthol in a trickle bed reactor has been investigated. Catalyst suffers only minor deactivation in transformation of citronellal to menthol, while more severe catalyst deactivation occurred in transforming citral to menthols. Noteworthy from the industrial point of view is that the product distribution obtained with the same catalyst under kinetic regime or under diffusional limitations differs from each other. The metal location and synthesis method of extrudates can have a major effect on the catalyst performance. Kinetic modelling of the data obtained from the trickle bed reactor considering the effectiveness factor is discussed.Graphical The results from one-pot synthesis of menthol finding applications in pharmaceuticals and fragrances from citral and its hydrogenated product, citronellal over bifunctional catalysts metal–acid are summarized. The relationship between the catalyst properties and the performance is discussed. In the continuous mode catalyst deactivation becomes apparent and in such mode of operation the product distribution might differ from those obtained in a batch reactor.

Analysis of deterministic and stochastic oscillatory regimes in nonlinear thermochemical kinetics

In this paper, we analyze mechanisms of generation of complex oscillatory regimes in thermochemical reactors. In this study, a mathematical model of the continuous stirred tank reactor (CSTR) is used. Various scenarios of transitions between equilibrium and oscillatory regimes (quasiharmonic and spiking) are studied, and corresponding local and global bifurcations are discussed. It is shown how inevitably present weak noise in the temperature of CSTR can generate complex mixed‐mode oscillatory regimes in parameter ranges where the unforced initial deterministic model exhibits a stable equilibrium as an attractor. In the study of such noise‐induced excitement, direct numerical simulation and a new mathematical technique based on the stochastic sensitivity and confidence domain method are effectively used.

Identification of homogeneous chemical kinetic regimes of methane-air ignition

Sensitivity analysis results for ignition delay time (IDT) may be very different depending on the initial temperature, pressure and equivalence ratio φ, but similar in some regions of these variables. This phenomenon was investigated systematically by carrying out ignition simulations and local sensitivity calculations of methane−air mixtures using the Aramco-II-2016 mechanism at 14,417 combinations of initial temperature (changed between 500 and 3000 K), initial pressure (0.05−500 atm) and φ (0.05−8.0) values. The cluster analysis of the sensitivity vectors identified five large kinetically homogeneous regions. Each region has well defined borders in the (T, p φ) space and can be characterized by different sets of important reactions. The related kinetic scheme is very different in each region. Regions 1 and 2 are dominated by catalytic cycles based on species CH3O2/CH3O2H and HO2/H2O2/CH3O, respectively. In regions 3, 4, and 5 the H atoms are converted to CH3 in an identical chain branching sequence, but the back conversion is via three different routes. Literature experimental data on the IDTs of methane−air mixtures were sorted according to these five regions. Regions 1 to 5 contain 214, 328, 3, 0, and 237 experimental data points, respectively. In regions 1, 2 and 5 the data points are well reproduced by the Aramco-II-2016 mechanism, but little or no experimental information is available about kinetic regions 3 and 4. Further experimental exploration of the ignition of methane−air mixtures may aim the study of these regions. A similar approach can be used for the characterization of other combustion systems and sorting the related experimental data.

Ge Microcrystals Photedetectors with Enhanced Infrared Responsivity

he direct epitaxial growth of germanium on silicon (Ge-on-Si) has fostered the development of near infrared detectors for telecom and imaging applications [1]. The long wavelength responsivity of these devices is limited to approximately 1550 nm corresponding to the direct energy gap of Ge EgΓ= 0.8 eV. Indeed, the absorption coefficient at the indirect gap EgL= 0.66 eV (λ≈1800 nm) is roughly two orders of magnitudes lower than that above the direct gap threshold. A sizable absorption within the 1550-1800 nm windows would, therefore, require exceedingly thick epilayers leading to wafer bowing and crack formation. An extended infrared absorption would, however, be beneficial for imaging applications since long wavelength radiation is less affected by Rayleigh and Mie scattering limiting visibility in fog and dusty conditions.A viable route to enhance the responsivity of Gen-on-Si photodetectors in the 1550-1800 nm region might be exploiting the micro-structuring of the absorbing layer to increase the effective volume of interaction between light and matter.In this work we report on a new type of detector, obtained from Ge micro-crystals epitaxially grown on a patterned Si substrate [2]. The faceted morphology and relatively high aspect ratio of the microcrystals is seen to enhance the detector responsivity in the wavelength region comprised between the direct (λ≈1550 nm) and indirect (λ≈1800 nm) gap of Ge, as compared to conventional planar devices.The epitaxial growth has been performed by means of Low-Energy Plasma-Enhanced CVD (LEPECVD). Microcrystal formation is based on the self-assembly of Ge crystals on a Si substrate, deeply patterned by optical lithography and reactive ion etching. 3D microcrystals, several micrometer tall and characterized by a limited lateral expansion, are obtained by using optimized growth parameters. Due to crystal faceting, light trapping effects are expected to take place within the microcrystals leading to increased in the fraction of absorbed light when compared to conventional epitaxial layers.Modelling of the near-IR absorption properties of the Ge-on-Si micro-crystals, and of conventional epilayer used as a reference,has been performed by finite difference time domain (FDTD) simulations. The ratio between the fraction of absorbed power of an array of Ge-on-Si micro-crystals and a planar Ge-on-Si epilayer is estimated to be always higher than one, with a factor of two increase in the spectral region between the direct and indirect gap (λ≈1550-1800 nm).Ge microcrystals photodetectors have been fabricated using graphene as a transparent top contact (see Fig. 1). A confocal microscope with a supercontinuum laser source (1300 - 1800 nm), has been used to obtain the photodetector responsivity. The spot size was smaller than the patterned area (100 μm x 100 μm) thus enabling the illumination of a few Ge-on-Si micro-crystals. The photocurrent measurements experimentally confirm the enhanced absorption in the 1550-1800 nm spectral region [4] with a responsivity exceeding, by a factor of seven, that of a reference conventional Ge-on-Si photodiode at 1700 nm.These results pave the way to a new class of photodetectors, exploiting light trapping phenomena in self assembled semiconductors microstructures. J. Michel, J. Liu, and L. C. Kimerling, High-performance Ge-on-Si photodetectors, Nat. Photonics 4, 527–534, (2010)C. V. Falub et al., Scaling Hetero-Epitaxy from Layers to Three-Dimensional Crystals, Science (80). 1330–1334, (2012).M. Albani et al. Faceting of Si and Ge crystals grown on deeply patterned Si substrates in the kinetic regime: phase-field modelling and experiments, Scientific Reports 11, 18825 (2021)V. Falcone et al., Graphene/Ge microcrystal photodetectors with enhanced infrared responsivity, APL Photonics 7, 046106 (2022) Figure 1